Receptors and Primary Afferents

Question 1

Describe peripheral nerve structure (3 layers)

Answer 1

endonerium: connective tissue around axons and Schwann cells
perinerium: connective tissue around nerve fasicles
epinerium: connective tissue around the entire nerve

Question 2

Describe blood supply in the nerve.

Answer 2

arterioles in the epinuerium yield a capillary plexus in the perineurium. blood vessels have tight junctions in that space.

Question 3

What are the fastest nerve fibers?

Answer 3

Ia (or A-alpha)

primary muscle spindle afferentes

Question 4

What are the fibers that sense pressure and pain?

Answer 4

III or A-delta

Question 5

What are the fibers that sense slow pain?

Answer 5

IV or C fibers. unmyelinated.

Question 6

What is the one part of the PNS with primary sensory bodies that are NOT in the PNS ganglia?

Answer 6

mesencephalic nucleus of V- primary cell bodies in lower midbrain

Question 7

What is another name for epicritic senses?

Answer 7

dorsal column/medial lemnisucs

Question 8

What is another name for protopathic senses?

Answer 8

anterolateral spinothalamic tracts

Question 9

What are two kinds of receptors>

Answer 9

quickly adapting and slowly adapting. quickly adapting generate an AP in response to a change in stimuli. slowly adapting transuduce a signal as long as the stimulus is still around

Question 10

What are differences in receptors between gabrous skin and hairy skin?

Answer 10

hairy skin has unique receptors associated with hair follicles.

Question 11

What two quickly adapting receptors that I should know about? What is the difference?

Answer 11

Meissner’s corpuscles (superficial, glabrous), hair follicle (superficial, hairy) and PAcinian corpuscle (deep)

Question 12

What two slowly adapting receptors should I know about ?

Answer 12

Merkel cell/neurite complex (superficial), ruffini (deep, relatively rare in glabrous skin but common in hairy skin)

Question 13

What is the purpose of free nerve endings in skin?

Answer 13

detect pain, warmth, tickle, cool

Question 14

What is a fast fatigable fiber?

Answer 14

rapid contraction and relaxation, but depend on glycolysis and anaerobic breakdown of glycogen for energy. relative lack of mitochondria and myoglobin (“white fibers”).

Question 15

What is a slow fiber?

Answer 15

longer, weaker contractions. resistnat to fatigue: high levels of mitochondria and myoglobin (“red fibers”)

Question 16

What is a fast fatigue resistant fiber?

Answer 16

intermediate. short contraction times but resistant to fatigue

Question 17

What is the general arrangement of fast to slow fibers?

Answer 17

fast fatibuable closer to the surface (less vascular access); slow fibers closer to the internal part of the msucle

Question 18

What is the size principle of recruitment?

Answer 18

small motor neurons are recruited first. they usually innervate slow/red fibers first. then, larger alpha motor neurons are recruited: fast fatigue0resistant fiber associated nuerns recruited next, than fast fatiguable neurons.

Question 19

What arhe the 3 functional consequenses of the size principle of recruitment?

Answer 19

1. output for m UMN dictates desired amt of force
2. contraction force incr. smoothly
3. preferential use of lower energy slower motor neurons.

Question 20

What is the name for the post synaptic terminal of the NMJ?

Answer 20

end-plate

Question 21

What are special features of the NMJ end plate?

Answer 21

junctional folds to incr. membrane area, basement membrane, and nACh receptors

Question 22

What is the specialized region of the NMJ where transmitter is released?

Answer 22

dense bars

Question 23

How does the muscle influence its innervating neuron?

Answer 23

releases neurotrophic factors that allow for survival. without this factor, neurons die

Question 24

How does an innervating neuron influence its muscle? (molecular level)

Answer 24

allows for specialization of the end-plate and the accumulation of ACh receptors. Also determines the makeup of ACh receptor subunits.
Axons release agrin, which binds to MuSK receptors on the muscles to mediate these effects.

Question 25

How does an innervating neuron influence its muscle (bigger level)? How is this seen in pathological states?

Answer 25

neuron firing rate influences development. slow firing induces differentiation into red fibers
ALS: denervation/renervation changes the normal checkerboard gropuing of muscle fiber tibes to a more grouped appearance