Illustrate the structure and functions of brain.

Describe the structure of spinal cord.

How nerve impulses are transferred from one neuron to next neuron?

Classify neurons based on its structure.

Our body contains a large number of cells ‘L’ which are the longest cells in the body. L has long and short branch called as ‘M’ and ‘N’ respectively. There is a gap ‘O’ between two ‘L’ cells, through which nerve pass.
Impulse transfer by release of chemical substance ‘P’.
(i) Name the cells L.
(ii) What are M and N?
(iii) What is the gap O?
(iv) Name the chemical substance P.