The Central Nervous System - The Spinal Cord
The spinal cord attaches to the brainstem providing a critical pathway for the flow of information from the skin, joints and muscles to the brain, and vice versa.
In cross sections of the spinal cord there is a H-shaped center of gray matter. The ventral (anterior) and dorsal (posterior) horns describes the sections of this core. The spinal cord core contains primarily three types of neurons: motor neurons, sensory neurons, and interneurons. The motor neurons (efferent) run through the ventral horn to supply skeletal muscle. Sensory (afferent) nerve fibers enter the spinal cord from the periphery by way of the dorsal horn. The white matter, containing the ascending and descending nerve tracts, surround the gray matter within the cord.
As previously mentioned, information going towards the brain is sensory information, such as touch, taste and also pain. So if you are working out and pull a muscle or drop a 45 lb plate on your small toe the nerves will travel up to the brain via afferent nerve fibers of the spinal and the information will be integrated there. Here the response will be traveling via afferent nerve fibers to produce a motor response.
Ascending Nerve Tracts
Ascending nerve tracts in the spinal cord send sensory information coming from peripheral receptors to the brain for processing. There are three neurons that typically make up sensory pathway.
1) The dorsal root ganglion contains the cell body of the first neuron whose axon relays information into the spinal cord.
2) The cell body of the second neuron lies within the spinal cord itself; its axon passes up the spinal cord to the thalamus.
3) The thalamus contains the third neuron's cell body. The axon of the third neuron passes up to the central command center of the cerebral cortex
Descending Nerve Tracts
Axons from the brain move downward through the spinal cord along two major pathways. The lateral or pyramidal tract activates the skeletal muscle (the muscles that you primarily use when working out). The second pathway named ventromedial or extrapyramidal tract, controls posture and muscle tone via the brainstem.
Kurt Kuhn - www.FUSIONBodybuilding.com