Introduction to the Nervous System

Question 1

What is a ganglion?

Answer 1

A collection of nerve bodies within the PNS

Question 2

What is a peripheral nerve?

Answer 2

A bundle of nerve fibers in the PNS

Question 3

Which roots make up a spinal nerve?

Answer 3

A dorsal (sensory) root and a ventral (motor) root

Question 4

What is a dorsal root ganglion and where is it located?

Answer 4

Located in the intervertebral foramen and is a collection of nerve cell bodies which are sensory

Question 5

What type of cell is a dorsal root sensory neuron?

Answer 5

A pseudounipolar neuron (these neurons are always sensory, and all dorsal root ganglion cells are pseudounipolar)

Question 6

What type of cells are motor neurons?

Answer 6

These cells are multipolar neurons

Question 7

Where are the bodies of the motor neurons located?

Answer 7

The cell bodies are located in the ventral horn of the spinal cord (this is why the ventral horn is larger)

Question 8

After the dorsal and ventral horn combine to form the spinal nerve, what does it split into?

Answer 8

The dorsal ramus (which supplies the skin and muscles of the back) and the ventral ramus (which supplies the skin and muscles of the anterior side of body and the limbs). Dorsal ramus is smaller compared to ventral ramus

Question 9

What are the components of a spinal nerve (which has sensory and motor mixed)?

Answer 9

1. Somatic sensory (conveys exteroceptive, pain, and proprioceptive sensations from skin, muscles, tendons, joints)
2. Somatic motor (sole target is skeletal muscle; voluntary control, causes them to contract)
3. Visceral fibers (divided into the visceral sensory and visceral motor; visceral sensory conveys organ distension, blood gas, blood pressure etc; visceral motor is aka autonomic nervous system)

Question 10

Where do the spinal nerve leave the respective segments of the spinal cord out of the intervertebral foramina?

Answer 10

Spinal nerve C1 exits between the occipital bone and the atlas
C2-C7 exit the spinal cord immediately above the corresponding vertebrae
C8 exits spinal cord between C7 and T1
All others exit below the vertebrae of the corresponding number

Question 11

In adults, where does the spinal cord terminate?

Answer 11

Terminates at the intervertebral disc between L1 and L2

Question 12

What is the cauda equina?

Answer 12

Collection of spinal nerve roots that must descend a distance within the vertebral canal to reach the respective intervertebral foramina, specifically the lumbar, sacral, and coccygeal spinal nerves.

Question 13

What are the two fusiform enlargements of the spinal cord?

Answer 13

Cervical enlargement C5 to T1 (reflects large number of neurons serving the brachial plexus)
Lumbar enlargement L1 to S3 (reflects large number of neurons serving the lumbosacral plexus) (note that the actual lumbar enlargement is at the vertebrae levels T11/T12 because the spinal cord grows past the column)

Question 14

What is another name for the termination of the spinal cord?

Answer 14

Conus medullaris

Question 15

What are the 3 meninges?

Answer 15

Dura mater (outermost tough layer)
Arachnoid mater (delicate membrane; houses subarachnoid space which lies between the pia and arachnoid)
Pia mater (delicate, highly vascular, innermost layer)

Question 16

What is the long tubular sheath within the vertebral canal formed by the dura called?

Answer 16

Dural sac

Question 17

What separates the spinal dura from the vertebrae?

Answer 17

The epidural space (contains adipose tissue and a venous blood plexus)

Question 18

What suspends the spinal cord within the dural sac which are lateral extensions of pia mater?

Answer 18

The denticulate ligaments (lateral extensions of pia mater midway between dorsal and ventral nerve roots; are attachment sites for spinal cord to dura; attach pia to inner surface of dura)

Question 19

What is the name of the continuation of the pia mater at the apex of the cord?

Answer 19

Filum terminale internum (continues to end of dural sac at S2)

Question 20

What does the subarachnoid space enclose?

Answer 20

Encloses the spinal cord and spinal nerve roots

Question 21

What is the name of the enlargement of the subarachnoid space caudal to the conus medullaris containing the cauda equina?

Answer 21

Lumbar cistern; extends from L2 vertebra to second segment of sacrum, which is where the dural sac ends

Question 22

Between which lumbar vertebra is a spinal tap (lumbar puncture) typically performed?

Answer 22

Between L4 and L5, generally in the lumbar cistern below L4

Question 23

Where do herniations of the nucleus pulposus usually extend?

Answer 23

Extend posterolaterally, where the anulus fibrosus is relatively thin and doesn’t receive support from anteiror or posterior logitudinal ligaments; may cause lower back pain because it compresses spinal cord or nerve roots of the cauda equina