SPINAL NERVES

Question 1

Define the conus medullaris, ventral/dorsal roots, spinal nerves and rami

Answer 1

Conus medullaris - ends at L1/L2, cauda equine starts below
Ventral roots - motor signals; Dorsal roots - sensory signals
Spinal nerves and Rami - have BOTH motor and sensory signals

Question 2

Contrast the dorsal rami from the ventral.

Answer 2

Dorsal rami innervate skin on back, zygopophyseal joints and intrinsic back muscles. Ventral rami innervate everything else (both front and back) and is physically bigger because of that

Question 3

Describe the two types of motor (efferent) pathways.

Answer 3

Somatic motor - involves an efferent impulse from ONE motor neuron in the ventral horn down to its effector muscle.
Autonomic visceral - impulses travel down TWO motor neurons (one from lateral horn and other from ganglion) to reach effector glands, SM or cardiac muscle.

Question 4

Describe the significance of the pre-ganglionic sympathetic chain.

Answer 4

Preganglionic cell bodies are found in the Lateral horn from T1-L2. Post-ganglionic cell bodies are found in the Para- or Pre-vertebral Ganglia.

Question 5

Trace the pathway for sympathetic innervation to anterior sweat glands at T2 dermatome.

Answer 5

Lateral horn at T2 spinal segment > ventral root > spinal nerve > ventral ramus > white ramus communicans > ParaVG > gray ramus communicans > ventral ramus T2

Question 6

Trace the pathway for SNS innervation to blood vessels in lateral side of upper limb.

Answer 6

Lateral horn at T1 Spinal segment > ventral root > spinal nerve > ventral ramus > White ramus communicans > ParaVG > Up to ParaVG @ C5 > Gray ramus communicans at C5 > upper limb dermatome

Question 7

Describe the two types of sensory (afferent) pathways.

Answer 7

Somatic sensory - pseudounipolar neurons in any DRG pick up pain, temperature and touch signals from skin, muscle and joints.
Visceral sensory - neurons in T1-L2 DRG pick up hunger, nausea or dissension signals from inner organs, glands and vessels

Question 8

Trace the pathway for referred heart pain.

Answer 8

Heart viscera > splanchnic nerve > ParaVG @ C2 > down to ParaVG @ T1 > white ramus communicans > ventral ramus > spinal nerve > DRG @ T2 > dorsal root > dorsal horn > up spinothalamic tract (for pain signals)