Sensory Physiology

Question 1

A-alpha afferent sensory fiber

Answer 1

Largest, fastest fiber 80-120m/s
Ia and Ib types
Primary muscle spindles, Golgi tendon organ

Question 2

A-beta afferent sensory fiber

Answer 2

Secondary muscle spindles, skin mechanoreceptors

Type II

Question 3

A-delta afferent sensory fiber

Answer 3

Skin mechanoreceptors, thermal receptors, nociceptors

Type III

Question 4

C afferent sensory fiber

Answer 4

Smallest, slowest fiber 0.5-2m/s
Type IV
Skin mechanoreceptors, thermal receptors, nociceptors

Question 5

A-alpha efferent motor fiber

Answer 5

Largest, fastest fiber

Motor for extrafusal skeletal muscle fibers

Question 6

A-gamma efferent motor fiber

Answer 6

Motor for intrafusal muscle fibers

Question 7

B efferent motor fiber

Answer 7

Preganglionic autonomic motor fibers

Question 8

C efferent motor fiber

Answer 8

Smallest, slowest fiber

Preganglionic autonomic motor fibers

Question 9

Meissner corpuscle

Answer 9

Low threshold, rapidly adapting
Found in glaborous skin
Touch and vibration (under 100Hz), flutter and tapping
Found in glaborous skin

Question 10

Pacinian corpuscle

Answer 10

Low threshold, rapidly adapting
Rapid indentation of skin such as during high frequency vibration (over 100Hz)
Found in both hairy and glaborous skin

Question 11

Ruffini corpuscle

Answer 11

Low threshold, slowly adapting
Magnitude and direction of stretch. Touch and pressure proprioception
Found in both hairy and glaborous skin

Question 12

Merkel cell

Answer 12

Low threshold, slowly adapting
Pressure
Found in glaborous skin

Question 13

Hair-follicle receptor

Answer 13

Rapidly and slowly adapting

Motion across the skin and directionality of that motion

Question 14

Tactile free-nerve ending

Answer 14

High threshold, slowly adapting

Pain and temperature

Question 15

Somatosensory area I - SI primary sensory cortex

Answer 15

Involved in integration of the information for position sense as well as size, shape discrimination
First stop for most cutaneous senses

Question 16

Somatosensory area II- S2

Answer 16

Responsible for comparisons between objects, different tactile sensation and determining whether something becomes a memory
Located in wall of sylvian fissure
Receives input from S1

Question 17

Parieto-temporal-occipital association area PTO

Answer 17

Responsible for high-level interpretation of sensory inputs
Analyzes spatial coordinates of self in environment
Identification of object

Question 18

Law of projection

Answer 18

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

Question 19

Hyperaesthesia

Answer 19

Increased sensitivity to stimulation, excluding the special senses

Question 20

Hyperalgesia

Answer 20

Increased pain from a stimulus that normally provokes pain

Question 21

Allodynia

Answer 21

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 22

A-delta vs C-fiber nociceptors

Answer 22

A-delta fibers are myelinated and faster than C-fibers, and carry info mainly from nociceptive-mechanical or mechanothermal specific nociceptors. They provide precise localization of pain.
C-fibers are slower and are activated by a variety of high-intensity mechanical, chemical and thermal stimulation from polymodal nociceptors. They comprise 70% of all fibers carrying noxious input. Less precise pain localization.

Question 23

Biphasic response to pain

Answer 23

First stimuli and carried by A-delta fibers and gives a sharp, localized pain. Second phase activates C-fibers and creates a dull, throbbing and less localized pain.

Question 24

TRPV1

Answer 24

Ligand gated non-selective cation channel
Expressed by many C-fibers
Sensitive to capsaicin
Activated by endogenous/exogenous compounds, especially bradykinin and heat greater than 43 Celsius
Leads to release of CGRP and substance-P
Sustained activation leads to buildup of those neuropeptides and causes vasodilation and pro-inflammatory mediator release causing a positive feedback loop
Migraine, dental pain, cancer, inflammation, neuropathic pain, visceral pain, osteoarthritis

Question 25

TRPA1

Answer 25

Most common recognized activator is active ingredient in mustard oil, wasabi and horseradish
Paradoxical pro-nociceptive effect from anesthetics
Involved in inflammatory pain states-Allergic contact dermatitis, chronic itch, painful bladder syndrome, IBS, pancreatitis

Question 26

TRPM8

Answer 26

Activated by innocuous cooling and noxious cold temperatures, as well as cooling agents like menthol

Question 27

Gate-control theory of pain

Answer 27

No pain is sensed because the inhibitory interneuron is blocking the nociceptive signal from continuing to move forward - gate is closed
Gate opens during strong C-fiber activation
Rubbing area of pain causes activation of A-beta fiber which activates an inhibitory interneuron and helps block stimuli from C-fiber

Question 28

Descending inhibition

Answer 28

Periaqueductal gray neurons activated by opiates, EAA and cannabinoids
Descending projections travel to locus coeruleus (NE) and raphe nucleus (serotonin)
Serotonin and NE released into dorsal horn activate inhibitory interneurons
Inhibitory interneurons release opiates (enkephalin) which activate mu receptors on C-fiber
Results in reduction of SP release from C-fiber and reduced nociception

Question 29

Central sensitization

Answer 29

Activity dependent synaptic plasticity in spinal cord that generates post-injury pain hypersensitivity
Reduced threshold of dorsal horn neurons to noxious stimuli
Commonly caused by chronic exposure to peripheral inflammation

Question 30

Peripheral sensitization

Answer 30

Neuroplastic changes related to function, chemical profile or structure of the peripheral nervous system that encompasses changes in receptor, ion channel and NT expression
At sites of inflammation, prostaglandin E (mast cells, neutrophils, macrophages) sensitizes peripheral nociceptors by reducing the firing threshold and increasing responsiveness

Question 31

Peptidergic nociceptors

Answer 31

Expresses neuropeptides like SP or CGRP
Responsive to NGF nerve growth factor
Most visceral afferents are peptidergic- contribute to chronic visceral pain syndromes
Half of cutaneous afferents are peptidergic
Chronic inflammation upregulates neuropeptides

Question 32

Non-peptidergic nociceptors

Answer 32

Do not express CGRP or SP
Responsive to GDNF glial derived neurotropic factor
Few visceral afferents are non-peptidergic, half of cutaneous afferents are
Involved in somatic chronic pain states such as diabetic neuropathy

Question 33

Nociceptive input distribution in cortex

Answer 33

S1 and S2 receive input and play role in localization
Insular cortex responsible for interpretation of pain, processes info about internal state of body, contributes to autonomic responses to pain, integrates pain signals- damage causes asymbolia (pain without unpleasantness)
Amygdala important for emotional component
Visceral input travels to hypothalamus and medulla, integrating physiological changes associated with visceral pain