Sensory pathways: Touch and proprioception

Question 1

What is proprioception?

Answer 1

Awareness of position

Question 2

What type of receptors detect all touch and proprioception?

Answer 2

Mechanoreceptors

Question 3

What receptors detect temperature and pain?

Answer 3

Thermoceptors and nociceptors

Question 4

What is a peritrichial ending?

Answer 4

When a nerve ending is wrapped around a hair

Question 5

What is a pacinian corpuscle?

Answer 5

A pacinian corpuscle is when there is an axonal ending in the middle and it is wrapped around several concentric circles of epithelial cells- this allows the receptor to be very sensitive to vibration

Question 6

What does it mean if a receptor has a high sensitivity

Answer 6

It has a low threshold of activation

Question 7

What is the difference between slow and fast adapting receptors

Answer 7

Slow adapting- continue to fire impulses for as long as the impulse is present
Fast adapting- Tend to fire at the start of the stimulus and when it is switched off but they fade in the middle

Question 8

What are the two methods of classifying axons?

Answer 8

One by anatomists is based on diameter of axons and one by physiologists is based on conduction velocity
Anatomical is labelled using letters and physiological is labelled using roman numerals

Question 9

Why is there an overlap between the two classifications?

Answer 9

As axon diameter increases, conduction velocity increases

Question 10

What are sensory neurones the convey touch and proprioception normally like?

Answer 10

Large and fast

Question 11

What is a receptive field?

Answer 11

Area of skin that is innervated by one axon

Question 12

In terms of receptive fields, what increases sensitivity?

Answer 12

Lots of innervation with small receptive fields

Question 13

How do the neurones code for the intensity of a stimulus?

Answer 13

It is coded for by the frequency of action potentials going down the sensory fibres, it is nothing to do with amplitude

Question 14

What route does sensory information in the leg take?

Answer 14

It comes in from the leg via the primary sensory neurone. As the axon goes into the dorsal horn, it passes straight into the white matter at the back of the spinal cord- dorsal columns

Question 15

What is the arrangement of the dorsal columns

Answer 15

Fibres coming from the lowest parts will be the most medial and from the highest will be the most lateral

Question 16

What are the two tracts of the axons in the dorsal column?

Answer 16

Cuneate fasciciulus- Waist up

Gracile fasciciulus- Waist down

Question 17

What is a fasciculus?

Answer 17

Bundle of axons

Question 18

What happens when the fasciculi reach the medulla?

Answer 18

In the medulla, the neurones synapse with two nuclei, cuneate and gracile, which then sends axons across the midline (at the decussation). After crossing the midline, the fibres head upwards and form a new pathway called the medial leminiscus

Question 19

What happens to the medial leminiscus after this?

Answer 19

It maintains the same position until it reaches the thalamus where the axons relay with the third neurone in the chain- one of the thalamic nuclei: ventral postern-lateral nucleus. Through this, information is passed to the primary somatosensory cortex

Question 20

What is the main sensory nerve of the face?

Answer 20

Trigeminal (CN V)

Question 21

What is the route of sensory information from the face?

Answer 21

The trigeminal comes into the middle of the pons where it synapses with a second order neurone in the trigeminal cranial nucleus. The axon of this second cell crosses the midline and joins the medial end of the medial leminiscus

Question 22

How does the dorsal column nuclei improve resolution of localising the stimuli?

Answer 22

Lateral inhibition- It takes place in the cuneate and gracile nuclei. Each axon doesn’t just activate the next nuclei but it also has lateral branches that are inhibitory to neighbouring axons.

Question 23

What is the somatosensory cortex important for?

Answer 23

Analysing and using sensory information

Question 24

What is the posterior parietal cortex involved in?

Answer 24

Spatial relationships

Question 25

What happens if there is damage to the sensory pathway?

Answer 25

Information going upto the primary somatosensory cortex will be halted, this will lead to anaesthesia (loss of sensation) or paraesthesia (sensation is there but not normal)

Question 26

What is peripheral neuropathy?

Answer 26

Disease of the peripheral nerves that tends start distally in hands and feet that progresses proximally

Question 27

What is the most common cause of peripheral neuropathy?

Answer 27

Diabetes mellitus