What type of skin covers the palms of the hands and the soles of the feet?
What is glabrous skin specialised for?
How is glabrous skin specialised for somatosensation?
Concentrated with receptors
Which broad class of receptors are found in glabrous skin?
Which four types of mechanoreceptors are found in glabrous skin?
Describe the location of the mechanoreceptors in the skin?
Meissner corpuscles and Merkel complexes are located close to the surface
Ruffini organs and Pacinian corpuscles are deeper
Describe the axons that innervate the mechanoreceptors?
Large and myelinated
Where do the cell bodies of the axons that innervate mechanoreceptors lie?
In dorsal root ganglia
What are the endings of mechanorecepptors composed of?
What are the connective tissue endings of each type of mechanoreceptor important for?
Determining the type of energy that the receptor will respond to
Which layers of the skin are the Ruffini and Pacinian corpuscles located in?
Ruffini corpuscles are located in the dermis
Pacinian corpuscles are located in the subcutaneous layer
What are the Ruffini and Pacinian corpuscles embedded in?
Which receptors detect distortion of the skin?
What is the range of distortion detected by the mechanoreceptors?
10nm to sub-damaging distortion
What is the sensitivity and dynamic range of the mechanoreceptors to distortion of the skin?
What is the receptove field of the mechanoreceptors that detect distortion of the skin?
10mm^2 to entire hand
How do mechanoreceptors respond to mechanical distortion?
Mechanical distortion > Na channels opened by mechanical force > Na inflow > AP generated
Describe why radiating forces are important for mechanoreception?
Force applied to skin radiates > at some point, the mechanoreceptor will experience some of that force > generate AP if stimulus reaches threshold
When will a mechanoreceptor generate an AP?
When the stimulus applied is strong enough to generate a large Na inflow that reaches threshold
What happens if a stimulus does not cause Na to reach threshold?
No AP generated > we have no sensory experience of the event that is occurring
Describe the difference between slowly adapting and rapidly adapting receptors?
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
Does the nervous system generally act like slowly adapting or rapidly adapting receptors?
Which of the mechanoreceptors are slowly adapting? Which are rapidly adapting?
Slowly adapting: Merkel complexes and Ruffini organs
Rapidly adapting: Meissner corpuscles and Pacinian corpuscles
Where are Merkel complexes and Meissner corpuscles located?
Merkel complexes are located at the tips of epidermal ridges
Meissner complexes are found near the skin surface
Which particular stimuli do each of the four mechanoreceptors respond to?
Meissner: transient response to skin movement
Ruffini: sustained response to skin movement
Pacinian: transient response to vibration
What types of connections do the axons of mechanoreceptors have in the spinal cord?
Local connections and ascending projections to the brain
Describe the difference in firing rate between tactile and nociceptive primary sensory afferents?
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
Describe the receptive fields of each of the four types of mechanorecptor?
Merkel: small, high density
Meissner: small, high density
Ruffini: large, low density
Pacinian: large, low density
Why are all four mechanorecpetors required?
To build a profile of information and make judgements about what we are touching/feeling
When performing a simple manipulation task, what do each of the four mechanoreceptors encode?
Meissner: rate of force
Merkel: grip force
Ruffini: hand posture
How does firing from each of the four mechanoreceptors change throughout a simple manipulation task?
Meissner and Pacinian have bursts of activity when there is change (rapidly adapting)
Merkel and Ruffini provide sustained information (slowly adapting)
What are the mechanoreceptors located in muscles called?
What does the two-point discrimination threshold describe?
Measures how much territory a single receptor is responsive to
Why does the two-point discrimination threshold vary across the body?
Size of receptive fields varies across the body
Small receptive fileds > can discriminate well
How does two-point discrimation vary between areas with large receptive fields and areas with small receptive fields?
Large receptive fields > hard to discriminate between two points
Small receptove fields > easier to discriminate between two points
What is the conduction velocity of the mechanoreceptors?
What is the axon diameter of the mechanoreceptors?
Why are dermatomal patterns different to spinal nerve distribution?
Presence of anastamoses
Describe the endings of nociceptors?
Free nerve endings
How does the spinal cord arrangement differ for mechanoreceptors and nociceptors?
Mechanoreceptors have an ipislateral arrangement
Nociceptors have a contralateral arrangement
Describe the spinal cord connections of nocicpetors?
Make their most significant connections in the spinal cord at the level that they enter