(3.1) Somatic Sensation

Question 1

Over what parts of the body can touch stimuli be most accurately localised and why?

Answer 1

Fingertips

• High receptor density
• Large receptive fields

Question 2

Why are you not continuously aware of the touch of your clothing as you sit still?

Answer 2

Adaptation of touch receptors

Question 3

What is meant by a topographical representation?

Answer 3

• A topographical representation suggests that each region of the somatosensory cortex receives
  an input from a specific part of the body

Question 4

Explain why following a superficial burn sensation may be retained, but is lost with a full thickness burn?

Answer 4

• Following a superficial burns the cutaneous receptors can recover
• With a full thickness burn the skin is destroyed and replaced by scar tissue
• The scar is invaded by pain fibres but has no other sensation.

Question 5

Why do sensory connections from the hand occupy a larger area of the cortex than those from the much larger area of the thigh?

Answer 5

• The area of the somatosensory cortex reflects the richness of the sensory innervation
• Hand has an especially large number of cutaneous sensory receptors and so a large representation on the cerebral cortex.

Question 6

On a diagram, outline the somatotopic organisation of

• lower limbs
• upper limbs
• face
• central body

Answer 6

https://www.google.co.uk/search?q=somatotopic+organisation&espv=2&biw=1200&bih=717&source=lnms&tbm=isch&sa=X&ved=0CAYQ_AUoAWoVChMIsNa89aa4yAIVwTsUCh0xYQiq#imgrc=cw5w_erbsnlaUM%3A

• lower limbs: medial dorsal
• upper limbs: lateral dorsal
• face: medial lateral
• central body: lateral ventral

Question 7

Suggest four types of skin receptors and state what modality they detect.

Answer 7

• Riffini Corpuscle: temperature
• Meissner’s Corpuscle: vibration & light touch
• Pacinian Corpuscle: vibration & pressure
• Merkel Discs: vibration & pressure & texture

Question 8

Suggest two types of proprinception receptors and state what modality they detect.

Answer 8

• Muscle spindle: length of muscle

- Golgi tendon:tension in tendon

Question 9

What affect does divergence have on acuity of touch?

Answer 9

• No effects, stimuli amplified

Question 10

What affect does convergence have on acuity of touch?

Answer 10

Decrease

Question 11

In terms of touch acuity, what do we mean when we talk about lateral inhibition?

Answer 11

The 2nd order neurones whose receptor fields are periphery to the stimulus are inhibited by interneurones

Question 12

What are the 3 main types of Nociceptors?

Answer 12

• Mechanical
• Thermal
• Polumodal (chemicals, toxins)

Question 13

Why does shingles cause intense pains in affected areas?

Answer 13

• Varicella zoster virus reactivates after chickenpox
• The virus increases sensitivity of the Dorsal root ganglion
• Causing burning, tingling sensations