The sensory system

Question 1

Which modalities are carried by the dorsal columns?

Answer 1

Proprioception
2 point discrimination
Vibration

Question 2

Which sensory modalities are carried by the spinothalamic tract?

Answer 2

Temperature
Pain
Pressure

Question 3

Does strong receptor activation from a strong sensory stimulus give high frequency or low frequency action potentials?

Answer 3

High frequency

Question 4

What is a rapidly adapting receptor?

Answer 4

They initially fire off a very high frequency of action potential that then slows down. Eg sitting down in a chair- at first you notice the chair pressing into your bum but then you become less aware of it.

Question 5

What are slow adapting receptors? What is an example?

Answer 5

The frequency of action potentials doesnt reallt change so the stimulus is felt the same all the time.

Eg nociceptors (for pain)

Question 6

If the region of skin supplied by a single neurone is small then how will this affect the sensory acuity ?

Answer 6

Sensory acuity will be very good as you will be able to tell one point from the other quite easily.

Question 7

Where does the cell body of 1st order neurones lie?

Answer 7

In the dorsal root ganglion

Question 8

Where does the cell body of 2nd order neurones lie?

Answer 8

In the dorsal horn/ medulla

Question 9

Where does the cell body of tertiary order neurones lie?

Answer 9

In the thalamus.

Question 10

In the dorsal column pathway where can fibres from the lower body be found?

Answer 10

Medially

Question 11

In the spinothalamic tract where can the sensory fibres from the lower body be found?

Answer 11

Laterally

Question 12

In the dorsal column medial lemniscus pathway where do 1st order neurones from the arms synapse with 2nd order neurones?

Answer 12

In the cuneate nucleus which is found in the floor of the 4th ventricle.

Question 13

In the dorsal column medial lemniscus pathway where do 1st order neurones from the legs synapse with 2nd order neurones?

Answer 13

In the gracile nucleus which lies in the floor of the 4th ventricle.

Question 14

Where does the medial lemniscus lie?

Answer 14

It is the pathway of sensory neurones from the dorsal columns travelling to the thalamus through the midbrain.

Question 15

Where do fibres from the dorsal columns decussate?

Answer 15

In the medulla

Question 16

Where do 2nd order neurones synapse with 3rd order neurones?

Answer 16

In the thalamus

Question 17

Where in the primary sensory cortex located?

Answer 17

In the post central gryus which is a part of the parietal lobe.

Question 18

Which parts of the body are represented most laterally on the sensory homunculus?

Answer 18

The face. The legs are most medial and the hand and arm lie inbetween.

Question 19

Isolated lesions of the dorsal column pathway will lead to signs contralaterally or ipsilaterally below the lesion?

Answer 19

Ipsilaterally

Question 20

Where do 1st order neurones synapse with 2nd order neurones in the spinothalamic tract?

Answer 20

In the dorsal horn

Question 21

What is the pathway of the 2nd order neurones in the spinothalamic tract?

Answer 21

They cross the ventral white commisure and then ascend up the spinal cord and synapse with 3rd order neurones in the thalamus.

Question 22

Isolated lesions of spinothalamic tract in the cord will lead to signs contralaterally or ipsilaterally below the lesion?

Answer 22

Contralaterally.

Question 23

Which fibres carry impulses from mechanoreceptors in the skin?

Answer 23

A fibres

Question 24

Which fibres carry pain from the skin to the spinal cord?

Answer 24

C fibres

Question 25

Why does activation of mechanoreceptors alleviate pain?

Answer 25

It excites inhibitory enkephalinergic interneurones in the cord which inhibit C fibre transmission.