Central Nervous System Brain and Spinal Cord. Central Nervous System The brain and spinal cord...

Central Nervous System

Brain and Spinal Cord

Central Nervous System

• The brain and spinal cord• Control center of the body• Receives, processes and

interprets the messages then determines what output occurs

The Brain• Contains about 12 billion neurons and weighs about 3 pounds • Wrinkled like a walnut and has a consistency of oatmeal• Regions of the brain

– Cerebrum (cerebral hemispheres)– Diencephalon – Brain Stem – Cerebellum

Cerebellum

Cerebrum (Cerebral Hemispheres)• Superior part of the brain composed of two hemispheres• Has gray matter, white matter and basal nuclei• Largest mass of the brain (83%)• Responsible for voluntary or conscious activities • Allows us to remember the past, plan for the future, and

imagine things that have not happened

Cerebrum (Cerebral Hemispheres)• Each hemisphere is divided

into regions called lobes• Four lobes named for their

skull bones that cover them– Frontal – Parietal– Temporal – Occipital

Cerebrum (Cerebral Hemispheres)

• Gyri (gyrus) – Elevated ridges of tissues

• Sulci (sulcus) – Shallow grooves

• Fissures – Deeper grooves – Usually separate large parts of the

brain

• Some fissures and sulci are used for anatomical landmarks

• Longitudinal fissure – Separates right and left

hemispheres

• Transverse fissure– Separates cerebrum and

cerebellum

Cerebrum (Cerebral Hemispheres)• Central sulcus

– Separates frontal and parietal lobes

• Parieto-occipital sulcus– Separates occipital and

parietal lobes

• Lateral sulcus– Separates temporal from

parietal and frontal lobe– Outlines temporal lobe

• Precentral gyrus– Anterior to central sulcus

• Postcentral gyrus– Posterior to central sulcus

Cerebral Cortex “Conscious Mind” • Cortex = outer layer composed

of gray matter• Neuron cell bodies, dendrites,

and glia • It has many convolutions that

triple the surface area• Function: aware of

surroundings, communicate, remember, understand and initiate voluntary movements

• Alzheimer’s disease – dementia producing lesions of the cerebral cortex

• Generalizations about the cerebral hemispheres

1. Three kinds of functional areas• Sensory, motor, and association areas

2. Each hemisphere is concerned with the functions of the opposite side of the body

3. Two hemispheres are not entirely equal in function

4. No functional area acts alone and conscious behaviors involve the entire cortex

Cerebral Cortex “Conscious Mind”

Cerebral Cortex “Conscious Mind”• Functional regions can be seen using modern imaging

techniques– PET scans show metabolic activity in the brain– fMRI reveal blood flow

• Specific motor and sensory functional areas can be mapped• Provide evidence that higher level thinking, memory and

language have overlapping areas

Motor Areas of the Cerebrum• Control voluntary movements• Located in the posterior part of the frontal lobes

1. Primary motor cortex

2. Premotor cortex

3. Broca’s areaPrimary motor cortex

Broca’s Area

Premotor cortex

Motor Areas of the Cerebrum• Primary motor cortex

– Precentral gyrus of the frontal lobe of each hemisphere

– Allow us to consciously control the precise, voluntary movements of our skeletal muscles

Motor Areas of the Cerebrum• Primary motor cortex

– The entire body is represented spatially in each hemisphere

– Areas with greater need for precise control are larger

– Damage to localized areas paralyzes the voluntarily controlled muscles of those areas (left affects right side)

Motor Areas of the Cerebrum• Premotor cortex

– Anterior to the precentral gyrus in the frontal lobe– Controls learned motor skills of a patterned nature– Coordinates the movement of several muscle groups – Involved in planning movements– Destruction results in a loss of the motor skills

programmed in that region

Motor Areas of the Cerebrum• Broca’s area

– Anterior to the inferior region of the premotor area (left side)

– Special motor speech area that directs the muscles involved in speech planning and production

– People who suffer damage to this area usually have aphasia – inability to create complete thoughts verbally

Sensory Areas of the Cerebrum• Concerned with conscious awareness of sensation• Occur in the parietal, temporal and occipital lobes

– Primary sensory cortex– Sensory association cortex– Visual areas– Auditory areas– Olfactory cortex– Gustatory cortex

Sensory Areas of the Cerebrum• Primary sensory cortex

– Located in the postcentral gyrus of the parietal lobe– Posterior to the primary motor cortex– Neurons receive information from the general sensory

receptors in the skin and from proprioceptors in skeletal muscles

– Identifies the body region being stimulated

Sensory Areas of the Cerebrum• Primary Sensory Cortex - Homunculus Man

– The body is represented spatially and upside-down according to the site of stimulus

– The right hemisphere receives input from the left side of the body

– The amount of sensory cortex devoted to a body region is related to the region’s sensitivity

– The face and fingertips are the most sensitive

Sensory Areas of the Cerebrum• Sensory association cortex

– Posterior to the primary sensory cortex in the parietal lobe– Integrates sensory inputs (temperature, pressure etc, not special

senses) from the primary sensory cortex – Produces an understanding of an object being felt: its size, texture,

and the relationship of its parts– Example: when you reach into your pocket, the stored memories of

the past sensory experiences perceive the objects you feel as coins– Damage to this area would hinder recognition of these objects

without looking at them

Sensory Areas of the Cerebrum• Primary visual cortex

– Posterior tip of the occipital lobe

– Receives visual information

– Damage to this area results in functional blindness

• Visual association area– Surrounds the primary visual cortex

– Uses past visual experiences to interpret visual stimuli (color, form, and movement)

– Enables us to recognize a flower and appreciate what we are seeing

– People with damage to this area can see but cannot comprehend what they are looking at

Sensory Areas of the Cerebrum• Auditory cortex

– Located in the superior margin of the temporal lobe– Interpreted sounds as pitch, loudness and location

• Auditory association area– Permits the perception of the sound– Allows us to ‘hear’ a speech, screams, music, etc.– Memories of sounds are stored here

Sensory Areas of the Cerebrum• Primary olfactory (smell) cortex

– Medial aspect of the temporal lobe – Conscious awareness of different odors– Very involved in memory and emotion

• Gustatory (taste) cortex– Located deep to the temporal lobe– Involved in the perception of taste

• Wernicke’s Area– Only in left parietal lobe– Comprehension of written and spoken

language

Association Areas of the Cerebrum• Analyzes sensory inputs from multiple senses • Sends outputs to multiple motor areas• Where sensations, thoughts, and emotions become

conscious• Information flows from:

– Sensory receptors primary sensory cortex sensory association cortex motor cortex

• Association cortex – Allows us to give meaning to the information that we receive– Store memories– Tie messages to previous experiences and knowledge – Decide what action to take– Relay it to the motor cortex

Association Areas of the Cerebrum• Prefrontal cortex

– Anterior part of frontal lobe– Thought, intelligence, motivation, personality– Sets humans apart from other animals– Tumors can cause wide mood swings, loss of attentiveness,

initiative and judgment– Prefrontal lobotomy is a surgical technique to treat severe mental

illness (rare)

Association Areas of the Cerebrum• Affective language areas

– Right side of frontal lobe– Opposite Broca’s area and Wernicke’s area– Involved in nonverbal, emotional components of

language

Lateralization of Cerebrum• Division of labor between hemispheres• Both cerebral hemispheres appear identical and are

used for almost every activity • Each hemisphere has unique abilities not shared by its

partner – lateralization

Lateralization of Cerebrum• Each half of the cerebrum deals mainly with the

opposite side of the body– Sensations from the left side of the body go to the

right hemisphere of the cerebrum and vice versa• One hemisphere tends to be more dominant for

language, speech, logic and analytical skills – cerebral dominance• The other hemisphere is more free-spirited, involved

in visual-spatial skills, emotion and creativity

Lateralization of Cerebrum• 90% of people are left

hemisphere dominant and are usually right-handed

• 10% of people are right hemisphere dominant and are usually left-handed and male– Some “lefties” have a cerebral

cortex that functions bilaterally are ambidextrous

• The two hemispheres have perfect and almost instantaneous communication with one another via connecting fiber tracts – corpus collusum

Hemisphere Inventory

LEFT BRAIN FUNCTIONSuses logicdetail orientedfacts rulewords and languagepresent and pastmath and sciencecan comprehendorder/pattern perceptionknows object namereality basedforms strategiespracticalsafe

RIGHT BRAIN FUNCTIONSuses feeling"big picture" orientedimagination rulessymbols and imagespresent and futurebelievesappreciatesspatial perceptionknows object functionfantasy basedpresents possibilitiesimpetuousrisk taking

Cerebral White Matter• White matter deep to the cortical gray matter is

responsible for communication between cerebral areas, cerebral cortex and lower CNS centers

• White matter consists largely of myelinated fibers bundled into large tracts

Cerebral White Matter• Fiber tracts are classified according to the direction in

which they run– Commisures connect corresponding gray areas of two

hemispheres enabling them to function as a whole• The largest is the corpus collosum

– Association fibers connect different parts of the same hemisphere– Projection fibers connects the cerebrum and lower brain areas

• Sensory information reaches the cerebral cortex and motor output leaves it through these fibers

Basal Nuclei• Gray matter (group of nuclei) deep within the white matter • Receives input from entire cerebral cortex• Output initiates and controls muscle movements directed

by primary motor cortex• Necessary to perform several activities at once• Disorders result in too much or too little movements like in

Parkinson’s disease

Diencephalon, Brain Stem and Cerebellum

Diencephalon

• Extends from the brain stem • Surrounded by the cerebrum• Regions of the diencephalon

– Thalamus– Hypothalamus– Epithalamus – Pituitary gland

Diencephalon• Thalamus “inner room”

– Location• Superior, egg shaped portion

– Composition• Gray matter

– Functions• Gateway to the cerebral cortex• Relay station for sensory inputs

and motor outputs• Sorts out and groups inputs

together– Imbalance

• Damage to the area causes increase in sensitivity to pain and loss of consciousness

Diencephalon• Hypothalamus

– Location• Below the thalamus and caps the brain stem

– Functions• Main visceral control center of the body• Vitally important in overall homeostasis1. Autonomic control center

– Regulates cardiac and smooth muscle and secretion of glands

– Influences blood pressure, rate and force of heart beat, digestive tract motility, eye pupil size, etc

2. Center for emotional response – “heart” of the limbic system– Nuclei involved in perception of pleasure,

fear, rage and biological rhythms and drives – Initiates the physical expressions of emotion

through the ANS

Diencephalon• Hypothalamus

3. Controls body temperature• Body’s thermostat is hypothalamus• Monitor blood temperature and receive

input from thermoreceptors • Initiates cooling (sweating) and heating

(shivering) as needed

4. Regulates food intake• Responds to changing blood levels of

certain nutrients of hormones by regulating feelings of hunger

5. Regulates water balance and thirst• Osmoreceptors regulate the

concentration of water• Neurons trigger the release of

antidiuretic hormone (ADH) from the pituitary gland to retain water

• Stimulates thirst center to drink more

Diencephalon• Hypothalamus

6. Regulates sleep-wake cycles• Sets the timing of the sleep cycle in

response to daylight-darkness cues received from visual pathways

7. Controls endocrine system functioning

• Acts as the helmsman of the endocrine system by releasing and inhibiting hormones of the pituitary gland

• Imbalance– Disorders include severe body wasting,

obesity, sleep disturbances, dehydration, emotional imbalances

Diencephalon• Epithalamus

– Location: most dorsal portion of diencephalon– Components and function

• Pineal gland – Secretes the hormone melatonin– Responsible for body rhythms (biological clock)

• Choroid plexus– Forms cerebrospinal fluid (CSF)

Diencephalon• Pituitary Gland

– Part of the endocrine system but located in the brain– Controlled by the hypothalamus– Secretes regulatory hormones

Brain Stem

• Location– Between the cerebrum and the spinal cord

• Composition– Deep gray matter surrounded by white matter fiber tracts

– Three regions

1. Midbrain

2. Pons means “bridge”

3. Medulla oblongata

• Functions– Provides a pathway for fiber tracts running between higher and

lower neural centers

– Produces the programmed, automatic behaviors necessary for survival

– Associated with 10 of the 12 cranial nerves – provides the main motor outputs and sensory inputs of the face and neck

Brain Stem• Midbrain

– Location• Between the diencephalon and the

pons• Superior part of brain stem

– Functions• Pain suppression• Link between the fear perceiving

amygdala and ANS pathways that control “fight or flight” response

• Visual reflexes that coordinate head and eye movement

• Auditory relay from the hearing receptors to the auditory cortex

• Startle reflex which causes you to turn you head toward and unexpected sound

Brain Stem

• Midbrain– Substantia nigra

• High content of melanin a precursor for dopamine

• Linked to the basal nuclei• Releases dopamine • Controls subconscious motor

movements• Degeneration of dopamine-

releasing neurons cause Parkinson’s disease

Brain Stem• Pons “bridge”

– Location• Bulging brain stem region • Wedged between the midbrain and the medulla oblongata

– Composition• Conduction tracts oriented in two opposite directions• Deep projection fibers run longitudinally and complete the pathway

between higher brain centers and spinal cord• Superficial ventral fibers run transversely and dorsally and connect

the pons bilaterally with the two sides of the cerebellum dorsally• Cranial nerve pairs = trigeminal, abducens, and the facial nerve

– Functions• Controls normal rhythm of breathing• Relays impulses from one side of the cerebellum to the other and

between the medulla and midbrain

Brain Stem• Medulla Oblongata

– Location• Most inferior part of the brain stem • Blends into the spinal cord at the foramen magnum

– Composition• Made of white and gray fibers called reticular formation• Above medulla- spinal cord junction fibers cross over to the opposite side before

traveling to the spinal cord– Functions

• Relays sensory information from spinal cord to sensory cortex• Autonomic reflex center for body homeostasis

– Cardiovascular center = adjusts force and rate of heart rate– Vasomotor center = regulates blood pressure– Respiratory center = controls rate and depth of breathing– Regulates vomiting, hiccupping, swallowing, coughing and sneezing

Medulla Oblongata

Cerebellum• Second largest part of the brain • Location

– Dorsal to the pons and medulla– Protrudes under the occipital lobes – Below and posterior to the cerebrum

• Composition– Outer gray matter and inner white forms arbor vitae

Cerebellum• Functions

– Subconscious aspects of skeletal movements– Provides precise timing of skeletal muscle contraction– Compares intended movements with what is actually happening

to smooth, skilled movements– Regulates posture, equilibrium and balance

• Imbalance– Damage produces ataxia (lack of coordination due to errors in

speed, force, direction of movement

Functional Brain Systems• Limbic System

– Associated with emotional brain– Emotional brain is the functional system involving cerebral and

diencephalon structures that mediates emotional response– Interacts with the cerebral cortex– Hypothalamus is gatekeeper of responses– Communications between the cerebral cortex and the limbic

system also permit us to refrain from acting out our emotions when reason warns that a particular response would be unwise

– Structures within the limbic system• Hippocampus• Amygdala – incorporates and store sensory perceptions into

fact memory; oversees the memory system• Mammillary bodies – olfaction and swallowing reflexes

– Damage to the hippocampus and amygdala causes amnesia

Brain Bankhttp://video.nationalgeographic.com/video/player/science/health-human-body-sci/human-body/brain-bank-sci.html

Central Nervous System• Brain and spinal cord are in

three layers of connective tissue called the meninges

• Three layers– Dura mater – double-layered

external covering– Arachnoid - middle layer– Pia mater – internal layer; clings to

the surface of the brain

• Meningitis – bacterial/viral inflammation of meninges, causes headache, fever, sore throat, back and neck pain

Cerebrospinal Fluid• Filled between the meninges and the

CNS• Similar to blood plasma composition• Clear, colorless and composed of water,

40-60% glucose, NaCl, K, protein and a few white blood cells

• Bathes skull, brain and spinal cord• Serves as a shock absorber for the brain

and spinal cord• Provides nutrients and waste removal for

brain tissue• 400-500 mL produced daily, only 140 mL

is circulating at any time• Circulates through the ventricles and into

the central canal and subarachnoid spaces and is absorbed back into the blood

Ventricles

• Cerebrospinal fluid filled spaces of the brain

• Formed by the choroid plexus • Four ventricles

1. Right lateral ventricle 2. Left lateral ventricle3. Foramen of Monro – connects

lateral ventricles with third ventricle4. Cerebral aqueduct - connects third

with fourth ventricle5. In the roof of the fourth ventricle

are openings that allow CSF to move into the cisterna magna

• Hydrocephalus – increased accumulation of CSF within the ventricles, causes cranium to enlarge unless treated with a shunt to remove excess fluid

Blood Brain Barrier• Protective mechanism that helps ensure that

the brain’s tissue remains stable• Brain cannot be subjected to drastic

variations in hormones, amino acids, ions – Could result in uncontrolled neural activity

• Permeable to water, nutrients, and fatty acids• Includes the least permeable capillaries of the

body• Excludes many potentially harmful

substances• Useless against some substances

– Fats and fat soluble molecules– Respiratory gases– Alcohol– Nicotine– Anesthesia

Homeostatic Imbalances• Cerebrovascular Accidents (CVA) – Stroke

– Caused by hemorrhage from cessation of blood flow through cerebral blood vessels

– Blood circulation to a brain area is blocked (blood clot, hemorrhage) and vital brain tissue dies

– Can cause injury to upper motor neurons

• Transient Ischemic Attack (TIA) – 5-30 minutes of paralysis– Numbness, impaired speech– Ischemia = loss of blood to any tissue

Homeostatic Imbalances• Dementia – “forgetfulness”

– Loss of brain function that occurs with certain diseases– General term of destruction of neurons of brain– Degenerative - nonreversible– Affects memory, language, attention span, intellect, personality,

cognitive skills– Most common type is Alzheimer’s– Parkinson’s disease, multiple sclerosis, or Huntington’s disease

are a few other diseases that can lead to dementia

Homeostatic Imbalances

• Epilepsy– Seizures caused by tumors or

chemical imbalances – Treated with drugs that block

synaptic transmission