The nervous system along with the endocrine system serves to integrate and coordinate the various body components. The nerve cell or neuron is the basic unit of the nervous system. In a typical neuron, the cytoplasm is drawn out into short processes called dendrites and a single long process called an axon. Among the more complicated multicellular animals there is a marked tendency for the cell bodies of neurons to be grouped into masses known as ganglia.
Ganglia tend to be lined up along one or more central nerve cords.
The spinal nerves are best studied in the frog because they are exposed on the dorsal wall of the body cavity, instead of being deep in the flesh as in the rat. The frog has 10 pairs of spinal nerves, one pair corresponding to each of its 10 vertebrae. Examine the frog and observe the spinal nerves, whitish, thread-like structures that emerge from between the vertebrae and lie along the dorsal wall of the body cavity. In the frog, it will go the chin region. The brachial nerve, running to the arm Spinal Nerve III Forms a connection with I and II before it passes laterally to the body wall.