Chapter 12: The Central Nervous System
Central Nervous System
• Brain and Spinal Cord• Body’s supercomputer• Cephalization – elaboration towards rostal
“towards the snout” or anterior portion of CNS
• Also increase in the number of neurons
Brain
• Adult male – 1600 g (3.5 lbs)• Adult female – 1450 g (3.2 lbs)• Brain mass per body mass - equal
Embryonic Development
1. 3 week embryo- ectoderm thickens along dorsal midline of body = neural plate
2. Neural tube invaginates – forms groove flanked by neural folds
3. Groove deepens – superior ridges fuse forming neural tube – detached from ectoderm and sinks into a deeper position
4. Neural tube differentiates into CNS – brain anterior and spinal cord - caudal
Embryonic Development5. Neural crest forms – gives rise to some neurons6. Neural tube – anterior end expands - 3 primary brain vesicles –
- 1. prosencephalon – forebrain- 2. mesencephalon – midbrain- 3. rhomben cephalon – hindbrain
7. Week 5 – primary vesicles secondary vesicles- Forebrain telencephalon (endbrain) + diencephalon
(hindbrain)- Hindbrain constricts – metencephalon “afterbrain”- Metencephalon – “spinal brain”
Embryonic Development8. 5 – secondary vesicles – develop into major structures of
adult brain • 2 cerebral hemispheres – cerebrum
– Diencephalon – hypothalamus– Thalamus– Epithalamus– Retina
• Mesencephalon = midbrain• Metencephalon = pons• Myelencephalon = cerebellum• Midbrain and hindbrain = spinal cord
Figure 12.1, step 1
The neural plate forms from surface ectoderm.1
Head
Tail
Surfaceectoderm
Neuralplate
Figure 12.1, step 2
The neural plate invaginates, forming the neuralgroove, flanked by neural folds.
2
Neural folds
Neuralgroove
Figure 12.1, step 3
Neural fold cells migrate to form the neural crest,which will form much of the PNS and many otherstructures.
3
Neural crest
Figure 12.1, step 4
The neural groove becomes the neural tube, whichwill form CNS structures.
4
Surfaceectoderm
Head
Tail
Neuraltube
(a)Neuraltube
(b) Primary brainvesicles
Anterior(rostral)
Posterior(caudal)
Rhombencephalon(hindbrain)
Mesencephalon(midbrain)
Prosencephalon(forebrain)
Figure 12.2a-b
(d) Adult brainstructures
(c) Secondary brainvesicles
Spinal cord
CerebellumBrain stem: medullaoblongata
Brain stem: pons
Brain stem: midbrain
Diencephalon(thalamus, hypothalamus,epithalamus), retina
Cerebrum: cerebralhemispheres (cortex,white matter, basal nuclei)
Myelencephalon
Metencephalon
Mesencephalon
Diencephalon
Telencephalon
Central canal
Fourthventricle
Cerebralaqueduct
Third ventricle
Lateralventricles
(e) Adultneural canalregions
Figure 12.2c-e
Regions of Brain
1. Cerebral Hemispheres2. Diencephalon3. Brain stem (pons, midbrain, and medulla)
Figure 12.4
CerebrumCerebellum
Migratorypattern ofneurons
Cortex ofgray matterInner graymatter
Gray matter
Outer whitematter
Central cavity
Central cavity
Inner gray matter
Gray matter
Outer white matter
Central cavity
Inner gray matter
Outer white matter
Region of cerebellum
Brain stem
Spinal cord
Pattern
• Central cavity surrounded by gray matter (neuron cell bodies)
• External – white matter (myelinated fiber tracts)
• Outer layer of gray matter – cortex – dissapears as you move down the brain stem
Ventricles
• Arise from expansions of lumen (cavity) of embryonic neural tube
• Filled with cerebral spinal fluid• Lined by ependymal cells
Figure 12.5
Anterior horn
Interventricularforamen
Inferiorhorn
Lateralaperture
(b) Left lateral view
Lateral ventricleSeptum pellucidum
Third ventricle
Cerebral aqueduct
(a) Anterior view
Fourth ventricleCentral canal
Inferior horn
Posteriorhorn
MedianapertureLateralaperture
Lateral Ventricles
• Deep in cerebral hemisphere• Large C – shaped chambers separated by septum
pellucidum• Communicate with 3rd ventricle – in diencephalon• Channel – intraventricular foramen• 3rd ventricle continuous with 4th – canal cerebral
aqueduct• 4th ventricle – 3 openings – 2 lateral apertures and
median aperture
Figure 12.5
Anterior horn
Interventricularforamen
Inferiorhorn
Lateralaperture
(b) Left lateral view
Lateral ventricleSeptum pellucidum
Third ventricle
Cerebral aqueduct
(a) Anterior view
Fourth ventricleCentral canal
Inferior horn
Posteriorhorn
MedianapertureLateralaperture
Cerebral Hemispheres
• Superior part of brain• 83 % of brain’s mass• Cover and obscure diencephalon and top of brain stem• Surface – gyri – elevated ridges• Sulci – grooves• Fissures – deeper grooves• Longitudinal fissure – separates cerebral hemispheres• Transverse cerebral fissure – separates cerebral from
cerebellum
Cerebral Hemisphere
• Divided into 5 lobes by sulci• Central sulcus – frontal plane – separates frontal
lobe from parietal lobe• Percentral gyrus and postcentral gyrus – border –
central sulcus• Occipital lobe – separate from parietal by
parietocciplital sulcus• Lateral sulcus – outlines temporal lobe• Insula – 5th lobe – deep in lateral sulcus – forms its
floor
Figure 12.6a
Postcentralgyrus
Centralsulcus
Precentralgyrus
Frontallobe
(a)
Parietal lobeParieto-occipital sulcus(on medial surfaceof hemisphere)Lateral sulcus
Transverse cerebral fissure
Occipital lobeTemporal lobe
CerebellumPons
Medulla oblongataSpinal cord
Cortex (gray matter)
Fissure(a deepsulcus)
Gyrus
SulcusWhite matter
Figure 12.6b
Centralsulcus
(b)
Frontal lobe
Temporal lobe(pulled down)
Gyri of insula
Figure 12.6c
Parietallobe
Frontal lobe
Right cerebralhemisphereOccipitallobe
Left cerebralhemisphere
Cerebral veinsand arteriescovered byarachnoidmater
Longitudinalfissure
Posterior(c)
Anterior
Figure 12.6d
Left cerebralhemisphere
TransversecerebralfissureCerebellum
Brain stem
(d)
Brain
• Fits snuggly in skull• Frontal lobes – lie in anterior cranial fossa• Middle cranial fossa – temporal lobe• Each hemisphere – 3 regions
1. cerebral cortex – gray2. internal white matter3. basal nuclei
Cerebral Cortex
• “executive suite” of NSconscious mind
• Enables awareness of ourselves, our sensations, and enables us to communicate, remember, and understand
• Also voluntary movement• Composed of gray matter – neuron cell bodies,
dendrites, glial and blood vessels
Cerebral Cortex
• Billions of neurons – arranged in 6 layers• 2-4 mm thick – 40 % of total brainmass• 52 cortical areas – Broadman areas
Cerebral Cortex• 3 functional areas –
– 1. motor area– 2. sensory area– 3. association area
• All neurons – interneurons• Each hemisphere – sensory and motor functions of opposite
sides of body• Hemispheres – not entirely equal in function
– Lateralization or specialization of cortical functions• No functional area acts alone• Conscious behavior involves the entire cortex
Figure 12.8a
Gustatory cortex(in insula)
Primary motor cortexPremotor cortexFrontal eye field
Working memoryfor spatial tasksExecutive area fortask managementWorking memory forobject-recall tasks
Broca’s area(outlined by dashes)
Solving complex,multitask problems
(a) Lateral view, left cerebral hemisphere
Motor areas
Prefrontal cortex
Sensory areas and relatedassociation areas
Central sulcus
Primary somatosensorycortexSomatosensoryassociation cortex
Somaticsensation
Taste
Wernicke’s area(outlined by dashes)
Primary visualcortexVisualassociation area
Vision
Auditoryassociation areaPrimaryauditory cortex
Hearing
Primary motor cortex Motor association cortex Primary sensory cortexSensory association cortex Multimodal association cortex
Motor Areas
• Control voluntary movement• Posterior part of frontal lobes: primary motor
cortex, premotor cortex, Broca’s area, and frontal eye field
Motor Area – Primary Motor Cortex
• Primary (somatic) motor cortex – • Located in precentral gyrus of frontal lobe• Large neurons – pyramidal cells • Allow control of precise or skilled voluntary movements• Long axons – project into spinal cord – pyramidal tracts• Somatotrophy – control of body structures mapped to
places• Muscles controlled by multiple spots
Figure 12.9
Toes
Swallowing
Tongue
Jaw
Primary motorcortex(precentral gyrus)
MotorMotor map inprecentral gyrus
Posterior
Anterior
Motor Area – Premotor Cortex
• Just anterior to precentral gyrus• Controls learned motor skills of repetitious
pattern or nature• Coordinates movements of several muscle
groups• Memory bank for skilled motor activites
Motor Area – Broca’s Area
• Lies anterior to inferior region of premotor area• Considered to be
1. present in one hemisphere only (usuallythe left)2. special motor speech area – directsmuscles involved in speechproduction
Recently shown to “light up” as we prepare to think or even think about voluntary activities other than speech
Motor Area – Frontal Eye Field
• Located partial in and anterior to premotor cortex and superior to Broca’s area
• Controls voluntary movement of eyes
Damage
• Damage to areas of primary motor cortex – paralyzes the body muscles controlled by those areas
• Voluntary control lost, muscles can still contract reflexively
• Premotor cortex - damage results in a loss in motor skills programmed in that region, but muscle strength and ability to perform movements are not
Sensory Areas
• Occur in parietal lobe, insular, temporal, and occipital lobes
1. Primary Somartosensory Cortex – • In post central gyrus of parietal lobe• Neurons receive info from general (somatic) sensory
receptors in the skin and proprioceptors (position sense receptors) in skeletal muscle, joints and tendons
• Neurons identify body region being stimulated – spatial discrimination
• Right hemisphere – receive input from left side of body• Face & fingertips – most sensitive – largest part
Figure 12.8a
Gustatory cortex(in insula)
Primary motor cortexPremotor cortexFrontal eye field
Working memoryfor spatial tasksExecutive area fortask managementWorking memory forobject-recall tasks
Broca’s area(outlined by dashes)
Solving complex,multitask problems
(a) Lateral view, left cerebral hemisphere
Motor areas
Prefrontal cortex
Sensory areas and relatedassociation areas
Central sulcus
Primary somatosensorycortexSomatosensoryassociation cortex
Somaticsensation
Taste
Wernicke’s area(outlined by dashes)
Primary visualcortexVisualassociation area
Vision
Auditoryassociation areaPrimaryauditory cortex
Hearing
Primary motor cortex Motor association cortex Primary sensory cortexSensory association cortex Multimodal association cortex
Sensory Areas
2. Somatosensory Association Cortex – posterior to primary somatosensory cortex
• Integrates sensory inputs – temp, pressure, etc. – relayed to produce understanding of object being felt – size, texture, relationship
Figure 12.9
Genitals
Intra-abdominal
Primary somato-sensory cortex(postcentral gyrus)
SensorySensory map inpostcentral gyrus
Posterior
Anterior
Sensory Areas
3. Visual Areas – primary visual (striate) cortex • Extreme posterior tip of occipital lobe• Most buried deep in calcarine sulcus• Largest • Receives visual input from retina• Visual association areas – surround primary –
uses past visual experiences to interpret stimuli
Sensory Areas
4. Auditory Areas – primary auditory cortex – superior margin of temporal lobe
• Impulses from ear transmitted here – interpreted as pitch, loudness, location, etc.
• Auditory Association area – permits perception of sound
• Memories of past sounds
Sensory Areas
5. Olfactory cortex – • Medial aspect of temporal lobes• Small region – piriform lobe • Smell receptors send impulses
Sensory Areas
6. Gustatory Cortex – taste stimuli• Insula just deep to temporal lobe
Sensory Areas
7. Visceral Sensory Area – conscious perception of visceral stimulation
• Upset stomach, full bladder, lung bursting – holding breath to long
Sensory Areas
8. Vestibular (equilibrium) cortex – difficult to find
• Imaging – shows it in the posterior part of insula and adjacent parietal cortex
Figure 12.9
Genitals
Intra-abdominal
Primary somato-sensory cortex(postcentral gyrus)
SensorySensory map inpostcentral gyrus
Posterior
Anterior
Multimodal Association Areas
• Cortex – complex• Input from multiple senses and outputs to
multiple areas• Meaning to info we receive, stores memories,
ties to previous experiences, and decide actions
• Sensations, thoughts, and emotions
Multimodal Association Areas
1. Anterior Association Areas – frontal lobe – prefrontal cortex
• Most complicated• Intellect, complex learning abilities (cognition),
recall, and personality • Working memory – abstract ideas, judgment,
reasoning, persistence, and planning• Abilities develop slowly in children – region of the
brain that matures slowly
Multimodal Association Areas
2. Posterior Association areas – large region encompassing part of temporal, parietal, and occipital lobes
• Recognizes patterns and faces
Multimodal Association Areas
3. Limbic Association Areas – cingulate gyrus• Parahippocampal gyrus• Hippocampus• Part of limbic system• Emotional impact• Sense of danger
Lateralization of Cortical Functioning
• Division of labor• Each hemisphere has unique abilities not shared by
its partner – lateralization• Cerebral dominance – designates hemisphere –
dominant for language• Left hemisphere – 90 % - language, math, and logic• Right – more free spirited – visual-spatial skills,
intuition, emotion, artistic and musical skills• Remaining 10 % of people – roles reversed• Typically – male and left handed
Cerebral White Matter
• White matter – deep to cortical gray matter – responsible for communication between cerebral area and cerebral cortex and lower CNS centers
• Consists of – myelinated fibers classified according to the direction they run –
1. Commissural fibers – connect gray area of 2 hemispheres
2. Association fibers – connect different parts of same hemisphere
3. Projection fibers – cortex to rest of NS
Figure 12.10a
Corona radiata
Projectionfibers
Longitudinal fissure
Gray matter
White matter
Associationfibers
Lateralventricle
Fornix
Thirdventricle
Thalamus
Pons
Medulla oblongataDecussationof pyramids
Commissuralfibers (corpus callosum)
Internalcapsule
Superior
Basal nuclei• Caudate• Putamen• Globuspallidus
(a)
Cerebral White Matter
• Basal nuclei - Subcortical nuclei• Deep within cerebral white matter• Input from entire cerebral cortex• Functions overlap with those of cerebellum• Part in regulating attention and cognition
Figure 12.11a
Fibers ofcorona radiata
Corpusstriatum
(a)
Projection fibersrun deep to lentiform nucleus
Caudatenucleus Thalamus
Tail ofcaudatenucleus
Lentiformnucleus• Putamen• Globus pallidus (deep to putamen)
Diencephalon
• Central core of forebrain• Surrounded by cerebral hemispheres• 3 parts – thalamus, hypothalamus, and
epithalamus
Figure 12.12
Corpus callosum
Choroid plexusThalamus(encloses third ventricle)
Pineal gland(part of epithalamus)
Posterior commissure
CorporaquadrigeminaCerebralaqueductArbor vitae (ofcerebellum)Fourth ventricleChoroid plexusCerebellum
Septum pellucidumInterthalamicadhesion(intermediatemass of thalamus)Interven-tricularforamenAnteriorcommissureHypothalamus
Optic chiasmaPituitary gland
Cerebral hemisphere
Mammillary bodyPonsMedulla oblongata
Spinal cord
Mid-brain
Fornix
Diencephalon - Thalamus
• Bilateral egg shaped nuclei• Superolateral walls of 3rd ventricle• 80 % of diencephalon• Relay station for info• Nuclei – each functional specialty receives
from a specific area• Info sorted and edited
Diencephalon - Hypothalamus
• Below thalamus• Caps brain stem and forms infolateral walls of
3rd ventricle• Extends from optic chiasma to mammillary
bodies• Infundibulum – stalk of hypothalamic tissue
connects pituitary• Main visceral controlling center of body
Diencephalon - Hypothalamus• Homeostatic roles – 1. Autonomic Control Center – influences BP, rate and force of heart
beat, digestive tract motility, pupil size, etc.2. Emotional response – perception of pleasure, fear, and rage,
biological rhythms and drives3. Body temperature – monitor blood temperature and other
thermoreceptors4. Food Intake – hunger and satiety in response to changing blood
levels5. Water balance and thirst – osmoreceptors, ADH6. Sleep – wake Cycles 7. Endocrine System functioning – releasing and inhibiting
hormones
Diencephalon - Hypothalamus
• Number of Disorders – • Obesity, sleep disturbances, dehydration,
emotional impulses• Infant failure to thrive – delay child’s growth
or development when deprived of a warm, nurturing relationship
Diencephalon - Epithalamus
• Most dorsal• Roof of 3rd ventricle• Pineal gland – secrets hormone melanin –
sleep signal and antioxidant
Figure 12.12
Corpus callosum
Choroid plexusThalamus(encloses third ventricle)
Pineal gland(part of epithalamus)
Posterior commissure
CorporaquadrigeminaCerebralaqueductArbor vitae (ofcerebellum)Fourth ventricleChoroid plexusCerebellum
Septum pellucidumInterthalamicadhesion(intermediatemass of thalamus)Interven-tricularforamenAnteriorcommissureHypothalamus
Optic chiasmaPituitary gland
Cerebral hemisphere
Mammillary bodyPonsMedulla oblongata
Spinal cord
Mid-brain
Fornix
Brain Stem
• Midbrain, pons, medulla oblongata• 2.5 % of total brain mass• Deep gray matter surrounded by white fibers• Automatic behaviors• Pathway• Innervation of head
Midbrain
• 2 cerebral peduncles – “little feet”• Cruscerbui – “leg”• Fight or flight• Reflexive responses – startle response
Figure 12.15a
Optic chiasmaView (a)
Optic nerve (II)
Mammillary bodyOculomotor nerve (III)
Crus cerebri ofcerebral peduncles (midbrain)
Trigeminal nerve (V)
Abducens nerve (VI)Facial nerve (VII)
Vagus nerve (X)Accessory nerve (XI)
Hypoglossal nerve (XII)
Ventral root of firstcervical nerve
Trochlear nerve (IV)
PonsMiddle cerebellarpeduncle
Pyramid
Decussation of pyramids
(a) Ventral view
Spinal cord
Vestibulocochlearnerve (VIII)
Glossopharyngeal nerve (IX)
Diencephalon• Thalamus• Hypothalamus
Diencephalon
Brainstem
ThalamusHypothalamusMidbrain
PonsMedullaoblongata
Pons
• Bulging brainstem region• Conduction tracts• Deep fibers – longitudinal• Superficial – transverse and dorsal• Cranial nerves
Figure 12.15b
View (b)
Crus cerebri ofcerebral peduncles (midbrain)
InfundibulumPituitary gland
Trigeminal nerve (V)
Abducens nerve (VI)Facial nerve (VII)
Vagus nerve (X)Accessory nerve (XI)
Hypoglossal nerve (XII)
Pons
(b) Left lateral view
Glossopharyngeal nerve (IX)
Diencephalon
Brainstem
ThalamusHypothalamusMidbrain Pons
Medullaoblongata
Thalamus
Superior colliculusInferior colliculusTrochlear nerve (IV)Superior cerebellar peduncleMiddle cerebellar peduncleInferior cerebellar peduncleVestibulocochlear nerve (VIII)Olive
Medulla Oblongata
• Medulla• Inferior part of brain stem• Visceral motor nuclei– Cardio center – adjusts heart rate • Vasomotor center – changes blood vessel diameter
– Respiratory = respiratory rhythm– Various others – vomiting, coughing, swallowing,
hiccupping , and sneezing
Figure 12.15c
View (c)
Diencephalon
Brainstem
ThalamusHypothalamusMidbrain Pons
Medullaoblongata
Pineal gland
Diencephalon
Anterior wall offourth ventricle
(c) Dorsal view
Thalamus
Dorsal root offirst cervical nerve
Midbrain• Superior
colliculus• Inferior
colliculus• Trochlear nerve (IV)• Superior cerebellar peduncle
Corporaquadrigeminaof tectum
Medulla oblongata• Inferior cerebellar peduncle• Facial nerve (VII)• Vestibulocochlear nerve (VIII)• Glossopharyngeal nerve (IX)• Vagus nerve (X)• Accessory nerve (XI)
Pons• Middle cerebellar peduncle
Dorsal median sulcus
Choroid plexus(fourth ventricle)
Cerebellum
• Cauliflower like• 11 % of total brain mass• Under occipital lobes• Input from – cerebral motor cortex, brain
stem, and sensory receptors• Coordinated movement – driving, typing, etc
Figure 12.17b
(b)Medullaoblongata
Flocculonodularlobe
Choroidplexus offourth ventricle
Posteriorlobe
Arborvitae
Cerebellar cortexAnterior lobe
Cerebellarpeduncles• Superior• Middle• Inferior
Cerebellum
• Anatomy – bilateral symmetry• 2 apple sized hemispheres• Fola – pleat-like gyri• Deep fissures• Outer cortex – gray matter and deeply
situated paired mass of gray matter• Neurons – Purkinje cells
Cerebellum
• Cerebellar Processing – functional scheme1. Cerebral cortex motor areas notify cerebellum
of intent to initiate voluntary muscle control2. Receives info from proprioceptors throughout
the body – body position and momentum3. Cerebellar cortex – calculated best way to
coordinate force, direction, and extent4. Superior peduncles – dispatches “blue print”
for coordinated movement
Functional Brain Systems
• Network of neurons that work together but span large distances in brain
• Cannot be localized to specific regions
Limbic System
• Group of structures located in medial aspect of each cerebral hemisphere and diencephalon
• Cerebral structures that encircle upper part of brain stem
• Emotional or affective (feelings) brain• Odors – trigger emotional reactions –
rhinencephalon – “smell brain”• Interacts with prefrontal lobes – intimate
relationship between feelings and thoughts
Reticular Formation• Extends central core of medulla oblongata, pons, and midbrain• Loosely clustered neurons
1. Midline raphe neuclei2. Medial (large cell) group3. Lateral (small cell) group
- flung axonal connections- Reticular activating system (RAS) – impulses from great
ascending sensory tracts – keep them active and enhance effect on cerebrum
- Filter sensory inputs- Inhibited sleep centers- Depressed by alcohol, sleep aid drugs, and tranquilizers
Higher Mental Functions
• Brainwaves reflect the electrical activity of higher mental functions
• Electroencephalogram – record some aspects of activity
• Electrodes on scalp measure potential energy differences
• Brainwaves – generated by synaptic activity at surface of cortex
Figure 12.20a
(a) Scalp electrodes are used to record brain waveactivity (EEG).
Brain Waves
• –4 categories1. Alpha Waves – 8-13 Hz- Regular rhythmic - Low amplitude- Synchronous waves- Brain – ‘idling’ – calm, relaxed state of
wakefulness
Brain Waves
2. Beta Waves – 14-30Hz – rhythmic, but not as regular, occur when mentally alert
3. Theta Waves – 4-7 Hz – irregular, common in children, uncommon in adults
4. Delta Waves – 4 Hz or less – high amplitude waves, deep sleep – reticular activating system is damped – anesthesia
- Indicated brain damage in awake adults
Brain Waves
• Change with age, sensory stimuli, brain disease and chemical state of body
• Flat EEG – clinical evidence of brain death• Epilepsy – seizures – torrent of electrical
charges of groups of brain neurons• Uncontrolled activity – no other messages can
get through
Figure 12.20b
Alpha waves—awake but relaxed
Beta waves—awake, alert
Theta waves—common in children
Delta waves—deep sleep
(b) Brain waves shown in EEGs fall intofour general classes.
1-second interval
Consciousness
• Encompass conscious perception of sensations, voluntary initiation and control of movements and capabilities associated with higher mental functioning
• Defined by behavior in response to stimuli– Alertness– Drowsiness or lethargy– Stupor– coma
Consciousness
• Difficult to determine• Current suppositions – 1. Simultaneous activity of large areas of
cerebral cortex2. It is superimposed on other types of neural
activity3. Is it holistic and totally interconnected
Consciousness
• Fainting or Syncope – brief loss of consciousness• Most often from inadequate cerebral blood flow due
to low BP• Coma – total unresponsiveness• Not deep sleep – oxygen level lower than deep sleep• Blows to head – widespread cerebral or brain stem
trauma• Tumors or infections, hypoglycemia, drug overdose,
kidney failure• Brain Death – irreparable damage to brain
Sleep and Sleep Wake Cycles
• Sleep – state of partial unconsciousness from which a person can be aroused by stimulation
• Coma – cannot be aroused
Types of Sleep
• 2 major types that alternate throughout the sleep cycle
1. Non-rapid eye movement (NREM)2. Rapid Eye movement (REM)- Defined by EEG patterns
Sleep• 1st 30 -45 minutes – 2 stages of NREM • Then stage 3 and 4 – NREM- slow wave sleep• Deeper sleep – EEG wave declines – amplitude increase• 90 minutes – NREM stage 4 – changes rapidly – appears to
backtrack until alpha waves appear – onset of REM sleep– Increase in heart rate– Increase respiratory rate– Increase in blood pressure– Decrease in gastrointestinal activity– Increase in oxygen use– Eyes move rapidly, skeletal muscles limp, dreams
Figure 12.21a
Awake
(a) Typical EEG patterns
REM: Skeletal muscles (except ocular muscles and diaphragm) are actively inhibited; most dreaming occurs.NREM stage 1:Relaxation begins; EEG shows alpha waves, arousal is easy.
NREM stage 2: IrregularEEG with sleep spindles (short high- amplitude bursts); arousal is more difficult.NREM stage 3: Sleep deepens; theta and delta waves appear; vital signs decline.
NREM stage 4: EEG is dominated by delta waves; arousal is difficult; bed-wetting, night terrors, and sleepwalking may occur.
Sleep Patterns• Alternating patterns of sleep and wakefulness• Natural circadian, or 24 hour, rhythm• Hypothalamus response• Suprachaismatic nucleus – biological clock
regulates preoptic nucleus – sleep inducing center
Sleep Patterns
• Young/middle aged adult – 4 stages of NREM then alternate with occasional partial analysis
• REM ~ every 90 minutes• 1st REM – 5-10 minutes long• Final REM – 20 -50 minutes long
• Wake – hypothermic neurons release peptides (exins) “wakeup” chemical
Figure 12.21b
(b) Typical progression of an adult through onenight’s sleep stages
Awake
REMStage 1Stage 2
NonREM Stage 3
Stage 4
Time (hrs)
Importance of Sleep
• Slow wave sleep – restorative – neural activity winds down
• REM – deprived – moody and depressed– Analyze days events– Get rid of meaning less communication
• Alcohol and sleep meds – suppress REM but not slow wave sleep
• Tranquilizers – suppress slow wave more than REM
Importance of Sleep
• Requirements – infant – 16 hrs• 7 ½ 8 ½ - early adulthood• REM – ½ sleep time in infants – declines until
10 years old• Stabilizes ~ 25%• Stage 4 – declines steadily – often disappears
by age 60
Sleep• Narcolepsy – lapse into REM from an awake state• Lasts ~ 15 min, can occur at any time, most often triggered by a
pleasurable event– Fewer cells in hypothalamus that secrete orexins
• Insomnia – inability to obtain amount or quantity of sleep needed to adequately function – Varies – 4 -9 hrs/day
• Sleep Apnea – temporary cessation of breathing during sleep – Victim wakes due to hypoxia– Associated with obesity – Made worse by alcohol– Must wear a mask when sleeping
Language
• Involves almost all of association cortex on left side
• 2 important areas – 1. Broca’s area – can’t speak, but can understand2. Wericke’s area – can speak but can’t understand
- Areas work together to form a single implementation system
Memory• Storage and retrieval of information essential for learning
and incorporating experiences• Stages1. Short term Memory (STM) – working memory- Limited to 7 or 8 chunks of information2. Long term Memory (LTM) – limitless capacity- Can be forgotten- Memory bank changes with time- Ability to store and retrieve information declines with
age
From STM to LTM -
1. Emotional state – we learn when surprised, alert, motivated, or aroused
- Norephinephrine released when excited2. Rehearsal – repetition – enhances memory3. Association – tying new info to old info already
stored4. Automatic Memory – not all impressions are
consciously formed- Memory consolidation – fitting new facts into
knowledge already stored
Figure 12.22
Outside stimuli
General and special sensory receptors
Data transferinfluenced by:ExcitementRehearsalAssociation ofold and new data
Long-termmemory(LTM)
Data permanentlylost
Afferent inputs
Retrieval
Forget
ForgetData selectedfor transferAutomatic
memory
Data unretrievable
Temporary storage(buffer) in cerebral cortex
Short-termmemory (STM)
Categories of Memory
• Declarative (fact) memory – learning explicit info – names, faces, dates
• Non-declarative memory – less conscious• Procedural (skills) memory – ex. Playing the
piano• Motor Memory – riding a bike• Emotional memory – pounding heart when
see a rattlesnake
Brain Structures
• Visual memories – stored in occipital cortex• Music – temporal cortex
• Damage to hippocampus and medial temporal lobe result in slight memory loss
• Bilateral destruction - amnesia
Protection of Brain
• Nervous tissue – soft and delicate • Brain – protected by bone, membranes, and
CSF• Harmful substances – blood-brain barrier
Figure 12.24
Skin of scalpPeriosteum
Falx cerebri(in longitudinalfissure only)
Blood vesselArachnoid villusPia materArachnoid mater
Duramater Meningeal
PeriostealBone of skull
Superiorsagittal sinus Subduralspace Subarachnoidspace
Meninges
• 3 connective tissue membranes that lie external to CNS organs
• Functions:– Cover and protect CNS– Protect blood vessels and enclose venous sinuses– Contain cerebral spinal fluid– Form partitions in skull
Meninges
• Dura Matter• “tough mother’• Strongest meninx• Surround brain – 2 layered sheet of fibrous CT• Dura septa –dura matter extends into brain, limit
excessive movement of brain• Arachnoid Matter• Middle meninx • Loose brain covering
Figure 12.24
Skin of scalpPeriosteum
Falx cerebri(in longitudinalfissure only)
Blood vesselArachnoid villusPia materArachnoid mater
Duramater Meningeal
PeriostealBone of skull
Superiorsagittal sinus Subduralspace Subarachnoidspace
Figure 12.25a
Falx cerebri
Superiorsagittal sinus
StraightsinusCrista galliof theethmoid bonePituitarygland
Falxcerebelli
(a) Dural septa
Tentoriumcerebelli
Meninges
• Pia Mater – “gentle matter”• Delicate connective tissue• Clings to brain
• Meningitis – inflammation of meninges • Serious threat – can spread to CNS• Encephalitis – brain inflammation
Cerebrospinal Fluid
• CSF – found in and around the brain• Liquid cushion• Prevents brain from crushing itself• Protects against trauma• Watery “broth” similar to blood plasma – less
proteins and plasma• CSF contains more Na, Cl, and H, and less Ca
and K
Figure 12.26a
Superiorsagittal sinus
Arachnoid villus
Subarachnoid spaceArachnoid materMeningeal dura materPeriosteal dura mater
Right lateral ventricle(deep to cut)Choroid plexusof fourth ventricle
Central canalof spinal cord
Choroidplexus Interventricularforamen
Third ventricle
Cerebral aqueductLateral apertureFourth ventricleMedian aperture
(a) CSF circulation
CSF is produced by thechoroid plexus of eachventricle.
1
CSF flows through theventricles and into the subarachnoid space via the median and lateral apertures. Some CSF flows through the central canal of the spinal cord.
2
CSF flows through thesubarachnoid space. 3
CSF is absorbed into the dural venoussinuses via the arachnoid villi. 4
1
2
3
4
Blood Brain Barrier• Protective mechanism that helps maintain a stable
environment for brain• If brain exposed to chemical variations in blood – neurons
would fire uncontrollably• Blood born substances must pass through 3 layers before
they reach neurons – 1. epithelium of capillary walls2. relatively thick basal lamina surrounding capillaries3. bulbous “feet” of astrocytes clinging to capillaries
- Barrier is selective – nutrients pass, wastes can not
Figure 11.3a
(a) Astrocytes are the most abundantCNS neuroglia.
Capillary
Neuron
Astrocyte
Homeostatic Imbalances of the Brain
• Traumatic brain injuries– Concussion—temporary alteration in function– Contusion—permanent damage– Subdural or subarachnoid hemorrhage—may force
brain stem through the foramen magnum, resulting in death
– Cerebral edema—swelling of the brain associated with traumatic head injury
Homeostatic Imbalances of the Brain
• Cerebrovascular accidents (CVAs)(strokes)– Blood circulation is blocked and brain tissue dies, e.g.,
blockage of a cerebral artery by a blood clot– Typically leads to hemiplegia, or sensory and speed deficits– Transient ischemic attacks (TIAs)—temporary episodes of
reversible cerebral ischemia– Tissue plasminogen activator (TPA) is the only approved
treatment for stroke
Homeostatic Imbalances of the Brain
• Degenerative brain disorders– Alzheimer’s disease (AD): a progressive degenerative
disease of the brain that results in dementia– Parkinson’s disease: degeneration of the dopamine-
releasing neurons of the substantia nigra– Huntington’s disease: a fatal hereditary disorder caused by
accumulation of the protein huntingtin that leads to degeneration of the basal nuclei and cerebral cortex
The Spinal Cord: Embryonic Development
• By week 6, there are two clusters of neuroblasts– Alar plate—will become interneurons; axons form
white matter of cord– Basal plate—will become motor neurons; axons
will grow to effectors• Neural crest cells form the dorsal root ganglia
sensory neurons; axons grow into the dorsal aspect of the cord
Figure 12.28
Whitematter
Neural tubecells
Centralcavity
Alar plate:interneurons
Dorsal root ganglion: sensoryneurons from neural crest
Basal plate:motor neurons
Spinal Cord
• Location– Begins at the foramen magnum – Ends as conus medullaris at L1 vertebra
• Functions– Provides two-way communication to and from the
brain– Contains spinal reflex centers
Spinal Cord: Protection
• Bone, meninges, and CSF• Cushion of fat and a network of veins in the
epidural space between the vertebrae and spinal dura mater
• CSF in subarachnoid space
Spinal Cord: Protection
• Denticulate ligaments: extensions of pia mater that secure cord to dura mater
• Filum terminale: fibrous extension from conus medullaris; anchors the spinal cord to the coccyx
Figure 12.30
Ligamentumflavum
Supra-spinousligament
Lumbar punctureneedle enteringsubarachnoidspace
Filumterminale
Inter-vertebraldisc
T12
L5
Cauda equinain subarachnoidspace
Duramater
L5
L4
S1
Arachnoidmatter
Figure 12.29a
Cervicalenlargement
Dura andarachnoidmater
LumbarenlargementConusmedullarisCaudaequinaFilumterminale
Cervicalspinal nerves
Lumbarspinal nerves
Sacralspinal nerves
Thoracicspinal nerves
(a) The spinal cord and its nerve roots, with the bony vertebral arches removed. The dura mater and arachnoid mater are cut open and reflected laterally.
Spinal Cord
• Spinal nerves– 31 pairs
• Cervical and lumbar enlargements– The nerves serving the upper and lower limbs
emerge here• Cauda equina– The collection of nerve roots at the inferior end of
the vertebral canal
Cross-Sectional Anatomy
• Two lengthwise grooves divide cord into right and left halves – Ventral (anterior) median fissure – Dorsal (posterior) median sulcus
• Gray commissure—connects masses of gray matter; encloses central canal
Figure 12.31a
(a) Cross section of spinal cord and vertebra
Epidural space(contains fat)
Pia materSpinalmeninges
Arachnoidmater Dura mater
Bone ofvertebra
Subdural spaceSubarachnoidspace(contains CSF)
Dorsal rootganglion
Bodyof vertebra
Figure 12.31b
(b) The spinal cord and its meningeal coverings
Dorsal funiculus
Dorsal median sulcus
Central canal
Ventral medianfissure
Pia materArachnoid mater
Spinal dura mater
Graycommissure Dorsal horn Gray
matterLateral hornVentral horn
Ventral funiculusLateral funiculus
Whitecolumns
Dorsal rootganglion
Dorsal root(fans out into dorsal rootlets)
Ventral root(derived from severalventral rootlets)
Spinal nerve
Gray Matter
• Dorsal horns—interneurons that receive somatic and visceral sensory input
• Ventral horns—somatic motor neurons whose axons exit the cord via ventral roots
• Lateral horns (only in thoracic and lumbar regions) –sympathetic neurons
• Dorsal root (spinal) gangia—contain cell bodies of sensory neurons
Figure 12.32
Somaticsensoryneuron
Dorsal root (sensory)
Dorsal root ganglion
Visceralsensory neuron
Somaticmotor neuron
Spinal nerve
Ventral root(motor)
Ventral horn(motor neurons)
Dorsal horn (interneurons)
Visceralmotorneuron
Interneurons receiving input from somatic sensory neurons
Interneurons receiving input from visceral sensory neurons
Visceral motor (autonomic) neurons
Somatic motor neurons
White Matter
• Consists mostly of ascending (sensory) and descending (motor) tracts
• Transverse tracts (commissural fibers) cross from one side to the other
• Tracts are located in three white columns (funiculi on each side—dorsal (posterior), lateral, and ventral (anterior)
• Each spinal tract is composed of axons with similar functions
Pathway Generalizations
• Pathways decussate (cross over)• Most consist of two or three neurons (a relay)• Most exhibit somatotopy (precise spatial
relationships)• Pathways are paired symmetrically (one on
each side of the spinal cord or brain)
Figure 12.33
Ascending tracts Descending tractsFasciculus gracilisDorsal
whitecolumn
Fasciculus cuneatus
Dorsalspinocerebellar tract
Lateralspinothalamic tract Ventral spinothalamictract
Ventral whitecommissure
Lateralcorticospinal tract
Lateralreticulospinal tract
Ventral corticospinaltract
Medialreticulospinal tract
Rubrospinaltract
Vestibulospinal tractTectospinal tract
Ventralspinocerebellartract
Ascending Pathways
• Consist of three neurons• First-order neuron– Conducts impulses from cutaneous receptors and
proprioceptors– Branches diffusely as it enters the spinal cord or
medulla– Synapses with second-order neuron
Ascending Pathways
• Second-order neuron– Interneuron– Cell body in dorsal horn of spinal cord or
medullary nuclei– Axons extend to thalamus or cerebellum
Ascending Pathways
• Third-order neuron– Interneuron– Cell body in thalamus – Axon extends to somatosensory cortex
Ascending Pathways
• Two pathways transmit somatosensory information to the sensory cortex via the thalamus– Dorsal column-medial lemniscal pathways– Spinothalamic pathways
• Spinocerebellar tracts terminate in the cerebellum
Dorsal Column-Medial Lemniscal Pathways
• Transmit input to the somatosensory cortex for discriminative touch and vibrations
• Composed of the paired fasciculus cuneatus and fasciculus gracilis in the spinal cord and the medial lemniscus in the brain (medulla to thalamus)
Figure 12.34a (2 of 2)
Medulla oblongataFasciculus cuneatus(axon of first-order sensory neuron)
Fasciculus gracilis(axon of first-order sensory neuron)
Axon offirst-orderneuronMuscle spindle(proprioceptor)
Joint stretchreceptor(proprioceptor)
Cervical spinal cord
Touchreceptor
Medial lemniscus (tract)(axons of second-order neurons)
Dorsalspinocerebellartract (axons ofsecond-orderneurons)
Nucleus gracilisNucleus cuneatus
Lumbar spinal cord
(a) Spinocerebellarpathway
Dorsal column–mediallemniscal pathway
Figure 12.34a (1 of 2)
Primarysomatosensorycortex
Axons of third-orderneurons
Thalamus
Cerebrum
Midbrain
Cerebellum
Pons
(a) Spinocerebellarpathway
Dorsal column–mediallemniscal pathway
Anterolateral Pathways
• Lateral and ventral spinothalamic tracts • Transmit pain, temperature, and coarse touch
impulses within the lateral spinothalamic tract
Figure 12.34b (2 of 2)
Axons of first-orderneurons
Temperaturereceptors
Lateralspinothalamictract (axons ofsecond-orderneurons)
Pain receptors
Medulla oblongata
Cervical spinal cord
Lumbar spinal cord
(b) Spinothalamic pathway
Figure 12.34b (1 of 2)
Primarysomatosensorycortex
Axons of third-orderneurons
Thalamus
Cerebrum
Midbrain
Cerebellum
Pons
(b) Spinothalamic pathway
Spinocerebellar Tracts
• Ventral and dorsal tracts• Convey information about muscle or tendon
stretch to the cerebellum
Figure 12.34a (2 of 2)
Medulla oblongataFasciculus cuneatus(axon of first-order sensory neuron)
Fasciculus gracilis(axon of first-order sensory neuron)
Axon offirst-orderneuronMuscle spindle(proprioceptor)
Joint stretchreceptor(proprioceptor)
Cervical spinal cord
Touchreceptor
Medial lemniscus (tract)(axons of second-order neurons)
Dorsalspinocerebellartract (axons ofsecond-orderneurons)
Nucleus gracilisNucleus cuneatus
Lumbar spinal cord
(a) Spinocerebellarpathway
Dorsal column–mediallemniscal pathway
Figure 12.34a (1 of 2)
Primarysomatosensorycortex
Axons of third-orderneurons
Thalamus
Cerebrum
Midbrain
Cerebellum
Pons
(a) Spinocerebellarpathway
Dorsal column–mediallemniscal pathway
Descending Pathways and Tracts
• Deliver efferent impulses from the brain to the spinal cord – Direct pathways—pyramidal tracts– Indirect pathways—all others
Descending Pathways and Tracts
• Involve two neurons:1. Upper motor neurons• Pyramidal cells in primary motor cortex
2. Lower motor neurons• Ventral horn motor neurons• Innervate skeletal muscles
The Direct (Pyramidal) System
• Impulses from pyramidal neurons in the precentral gyri pass through the pyramidal (corticospinal)l tracts
• Axons synapse with interneurons or ventral horn motor neurons
• The direct pathway regulates fast and fine (skilled) movements
Figure 12.35a (1 of 2)
Primary motor cortex
Internal capsule
Cerebralpeduncle
Midbrain
Cerebellum
Cerebrum
Pons
(a)
Pyramidal cells(upper motor neurons)
Pyramidal (lateral and ventral corticospinal) pathways
Figure 12.35a (2 of 2)
Medulla oblongata
Cervical spinal cord
Skeletalmuscle
PyramidsDecussationof pyramidLateralcorticospinaltract
Ventralcorticospinaltract
Lumbar spinal cord
Somatic motor neurons(lower motor neurons)
(a) Pyramidal (lateral and ventral corticospinal) pathways
Indirect (Extrapyramidal) System
• Includes the brain stem motor nuclei, and all motor pathways except pyramidal pathways
• Also called the multineuronal pathways
Indirect (Extrapyramidal) System
• These pathways are complex and multisynaptic, and regulate:– Axial muscles that maintain balance and posture– Muscles controlling coarse movements – Head, neck, and eye movements that follow
objects
Indirect (Extrapyramidal) System
• Reticulospinal and vestibulospinal tracts—maintain balance
• Rubrospinal tracts—control flexor muscles• Superior colliculi and tectospinal tracts
mediate head movements in response to visual stimuli
Figure 12.35b (1 of 2)
Midbrain
Cerebellum
Cerebrum
Red nucleus
Pons
Rubrospinal tract(b)
Figure 12.35b (2 of 2)
Medulla oblongata
Cervical spinal cord
Rubrospinal tract
Rubrospinal tract(b)
Spinal Cord Trauma
• Functional losses– Parasthesias• Sensory loss
– Paralysis• Loss of motor function
Spinal Cord Trauma
• Flaccid paralysis—severe damage to the ventral root or ventral horn cells– Impulses do not reach muscles; there is no
voluntary or involuntary control of muscles– Muscles atrophy
Spinal Cord Trauma
• Spastic paralysis—damage to upper motor neurons of the primary motor cortex – Spinal neurons remain intact; muscles are
stimulated by reflex activity– No voluntary control of muscles
Spinal Cord Trauma
• Transection– Cross sectioning of the spinal cord at any level– Results in total motor and sensory loss in regions
inferior to the cut– Paraplegia—transection between T1 and L1
– Quadriplegia—transection in the cervical region
Poliomyelitis
• Destruction of the ventral horn motor neurons by the poliovirus
• Muscles atrophy• Death may occur due to paralysis of
respiratory muscles or cardiac arrest• Survivors often develop postpolio syndrome
many years later, as neurons are lost
Amyotrophic Lateral Sclerosis (ALS)
• Also called Lou Gehrig’s disease• Involves progressive destruction of ventral
horn motor neurons and fibers of the pyramidal tract
• Symptoms—loss of the ability to speak, swallow, and breathe
• Death typically occurs within five years• Linked to glutamate excitotoxicity, attack by
the immune system, or both
Developmental Aspects of the CNS
• CNS is established during the first month of development• Gender-specific areas appear in both brain and spinal
cord, depending on presence or absence of fetal testosterone
• Maternal exposure to radiation, drugs (e.g., alcohol and opiates), or infection can harm the developing CNS
• Smoking decreases oxygen in the blood, which can lead to neuron death and fetal brain damage
Developmental Aspects of the CNS
• The hypothalamus is one of the last areas of the CNS to develop
• Visual cortex develops slowly over the first 11 weeks
• Neuromuscular coordination progresses in superior-to-inferior and proximal-to-distal directions along with myelination
Developmental Aspects of the CNS
• Age brings some cognitive declines, but these are not significant in healthy individuals until they reach their 80s
• Shrinkage of brain accelerates in old age• Excessive use of alcohol causes signs of
senility unrelated to the aging process