A&P Chapter 7 The Nervous System
1. Outline the structural organization of the nervous system.
---structural classification, which includes all nervous system
organs has two subdivisions
--central nervous system (CNS) consists of brain and spinal
cord
--peripheral nervous system (PNS) is part outside the CNS and
consists mainly of nerves that extend from brain and spinal
cord
-spinal nerves carry impulses to and from spinal cord
-cranial nerves carry impulses to and from the brain
2. Outline the functional organization of the nervous system.
---functional scheme is concerned ONLY with PNS structures
---sensory (afferent) division conducts impulses TO THE CENTRAL
NERVOUS SYSTEM
--sensory fibers from skin, skeletal muscles, and joints
called somatic sensory (afferent) fibers
--sensory fibers from visceral organs called visceral sensory
fibers (visceral afferents)
--sensory division keeps CNS constantly informed of events
going on both inside and outside the body
---motor (efferent) division carries impulses FROM THE CENTRAL
NERVOUS SYSTEM to effector organs, the muscles, and glands
--impulses activate muscles/glands
--they effect (bring about) a motor response
--**motor division has two subdivisions
-somatic nervous system and autonomic nervous system
3. Discuss the autonomic nervous system: Level of control,
effectors, and two distinct divisions.
---autonomic nervous system (ANS) is motor subdivision of PNS
that controls body activities automatically (involuntary)
---composed of special group of neurons that regulate cardiac
muscle, smooth muscles, and glands
---ANS also called involuntary nervous system
---ANS composed of two distinct systems: sympathetic and
parasympathetic
---both serve same organs but cause essentially opposite effects
--counterbalance each other’s activities to keep body systems
running smoothly
---preganglionic axons of sympathetic division release
acetylcholine; postganglionic axons release norepinephrine
and/or epinephrine (called adrenergic fibers)
---preganglionic axons and postganglionic axons of the
parasympathetic division release acetylcholine (called
cholinergic fibers)
---sympathetic part mobilizes body during extreme situations
(fear, exercise, or rage)
--E for exercise, excitement, emergency, and embarrassment
---parasympathetic division allows body to “unwind” and conserve
energy
--D for digesting, defecation, and diuresis (urination)
4. Discuss the somatic motor nervous system: effectors
activated and neurotransmitter released.
---somatic motor nervous system allows us to consciously, or
voluntary control skeletal muscles
---this subdivision often referred to voluntary nervous system
---in somatic division, cell bodies of motor neurons are inside
central nervous system and their axons (in spinal nerves)
extend all the way to skeletal muscles they serve
---skeletal muscle are the effectors of the somatic motor
nervous system
---neurotransmitter is acetylcholine
5. Outline the cells of nerve tissue.
---nervous tissue composed of two principal types of cells
--neurons and supporting cells
---supporting cells in CNS are lumped together as neuroglia
(nerve glue)
---neuroglia (also called glia) support, insulate, and protect
delicate neurons
---astrocytes account for nearly half of neural tissue
--brace and anchor neurons to blood capillaries
--form a living barrier between capillaries and neurons
and play role in making exchanges between the two
--help protect neurons from harmful substances in blood
--help control chemical environment by picking up excess
ions and recapturing released neurotransmitters
---microglia are phagocytes that dispose of debris-dead brain
cells, bacteria, etc.
---ependymal cells line cavities of brain and spinal cord
--beating of their cilia help circulate the cerebrospinal
fluid that fills those cavities and forms protective
cushion around CNS
---oligodendrocytes wrap their flat extensions around nerve
fibers, producing fatty insulating coverings called myelin
sheaths
---**neuroglia are NOT able to transmit nerve impulses and they
never lose their ability to divide
--most brain tumors are gliomas or tumors formed by glial
cells
---supporting cells in PNS come in two major varieties
--Schwann cells form myelin sheaths around nerve fibers
that are found in PNS
--satellite cells act as protective, cushioning cells
---neurons (nerve cells) are highly specialized to carry
impulses (transmit messages)
---all neurons have cell body (soma) and one or more slender
processes extending from cell body
--neuron processes that conduct electrical impulses toward
cell body are dendrites
--neuron processes that conduct electrical impulses away
from cell body are axons
---neuron may have 100s of dendrites but only ONE axon
--axons branch profusely at terminal end forming 100s to
1000s of axonal termials
6. State the functions of the various parts of a neuron.
---cell body contains the nucleus and is the metabolic center
of the neuron
---dendrites responsible for transmitting electrical impulses
to the cell body
---the axon is responsible for transmitting the electrical
impulse away from the cell body to either another neuron or
to the effector
---most long neurons are covered with whitish, fatty material
called myelin
--myelin protects and insulates the fibers and increase the
transmission rate of nerve impulses
---axons outside CNS are myelinated by Schwann cells-specialized
supporting cells that wrap tightly around axon jelly-roll
fashion
--when wrapping done, tight coil of wrapped membranes called
the myelin sheath encloses axon
--most of Schwann cell cytoplasm ends up just beneath
the outermost part of its plasma membrane
--this part of Schwann cell, external to myelin sheath
called the neurilemma
---since myelin sheath is formed by many individual Schwann
cells, it has gaps or indentations called nodes of Ranvier
at regular intervals
---myelin sheaths in neurons of CNS are formed by the
oligodendrocytes
--CNS myelin sheaths lack a neurilemma
7. Distinguish between nuclei and ganglia; nerves and tracts;
white matter and gray matter.
---cell bodies are found in the CNS in clusters called nuclei
--this well-protected location essential to well-being
of nervous system
---small collections of cell bodies called ganglia are found
in a few sites outside CNS in the PNS
---bundles of nerve fibers (neuron processes) running through
CNS are called tracts
---bundles of nerve fibers (neuron processes) running through
PNS are called nerves
---terms white matter and gray matter refer respectively to
myelinated versus unmyelinated regions of the CNS
---as general rule, white matter consists of dense collections
of myelinated fibers (tracts)
---gray matter contains mostly unmyelinated fibers and cell
bodies
8. Outline the classification of neurons.
---neurons may be classified according to how they function or
according to their structure
---FUNCTIONAL classification based on direction impulse is
traveling relative to CNS
---there are sensory, motor, and association neurons
---sensory (afferent) neurons carry impulses from sensory
receptors (in internal organs or skin) to the CNS
--cell bodies of sensory neurons always found in a
ganglion outside the CNS
--inform about what is happening inside and outside the body
---motor (efferent) neurons carry impulses from CNS to viscera,
and/or muscles and glands
--cell bodies of motor neurons always located in CNS
---association (interneurons) neurons connect sensory and
motor neurons in neural pathways
--association neuron’s cell bodies always located in CNS
---STRUCTURAL classification based on number of processes
extending from cell body
---multipolar neuron has several processes
--since all motor and association neurons are multipolar
this is most common structural type
---bipolar neuron has two processes-a dendrite and an axon
--rare in adults, found only in some special sense organs
(eye, ear) where they act as sensory receptor cells
---unipolar neuron has single process emerging from cell body
--very short and divides almost immediately into proximal
(central) and distal (peripheral) fibers
--unique in that only small branches at end of peripheral
process are dendrites
--remainder of peripheral process and central process
function as axons
--this in unipolar neuron, axon conducts impulse both toward
and away from cell body
--sensory neurons found in PNS ganglia are unipolar
9. Explain the resting state of a neuron.
---plasma membrane of a resting (inactive) neuron is polarized
---means there are fewer positive ions sitting on inner surface
of neuron’s plasma membrane than there are on its outer face
in the tissue fluid that surrounds it
---major positive ions inside the cell are potassium (K+) and
major positive ions outside the cell are sodium (Na+) ions
---**as long as the inside remains more negative as compared to
the outside, the neuron will stay inactive (resting)
---resting potential of neuron is about –70 millivolts
10. Explain the action potential.
---could be called “nerve impulse”
---stimulus changes permeability of “patch” of membrane and
sodium ions diffuse rapidly into cell
---this changes polarity of membrane at that location
--inside becomes more positive; outside becomes more negative
---event called depolarization
---is stimulus is strong enough, (at or above threshold level)
action potential is initiated
---depolarization of first membrane patch causes permeability
changes in adjacent membrane, and event is repeated
---membrane potential goes from –70 mv to + 30 mv
---action potential propagates rapidly along entire length of
membrane
11. Explain the repolarization that follows an action potential.
---after area (patch) of membrane depolarizes, it repolarizes
---membrane permeability changes and potassium ions diffuse OUT
OF CELL
---restores negative charge inside cell and positive outside
---repolarization occurs in same direction as depolarization
---**sodium-potassium pump used to restore ionic conditions
of the resting neuron
---resting potential of –70 mv restored
12. Define reflexes and distinguish somatic and autonomic
reflexes.
---reflex is a rapid, predictable and involuntary response
to a stimulus
---reflexes occur over neural pathways called reflex arcs
---somatic reflexes include all reflexes that stimulate the
skeletal muscles
--dendrite of sensory neuron carries impulse to CNS
--processing of impulse may or may not occur in CNS
--axon of motor neuron carries impulse to effector
--pull hand away from hot object = somatic reflex
---autonomic reflexes regulate activity of smooth muscles, the
heart, and the glands
--secretion of saliva and size of eye pupils are two examples
---ALL reflex arcs have minimum of five elements
--(1) sensory receptor which reacts to stimulus
--(2) effector organ (muscle or gland eventually stimulated)
--(3) afferent neuron/(4) efferent neuron to connect the two
--(5) integration center located in CNS
---two-neuron reflex (patellar knee-jerk) is most simple
---three-neuron reflex (flexor or withdrawal reflex) more
complex
13. Who is responsible for losing IO #13?
14. Describe examples of somatic reflexes: Patellar and
withdrawal.
---patellar reflex: receptors in patellar tendon
--effectors are upper leg muscles that cause leg extension
---withdrawal reflex: touching a hot object or finger stick
---can be used as diagnostic tool
15. List the functions of the cerebrum.
---speech, memory, logic, emotional response, consciousness,
interpretation of sensation, voluntary movements
16. List the functions of the basal nuclei (basal ganglion).
---modify instructions from the cerebrum to the skeletal
muscles
---problems with basal nuclei lead to inability to carry
movements in normal way
--Huntington’s chorea (disease) results in inability
to control muscles, individual exhibits abrupt, jerky,
and almost continuous movements
--sufferers helped by drugs that block dopamine’s effect
--Parkinson’s disease results in individual having trouble
initiating movement or in getting muscles going
-have persistent hand tremor in which thumb and index
finger make continuous circles with one another
-due to deficit of neurotransmitter dopamine
17. List the functions of the thalamus.
---part of the diencephalon (innerbrain) that sits atop the
brain stem and enclosed by cerebral hemispheres
---thalamus encloses the third ventricle of the brain
---relay station for sensory impulses headed toward cerebrum
---provides “crude” recognition of whether sensation about to
have is pleasant or unpleasant
--actual interpretation occurs in neurons of cerebral cortex
18. Summarize the functions of the hypothalamus.
---also part of the diencephalon
---an important autonomic nervous system center
---plays role regulation of body temperature, water balance,
and metabolism
---also center for many drives and emotions
--important part of the limbic system (emotional-visceral
brain)
---thirst, appetite, sex, pain, and pleasure centers located in
hypothalamus
---regulates the pituitary gland and produces two hormones:
ADH and oxytocin
19. Summarize the functions for the midbrain.
---midbrain small part of the brain stem
---anteriorly composed of two bulging fiber tracts (cerebral
peduncles) that convey ascending and descending impulses
---dorsally composed of four rounded protrusions called
corpora quadrigemina which are reflex centers involved with
vision and hearing
20. Summarize the functions of the pons.
---pons is rounded structure that protrudes just below midbrain
---as “bridge,” ascending and descending impulses pass through
this area
---contains important nuclei involved in breathing
21. Summarize the functions of the medulla oblongata.
---medulla oblongata most inferior part of brain stem
---merges into spinal cord below with no obvious change in
structure
---like pons, is an important fiber tract area
---contains many nuclei that regulate vital visceral activities
---heart rate, blood pressure, breathing, swallowing, and
vomiting
22. Summarize the functions of the cerebellum.
---like cerebrum, cerebellum has 2 hemispheres and convoluted
surface
---has outer cortex made up of gray matter and inner region
of white matter
---provides precise timing for skeletal muscle activity,
controls balance and equilibrium
---because of its activity, body movements are smooth and
coordinated
---continually monitors the brain’s intentions with actual body
performance by monitoring body position and amount of tension
in various body parts
23. Explain how the CNS is protected.
---CNS protected by enclosure within bone (skull and vertebral
column), by a watery cushion (cerebrospinal fluid), and by
enclosing within membranes (meninges)
---is also protected from harmful substances in blood by the
blood-brain barrier
24. Discuss the meninges and define meningitis.
---three connective tissues membranes covering and protecting
CNS structures are called meninges
---dura mater is the leathery, outermost layer
--is double-layered membrane where surrounds brain
--periosteal layer is attached to inner surface of skull
--meningeal layer forms outermost covering of brain and
continues as dura mater of spinal cord
---arachnoid mater is weblike middle meningeal layer
--its threadlike extensions span subarachnoid space to
attach it to innermost membrane, the pia mater
---pia mater (gentle mother) clings tightly to surface of
brain and spinal cord by following every fold
---meningitis is an inflammation of the meninges and is
serious threat to the brain because bacterial or
viral meningitis may spread to nervous tissue of CNS
---condition of brain inflammation is called encephalitis
---meningitis usually diagnosed by taking sample of CSF
from subarachnoid space
25. Discuss cerebrospinal fluid: Origin, where it circulates,
composition, tapping, and hydrocephalus.
---cerebrospinal fluid (CSF) continually formed from blood
by the choroid plexuses (clusters of capillaries that hang
from roof in each of brain’s ventricles
---forms watery cushion in and around brain and cord that
protects fragile nervous tissue from blows & other trauma
---CSF continually moving from lateral hemispheres into third
ventricle, then through cerebral aqueduct of midbrain into
fourth ventricle dorsal to pons/medulla oblongata
---some fluid reaching 4th ventricle continues down central
canal of spinal cord but MOST circulates into subarachnoid
space through three openings in wall of 4th ventricle
---fluid returned to blood through arachnoid villi
---CSF contains water, glucose, proteins, and sodium chloride
ions
---lumbar spinal tap used to collect sample of CSF for testing
---is something affects CSF drainage, it begins to accumulate
and exert pressure on brain
---results in hydrocephalus (water on the brain)
--risks and treatments
26. Define selected traumatic brain injuries.
---head injuries are leading cause of accidental death in U.S.
---brain damage caused NOT only by injury at site of blow, but
also by effect of ricocheting brain hitting opposite end of
skull
---concussion occurs when brain injury is slight
--dizzy, brief unconsciousness but no permanent brain damage
---contusion is result of marked tissue destruction
--brain stem contusion results in coma (hours to lifetime)
---cerebral edema is swelling of brain due to inflammatory
response to injury
---intracranial hemmorhage is bleeding from ruptured vessels
27. Discuss cerebrovascular accidents: Cause, opposite side, and
aphasias.
---commonly called strokes and are third leading cause of death
in U.S.
---CVAs occur when blood circulation to brain area is blocked by
blood clot or ruptured blood vessel
--vital brain tissue dies
---after CVA, often possible to determine area of brain damage
by observing patient’s symptoms
--left-sided paralysis, right motor cortex likely damaged
---aphasias common result of damage to left cerebral hemisphere
where language areas located
---motor aphasia involves damage to Broca’s area and a loss
of ability to speak
---sensory aphasia in which person loses ability to understand
written or spoken language
---**temporary brain ischemic (transient ischemic attack or TIA)
is uncompleted “stroke”
--last from 5 to 50 minutes
--numbness, temporary paralysis, and impaired speech
--symptoms not permanent, but are RED FLAG that warn of
more serious impending CVAs
28. Generally describe Alzheimer’s Disease.
---progressive degenerative disease of brain that ultimately
results in dementia (mental deterioration)
---may begin in middle age
---have memory loss (particularly of recent events), become
moody, irritable, confused, and sometimes violent
--ultimately, hallucinations occur
---structural changes occur in brain in area concerned with
cognitive functions and memory
--abnormal protein deposits (plaques) and twisted fibers
appear within neurons and there is local brain atrophy
---influx of calcium into brain cells implicated
29. Discuss the spinal cord: Conduction system, reflex center,
where it ends, and number of nerves given off.
---cylindrical spinal cord (approx. 42 cm/17 in long) is
continuation of brain stem
---provides two-way conduction pathway to and from brain
---is major reflex center (spinal reflexes completed at this
level)
---enclosed within vertebral column, extends from foramen
magnum of skull to first or second lumbar vertebra
--ends just below ribs
---meningeal coverings do NOT end at L2 but extend well beyond
end of spinal cord in vertebral column
---**not possible to damage cord below L3, good place to draw
CSF
---collection of spinal nerves at inferior end of vertebral
canal called cauda equina (horse’s tail)
---31 pairs of spinal nerves arise from the spinal cord
30. Describe the gray matter of the spinal cord: Shape, content,
and results of damage.
---gray matter of spinal cord looks like butterfly or letter “H”
in xs
---gray matter surrounds the central canal of cord which
contains CSF
---two dorsal (posterior) horns and two ventral (anterior) horns
---dorsal horns contain association neurons (interneurons) so
is sensory in nature
---ventral horns contain cell bodies of motor neurons of the
somatic (voluntary) nervous system
---damage of ventral root results in flaccid paralysis of
muscles served
--nerve impulses DO NOT reach muscles affected, so no
voluntary movement possible-muscles begin to atrophy
because no longer stimulated
---damage to dorsal root (or its ganglion) results in
loss of sensation from body area served
31. Describe the white matter of the spinal cord: Organization,
composition, and tracts.
---white matter composed of myelinated fiber tracts
---organized into columns (regions) by irregular shape of gray
matter
--posterior, lateral, and anterior columns
--each column contains number of fiber tracts make up of
axons with same destination and function
---descending tracts are motor (efferent)
---ascending tracts are sensory (afferent)
---posterior column has ONLY ascending tracts (sensory)
---anterior and lateral columns contain both ascending
and descending tracts
32. Discuss spinal transection: Results, quidriplegia, and
paraplegia.
---spinal cord transected (cut crosswise) or crushed, spastic
paralysis results
---muscles stay healthy because still stimulated by spinal
reflex arcs and movement of muscles does occur
---ALL movements are involuntary
---because spinal cord carries both sensory and motor impulses,
loss of feeling or sensory input occurs in body areas below
the point of cord destruction
---if spinal injury occurs high in the cord and affects all four
limbs, the individual is a quadriplegic
---if injury low enough that only legs are affected, the
individual is a paraplegic
33. Describe the anatomy of a typical nerve.
---nerve is a bundle of neuron fibers found outside the CNS
---within nerve, neuron fibers (processes) are wrapped in
protective connective tissue coverings
---each fiber surrounded by endoneurium-->groups of fibers then
surrounded by perineurium to form fiber bundles, or fascicles
-->all fascicles bound together by tough fibrous sheath
called epineurium to form cordlike nerve
---nerves carrying both sensory and motor fibers are called
mixed nerves (all spinal nerves are mixed nerves)
---are afferent (sensory) nerves that carry impulses toward CNS
and efferent (motor) nerves that carry impulses away from CNS
34. Summarize the cranial nerves: number of pairs and discuss
the vagus.
---there are 12 pairs of cranial nerves that serve the head and
neck
---only one pair of cranial nerves, the vagus nerves, extends
to thoracic and abdominal cavities
---most cranial nerves are mixed nerves except for the
optic, olfactory, and vestibulocochlear nerves which are
purely sensory
---“Oh, oh, oh, to touch and feel very good velvet, ah.”
---olfactory, optic, oculomotor, trochlear, trigemnal, abducens,
facial, vestibulocochlear, glosspharyngeal, vagus, accessory,
hypoglossal
35. Describe the spinal nerves: Number of pairs, formation,
naming, and rami.
---31 pairs of spinal nerves formed by combination of ventral
and dorsal roots of spinal cord
---spinal nerves are named for the region of the cord from
which they arise
---cervical (8); throacic (12); lumbar (5); sacral (5);
and coccygeal (1)
---almost immediately after being formed, each spinal nerve
divides into dorsal and ventral rami making each spinal
nerve only about ½ inch long
---rami contain both sensory and motor fibers
---smaller dorsal rami serve skin and muscles of posterior
trunk whereas ventral rami form complex networks of nerves
called plexuses which serve the motor and sensory needs of
the limbs
---ventral rami of T1 through T12 form intercostal nerves
which supply muscles between ribs/skin and truck of anterior
and lateral trunk
36. Outline the plexuses: Formation and four major ones.
---ventral rami form complex networks of nerves
called plexuses which serve the motor and sensory needs of
the limbs
---formed by ventral rami of spinal nerves other than T1-T12
---Cervical (C1-C5); Brachial (C5-C8, T1); Lumbar (L1-L4);
and Sacral (L4-L5, S1-S4)
---major nerves of body emanate from a plexus
37. Name and give function for four major nerves of the body:
Phrenic, radial, ulnar, and sciatic.
---phrenic nerve = breathing
---radial nerve = damage causes wrist drop
---ulnar nerve = clawhand, can’t spread fingers
---sciatic nerve = largest nerve in body; sciatica (pain
along peripheral distribution of nerve)
38. Summarize the function of the autonomic nervous system.
---ANS is motor subdivision of PNS that controls body
activities automatically
---composed of special group of neurons that regulate cardiac
muscle, smooth muscles (walls of visceral organs and blood
vessels), and glands
---relative stability of homeostasis depends on workings of ANS
---ANS called the involuntary nervous system
39. Compare the ANS with somatic motor division.
---somatic motor division cell bodies are inside the CNS and
their axons extend to skeletal muscle they serve
---autonomic system has chain of two motor neurons
--first of each pair is in the brain or spinal cord
--its axon (preganglionic axon) leaves CNS to synapse
with second motor neuron in a ganglion outside CNS
--axon of second neuron (postganglionic axon) extends to
organ it serves
---autonomic nervous system has two arms: sympathetic and
parasympathetic
40. Describe the autonomic 2-neuron pathway.
---see #39 above
41. State the divisions of the ANS.
---see #39 above
42. Describe the parasympathetic division.
---most active when body is at rest and not threatened in any
way
---sometimes called “resting and digesting system”
---mainly concerned with promoting normal digestion and
elimination of urine and feces, and with conserving body
energy particularly by decreasing demands on cardiovascular
system
---acetylcholine is neurotransmitter pre- and postganglionic
43. Describe the sympathetic division.
---acetylcholine as preganglionic; norepinephrine and
epinephrine as postganglionic
---called the “fight or flight” system
---increases heart rate, blood pressure, blood glucose levels,
dilates bronchioles of lungs, dilation of skeletal blood
vessels, and withdrawal of blood from digestive organs
---**important to note that only sympathetic division controls
blood vessels