Principles of Neuroscience Lecture 8, Touch

Question 0

What are the cells that detect motion on the skin and deeper tissues called?

Answer 0

Mechanoreceptors

Question 1

Describe the different skin surfaces on the body

Answer 1

Hairy and glaborous. Glaborous is characterised by ridges on the skin

Question 2

Which two are located in the epidermis?

Answer 2

Meissner and Merkel

Question 3

Which two are located deeper in the skin?

Answer 3

Pacinian and Ruffini

Question 4

Which two are quickly adapting?

Answer 4

Meissner and Pacinian

Question 5

Which two are slowly adapting?

Answer 5

Merkel and Ruffini

Question 6

Which two are high density, and which two are low density?

Answer 6

High : meissner and Merkel

Low : Ruffini and Pacinian

Question 7

Which two have big receptive fields, which two small?

Answer 7

Big receptive fields: Pacinian & Ruffini

Small receptive fields: Merkel & Meissner

Question 8

How does mechanical transduction occur? Outline the pathway

Answer 8

1. Touch causes the ion channels on the mechanoreceptors to open.
2. Na+ rushes in, depolarising the cell
3. If the threshold for action potential is reached, neurotransmitters are released from vesicles onto the primary motor neurons
4. This is conducted to the spinal cord etc.

Question 9

Which ion rushes in?

Answer 9

Sodium

Question 10

Describe what is meant by slowly and quickly adapting mechanoreceptors

Answer 10

Slowly: like transient, the mechanoreceptor responds to dynamic and static touch. The action potentials fire for as long as the stimulus is there.

Quickly: there is a burst of action potential, then they stop, even whilst the stimulus is still present.

Question 11

What test demonstrates how receptive fields overlap

Answer 11

The two point discrimination test

Question 12

Which two areas do touch afferents connect?

Answer 12

Mechanoreceptors and the spinal cord

Question 13

Describe the axons of touch afferents, and why this is so

Answer 13

They are thick so that there is very quick transmission of action potentials along the axon. They have very thick myelin sheaths

Question 14

Describe the path from the mechanoreceptor to the brain

Answer 14

Mechanoreceptor
Touch afferent
(Cell body in dorsal root ganglion)
Spinal cord (ipsilateral up the dorsal columns)
Medulla: (synapse, crossing over -> Contralteral)
Thalamus: VP complex (Ventral posterior complex), Ventral Posterior Medial Nucleus, Ventral Posterior Lateral Nucleus, synapse
Primary somatosensory complex on post-central gyrus
Secondary somatosensory complex
Parietal areas

Question 15

What is the name of the region in the thalamus through which the neurons travel?

Answer 15

Ventral Posterior complex, comprised of:
Ventral Posterior Medial nucleus
Ventral Posterior Lateral nucleus

Question 16

Where do the neurons first synapse?

Then?

Answer 16

Medulla (dorsal root columns)

Thalamus (VP complex)

Question 17

Do the neurons cross over at any point?

Answer 17

In the medulla, the neurons go from being ipsilateral to contralateral

Question 18

What is S1?

Answer 18

Primary Somatosensory Cortex

Question 19

Describe the functional and structural organisation of the Primary Somatic Sensory Cortex

Answer 19

4 Brodmann’s areas that contain a full map of the body.

Areas: 1, 2, 3a & 3b

Question 20

What is meant by Brodmann’s areas?

Answer 20

These are functional areas in the brain, whose neurons are different enough to warrant different names.

In the S1, there are 4

Question 21

Where does information travel after S1?

Answer 21

Secondary Somatosensory cortex, S2

Parietal areas

Question 22

Why is the brain plastic?

Answer 22

This gives us the most effective arrangement at a given point in time
We can adapt to a changing environment

Question 23

Describe four examples of brain plasticity

Answer 23

1. Lactation in monkeys
2. Amputation of digits
3. Anaesthetic of digits
4. Functional expansion of area due to repetitive behavioural tasks

Question 24

Where are Merkel receptors located?

Answer 24

Tip of the epidermal ridges

Question 25

Where are Meissner cells located?

Answer 25

Just near the skin surface (epidermis)

Question 26

Where are Pacinian cells located?

Answer 26

Deep in the dermis and hypodermis

Question 27

Where are Ruffini cells located?

Answer 27

In the upper dermis

Question 28

A large receptive field equates to … Sensitivity

Answer 28

Decreased

Question 29

How is the size of the receptive field tested for?

Answer 29

Two point discrimination threshold test.

Calipers on skin
Slowly move them further apart
Record distance between calipers when the subject can distinguish between the points

Question 30

Which areas of the body have large receptive fields, and which ones small?

Answer 30

Small: nose, lip, fingers

Large: thigh, calf, shoulder, upper arms

Question 31

Explain the differences in the brain mapping between lactating and non lactating rats

Answer 31

Lactating rats will have a much larger Ventrum

Non lactating rats have a smaller amount of space taken up by this area

Question 32

What are dermatomes?

Answer 32

This is the area innervated by sensory neurons from a single dorsal root ganglion

Question 33

After S1, where do the projections go?

Answer 33

• S2

- Parietal areas

Question 34

Where does S2 then lead to?

Answer 34

Hippocampus and amygdala

The memory and affect of touch

Question 35

Where do the parietal areas then lead to?

Answer 35

The motor and pre motor areas

We perform motor planning; deciding what we want to do, in response to sensory information

Question 36

Describe the functionally distinct columns in the primary somatosensory cortex

Answer 36

There are columns within each area (1,2,3a,3b) that receive information about distinct areas, such as digits and hand pads