Principles of Neuroscience Lecture 8, Touch Flashcards
What are the cells that detect motion on the skin and deeper tissues called?
Mechanoreceptors
Describe the different skin surfaces on the body
Hairy and glaborous. Glaborous is characterised by ridges on the skin
Which two are located in the epidermis?
Meissner and Merkel
Which two are located deeper in the skin?
Pacinian and Ruffini
Which two are quickly adapting?
Meissner and Pacinian
Which two are slowly adapting?
Merkel and Ruffini
Which two are high density, and which two are low density?
High : meissner and Merkel
Low : Ruffini and Pacinian
Which two have big receptive fields, which two small?
Big receptive fields: Pacinian & Ruffini
Small receptive fields: Merkel & Meissner
How does mechanical transduction occur? Outline the pathway
- Touch causes the ion channels on the mechanoreceptors to open.
- Na+ rushes in, depolarising the cell
- If the threshold for action potential is reached, neurotransmitters are released from vesicles onto the primary motor neurons
- This is conducted to the spinal cord etc.
Which ion rushes in?
Sodium
Describe what is meant by slowly and quickly adapting mechanoreceptors
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.
What test demonstrates how receptive fields overlap
The two point discrimination test
Which two areas do touch afferents connect?
Mechanoreceptors and the spinal cord
Describe the axons of touch afferents, and why this is so
They are thick so that there is very quick transmission of action potentials along the axon. They have very thick myelin sheaths
Describe the path from the mechanoreceptor to the brain
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
What is the name of the region in the thalamus through which the neurons travel?
Ventral Posterior complex, comprised of:
Ventral Posterior Medial nucleus
Ventral Posterior Lateral nucleus
Where do the neurons first synapse?
Then?
Medulla (dorsal root columns)
Thalamus (VP complex)
Do the neurons cross over at any point?
In the medulla, the neurons go from being ipsilateral to contralateral
What is S1?
Primary Somatosensory Cortex
Describe the functional and structural organisation of the Primary Somatic Sensory Cortex
4 Brodmann’s areas that contain a full map of the body.
Areas: 1, 2, 3a & 3b
What is meant by Brodmann’s areas?
These are functional areas in the brain, whose neurons are different enough to warrant different names.
In the S1, there are 4
Where does information travel after S1?
Secondary Somatosensory cortex, S2
Parietal areas
Why is the brain plastic?
This gives us the most effective arrangement at a given point in time
We can adapt to a changing environment
Describe four examples of brain plasticity
- Lactation in monkeys
- Amputation of digits
- Anaesthetic of digits
- Functional expansion of area due to repetitive behavioural tasks
Where are Merkel receptors located?
Tip of the epidermal ridges
Where are Meissner cells located?
Just near the skin surface (epidermis)
Where are Pacinian cells located?
Deep in the dermis and hypodermis
Where are Ruffini cells located?
In the upper dermis
A large receptive field equates to … Sensitivity
Decreased
How is the size of the receptive field tested for?
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
Which areas of the body have large receptive fields, and which ones small?
Small: nose, lip, fingers
Large: thigh, calf, shoulder, upper arms
Explain the differences in the brain mapping between lactating and non lactating rats
Lactating rats will have a much larger Ventrum
Non lactating rats have a smaller amount of space taken up by this area
What are dermatomes?
This is the area innervated by sensory neurons from a single dorsal root ganglion
After S1, where do the projections go?
- S2
- Parietal areas
Where does S2 then lead to?
Hippocampus and amygdala
The memory and affect of touch
Where do the parietal areas then lead to?
The motor and pre motor areas
We perform motor planning; deciding what we want to do, in response to sensory information
Describe the functionally distinct columns in the primary somatosensory cortex
There are columns within each area (1,2,3a,3b) that receive information about distinct areas, such as digits and hand pads
