Transcript Bio211 Lecture 19

Marieb’s Human
Anatomy and Physiology
Marieb w Hoehn
Chapter 12
The Central Nervous System
Lecture 19
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Divisions of the Nervous System
You are
here
CNS
PNS
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Brain – Embryology & Overview
Table & Figure From: Marieb &
Hoehn, Human Anatomy &
Physiology, 9th ed., Pearson, 2013
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Overview of the Brain
Functions
• regulates visceral activities
• coordinates muscular
movements
• interprets sensations
• determines perception
• stores memory
• carries out reasoning
• makes decisions
• determines personality
Major Parts
• diencephalon
• thalamus
• hypothalamus
• brain stem
• midbrain (mesencephalon)
• pons
• medulla oblongata
• cerebellum
• cerebrum (two hemispheres)
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Protection of the Brain
• The brain is protected
– Mechanically by
• The skull bones
• The meninges
• The cerebrospinal (CSF) fluid
– Biochemically by the blood-brain barrier
• Capillaries interconnected by tight junctions
• Astrocytes/ependymal cells control permeability of
general capillaries/choroid capillaries
• May be obstacle to delivery of drugs
• May become more permeable during stress
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Meninges of the Brain
- dura mater – outer, tough (anchoring dural folds)
- Subdural space – like interstitial fluid
- arachnoid mater – web-like
*Singular of
meninges is
meninx
- Subarachnoid space – CSF
- pia mater – inner, delicate
Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed.,
Pearson, 2013
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Dural Folds
Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed.,
Pearson, 2013
Falx Cerebri – within longitudinal fissure; separates
cerebral hemispheres
Tentorium Cerebelli – above cerebellum; separates
occipital lobe from cerebellum
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Ventricles of the Brain
• interconnected cavities
• within cerebral
hemispheres and brain
stem
• continuous with central
canal of spinal cord
• filled with cerebrospinal
fluid (CSF)
• lateral ventricles (1, 2)
• third ventricle (3)
• fourth ventricle (4)
• cerebral aqueduct
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Cerebrospinal Fluid
• secreted by choroid plexus
of ventricles (~500 ml/day)
• circulates in ventricles,
central canal of spinal cord,
and subarachnoid space
• completely surrounds brain
and spinal cord
• clear liquid (more Na+ and
Cl-, but less K+, Ca2+, glucose,
and protein than plasma)
• nutritive and protective
• helps maintain stable ion
concentrations in CNS
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Flow of CSF
(Monro)
(Luscka)
(Magendie)
Know
Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed.,
Pearson, 2013
11
Overview of the Cerebrum of the Brain
Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed.,
Pearson, 2013
-Over 85% of brain mass, with about 14 billion multipolar neurons in cortex
- Lobes named for overlying bones. (See sulci above for divisions)
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Functions of Cerebrum
• interpretation
• initiating voluntary movements
• storing memory
• retrieving memory
• reasoning
• center for intelligence and personality
The cerebrum can be divided into several functional areas:
- Motor (frontal cortex)
- Sensory (parietal, occipital, and temporal cortex)
- Association (all lobes)
Points to keep in mind:
- Each cerebral hemisphere receives information from, and sends
information to, the opposite side of the body
- Although symmetrical, the cerebral hemispheres are not entirely
equal in function
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Functions of Parts of Brain
Part of Brain
Motor areas
Primary motor cortex (Precentral gyrus)
Broca’s area (motor speech area)
Major Function
Voluntary control of skeletal muscles
Controls muscles needed for speech
Frontal eye field
Sensory areas
Cutaneous Sensory Area (postcentral gyrus)
Controls muscles needed for eye movement
Visual area (occipital lobe)
Auditory area (temporal lobe)
Association areas (all lobes)
Receives visual sensations
Receives auditory sensations
Analyze and interpret sensory experiences; coordinate motor responses
memory, reasoning, verbalization, judgment, emotions
Subconscious control certain muscular activities, e.g., learned movement patterns (a nucleus is a
collection of neuron cell bodies in the CNS); putamen, globus pallidus, caudate
controls emotions , produces feelings, interprets sensory impulses, facilitates memory storage and
retrieval (learning!)
Basal nuclei
Limbic system
Diencephalon
Thalamus
Hypothalamus
Brainstem
Midbrain
Pons
Medulla Oblongata
Reticular formation (system)
Cerebellum
Receives somatic sensations
gateway for sensory impulses heading to cerebral cortex, receives all sensory impulses (except
smell)
Vital functions associated with homeostasis
Major connecting center between spinal cord and brain and parts of brainstem; contains corpora
quadrigemina (visual and auditory reflexes)
Helps regulate rate and depth of breathing, relays nerve impulses to and from medulla oblongata
and cerebellum
Contains cardiac, vasomotor, and respiratory control centers, contains various nonvital reflex
control centers (coughing, sneezing, vomiting)
Filters incoming sensory information; habituation , modulates pain, arouses cerebral cortex into
state of wakefulness (reticular activating system)
Subconscious coordination of skeletal muscle activity, maintains posture
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Brain – Sensory and Motor Areas
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5
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2
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3
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(Gnostic)
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Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed., Pearson, 2013
*Somatosensory = Somesthetic
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Cerebral Cortex Motor/Sensory Homunculi
Notice the relative amount of cortical tissue devoted to each sensory function.
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Hemispheric (Cerebral) Lateralization
Figure from: Martini,
Anatomy & Physiology,
Prentice Hall, 2001
Categorical
hemisphere
Representational
hemisphere
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Basal Nuclei (formerly basal ganglia)
• nuclei are masses of
gray matter in CNS
• deep within cerebral
hemispheres
• three nuclei: caudate
nucleus and putamen,
(together called the
striatum), and the
globus pallidus
• subconscious control
certain muscular
activities, e.g., learned
movement patterns
1.
Receive input from entire cerebral cortex.
2.
Relay motor impulses originating in the substantia
nigra, along with their own output, through the
thalamus to the motor cortex to influence muscle
movement.
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Brain – Cerebral White Matter
Three types of myelinated
tracts form cerebral white
matter:
1. Association – same
hemisphere
2. Commisural – between
corresponding gyri in opposite
hemispheres
3. Projection – Ascending and
descending tracts
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Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed., Pearson, 2013
Limbic System
Consists of
• portions of frontal lobe
• portions of temporal lobe
• hypothalamus
• thalamus
• basal nuclei
• other deep nuclei
• associated with sense of
smell (less significant)
Functions
• controls emotions
• produces feelings
• interprets sensory impulses
• facilitates memory storage
and retrieval (learning!)
The motivational system
Figure from: Saladin,
Anatomy & Physiology,
McGraw Hill, 2007
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Memory
• A “Memory” is the persistence of knowledge that can be
accessed (we hope!) at a later time.
• Memories are not stored in individual “memory cells” or
neurons; they are stored as pathways called engrams, or
memory traces that use strengthened or altered synapses.
• Immediate memory lasts a few seconds, e.g., remembering
the earliest part of a sentence to make sense of it.
• Short-term memory (STM) lasts a few seconds to a few
hours
– Working memory is a form of this (repeating a phone number over
to yourself just long enough to dial it – and then forget it!)
– Limited to a few ‘bits’ of information (about 7-9). So, ‘chunk up’!
• Long-term memory (LTM) can last a lifetime
– Can hold much more information that STM
– Declarative (events and facts)
– Procedural (motor skills)
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Diencephalon
• between cerebral hemispheres and brainstem
• surrounds third ventricle
• thalamus
• hypothalamus
• epithalamus
(Tectum)
• optic tracts
• optic chiasm
• infundibulum
• posterior pituitary
• mammillary bodies
• pineal gland
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Diencephalon - Thalamus
Ventral nuclei
- Posterior; relay for taste
- Anterior and Lateral;
voluntary motor
- Forms wall of third ventricle
- Crude interpretation center for pain,
touch, pressure, temperature
Figure From: Marieb & Hoehn, Human Anatomy &
Physiology, 9th ed., Pearson, 2013
Relay for
hearing
Relay for
vision
The ‘gateway’ to the cerebral cortex. Major relay for sensory
information coming into the cerebral cortex, roles in cortical arousal,
learning, and memory
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Diencephalon - Hypothalamus
Hypothalamus - maintains homeostasis by regulating visceral activities (see
list below for examples…)
- Heart rate and blood pressure
- Body temperature
- Stimulation of the pituitary
(links nervous and endocrine)
- Water balance (ADH)
- SM contraction (OT)
- Feeding/satiety centers
- Movement/secretions of glands
and intestines
- Sleep and wakefulness
- Rage/aggression
- Psychosomatic illness
Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed., Pearson, 2013
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Brain Stem
Three Parts
1. Midbrain
2. Pons
3. Medulla Oblongata
(Tectum)
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Midbrain
• between diencephalon and
pons
• contains bundles of fibers
that join lower parts of
brainstem and spinal cord
with higher part of brain
Major connecting center between spinal
cord and brain and parts of brainstem
(Tectum)
• cerebral aqueduct
• cerebral peduncles –
bundles of nerve fibers
• contains red nucleus
(rubro-) and substantia
nigra
• corpora quadrigemina –
centers for visual and
auditory reflexes
Figure from: Saladin, Anatomy
& Physiology, McGraw Hill,
2007
Origins of: CN III, IV
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Pons
• rounded bulge on underside
of brainstem
• between medulla oblongata
and midbrain
• helps regulate rate and
depth of breathing
• relays nerve impulses to and
from
1. medulla oblongata
and brainstem via
longitudinal tracts
2. cerebellum via
transverse tracts
Origins of CN V, VI, VII, VIII
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Medulla Oblongata
• enlarged continuation of
spinal cord running through
foramen magnum of skull
• conducts all ascending
(olive) and descending
(pyramids - decussation)
impulses between brain and
spinal cord
• contains cardiac,
vasomotor, and respiratory
control centers
• nucleus gracilis and
nucleus cunneatus on dorsal
side; sensory info, cross
over, then send to thalamus
Origins (nuclei) of: CN IX, X, XI, and XII
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Reticular Formation
• complex network of
nerve fibers scattered
throughout the brain stem
• extends into the
diencephalon
• connects to centers of
hypothalamus, basal
nuclei, cerebellum, and
cerebrum
• filters incoming sensory
information; habituation
• modulates pain
• arouses cerebral cortex
into state of wakefulness
Ascending portion is called the
‘reticular activating system’
(prefix = reticulo-)
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Cerebellum
• integrates sensory
information concerning
position of body parts
• coordinates skeletal
muscle activity
• helps to maintain
posture
•May also be involved in
several sensory,
linguistic, emotional and
non-motor functions
• virtually all fibers
entering and leaving are
ispsilateral
Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007
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Spinal Cord Structure
• extends from the
foramen magnum to 2nd
lumbar vertebra
• cervical and lumbar
enlargements
• cauda equina (horse’s
tail) – thin nerve fibers
that exit at different
level than they arise
(note that spinal cord
does not extend into this
area of the lumbar
spine). Begins around
L2 and extends to S5.
Good area for lumbar
puncture and collection
of CSF.
Figure from: Saladin,
Anatomy & Physiology,
McGraw Hill, 2007
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Meninges of the Spinal Cord
Figures from: Saladin,
Anatomy & Physiology,
McGraw Hill, 2007
Denticulate ligaments –
branches of pia mater
connecting to the arachnoid
Space between the
dura mater and the
vertebral body is
called the epidural
space
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Cross Section of Spinal Cord
The spinal cord…
• is a center for spinal reflexes
• aids in locomotion
• is a conduit for nerve impulses to and from
the brain
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Organization of Spinal Gray Matter
You should know the
major areas of gray
matter of within the
spinal cord:
Posterior = sensory
Lateral = visceral
motor
Anterior = somatic
motor
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
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Spinal Cord and Nerve Roots
Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed., Pearson, 2013
Ventral root - axons of motor neurons whose cell bodies are in spinal cord
Dorsal root - axons of sensory neurons in the dorsal root ganglion
Dorsal root ganglion - cell bodies of sensory neurons
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Organization of Spinal White Matter
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
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Tracts of the Spinal Cord
• Ascending tracts conduct sensory impulses to the brain
• Descending tracts conduct motor impulses from the brain to
motor neurons reaching muscles and glands
All the axons in a tract
share a common origin
and destination
Tracts are usually
named for their place
of origin (1st) and
termination (2nd)
Most axons cross over
during their travel.
What will this mean
clinically?
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Ascending Tracts
• fasciculus cuneatus/gracilis
- fine touch, pressure, body
movement
- cross (decussate) in
medulla
3
• spinothalamic
- crude pain, temperature,
pressure, and touch
- cross in spinal cord
• spinocerebellar
- subconscious coordination of
muscle movements
(1st and 2nd order neurons)
- ipsilateral
Decussation
(crossing over)
2
1
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1st, 2nd, and 3rd Order Sensory Neurons
1st order neuron – from
receptor to the spinal cord
(cell bodies are located in the
dorsal root ganglion)
3
2nd order neuron – from
spinal cord to thalamus
3rd order neuron – from
thalamus to sensory cerebral
cortex - terminate in the
cerebral cortex
Decussation
2
1
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Descending Tracts
• corticospinal (direct, pyramidal)
- voluntary movement of
skeletal muscles
- lateral cross in medulla
- contralateral
Upper motor
– begin in
precentral
gyrus of
cortex
• reticulospinal (indirect,
extrapyramidal)
- subconscious muscle tone,
sweat glands
- some lateral cross, anterior do
not cross
• rubrospinal (indirect,
extrapyramidal)
- subconscious regulation of
upper limb tone/movement
- cross in brain (less important in
humans)
Decussation
Lower
Upper MN – Cerebral cortex to spinal cord
Lower MN – Spinal cord to effector
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Review
• The brain is protected by the
–
–
–
–
Skull bones
Meninges
CSF
Blood-brain barrier
• The meninges of the brain and spinal cord
consist of the
– Dura mater
– Arachnoid (membrane)
– Pia mater
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Review
• Important motor areas of cerebral cortex
– Precentral gyrus (Primary motor area)
– Broca’s area
– Frontal eye field
• Important sensory areas of cerebral cortex
– Postcentral gyrus (Primary cutaneous sensory)
– Visual area (occipital lobe)
– Auditory area (temporal lobe)
• The spinal cord is a
– Center for spinal reflexes
– Conduit for nerve impulses to and from the brain
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Review
46
Review
Spinal cord contains
nerve tracts
Ascending = sensory
Descending = motor
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