Chapter 12: The Central Nervous System

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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 Development
5. Neural crest forms – gives rise to some neurons
6. 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 Development
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
Surface
ectoderm
Head
Neural
plate
Tail
1 The neural plate forms from surface ectoderm.
Figure 12.1, step 1
Neural folds
Neural
groove
2 The neural plate invaginates, forming the neural
groove, flanked by neural folds.
Figure 12.1, step 2
Neural crest
3 Neural fold cells migrate to form the neural crest,
which will form much of the PNS and many other
structures.
Figure 12.1, step 3
Head
Surface
ectoderm
Neural
tube
Tail
4 The neural groove becomes the neural tube, which
will form CNS structures.
Figure 12.1, step 4
(a)
Neural
tube
Anterior
(rostral)
(b) Primary brain
vesicles
Prosencephalon
(forebrain)
Mesencephalon
(midbrain)
Rhombencephalon
(hindbrain)
Posterior
(caudal)
Figure 12.2a-b
(d) Adult brain
structures
(e) Adult
neural canal
regions
Telencephalon
Cerebrum: cerebral
hemispheres (cortex,
white matter, basal nuclei)
Lateral
ventricles
Diencephalon
Diencephalon
(thalamus, hypothalamus,
epithalamus), retina
Third ventricle
Mesencephalon
Brain stem: midbrain
Cerebral
aqueduct
Metencephalon
Brain stem: pons
(c) Secondary brain
vesicles
Cerebellum
Myelencephalon
Brain stem: medulla
oblongata
Spinal cord
Fourth
ventricle
Central canal
Figure 12.2c-e
Regions of Brain
1. Cerebral Hemispheres
2. Diencephalon
3. Brain stem (pons, midbrain, and medulla)
Cortex of
gray matter
Inner gray
matter
Central cavity
Migratory
pattern of
neurons
Cerebrum
Cerebellum
Region of cerebellum
Outer white
matter
Gray matter
Central cavity
Inner gray matter
Outer white matter
Brain stem
Gray matter
Central cavity
Outer white matter
Spinal cord
Inner gray matter
Figure 12.4
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
Lateral ventricle
Septum pellucidum
Anterior horn
Inferior
horn
Lateral
aperture
Interventricular
foramen
Third ventricle
Inferior horn
Cerebral aqueduct
Fourth ventricle
Central canal
(a) Anterior view
(b) Left lateral
Posterior
horn
Median
aperture
Lateral
aperture
view
Figure 12.5
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
Lateral ventricle
Septum pellucidum
Anterior horn
Inferior
horn
Lateral
aperture
Interventricular
foramen
Third ventricle
Inferior horn
Cerebral aqueduct
Fourth ventricle
Central canal
(a) Anterior view
(b) Left lateral
Posterior
horn
Median
aperture
Lateral
aperture
view
Figure 12.5
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
Precentral
gyrus
Frontal
lobe
Central
sulcus
Postcentral
gyrus
Parietal lobe
Parieto-occipital sulcus
(on medial surface
of hemisphere)
Lateral sulcus
Occipital lobe
Temporal lobe
Transverse cerebral fissure
Cerebellum
Pons
Medulla oblongata
Spinal cord
Fissure
(a deep
sulcus)
Gyrus
Cortex (gray matter)
Sulcus
White matter
(a)
Figure 12.6a
Frontal lobe
Central
sulcus
Gyri of insula
Temporal lobe
(pulled down)
(b)
Figure 12.6b
Anterior
Longitudinal
fissure
Frontal lobe
Cerebral veins
and arteries
covered by
arachnoid
mater
Parietal
lobe
Right cerebral
hemisphere
Occipital
lobe
Left cerebral
hemisphere
(c)
Posterior
Figure 12.6c
Left cerebral
hemisphere
Brain stem
Transverse
cerebral
fissure
Cerebellum
(d)
Figure 12.6d
Brain
•
•
•
•
Fits snuggly in skull
Frontal lobes – lie in anterior cranial fossa
Middle cranial fossa – temporal lobe
Each hemisphere – 3 regions
1. cerebral cortex – gray
2. internal white matter
3. basal nuclei
Cerebral Cortex
• “executive suite” of NS
conscious 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
Motor areas
Central sulcus
Primary motor cortex
Premotor cortex
Frontal eye field
Broca’s area
(outlined by dashes)
Prefrontal cortex
Working memory
for spatial tasks
Executive area for
task management
Working memory for
object-recall tasks
Solving complex,
multitask problems
(a) Lateral view, left cerebral hemisphere
Sensory areas and related
association areas
Primary somatosensory
cortex
Somatic
Somatosensory
sensation
association cortex
Gustatory cortex
(in insula)
Taste
Wernicke’s area
(outlined by dashes)
Primary visual
cortex
Visual
association
area
Auditory
association area
Primary
auditory cortex
Vision
Hearing
Motor association cortex
Primary sensory cortex
Primary motor cortex
Sensory association cortex
Multimodal association cortex
Figure 12.8a
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
Posterior
Motor
Motor map in
precentral gyrus
Anterior
Toes
Jaw
Tongue
Swallowing
Primary motor
cortex
(precentral gyrus)
Figure 12.9
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 (usually
the left)
2. special motor speech area – directs
muscles involved in speech
production
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
Motor areas
Central sulcus
Primary motor cortex
Premotor cortex
Frontal eye field
Broca’s area
(outlined by dashes)
Prefrontal cortex
Working memory
for spatial tasks
Executive area for
task management
Working memory for
object-recall tasks
Solving complex,
multitask problems
(a) Lateral view, left cerebral hemisphere
Sensory areas and related
association areas
Primary somatosensory
cortex
Somatic
Somatosensory
sensation
association cortex
Gustatory cortex
(in insula)
Taste
Wernicke’s area
(outlined by dashes)
Primary visual
cortex
Visual
association
area
Auditory
association area
Primary
auditory cortex
Vision
Hearing
Motor association cortex
Primary sensory cortex
Primary motor cortex
Sensory association cortex
Multimodal association cortex
Figure 12.8a
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
Posterior
Sensory
Anterior
Sensory map in
postcentral gyrus
Genitals
Primary somatosensory cortex
(postcentral gyrus)
Intraabdominal
Figure 12.9
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
Posterior
Sensory
Anterior
Sensory map in
postcentral gyrus
Genitals
Primary somatosensory cortex
(postcentral gyrus)
Intraabdominal
Figure 12.9
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
Longitudinal fissure
Lateral
ventricle
Superior
Commissural
fibers (corpus
callosum)
Association
fibers
Basal nuclei
• Caudate
• Putamen
• Globus
pallidus
Corona radiata
Thalamus
Internal
capsule
Fornix
Gray matter
Third
ventricle
White matter
Pons
Projection
fibers
Medulla oblongata
(a)
Decussation
of pyramids
Figure 12.10a
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
Fibers of
corona radiata
Caudate
nucleus
Lentiform
Corpus
nucleus
striatum • Putamen
• Globus pallidus
(deep to putamen)
Projection fibers
run deep to
lentiform nucleus
(a)
Thalamus
Tail of
caudate
nucleus
Figure 12.11a
Diencephalon
• Central core of forebrain
• Surrounded by cerebral hemispheres
• 3 parts – thalamus, hypothalamus, and
epithalamus
Cerebral hemisphere
Septum pellucidum
Interthalamic
adhesion
(intermediate
mass of
thalamus)
Interventricular
foramen
Anterior
commissure
Hypothalamus
Optic chiasma
Pituitary gland
Mammillary body
Pons
Medulla oblongata
Corpus callosum
Fornix
Choroid plexus
Thalamus
(encloses third
ventricle)
Posterior commissure
Pineal gland
(part of epithalamus)
Corpora
quadrigemina MidCerebral
brain
aqueduct
Arbor vitae (of
cerebellum)
Fourth ventricle
Choroid plexus
Cerebellum
Spinal cord
Figure 12.12
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 drives
3. Body temperature – monitor blood temperature and
other thermoreceptors
4. Food Intake – hunger and satiety in response to changing
blood levels
5. Water balance and thirst – osmoreceptors, ADH
6. 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
Cerebral hemisphere
Septum pellucidum
Interthalamic
adhesion
(intermediate
mass of
thalamus)
Interventricular
foramen
Anterior
commissure
Hypothalamus
Optic chiasma
Pituitary gland
Mammillary body
Pons
Medulla oblongata
Corpus callosum
Fornix
Choroid plexus
Thalamus
(encloses third
ventricle)
Posterior commissure
Pineal gland
(part of epithalamus)
Corpora
quadrigemina MidCerebral
brain
aqueduct
Arbor vitae (of
cerebellum)
Fourth ventricle
Choroid plexus
Cerebellum
Spinal cord
Figure 12.12
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
View (a)
Optic chiasma
Optic nerve (II)
Crus cerebri of
cerebral peduncles
(midbrain)
Diencephalon
• Thalamus
• Hypothalamus
Mammillary body
Thalamus
Hypothalamus
Diencephalon
Midbrain
Oculomotor nerve (III)
Trochlear nerve (IV)
Pons
Brainstem
Medulla
oblongata
Trigeminal nerve (V)
Pons
Facial nerve (VII)
Middle cerebellar
peduncle
Abducens nerve (VI)
Vestibulocochlear
nerve (VIII)
Pyramid
Glossopharyngeal nerve (IX)
Hypoglossal nerve (XII)
Vagus nerve (X)
Ventral root of first
cervical nerve
Decussation of pyramids
Accessory nerve (XI)
Spinal cord
(a) Ventral view
Figure 12.15a
Pons
•
•
•
•
•
Bulging brainstem region
Conduction tracts
Deep fibers – longitudinal
Superficial – transverse and dorsal
Cranial nerves
Crus cerebri of
cerebral peduncles
(midbrain)
Thalamus
View (b)
Infundibulum
Pituitary gland
Superior colliculus
Inferior colliculus
Trochlear nerve (IV)
Trigeminal nerve (V)
Pons
Superior cerebellar peduncle
Middle cerebellar peduncle
Facial nerve (VII)
Abducens nerve (VI)
Glossopharyngeal nerve (IX)
Hypoglossal nerve (XII)
Inferior cerebellar peduncle
Vestibulocochlear nerve (VIII)
Olive
Thalamus
Vagus nerve (X)
Hypothalamus
Diencephalon
Midbrain
Accessory nerve (XI)
Pons
Brainstem
Medulla
oblongata
(b) Left lateral view
Figure 12.15b
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
Thalamus
View (c)
Diencephalon
Pineal gland
Anterior wall of
fourth ventricle
Choroid plexus
(fourth ventricle)
Dorsal median sulcus
Dorsal root of
first cervical nerve
Midbrain
• Superior
Corpora
colliculus quadrigemina
• Inferior
of tectum
colliculus
• Trochlear nerve (IV)
• Superior cerebellar peduncle
Pons
• Middle cerebellar peduncle
Medulla oblongata
• Inferior cerebellar peduncle
• Facial nerve (VII)
• Vestibulocochlear nerve (VIII)
• Glossopharyngeal nerve (IX)
• Vagus nerve (X)
• Accessory nerve (XI)
Thalamus
Hypothalamus
Midbrain
Pons
(c) Dorsal view
Diencephalon
Brainstem
Medulla
oblongata
Figure 12.15c
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
Anterior lobe
Cerebellar cortex
Arbor
vitae
Cerebellar
peduncles
• Superior
• Middle
• Inferior
Medulla
oblongata
(b)
Flocculonodular
lobe
Posterior
lobe
Choroid
plexus of
fourth
ventricle
Figure 12.17b
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 scheme
1. Cerebral cortex motor areas notify cerebellum
of intent to initiate voluntary muscle control
2. Receives info from proprioceptors throughout
the body – body position and momentum
3. Cerebellar cortex – calculated best way to
coordinate force, direction, and extent
4. 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.
2.
3.
-
-
Midline raphe neuclei
Medial (large cell) group
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
(a) Scalp electrodes are used to record brain wave
activity (EEG).
Figure 12.20a
Brain Waves
• –4 categories
1. 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
1-second interval
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 into
four general classes.
Figure 12.20b
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 cortex
2. It is superimposed on other types of neural
activity
3. 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
Awake
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: Irregular
EEG with sleep spindles
(short high- amplitude
bursts); arousal is more
difficult.
NREM stage 3: Sleep
deepens; theta and
delta waves appear;
vital signs decline.
(a) Typical EEG patterns
NREM stage 4: EEG is
dominated by delta
waves; arousal is difficult;
bed-wetting, night terrors,
and sleepwalking may
occur.
Figure 12.21a
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
Awake
REM
Stage 1
Stage 2
Non
REM Stage 3
Stage 4
Time (hrs)
(b) Typical progression of an adult through one
night’s sleep stages
Figure 12.21b
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 understand
2. 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
• Stages
1. Short term Memory (STM) – working memory
- Limited to 7 or 8 chunks of information
2. 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 excited
2. Rehearsal – repetition – enhances memory
3. Association – tying new info to old info already
stored
4. Automatic Memory – not all impressions are
consciously formed
- Memory consolidation – fitting new facts into
knowledge already stored
Outside stimuli
General and special sensory receptors
Afferent inputs
Temporary storage
(buffer) in
cerebral cortex
Automatic
memory
Data permanently
lost
Data selected
for transfer
Short-term
memory (STM)
Forget
Forget
Data transfer
influenced by:
Retrieval
Excitement
Rehearsal
Association of
old and new data
Long-term
memory
(LTM)
Data unretrievable
Figure 12.22
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
Superior
sagittal sinus
Subdural
space
Subarachnoid
space
Skin of scalp
Periosteum
Bone of skull
Periosteal Dura
Meningeal mater
Arachnoid mater
Pia mater
Arachnoid villus
Blood vessel
Falx cerebri
(in longitudinal
fissure only)
Figure 12.24
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
Superior
sagittal sinus
Subdural
space
Subarachnoid
space
Skin of scalp
Periosteum
Bone of skull
Periosteal Dura
Meningeal mater
Arachnoid mater
Pia mater
Arachnoid villus
Blood vessel
Falx cerebri
(in longitudinal
fissure only)
Figure 12.24
Superior
sagittal sinus
Straight
sinus
Crista galli
of the
ethmoid
bone
Pituitary
gland
Falx cerebri
Tentorium
cerebelli
Falx
cerebelli
(a) Dural septa
Figure 12.25a
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
Superior
sagittal sinus
4
Choroid
plexus
Arachnoid villus
Interventricular
foramen
Subarachnoid space
Arachnoid mater
Meningeal dura mater
Periosteal dura mater
1
Right lateral ventricle
(deep to cut)
Choroid plexus
of fourth ventricle
3
Third ventricle
1 CSF is produced by the
Cerebral aqueduct
Lateral aperture
Fourth ventricle
Median aperture
Central canal
of spinal cord
(a) CSF circulation
2
choroid plexus of each
ventricle.
2 CSF flows through the
ventricles and into the
subarachnoid space via the
median and lateral apertures.
Some CSF flows through the
central canal of the spinal cord.
3 CSF flows through the
subarachnoid space.
4 CSF is absorbed into the dural venous
sinuses via the arachnoid villi.
Figure 12.26a
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 walls
2. relatively thick basal lamina surrounding capillaries
3. bulbous “feet” of astrocytes clinging to capillaries
- Barrier is selective – nutrients pass, wastes can not
Capillary
Neuron
Astrocyte
(a) Astrocytes are the most abundant
CNS neuroglia.
Figure 11.3a
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 dopaminereleasing 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
Dorsal root ganglion: sensory
neurons from neural crest
Alar plate:
interneurons
White
matter
Basal plate:
motor neurons
Neural tube
cells
Central
cavity
Figure 12.28
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
T12
Ligamentum
flavum
Lumbar puncture
needle entering
subarachnoid
space
L5
L4
Supraspinous
ligament
L5
Filum
terminale
S1
Intervertebral
disc
Arachnoid
matter
Dura
mater
Cauda equina
in subarachnoid
space
Figure 12.30
Cervical
enlargement
Dura and
arachnoid
mater
Lumbar
enlargement
Conus
medullaris
Cauda
equina
Filum
terminale
(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.
Cervical
spinal nerves
Thoracic
spinal nerves
Lumbar
spinal nerves
Sacral
spinal nerves
Figure 12.29a
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
Epidural space
(contains fat)
Subdural space
Subarachnoid
space
(contains CSF)
Pia mater
Arachnoid
mater
Dura mater
Spinal
meninges
Bone of
vertebra
Dorsal root
ganglion
Body
of vertebra
(a) Cross section of spinal cord and vertebra
Figure 12.31a
Dorsal median sulcus
Dorsal funiculus
White
Ventral funiculus
columns Lateral funiculus
Dorsal root
ganglion
Gray
commissure
Dorsal horn Gray
Ventral horn matter
Lateral horn
Spinal nerve
Dorsal root
(fans out into
dorsal rootlets)
Ventral root
(derived from several
ventral rootlets)
Central canal
Ventral median
fissure
Pia mater
Arachnoid mater
Spinal dura mater
(b) The spinal cord and its meningeal coverings
Figure 12.31b
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
Dorsal root (sensory)
Dorsal root ganglion
Dorsal horn (interneurons)
Somatic
sensory
neuron
Visceral
sensory
neuron
Visceral
motor
neuron
Somatic
motor neuron
Spinal nerve
Ventral root
(motor)
Ventral horn
(motor neurons)
Interneurons receiving input from somatic sensory neurons
Interneurons receiving input from visceral sensory neurons
Visceral motor (autonomic) neurons
Somatic motor neurons
Figure 12.32
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)
Ascending tracts
Fasciculus gracilis
Dorsal
white Fasciculus cuneatus
column
Dorsal
spinocerebellar
tract
Ventral
spinocerebellar
tract
Lateral
spinothalamic tract
Ventral spinothalamic
tract
Descending tracts
Ventral white
commissure
Lateral
reticulospinal tract
Lateral
corticospinal tract
Rubrospinal
tract
Medial
reticulospinal
tract
Ventral corticospinal
tract
Vestibulospinal tract
Tectospinal tract
Figure 12.33
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)
Dorsal
spinocerebellar
tract (axons of
second-order
neurons)
Medial lemniscus (tract)
(axons of second-order neurons)
Nucleus gracilis
Nucleus cuneatus
Medulla oblongata
Fasciculus cuneatus
(axon of first-order sensory neuron)
Axon of
first-order
neuron
Muscle spindle
(proprioceptor)
(a) Spinocerebellar
pathway
Joint stretch
receptor
(proprioceptor)
Cervical spinal cord
Fasciculus gracilis
(axon of first-order sensory neuron)
Lumbar spinal cord
Dorsal column–medial
lemniscal pathway
Touch
receptor
Figure 12.34a (2 of 2)
Primary
somatosensory
cortex
Axons of third-order
neurons
Thalamus
Cerebrum
Midbrain
Cerebellum
Pons
(a) Spinocerebellar
pathway
Dorsal column–medial
lemniscal pathway
Figure 12.34a (1 of 2)
Anterolateral Pathways
• Lateral and ventral spinothalamic tracts
• Transmit pain, temperature, and coarse touch
impulses within the lateral spinothalamic tract
Lateral
spinothalamic
tract (axons of
second-order
neurons)
Medulla oblongata
Pain receptors
Cervical spinal cord
Lumbar spinal cord
Axons of first-order
neurons
Temperature
receptors
(b) Spinothalamic pathway
Figure 12.34b (2 of 2)
Primary
somatosensory
cortex
Axons of third-order
neurons
Thalamus
Cerebrum
Midbrain
Cerebellum
Pons
(b) Spinothalamic pathway
Figure 12.34b (1 of 2)
Spinocerebellar Tracts
• Ventral and dorsal tracts
• Convey information about muscle or tendon
stretch to the cerebellum
Dorsal
spinocerebellar
tract (axons of
second-order
neurons)
Medial lemniscus (tract)
(axons of second-order neurons)
Nucleus gracilis
Nucleus cuneatus
Medulla oblongata
Fasciculus cuneatus
(axon of first-order sensory neuron)
Axon of
first-order
neuron
Muscle spindle
(proprioceptor)
(a) Spinocerebellar
pathway
Joint stretch
receptor
(proprioceptor)
Cervical spinal cord
Fasciculus gracilis
(axon of first-order sensory neuron)
Lumbar spinal cord
Dorsal column–medial
lemniscal pathway
Touch
receptor
Figure 12.34a (2 of 2)
Primary
somatosensory
cortex
Axons of third-order
neurons
Thalamus
Cerebrum
Midbrain
Cerebellum
Pons
(a) Spinocerebellar
pathway
Dorsal column–medial
lemniscal pathway
Figure 12.34a (1 of 2)
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
Pyramidal cells
(upper motor
neurons)
Primary motor cortex
Internal capsule
Cerebrum
Midbrain
Cerebral
peduncle
Cerebellum
Pons
(a) Pyramidal (lateral and ventral corticospinal) pathways
Figure 12.35a (1 of 2)
Ventral
corticospinal
tract
Pyramids
Decussation
of pyramid
Lateral
corticospinal
tract
Medulla oblongata
Cervical spinal cord
Skeletal
muscle
Lumbar spinal cord
Somatic motor neurons
(lower motor neurons)
(a) Pyramidal (lateral and ventral corticospinal) pathways
Figure 12.35a (2 of 2)
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
Cerebrum
Red nucleus
Midbrain
Cerebellum
Pons
(b)
Rubrospinal tract
Figure 12.35b (1 of 2)
Rubrospinal tract
Medulla oblongata
Cervical spinal cord
(b)
Rubrospinal tract
Figure 12.35b (2 of 2)
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

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