THE SPINAL CORD

The spinal cord performs two important functions in the animals body.

  1. One of these is that, it acts as a connecting link between the brain and most of the body parts

  2. The second one is that, it controls the spinal reflex action.


A reflex is a predictable, involuntary feedback to a stimulus.

Reflexes control the movement of both voluntary and involuntary limbs. Many functions of organs also depends on this link. The spinal cord is a segment of central nervous system. It elongate from the brain to the tail.

It has following parts:

1. Neural canal


It is present in the mid. region (center) of the spinal cord. This canal carry cerebrospinal fluid.

2. Grey matter


The grey matter contains cell bodies ( prominent nucleus) and dendrites of neurons. It controls reflexes in the spinal cord.

3. Nerve roots


The ventral and dorsal roots of the spinal nerves are present on the spinal cord. These roots contains main motor, sensory fibers ( axons or dendrites).

4. White matter


Axons of the spinal cord are covered by the whitish myelin sheath. Therefore, it's called white matter.

5. Meninges


There are three layers of protective membranes are called meninges. They protects the spinal cord. The contains layers that covers the brain.

These layers are

(a) Dura mater


The outermost layer is called dura mater. It is a tough (hard or rigid) and fibrous membrane.

(b) Arachnoids


It's called a middle layer. It is delicate. It is connected to the innermost layer.

(c) Pia mater


The innermost covering is called pia mater. Its carries small blood vessels. It provide nourishment to the spinal cord.


Spinal Nerves


The number of spinal nerves is directly related to the numbers of segments in the trunk & tail of a vertebrate. A frog has a stronger thin legs for swimming or jumping. It has a reduced trunk. It has no tail in the adults.  It has only twenty spinal nerves. But snake has long trunk and tail. It has several hundred pairs of spinal nerve.

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