Peripheral Nervous System

Question 1

What are the major anatomical structures comprising the peripheral nervous system?

Answer 1

• Nerves (spinal nerves, peripheral nerves, both afferent and efferent)
• ganglia (clusters of cell bodies - sensory in dorsal root ganglia, autonomic ganglia for efferents to smooth muscle/glands)
• sensory receptors

Question 2

What is the difference between exteroceptors and interoceptors?

Answer 2

exteroceptors are superficially located ie in the skin

interocetors are deep body ie proprioceptors (spindles, golgi tendon organ) or visceroceptors on organs

Question 3

What are the 3 layers of skin

Answer 3

epidermis dermis, subcutaneous

Question 4

What are the 3 types of non-encapsulated sensory endings?

Answer 4

1. Free nerve ending - in all layers, mainly detect pain
2. Merkel’s disk - epidermis, branches, fine touch/pressure
3. hair follicle receptors - aka petrichial endings, wind around hair follicle, detect hair movement

Question 5

What are the 4 types of encapsulated sensory endings?

Answer 5

1. pacinian corpuscle - lollipop, dermis layer, detect pressure & vibration
2. Ruffini corpuscle - flat/floppy, dermis of hairy skin, temperature, skin stretch, sustained pressure, slow adapting
3. Meissner’s Corpuscle - fine touch, low vibration, upper dermis, leaf looking, fingertips
4. Krause end bulbs, - fingertips, lips, genitals, touch & temperature

Question 6

What are 2 proprioceptors?

Answer 6

• muscle spindles - 1a sensory endings in intrafusal muscle fibers, detect muscle stretch
• golgi tendon organs - 1b sensory endings, interwoven with collagen fibres in tendon, detect tension

Question 7

what are visceral nociceptors?

Answer 7

free nerve endings in connective & adipose tissue

Question 8

Describe motor endings

Answer 8

on skeletal muscle: motor neurons end at the neuromuscular junction - synapse onto motor end plate of muscle fibers, ACh signalling
viscera: neuroeffector endings synapse director onto cardiac, smooth muscle, exocrine and endocrine glands

Question 9

What are the 2 types of ganglia?

Answer 9

Spinal ganglia
* dorsal root ganglia
* cell bodies of sensory neurons

Autonomic ganglia
* sympathetic trunk ganglia, ganglia in plexuses of trunk (ie mesenteris plexus ganglia), viscera ganglia
* cell bodies of autonomic efferent neurons

Question 10

What are the rami?

Answer 10

grey & white rami contain both sensory or motor info from viscera/non-skeletal muscles (before it splits into ventral/ dorsal roots). where the spinal roots join up, it splits off before they form the spinal nerve

Question 11

Compare sympathetic and parasympathetic autonomic innervation

Answer 11

Ganglion: Sympathetic cell bodies in sympathetic trunk next to spinal cord, parasympathetic in ganglia near target organ.
Lengths: Sympathetic short pre-ganglionic, long post-ganglionic (bs ganglion at SC). Parasympathetic long pre-ganglionic, short post-ganglionic (bc ganglion near organ)
NT: preganglionic always ACh. Post different. sympathetic Ach, NE, E. Parasympathetic usually ACh

Question 12

Describe the ensheathment of peripheral nerve fibres

Answer 12

• axon
• myselin sheath
• endoneurium
• bundle of axons surrounded by endoneurium is wrapped in perineurium and called a fascicle
• multiple fascicles, with blood vesicles, wrapped in epineurium and called a nerve

Question 13

Differentiate myelinated and unmyelinated nerves in PNS

Answer 13

• myelinated have myelin sheaths, in PNS 1 schwann cell = 1 internode
• unmyelinated still have schwann cells around, vaguely swallowing up to 15 of them (remak fibre)

Question 14

Compare the name, type, diameter and velocity of PNS nerve fibres

Answer 14

A-alpha/1A - myelinated, diameter 12-20um, 70-120m/sec, proprioception/skeletal muscles
A-beta/1B - myelinated, diameter 5-15, 30-80m/sec, golgi tendon organ/ruffini, meissner, pacinian endings
A-gamma - myelinated, diameter 3-8um, 15-40m/sec, motor to intrafusal
A-delta - myelinated, diameter 3-8um, 10-30m/sec, sensory hair follicles, temp, pain
B - myelinated, diameter 1-2um, 5-15m/sec, preganglionic autonomic
C - unmyelinated, diameter 0.2-1.5, 0.5-2.5m/sec, pain, temp, olfaction, postganglionic autonomic

Question 15

Compare the name, type, diameter and velocity of PNS nerve fibres

Answer 15

A-alpha/1A - myelinated, diameter 12-20um, 70-120m/sec, proprioception/skeletal muscles
A-beta/1B - myelinated, diameter 5-15, 30-80m/sec, golgi tendon organ/ruffini, meissner, pacinian endings
A-gamma - myelinated, diameter 3-8um, 15-40m/sec, motor to intrafusal
A-delta - myelinated, diameter 3-8um, 10-30m/sec, sensory hair follicles, temp, pain
B - myelinated, diameter 1-2um, 5-15m/sec, preganglionic autonomic
C - unmyelinated, diameter 0.2-1.5, 0.5-2.5m/sec, pain, temp, olfaction, postganglionic autonomic