Chapter 14 Part 1

Principles of Human Anatomy and Physiology, 11e 1

Chapter 14Part 1

The Brain and Cranial Nerves

Lecture Outline


INTRODUCTION

• The brain is the center for registering sensations, correlating them with one another and with stored information, making decisions, and taking action.

• It is also the center for intellect, emotions, behavior, and memory.

• It also directs our behavior towards others.• In this chapter we will consider the principal parts of the

brain, how the brain is protected and nourished, and how it is related to the spinal cord and to the 12 pairs of cranial nerves.


Chapter 14The Brain and Cranial

Nerves

• Largest organ in the body at almost 3 lb.• Brain functions in sensations, memory, emotions, decision making,

behavior


OVERVIEW OF BRAIN ORGANIZATION AND BLOOD SUPPLY

• The major parts of the brain are the brain stem, diencephalon, cerebrum, and cerebellum (Figure 14.1).

• The CNS develops from an ectodermal neural tube– Three primary vesicles: prosencephalon,

mesencephalon, and rhombencephalon develop from the neural tube. (Figure 14.29)

• The embryologic development of the CNS is summarized in table 14.1


Principal Parts of the Brain

• Cerebrum• Diencephalon

– thalamus & hypothalamus• Cerebellum• Brainstem

– medulla, pons & midbrain


Blood Supply to Brain

• Arterial blood supply is branches from circle of Willis on base of brain• Vessels on surface of brain----penetrate tissue• Uses 20% of our bodies oxygen & glucose needs

– blood flow to an area increases with activity in that area– deprivation of O2 for 4 min does permanent injury

• at that time, lysosome release enzymes• Blood-brain barrier (BBB)

– protects cells from some toxins and pathogens• proteins & antibiotics can not pass but alcohol & anesthetics do

– tight junctions seal together epithelial cells, continuous basement membrane, astrocyte processes covering capillaries


Blood Flow and the Blood-Brain Barrier

• An interruption of blood flow for 1 or 2 minutes impairs neuronal function. – A total deprivation of oxygen for 4 minutes causes

permanent injury.• Because carbohydrate storage in the brain is limited, the

supply of glucose to the brain must be continuous. – Glucose deficiency may produce mental confusion,

dizziness, convulsions, and unconsciousness.


BBB

• A blood-brain barrier (BBB) protects brain cells from harmful substances and pathogens by serving as a selective barrier to prevent passage of many substances from the blood to the brain.

• An injury to the brain due to trauma, inflammation, or toxins causes a breakdown of the BBB, permitting the passage of normally restricted substances into brain tissue.

• The BBB may also prevent entry of drugs that could be used as therapy for brain cancer or other CNS disorders, so research is exploring ways to transport drugs past the BBB.


Protective Covering of the Brain

• The brain is protected by the cranial bones (Figure 7.4) and the cranial meninges (Figure 14.2).– The cranial meninges are continuous with the spinal

meninges and are named dura mater, arachnoid, and pia mater.

– Three extensions of the dura mater separate parts of the brain: the falx cerebri, falx cerebelli, and the tentorium cerebelli.


Protective Coverings of the Brain

• Bone, meninges & fluid• Meninges same as around the

spinal cord– dura mater– arachnoid mater– pia mater

• Dura mater extensions– falx cerebri– tentorium cerebelli– falx cerebelli


CEREBROSPINAL FLUID

• Cerebrospinal fluid (CSF) is a clear, colorless liquid that protects the brain and spinal cord against chemical and physical injuries.


Cerebrospinal Fluid (CSF)

• 80-150 ml (3-5oz)• Clear liquid containing glucose, proteins, & ions• Functions

– mechanical protection • floats brain & softens impact with bony walls

– chemical protection• optimal ionic concentrations for action

potentials– circulation

• nutrients and waste products to and from bloodstream


Ventricles

• There are four CSF filled cavities within the brain called ventricles (Figure 14.3). – A lateral ventricle is located in each hemisphere of the

cerebrum. The lateral ventricles are separated by the septum pellucidum.

– The third ventricle is a narrow cavity along the midline superior to the hypothalamus and between the right and left halves of the thalamus.

– The fourth ventricle is between the brain stem and the cerebellum.


Origin of CSF

• Choroid plexus = capillaries covered by ependymal cells– 2 lateral ventricles, one within each cerebral hemisphere– roof of 3rd ventricle– fourth ventricle


Drainage of CSF from Ventricles

• One median aperture & two lateral apertures allow CSF to exit from the interior of the brain


Flow of Cerebrospinal Fluid


Reabsorption of CSF

• Reabsorbed through arachnoid villi– grapelike clusters of arachnoid penetrate dural venous sinus

• 20 ml/hour reabsorption rate = same as production rate• Reabsorption of CSF

– Reabsorbed through arachnoid villi» grapelike clusters of arachnoid penetrate dural venous sinus

– 20 ml/hour reabsorption rate = same as production rate


Hydrocephalus

• Blockage of drainage of CSF (tumor, inflammation, developmental malformation, meningitis, hemorrhage or injury)– Continued production cause an increase in

pressure --- hydrocephalus– In newborn or fetus, the fontanels allow this

internal pressure to cause expansion of the skull and damage to the brain tissue

• Neurosurgeon implants a drain shunting the CSF to the veins of the neck or the abdomen


THE BRAIN STEM


Medulla Oblongata

• Continuation of spinal cord• Ascending sensory tracts• Descending motor tracts• Nuclei of 5 cranial nerves• Cardiovascular center

– force & rate of heart beat– diameter of blood vessels

• Respiratory center– medullary rhythmicity area sets basic rhythm of breathing

• Information in & out of cerebellum• Reflex centers for coughing, sneezing, swallowing etc.


Ventral Surface of Medulla Oblongata

• Ventral surface bulge – pyramids– large motor tract– decussation of most fibers

• left cortex controls right muscles

• Olive = olivary nucleus– neurons send input to cerebellum– proprioceptive signals– gives precision to movements


Dorsal Surface of Medulla Oblongata

• Nucleus gracilis & nucleus cuneatus = sensory neurons– relay information to thalamus on opposite side of brain

• 5 cranial nerves arise from medulla -- 8 thru 12


XII = Hypoglossal Nerve

• Controls muscles of tongue during speech and swallowing

• Injury deviates tongue to injured side when protruded

• Mixed, primarily motor


XI = Spinal Accessory Nerve

• Cranial portion– arises medulla– skeletal mm of throat & soft

palate• Spinal portion

– arises cervical spinal cord– sternocleidomastoid and

trapezius mm.


X = Vagus Nerve

• Receives sensations from viscera

• Controls cardiac muscle and smooth muscle of the viscera

• Controls secretion of digestive fluids


IX = Glossopharyngeal Nerve

• Stylopharyngeus m. (lifts throat during swallowing)

• Secretions of parotid gland• Somatic sensations & taste

on posterior 1/3 of tongue


VIII = Vestibulocochlear Nerve

• Cochlear branch begins in medulla– receptors in cochlea– hearing– if damaged deafness or tinnitus

(ringing) is produced• Vestibular branch begins in pons

– receptors in vestibular apparatus

– sense of balance– vertigo (feeling of rotation)– ataxia (lack of coordination)


Injury to the Medulla

• Hard blow to the back of the head may be fatal• Cranial nerve malfunctions on same side as injury;

loss of sensation or paralysis of throat or tongue; irregularities in breathing and heart rhythm


Pons

• The pons is located superior to the medulla. It connects the spinal cord with the brain and links parts of the brain with one another by way of tracts (Figures 14.1, 14.5).– relays nerve impulses related to voluntary skeletal

movements from the cerebral cortex to the cerebellum.– contains the pneumotaxic and apneustic areas, which

help control respiration along with the respiratory center in the medulla (Figure 23.24).

– contains nuclei for cranial nerves V trigeminal, VI abducens, VII facial, and VIII vestibulocochlear (vestibular branch only).(Figure 14.5).


Pons

• One inch long• White fiber tracts

ascend and descend• Pneumotaxic &

apneustic areas help control breathing

• Middle cerebellar peduncles carry sensory info to the cerebellum

• Cranial nerves 5 through 7


VII = Facial Nerve

• Motor portion– facial muscles– salivary & nasal and oral

mucous glands & tears• Sensory portion

– taste buds on anterior 2/3’s of tongue


VI = Abducens Nerve

• Lateral rectus eye muscle


V = Trigeminal Nerve

• Motor portion– muscles of mastication

• Sensory portion– touch, pain, &

temperature receptors of the face

• ophthalmic branch• maxillary branch• mandibular branch


Midbrain

• One inch in length• Extends from pons

to diencephalon• Cerebral aqueduct

connects 3rd ventricle above to 4th ventricle below


Midbrain in Section

• Cerebral peduncles---clusters of motor & sensory fibers• Substantia nigra---helps controls subconscious muscle activity• Red nucleus-- rich blood supply & iron-containing pigment

– cortex & cerebellum coordinate muscular movements by sending information here from the cortex and cerebellum


Dorsal Surface of Midbrain

• Corpora quadrigemina = superior & inferior colliculi– coordinate eye movements with visual stimuli– coordinate head movements with auditory stimuli


IV = Trochlear Nerve

• Superior oblique eye muscle


III = Oculomotor Nerve

• Levator palpebrae raises eyelid (ptosis)

• 4 extrinsic eye muscles• 2 intrinsic eye muscles

– accomodation for near vision (changing shape of lens during reading)

– constriction of pupil


Reticular Formation

• Scattered nuclei in medulla, pons & midbrain• Reticular activating system

– alerts cerebral cortex to sensory signals (sound of alarm, flash light, smoke or intruder) to awaken from sleep

– maintains consciousness & helps keep you awake with stimuli from ears, eyes, skin and muscles

• Motor function is involvement with maintaining muscle tone


Cerebellum

• 2 cerebellar hemispheres and vermis (central area)• Function

– correct voluntary muscle contraction and posture based on sensory data from body about actual movements

– sense of equilibrium


Cerebellum

• Transverse fissure between cerebellum & cerebrum• Cerebellar cortex (folia) & central nuclei are grey matter• Arbor vitae = tree of life = white matter


Cerebellar Peduncles

• Superior, middle & inferior peduncles attach to brainstem– inferior carries sensory information from spinal cord– middle carries sensory fibers from cerebral cortex & basal

ganglia– superior carries motor fibers that extend to motor control areas


THE DIENCEPHALON


Diencephalon Surrounds 3rd Ventricle

• Surrounds 3rd ventricle• Superior part of walls is thalamus

• Inferior part of walls & floor is hypothalamus


Thalamus

• The thalamus is located superior to the midbrain and contains nuclei that serve as relay stations for all sensory impulses, except smell, to the cerebral cortex (Figure 14.9).– seven major groups of thalamic nuclei on each side

(Figure 14.9 c and d). – They are the Anterior nucleus, medial nuclei, lateral

group, ventral group, intralaminar nuclei, midline nucleus, and the reticular nucleus.

• It also registers conscious recognition of pain and temperature and some awareness of light touch and pressure.

• It plays an essential role in awareness and the acquisition of knowledge (cognition.)


Thalamus

• 1 inch long mass of gray mater in each half of brain (connected across the 3rd ventricle by intermediate mass)

• Relay station for sensory information on way to cortex• Crude perception of some sensations


Thalamic Nuclei

• Nuclei have different roles– relays auditory and visual impulses, taste and somatic

sensations – receives impulses from cerebellum or basal ganglia– anterior nucleus concerned with emotions, memory and

acquisition of knowledge (cognition)


Hypothalamus

• The hypothalamus – inferior to the thalamus, has four major regions

(mammillary, tuberal, supraoptic, and preoptic)– controls many body activities, and is one of the major

regulators of homeostasis (Figure 14.10).• The hypothalamus has a great number of functions.

– It controls the ANS.– It produces hormones.– It functions in regulation of emotional and behavioral patterns.– It regulates eating and drinking through the feeding center, satiety

center, and thirst center.– It aids in controlling body temperature.– It regulates circadian rhythms and states of consciousness.


Hypothalamus

• Dozen or so nuclei in 4 major regions – mammillary bodies are relay station for olfactory reflexes;

infundibulum suspends the pituitary gland• Major regulator of homeostasis

– receives somatic and visceral input, taste, smell & hearing information; monitors osmotic pressure, temperature of blood


Epithalamus

• The epithalamus lies superior and posterior to the thalamus and contains the pineal gland and the habenular nuclei (Figure 14.7).– The pineal gland secretes melatonin to influence diurnal

cycles in conjunction with the hypothalamus.– The habenular nuclei (Figure 14.7a) are involved in

olfaction, especially emotional responses to odors.


Epithalamus

• Pineal gland– endocrine gland the

size of small pea– secretes melatonin

during darkness– promotes sleepiness

& sets biological clock

• Habenular nuclei– emotional responses

to odors


Subthalamus

• The subthalamus lies immediately inferior to the thalamus and includes tracts and the paired subthalamic nuclei, which connect to motor areas of the cerebrum.– The subthalamic nuclei and red nucleus and substantia

nigra of the midbrain work together with the basal ganglia, cerebellum, and cerebrum in control of body movements.

• Table 14.2 summarizes the functions of the parts of the diencephalon.


Circumventricular Organs

• Parts of the diencephalon, called circumventricular organs (CVOs), can monitor chemical changes in the blood because they lack a blood-brain barrier.

• CVOs include – part of the hypothalamus, – the pineal gland, – the pituitary gland, and a few other nearby structures.

• They function to coordinate homeostatic activities of the endocrine and nervous systems.

• They are also thought to be the site of entry into the brain of HIV.


THE CEREBRUM

• The cerebrum is the largest part of the brain .– The surface layer, the cerebral cortex, is 2-4 mm thick

and is composed of gray matter. The cortex contains billions of neurons.

– The cortex contains gyri (convolutions), deep grooves called fissures, and shallower sulci. (Figure 14.11a)

• Beneath the cortex lies the cerebral white matter, tracts that connect parts of the brain with itself and other parts of the nervous system.

• The cerebrum is nearly separated into right and left halves, called hemispheres, by the longitudinal fissure. – Internally it remains connected by the corpus callosum, a

bundle of transverse white fibers. Figure 14.12)


Chapter 14Part 2


Lecture Outline


Cerebrum (Cerebral Hemispheres)

• Cerebral cortex is gray matteroverlying white matter– 2-4 mm thick containing

billions of cells– grew quickly; formed folds

(gyri) and grooves (sulci or fissures)

• Longitudinal fissure separates left & right cerebral hemispheres– Corpus callosum is a

commisure (band of white matter) connecting left and right cerebral hemispheres

• Each hemisphere is subdivided into 4 lobes


Lobes

• Each cerebral hemisphere is further subdivided into four lobes by sulci or fissures (Figure 14.11 a,b)– frontal, parietal, temporal, and occipital.

• A fifth part of the cerebrum, the insula, lies deep to the parietal, frontal, and temporal lobes and cannot be seen in an external view of the brain.



Lobes and Fissures• Longitudinal fissure

(green)• Frontal lobe• Central sulcus (yellow)

– precentral & postcentral gyrus

• Parietal lobe• Parieto-occipital sulcus• Occipital lobe• Lateral sulcus (blue)• Temporal lobe• Insula


Insula within Lateral Fissure


White Matter

• The white matter is under the cortex and consists of myelinated axons running in three principal directions (Figure 14.12).– Association fibers connect and transmit nerve impulses

between gyri in the same hemisphere.– Commissural fibers connect gyri in one cerebral

hemisphere to the corresponding gyri in the opposite hemisphere.

– Projection fibers form ascending and descending tracts that transmit impulses from the cerebrum to other parts of the brain and spinal cord.


Cerebral White Matter

• Association fibers between gyri in same hemisphere• Commissural fibers from one hemisphere to other • Projection fibers form descending & ascending tracts


Basal Ganglia

The basal ganglia are paired masses of gray matter in each cerebral hemisphere (Figure 14.13).

• Connections to red nucleus, substantia nigra & subthalamus

• Input & output with cerebral cortex, thalamus & hypothalamus

• Control large automatic movements of skeletal muscles



Caudate nucleus

• Lentiform and caudate nuclei are known as the corpus striatum.– Nearby structures functionally linked to the basal ganglia

are the substantia nigra and the subthalamic nuclei.– They are responsible for helping to control muscular

movements.• Damage to the basal ganglis results in tremor, rigidity, and involuntary

muscle movements. In Parkinson’s disease neurons from the substantia nigra to the putamen and cuadate nucleus degenerate.

• Basal ganglia also help initiate and terminate some cognitive processes. Obsessive compulsive disorder, schizophrenia, chronic anxiety are thought to involve dysfunction of the circuits between the basal ganglis and limbic system


Limbic System

• The limbic system is found in the cerebral hemispheres and diencephalon (Figure 14.14).– limbic lobe– dentate gyrus– amygdala– septal nuclei– mammilary bodies, mammilothalmic tract– anterior and medial nuclei of the thalamus, – olfactory bulbs– fornix, stria terminalis, stria medulllaris, – medial forebrain bundle

• It functions in emotional aspects of behavior and memory, and is associated with pleasure and pain.


Limbic System

• Emotional brain--intense pleasure & intense pain• Strong emotions increase efficiency of memory


Brain Injuries

• Brain injuries are commonly associated with head injuries and result, in part, from displacement and distortion of neuronal tissue at the moment of impact and in part from the release of disruptive chemicals from injured brain cells.

• Various degrees of brain injury are described by the terms – concussion, contusion, and laceration.


Brain Injuries

• Causes of damage– displacement or distortion of tissue at impact– increased intracranial pressure– infections– free radical damage after ischemia

• Concussion---temporary loss of consciousness– headache, drowsiness, confusion, lack of concentration

• Contusion--bruising of brain (less than 5 min unconsciousness but blood in CSF)

• Laceration--tearing of brain (fracture or bullet)– increased intracranial pressure from hematoma


Sensory Areas

• The sensory areas of the cerebral cortex are concerned with the reception and interpretation of sensory impulses.

• Some important sensory areas include – primary somatosensory area, – primary visual area, – primary auditory area, and – primary gustatory area


Sensory Areas of Cerebral Cortex

Receive sensory information from the thalamusPrimary somatosensory area = postcentral gyrus = 1,2,3Primary visual area = 17Primary auditory area = 41 & 42Primary gustatory area = 43


Motor Areas

• The motor areas are the regions that govern muscular movement.

• Two important motor areas are – primary motor area and– Broca’s speech area. (Figure 14.15)


Motor Areas of Cerebral Cortex

• Voluntary motor initiation– Primary motor area = 4 = precentral gyrus

• controls voluntary contractions of skeletal muscles on other side– Motor speech area = 44 = Broca’s area

• production of speech -- control of tongue & airway


Association Areas of Cerebral Cortex

• Somatosensory area = 5 & 7 (integrate & interpret)• Visual association area = 18 & 19 (recognize & evaluate)• Auditory association area(Wernicke’s) = 22(words become speech)• Gnostic area = 5,7,39 & 40 (integrate all senses & respond)• Premotor area = 6 (learned skilled movements such as typing)• Frontal eye field =8 (scanning eye movements such as phone book)


Association Areas

• The association areas are concerned with complex integrative functions such as memory, emotions, reasoning, will, judgment, personality traits, and intelligence. (Figure 14.15)– Injury to the association or motor speech areas results in

aphasia, an inability to use or comprehend words. (Clinical Application)


Aphasia

Language areas are located in the left cerebral hemisphere of most people

Inability to use or comprehend words = aphasia• nonfluent aphasia = inability to properly form words

– know what want to say but can not speak – damage to Broca’s speech area

• fluent aphasia = faulty understanding of spoken or written words– faulty understanding of spoken or written words

• word deafness = an inability to understand spoken words• word blindness = an inability to understand written words

– damage to common integrative area or auditory association area


Hemispheric Lateralization

• Although the two cerebral hemispheres share many functions, each hemisphere also performs unique functions.

• hemispheric lateralization (Figure 14.16).– The left hemisphere is more important for right-handed

control, spoken and written language, and numerical and scientific skills.

– The right hemisphere is more important for left-handed control, musical and artistic awareness, space and pattern perception, insight, imagination, and generating mental images of sight, sound, touch, taste, and smell.

• Table 14.3 summarizes some of the distinctive functions that are more likely to reside in the left or right hemisphere.



• Functional specialization of each hemisphere more pronounced in men

• Females generally have larger connections between 2 sides

• Damage to left side produces aphasia

• Damage to same area on right side lead to speech with little emotional inflection


Brain Waves

• An EEG may be used to diagnose epilepsy and other seizure disorders, infectious diseases, tumors, trauma, hematomas, metabolic abnormalities, degenerative diseases, and periods of unconsciousness and confusion; it may also provide useful information regarding sleep and wakefulness.

• An EEG may also be one criterion in confirming brain death (complete absence of brain waves in two EEGs taken 24 hours apart).

• Figure 14.17 shows four kinds of brain waves that can be recorded from normal individuals.


Electroencephalogram (EEG)

• Brain waves are millions of nerve action potentials in cerebral cortex– diagnosis of brain

disorders (epilepsy)– brain death (absence of

activity in 2 EEGs 24 hours apart)

• Alpha -- awake & resting• Beta -- mental activity• Theta -- emotional stress• Delta -- deep sleep


II -- Optic Nerve

• Connects to retina supplying vision


I -- Olfactory Nerve

• Extends from olfactory mucosa of nasal cavity to olfactory bulb

• Sense of smell


Developmental Anatomy of the NS

• Begins in 3rd week– ectoderm forms thickening (neural

plate)– plate folds inward to form neural

groove– edges of folds join to form neural tube

• Neural crest tissue forms:– spinal & cranial nerves– dorsal root & cranial nerve ganglia– adrenal gland medulla

• Layers of neural tube form:– marginal layer which forms white

matter– mantle layer forms gray matter– ependymal layer forms linings of

cavities within NS


Dorsal View of Neural Groove


Development of Principal Parts• By end of 4th week, 3 anterior enlargements occur

– prosencephalon– mesencephalon– rhombencephalon


Development of Principal Parts

• By 5th week, 5 enlarged areas exist• Prosencephalon

– telencephalon– diencephalon

• Mesencephalon• Rhombencephalon

– metencephalon– myelencephalon

• Neural tube defects– associated with low levels of folic acid (B vitamins)– spina bifida is failure to close of vertebrae– anencephaly is absence of skull & cerebral

hemispheres



Aging & the Nervous System

• Years 1 to 2– rapid increase in size due to increase in size of neurons,

growth of neuroglia, myelination & development of dendritic branches

• Early adulthood until death– brain weight declines until only 93% by age 80– number of synaptic contacts declines– processing of information diminishes– conduction velocity decreases– voluntary motor movements slow down– reflexes slow down


DISORDERS: HOMEOSTATIC IMBALANCES• The most common brain disorder is a cerebrovascular

accident (CVA or stroke).• Third leading cause of death after heart attacks and cancer• CVAs are classified into two principal types:

– ischemic (the most common type), due to a decreased blood supply

– hemorrhagic, due to a blood vessel in the brain that bursts.

• Common causes of CVAs are intracerebral hemorrhage, emboli, and atherosclerosis.

• Tissue plasminogen activator (t-PA) used within 3 hours of ischemic CVA onset will decrease permanent disability


Transient Ischemic Attack (TIA)

• Episode of temporary cerebral dysfunction• Cause

– impaired blood flow to the brain• Symptoms

– dizziness, slurred speech, numbness, paralysis on one side, double vision

– reach maximum intensity almost immediately– persists for 5-10 minutes & leaves no deficits

• Treatment is aspirin or anticoagulants; artery bypass grafting or carotid endarterectomy


Alzheimer Disease (AD)

• Dementia = loss of reasoning, ability to read, write, talk, eat & walk

• Afflicts 11% of population over 65• Great loss of neurons in specific regions (e.g.,

hippocampus and cerebral cortex); loss of neurons that release acetylcholine

• Plaques of abnormal proteins deposited outside neurons (amyloid plaques).

• Tangled protein filaments within neurons (neurofibrillary tangles).


Tumors

• Brain tumor is an abnormal growth of tissue it may be malignant or benign.

• Attention Deficit Hyperactivity Disorder (ADHD) is a laerning disorder characterized by poor attention span, hyperactivity and inappropriate impulsiveness.


CRANIAL NERVE Review

• Twelve pairs of cranial nerves originate from the brain (Figure 14.5)– named primarily on the basis of distribution and

numbered by order of attachment to the brain.• Some cranial nerves (I, II, and VIII) contain only sensory

fibers and are called sensory nerves. The rest are mixed nerves because they contain both sensory and motor fibers.

• Figures 14.18 – 14.27 illustrate the distribution of many of the cranial nerves.

• Table 14.4 presents a summary of cranial nerves, including clinical applications related to their dysfunction.


Cranial Nerve Review




















end


Chapter 14Part 2


Lecture Outline


Cerebrum (Cerebral Hemispheres)

• Cerebral cortex is gray matteroverlying white matter– 2-4 mm thick containing

billions of cells– grew quickly; formed folds

(gyri) and grooves (sulci or fissures)

• Longitudinal fissure separates left & right cerebral hemispheres– Corpus callosum is a

commisure (band of white matter) connecting left and right cerebral hemispheres

• Each hemisphere is subdivided into 4 lobes


Lobes

• Each cerebral hemisphere is further subdivided into four lobes by sulci or fissures (Figure 14.11 a,b)– frontal, parietal, temporal, and occipital.

• A fifth part of the cerebrum, the insula, lies deep to the parietal, frontal, and temporal lobes and cannot be seen in an external view of the brain.



Lobes and Fissures• Longitudinal fissure

(green)• Frontal lobe• Central sulcus (yellow)

– precentral & postcentral gyrus

• Parietal lobe• Parieto-occipital sulcus• Occipital lobe• Lateral sulcus (blue)• Temporal lobe• Insula


Insula within Lateral Fissure


White Matter

• The white matter is under the cortex and consists of myelinated axons running in three principal directions (Figure 14.12).– Association fibers connect and transmit nerve impulses

between gyri in the same hemisphere.– Commissural fibers connect gyri in one cerebral

hemisphere to the corresponding gyri in the opposite hemisphere.

– Projection fibers form ascending and descending tracts that transmit impulses from the cerebrum to other parts of the brain and spinal cord.


Cerebral White Matter

• Association fibers between gyri in same hemisphere• Commissural fibers from one hemisphere to other • Projection fibers form descending & ascending tracts


Basal Ganglia

The basal ganglia are paired masses of gray matter in each cerebral hemisphere (Figure 14.13).

• Connections to red nucleus, substantia nigra & subthalamus

• Input & output with cerebral cortex, thalamus & hypothalamus

• Control large automatic movements of skeletal muscles



Caudate nucleus

• Lentiform and cuadate nuclei are known as the corpus striatum.– Nearby structures functionally linked to the basal ganglia

are the substantia nigra and the subthalamic nuclei.– They are responsible for helping to control muscular

movements.• Damage to the basal ganglis results in tremor, rigidity, and involuntary

muscle movements. In Parkinson’s disease neurons from the substantia nigra to the putamen and cuadate nucleus degenerate.

• Basal ganglia also help initiate and terminate some cognitive processes. Obsessive compulsive disorder, schizophrenia, chronic anxiety are thought to involve dysfunction of the circuits between the basal ganglis and limbic system


Limbic System

• The limbic system is found in the cerebral hemispheres and diencephalon (Figure 14.14).– limbic lobe– dentate gyrus– amygdala– septal nuclei– mammilary bodies, mammilothalmic tract– anterior and medial nuclei of the thalamus, – olfactory bulbs– fornix, stria terminalis, stria medulllaris, – medial forebrain bundle

• It functions in emotional aspects of behavior and memory, and is associated with pleasure and pain.


Limbic System

• Emotional brain--intense pleasure & intense pain• Strong emotions increase efficiency of memory


Brain Injuries

• Brain injuries are commonly associated with head injuries and result, in part, from displacement and distortion of neuronal tissue at the moment of impact and in part from the release of disruptive chemicals from injured brain cells.

• Various degrees of brain injury are described by the terms – concussion, contusion, and laceration.


Brain Injuries

• Causes of damage– displacement or distortion of tissue at impact– increased intracranial pressure– infections– free radical damage after ischemia

• Concussion---temporary loss of consciousness– headache, drowsiness, confusion, lack of concentration

• Contusion--bruising of brain (less than 5 min unconsciousness but blood in CSF)

• Laceration--tearing of brain (fracture or bullet)– increased intracranial pressure from hematoma


Sensory Areas

• The sensory areas of the cerebral cortex are concerned with the reception and interpretation of sensory impulses.

• Some important sensory areas include – primary somatosensory area, – primary visual area, – primary auditory area, and – primary gustatory area


Sensory Areas of Cerebral Cortex

Receive sensory information from the thalamusPrimary somatosensory area = postcentral gyrus = 1,2,3Primary visual area = 17Primary auditory area = 41 & 42Primary gustatory area = 43


Motor Areas

• The motor areas are the regions that govern muscular movement.

• Two important motor areas are – primary motor area and– Broca’s speech area. (Figure 14.15)


Motor Areas of Cerebral Cortex

• Voluntary motor initiation– Primary motor area = 4 = precentral gyrus

• controls voluntary contractions of skeletal muscles on other side– Motor speech area = 44 = Broca’s area

• production of speech -- control of tongue & airway


Association Areas of Cerebral Cortex

• Somatosensory area = 5 & 7 (integrate & interpret)• Visual association area = 18 & 19 (recognize & evaluate)• Auditory association area(Wernicke’s) = 22(words become speech)• Gnostic area = 5,7,39 & 40 (integrate all senses & respond)• Premotor area = 6 (learned skilled movements such as typing)• Frontal eye field =8 (scanning eye movements such as phone book)


Association Areas

• The association areas are concerned with complex integrative functions such as memory, emotions, reasoning, will, judgment, personality traits, and intelligence. (Figure 14.15)– Injury to the association or motor speech areas results in

aphasia, an inability to use or comprehend words. (Clinical Application)


Aphasia

Language areas are located in the left cerebral hemisphere of most people

Inability to use or comprehend words = aphasia• nonfluent aphasia = inability to properly form words

– know what want to say but can not speak – damage to Broca’s speech area

• fluent aphasia = faulty understanding of spoken or written words– faulty understanding of spoken or written words

• word deafness = an inability to understand spoken words• word blindness = an inability to understand written words

– damage to common integrative area or auditory association area



• Although the two cerebral hemispheres share many functions, each hemisphere also performs unique functions.

• hemispheric lateralization (Figure 14.16).– The left hemisphere is more important for right-handed

control, spoken and written language, and numerical and scientific skills.

– The right hemisphere is more important for left-handed control, musical and artistic awareness, space and pattern perception, insight, imagination, and generating mental images of sight, sound, touch, taste, and smell.

• Table 14.3 summarizes some of the distinctive functions that are more likely to reside in the left or right hemisphere.



• Functional specialization of each hemisphere more pronounced in men

• Females generally have larger connections between 2 sides

• Damage to left side produces aphasia

• Damage to same area on right side lead to speech with little emotional inflection


Brain Waves

• An EEG may be used to diagnose epilepsy and other seizure disorders, infectious diseases, tumors, trauma, hematomas, metabolic abnormalities, degenerative diseases, and periods of unconsciousness and confusion; it may also provide useful information regarding sleep and wakefulness.

• An EEG may also be one criterion in confirming brain death (complete absence of brain waves in two EEGs taken 24 hours apart).

• Figure 14.17 shows four kinds of brain waves that can be recorded from normal individuals.


Electroencephalogram (EEG)

• Brain waves are millions of nerve action potentials in cerebral cortex– diagnosis of brain

disorders (epilepsy)– brain death (absence of

activity in 2 EEGs 24 hours apart)

• Alpha -- awake & resting• Beta -- mental activity• Theta -- emotional stress• Delta -- deep sleep


II -- Optic Nerve

• Connects to retina supplying vision


I -- Olfactory Nerve

• Extends from olfactory mucosa of nasal cavity to olfactory bulb

• Sense of smell


Developmental Anatomy of the NS

• Begins in 3rd week– ectoderm forms thickening (neural

plate)– plate folds inward to form neural

groove– edges of folds join to form neural tube

• Neural crest tissue forms:– spinal & cranial nerves– dorsal root & cranial nerve ganglia– adrenal gland medulla

• Layers of neural tube form:– marginal layer which forms white

matter– mantle layer forms gray matter– ependymal layer forms linings of

cavities within NS


Dorsal View of Neural Groove


Development of Principal Parts• By end of 4th week, 3 anterior enlargements occur

– prosencephalon– mesencephalon– rhombencephalon


Development of Principal Parts

• By 5th week, 5 enlarged areas exist• Prosencephalon

– telencephalon– diencephalon

• Mesencephalon• Rhombencephalon

– metencephalon– myelencephalon

• Neural tube defects– associated with low levels of folic acid (B vitamins)– spina bifida is failure to close of vertebrae– anencephaly is absence of skull & cerebral

hemispheres



Aging & the Nervous System

• Years 1 to 2– rapid increase in size due to increase in size of neurons,

growth of neuroglia, myelination & development of dendritic branches

• Early adulthood until death– brain weight declines until only 93% by age 80– number of synaptic contacts declines– processing of information diminishes– conduction velocity decreases– voluntary motor movements slow down– reflexes slow down


DISORDERS: HOMEOSTATIC IMBALANCES• The most common brain disorder is a cerebrovascular

accident (CVA or stroke).• Third leading cause of death after heart attacks and cancer• CVAs are classified into two principal types:

– ischemic (the most common type), due to a decreased blood supply

– hemorrhagic, due to a blood vessel in the brain that bursts.

• Common causes of CVAs are intracerebral hemorrhage, emboli, and atherosclerosis.

• Tissue plasminogen activator (t-PA) used within 3 hours of ischemic CVA onset will decrease permanent disability


Transient Ischemic Attack (TIA)

• Episode of temporary cerebral dysfunction• Cause

– impaired blood flow to the brain• Symptoms

– dizziness, slurred speech, numbness, paralysis on one side, double vision

– reach maximum intensity almost immediately– persists for 5-10 minutes & leaves no deficits

• Treatment is aspirin or anticoagulants; artery bypass grafting or carotid endarterectomy


Alzheimer Disease (AD)

• Dementia = loss of reasoning, ability to read, write, talk, eat & walk

• Afflicts 11% of population over 65• Great loss of neurons in specific regions (e.g.,

hippocampus and cerebral cortex); loss of neurons that release acetylcholine

• Plaques of abnormal proteins deposited outside neurons (amyloid plaques).

• Tangled protein filaments within neurons (neurofibrillary tangles).


Tumors

• Brain tumor is an abnormal growth of tissue it may be malignant or benign.

• Attention Deficit Hyperactivity Disorder (ADHD) is a laerning disorder characterized by poor attention span, hyperactivity and inappropriate impulsiveness.


CRANIAL NERVE Review

• Twelve pairs of cranial nerves originate from the brain (Figure 14.5)– named primarily on the basis of distribution and

numbered by order of attachment to the brain.• Some cranial nerves (I, II, and VIII) contain only sensory

fibers and are called sensory nerves. The rest are mixed nerves because they contain both sensory and motor fibers.

• Figures 14.18 – 14.27 illustrate the distribution of many of the cranial nerves.

• Table 14.4 presents a summary of cranial nerves, including clinical applications related to their dysfunction.






















end


Chapter 15

The Autonomic Nervous System

Lecture Outline


INTRODUCTION

• The autonomic nervous system (ANS) operates via reflex arcs.

• Operation of the ANS to maintain homeostasis, however, depends on a continual flow of sensory afferent input, from receptors in organs, and efferent motor output to the same effector organs.

• Structurally, the ANS includes autonomic sensory neurons, integrating centers in the CNS, and autonomic motor neurons.

• Functionally, the ANS usually operates without conscious control.

• The ANS is regulated by the hypothalamus and brain stem.


Chapter 15 The Autonomic Nervous System

• Regulate activity of smooth muscle, cardiac muscle & certain glands

• Structures involved– general visceral afferent neurons– general visceral efferent neurons– integration center within the brain

• Receives input from limbic system and other regions of the cerebrum


SOMATIC AND AUTONOMIC NERVOUS SYSTEMS

• The somatic nervous system contains both sensory and motor neurons.

• The somatic sensory neurons receive input from receptors of the special and somatic senses.

• These sensations are consciously perceived.• Somatic motor neurons innervate skeletal muscle to

produce conscious, voluntary movements.• The effect of a motor neuron is always excitation.


SOMATIC AND AUTONOMIC NERVOUS SYSTEMS

• The autonomic nervous system contains both autonomic sensory and motor neurons.– Autonomic sensory neurons are associated with

interoceptors.– Autonomic sensory input is not consciously perceived.

• The ANS also receives sensory input from somatic senses and special sensory neurons.

• The autonomic motor neurons regulate visceral activities by either increasing (exciting) or decreasing (inhibiting) ongoing activities of cardiac muscle, smooth muscle, and glands.– Most autonomic responses can not be consciously

altered or suppressed.


SOMATIC vs AUTONOMIC NERVOUS SYSTEMS

• All somatic motor pathways consist of a single motor neuron

• Autonomic motor pathways consists of two motor neurons in series – The first autonomic neuron motor has its cell body in the

CNS and its myelinated axon extends to an autonomic ganglion.

• It may extend to the adrenal medullae rather than an autonomic ganglion

– The second autonomic motor neuron has its cell body in an autonomic ganglion; its nonmyelinated axon extends to an effector.


Somatic versus Autonomic NS


Basic Anatomy of ANS

• Preganglionic neuron– cell body in brain or spinal cord – axon is myelinated type B fiber that extends to autonomic

ganglion• Postganglionic neuron

– cell body lies outside the CNS in an autonomic ganglion– axon is unmyelinated type C fiber that terminates in a visceral

effector


Sympathetic vs. Parasympathetic NS


AUTONOMIC NERVOUS SYSTEM

• The output (efferent) part of the ANS is divided into two principal parts: – the sympathetic division– the parasympathetic division– Organs that receive impulses from both sympathetic and

parasympathetic fibers are said to have dual innervation.• Table 15.1 summarizes the similarities and differences

between the somatic and autonomic nervous systems.


Sympathetic ANS vs. Parasympathetic ANS


Divisions of the ANS

• 2 major divisions– parasympathetic– sympathetic

• Dual innervation– one speeds up organ– one slows down organ– Sympathetic NS

increases heart rate– Parasympathetic NS

decreases heart rate


Divisions of the ANS

• 2 major divisions– parasympathetic– sympathetic

• Dual innervation– one speeds up organ– one slows down organ– Sympathetic NS

increases heart rate– Parasympathetic NS

decreases heart rate


Autonomic Ganglia


Sympathetic Ganglia

• These ganglia include the sympathetic trunk or vertebral chain or paravertebral ganglia that lie in a vertical row on either side of the vertebral column (Figures 15.2).

• Other sympathetic ganglia are the prevertebral or collateral ganglia that lie anterior to the spinal column and close to large abdominal arteries. – celiac– superior mesenteric– inferior mesenteric ganglia– (Figures 15.2 and 15.4).


Parasympathetic Ganglia

• Parasympathetic ganglia are the terminal or intramural ganglia that are located very close to or actually within the wall of a visceral organ.

• Examples of terminal ganglia include (Figure 15.3)– ciliary, – pterygopalatine, – submandibular,– otic ganglia


Sympathetic ANS vs. Parasympathetic ANS


Dual Innervation, Autonomic Ganglia

• Sympathetic (thoracolumbar) division– preganglionic cell bodies in

thoracic and first 2 lumbar segments of spinal cord

• Ganglia– trunk (chain) ganglia near

vertebral bodies– prevertebral ganglia near

large blood vessel in gut (celiac, superior mesenteric, inferior mesenteric)

• Parasympathetic (craniosacral) division– preganglionic cell

bodies in nuclei of 4 cranial nerves and the sacral spinal cord

• Ganglia– terminal ganglia in wall

of organ


Autonomic Plexuses

• These are tangled networks of sympathetic and parasympathetic neurons (Figure 15.4) which lie along major arteries.

• Major autonomic plexuses include – cardiac, – pulmonary, – celiac, – superior mesenteric, – inferior mesenteric, – renal and – hypogastric


Autonomic Plexuses

• Cardiac plexus• Pulmonary plexus• Celiac (solar) plexus• Superior mesenteric• Inferior mesenteric• Hypogastric


Autonomic Plexuses

• Cardiac plexus• Pulmonary plexus• Celiac (solar) plexus• Superior mesenteric• Inferior mesenteric• Hypogastric


Structures of Sympathetic NS

• Preganglionic cell bodies at T1 to L2• Rami communicantes

– white ramus = myelinated = preganglionic fibers– gray ramus = unmyelinated = postganglionic fibers

• Postganglionic cell bodies– sympathetic chain ganglia along the spinal column– prevertebral ganglia at a distance from spinal cord

• celiac ganglion• superior mesenteric ganglion• inferior mesenteric ganglion


Postganglionic Neurons: Sympathetic vs. Parasympathetic

• Sympathetic preganglionic neurons pass to the sympathetic trunk. They may connect to postganglionic neurons in the following ways. (Figure 17.5).– May synapse with postganglionic neurons in the ganglion

it first reaches.– May ascend or descend to a higher of lower ganglion

before synapsing with postganglionic neurons.– May continue, without synapsing, through the

sympathetic trunk ganglion to a prevertebral ganglion where it synapses with the postganglionic neuron.

• Parasympathetic preganglionic neurons synapse with postganglionic neurons in terminal ganglia (Figure 17.3).


Pathways of Sympathetic Fibers

• Spinal nerve route– out same level

• Sympathetic chain route– up chain & out spinal

nerve• Collateral ganglion route

– out splanchnic nerve to collateral ganglion


Organs Innervated by Sympathetic NS

• Structures innervated by each spinal nerve– sweat glands, arrector pili mm., blood vessels to skin

& skeletal mm.• Thoracic & cranial plexuses supply:

– heart, lungs, esophagus & thoracic blood vessels– plexus around carotid artery to head structures

• Splanchnic nerves to prevertebral ganglia supply:– GI tract from stomach to rectum, urinary &

reproductive organs


Ganglia & Plexuses of Sympathetic NS


Circuitry of Sympathetic NS

• Divergence = each preganglionic cell synapses on many postganglionic cells

• Mass activation due to divergence– multiple target organs– fight or flight response explained

• Adrenal gland– modified cluster of postganglionic cell bodies that

release epinephrine & norepinephrine into blood


Application

• In Horner’s syndrome, the sympathetic innervation to one side of the face is lost.


Structure of the Parasympathetic Division

• The cranial outflow consists of preganglionic axons that extend from the brain stem in four cranial nerves. (Figure 15.3). – The cranial outflow consists of four pairs of ganglia and

the plexuses associated with the vagus (X) nerve.• The sacral parasympathetic outflow consists of

preganglionic axons in the anterior roots of the second through fourth sacral nerves and they form the pelvic splanchnic nerve. (Figure15.3)


Anatomy of Parasympathetic NS

• Preganglionic cell bodies found in– 4 cranial nerve nuclei in

brainstem – S2 to S4 spinal cord

• Postganglionic cell bodies very near or in the wall of the target organ in a terminal ganglia


Parasympathetic Cranial Nerves

• Oculomotor nerve– ciliary ganglion in orbit– ciliary muscle & pupillary constrictor muscle inside eyeball

• Facial nerve– pterygopalatine and submandibular ganglions– supply tears, salivary & nasal secretions

• Glossopharyngeal– otic ganglion supplies parotid salivary gland

• Vagus nerve– many brs supply heart, pulmonary and GI tract as far as the

midpoint of the colon


Parasympathetic Sacral Nerve Fibers

• Form pelvic splanchnic nerves

• Preganglionic fibers end on terminal ganglia in walls of target organs

• Innervate smooth muscle and glands in colon, ureters, bladder & reproductive organs


ANS NEUROTRANSMITTERS AND RECEPTORS


ANS Neurotransmitters

• Classified as either cholinergic or adrenergic neurons based upon the neurotransmitter released

• Adrenergic

• Cholinergic


Cholinergic Neurons and Receptors

• Cholinergic neurons release acetylcholine – all preganglionic neurons– all parasympathetic

postganglionic neurons– few sympathetic

postganglionic neurons (to most sweat glands)

• Excitation or inhibition depending upon receptor subtype and organ involved.


Cholinergic Neurons and Receptors

• Cholinergic receptors are integral membrane proteins in the postsynaptic plasma membrane.

• The two types of cholinergic receptors are nicotinic and muscarinic receptors (Figure 15.6 a , b).– Activation of nicotinic receptors causes excitation of the

postsynaptic cell.• Nicotinic receptors are found on dendrites & cell

bodies of autonomic NS cells (and at NMJ.)– Activation of muscarinic receptors can cause either

excitation or inhibition depending on the cell that bears the receptors.

• Muscarinic receptors are found on plasma membranes of all parasympathetic effectors


Adrenergic Neurons and Receptors

• Adrenergic neurons release norepinephrine (NE) )– from postganglionic

sympathetic neurons only

• Excites or inhibits organs depending on receptors

• NE lingers at the synapse until enzymatically inactivated by monoamine oxidase (MAO) or catechol-O-methyltransferase (COMT)


Adrenergic Neurons and Receptors

• The main types of adrenergic receptors are alpha and beta receptors. These receptors are further classified into subtypes.– Alpha1 and Beta1 receptors produce excitation– Alpha2 and Beta2 receptors cause inhibition– Beta3 receptors (brown fat) increase thermogenesis

• Effects triggered by adrenergic neurons typically are longer lasting than those triggered by cholinergic neurons.

• Table 15.2 describes the location of the subtypes of cholinergic and adrenergic receptors and summarizes the responses that occur when each type of receptor is activated.


Receptor Agonists and Antagonists

• An agonist is a substance that binds to and activates a receptor, mimicking the effect of a natural neurotransmitter or hormone.

• An antagonist is a substance that binds to and blocks a receptor, preventing a natural neurotransmitter or hormone from exerting its effect.

• Drugs can serve as agonists or antagonists to selectively activate or block ANS receptors.


Physiological Effects of the ANS

• Most body organs receive dual innervation– innervation by both sympathetic & parasympathetic

• Hypothalamus regulates balance (tone) between sympathetic and parasympathetic activity levels

• Some organs have only sympathetic innervation

– sweat glands, adrenal medulla, arrector pili mm & many blood vessels

– controlled by regulation of the “tone” of the sympathetic system


Sympathetic Responses• Dominance by the sympathetic system is caused by physical

or emotional stress -- “E situations”– emergency, embarrassment, excitement, exercise

• Alarm reaction = flight or fight response– dilation of pupils– increase of heart rate, force of contraction & BP– decrease in blood flow to nonessential organs– increase in blood flow to skeletal & cardiac muscle– airways dilate & respiratory rate increases– blood glucose level increase

• Long lasting due to lingering of NE in synaptic gap and release of norepinephrine by the adrenal gland


Parasympathetic Responses

• Enhance “rest-and-digest” activities• Mechanisms that help conserve and restore body energy

during times of rest• Normally dominate over sympathetic impulses• SLUDD type responses = salivation, lacrimation, urination, digestion

& defecation and 3 “decreases”--- decreased HR, diameter of airways and diameter of pupil

• Paradoxical fear when there is no escape route or no way to win– causes massive activation of parasympathetic division– loss of control over urination and defecation


PHYSIOLOGICAL EFFECTS OF THE ANS - Summary

• The sympathetic responses prepare the body for emergency situations (the fight-or-flight responses).

• The parasympathetic division regulates activities that conserve and restore body energy (energy conservation-restorative system).

• Table 15.4 summarizes the responses of glands, cardiac muscle, and smooth muscle to stimulation by the ANS.


INTEGRATION AND CONTROL OF AUTONOMIC FUNCTIONS


Autonomic or Visceral Reflexes

• A visceral autonomic reflex adjusts the activity of a visceral effector, often unconsciously.– changes in blood pressure, digestive functions etc– filling & emptying of bladder or defecation

• Autonomic reflexes occur over autonomic reflex arcs. Components of that reflex arc:– sensory receptor– sensory neuron– integrating center– pre & postganglionic motor neurons– visceral effectors


Control of Autonomic NS

• Not aware of autonomic responses because control center is in lower regions of the brain

• Hypothalamus is major control center– input: emotions and visceral sensory information

• smell, taste, temperature, osmolarity of blood, etc– output: to nuclei in brainstem and spinal cord– posterior & lateral portions control sympathetic NS

• increase heart rate, inhibition GI tract, increase temperature

– anterior & medial portions control parasympathetic NS• decrease in heart rate, lower blood pressure,

increased GI tract secretion and mobility


Autonomic versus Somatic NS - Review

• Somatic nervous system– consciously perceived sensations– excitation of skeletal muscle– one neuron connects CNS to organ

• Autonomic nervous system– unconsciously perceived visceral sensations – involuntary inhibition or excitation of smooth muscle,

cardiac muscle or glandular secretion– two neurons needed to connect CNS to organ

• preganglionic and postganglionic neurons


DISORDERS

• Raynaud’s phenomenon is due to excessive sympathetic stimulation of smooth muscle in the arterioles of the digits as a result the digits become ischemic after exposure to cold or with emotional stress.


Autonomic Dysreflexia

• Exaggerated response of sympathetic NS in cases of spinal cord injury above T6

• Certain sensory impulses trigger mass stimulation of sympathetic nerves below the injury

• Result– vasoconstriction which elevates blood pressure– parasympathetic NS tries to compensate by slowing heart

rate & dilating blood vessels above the injury– pounding headaches, sweating warm skin above the injury

and cool dry skin below– can cause seizures, strokes & heart attacks


end


Chapter 16

Sensory, Motor & Integrative Systems

Lecture Outline


INTRODUCTION

• The components of the brain interact to receive sensory input, integrate and store the information, and transmit motor responses.

• To accomplish the primary functions of the nervous system there are neural pathways to transmit impulses from receptors to the circuitry of the brain, which manipulates the circuitry to form directives that are transmitted via neural pathways to effectors as a response.


Chapter 16Sensory, Motor & Integrative Systems

• Levels and components of sensation• Pathways for sensations from body to brain• Pathways for motor signals from brain to body• Integration Process

– wakefulness and sleep– learning and memory


SENSATION

• Sensation is a conscious or unconscious awareness of external or internal stimuli.


Is Sensation Different from Perception?

• Perception is the conscious awareness & interpretation of a sensation.– precisely localization & identification– memories of our perceptions are stored in the cortex

• Sensation is any stimuli the body is aware of– Chemoreceptors, thermoreceptors, nociceptors, baroreceptors– What are we not aware of?

• X-rays, ultra high frequency sound waves, UV light– We have no sensory receptors for those stimuli


Sensory Modalities

• Sensory Modality is the property by which one sensation is distinguished from another.

• Different types of sensations– touch, pain, temperature, vibration, hearing, vision– Generally, each type of sensory neuron can respond

to only one type of stimulus.• Two classes of sensory modalities

– general senses – special senses


Sensory Modalities

• The classes of sensory modalities are general senses and special senses.– The general senses include both somatic and visceral

senses, which provide information about conditions within internal organs.

– The special senses include the modalities of smell, taste, vision, hearing, and equilibrium.


Process of Sensation

• Sensory receptors demonstrate selectivity– respond to only one type of stimuli

• Events occurring within a sensation– stimulation of the receptor– transduction (conversion) of stimulus into a graded

potential• vary in amplitude and are not propagated

– generation of impulses when graded potential reaches threshold

– integration of sensory input by the CNS


Sensory Receptors

• Receptor Structure may be simple or complex– General Sensory Receptors (Somatic Receptors)

• no structural specializations in free nerve endings that provide us with pain, tickle, itch, temperatures

• some structural specializations in receptors for touch, pressure & vibration

– Special Sensory Receptors (Special Sense Receptors)• very complex structures---vision, hearing, taste, &

smell


Alternate Classifications of Sensory Receptors

• Structural classification• Type of response to a stimulus• Location of receptors & origin of stimuli• Type of stimuli they detect


Structural Classification of Receptors

• Free nerve endings– bare dendrites– pain, temperature, tickle, itch & light touch

• Encapsulated nerve endings– dendrites enclosed in connective tissue capsule– pressure, vibration & deep touch

• Separate sensory cells– specialized cells that respond to stimuli– vision, taste, hearing, balance


Structural Classification

• Compare free nerve ending, encapsulated nerve ending and sensory receptor cell


Classification by Stimuli Detected

• Mechanoreceptors– detect pressure or stretch– touch, pressure, vibration, hearing, proprioception,

equilibrium & blood pressure• Thermoreceptors detect temperature• Nociceptors detect damage to tissues• Photoreceptors detect light• Chemoreceptors detect molecules

– taste, smell & changes in body fluid chemistry


Classification by Response to Stimuli

• Generator potential– free nerve endings, encapsulated nerve endings &

olfactory receptors produce generator potentials– when large enough, it generates a nerve impulse in a first-

order neuron• Receptor potential

– vision, hearing, equilibrium and taste receptors produce receptor potentials

– receptor cells release neurotransmitter molecules on first-order neurons producing postsynaptic potentials

– PSP may trigger a nerve impulse• Amplitude of potentials vary with stimulus intensity


Classification by Location

• Exteroceptors– near surface of body– receive external stimuli– hearing, vision, smell, taste, touch, pressure, pain,

vibration & temperature

• Interoceptors– monitors internal environment (BV or viscera)– not conscious except for pain or pressure

• Proprioceptors– muscle, tendon, joint & internal ear– senses body position & movement


Adaptation in Sensory Receptors

• Most sensory receptors exhibit adaptation – the tendency for the generator or receptor potential to decrease in amplitude during a maintained constant stimulus.

• Receptors may be rapidly or slowly adapting.


Adaptation of Sensory Receptors

• Change in sensitivity to long-lasting stimuli – decrease in responsiveness of a receptor

• bad smells disappear• very hot water starts to feel only warm

– potential amplitudes decrease during a maintained, constant stimulus

• Variability in tendency to adapt:– Rapidly adapting receptors (smell, pressure, touch)

• specialized for detecting changes– Slowly adapting receptors (pain, body position)

• nerve impulses continue as long as the stimulus persists – Pain is not easily ignored.


SOMATIC SENSATIONS

• Receptors for somatic sensation are summarized in Table 16.2)


Tactile Sensations

• Tactile sensations are touch, pressure, and vibration plus itch and tickle.

• receptors include (Figure 16.2)– corpuscles of touch (Meissner’s corpuscles), – hair root plexuses, – type I (Merkel’s discs)– type II cutaneous (Ruffini’s corpuscles) – mechanoreceptors, – lamellated (Pacinian) corpuscles, – free nerve endings


Touch

• Crude touch refers to the ability to perceive that something has simply touched the skin

• Discriminative touch (fine touch) provides specific information about a touch sensation such as location, shape, size, and texture of the source of stimulation.

• Receptors for touch include corpuscles of touch (Meissner’s corpuscles) and hair root plexuses; these are rapidly adapting receptors.

• Type I cutaneous mechanoreceptors (tactile or Merkel discs) and type II cutaneous mechanoreceptors (end organs of Ruffini) are slowly adapting receptors for touch (Figure 16.2).


Pressure and Vibration• Pressure is a sustained sensation that is felt over a larger area

than touch.

– Pressure sensations generally result from stimulation of tactile receptors in deeper tissues and are longer lasting and have less variation in intensity than touch sensations

– Receptors for pressure are type II cutaneous mechanoreceptors and lamellated (Pacinian) corpuscles.

• Like corpuscles of touch (Meissner’s corpuscles), lamellated corpuscles adapt rapidly.

• Vibration sensations result from rapidly repetitive sensory signals from tactile receptors

– receptors for vibration sensations are corpuscles of touch and lamellated corpuscles, which detect low-frequency and high-frequency vibrations, respectively.


Itch and Tickle

• Itch and tickle receptors are free nerve endings.– Tickle is the only sensation that you may not elicit on

yourself.


Meissner’s Corpuscle

• Dendrites enclosed in CT in dermal papillae of hairless skin

• Discriminative touch & vibration-- rapidly adapting

• Generate impulses mainly at onset of a touch


•Free nerve endings found around follicles, detects movement of hair

Hair Root Plexus


Merkel’s Disc

• Flattened dendrites touching cells of stratum basale

• Used in discriminative touch (25% of receptors in hands)


Ruffini Corpuscle

• Found deep in dermis of skin• Detect heavy touch, continuous touch, & pressure


Pacinian Corpuscle

• Onion-like connective tissue capsule enclosing a dendrite

• Found in subcutaneous tissues & certain viscera

• Sensations of pressure or high-frequency vibration


Somatic Tactile Sensations - Summary

• Touch– crude touch is ability to perceive something has touched

the skin– discriminative touch provides location and texture of

source

• Pressure is sustained sensation over a large area• Vibration is rapidly repetitive sensory signals • Itching is chemical stimulation of free nerve endings• Tickle is stimulation of free nerve endings only by someone

else


Thermal Sensations

• Free nerve endings with 1mm diameter receptive fields on the skin surface– Cold receptors in the stratum basale respond to

temperatures between 50-105 degrees F– Warm receptors in the dermis respond to temperatures

between 90-118 degrees F• Both adapt rapidly at first, but continue to generate

impulses at a low frequency • Pain is produced below 50 and over 118

degrees F.


Pain Sensations

• Pain receptors (nociceptors) are free endings that are located in nearly every body tissue– Free nerve endings found in every tissue of body

except the brain– adaptation is slight if it occurs at all.

• Stimulated by excessive distension, muscle spasm, & inadequate blood flow

• Tissue injury releases chemicals such as K+, kinins or prostaglandins that stimulate nociceptors


Types of Pain

• Fast pain (acute)– occurs rapidly after stimuli (.1 second)– sharp pain like needle puncture or cut– not felt in deeper tissues– larger A nerve fibers

• Slow pain (chronic)– begins more slowly & increases in intensity– aching or throbbing pain of toothache– in both superficial and deeper tissues– smaller C nerve fibers


Types of Pain

• Somatic pain that arises from the stimulation of receptors in the skin is superficial, while somatic pain that arises from skeletal muscle, joints, and tendons is deep.

• Visceral pain, unlike somatic pain, is usually felt in or just under the skin that overlies the stimulated organ– localized damage (cutting) intestines may cause

no pain, but diffuse visceral stimulation can be severe

• distension of a bile duct from a gallstone• distension of the ureter from a kidney stone

– pain may also be felt in a surface area far from the stimulated organ in a phenomenon known as referred pain (Figure 16.3).


Referred Pain

• Visceral pain that is felt just deep to the skin overlying the stimulated organ or in a surface area far from the organ.

• Skin area & organ are served by the same segment of the spinal cord.– Heart attack is felt in skin along left arm since both are supplied by

spinal cord segment T1-T5


Pain Relief

Multiple sites of analgesic action:• Aspirin and ibuprofen block formation of prostaglandins that

stimulate nociceptors• Novocaine blocks conduction of nerve impulses along pain

fibers• Morphine lessen the perception of pain in the brain.


Proprioceptive Sensations

• Receptors located in skeletal muscles, in tendons, in and around joints, and in the internal ear convey nerve impulses related to muscle tone, movement of body parts, and body position. This awareness of the activities of muscles, tendons, and joints and of balance or equilibrium is provided by the proprioceptive or kinesthetic sense.


Proprioceptive or Kinesthetic Sense

• Awareness of body position & movement– walk or type without looking– estimate weight of objects

• Proprioceptors adapt only slightly• Sensory information is sent to cerebellum & cerebral

cortex– signals project from muscle, tendon, joint capsules

& hair cells in the vestibular apparatus– receptors discussed here include muscle spindles,

tendon organs (Golgi tendon organs), and joint kinesthetic receptors (Figure 16.4).


Muscle Spindles

• Specialized intrafusal muscle fibers enclosed in a CT capsule and innervated by gamma motor neurons

• Stretching of the muscle stretches the muscle spindles sending sensory information back to the CNS

• Spindle sensory fiber monitor changes in muscle length• Brain regulates muscle tone by controlling gamma fibers


Golgi Tendon Organs

• Found at junction of tendon & muscle• Consists of an encapsulated bundle of collagen fibers laced with

sensory fibers• When the tendon is overly stretched, sensory signals head for the

CNS & resulting in the muscle’s relaxation


Joint Receptors

• Ruffini corpuscles– found in joint capsule– respond to pressure

• Pacinian corpuscles– found in connective tissue around the joint– respond to acceleration & deceleration of joints


SOMATIC SENSORY PATHWAYS

• Somatic sensory pathways relay information from somatic receptors to the primary somatosensory area in the cerebral cortex.

• The pathways consist of three neurons– first-order, – second-order, and – third-order

• Axon collaterals of somatic sensory neurons simultaneously carry signals into the cerebellum and the reticular formation of the brain stem.


Somatic Sensory Pathways

• First-order neuron conduct impulses to the CNS (brainstem or spinal cord)– either spinal or cranial nerves

• Second-order neurons conducts impulses from brain stem or spinal cord to thalamus– cross over to opposite side of body

• Third-order neuron conducts impulses from thalamus to primary somatosensory cortex (postcentral gyrus of parietal lobe)


Posterior Column-Medial Lemniscus Pathway to the Cortex

• The nerve impulses for conscious proprioception and most tactile sensations ascend to the cortex along a common pathway formed by three-neuron sets (Figure 16.16a).

• These neurons are a part of the posterior (dorsal) columns– consist of the gracile fasciculus and cuneate fasciculus

• Impulses conducted along this pathway – fine touch, – stereognosis, – proprioception, and – vibratory sensations


Posterior Column-Medial Lemniscus Pathway of CNS

• Proprioception, vibration, discriminative touch, weight discrimination & stereognosis

• Signals travel up spinal cord in posterior column

• Fibers cross-over in medulla to become the medial lemniscus pathway ending in thalamus

• Thalamic fibers reach cortex


Anterolateral Pathways to the Cortex

• 3-neuron pathway• The anterolateral or spinothalamic pathways carry

mainly pain and temperature impulses (Figure 16.5b).• They also relay the sensations of tickle and itch and

some tactile impulses.


Spinothalamic Pathway of CNS

• Lateral spinothalamic tract carries pain & temperature

• Anterior tract carries tickle, itch, crude touch & pressure

• First cell body in DRG with synapses in cord

• 2nd cell body in gray matter of cord, sends fibers to other side of cord & up through white matter to synapse in thalamus

• 3rd cell body in thalamus projects to cerebral cortex


Somatosensory Map of Postcentral Gyrus

• Relative sizes of cortical areas– proportional to number of

sensory receptors – proportional to the

sensitivity of each part of the body

• Can be modified with learning– learn to read Braille & will

have larger area representing fingertips


Somatic Sensory Pathways to the Cerebellum

• The posterior spinocerebellar and the anterior spinocerebellar tracts are the major routes whereby proprioceptive impulses reach the cerebellum.– impulses conveyed to the cerebellum are critical for

posture, balance, and coordination of skilled movements.

• Table 16.3 summarizes the major sensory tracts in the spinal cord and pathways in the brain.


Sensory Pathways to the Cerebellum

• Major routes for proprioceptive signals to reach the cerebellum– anterior spinocerebellar tract– posterior spinocerebellar

tract• Subconscious information used

by cerebellum for adjusting posture, balance & skilled movements

• Signal travels up to same side inferior cerebellar peduncle


Clinical Application - Syphilis

Syphilis causes a progressive degeneration of the posterior portions of the spinal cord.– Sexually transmitted disease caused by bacterium

Treponema pallidum.– Third clinical stage known as tertiary syphilis– Progressive degeneration of posterior portions of spinal

cord & neurological loss • loss of somatic sensations• proprioceptive impulses fail to reach cerebellum

– People watch their feet while walking, but are still uncoordinated and jerky


SOMATIC MOTOR PATHWAYS

• Lower motor neurons extend from the brain stem or spinal cord to skeletal muscles.

• These lower motor neurons are called the final common pathway because many regulatory mechanisms converge on these peripheral neurons.


Somatic Motor Pathways - Overview

• Control of body movement– motor portions of cerebral cortex

• initiate & control precise movements– basal ganglia help establish muscle tone &

integrate semivoluntary automatic movements– cerebellum helps make movements smooth &

helps maintain posture & balance

• Somatic motor pathways– direct pathway from cerebral cortex to spinal cord

& out to muscles– indirect pathway includes synapses in basal

ganglia, thalamus, reticular formation & cerebellum



• Four distinct neural circuits (somatic motor pathways) participate in control of movement by providing input to lower motor neurons (Figure 16.7).– Local circuit neurons are located close to lower motor

neuron cell bodies in the brain stem and spinal cord.– Local circuit neurons and lower motor neurons receive

input from upper motor neurons.– Neurons of the basal ganglia provide input to upper

motor neurons.– Cerebellar neurons also control activity of upper motor

neurons.



• Organization of upper motor neuron pathways– Direct motor pathways provide input to lower motor

neurons via axons that extend directly from the cerebral cortex.

– Indirect pathways provide input to lower motor neurons from motor centers in the brain stem

• Paralysis: damage of lower motor neurons produces flaccid paralysis while injury to upper motor neurons causes spastic paralysis.


Primary Motor Cortex • The primary motor area is located in the precentral gyrus of the frontal lobe (Figure 16.6b)– upper motor neurons initiate

voluntary movement• The adjacent premotor area and

somatosensory area of the postcentral gyrus also contribute axons to descending motor pathways.

• The cortical area devoted to a muscle is proportional to the number of motor units.– More cortical area is needed if

number of motor units in a muscle is high

• vocal cords, tongue, lips, fingers & thumb


Direct motor pathways

• The direct pathways (pyramidal tracts) include (Figure 16.8).– lateral and anterior corticospinal tracts – corticobulbar tracts

• The various tracts of the pyramidal system convey impulses from the cerebral cortex that result in precise muscular movements.

• Table 16.4 summarizes the functions and pathways of the tracts in the direct motor pathways.


Direct Pathways (Pyramidal Pathways)

• 1 million upper motor neurons in cerebral cortex• Axons form internal capsule in cerebrum and pyramids

in the medulla oblongata• 90% of fibers decussate (cross over) in the medulla

– right side of brain controls left side muscles• Terminate on interneurons which synapse on lower

motor neurons in either:

– nuclei of cranial nerves – anterior horns of spinal cord

• Integrate excitatory & inhibitory input to become final common pathway


Details of Pyramidal Pathways

• Lateral corticospinal tracts– cortex, cerebral peduncles, 90%

decussation of axons in medulla, tract formed in lateral column.

– skilled movements (hands & feet)• Anterior corticospinal tracts

– the 10% of axons that do not cross– controls neck & trunk muscles

• Corticobulbar tracts– cortex to nuclei of CNs

• III, IV, V, VI, VII, IX, X, XI & XII– movements of eyes, tongue,

chewing, expressions & speech


Location of Direct Pathways

• Lateral corticospinal tract• Anterior corticospinal tract• Corticobulbar tract


Application

• Amyotrophic Lateral Sclerosis (ALS) is a disease hat attacks motor areas of the cerebral cortex, axons of upper motor neurons and cell bodies of lower motor neurons.

• It causes progressive muscle weakness. • There are several theories as to its cause. While there is no

cure, several drugs are used to treat the symptoms.


Paralysis

• Flaccid paralysis = damage lower motor neurons– no voluntary movement on same side as damage– no reflex actions– muscle limp & flaccid– decreased muscle tone

• Spastic paralysis = damage upper motor neurons– paralysis on opposite side from injury– increased muscle tone– exaggerated reflexes


Indirect Pathways

• Indirect or extrapyramidal pathways include all somatic motor tracts other than the corticospinal and corticobulbar tracts.– involve the motor cortex, basal ganglia, thalamus,

cerebellum, reticular formation, and nuclei in the brain stem (Figure 16.8).

– indirect tracts are the rubrospinal, tectospinal, vestibulospinal, lateral reticulospinal and medial reticulospinal tracts.

• Table 16.4 summarizes the major motor tracts, their functions, and pathways in the brain.


Indirect Pathways

• All other descending motor pathways

• Complex polysynaptic circuits– include basal ganglia,

thalamus, cerebellum, reticular formation

• Descend in spinal cord as 5 major tracts

• All 5 tracts end upon interneurons or lower motor neurons


Final Common Pathway

• Lower motor neurons receive signals from both direct & indirect upper motor neurons

• Sum total of all inhibitory & excitatory signals determines the final response of the lower motor neuron & the skeletal muscles


Roles of the basal ganglia

• The circuit from the cerebral cortex to basal ganglia to thalamus to cortex seems to function in initiating and terminating movement.– basal ganglia also suppress unwanted movements– basal ganglia may influence aspects of cortical function

including sensory, limbic, cognitive, and linguistic functions.

• Damage to the basal ganglia results in uncontrollable, abnormal body movements, often accompanied by muscle rigidity and tremors.

• Parkinson disease and Huntington disease result from damage to the basal ganglia.


Basal Ganglia

• Helps to program automatic movement sequences– walking and arm swinging or laughing at a joke

• Set muscle tone by inhibiting other motor circuits


Basal Ganglia Connections - Review

• Circuit of connections– cortex to basal ganglia to

thalamus to cortex– planning movements

• Output from basal ganglia to reticular formation– reduces muscle tone– damage produces rigidity

of Parkinson’s disease


Modulation of Movement by the Cerebellum

• The cerebellum is active in both learning and performing rapid, coordinated, highly skilled movements and in maintaining proper posture and equilibrium.

• The four aspects of cerebellar function (Figure 16.9)– monitoring intent for movement, – monitoring actual movement, – comparing intent with actual performance, and – sending out corrective signals

• Damage to the cerebellum is evidenced by ataxia and intention tremors.


Cerebellar Function

Aspects of Function• learning• coordinated &

skilled movements• posture &

equilibrium

1. Monitors intentions for movements -- input from cerebral cortex

2. Monitors actual movements with feedback from proprioceptors

3. Compares intentions with actual movements

4. Sends out corrective signals to motor cortex


INTEGRATIVE FUNCTIONS OF THE CEREBRUM

• The integrative functions include sleep and wakefulness, memory, and emotional responses.

(discussed in Chapter 14).


Wakefulness and Sleep

Role of the Reticular Activating System (RAS)• Sleep and wakefulness are integrative functions that are

controlled by the reticular activating system (Figure 16.10).– Arousal, or awakening from a sleep, involves increased

activity of the RAS.– When the RAS is activated, the cerebral cortex is also

activated and arousal occurs.– The result is a state of wakefulness called

consciousness.


Reticular Activating System

• RAS has connections tocortex & spinal cord.

• Many types of inputs canactivate the RAS---pain,light, noise, muscle activity, touch

• Coma is sleep-like state– A person in a deep

coma has no reflexes.


Wakefulness and Sleep

• Circadian rhythm– 24 hour cycle of sleep and awakening– established by hypothalamus

• EEG recordings show large amount of activity in cerebral cortex when awake


Sleep

• During sleep, a state of altered consciousness or partial unconsciousness from which an individual can be aroused by different stimuli,

• During sleep activity in the RAS is very low.• Normal sleep consists of two types:

– non-rapid eye movement sleep (NREM) and – rapid eye movement sleep (REM)


Sleep

• Triggers for sleep are unclear– adenosine levels increase with brain activity– adenosine levels inhibit activity in RAS– caffeine prevents adenosine from inhibiting RAS

• Non-rapid eye movement or slow wave sleep consists of four stages, each of which gradually merges into the next.

• Most dreaming occurs during rapid eye movement sleep.


Non-Rapid Eye Movement Sleep

• Stage 1– person is drifting off with eyes

closed (first few minutes)• Stage 2

– fragments of dreams– eyes may roll from side to side

• Stage 3– very relaxed, moderately deep– 20 minutes, body temperature & BP have dropped

• Stage 4 = deep sleep– bed-wetting & sleep walking occur in this phase


REM Sleep

• Most dreams occur during REM sleep• In first 90 minutes of sleep:

– go from stage 1 to 4 of NREM,– go up to stage 2 of NREM– to REM sleep

• Cycles repeat until total REM sleep totals 90 to 120 minutes

• Neuronal activity & oxygen use is highest in REM sleep• Total sleeping & dreaming time decreases with age


Learning and Memory

• Learning is the ability to acquire new knowledge or skills through instruction or experience.

• Memory is the process by which that knowledge is retained over time.

• For an experience to become part of memory, it must produce persistent functional changes that represent the experience in the brain.

• The capability for change with learning is called plasticity.


Learning and Memory

• Memory occurs in stages over a period and is described as immediate memory, short term memory, or long term memory.– Immediate memory is the ability to recall for a few

seconds.– Short-term memory lasts only seconds or hours and is

the ability to recall bits of information; it is related to electrical and chemical events.

– Long-term memory lasts from days to years and is related to anatomical and biochemical changes at synapses.


Amnesia

• Amnesia refers to the loss of memory• Anterograde amnesia is the loss of memory for events that

occur after the trauma; the inability to form new memories.• Retrograde amnesia is the loss of memory for events that

occurred before the trauma; the inability to recall past events.


DISORDERS: HOMEOSTATIC IMBALANCES

• Phantom pain is the sensations of pain in a limb that has been amputated; the brain interprets nerve impulses arising in the remaining proximal portions of the sensory nerves as coming from the nonexistent (phantom) limb. Another explanation is that the neurons in the brain that received input from the missing limbs are still active.


Spinal Cord Injury

• Spinal cord injury can be due to damage in a number of ways, such as compression or transection, and the location and extent of damage determines the type and degree of loss in neural abilities.– tumor, herniated disc, clot, trauma …

• Paralysis– monoplegia is paralysis of one limb only– diplegia is paralysis of both upper or both lower– hemiplegia is paralysis of one side– quadriplegia is paralysis of all four limbs

• Spinal shock is loss of reflex function (areflexia)– slow heart rate, low blood pressure, bladder problem– reflexes gradually return


Cerebral Palsy

• Loss of motor control and coordination• Damage to motor areas of the brain

– infection of pregnant woman with rubella virus– radiation during fetal life– temporary lack of O2 during birth

• Not a progressive disease, but irreversible


Parkinson Disease

• Parkinson’s disease is a progressive degeneration of CNS neurons of the basal nuclei region due to unknown causes that decreases dopamine neurotransmitter production.– Environmental toxins may be the cause in some cases

• Neurons from the substantia nigra do not release enough dopamine onto basal ganglia– tremor, rigidity, bradykinesia (slow movement) or hypokinesia

(decreasing range of movement)– may affect walking, speech, and facial expression

• Treatments– drugs to increase dopamine levels (L-Dopa), or to prevent its

breakdown– surgery to transplant fetal tissue or removal of part of globus

pallidus to slow tremors– acetylcholine inhibitors


end

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Chapter 14 Part 1