Peripheral sensory mechanisms

Question 1

What type of skin covers the palms of the hands and the soles of the feet?

Answer 1

Glabrous skin

Question 2

What is glabrous skin specialised for?

Answer 2

Somatosensation

Question 3

How is glabrous skin specialised for somatosensation?

Answer 3

Skin ridges

Concentrated with receptors

Question 4

Which broad class of receptors are found in glabrous skin?

Answer 4

Mechanorecptors

Question 5

Which four types of mechanoreceptors are found in glabrous skin?

Answer 5

Meissner corpuscles

Merkel complexes

Ruffini organs

Pacinian corpuscles

Question 6

Describe the location of the mechanoreceptors in the skin?

Answer 6

Meissner corpuscles and Merkel complexes are located close to the surface

Ruffini organs and Pacinian corpuscles are deeper

Question 7

Describe the axons that innervate the mechanoreceptors?

Answer 7

Large and myelinated

Question 8

Where do the cell bodies of the axons that innervate mechanoreceptors lie?

Answer 8

In dorsal root ganglia

Question 9

What are the endings of mechanorecepptors composed of?

Answer 9

Connective tissue

Question 10

What are the connective tissue endings of each type of mechanoreceptor important for?

Answer 10

Determining the type of energy that the receptor will respond to

Question 11

Which layers of the skin are the Ruffini and Pacinian corpuscles located in?

Answer 11

Ruffini corpuscles are located in the dermis

Pacinian corpuscles are located in the subcutaneous layer

Question 12

What are the Ruffini and Pacinian corpuscles embedded in?

Answer 12

Connective tissue

Question 13

Which receptors detect distortion of the skin?

Answer 13

Mechanoreceptors

Question 14

What is the range of distortion detected by the mechanoreceptors?

Answer 14

10nm to sub-damaging distortion

Question 15

What is the sensitivity and dynamic range of the mechanoreceptors to distortion of the skin?

Answer 15

0-1000 Hz

Question 16

What is the receptove field of the mechanoreceptors that detect distortion of the skin?

Answer 16

10mm^2 to entire hand

Question 17

How do mechanoreceptors respond to mechanical distortion?

Answer 17

Mechanical distortion > Na channels opened by mechanical force > Na inflow > AP generated

Question 18

Describe why radiating forces are important for mechanoreception?

Answer 18

Force applied to skin radiates > at some point, the mechanoreceptor will experience some of that force > generate AP if stimulus reaches threshold

Question 19

When will a mechanoreceptor generate an AP?

Answer 19

When the stimulus applied is strong enough to generate a large Na inflow that reaches threshold

Question 20

What happens if a stimulus does not cause Na to reach threshold?

Answer 20

No AP generated > we have no sensory experience of the event that is occurring

Question 21

Describe the difference between slowly adapting and rapidly adapting receptors?

Answer 21

SLOW: Show an initial bit of enthusiasm in response to a stimulus

Over time, encode the size of the stimulus

RAPID: Short initial excitement

After that, only respond when there is a change in stimulus

Question 22

Does the nervous system generally act like slowly adapting or rapidly adapting receptors?

Answer 22

Rapidly adapting

Question 23

Which of the mechanoreceptors are slowly adapting? Which are rapidly adapting?

Answer 23

Slowly adapting: Merkel complexes and Ruffini organs

Rapidly adapting: Meissner corpuscles and Pacinian corpuscles

Question 24

Where are Merkel complexes and Meissner corpuscles located?

Answer 24

Merkel complexes are located at the tips of epidermal ridges

Meissner complexes are found near the skin surface

Question 25

Which particular stimuli do each of the four mechanoreceptors respond to?

Answer 25

Merkel: indentation Meissner: transient response to skin movement Ruffini: sustained response to skin movement Pacinian: transient response to vibration

Question 26

What types of connections do the axons of mechanoreceptors have in the spinal cord?

Answer 26

Local connections and ascending projections to the brain

Question 27

Describe the difference in firing rate between tactile and nociceptive primary sensory afferents?

Answer 27

Tactile: don't change firing rate with increased force Nociceptive: increased firing rate with increased stimulus, as well as increased firing once stimulus is removed

Question 28

Describe the receptive fields of each of the four types of mechanorecptor?

Answer 28

Merkel: small, high density Meissner: small, high density Ruffini: large, low density Pacinian: large, low density

Question 29

Why are all four mechanorecpetors required?

Answer 29

To build a profile of information and make judgements about what we are touching/feeling

Question 30

When performing a simple manipulation task, what do each of the four mechanoreceptors encode?

Answer 30

Meissner: rate of force Merkel: grip force Pacinian: vibrations Ruffini: hand posture

Question 31

How does firing from each of the four mechanoreceptors change throughout a simple manipulation task?

Answer 31

Meissner and Pacinian have bursts of activity when there is change (rapidly adapting) Merkel and Ruffini provide sustained information (slowly adapting)

Question 32

What are the mechanoreceptors located in muscles called?

Answer 32

Muscle spindles

Question 33

What does the two-point discrimination threshold describe?

Answer 33

Measures how much territory a single receptor is responsive to

Question 34

Why does the two-point discrimination threshold vary across the body?

Answer 34

Size of receptive fields varies across the body Small receptive fileds \> can discriminate well

Question 35

How does two-point discrimation vary between areas with large receptive fields and areas with small receptive fields?

Answer 35

Large receptive fields \> hard to discriminate between two points Small receptove fields \> easier to discriminate between two points

Question 36

What is the conduction velocity of the mechanoreceptors?

Answer 36

35-75 m/s Fast

Question 37

What is the axon diameter of the mechanoreceptors?

Answer 37

6-12 um Large

Question 38

Why are dermatomal patterns different to spinal nerve distribution?

Answer 38

Presence of anastamoses

Question 39

Describe the endings of nociceptors?

Answer 39

Free nerve endings

Question 40

How does the spinal cord arrangement differ for mechanoreceptors and nociceptors?

Answer 40

Mechanoreceptors have an ipislateral arrangement Nociceptors have a contralateral arrangement

Question 41

Describe the spinal cord connections of nocicpetors?

Answer 41

Make their most significant connections in the spinal cord at the level that they enter