Ten pairs of nerves coming out from the brain of the toad extend up to the peri. pheral region of the body. These nerves are called cranial nerves. Some of these nerves conduct stimuli from outside the body to the inner side, some carry directives to some definite organs from inner side of the body. Again some carry out both the orders and the stimuli.
According to the nature of work the peripheral nerves can be divided into three divisions, such as Sensory nerves, Motor nerves and Mixed nerves.
A. Sensory nerves: The nerves which carry stimuli from the peripheral organs of the body to the central nervous system are called sensory nerves. For example, the optic nerve of the eye, the olfactory nerve of the nasal aperture and auditory nerves of the internal ear.
The cranial nerves of toad originating from definite locations of the brain come out through the apertures of the skull and communicate with the various parts of the head. The origin, passage, distribution and functions of the ten pairs of nerves are given in the table.
Spinal cord: Spinal cord is the extension of medulla oblongata through theneural canal of vertebrae it extends up to the urostyle. Like the brain, the spinal cord is also covered by meninges. Towards the inner side of the spinal-cord remains the grey matter and towards the outer side there is white matter. From the spinal cord of toad comes out ten pairs of nerves.
1. It contains the nerves originating from the spinal cord and exchange information and directions of the brain.
2. It assist to perform instant work.