The Somatosensory System

Question 1

What is generator potential? (a.k.a. receptor potential)

Answer 1

A stationary depolarization of a receptor that occurs in response to a stimulus and is graded according to stimulus intensity. It results in an action potential when the appropriate threshold is reached

Question 2

Which structure in the muscle is responsible for sensation?

Answer 2

Muscle Spindle (responsive to stretch)

Question 3

Which kind of receptor mediates touch vibration and pressure?

Answer 3

Low threshold mechanoreceptor

Question 4

Which kind of receptor mediates cold, indifferent, warm and hot sensation?

Answer 4

Low threshold thermoreceptors

Question 5

Which kind of receptors respond to high intensity mechanical stimuli? e.g. hammer to the thumb

Answer 5

High threshold mechanoreceptors (a.k.a. mechanical nociceptors)

Question 6

Which kind of receptors respond to extremes of temperature?

Answer 6

High threshold thermoreceptors (a.k.a. thermal nociceptors)

Question 7

Which kind of receptors respond to inflammatory substances in tissues? e.g. prostaglandins, histamine etc.

Answer 7

Chemical nociceptors

Question 8

If a receptor responds to more than one type of noxious stimuli, it is called ______?

Answer 8

A polymodal nociceptor

Question 9

If a neurone fires constantly throughout a constant stimulus, it could be described as ______?

Answer 9

Slowly-adapting

Question 10

If a neurone becomes less sensitive over time, or alters its firing in response to a change in stimulus strength, it could be described as ______?

Answer 10

Rapidly-adapting

Question 11

Classifications of axons from the skin, in decreasing order of diameter, degree of myelination and conduction velocity.

Answer 11

Aα, Aβ, Aδ, C

Question 12

Which axon classification is responsible for proprioception of skeletal muscle?

Answer 12

Aα

Question 13

Which axon classification is responsible for mechanoreception in the skin?

Answer 13

Aβ

Question 14

Which axon classification is responsible for temperature and pain?

Answer 14

Aδ

Question 15

Which axon classification is responsible for temperature, pain and itch?

Answer 15

C

Question 16

What is the receptive field of a neurone?

Answer 16

The region that when stimulated with an adequate stimulus causes a response in that neurone. The size of each RF differs greatly across the body.

Question 17

How is the grey matter in the spinal cord divided?

Answer 17

Dorsal (posterior) and Ventral (anterior) horns + 10 laminae of Rexed

Question 18

What does the Dorsal Column Medial Leminscal Pathway (DCML) convey?

Answer 18

Touch, pressure, vibration and proprioception (Aα + Aβ)

Question 19

What does the Spinothalamic Tract (STT) convey?

Answer 19

Pain, temperature, crude touch, itch (Aδ + C)

Question 20

Where do fibres decussate (cross over) in the DCLM?

Answer 20

All fibres travel ipsilaterally and cross together in the brainstem

Question 21

Where do fibres decussate (cross over) in the STT?

Answer 21

These fibres each cross independently, synapsing shortly after entering the spinal cord, then travel contralaterally.

Question 22

What are the 2 subsections of the dorsal column?

Answer 22

Fasciulus Gracilis (medial) and Fasiculus Cuneatus (lateral)

Question 23

What travels in the Fasiculus Gracilis?

Answer 23

Sensory input from below T6

Question 24

What travels in the Fasiculus Cuneatus?

Answer 24

Sensory input from above T6

Question 25

What is lateral inhibition?

Answer 25

The capacity of an excited neuron to reduce the activity of its neighbours. Lateral inhibition disables the spreading of action potentials from excited neurons to neighboring neurons in the lateral direction. This creates a contrast in stimulation that allows increased sensory perception.

Question 26

How does somatic information from the anterior head reach the brain?

Answer 26

The Trigeminal Nerve (CN V)

Question 27

Where is the soma of the trigeminal nerve located?

Answer 27

Trigeminal Sensory Ganglion

Question 28

Where is the somatosensory cortex located?

Answer 28

The post-central gyrus of the parietal cortex, immediately posterior to the central sulcus.

Question 29

The somatosensory cortex can be divided functional areas known as _______?

Answer 29

Brodmann Areas (BA)

Question 30

What is the input to BA 3a?

Answer 30

Muscle spindles (proprioception) - body position

Question 31

What is the input to BA 3b?

Answer 31

Cutaneous mechanoreceptors + BA 3a (touch)

Question 32

What is the input to BA 1?

Answer 32

Cutaneous mechanoreceptors + BA 3b (texture discrimination)

Question 33

What is the input to BA 2?

Answer 33

Joint afferents, Golgi tendon organs, BA 3a, BA 3b

Question 34

What happens to the area responsible for sensory interpretation if a corresponding body part is lost?

Answer 34

The area int he cortex becomes responsive to the input from the area around the site of loss. This can cause phantom limbs.

Question 35

What happens to the area responsible for sensory interpretation if input from the corresponding body part is increased?

Answer 35

The cortical representation of that area, over months, increases, relative that of inputs generating less activity

Question 36

What is the function of the posterior cortex?

Answer 36

It receives information from cortical areas (Brodmann areas, visual, auditory) and sub-cortical areas. it deciphers the deeper meaning.