Overview of Nervous System

Question 1

what is the largest component of the peripheral nervous system?

Answer 1

enteric nervous system

Question 2

grey matter vs white matter

distinguish organization pattern in brain vs spinal cord

Answer 2

grey matter = neuron cell bodies
white matter = myelinated axons

brain: white matter surrounded by grey matter
spinal cord: grey matter surrounded by white matter

Question 3

afferent vs efferent nerve fibers

Answer 3

afferent ascend to CNS (sensory)
efferent exit CNS (effective)

Question 4

what shape are sensory vs motor neurons?

Answer 4

sensory neurons: pseudo-unipolar (cell body in middle)

motor: multipolar (cell body on one end)

Question 5

what are the 3 CNS meninges from outer to inner

Answer 5

outermost: dura mater (thick, fibrous)
middle: arachnoid mater
inner: pia mater (denticulate ligaments)

*remember CNS includes brain and spinal cord so these continue into the spinal cord

Question 6

at what vertebral level does the spinal cord end in adults?

Answer 6

L1/L2

Question 7

how many pairs of spinal nerves are there? how many in each category?

Answer 7

31 pairs:
8 cervical
12 thoracic
5 lumbar
5 sacral
1 coccygeal

Question 8

describe how the cauda equina develops

Answer 8

prenatal length: spinal cord extends length of vertebral canal to coccyx, and spinal cord and vertebral canal are growing at same rate

but rate of growth becomes faster in vertebral column than spinal cord, so at birth spinal cord stops at L3/L4 and dural sac continues down to bottom of vertebral canal

in adult spinal cord stops at L1/L2

cauda equina: nerves exiting below the spinal cord

Question 9

where is it safe to take a lumbar puncture and why is this so?

Answer 9

safe to perform lumbar puncture between 3rd/4th lumbar vertebrae - the cauda equina is here, while the spinal cord ends at L1/2 in adults

unlikely to hit a nerve in the cauda equina (like trying to “pierce spaghetti in a bowl of soup”)

Question 10

what kind of nerves are found in the ventral, lateral, and dorsal horns of the spinal cord?

Answer 10

ventral/anterior: motor
lateral: autonomic
dorsal/posterior: sensory

Question 11

where does mixing of sensory and motor fibers occur in the spinal cord? what happens after that?

Answer 11

sensory (dorsal root) and motor (ventral root) fibers mix in the spinal nerve, which then divides into an anterior and posterior rami

anterior/ventral rami are larger and contribute to plexuses
posterior/dorsal rami are smaller and innervate intrinsic back muscles and skin

all rami are mixed

Question 12

where are the presynaptic cell bodies for parasympathetic and sympathetic motor neurons found, respectively?

Answer 12

presynaptic parasympathetic motor neurons: craniosacral - cell bodies in brain stem and S2, S3, S4

presynaptic sympathetic motor neurons: thoracolumbar - cell bodies in T1-T12

Question 13

how does the sympathetic nervous system innervate the heart?

Answer 13

sympathetic innervation to heart arises from superior cervical ganglion to T3 ganglion

travels to cardiac plexus via sympathetic nerve

innervation increases heart rate through stimulation at both SA and AV nodes

Question 14

which nerve carries the majority of parasympathetic innervation?

Answer 14

vagus nerve (cranial nerve X) carries ~75% of parasympathetic innervation throughout the body