Lecture 28: Touch Receptor Mechanism

Question 1

Is skin uniform?

Answer 1

No there are different types of skin and the mechanoreceptors within them and expression vary with skin types.

i.e hairy skin, smooth (fingers = increased sensitivity to touch)

affects;

• acuity
• modality

Question 2

What are the four main touch receptors?

Answer 2

Ruffini Endings
Meissner corpuscles
Pacinian corpuscles
Merkel cells

Question 3

Apart from different receptor endings what affects encoding of touch information?

Answer 3

The different types of afferent nerve fibres

Question 4

What are the types of touch afferent fibres?

Answer 4

A alpha, A beta, A delta, A gamma and type C fibres.

Question 5

How can A beta fibres be further categorised?

Answer 5

RA = rapidly adapting
SA 1 = slow adapting 1
SA 2 = slow adapting 2

Question 6

Describe the receptive fields of the four main receptors

Answer 6

Meirkel + Meissner = small receptive field

Pacinian + ruffini = large receptive fields

Question 7

What is the sensory function of merkel receptors?

Answer 7

Form and texture

= edges, points, corners, curves

Question 8

What is the sensory function of meissner receptors?

Answer 8

Motion detection + Grip control

= Skin motion

Question 9

What is the function of pacinian receptors?

Answer 9

Detects deep / distant vibration

Question 10

what is the function of ruffini corpuscles?

Answer 10

Tangenital force, hand shape, motion detection

= skin stretch

Question 11

What makes a key difference in the way information is coded;

Answer 11

The afferent fibres and the types of receptors i.e neuron vs corpuscle

Question 12

how does receptive field and receptor density relate?

Answer 12

Large receptive fields will have lower receptor density and vice versa, product of their function

Question 13

What 4 receptors to rapidly adapting afferents innervate?

Answer 13

Pacinian (vibration)
Meissner (movement)
Lanceolate endings (hairs)
Circumferential endings

LMPC

lets make poor choices

Question 14

What does rapidly adapting afferent mean;

Answer 14

Stimulus applied, on/off rapidly

then no change until stimulus off

Question 15

What does the slow afferent type one innervate?

Answer 15

Merkel (shape,texture; high resolution spatial info)

Question 16

What do slow adapting type two afferents innervate?

Answer 16

Ruffini (directional information)

Question 17

How do slow afferents fire?

Answer 17

Throughout the stimuli, sustained firing, but Hz alters = different information

Question 18

What sort of neuron is the SA1,2 an RA1 class neurons?

Answer 18

A beta fibres

= thickly myelonated

Question 19

Describe A delta fibres;

Answer 19

AdFibers
- Thinly myelinated =
Lanceolate endings 
Circumferential endings 
A-Mechanonociceptor

Question 20

Describe type c fibres;

Answer 20

C Fibers
Unmyelinated
Nociceptors
Low threshold mechanoreceptor

Question 21

Describe pacinian and meissner morphology;

Answer 21

Pacinian and Meissner
◦Corpuscles
◦Continuous with neuron
◦Receptor potential activates AP
◦Has Voltage gates Na channels

Question 22

Describe merkel and ruffini morphology;

Answer 22

Merkel cell neurite and Ruffini endings
◦Form separate receptors
◦Have synaptic connection to neurons
◦Amplified by neuro `modulators

Question 23

What are the channels present in the receptors;

Answer 23

Na+ and K+ voltage gated ion channels

Inward rectifying K+channels`

Question 24

What are the neurotransmitters of the receptor afferent synapses;

Answer 24

Glutamate (excite)
GABA (inhib)
ATP

Question 25

How do receptors respond to a stimulus

Answer 25

Membrane channels open due to mechanical stimulus

Receptor potential elicited due to channels openingVoltage gated Na+ and K+ channels located on receptors

When threshold reached elicits Action potential on first node of ranvier

Question 26

Describe the transient receptor potential for RA currents;

Answer 26

RA Currents
◦Fast kinetics of activation and desensitization◦
Inhibited by Ca2+ , Gd2+ , and conotoxin
◦Na+sensitive

Question 27

Describe the transient receptor potential for SA currents;

Answer 27

SA Currents
◦Inhibited by Gd2+ and conotoxin
◦Ca2+ and Na+ sensitive

Question 28

Write notes on how the pacinian corpuscle is formed;

Answer 28

• Encapsulated ending ((inner)Schwann lamellae layer+ Fibroblasts lamellae layer (outer))

Capsule provides coding for information (forms the corpuscle, two layers)

Question 29

Describe pacinian corpuscle features;

Answer 29

• Stretch receptor selective to Na+TTX sensitive voltage gated Na+ channel
• Rapid Adaptation aided by
• Neuromodulation;
  ◦Glutamate ◦GABA

Question 30

How do pacinian and merkel receptors different?

Answer 30

Pacinian is extension of neuron

merkel forms synapse with afferent fibre

Question 31

If a neuron has a leak K channel what will it do?

Answer 31

Hyperpolarise the cell

However neuromodulators or neurotransmitters can alter this function thus altering the cells ability to depolarise and depolarising frequency

Question 32

Describe the mechanisms for RA;

Answer 32

Lamaellae sense mechanical stimuli, release Glutamte and excite nurite

Neurite releases GABA and shuts down lamaellae

Question 33

Describe merkel cell neurite;

Answer 33

Basal layer of the epidermis
Contains a variety of Neuropeptides
Each touch dome 30-70 merkelcells
Mechanical transducer
Ligangated Ion channels

Question 34

Write some short notes on non-mechanical receptors;

Answer 34

Temperature
◦Transient receptor potential (TRP) family
◦Cation channels

TRPV1 (Vanilloid1) Responds to Capsaicin & Heat (above 42)

TRPM8 Responds to Menthol and Cold