The Brain - Homunclui, Language and Speech

Question 1

What is a homunculus?

Answer 1

Drawing of the relationship between the complexity of innervation of different parts of the body and the areas and positions in the cerebral cortex that represent them.

Question 2

What is a sensory homunculus?

Answer 2

• Shows the relative sensitivity of different parts of the body, as represented in the sensory cortex.
• The most sensitive areas of the body are shown with the largest area in the drawing.
• The tounge, lips , fingers and genitals are the most sensitive areas and so they are largest in the sensory homunculus.
• They are the most sensitive because they have the highest density of sense receptors and sensory neurones coming from them. Therefore the areas of the brain that receives their nervous impulses are correspondingly larger.

Question 3

What is the motor homunculus?

Answer 3

• Shows motor control in different parts of the body as represented in the motor cortex.
• It is very similar to the sensory homunculus but areas of the cortex associated with some organs are different.
• The muscles of hands can make fine movments, 43 muscles control facial expressions some of which are fleeting and a large number of motor fibres finely control the contraction and relaxation of the hand and face muscles and so much of the motor cortex relates to them.
• Accordingly, the face and hands have a large representation in the motor homunculus.