Chapter 12: The Central Nervous System. Central Nervous System Brain and Spinal Cord Body’s supercomputer Cephalization – elaboration towards rostal “towards.

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


5. 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”


8. 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

Cerebellum

Brain 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 ventricle

Septum 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


Inferiorhorn

Lateralaperture


Lateral ventricle

Septum 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 cerebralhemisphere

Occipitallobe

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 cortex

Premotor cortex

Frontal 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 cortex

Sensory 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)


Premotor cortex

Frontal 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 cortex

Sensory 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


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


2. Posterior Association areas – large region encompassing part of temporal, parietal, and occipital lobes

• Recognizes patterns and faces


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 pellucidum

Interthalamicadhesion(intermediatemass of thalamus)Interven-tricularforamenAnteriorcommissure

Hypothalamus

Optic chiasma

Pituitary 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


• 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


• 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 pellucidum

Interthalamicadhesion(intermediatemass of thalamus)Interven-tricularforamenAnteriorcommissure

Hypothalamus

Optic chiasma

Pituitary 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 body

Oculomotor 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

Thalamus

Hypothalamus

Midbrain

Pons

Medullaoblongata

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


Glossopharyngeal nerve (IX)

Diencephalon

Brainstem

Thalamus

Hypothalamus

Midbrain

Pons

Medullaoblongata

Thalamus

Superior colliculusInferior colliculusTrochlear nerve (IV)

Superior cerebellar peduncle

Middle cerebellar peduncle

Inferior cerebellar peduncle

Vestibulocochlear 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

Thalamus

Hypothalamus

Midbrain

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 cortex

Anterior 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

REM

Stage 1

Stage 2NonREM 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

Forget

Data selectedfor transfer

Automaticmemory

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

Periosteal

Bone 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

Periosteal

Bone of skull


Subduralspace

Subarachnoidspace

Figure 12.25a

Falx cerebri


Straightsinus

Crista galliof theethmoid bone

Pituitarygland

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


Arachnoid villus

Subarachnoid spaceArachnoid materMeningeal dura materPeriosteal dura mater

Right lateral ventricle(deep to cut)Choroid plexusof fourth ventricle

Central canalof spinal cord

Choroidplexus


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


• 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


• 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

LumbarenlargementConusmedullarisCaudaequina

Filumterminale

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 mater

Spinalmeninges

Arachnoidmater Dura mater

Bone ofvertebra

Subdural space

Subarachnoidspace(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 mater

Arachnoid 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 tracts

Fasciculus gracilisDorsalwhitecolumn

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


Primarysomatosensorycortex

Axons of third-orderneurons

Thalamus

Cerebrum

Midbrain

Cerebellum

Pons



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


Lumbar spinal cord

(b) Spinothalamic pathway




Thalamus

Cerebrum

Midbrain

Cerebellum

Pons

(b) Spinothalamic pathway

Spinocerebellar Tracts

• Ventral and dorsal tracts• Convey information about muscle or tendon

stretch to the cerebellum


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)


Touchreceptor

Medial lemniscus (tract)(axons of second-order neurons)

Dorsalspinocerebellartract (axons ofsecond-orderneurons)

Nucleus gracilisNucleus cuneatus

Lumbar spinal cord






Thalamus

Cerebrum

Midbrain

Cerebellum

Pons



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



Internal capsule

Cerebralpeduncle

Midbrain

Cerebellum

Cerebrum

Pons

(a)

Pyramidal cells(upper motor neurons)

Pyramidal (lateral and ventral corticospinal) pathways


Medulla oblongata


Skeletalmuscle

Pyramids

Decussationof 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


• 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


• Reticulospinal and vestibulospinal tracts—maintain balance

• Rubrospinal tracts—control flexor muscles• Superior colliculi and tectospinal tracts

mediate head movements in response to visual stimuli


Midbrain

Cerebellum

Cerebrum

Red nucleus

Pons

Rubrospinal tract(b)


Medulla oblongata


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


• 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


• 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

Chapter 12: The Central Nervous System. Central Nervous System Brain and Spinal Cord Body’s supercomputer Cephalization – elaboration towards rostal “towards.

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