Biology

The Spinal Cord

31 pairs of spinal nerves arise along the spinal cord. These are "mixed" nerves because each contain both sensory and motor axons. However, within the spinal column

• all the sensory axons pass into the dorsal root ganglion where their cell bodies are located and then on into the spinal cord itself.
• all the motor axons pass into the ventral roots before uniting with the sensory axons to form the mixed nerves.

 The spinal cord carries out two main functions:

• It connects a large part of the peripheral nervous system to the brain. Information (nerve impulses) reaching the spinal cord through sensory neurons are transmitted up into the brain. Signals arising in the motor areas of the brain travel back down the cord and leave in the motor neurons.
• The spinal cord also acts as a minor coordinating center responsible for some simple reflexes like the withdrawal reflex.

The interneurons carrying impulses to and from specific receptors and effectors are grouped together in spinal tracts.

Crossing Over of the Spinal Tracts

Impulses reaching the spinal cord from the left side of the body eventually pass over to tracts running up to the right side of the brain and vice versa. In some cases this crossing over occurs as soon as the impulses enter the cord. In other cases, it does not take place until the tracts enter the brain itself.

edit @ 19 Jan 2009 21:25:13 by Dhachdanai