Central Nervous System
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The central nervous system (CNS) consists of the brain and spinal cord. The principal roles of the CNS are to integrate and coordinate incoming and outgoing neural signals and to carry out higher mental functions, such as thinking and learning.
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A nucleus is a collection of nerve cell bodies in the CNS. A bundle of nerve fibers (axons) within the CNS connecting neighboring or distant nuclei of the cerebral cortex is a tract.
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The brain and spinal cord are composed of gray matter and white matter.
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The nerve cell bodies lie within and constitute the gray matter; the interconnecting fiber tract systems form the white matter.
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In transverse sections of the spinal cord, the gray matter appears roughly as an H-shaped area embedded in a matrix of white matter.
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The struts (supports) of the H are horns; hence, there are right and left posterior (dorsal) and anterior (ventral) gray horns.
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Three membranous layers—pia mater, arachnoid mater, and dura mater— collectively constitute the meninges.
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The meninges and the cerebrospinal fluid (CSF) surround and protect the CNS.
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The brain and spinal cord are intimately covered on their outer surface by the innermost meningeal layer, a delicate, transparent covering, the pia mater.
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The CSF is located between the pia mater and the arachnoid mater. External to the pia mater and arachnoid mater is the thick, tough dura mater.
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The dura mater of the brain is intimately related to the internal aspect of the bone of the surrounding neurocranium (braincase); the dura mater of the spinal cord is separated from the surrounding bone of the vertebral column by a fat-filled epidural space.