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added spinal cord
Neurons and [[axons]] are distributed non-uniformly through the CNS. The [[soma|cell body]] and [[dendrites]] of the neurons cluster in [[cortical]] regions which are essentially flattened sheets of cells called [[laminae]]. These areas are located primarily on the cerebral hemispheres or in areas beneath the surface of all the sub-divisions of the CNS called [[nuclei]]. Axons are then distributed through out the system in regions called tracts. In live tissue the regions populated by cell bodies and dendrites appear gray while the tract's of axons appear white. These areas are called [[gray matter]] and [[white matter]] respectively.
Neurons and [[axons]] are distributed non-uniformly through the CNS. The [[soma|cell body]] and [[dendrites]] of the neurons cluster in [[cortical]] regions which are essentially flattened sheets of cells called [[laminae]]. These areas are located primarily on the cerebral hemispheres or in areas beneath the surface of all the sub-divisions of the CNS called [[nuclei]]. Axons are then distributed through out the system in regions called tracts. In live tissue the regions populated by cell bodies and dendrites appear gray while the tract's of axons appear white. These areas are called [[gray matter]] and [[white matter]] respectively.
==Spinal cord==
The spinal cord is the primary tract for sensory information coming in from the periphery to the brain and voluntary muscle control signals moving from the brain to the periphery. Information traveling to the brain moves through a series of axons called the [[afferent]] nerves and information traveling to the periphery move through axons called the [[efferent]] nerves. The spinal cord can also help processes and integrate sensory information before passing it on. In a few cases it can receive input and coordinate behavioral responses without ever recruiting the brain, these behaviors are commonly called [[reflexes]].
The spinal cord is segmental with the overall organization being modular, all the segments are the same basic structure repeated in tandem. Each segment has a pair of nerves, the [[dorsal]] root and the [[ventral]] root. The dorsal root contains only the sensory, afferent axons. The ventral root contains the motor, or efferent axons.
==The brain stem and cerebellum==
==The brain stem and cerebellum==