Terms From Resource Guide

Question 1

Dorsal Root Ganglion

Answer 1

A swelling of the dorsal root which contains neuronal cell bodies that give rise to general somatic afferent (GSA) and visceral afferent nerve fibers. The “little brain” of the PNS

Question 2

Afferent Stimuli

Answer 2

Stimuli to the nerve endings within somatic tissues generate electrochemical impulses that travel to the dorsal root ganglion via axons. These encoded signals enter into the dorsal horn of the spinal cord through dorsal root. GSA fibers are synonymous with sensory axons.

Question 3

Efferent Stimuli

Answer 3

Impulses generated by a neuron within the central nervous system (i.e., alpha motor neuron in the anterior gray column) that travel away from the central nervous system to stimulate an effector organ such as voluntary (skeletal) muscle. These impulses travel along motor axons called general somatic efferent nerve fibers. Visceral efferent nerve fibers innervate smooth muscle, cardiac muscle, and glands. Visceral efferents are part of the autonomic nervous system.

Question 4

Reflex Arc

Answer 4

The afferent nerve fibers entering the spinal cord ultimately synapse with short inter-neurons within the gray matter of the spinal cord. The interneurons synapse with alpha motor neurons within the anterior horn. The myotatic reflex arc occurs when a quick stretch to a muscle tendon produces a sudden muscle twitch or “jerk” response.

Question 5

Motor Unit

Answer 5

The alpha motor neuron to muscle cell (fiber) connection. A single alpha motor neuron gives rise to a single axon. A somatic motor nerve fiber is ultimately conveyed to a group of muscle fibers. The synapse between a motor axon and muscle fiber ignites the physiological processes that produce a muscle contraction. An injury (lesion) impacting neuronal conductivity through the motor axons can result in paresis (muscle weakness).

Question 6

Nerve Plexus

Answer 6

A network of nerve branches that intersect and connect. In the somatic nervous system, the ventral rami of adjacent spinal nerves mix and mingle together to form the various trunks and divisions, which ultimately convey both afferent and efferent nerve fibers to multiple terminal nerve branches (i.e. peripheral nerves). The nerve plexuses of the somatic nervous system are the following: cervical, brachial, lumbar, and lumbosacral. The autonomic nervous system contains plexuses within the body cavities.

Question 7

Dermatome

Answer 7

The unilateral area of skin supplied by a single spinal nerve (i.e., specific segmental level of the spinal cord).

Question 8

Myotome

Answer 8

The unilateral mass of muscle supplied by a single spinal nerve (i.e., specific segmental level of the spinal cord).