Download Ch 7 The Nervous System Notes

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Ch 7 The Nervous System Notes
Lisa Peck
I. Organization of the Nervous System (pp 222-224)
Nervous system- the master controlling and communicating system of the body
3 functions: 1. sensory receptors to monitor changes occurring inside & outside body
stimuli- changes
sensory input- gathered information
2. processes and interprets the sensory input
integration- nervous system makes decisions about what should be done
3. effects a response by activating muscles or glands (effectors) via motor output
Regulating and Maintaining Homeostasis
nervous system - fast-acting control via electrical impulses
endocrine system- slow-acting control via hormones release into the blood
Structural Classification
(p 223)
2 subdivisions: Central Nervous System
Peripheral Nervous System
1. Central Nervous System (CNS)
consists of: brain
spinal cord
functions: integrating center.........interpret incoming sensory information
command center..........issue instructions based on past experience & current conditions
2. Peripheral Nervous System (PNS)
consists of: nerves 2 types: cranial nerves- carry impulses to and from the brain
spinal nerves- carry impulses to and from the spinal cord
ganglia- groups of nerve cell bodies
function: communication lines, linking all parts of the body
Functional Classification
2
(pp 223-224)
only deals with peripheral nervous system (PNS)
1. Sensory (Afferent) Division- nerve fibers that carry impulses to the CNS from sensory
receptors located throughout body
sensory fibers types: 1. somatic sensory fibers- delivering impulses from the skin, skeletal
muscles, & joints
2. visceral sensory fibers- transmitting impulses from the visceral
organs
2. Motor (Efferent) Division- nerve fibers that carry impulses from the CNS to effector organs
ossicles and glands, bringing about a motor response
2 types: 1. somatic nervous system: conscious control of skeletal muscles
voluntary control
skeletal muscles
2. autonomic nervous system (ANS)- regulates activities that are automatic
involuntary
cardiac muscle
smooth muscle
glands
2 nerve types that target same organ but yield opp. effects
exception: targeted only by sympathetic: some glands,
most blood vessels, most structures of the skin
2 types: 1. sympathetic-” fight or flight”
f’ns during extreme situations
ex: increase heart rate
rapid breathing
cold, sweaty skin
dilated pupils
2. parasympathetic- “resting & digesting”
most active when body at rest
causing normal digestion, voiding
feces & urine
goal: conserving energy
Nervous Tissue: Structure and function (pp 224-235)
2 types of cells: 1. neuroglia- supporting cells
not able to conduct impulses
can undergo cell division
most brain tumors are gliomas- formed by glial cells
2. neurons nerve cells that transmit impulses
functional unit of nervous system
neurglia
not able to conduct impulse
glia (glial cells)- f’n: support, insulation, & protection
(pp 224-226)
CNS: 4 types: astrocytes
microglia
ependymal
oligodendrocytes
~90% cells in brain are glial cells
PNS: 2 types
schwann cells
satellite cells
1. Astrocytes- star-shaped cells
account for over half of neural tissue
numerous projections have swollen ends that cling to neurons
f’n: 1. brace and anchor neurons to capillaries
intermediary cell b/w neuron and capillary (aids in exchange)
protects neurons from harmful substances present in blood
2. control chemical environment in brain by picking up excess ions &
recapturing released neurotransmitters
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neurglia
2. Microglia- spiderlike phagocytes
dispose of debris (dead brain cells & bacteria)
smallest of glial cells
3. Ependymal- line cavities of the brain & spinal cord
f’n- beating of cilia helps circulate cerebrospinal fluid
that fills cavities & forms protective cushion around CNS
4. Oligodendrocytes- (CNS)
wrap their flat extensions around axons of many nerves
forms myelin sheath- fatty insulating covering
protects and cushions nerves
speeds up nerve transmission speed
gives rise to white matter of brain
fewer extensions than astrocytes
PNS: 2 types:
1. Schwann cells- cells of PNS that myelinate axons
2. satellite cells- protective & cushioning cells of PNS neurons
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B. Neurons (pp 226-235)
1. Anatomy (of a generalized neuron)
cell body- metabolic center
contains typical cell organelles
(exception: no centrioles .....no mitosis -amitotic)
axon- one per cell,
process of neuron
conduct impulses away from the cell body
dendrites- many per cell, extension of neuron (often branched extensively)
conduct impulses toward cell body
axon hillock- axon arises form this conelike
region of cell body
axon terminals- 100’s to 1000’s branches at terminal end of axon
contain vessicles of neurotransmitters
collateral branch- branch off of an axon
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Nerve Anatomy
synaptic cleft (synapse)- separation b/w axon terminal and next neuron
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myelin- covering of most long neurons (axon)
whitish, fatty substance
protects, insulates, speeds up neural transmission
CNS:
oligodendrocytes- form myelin sheath
lacks neurolemma
f’n- protects and cushions nerve
increases speed of nerve transmission
located in CNS
PNS:
schwann cell’s form myelin sheath
covering of most long neurons
formed by wrapping of a Schwann cell
schwann cell- specialized supportive cells
wrap tightly around axon
neurolemma- outermost part of schwann cell
aids in neuron regeneration
nodes of Ranvier- gaps of myelin sheath
b/ w Schwann cells
loc. @ regular intervals
action potential jumps from
node to node- faster
CNS
white matter- dense bundles of myelinated fibers (tracts)
gray matter- unmyelinated fibers and cell bodies
CNS
nuclei
PNS
ganglia groups of cell bodies
tracts
nerves
bundles of nerve fibers
brain- inside
spinal cord- surface
brain- surface spinal cord- inside
Classification of Neurons
functional classification- according to direction of impulse is traveling relative to CNS
1. sensory neuron- nerve impulse travels towards CNS
afferent
cell bodies outside CNS in ganglion
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receptors- dendrite endings that are specialized
activated by specific changes nearby (stimuli)
taste, hearing, sight, equilibrium, smell
cutaneous sense organspacinian & meissner corpuscles
proprioceptors- loc. in muscles & tendons
detects amt. of stretch or tension
determines location, posture, and tone
muscle spindle
golgi tendon organs
pain receptors- bare dendrite endings
least specialized cutaneous receptor
most numerous cutaneous receptor
2. motor neuron- nerve impulse travels away from CNS
efferent neuron
cell bodies inside CNS in nuclei
3. association neurons (interneurons)- connect motor and sensory neurons
cell bodies in CNS
Classification of Neurons
structural classification- based on number of processes extending from cell body
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multipolar- several processes
all motor neurons
all association neurons
most common neuron type
bipolar- 2 process on cell body
axon & dendrite
rare in adults (eg; eye & nose)
unipolar- one process on cell body
single process is very short
process divides into 2
peripheral process- (distal)
contains dendrites on end
central process- (proximal)
contains axon terminals
axon- both peripheral & central
processes
conducts impulses in both
directions (toward & away from cell body)
sensory neurons located in PNS ganglia are all unipolar
3. Physiology
nerve impulse generation (action potential)
reflex arcs- neural pathways involve both CNS & PNS
reflexes- rapid, predictable and involuntary responses to stimuli
once reflex begins...always goes in same direction
types: somatic reflexes- stimulate the skeletal muscles
eg: pull hand away from hot stove
autonomic reflexes- regulate the activity of smooth muscles, heart, & glands
eg: secretion of saliva, changes in pupil size,
regulates: digestion, elimination, blood pressure, & sweating
III. Central Nervous system
(pp 235-249)
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Functional Anatomy of the Brain (pp 235-241)
Brain- 3 parts
1. forebrain- cerebrum
diencephalon- thalamus
hypothalamus
2. midbrain- small superior part of brain stem
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3. hindbrain- cerebellum
brain stem (part of it)- medulla oblongata
pons
Forebrain
2 parts: 1. cerebrum (cerebral hemispheres)
2. diencephalon
Cerebrum: largest part of brain
divided into left and right hemispheres-cerebral hemispheres
separated by corpus callosum (internally)- large fiber tract connecting hemispheres
longitudinal fissure (surface)
the spinal tracts cross over -------> left hemisphere deals w/ right side of body
right hemisphere deals w/ left side of body
surface is highly convoluted- increasing surface area (increases # of neurons)
cortex- (exterior) gray matter
thin surface layer (1-4 mm thick)
Interior- white matter, nerve tract relaying impulses
to & from cerebral cortex
gyrus (gyri)- elevated ridges on cerebral cortex
sulcus (sulci)- shallow grooves in cortex
fissure- deep sulcus in cortex
sulci divide hemispheres into 4 lobes
separate large areas of brain
frontal lobe
parietal lobe
occipital lobe
temporal lobe
Functional Anatomy of the Brain (pp 235-241)
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Forebrain
Cerebrum- cerebral cortex: 4 lobes
f’n- speech, memory, logical & emotional response, consciousness, interpretation of sensation,
voluntary movement, problem solving
frontal lobe
primary motor area- located anterior to central sulcus
initiates voluntary movement of skeletal muscles (motor language too)
premotor area- located anterior to primary motor area
process input regarding body movement, modify movements
prefrontal area- anterior frontal lobe
higher level thought, decision making, planning, impulsivity control
selective attention, personality, problem solving, behavior, emotions
Broca’s area- inferior left frontal gyrus
controls facial neurons & speech production- articulation
(works in junction with Wernicke’s Area- language comprehension)
parietal lobe
somatic sensory area- located posterior to central sulcus
interprets input from sensory receptors (except specialized senses)
aids in spacial orientation
sensory pathways are crossed pathways (left sensory area receives input from right side of body)
temporal lobe- auditory processing
olfactory area (located deep temporal)
memory: right lobe- visual memory (pictures, faces)
left lobe- verbal memory (words, names)
occipital lobe- visual center , processes visual info and visual recognition of shapes & colors
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Forebrain
1. Cerebrum- “telencephalon”
2. Diencephalon- located superior to brain stem & enclosed by cerebral hemispheres
3 parts- thalamus- relay station for sensory impulses passing upward to somatic sensory cortex
all sensory input passes thru thalamus to cortex (except olfaction)
signals from cerebellum pass thru thalamus up to motor area of cortex
encloses 3rd ventricle (spaces filled w/ cerebrospinal fluid...aids in circulation)
hypothalamus-”seat” of autonomic nervous system
regulates homeostasis
both nervous & endocrine f’ns
source of 8 hormones
regulation of: body temp, water balance, blood chemistry, metabolism
heart rate,
death results if damaged
plays imp. part in limbic system- “emotional-visceral brain”
emotion, motivation
epithalamus- forms roof of 3rd ventricle
choroid plexus- knots of capillaries w/ in ea. ventricle forms CSF
pineal body- endocrine gland
releases melatonin- regulates daily body rhythms
eg: day/ night cycle melatonin released @ night
Brain Stem- pathway for ascending & descending tracts, has gray areas- cranial nerves
help control breathing, heart rate etc.
1. midbrain
2. pons
3. medulla oblongata
reticular formation- extends length of brain stem (middle of hindbrain to midbrain)
role in consciousness & awake/ sleep cycles damaged- coma
Midbrain
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located upper part of brain stem
very small portion of brain stem
evolutionarily: the oldest part of brain
only used for eye reflexes
reticular formation- collects input from higher brain centers & passes it on to motor neurons
substantia nigra- helps “smooth” out body movements damaged-Parkinson’s Disease
ventral tegmental area (VTA)- loaded w/ dopamine-releasing neurons that are activated
by nicotinic acetylcholine receptors & synapse deep w/ in
forebrain
VTA involved in pleasure: nicotine, amphetamines & cocaine
bind to and activate its dopamine-releasing neuronsmay account for their addictive qualities
Hindbrain-consists of
part of brain stem: 1. pons
2. medulla oblongata
3. cerebellum
pons- rounded structure protruding below midbrain
unconscious control of breathing (reflexive breathing)
reticular formation- area receives sensory input from forebrain & passes to thalamus
involved in sleep, arousal & vomiting
relay center b/w cerebral cortex (impulses from eyes, ears, & touch receptors) & cerebellum
medulla oblongata- closest to spinal cord most inferior part of brain stem
f’n- regulation of heart beat, breathing, vasoconstriction (blood pressure),
reflex centers for vomiting, coughing, sneezing, swallowing, & hiccups
important fiber tract area
damaged- death
4th ventricle lies posterior to medulla oblongata
cerebellum- second largest part of brain
2 convoluted hemispheres
surface layer is gray matter and internal area is white matter
f’n- muscle coordination
maintain normal muscle tone & posture balance & equilibrium
Limbic System- receives input from association areas in cortex & passes signals cerebrum
2 parts: hippocampus- essential for formation of long term memories
amygdala- center of emotions (eg fear)
send signals to hypothalamus& medulla wh/ can activate
“fight or flight”
receives signals form olfactory system....may account for
powerful effect that odor has on memory
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Protection of the Central Nervous System (pp 241-244)
1. Bones of skull and vertebral column
2. Meninges
dura mater- outermost
arachnoid matter- middle
pia matter- innermost
Protection of the Central Nervous System (pp 241-244)
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2. Meninges- 3 continuous sheets covering both spinal cord and brain
dura mater- outermost, pressed against bony surface on interior of vertebrae & cranium
arachnoid mater- middle layer, weblike, threadlike extensions pass thru subarachnoid
space & attach to pia mater
pia mater- innermost layer, thin, attached to surface of spinal cord & brain
3. Cerebrospinal Fluid (CSF)
fluid similar to blood plasma containing protein, vit. C, and ions
bathes cells of CNS protecting them from physical trauma
returns to blood thru veins drainging the brain
choroid plexus- capillaries that secrete CSF
located hanging from roof of each ventricle ( 2 lateral, 3rd & 4th)
CSF location
4. Blood-Brain Barrier
C. Brain Dysfunctions (pp 244-247)
1. Traumatic Brain Injuries
concussion- reversible damage
contusions- nonreversible damage
2. Cerebrovascular Accidents (CVA)- stroke
visual impairment
paralysis
aphasias
3. Alzheimer’s Disease
4. Huntington’s Disease
5. Parkinson’s Disease
6. Diagnosis (pp 262-263)
electroencephalogram (EEG)
simple reflex tests
angiography
CT scans
PET scans
MRI & Functional MRI scans
D. Spinal Cord (247-249)
~17 inches from foramen magnum to L1 or L2
cauda equina- cord ends w/ spinal nerves @ L2
31 pairs of spinal nerves (dorsal & ventral roots)
Gray Matter of Spinal Cords & Spinal Roots
gray matter in middle around central canal (H shape)
2 dorsal (post.) horns- contains interneurons connected to sensory neurons from dorsal root
2 ventral (ant.) horns- cell bodies of motor neurons whose axons leave via ventral root
White Matter of the Spinal Cord 3 regions
anterior column: ascending tracts only (incoming sensory)
lateral column: both ascending & descending
posterior column: both ascending & descending
spinal nerve- fused dorsal & ventral roots (a mixed nerve- sensory & motor neurons)
dorsal root: entering sensory neurons
dorsal root ganglia- sensory nerve
cell bodies
ventral root: motor nerve axons
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Peripheral Nervous System (pp
249-263)
contain only nerves (no glial cells)
Structure of a Nerve
nerve- bundle of neuron fibers (held tog. w/ connective tissue)
endoneurium- surrounds each never fiber
perineurium- binds groups of fibers into fasicles
epineurium- bind fascicles together
12 Pairs of Cranial Nerves
numbered in order from front to back
most are mixed nerves (3 sensory only)
I
olfactory
sensory 4 smell
II
optic
sensory 4 vision
III oculomotor
motor fibers to eye muscles
IV trochlear
motor fibers to eye muscles
V trigeminal
sensory 4 face
motor fibers to chewing muscles
VI abducens
motor fibers to eye muscles
VII facial
sensory 4 taste
motor fibers to face
VIII vestibulocochlear
sensory 4 hearing & balance
IX glossopharyngeal
sensory 4 taste
motor fibers to pharynx
X
vagus
sensory & motor 4 pharynx,
larynx, & viscera
XI accessory
motor nerve to neck &
upper back
XII hypoglossal
motor fibers to tongue
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31 Pairs of Spinal Nerves and Nerve Plexuses
spinal nerves formed by combo of venrtral & dorsal roots of spinal cord
spinal nerves named for region from which they arise
spinal nerves divide after leave spinal cord
dorsal rami- serve skin & posterior trunk muscles
ventral rami- form plexus for the anterior
plexuses- ventral rami of spinal nerves form complex networks that serve motor & sensory
needs of limbs
4 plexus: cervical, brachial, lumbar, & sacral
classification of nerves by direction of impulse
mixed nerve- travels to & from CNS
inlcudes both sensory and motor nerve fibers
sensory nerve- carry impulse towards CNS (afferent)
motor nerve- carry impulse away from CNS (efferent)
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Autonomic Nervous System
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somatic & autonomic nervous systems compared
Somatic NS
Nerves
Autonomic NS
one motor neuron
preganglionic nerves
postganglionic nerves
Effector Organs
skeletal muscle
smooth muscle
cardiac muscle
glands
Neurotransmitters
always use acetylcholine
acetylcholine
epinephrine
norepinephrine
Autonomic Nervous System: involuntary control
2 divisions that serve same effector (smooth or cardiac muscle or a gland)
2 divisions bring about opposite effects, coutner balance ea. other
major difference 1) location of origin in CNS
parasympathetic- brain stem or S1-S4
sympathetic- T1-L2
2) location of ganglia
parasympathetic- ganglia near spinal cord
sympathetic- ganglia near effector organ
Autonomic Nervous System
Parasympathetic division (PaNS)
“housekeeping activities”
conserves energy
maintains daily necessary body functions
“D” division: digestion, defecation, and diuresis
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constricts pupils
conserve E
stimulates digestive (increase saliva)
stimulates urinary organs (increase urine production)
inhibit cardiovascular system (slow heart rate)
inhibit respiratory systems (constrict airways,
slow respirations)
Sympathetic division (SyNS)
“fight-or-flight”
response to unusual stimulus
takes over to increase activities
“E” division: exercise, excitement, emergency, & embarrassment
pupils dialate
stimulate respiratory organs (increase breathing rate & open airways)
stimulate cardiovasculary system (increase heart rate)
stimulate adrenal glands (release epinephrine and norepinephrine...stimulate liver)
stimulated liver (convert glycogen into glucose....release into blood)
inhibit digesitve system (decrease saliva...dry mouth)
inhibit urinary system
increase glucose use....generates heat and water...increase sweat, reddened skin
polygraph- measures stress incurred when tell a lie. You know it is wrong to lie, when you do lie
your sympathetic NS kicks in and your adrenal glands cause heart rate to increase.
measures changes in heart rate
Developmental Aspects of the Nervous System (pp 263-266)
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nervous system if formed during the first month of embryonic development
any maternal infection can have extremely harmful effects
the hypothalamus is one of the last areas of the brain to develop
it controls body temperature: premature babies and infants can not maintain body temp
there are no more neurons formed after birth, but growth and maturation continues for several years
neurons will develop myelination during maturation- increases neuromuscular control
the brain reaches maximum weight as a young adult
A. Embryonic Brain Development
cerebral palsy
anencephaly
hydrocephalus
spina bifida
B. Premature Infants
temperature regulation via hypothalamus