Introduction to the Nervous System Flashcards
nervous system is structurally divided into ___ & ___
central nervous system (CNS) - brain (encased in skull) & spinal cord (encased within vertebral column)
peripheral nervous system (PNS) - cranial nerves (12) & spinal nerves (31)
nervous system is functionally divided into ___ & ___ & is found throughout the ___ & ___ nervous systems
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
somatic & visceral nervous systems are both divided into ___ & ___, & further into ___
motor (efferent)
sensory (afferent)
visceral motor: autonomic nervous system –> sympathetic & parasympathetic
neuron (definition)
structural & functional unit of nervous system that’s specialized for rapid communication
neuron (components)
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
neuron (communication)
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
multipolar cell
contains many processes (dendrites & axons)
peripheral nervous system
consists of nerve fibers & cell bodies outside central nervous system
peripheral nerve
bundle of nerve fibers (axons) in PNS
ganglion
collection of nerve cell bodies in PNS
cranial nerves
originate from brain & exit cranial cavity through foramina (openings in skull bones)
12 sets of cranial nerves
spinal nerves
arise from spinal cord & exit through intervertebral foramina in vertebral column
31 sets of spinal nerves
typical spinal nerve
two roots: ___ & ___
arises from spinal cord by rootlets which converge to form two nerve roots
dorsal (sensory) root
ventral (motor) root
dorsal root:
carries ___ (___) impulses ___
sensory neuron cell bodies located in ___ located in ___
sensory neurons have a ___ process that ___, & these cells are termed ___
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
central root:
carries ___ (___) impulses ___
motor neuron cell bodies located in ___
motor neurons have ___ processes & these cells are termed ___
motor, efferent, away from CNS toward some peripheral structure (muscle, gland, etc.)
central horn of spinal cord
many (numerous dendrites & one axon), multipolar neurons
immediately after the dorsal & ventral roots join forming the ___, it splits into a ___ & ___
both of these have ___ components
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
somatic sensory fibers:
general somatic ___
reach ___ level
they may be ___ or ___ sensations
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
somatic motor fibers:
general somatic ___
sole target tissue of somatic motor fibers is ___ & their only effect is to ___ them & cause them to ___
efferent (GSE)
skeletal muscle fibers, stimulate, contract
visceral sensory fibers:
general visceral ___
fibers transmit ___
reach ___ level
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)
visceral motor fibers:
general visceral ___
aka ___
fibers innervate ___
fibers may have a ___effect on target tissue
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
spinal cord
cylindrical structure extending from foramen magnum to intervertebral disc b/n L1 & L2 (not all the way to tip of coccyx)
ordered segmented pattern throughout spinal cord’s length gives rise to 31 pairs of spinal nerves
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
spinal cord & vertebral column grow at ___ rate until ___, after which the ___ grows much more ___ than the ___
same
end of 3rd month of fetal development
vertebral canal
rapidly
spinal cord
at six months of fetal development, spinal cord ___
terminates at S1
at birth, spinal cord ___
terminates at L3
in adults, spinal cord terminates at ___
intervertebral disc b/n L1 & L2
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 ___
L1, L2
lumbar, sacral, coccygeal, a considerable distance within the vertebral canal to reach their respective intervertebral foramina
cauda equina
two fusiform enlargements of spinal cord
below the lower enlargement, the spinal cord tapers off into the ___
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
meninges
protective barrier (membrane) b/n bone & soft tissue of CNS
dura mater:
definition
spinal dura is separated from vertebrae by ___ which contains ___
the dura forms the ___ which continues down to the ___ vertebrae
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
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 ___
delicate membrane of meninges
inner surface, cerebrospinal fluid
arachnoid, pia mater, cerebrospinal fluid
arachnoid trabeculae, subarachnoid space
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
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
subarachnoid space:
lies below ___
encloses ___
enlargement caudal to conus medullaris containing cauda equina is ___ which extends from ___ to ___
arachnoid mater
spinal cord & spinal nerve roots
lumbar cistern, L2, S2
lumbar puncture (spinal tap)
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
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 ___
lower back pain & lower limb pain
compression anteriorly, stretching/tension posteriorly, posteriorly
herniate, compress
posterolaterally, thin, ligaments
symptomatic, spinal nerve roots
spinal cord segment
region of spinal cord to which a spinal nerve is attached
dermatome
area of skin supplied by dorsal (sensory) root of spinal nerve
myotome
muscle mass innervated by ventral (motor) root of spinal nerve
nerve plexus
network of nerve fibers
somatic nerve plexus
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
autonomic nerve plexus
network of sympathetic & parasympathetic nerve fibers
