Nervous system The
nervous system is the system of
neurons, or nerve cells that relay electrical signals through the brain and body. A nerve cell receives signals from other nerve cells through tree-branch-like extensions called
dendrites and passes signals through a long extension called an
axon (or nerve fiber).
Synapses are places where one cell's axon passes information to another cell's
dendrite by sending chemicals called
neurotransmitters across a small gap called a
synaptic cleft. Synapses occur in various locations, including
ganglia (singular: ganglion), which are masses of nerve cell bodies. Preganglionic nerve cells in the
sympathetic nervous system (all of which come from the lateral grey column), use the neurotransmitter
acetylcholine, while postganglionic sympathetic nerve cells use
norepinephrine.
Sympathetic nervous system The
nervous system is divided into the
central nervous system (brain and spinal cord) and the
peripheral nervous system (everything else). The peripheral nervous system is divided into the
somatic nervous system (voluntary processes) and the
autonomic nervous system (involuntary processes). The autonomic nervous system is divided into the
parasympathetic nervous system (normal functioning) and the
sympathetic nervous system (emergency functioning). The lateral grey column mediates the functions of the sympathetic nervous system.
Spinal cord The
spinal cord is divided into 31 segments, located between the
vertebrae. Each segment is defined by a
posterior root entering it and an
anterior root exiting it. Each of these roots is the end of a spinal nerve connecting the spinal cord to the body. The
vertebral column is divided into four groups of vertebrae: (from top to bottom)
cervical,
thoracic,
lumbar, and
sacral. ==Structure==