Neuro - Peripheral Nerves

Question 1

Name each of the four functional components found in a peripheral nerve and describe their functions.

Answer 1

• somatic afferent - pain, touch, temperature, and position sense
• somatic efferent - motor signals that control striated muscles
• visceral afferent - “visceral sensibility” like peristaltic activity, blood pressure, bladder fullness, etc.
• visceral efferent - autonomic nervous system; two neurons linked together

Question 2

What tissues are innervated by somatic afferent neurons?

Answer 2

skin (pain, touch, temperature, conscious proprioception, awareness of limb position)

Question 3

What tissues are innervated by somatic efferent neurons?

Answer 3

striated (voluntary) muscles

Question 4

What tissues are innervated by visceral efferent neurons?

Answer 4

contraction of smooth muscle and secretion of glands; preganglionic and postganglionic neuron chains

Question 5

What tissues are innervated by visceral afferent neurons?

Answer 5

organs to monitor internal environment like heart rate, blood pressure, smooth muscle contractility, and bladder/bowel fullness

Question 6

What is the location of the preganglionic nerve cell bodies? The postganglionic nerve cell bodies?

Answer 6

• preganglionic - nerve cell body in CNS; axon extends to autonomic ganglion
• postganglionic - nerve cell body in autonomic ganglion; axon extends to visceral target

Question 7

What are the functional components and target tissue of nerve fibers found in the posterior root?

Answer 7

• functional component - sensory (somatic afferent and visceral afferent)
• target tissue - skin, internal organs

Question 8

What are the functional components and target tissue of nerve fibers found in the anterior root?

Answer 8

• functional component - motor (somatic efferent)

- target tissue - striated muscle, internal organs

Question 9

What is the functional component and target tissue of nerve fibers found in the posterior ramus?

Answer 9

• functional component - sensory and motor

- target tissue - back

Question 10

What is the functional component and target tissue of nerve fibers found in the anterior ramus?

Answer 10

• functional component - sensory and motor

- target tissue - anterior and lateral body as well as limbs

Question 11

What is the function and relative speed of an A-alpha afferent nerve fiber?

Answer 11

• function - myotatic reflex

- velocity - 70-120 m/sec

Question 12

What is the function and relative speed of an A-beta nerve fiber?

Answer 12

• function - deep touch

- velocity - 60-80 m/sec

Question 13

What is the function and relative speed of an A-delta nerve fiber?

Answer 13

• function - light touch, fast pain

- velocity - 10-30 m/sec

Question 14

What is the function and relative speed of a C nerve fiber?

Answer 14

• function - slow pain

- velocity - 0.5-2.5 m/sec

Question 15

List the events seen during the degeneration of a nerve fiber.

Answer 15

• if an axon is crushed (or cut), the axon distal to the crush will degenerate
• the axon proximal to the crush will die back a short distance
• the cell body will respond by becoming more metabolically active (chromatolysis)
• the axon and myelin degenerate (but not Schwann cells) and macrophage cells engulf the debris

Question 16

List the events seen during the regeneration of a nerve fiber.

Answer 16

• axons sprout and exhibit growth cones
• Schwann cells undergo mitosis and form guiding route for the growth cone
• Schwann cells produce new myelin
• greater number of Schwann cells means: shorter internodal distance and slower conduction time

Question 17

What is the “knee jerk” reflex? How does it work? How is it modified?

Answer 17

• when the muscle is stretched (by hitting the knee), the neuromuscular spindle is also stretched
• A-alpha sensory fiber conducts stretch signal back to spinal cord
• sensory fiber has a single synapse with an alpha motor neuron which moves the extrafusal muscle fibers to move the limb
• this is monosynaptic and cannot be modified

Question 18

What is the lower motor neuron?

Answer 18

the nerve cell body (located in the CNS) and its axon (located in the PNS) that innervates a striated muscle

Question 19

What are the signs and symptoms of a lower motor neuron lesion?

Answer 19

• flaccid paralysis
• atonia - loss of normal muscle tone
• areflexia - loss of the stretch (myotatic) reflex
• fasciculations - spontaneous contraction of bundles of muscle fibers
• muscle atrophy

Question 20

A lower motor neuron lesion results form a lesion of what?

Answer 20

• peripheral nerve
• anterior root
• anterior horn motor neurons

Question 21

What is muscle tone?

Answer 21

slight contraction of the muscles that does not produce movement or active resistance, but gives the muscles firmness, assisting the stability of joints and the maintenance of posture

Question 22

What is the neuroanatomical basis of muscle tone?

Answer 22

the activation of the gamma and alpha motor neurons

Question 23

What are the functional components and target tissue of nerve fibers found in the anterior root?

Answer 23

• functional component - motor (somatic efferent)

- target tissue - striated muscle, internal organs