Nervous System

Question 1

Collection of nerve cell bodies and nerve axons (fibers) in the CNS and PNS

Answer 1

CNS
cell bodies - nucleus
fibers - tract

PNS
cell bodies - ganglion
fibers - peripheral nerve

Question 2

Cranial nerves

Answer 2

12 pairs of nerves CN I-XII

Most arise from the brain

ALL exit the cranial cavity via foramina

Question 3

Organization of spinal nerves

Answer 3

31 pairs total

C8 (BUT only 7 vertebrae)
T12
L5
S5
Co

Question 4

Where do spinal nerves exit?

Answer 4

C1 spinal nerve exits between skull and C1 so there are 8 cervical nerves but only 7 cervical vertebrae.

All other nerves exit through intervertebral foramina.

Question 5

Parts of a spinal nerve

Answer 5

Nerve arises from spinal cord via rootlets.

Rootlets converge to form ventral / dorsal root.

Roots converge to form spinal nerve.

Nerve divides into ventral / dorsal rami.

Question 6

Somatic NS

Answer 6

Motor to skeletal muscle

Sensory from skin (pain, temperature, touch)

Sensory from joints, muscles, and tendons (proprioception)

Question 7

Autonomic NS (aka Visceral motor)

Answer 7

Motor to smooth muscle (organs), cardiac muscle, and glands

Question 8

Visceral Sensory

Answer 8

Sensory from organs (ischemia, stretch)

Question 9

Somatic motor pathway

Answer 9

Location of motor cell body: ventral horn

Motor fiber EXITS spinal cord via ventral root, spinal nerve, and ventral or dorsal ramus

Question 10

Somatic sensory pathway

Answer 10

Location of sensory cell body: dorsal root ganglia

Sensory fiber travels via ventral or dorsal rami, spinal nerve, and ENTERS spinal cord through dorsal root

Question 11

Ventral rami and dorsal rami innervate what regions?

Answer 11

Ventral rami innervate majority of body wall

Dorsal rami innervate small region of skin/muscle along dorsal midline

Question 12

Carry what kind of fibers?

Answer 12

Ventral root - motor fibers only

Dorsal root - sensory fibers only

Ventral ramus, dorsal ramus, and spinal nerve - both

Question 13

Brachial plexus

Answer 13

Network of ventral rami to upper extremity

Question 14

Lumbosacral plexus

Answer 14

Network of ventral rami to lower extremity and perineum

Question 15

Sympathetic NS

Answer 15

“Fight or flight”

Innervates tissues in the body wall (sweat glands, arrector pilli muscles, peripheral blood vessels) and body cavities

Question 16

Parasympathetic NS

Answer 16

“Rest and digest”

Innervates tissues in the body cavities, head, and external genitalia

Question 17

How many neurons in autonomic NS?

Answer 17

2 neurons

preganglionic cell body and fiber

postganglionic cell body and fiber

Question 18

Location of preganglion cell bodies in sympathetic and parasympathetic

Answer 18

Sympathetic - lateral horn of thoracolumbar segments of spinal cord

Parasympathetic - craniosacral (brain and sacral segments of spinal cord)

Question 19

Location of postganglion cell bodies in sympathetic and parasympathetic

Answer 19

Sympathetic - prevertebral ganglia and paravertebral ganglia

Parasympathetic - ganglia in the head or walls of organs

Question 20

How many paravertebral ganglia are associated with each spinal nerve?

Answer 20

Usually one per nerve. But there are only 3 paravertebral ganglia associated with the 8 cervical spinal nerves.

Question 21

Sympathetic trunk

Answer 21

Paravertebral ganglia on each side are linked to form the sympathetic trunk that extends length of vertebral column.

Although all preganglionic sympathetic cell bodies originate in a confined area (thoracolumbar spinal cord), the sympathetic trunk allows for the distribution of sympathetic fibers throughout the body.

Question 22

How does the sympathetic trunk attach?

Answer 22

Sympathetic trunks are tethered to the ventral rami via the white and gray rami communicans. White is entrance and gray is exit.

Question 23

Sympathetic pathway - body wall

Answer 23

1. Lateral horn
2. Ventral root
3. Spinal nerve
4. Ventral ramus
5. White ramus communicans
6. Sympathetic trunk
7. Paravertebral ganglia (synapse)
8. Gray ramus communicans
9. Ventral or dorsal ramus
10. Body wall - blood vessels, sweat glands, arrector pilli muscles

Question 24

Sympathetic pathway - thoracic organs

Answer 24

1. Lateral horn
2. Ventral root
3. Spinal nerve
4. Ventral ramus
5. White ramus communicans
6. Sympathetic trunk
7. Paravertebral ganglia (synapse)
8. Cardiac / pulmonary nerves
9. Heart or lungs

Question 25

Sympathetic pathway - abdominal organs

Answer 25

1. Lateral horn
2. Ventral root
3. Spinal nerve
4. Ventral ramus
5. White ramus communicans
6. Sympathetic trunk
7. Splanchnic nerve
8. Prevertebral ganglia (synapse)
9. Abdominal and pelvic viscera

Question 26

Visceral Sensory

Answer 26

Sensory from organs, e.g. ischemia, stretch

Single neuron

Enters dorsal root

Travels to spinal cord along sympathetic OR parasympathetic fibers

Question 27

Referred pain

Answer 27

Phenomenon of visceral (organ) pain being perceived as somatic (body wall) pain

Mechanism is unclear. Visceral and somatic sensory neurons enter the spinal cord via the same dorsal roots and have cell bodies located in the same dorsal root ganglia.

The CNS appears to misinterpret an incoming visceral signal as somatic sensory.