1. Central Neural System and Peripheral Neural System:
The CNS includes the brain and the spinal cord and is the site of information processing and control. The PNS comprises of all the nerves of the body associated with the CNS (brain and spinal cord).
2. Resting Potential and Action Potential:
The electrical difference across the resting plasma membrane is called as the resting potential. When a stimulus is applied at a site on the polarised membrane, the membrane at the site becomes freely permeable to Na++.
The electrical potential difference across the plasma membrane at the site of stimulus is called the action potential, which is in fact termed as a nerve impulse.
3. Choroid and Retina.
The middle layer, choroid, contains many blood vessels and looks bluish in colour. The choroid layer is thin over the posterior two-third of the eye ball, but it becomes thick in the anterior part to form the ciliary body.
The inner layer is the retina and it contains three layers of cells – from inside to outside – ganglion cells, bipolar cells and photoreceptor cells.
