Spinal cord structure and functions

Spinal Cord 
Structure 
The spinal cord extends from the base of the brain through the foramen magnum of the skull into the vertebral canal formed by the vertebrae. The spinal cord terminates be­tween the first and second lumbar vertebrae.
A cross section of the spinal cord reveals the central canal and distinct white and gray areas. The gray matter is centrally located and shaped like the letter H. It is gray because it contains cell bodies and short, unmyeli­nated fibers. The two posterior projections of the H are the dorsal (posterior) horns, and the two anterior projections of the H are the ventral ( anterior) horns. Sensory neurons enter the spinal cord through the dorsal roots; motor neu­rons exit the spinal cord through the ventral roots. The dorsal and ventral roots join to form the spinal nerves.
The white matter fills in the areas around the gray mat­ter. The white matter contains bundles of myelinated fibers within tracts that form columns. Ascending tracts take nerve impulses up through the spinal cord and the brain, and descending tracts take nerve impulses down through the brain and the spinal cord.
Functions 
The spinal cord has two main functions. First, it is the cen­ter for thousands of reflex arcs. A nerve impulse generated by a receptor passes along a sen­sory neuron to an interneuron in the spinal cord. The in­terneuron passes the nerve impulse to a motor neuron that brings about a reflex. The tracts cross over in the medulla, and therefore, the right side of the brain controls the left side of the body, and vice versa. Reflexes allow quick response to a stimulus bocause they do not require conscious thought.
The spinal cord's second function is that it provides a means of communication between the brain and the pe­ripheral nerves that leave the cord. Sensory impulses travel up the cord to the brain in ascending tracts, and motor im­pulses travel down the cord from the brain in descending tracts. Sensory impulses that reach the cerebrum result in sensation, and motor impulses that travel from the cere­brum allow us to voluntarily control our limbs and other body parts. If the spinal cord is injured, we suffer a loss of sensation and a loss of voluntary control-that is, we suf­fer a paralysis.
The spinal cord extends from the base of the brain into the vertebral canal formed by the vertebrae. It is a center for reflex action and allows communication between the brain and the peripheral nerves leaving the spinal cord.