Lecture 7

Question 1

What axons are in a spinal nerve?

Answer 1

Somatic motor axons
Somatic sensory axons
Autonomic axons

Question 2

How are sensory receptors classified, and what are the 3 types of sensory receptors

Answer 2

Classified based on source of stimulus
Exteroceptor, Interoceptor/Visceroreceptor, Proprioceptor

Question 3

Exteroreceptors

Answer 3

Responds to external stimuli (touch, temperature, pressure, sight, smell, taste, hearing)

Question 4

Interoceptors/Visceroreceptors

Answer 4

Respond to stimuli within the body (respiration, cardiovascular, digestion, reproductive, urinary)

Question 5

Proprioceptors

Answer 5

Interoceptors of muscle stretch and movement (tendons, ligament, joints, skeletal muscles, connective tissue covering the bones and muscles)

Question 6

Mechanoreceptors and 4 types

Answer 6

Aβ exteroceptors and proprioceptors
Merkel’s disc
Meissner’s corpuscle
Pacinian corpuscle
Ruffini’s endings

Question 7

Merkel’s disc (disc-shaped receptor)

Answer 7

Sense touch
Located between dermis and epidermis
Slow adapting (respond as long as stimulus is present)

Question 8

Meissner’s corpuscle (encapsulated stack of flattened cells)

Answer 8

Sense light touch
Located in the dermis near epidermis
Respond to stimulation with a burst of firing in the beginning and end of stimulation

Question 9

Pacinian corpuscle (encapsulated onion-like capsule surrounding a nerve fiber)

Answer 9

Sense pressure
Located in the dermis in subcutaneous fat
Respond to stimulation with a burst of firing in the beginning and end of stimulation

Question 10

Ruffini’s endings (branches of fibers in a cylindrical capsule)

Answer 10

Sense skin stretch & temperature
Located in the dermis
Slow adapting (respond as long as stimulus is present)

Question 11

Free nerve endings

Answer 11

Sense pain
Located in the epidermis?
Moderate adapting

Question 12

Aα fibers

Answer 12

Unconscious proprioception from muscle spindles and golgi organ tendons (spinocerebellar tract)
Fastest conduction velocity
Thickly myelinated, largest diameter
For reflex arcs and position sense

Question 13

Aβ fibers (mechanoreceptors)

Answer 13

Touch, pressure, vibration (dorsal column - medial lemniscal pathway)
Fast conduction velocity
Myelinated, not as large as Aα

Question 14

Aδ fibers (free nerve endings)

Answer 14

Fast warning pain (sharp), cold (spinothalamic tract)
Moderate conduction velocity
Thinly myelinated
Preserved in dorsal column lesion
Enter through Lissauers’ tract and synapse at lamina II/III

Question 15

C fibers (free nerve endings)

Answer 15

Slow long-lasting pain (burning, aching), warmth
Slowest conduction velocity
Unmyelinated, smallest diameter
Enter through Lissauers’ tract and synapse at lamina II/III

Question 16

Which type of nerve fiber is the most abundant?

Answer 16

Aδ and C fibers (nociceptors)

Question 17

How are mechanoreceptors categorized?

Answer 17

Based on rate of adaptation (slow, moderately, and rapidly adapting)
Based on receptive field (area that elicits neuronal response when stimulated)

Question 18

Nociceptive pain

Answer 18

Pain arising from tissue damage (nociceptor activation)

Question 19

Inflammatory pain

Answer 19

Pain arising by inflammation from an autoimmune response (eg. gout, rheumatoid arthritis)

Question 20

Neuropathic pain

Answer 20

Pain arising from nerve damage/somatosensory system (eg. diabetic neuropathy, carpal tunnel, complex regional pain syndrome, trigeminal neuralgia)

Question 21

Nociplastic pain

Answer 21

Pain arising with no clear evidence of tissue damage (eg. fibromyalgia, chronic lower back pain, irritable bowel syndrome)

Question 22

Where are nociceptors found?
What do nociceptors respond to?

Answer 22

Found in all tissues of the body except for the brain
Respond to the extremes of temperature, mechanical/chemical stimuli

Question 23

Gate control theory of pain (modulates the 2nd order neuron via GABA)

Answer 23

Activating pressure receptors (Aβ fibers, DC-ML pathway) will send collateral branches to inhibit the spinothalamic tract that was initiated by C fibers

Question 24

Descending analgesic system process

Answer 24

STT sends collateral axons - periaqueductal grey matter and reticular formation (locus coeruleus and raphe nuclei) - NE (locus coeruleus) & 5-HT (raphe nuclei) released to inhibitory interneurons - natural opioids released to C fibers - decrease C fiber release of Substance P and activation of STT = pain modulation

Question 25

Endogenous opioids released in descending analgesic system

Answer 25

Dynorphins, enkephalins, endorphins

Question 26

What activates the nuclei of the descending analgesic system - PAG, locus coeruleus, & raphe nuclei (3)

Answer 26

Anterolateral system (STT collateral branches) Sensory cortex Limbic system