Nervous system: The somatosensory system

Question 1

Broadly speaking what is the somatosensory system?

Answer 1

Carries conscious sensation from the body wall - the skin, the lining of the pharynx and oral cavity, anal mucosa and parietal pleura and peritoneum

Question 2

What are the first, second and third order neurones?

Answer 2

First order neurone: the primary sensory neurone, enters the CNS and synapses onto 2nd.
Second order neurone: located entirely in the CNS, crosses the midline (important), projects onto 3rd
Third order neurone: Cell body found in the thalamus, project up to the cerebral cortex

Question 3

What is the function of the dorsal column medial lemniscus system?

Answer 3

• fine touch
• 2 point discrimination
• vibration sense

Question 4

What is the function of the spinothalamic system?

Answer 4

• crude touch
• pain
• temperature sensation

Question 5

What is the difference between phasic and tonic receptors?

Answer 5

Phasic receptors rapidly adapt therefore the rate of firing decreases for non-important stimuli eg mechanoreceptors in the skin stop sensing the clothes on your skin.

Tonic recepters fire at a constant rate

Question 6

Describe lateral inhibition

Answer 6

If a sharp object touches the skin the central neurone will be maximally activated and adjacent neurones will also be activated but to a lesser extent.
The central neurone will synapse onto inhibitory interneurones which will inhibit the second degree neurones of the adjacent neurones.

Question 7

What is a tract?

Answer 7

A white mater tract which runs one way between 2 grey tracts

Question 8

Why is the hand vulnerable to sensory changes in brain lesions affecting the cerebral cortex?

Answer 8

The hand covers the largest portion of the somatosensory cortex

Question 9

What is ‘glove and stocking’ paraesthesia?

Answer 9

Loss of sensation to the hands and feet - cannot be explained by hidjidjiwjdw