Somatosensory Perception

Question 1

Somatosensory stimuli is a ________ pattern

Answer 1

Spatio-temporal

Question 2

Describe the structure and localisation of mechanoreceptors

Answer 2

Mechanoreceptors are basically neurons but instead of dendrites they have mechanoreceptors in the skin (allows regeneration if damaged) This means their cell bodies are necessarily not there. In fact they are localized in a group of cell bodies known as a ganglion, and it is found close to the spinal cord towards the back of the body, therefore it is known as the dorsal root ganglion. The mechanoreceptor then synapses in the spinal cord, within the grey matter

Question 3

Name the three types of mechanoreceptors, and the varying subsets of each (3, 2 and 1, respectively)

Answer 3

Encapsulated receptors (Meissner's, Ruffini, and Pacinian corpuscles)
Receptors with accessory structures (Merkel discs and tactile hairs)
And straight up just free nerve endings

Question 4

What are the two types of adapting mechanoreceptors, and how are they different/

Answer 4

Fast adapting - fire only when immediately grabbing or letting go (do not fire while holding onto something)
Slow adapting - fire as soon as something is held, then slowly fire less and less until a baseline (they do not stop)

The combination of FA and SA on the surface as well as deeper in the skin allow for full somatosensory perception

Question 5

What are the two types of slow adapting mechanoreceptor? What specialized endings do they have? Where are they located? How are they distributed?

What is their spatial resolution? What skin deformation elicits the strongest response? What functions are supported?

Answer 5

SA I, merkel cell, upper dermis, dense (esp in fingertips)
High spatial resolution, indentations, perceiving pattern/texture/shape

SA II, [unknown], dermis, sparse
Low resolution, stretch, perceiving skin stretch and hand conformation

Question 6

What are the two types of fast adapting mechanoreceptor? What specialized endings do they have? Where are they located? How are they distributed?

What is their spatial resolution? What skin deformation elicits the strongest response? What functions are supported?

Answer 6

FAI, Meissner corpuscle, upper dermis, dense (esp in fingertips)
High spatial resolution, motion, low freq vibrations, perceiving slip/grip control

FAII, pacinian corpuscle, lower dermis, sparse, lower dermis
Low resolution, high frequency vibrations, perceiving fine textures through vibrations

Question 7

Which mechanoreceptions are most useful in reading braille?

Answer 7

SAI and FAI (mostly SAI, and others are simply too noisy)

Question 8

Which Mechanoreceptor is used to convey hand conformation (i.e. hand stretching/clenching)

Answer 8

SAII

Question 9

True/False? a cell can have an optimal frequency to vibrate at

Answer 9

True

Question 10

FAII receptors have sensitivity to ____-frequency vibrations, and thus are sensitive to ____ amplitude changes that occur in ___ temporal frequencies

Answer 10

High
Small
High

Eg, feeling fine textures such as hair, or holding a pen/scraping with a knife

Question 11

Which has more somatosensory acuity?

A wet hand or a dry hand

Answer 11

A wet hand

Question 12

How is somatosensory perception mapped on the body?

Answer 12

By dermatomes - areas of skin that is supplied by one spinal nerve (these dermatomes can be mapped)

Question 13

What is proprioception? What is haptic perception? what senses these?

Answer 13

Proprioception: the sense of organization of a person’s body parts
Sensed by spindle nerve fibres in muscle spindles or by tendon organ nerve fibres in golgi tendon organs

Question 14

What are the two ways somatosensation can travel upwards to the brain?

Answer 14

Either by crossing over in the spinal plate and ascending the anterolateral pathway, or by ascending the dorsal column, crosing over into the medial lemniscus, and then entering the brain

Both pathways enter the medial lemniscus, and enter the thalamus which then sends sensation to the postcentral gyrus

Question 15

What is the ontological difference between motor and somatosensory motor maps, and what is the difference in their homunculi?

Answer 15

Motor map shows how much of the motor cortex is mapped to different body parts and how, and the same for somatosensation

Both homunculi have exaggerated hands and mouths (motor has larger hands and thinner body, difference is more exaggerated)

Question 16

What is the concept of a cortical column?

Answer 16

A section of brain cortex that contains neurons mapping the same area for a given depth. Typically, neighboring neurons are related to the initial neuron

eg, a given point is mapped to SA for the second digit of the left hand. Pushing the electrode deeper will stimulate more SAs for the second digit of the left hand, whereas moving the electrode laterally would stimulate other fingers

Question 17

What is the difference between skin sensitivity and skin acuity? Are these necessarily linearly correlated?

Answer 17

Sensitivity: the mean pressure required to trigger stimulus
Acuity: The distance required to discriminate two points

Question 18

What is the most sensitive part of the body? Is it the most acute?

Answer 18

The lips, and no (fingers are more acute)