The spinal cord is a white, soft and cord (rope) like substance running through the backbone. The internal structure of the spinal cord is much simpler and more uniform throughout its various parts than that of the brain. No matter where it is sectioned, it gives the same general appearance. The interior of the spinal cord looks gray because it is filled with neurons without having myelin sheath in their axons (unmyelinated axons).
In other words, the interior of the spinal cord is filled with some gray matter. Interestingly, the gray matter is so distributed that the interior looks almost as a butterfly whose essential form is the English capital letter "H". The outer of the spinal cord looks white as it is filled with some myelinated axons, in other words, the outer of the spinal cord is filled with some white matter. The chief function of the gray part of the spinal cord is integrative in nature, whereas the chief function of the white part is communicative in nature.
There are thirty-one pairs of peripheral spinal nerves connected to the spinal cord. The sensory spinal nerves are connected to the cord at the back or dorsal part. In fact, there are two (left and right) dorsal roots through which sensory information enter into the spinal cord. The motor spinal nerves are connected to the cord at the front or ventral part. There are two (left and right) ventral roots through which motor information go out of the spinal cord. The sensory information go towards the brain in the two dorsal columns of neurons and motor information go downward of the spinal cord in the two ventral columns of neurons. There are also two sets of lateral (side) columns of neurons whose function is both sensory and motor in nature.
The spinal cord has two major functions: (a) carrying information, and (b) coordinating reflexes.
First, it receives sensory information through the afferent nerves from the sensory receptors throughout the body, and sends them to the brain. It also carries information from the brain through efferent fibers to the muscles and glands. Second, it coordinates reflexes without the involvement of the brain, thus, the spinal cord has both communicative and integrative functions.
Excepting the above sensory and motor functions, spinal cord controls some other important functions also. These are called as reflex actions. In order to control reflex actions, the spinal cord does not take any assistance from the brain. Reflex actions are automatic, unlearned, involuntary, and inborn responses. Therefore, these actions are sudden in nature and have a purpose of protecting the individual or his organs from sudden danger.
For Example if someone throws a stone towards you; suddenly you move your body to avoid the incoming danger of being hurt. The path through which reflex action is conducted is known as "reflex arc", which involves (a) receptor (b) afferent neuron (c) spinal cord (d) inter- neuron (e) efferent neuron (f) muscles or gland.