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Chapter 12
The Central Nervous System
Lecture 19
Marieb’s HumanAnatomy and
Physiology
Marieb Hoehn
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Divisions of the Nervous System
CNS PNS
You are here
Brain – Embryology & Overview
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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)
- arachnoid mater – web-like
- pia mater – inner, delicate
- Subdural space – like interstitial fluid
- Subarachnoid space – CSF
*Singular of meninges is meninx
Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed., Pearson, 2013
Dural Folds
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Falx Cerebri – within longitudinal fissure; separates cerebral hemispheres
Tentorium Cerebelli – above cerebellum; separates occipital lobe from cerebellum
Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed., Pearson, 2013
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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
Flow of CSF
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(Luscka)
(Magendie)
(Monro)
Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed., Pearson, 2013
Know
Overview of the Cerebrum of the Brain
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-Over 85% of brain mass, with about 14 billion multipolar neurons in cortex- Lobes named for overlying bones. (See sulci above for divisions)
Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed., Pearson, 2013
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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
Functions of Parts of Brain
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Part of Brain Major FunctionMotor areas Primary motor cortex (Precentral gyrus) Voluntary control of skeletal muscles
Broca’s area (motor speech area) Controls muscles needed for speech
Frontal eye field Controls muscles needed for eye movementSensory areas Cutaneous Sensory Area (postcentral gyrus) Receives somatic sensations
Visual area (occipital lobe) Receives visual sensations Auditory area (temporal lobe) Receives auditory sensationsAssociation areas (all lobes) Analyze and interpret sensory experiences; coordinate motor responses
memory, reasoning, verbalization, judgment, emotions Basal nuclei 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, caudateLimbic system controls emotions , produces feelings, interprets sensory impulses, facilitates memory storage and
retrieval (learning!)Diencephalon Thalamus gateway for sensory impulses heading to cerebral cortex, receives all sensory impulses (except
smell) Hypothalamus Vital functions associated with homeostasisBrainstem Midbrain Major connecting center between spinal cord and brain and parts of brainstem; contains corpora
quadrigemina (visual and auditory reflexes) Pons Helps regulate rate and depth of breathing, relays nerve impulses to and from medulla oblongata
and cerebellum Medulla Oblongata Contains cardiac, vasomotor, and respiratory control centers, contains various nonvital reflex
control centers (coughing, sneezing, vomiting)Reticular formation (system) Filters incoming sensory information; habituation , modulates pain, arouses cerebral cortex into
state of wakefulness (reticular activating system)
Cerebellum Subconscious coordination of skeletal muscle activity, maintains posture
Brain – Sensory and Motor Areas
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Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed., Pearson, 2013
*Somatosensory = Somesthetic
(Gnostic)
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184142 22
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75
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Cerebral Cortex Motor/Sensory Homunculi
17Notice 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.
Brain – Cerebral White Matter
20Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed., Pearson, 2013
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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Limbic SystemConsists of
• portions of frontal lobe• portions of temporal lobe• hypothalamus• thalamus• basal nuclei• other deep nuclei• associated with sense of smell (less significant)
The motivational system
Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007
Functions• controls emotions• produces feelings• interprets sensory impulses• facilitates memory storage and retrieval (learning!)
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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
• optic tracts• optic chiasm• infundibulum• posterior pituitary• mammillary bodies• pineal gland
(Tectum)
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Diencephalon - Thalamus
Relay for vision
Relay for hearing
Ventral nuclei
- Posterior; relay for taste
- Anterior and Lateral; voluntary motor
- Forms wall of third ventricle
- Crude interpretation center for pain, touch, pressure, temperature
The ‘gateway’ to the cerebral cortex. Major relay for sensory information coming into the cerebral cortex, roles in cortical arousal, learning, and memory
Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed., Pearson, 2013
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Diencephalon - Hypothalamus
- 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
Hypothalamus - maintains homeostasis by regulating visceral activities (see list below for examples…)
Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed., Pearson, 2013
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Brain Stem
Three Parts1. Midbrain2. Pons3. 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
• cerebral aqueduct
• cerebral peduncles – bundles of nerve fibers
• contains red nucleus (rubro-) and substantia nigra
• corpora quadrigemina – centers for visual and auditory reflexes
(Tectum)
Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007
Major connecting center between spinal cord and brain and parts of brainstem
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
Space between the dura mater and the vertebral body is called the epidural space
Figures from: Saladin, Anatomy & Physiology, McGraw Hill, 2007
Denticulate ligaments – branches of pia mater connecting to the arachnoid
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Cross Section of Spinal Cord
• is a center for spinal reflexes• aids in locomotion• is a conduit for nerve impulses to and from the brain
The spinal cord…
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Organization of Spinal Gray Matter
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
You should know the major areas of gray matter of within the spinal cord:
Posterior = sensory
Lateral = visceral motor
Anterior = somatic motor
Spinal Cord and Nerve Roots
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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
Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed., Pearson, 2013
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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
• spinothalamic - crude pain, temperature, pressure, and touch - cross in spinal cord
• spinocerebellar - subconscious coordination of muscle movements (1st and 2nd order neurons) - ipsilateral
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2
1
Decussation
(crossing over)
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1st, 2nd, and 3rd Order Sensory Neurons
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2
1
1st order neuron – from receptor to the spinal cord (cell bodies are located in the dorsal root ganglion)
2nd order neuron – from spinal cord to thalamus
3rd order neuron – from thalamus to sensory cerebral cortex - terminate in the cerebral cortex
Decussation
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Descending Tracts• corticospinal (direct, pyramidal) - voluntary movement of skeletal muscles - lateral cross in medulla - contralateral
• 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)
Upper motor – begin in precentral gyrus of cortex
Lower
Upper MN – Cerebral cortex to spinal cord
Lower MN – Spinal cord to effector
Decussation
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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
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Review
Spinal cord contains nerve tracts
Ascending = sensory
Descending = motor