Introduction to the Nervous System

Question 1

nervous system is structurally divided into ___ & ___

Answer 1

central nervous system (CNS) - brain (encased in skull) & spinal cord (encased within vertebral column)

peripheral nervous system (PNS) - cranial nerves (12) & spinal nerves (31)

Question 2

nervous system is functionally divided into ___ & ___ & is found throughout the ___ & ___ nervous systems

Answer 2

somatic nervous system (body wall) - innervates structures derived from embryonic somites or branchial arches (ex. skin & body wall, skeletal muscles, skeletal system, joints, etc.)

visceral nervous system (internal organs) - innervates visceral structures of body (ex. heart & blood vessels, digestive systems, respiratory system, urinary system, reproductive system, glands, smooth muscle, etc.)

central & peripheral

Question 3

somatic & visceral nervous systems are both divided into ___ & ___, & further into ___

Answer 3

motor (efferent)

sensory (afferent)

visceral motor: autonomic nervous system –> sympathetic & parasympathetic

Question 4

neuron (definition)

Answer 4

structural & functional unit of nervous system that’s specialized for rapid communication

Question 5

neuron (components)

Answer 5

cell body

dendrites - carry impulses toward cell body (often, not always)

axon (fiber) - carries impulses away from cell body, neurons always have one and only one axon

Question 6

neuron (communication)

Answer 6

neurons communicate w/ each other at synapses

communication occurs by means of chemical agents called neurotransmitters secreted by one of the neurons

neurotransmitter may either excite or inhibit another neuron

Question 7

multipolar cell

Answer 7

contains many processes (dendrites & axons)

Question 8

peripheral nervous system

Answer 8

consists of nerve fibers & cell bodies outside central nervous system

Question 9

peripheral nerve

Answer 9

bundle of nerve fibers (axons) in PNS

Question 10

ganglion

Answer 10

collection of nerve cell bodies in PNS

Question 11

cranial nerves

Answer 11

originate from brain & exit cranial cavity through foramina (openings in skull bones)

12 sets of cranial nerves

Question 12

spinal nerves

Answer 12

arise from spinal cord & exit through intervertebral foramina in vertebral column

31 sets of spinal nerves

Question 13

typical spinal nerve

two roots: ___ & ___

Answer 13

arises from spinal cord by rootlets which converge to form two nerve roots

dorsal (sensory) root

ventral (motor) root

Question 14

dorsal root:

carries ___ (___) impulses ___

sensory neuron cell bodies located in ___ located in ___

sensory neurons have a ___ process that ___, & these cells are termed ___

Answer 14

sensory, afferent, toward CNS

a swelling on the dorsal root called the dorsal root ganglion, intervertebral foramen

single, emanates from the cell body which splits in a t-like fashion into a peripheral & a central process, pseudounipolar neurons

Question 15

central root:

carries ___ (___) impulses ___

motor neuron cell bodies located in ___

motor neurons have ___ processes & these cells are termed ___

Answer 15

motor, efferent, away from CNS toward some peripheral structure (muscle, gland, etc.)

central horn of spinal cord

many (numerous dendrites & one axon), multipolar neurons

Question 16

immediately after the dorsal & ventral roots join forming the ___, it splits into a ___ & ___

both of these have ___ components

Answer 16

mixed (sensory & motor) spinal nerve

dorsal ramus - supplies skin & muscles of back

ventral ramus - supplies skin & muscles of anterior side of body & limbs

sensory & motor

Question 17

somatic sensory fibers:

general somatic ___

reach ___ level

they may be ___ or ___ sensations

Answer 17

afferent (GSA)

conscious

exteroceptive (touch, pressure, vibration, pain, & temperature) from skin

pain & proprioceptive from muscles, tendons, & joints - convey info on joint position & tension of tendons & muscles, providing info on how body & limbs are oriented in space

Question 18

somatic motor fibers:

general somatic ___

sole target tissue of somatic motor fibers is ___ & their only effect is to ___ them & cause them to ___

Answer 18

efferent (GSE)

skeletal muscle fibers, stimulate, contract

Question 19

visceral sensory fibers:

general visceral ___

fibers transmit ___

reach ___ level

Answer 19

afferent (GVA)

pain or subconscious visceral reflex sensations (e.g. info concerning organ distension, blood gas & blood pressure levels, etc.)

not conscious (internal bodily functions)

Question 20

visceral motor fibers:

general visceral ___

aka ___

fibers innervate ___

fibers may have a ___effect on target tissue

Answer 20

efferent (GVE)

autonomic nervous system (ANS)

a wide variety of visceral structures (e.g. smooth muscle, glands, blood vessels, the heart, etc.)

stimulatory or inhibitory

Question 21

spinal cord

Answer 21

cylindrical structure extending from foramen magnum to intervertebral disc b/n L1 & L2 (not all the way to tip of coccyx)

Question 22

ordered segmented pattern throughout spinal cord’s length gives rise to 31 pairs of spinal nerves

Answer 22

8 cervical - 7 vertebrae, 1st nerve b/n skull & C1 (b/n occipital bone & atlas), 2nd-7th exit above vertebra, 8th nerve exits under vertebra

all following nerves exit under vertebra

12 thoracic

5 lumbar

5 sacral

1 coccygeal

Question 23

spinal cord & vertebral column grow at ___ rate until ___, after which the ___ grows much more ___ than the ___

Answer 23

same

end of 3rd month of fetal development

vertebral canal

rapidly

spinal cord

Question 24

at six months of fetal development, spinal cord ___

Answer 24

terminates at S1

Question 25

at birth, spinal cord ___

Answer 25

terminates at L3

Question 26

in adults, spinal cord terminates at ___

Answer 26

intervertebral disc b/n L1 & L2

Question 27

in adults, the coccygeal spinal cord segment is located at the level of the intervertebral disc b/n ___ & ___ vertebrae

dorsal & ventral roots of lower ___, ___, & ___ spinal nerves must descend ___

collection of spinal nerve roots forms ___

Answer 27

L1, L2

lumbar, sacral, coccygeal, a considerable distance within the vertebral canal to reach their respective intervertebral foramina

cauda equina

Question 28

two fusiform enlargements of spinal cord

below the lower enlargement, the spinal cord tapers off into the ___

Answer 28

cervical enlargement (C4/C5 - T1) - reflects large number of neurons serving brachial plexus (upper limbs)

lumbar enlargement (L1 - S3) - reflects large number of neurons serving lumbosacral plexus (lower limbs)

conus medullaris (termination of cord)

*refers to nerves, not vertebrae

Question 29

meninges

Answer 29

protective barrier (membrane) b/n bone & soft tissue of CNS

Question 30

dura mater:

definition

spinal dura is separated from vertebrae by ___ which contains ___

the dura forms the ___ which continues down to the ___ vertebrae

Answer 30

outermost tough, dense, fibrous layer of meninges

epidural space, adipose tissue & a venous blood plexus (veins)

dural sac (a long tubular sheath within the vertebral canal that houses both brain & spinal cord), S2

Question 31

arachnoid mater:

definition

held against the___ of the dura by the pressure of ___

the subarachnoid space lies between the ___ & the ___ and contains ___

delicate strands of connective tissue called ___ span the ___

Answer 31

delicate membrane of meninges

inner surface, cerebrospinal fluid

arachnoid, pia mater, cerebrospinal fluid

arachnoid trabeculae, subarachnoid space

Question 32

pia mater:

definition

closely adherent to ___

spinal cord suspended in dural sac by ___

at apex of cord, a continuation of pia mater continues as ___ which continues to end of dural sac at ___, pierces the dural sac & receives an investment of arachnoid & dura mater & is now referred to as the ___ which attaches to the tip of the coccyx

Answer 32

delicate, highly vascular, innermost layers of meninges

neural tissue

saw-toothed denticulate ligaments - lateral extensions of pia mater midway b/n dorsal & ventral nerve roots, attach to inner surface of dura mater, anchor spinal cord within sac

filum terminal interum (after conus medullaris), S2, filum terminale externum or coccygeal ligament

Question 33

subarachnoid space:

lies below ___

encloses ___

enlargement caudal to conus medullaris containing cauda equina is ___ which extends from ___ to ___

Answer 33

arachnoid mater

spinal cord & spinal nerve roots

lumbar cistern, L2, S2

Question 34

lumbar puncture (spinal tap)

Answer 34

performed to withdraw a sample of cerebrospinal fluid for examination

spinal cord terminates at level of L1/L2, while lumbar cistern of subarachnoid space extends down to lower border of S2

a needle introduced into lumbar cistern below L4 pushes nerve roots of cauda equina aside w/o causing damage

Question 35

herniation of nucleus pulposes:

herniation/protrusion of gelatinous nucleus pulposus into/through anulus fibrosus is a well-recognized cause of ___

flexion of the vertebral column produces ___ & ___, squeezing the nucleus pulposus further ___ toward the thinnest part of the annulus fibrosus

if the annulus fibrosus has degenerated, the nucleus pulposus may ___ into the vertebral canal & ___ the spinal cord or the nerve roots of the cauda equina

herniations of the nucleus pulposus usually extend ___, where the anulus fibrosus is relatively ___ & doesn’t receive support from either the anterior or posterior longitudinal ___

a posterolateral herniated IV disc is more likely to be ___ b/c of the proximity of ___

Answer 35

lower back pain & lower limb pain

compression anteriorly, stretching/tension posteriorly, posteriorly

herniate, compress

posterolaterally, thin, ligaments

symptomatic, spinal nerve roots

Question 36

spinal cord segment

Answer 36

region of spinal cord to which a spinal nerve is attached

Question 37

dermatome

Answer 37

area of skin supplied by dorsal (sensory) root of spinal nerve

Question 38

myotome

Answer 38

muscle mass innervated by ventral (motor) root of spinal nerve

Question 39

nerve plexus

Answer 39

network of nerve fibers

Question 40

somatic nerve plexus

Answer 40

nerve plexus formed by ventral rami of certain spinal nerves

ex. cervical plexus, brachial plexus, lumbar plexus, sacral plexus

does have autonomic components, but principally sensory

Question 41

autonomic nerve plexus

Answer 41

network of sympathetic & parasympathetic nerve fibers