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1
Central Nervous SystemChapter 13 – Lecture Notes
to accompany
Anatomy and Physiology: From Science to Life
textbook by
Gail Jenkins, Christopher Kemnitz, Gerard Tortora
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Chapter Overview13.1 Central Nervous System13.2 Protection and Nourishment of the CNS13.3 Cerebrum13.4 Limbic System13.5 Signal Processing in the Cerebrum13.6 Diencephalon13.7 Brain Stem13.8 Cerebellum13.9 Spinal Cord13.10 Propagation of Impulses
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Essential TermsCentral Nervous System (CNS)
brain and spinal cord control center for
thoughts emotions creativity wisdom memories activities behaviors
Tract bundle of axons
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Introduction CNS made up of ~100 billion neurons Adult brain mass of ~1300g (3 lbs) Spinal cord
mediates rapid reactions reflexes
pathway for sensory nerve impulses to brain pathway for motor nerve impulses from brain
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CNSBrain
1. cerebrum– cerebral hemispheres
2. diencephalon3. brain stem4. cerebellum
Spinal Cord medulla oblongata to superior edge of L2Protection of CNS two types of connective tissues
bony skull cranial and spinal meninges
cushion of cerebrospinal fluid
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Skeletal Protection
Brain is located in cranial cavity of skull
Spinal cord is located within vertebral canal of vertebral column
vertebral foramina of vertebrae stacked one on top of one another form the vertebral canal
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Meninges
three connective tissue coverings that encircle brain and spinal cord
cranial meninges spinal meninges superficial to deep
dura mater arachnoid mater pia mater
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Dura Mater of Brain most superficial adheres to periosteum
of cranial bones strongest menix extensions separate portions of brain
falx cerebri two hemispheres of cerebrum
falx cerebelli two hemispheres of cerebellum
tentorium cerebelli separates cerebrum from cerebellum
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Dura Mater of Spinal Cord between dura mater and all of
vertebral canal epidural space
cushion of fat dura mater tissue sinuses that act as collection points
for interstitial fluid and blood leaving brain
return interstitial fluid and blood to internal jugular veins of neck
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Arachnoid Mater avascular collagen fibers some elastic fibers surrounds both brain and spinal cord subdural space
thin space between dura mater and arachnoid matter
contains interstitial fluid
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Pia Mater innermost membrane tightly adheres to surface of CNS interlacing bundles of collagen fibers some fine elastic fibers surrounds both brain and spinal cord subarachnoid space
thin space between arachnoid mater and pia matter
contains cerebrospinal fluid also covers surface blood vessels of
CNS
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Meninges and Spinal Nerves All three
cover spinal nerves up to point of exit from spinal column through intervertebral foramina
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Denticulate Ligaments suspend spinal cord in middle of dural
sheath membranous extensions of pia mater project laterally and fuse with
arachnoid mater and inner surface of dura mater between anterior and posterior nerve
roots of spinal nerves on either side protect spinal cord against shock and
sudden displacement
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Blood Flow to CNS to brain via
internal carotid and vertebral arteries flows into dural sinuses empties into internal jugular veins
to spinal cord via posterior intercostal and lumbar arteries empties into posterior intercostal and
lumbar veins
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Blood Flow to Brain Brain at rest uses 20% of oxygen and
glucose even though only 2% of mass of adult
Neurons synthesize ATP almost exclusively from glucose
when activity increases in a particular region, blood flow to that area also increases
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Blood Flow to Brain decreased blood flow to brain
short time can cause unconsciousness 1 to 2 minutes impairs neuronal function 4 minutes causes permanent injury virtually no glucose stored in the brain low blood glucose to brain can cause
mental confusion dizziness convulsions loss of consciousness
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Blood Flow to Brain Blocked blood flow to brain
arterial blockage can damage brain CVA cerebrovascular accident
stroke most common brain disorder affect 500,000 people per year in US 1/3 leading cause of death
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Blood Brain Barrier
Physiology protects CNS from harmful
substances pathogens
prevents passage from blood into interstitial fluid of neural tissue
water soluble substances usually pass by active transport
others pass slowly lipid soluble substances pass readily
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Blood Brain Barrier
Anatomy cerebral arteries divide quickly into capillaries tight junctions seal together endothelial cells of
CNS capillaries capillaries also surrounded by thick basement
membrane astrocyte processes press against capillaries
selectively pass some substances and inhibit others
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Cerebrospinal Fluid (CSF) 80-150 ml volume clear colorless liquid protects and nourishes brain & spinal cord
protects against chemical and physical injuries acting as shock absorber on which brain floats
nourishes by carrying oxygen glucose other chemicals
continuously circulates through cavities in and around CNS in subarachnoid space
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Cerebrospinal Fluid (CSF)
Contributes to homeostasis in three ways: 1. mechanical protection
1. shock absorber2. chemical protection3. circulation
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Formation of CSF CSF fills ventricles
lateral ventricles located in each hemisphere of cerebrum separated by septum pellucidum
third ventricle fourth ventricle
CSF produced in choroid plexuses capillaries in walls of ventricles covered by ependymal cells that form CSF from
blood plasma by filtration and secretion
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Circulation of CSF Cilia on ependymal cells assist with flow from lateral ventricles through interventricular foramina to third ventricle then through cerebral aqueduct into fourth ventricle enters subarachnoid space through
median aperture pair of lateral apertures
reabsorbed into blood arachnoid villi
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Cerebrum Seat of intelligence
interprets sensory impulses controls muscular movements functions in emotional and intellectual processes
Cerebral Cortex gray matter on outside
receives & integrates incoming & outgoing information
White matter on inside white is myelination
Gray matter nuclei deep within white matter
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Cerebral Cortex enlarges faster during embryonic development
than white matter rolls and folds forming
gyri (singular = gyrus) bulges or folds
fissures deep grooves
longitudinal fissure separates cerebrum into left and right hemispheres
connected internally by corpus callosum
sulci (singular = sulcus) shallow fissures
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Cerebral White Matter has tracts
myelinated and unmyelinated axons communicate between regions of
CNS three types
1. association tracts• between gyri in same hemisphere
2. commissural tracts• from gyri in one hemisphere to
corresponding gyri in other hemisphere3. projection tracts
• from cerebrum to lower parts of CNS
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Basal Nuclei mass of cell bodies two are side by side just lateral to thalamus
globus pallidus and putamen third is caudate nucleus
large “head” connected to smaller “tail” by long comma-shaped “body”
receive input from cerebral cortex provide output to motor portions control subconscious contractions of skeletal
muscles
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Limbic System controls emotion, behavior, and memory encircles upper part of brain stem and corpus
callosum ring of structures on inner border of cerebrum
and floor of diencephalon controls most involuntary aspects of behavior
related to survival intense pain extreme pleasure anger/rage affection recognition of fear
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Functional Areas of Cerebrum Sensory areas
receive sensory impulses Motor areas
initiate movements Association areas
complex integrative functions memory emotions reasoning will judgment personality traits intelligence
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Sensory Areas Posterior half of both hemispheres
behind central sulci most direct connections with peripheral
sensory receptors primary somatosensory area
receives impulses for touch, proprioception, pain, itching, tickle, thermal sensations
localize exactly the points where sensations originate primary visual area
receives impulses for vision eye to thalamus to primary visual area
shape, color, movement of visual stimuli
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