The diagram given below is an external view of the human brain. Study the same and answer the questions that follow: The diagram given below is an external view of the human brain. Study the same and answer the questions that follow:
What are the structural and functional units of the brain? How are the parts of these units arranged in A and C?
Topic: Neurons and the arrangement of grey and white matter
Answer
The structural and functional units are the NEURONS (nerve cells).
In A (the CEREBRUM): the CYTONS lie OUTSIDE, forming the outer GREY matter, and the AXONS lie INSIDE, forming the inner WHITE matter.
In C (the SPINAL CORD): the arrangement is REVERSED — the AXONS lie OUTSIDE (outer white matter) and the CYTONS INSIDE (inner grey matter).
Answer all three parts: the UNIT, and the arrangement in EACH of the two structures. The whole question turns on the REVERSAL, so make the contrast explicit.
Grey matter is made of CYTONS (cell bodies); white matter of AXONS, which look white because of their myelin sheaths.
WHY THE BRAIN IS BUILT ONE WAY: putting the cell bodies on the SURFACE allows the cerebrum to be deeply FOLDED, greatly increasing the area available for them within a skull of fixed size. More cell bodies means greater capacity for thought and memory.
WHY THE SPINAL CORD IS THE OPPOSITE: its main job is to CONDUCT impulses up and down, and the long myelinated axons that do so run lengthwise on the outside, with the cell bodies handling reflexes protected in the centre. In section that inner grey matter is shaped like a BUTTERFLY or the letter H.