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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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Concept 13.1

Central Nervous System

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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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Figure 13.1a

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Figure 13.1c

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Figure 13.2

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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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Figure 13.3a

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Figure 13.4a

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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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Concept 13.2 Nourishment and Protection

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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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Figure 20.20c

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Figure 20.20d

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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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Figure 13.5a

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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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Figure 13.6a

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Figure 13.3a

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Figure 13.6c

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Concept 13.3 Cerebrum

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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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Figure 13.7a

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Figure 13.7b

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Figure 13.7c

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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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Table 13.2 part 1

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Table 13.2 part 2

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Table 13.2 part 3

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Table 13.2 part 4

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Table 13.2 part 5

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Concept 13.4 Limbic System

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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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Concept 13.5 Functional Areas of Cerebrum

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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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Figure 13.10

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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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Sensory Areas primary auditory area

receives impulses for basic characteristics of sound pitch and rhythm

primary gustatory area receives impulses for taste

primary olfactory area receives impulses for smell