It is the long cylindrical part of CNS. It is present in the neural canal of the vertebral column. It is the center of all reflex actions. Grey matter, which has a pinkish-grey color in the living brain, contains the cell bodies, dendrites and axon terminals of neurons, so it is where all synapses are. White matter is made of axons connecting different parts of grey matter to each other. In spinal cord grey matter is inside and white matter is outside. Major functions of spinal cord are:
It is defined as an involuntary action performed by muscles under the direction of the spinal cord in response to the stimulus. The best example of the reflex action is pulling of hand when we touch hot or very cold objects and contraction of the pupil when the light is shown in the eye.
The path which is followed by impulses during the reflex action is called the reflex arc. It consists of an afferent (or sensory) nerve, usually one or more interneurons within the central nervous system, and an efferent (motor, secretory, or secretomotor) nerve.
When a pin is suddenly pricked in foot, the stimulus is transferred by the following ways:
i. Receptor: tip of nerve of skin of foot.
ii. Sensory nerve: to carry the message from receptor to spinal cord.
iii. Intermediate nerve: to send the stimulus from top to bottom of the spinal cord.
iv. Motor nerve: to carry the stimulus from spinal cord to muscle.
v. Effector: to receive the stimulus in the muscle. Thus the pin is suddenly pricked in the foot, the stimulus transfers to the spinal cord through the nerves of skin. After that the spinal cord sends message to muscle of leg to withdraw the leg immediately.
A man jumped with fear because of reflex action when his bare foot touched the cold object on the ground. During this, the nerves in the skin transmitted the information to spinal cord through sensory nerve, from when an instruction is sent to the muscle through motor nerve.
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