Lecture 11: Sensory Physiology

Question 1

Sensory Aα
What is its classification of afferent fibers? 
Is the fiber diameter large of small?
What is its conduction velocity?
What receptors does it supply?

Answer 1

Ia and Ib
large
80-120 m/s (fast)
Primary muscle spindles and Golgi tendon organs

Question 2

Sensory Aβ
What is its classification of afferent fibers?
What receptors does it supply?

Answer 2

II

Secondary muscle spindles, skin mechanoreceptors

Question 3

Sensory Aδ
What is its classification of afferent fibers?
What receptors does it supply?

Answer 3

III

Skin mechanoreceptors, thermal receptors, and nociceptors

Question 4

Sensory C
What is its classification of afferent fibers? 
Is the fiber diameter large of small?
What is its conduction velocity?
What receptors does it supply?

Answer 4

IV
small
0.5-2 m/s (slow)
Skin mechanoreceptors, thermal receptors, and nociceptors

Question 5

Motor Aα

What receptors does it supply?

Answer 5

Extrafusal skeletal muscle fibers

Question 6

Motor Aβ

What receptors does it supply?

Answer 6

Intrafusal skeletal muscle fibers

Question 7

Motor B

What receptors does it supply?

Answer 7

Preganglionic autonomic fibers

Question 8

Motor C

What receptors does it supply?

Answer 8

Postganglionic autonomic fibers

Question 9

What does Meissner corpuscle sense?

Answer 9

Touch and vibration; flutter and tapping

<100 Hz

Question 10

Where is Meissner corpuscle located?

Answer 10

Glaborous skin

Question 11

What does Pacinian corpuscle sense?

Answer 11

High frequency vibration

Question 12

Where is Pacinian corpuscle located?

Answer 12

Both hairy and glaborous skin

Question 13

What does Ruffini corpuscle sense?

Answer 13

Magnitude and direction of stretch

Touch, pressure, and proprioception

Question 14

Where is Ruffini corpuscle located?

Answer 14

Both hairy and glaborous skin

Question 15

What does a Merkel cell sense?

Answer 15

Pressure

Question 16

Where is a Merkel cell corpuscle located?

Answer 16

Glaborous skin

Question 17

What does a hair follicle receptor sense?

Answer 17

Motion across skin and directionality of that motion

Question 18

What does a tactile free-nerve ending sense?

Answer 18

Pain and temperature

Question 19

What is two point discrimination?

Answer 19

Ability to distinguish between two stimuli applied at a close distance is determined by measuring the minimum distance between the two stimuli

Question 20

Where is tactile acuity the highest?

Are receptive fields small or large?

Answer 20

Fingertips and lips

Small

Question 21

Where is tactile acuity the lowest?

Are receptive fields small or large?

Answer 21

Calf, back, thigh

Large

Question 22

Where is Somatosensory area 1 located?

Answer 22

Post central gyus

Question 23

What is the function of Somatosensory area 1?

Answer 23

Integration of information for position sense, size, and shape discrimination

Question 24

Where is Somatosensory area 2 located?

Answer 24

Wall of Sylvian Fissure

Receives input from S1

Question 25

What is the function of Somatosensory area 2?

Answer 25

Responsible for comparisons between objects, different tactile sensation, and deciding what becomes a memory

Question 26

What is the function of parieto-temporal-occipital association area?

Answer 26

High level interpretation of sensory inputs

Question 27

What is the law of projection?

Answer 27

Regardless of the place along an afferent pathway that is stimulated, the sensation is perceived to come from the place that the innervation arises.

Question 28

What phenomenon can the law of projection explain?

Answer 28

Phantom limb

Question 29

What is pain?

Answer 29

An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.

Question 30

What is nociception?

Answer 30

The neural process of encoding noxious stimuli

Question 31

What is hypersensitivity?

Answer 31

Increased responsiveness of nociceptive neurons to their normal input, and/or recruitment of a response to normally subthreshold inputs

Question 32

What is hyperaesthesia?

Answer 32

Increased sensitivity to stimulation, excluding the special senses

Question 33

What is hyperalgesia?

Answer 33

Increased pain from a stimulus that normally provokes pain

Question 34

What is allodynia?

Answer 34

Pain due to a stimulus that does not normally provoke pain. | Classic example is the lay of sheets on skin that has been sunburned.

Question 35

What fibers provide precise localization of pain?

Answer 35

Aδ

Question 36

What fibers provide pain information?

Answer 36

Aδ (sharp localized) and C fibers (dull, throbbing)

Question 37

What are mechanical nociceptors?

Answer 37

Response to mechanical forces ranging from moderate pressure with a blunt object to overtly tissue-damaging stimuli

Question 38

What are chemical nociceptors?

Answer 38

Response to endogenous or exogenous chemical compounds, such as pro-inflammatory mediators, acids, or capsaicin

Question 39

What are thermal nociceptors?

Answer 39

Response to noxious heat and cold will directly activate thermal receptors expressed by nociceptors

Question 40

What is the function of the transient receptor potential (TRP) family of receptor ion channels?

Answer 40

Sense a broad range of changing environments in the body tissue: pH, inflammatory mediators, heat, cold, and exogenous chemicals.

Question 41

What does TRPV1 sense?

Answer 41

Sensitive to vanilloid compounds, most notably, capsaicin

Question 42

What pain conditions is TRPV1 involved with?

Answer 42

``` Migraine Dental pain Cancer pain Inflammatory pain Neuropathic pain Visceral pain Osteoarthritis ```

Question 43

What pain conditions is TRPA1 involved with?

Answer 43

``` Dermatitis Chronic itch Painful bladder syndrome Migraine Irritable bowel syndrome Pancreatitis ```

Question 44

What activates TRMP8

Answer 44

Cold temperatures and agents

Question 45

What happens where there are no pain inputs to the C fibers?

Answer 45

Inhibitory interneurons suppress pain pathway

Question 46

What happens when there are pain inputs to the C fiber?

Answer 46

C fibers stop the inhibitory interneurons and send a strong signal to brain

Question 47

How can pain be modulated?

Answer 47

1. Aβ fiber is activated and travels to dorsal horn and synapses on an inhibitory neuron, releasing an EAA. 2. Released glycine inhibits secondary sensory neuron on nociceptive pathway.

Question 48

How are pain signals reduced?

Answer 48

1. Activation of PAG leads to fibers going to Locus Coeruleus (NE) and Raphe nucleus (serotonin) 2. NE and serotonin released into dorsal horn and activate inhibitory interneurons 3. Opiates released and activates mu receptors on terminals of C-fibers, reducing nociception

Question 49

What does the theory of central sensitization say?

Answer 49

1. Level of spinal cord, higher brain areas, or both 2. Reduces threshold of involved neurons to noxious stimuli 3. Synaptic Plasticity: Persistent stimulation of NMDA receptors and intracellular signaling cascades 4. Central Inflammation

Question 50

What does the theory of peripheral sensitization say?

Answer 50

1. Inflammation can make nociceptors in injured tissues more sensitive (e.g. Prostaglandins and bradykinin) 2. Body more sensitive to thermal changes, activating TRPV1

Question 51

What role does the primary sensory cortex play when it comes to the sensory system?

Answer 51

Recognizes crude senses

Question 52

What role does the secondary sensory cortex play when it comes to the sensory system?

Answer 52

Cognitive interpretation of crude senses

Question 53

What role does the PTO play when it comes to the sensory system?

Answer 53

High level integration of many senses

Question 54

What role do the primary and secondary sensory cortices play when it comes to pain?

Answer 54

Crude localization

Question 55

What role does the insular cortex play when it comes to pain?

Answer 55

Interpretation fo pain

Question 56

What role does the amygdala play when it comes to pain?

Answer 56

Emotional component

Question 57

What role does the hypothalamus/medulla play when it comes to pain?

Answer 57

Physiologic integration

Question 58

What neuropeptides do peptidergic nociceptors express?

Answer 58

Substance P and CGRP

Question 59

What up-regulates neuropeptides?

Answer 59

Chronic inflammation

Question 60

What are non-peptidergic nociceptors involved in?

Answer 60

Somatic chronic pain (e.g. diabetic neuropathy)