Nervous System

Question 1

Explain the path from roots to rami

Answer 1

Each spinal nerve is attached to the spinal cord via a ventral (motor) root and a dorsal (sensory) root. The ventral root carries only motor nerve fibers and the dorsal root carries only sensory nerve fibers. These roots merge to form the mixed (motor and sensory fibers) spinal nerve. The spinal nerve divides into two forming a ventral ramus and a dorsal ramus which are also mixed nerves. Dorsal rami innervate three things: skin of the back, true back muscles and zygapophyseal joints. Ventral rami innervate the remainder of the skin and skeletal muscles of the neck, trunk and limbs.

Question 2

Sympathetic Motor

Answer 2

Primary Functions: Promotes “Fight or Flight” response: increased heart rate, blood flow to muscles, decreased blood flow to digestive tract and skin, pupils dilate, etc. Generally causes vasoconstriction of blood vessels and stimulation of sweat glands

Location of Preganglionic Cell Bodies: Lateral horn of spinal cord segments T1-L2. Referred to as thoracolumbar outflow.

Location of Postganglionic Cell Bodies: Paravertebral and Prevertebral Ganglia

All preganglionic
sympathetic fibers enter
paravertebral ganglia from T1-L2
via white rami communicans before
being distributed.

Question 3

Parasympathetic Motor

Answer 3

Primary Fxns: Recline and Dine Promotes vegetative, digestive visceral functions such as slowing heart rate and breathing and stimulating peristaltic contraction of digestive tract and saliva production. Often reverses the
effects of sympathetic stimulation.

Location of Preganglionic Cell Bodies: Brainstem nuclei and lateral horn of spinal cord segments S2-S4
Referred to as craniosacral outflow.

Location of Postganglionic Cell Bodies: 4 discrete ganglia of the head and enteric ganglia of the gut.

Question 4

Lateral Horn

Answer 4

Location of preganglionic cell bodies found only from T1-L2 spinal cord segments

Question 5

Ventral Root

Answer 5

Carries preganglionic sympathetic axons to spinal nerve. (Also carries somatic motor
axons)

Question 6

Spinal Nerve

Answer 6

All spinal nerves carry somatic motor axons, somatic sensory fibers and postganglionic
sympathetic axons. Spinal nerves from T1-L2 carry all of those fibers plus visceral sensory and
preganglionic sympathetic axons.

Question 7

Ventral Ramus

Answer 7

Carries pre- and postganglionic sympathetic axons. (Also carries somatic motor and
sensory fibers and visceral sensory fibers)

Question 8

White Ramus Communicans

Answer 8

Connects ventral rami of spinal nerves T1-L2 with paravertebral
ganglia. Carries preganglionic sympathetic axons. (Also carries visceral sensory fibers)

Question 9

Gray Ramus Communicans

Answer 9

Connects ventral rami of all spinal nerves with paravertebral ganglia.
Carries postganglionic sympathetic axons that are distributed to somatic structures.

Question 10

Paravertebral Ganglia

Answer 10

Sympathetic chain of ganglia located alongside the vertebral column.
Contain postganglionic cell bodies.

Question 11

Splanchnic Nerve:

Answer 11

Connects paravertebral and prevertebral ganglia. Carries preganglionic
sympathetic axons. (Also carries visceral sensory fibers)

Question 12

Prevertebral Ganglia

Answer 12

Contain postganglionic cell bodies whose axons are distributed to
abdominopelvic viscera.

Question 13

Sympathetic Distribution (Pathway)

Answer 13

1. Multipolar motor neuron firest in lateror horn (T1-L2)
2. Exits ventrally (bc motor neuron) from ventral root –> spinal nerve –> ventral ramus
3. [enter paravertebral ganglion via white ramus communicans to ascend/descend sympathetic chain to reach corresponding ganglion]
4. Synsapse in collection of postganglionic sympathetic cel bodies/paravertebral ganglion
5. Exit to corresponding spinal nerve (any level) via corresponding gray ramus communicans.

Question 14

Visceral Afferents

Answer 14

Follow course taken by efferents; return to the same spinal cord segment as efferents.

Ex: Sympathetic Innervation to the Heart:

1. Efferent motor synapse in lateral horn of T2
2. white ramus communicans
3. ascent to servical ganglion: synpase
4. exit to viseral nerve –> directly to heart

• Afferent sensory (ie: ischmia/pain in heart): senstation of pain in heart enters via visceral nerve
• descend down chain
• exit chain and enter spinal nerve a white ramus at appropriate level (cell body located at T2 DRG)
• fibers come in dorsal root at T2 into dorsal horn at T2

Question 15

Autonomic Sensory (Afferent) Innervation

Answer 15

Innervates: Skin, Muscle, Joints

Sensations Conveyed: Pain, Temperature, Touch,
Proprioception

Location of Cell Bodies: Dorsal Root Ganglia from
C2-Co.

Pathway: Same as motor pathway up to spinal nerve
then follows dorsal root to dorsal horn

Question 16

Autonomic Sensory (Afferent) Innervation: Visceral Sensory Neurons

Answer 16

Innervates: Viscera, Glands, Blood Vessels

Sensations Conveyed: Distension, Nausea, Hunger

Location of Cell Bodies: Dorsal Root Ganglia from
T1-L2.

Pathway: Same as motor pathway up to spinal nerve
then follows dorsal root to dorsal horn. Note that the
sensory pathway involves only a single neuron while
the motor pathway requires two neurons.