Midterm 2: Reflex Arcs (Ben)

Question 1

What type of sensory neuron is involved in the stretch reflex arc?

Answer 1

Type IA muscle sensory neuron

Pseudounipolar w/ peripheral branch in spindle

Question 2

What are the fibers within muscle spindles called?

Answer 2

intrafusal fibers

Question 3

Where do collateral branches of the central branch of stretch reflex sensory neurons go?

Answer 3

to Clark’s column via the dorsal funiculus

• eventually leading to the brainstem

Question 4

No interneurons are directly involved in stretch reflex arcs.

But what interneurons are involved?

And how?

Answer 4

inhibitory interneurons (in intermediate zone)

• descend 1-2 segments and innervate muscles antagonistic to the reflex arc

Question 5

How does the CNS play a role in the stretch reflex arc?

Via what kind of neurons and why?

Answer 5

Descending pathways from CNS innervate Aγ motorneurons in the ventral horn

• these motorneurons innervate intrafusal fibers of the spindle to set its length + allow it to function despite contraction of the muscle it is within

Question 6

What type of sensory fibers are involved in withdrawal reflex arcs?

Answer 6

C-type (or also Aδ type)

Question 7

Where do the central branches of sensory neurons involved in withdrawal reflex arcs go in the spinal cord?

And where do they terminate?

Answer 7

• rostrally and caudally within Lissauer’s Dorsolateral Tract
• terminate in Lamina I and II (Marginal Zone + Substantia Gelatinosa) and Lamina V

Question 8

Where do the interneurons involved in withdrawal reflex arcs go?

Answer 8

Ipsilateral - innervate Aα motorneurons of flexors

Contralateral - cross through white commissure and innervate Aα motorneurons of extensors

• also contralaterally ascend in spinothalamic tract (ventrolateral funiculus), eventually leading to sensory cerebral cortex

Question 9

How can pain sensations in withdrawal reflex arcs be modified?

Answer 9

Via the Raphe nuclei of the brainstem using serotonin

Question 10

What kind of sensory nerve fibers are involved in the autonomous reflex arc?

Answer 10

C-type (unmyelinated)

or

Aδ (fine myelinated)

Question 11

Where do the central branches of sensory neurons in autonomous reflex arcs go?

And eventually terminate?

Answer 11

bifurcate rostrally and caudally in Lissauer’s dorsolateral tract

• collateral branches terminate in Lamina I + V

Question 12

How many interneurons are involved in autonomous reflex arcs?

And where are they found?

Answer 12

one to several of the same interneurons involved in withdrawal reflexes

found in the dorsal horn + intermediate zone

Question 13

Where is the first neuron after the interneurons of autonomic reflex arcs called?

And what is it called?

Answer 13

Preganglionic Sympathetic Neurons

are found in the lateral horn of thoracic and upper lumbar segments

Question 14

Describe the course of preganglionic sympathetic fibers involved in autonomous reflex arcs.

Answer 14

1. Leave Lateral Horn and join with motorneuron fibers exiting via Ventral Root
2. Split off into the White Communicating Rami
3. Once in the Sympathetic Trunk, they can:
   
   1. terminate in an Paravertebral Ganglion along the trunk (at the same level or above/below)
   2. descend and join a Splanchnic Nerve to terminate in an abdominal Prevertebral Ganglion (often Celiac)

Question 15

How do postganglionic sympathetic neurons in autonomic reflex arcs exit ganglia?

Answer 15

via the gray communicating ramus (unmyelinated = gray)

Question 16

What are 4 possible destinations for efferent autonomic innervation?

Answer 16

1. blood vessels (vasomotor)
2. arrector pilae (pilomotor)
3. sweat glands (sudomotor)
4. viscera (smooth muscle, blood vessels, glands)

Question 17

What is the terminal ramification of efferent axons in autonomic reflex arcs called?

Answer 17

Groundplexus