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Flashcards in Somatosensation Deck (24)
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1
Q

what type of channel transduce touch signal?

A

Mechanically gated cation channels transduce touch signals (non specific cation channel)

2
Q

what is the different type of Mechanically gated cation channels ?

A

cation channel that activate directly through lipid tension
cation channel that directly activate via a structural protein Linking proteins may be:
intracellular (cytoskeleton)
extracellular (surrounding tissue)
Cation channel that open via indirect action through membrane structural protein
The effects of physically gated G-protein coupled receptors will be slow to activate and long-lasting => may be involved in pain sensation

3
Q

Each axon is associated with how many mechanoreceptor?

A

Each axon is associated with only a single type of mechanoreceptor.
hence it can only transmit the sensory information detected by one type of mechanoreceptor in the form of electrical signal

4
Q

Glabrous skin vs hairy skin

A
  • Glabrous skin = no hair follicles. This includes lips, palms of hands, soles of feet. More sensitivity
  • Hairy skin = everywhere else (even if you shave).
5
Q

where are the cell body of the sensory afferent located at?

A

The cell bodies of sensory afferents are in the Dorsal Root Ganglion

6
Q

sensory afferen

A

Sensory afferents:
Unipolar neurons
Spike initiation zone is near the specialised accessory structure
Cell body is outside the spinal cord in the DRG
Action potential is generated as a result of the receptor potential – travels along entire axon

7
Q

Action potentials can be recorded from sensory axons in awake humans

A

For each receptor type, we can characterise:
Receptive field (where on skin we can touch to change membrane potential)
Optimal stimulus properties
Frequency sensitivity
Adaptation rate: how the firing rate of a neuron changes over time in response to a constant stimulus.
Axon type and conduction velocity

8
Q

Receptive field

A

field (where on skin we can touch to change membrane potential)

The receptive field encompasses the sensory receptors that feed into sensory neurons and thus includes specific receptors on a neuron as well as collectives of receptors that are capable of activating a neuron via synaptic connection

9
Q

Adaptation rate

A

how the firing rate of a neuron changes over time in response to a constant stimulus.

10
Q

what do the mechanoreceptors differ in?

A

Mechanoreceptors differ in receptive field size and adaptation rate

11
Q

what is the size of superficial mechanorecepotors and why?

A

Superficial receptors have smaller receptive fields => they contribute more to fine position discrimination
Meissner and markel cell

12
Q

which two mechanoreceptor adapt rapidly?

A

Meissner and Pacinian corpuscles rapidly adapt

- firing rate drops in response to sustained stimuli, they respond to few initially touches

13
Q

how many axons and neurons are the deep receptors (Pacinian corpuscles and Ruffini endings) associated with?

A

The deep receptors are associated with a single axon and neuron

14
Q

how many superficial receptors are associated with a single axon and a single neuron ?

A

Multiple superficial receptors of the same type may be associated with a single axon and neuron

15
Q

Describe the structure of Pacinian corpuscles and how it relates to it’s function?

A

Concentric, fluid-filled layers of connective tissue around the axon terminal
Most sensitive mechanoreceptor, but rapidly adapt to sustained pressure
Respond to high vibration frequencies (30-500 Hz)

Like an onion – different layers can shift relative to one another. Thus, only initial part of sustained touch is signalled by Pacinian corpuscles.
However, each cycle of an oscillating stimulus can lead to shifting of the layers, causing action potentials.

16
Q

what is the advantage of corpuscle in Pacinian corpuscles for its function?

A

The physical structure of the corpuscle provides an additional, mechanical form of rapid adaptation.
-The corpuscle is like an onion – different layers can shift relative to one another. Thus, only the initial part of sustained touch is transferred by Pacinian corpuscles to a compression of the axon.

  • With the capsule it undergoes deformation, absorbed the deformation and it undergoes different type of deformation when that stimuli is removed so another AP is generated. Hence it signals the initial touch and the removal touch
  • However, each cycle of an oscillating stimulus can lead to shifting of the layers, causing action potentials.
17
Q

Receptor structure accounts for function – Merkel discs

A

Merkel discs (SA1) encode the shape and size of objects touching the hand.

Smaller stimuli activate fewer receptors, but activate them more strongly.
As stimulus get larger, it is actually moving in the surround of the receptive field and it is inhibiting the response of the neurons some how
Center-surround structure – required for precise localisation.

18
Q

SA1 (Merkel cell)

A

location: Superficial - tip of epidermal sweat ridges
skin type: Hairy + glabrous
relative receptive field size: Small (~2 mm)
Adaptation rate: slowly adapting
Response to sustained indentation: sustained
Best stimulus:Edges & points
Threshold for indentation or vibration:8 µm

Density is inversely proportional to RF size – highest density are Meissner’s corpuscles and Merkels disks

19
Q

RA1 (Meissner corpuscle)

A
location: Superficial - dermal papillae
skin type: glabrous
relative receptive field size: Small (~ 5 mm)
Adaptation rate: Rapidly adapting 
Response to sustained indentation: none
Best stimulus:lateral motion 
Threshold for indentation or vibration:2 µm
Superficial receptors have small RF.
20
Q

SA2 (Ruffini ending)

A

location:Deep tissue - dermis
skin type: Hairy + glabrous
relative receptive field size: Large (~ 8 mm)
Adaptation rate: slowly adapting
Response to sustained indentation: sustained
Best stimulus:skin stretch
Threshold for indentation or vibration:40 µm

21
Q

RA2 (Pacinian corpuscle)

A

location:Deep tissue - dermis
skin type: Hairy + glabrous
relative receptive field size: Large (~ 8 mm)
Adaptation rate: rapidly adapting
Response to sustained indentation: none
Best stimulus: Vibration
Threshold for indentation or vibration:0.01 µm

22
Q

Sensory pathway to the brain:the Dorsal Column–Medial Lemniscal Pathway

A
  1. Axons from sensory receptors enter the spinal cord via the dorsal root
  2. The axons branch, synapsing onto neurons within the dorsal horns for mediating local circuitry
  3. The other axon branch ascends the spinal cord in the dorsal column, synapsing in the dorsal column nuclei
  4. The axons decussate (cross to the other side of the body
  5. Dorsal column neurons target neurons in the VP nucleus of the thalamus, which projects to primary somatosensory cortex (S1)
23
Q

What is “primary” about a primary sensory area?

A

Area 3b (S1):
First cortical area to receive somatosensory information - dense inputs from thalamus (VP nucleus)
neurons are responsive to somatosensory stimuli (but not other senses)
lesions impair touch sensation
Electrical stimulation evokes touch sensation

24
Q

How else might we quantitatively test touch perception

A

Performance on complex tasks can be related to mechanoreceptor properties, and tuning properties of cortical neurons
Detection of a gap (i.e. is there a gap or not)
Discrimination of grating orientation (horizontal vs vertical)
Identification of one item from a large collection of possibilities
Most common psychophysical testing