Peripheral Sensory Mechanisms Flashcards
What does the somatosensory system do?
Mediate sensations from whole body surface, including skin and deeper tissues
Extrareceptor sense - tells us about outside world
What is the structure of the skin?
Most of body covered by hair skin
Palmar surface of hands and soles of feet covered by glabrous skin - skin ridges prominent
Why is the skin different on the hands and lips?
Specialised to obtain perceptual information from these body parts
How many mechanoreceptor types, in terms of sense of touch, are there in glabrous skin?
4
Which receptors are close to the surface?
Meissner corpuscles
Merkel complexes
Which receptors are deeper in the skin?
Ruffini organs
Pacinian corpuscles
What type of axons are these receptors innervated by?
Large myelinated axons
Cell bodies in dorsal root ganglia
Can you tell the receptor type by the axon?
No, all the axons look the same
Where are Meissner corpuscles?
Tips of dermal-epidermal folds
Where are Merkel cells?
In valleys of dermal-epidermal folds
Where are Ruffini corpuscles?
In upper dermis
Where are Pacinian corpuscles?
In deep dermis and hypodermis
What is the structure of touch receptor?
Cells of non-neural origin form capsules around nerve endings
Tethered into structure of skin
Each detects slightly different aspect of force
How is mechanical force detected by touch receptors?
Mechanical force applied
Radiates minute force through skin
Deforms receptors
What happens when the force gets too high; ie: is damaging?
Touch receptors don’t give any information - they’ve plateaued out
What happens to the ion channels in the touch receptors when a force is applied?
Membrane stretches
Na ion channels physically open
If Na depolarises membrane enough, action potential initiated
What determines receptor size?
Location of receptor
Why do deeper receptors have larger receptor fields?
Detect radiating forces over larger areas
Why do more superficial receptors have smaller receptor fields?
Detect forces over smaller areas
Define a slowly adapting receptor
Give off action potentials that are constant with stimulus applied
Have slight increase in receptor firing when stimulus first applied
Define a rapidly adapting receptor
Detects changes in stimulus only
Don’t signal if stimulus is continued to be applied, but doesn’t change over time
What are tactile responses related to?
A stimulus activating it
When do rapidly adapting receptors firer?
When stimulus is applied and then removed
How do nociceptors respond to a stimulus?
Increase in firing rate when stimulus is removed
Are nociceptors extrareceptors or intrareceptors?
Intrareceptors - respond when tissue itself has changed its status
What are the two slowly adapting touch receptors?
Merkel complexes
Ruffini endings
What do Merkel complexes respond to?
Indentation
What do Ruffini endings respond to?
Sustained skin movement
What are the two rapidly adapting touch receptors?
Meissner receptors
Pacinian receptors
What do Meissner receptors respond to?
Transient response to skin movement
What do Pacinian receptors respond to?
Transient response to vibration
Which touch receptor has the smallest receptor field?
Merkel complex
Out of the two, which is more sensitive: Merkel complex or Meissner corpuscle?
Meissner corpuscle
Which touch receptor can be classified as “proprioceptive”, and what does this really mean?
Ruffini organ
Tells a lot about shape of hand
- Bigger receptor field
- Responds best to stretch of skin or something moving across skin
Which touch receptor is the most sensitive?
Pacinian corpuscle
What are the proportions of touch receptors?
Pacinian corpuscles = 15%
Ruffini organs = 20%
Merkel complexes = 25%
Meossner corpuscles = 40%
When doing a simple manipulation task, what information does each touch receptor relay?
Meissner encodes rate of force
Merkel encodes grip force
Pacinian encodes vibrations
Ruffini encodes hand posture
Where else are different types of mechanoreceptors used?
In muscles detecting force and stretch
Transduction in auditory system
Which region is more sensitive to two point discrimination: fingertips, or wrist?
Fingertips
Are dermatomes discrete?
No, all dermatomes overlap extensively
If sensitivity loss follows a dermatome pattern, where is the damage likely to be?
At spinal segment level
Is dermatomal pattern of loss the same as the pattern of loss that occurs when there’s damage beyond a nerve plexus?
No, and it’s important to distinguish the two patterns
What nerve innervates the somatosensory structures in the face?
Trigeminal nerve
