Description
The central nervous system (CNS) refers to the brain and spinal cord. These structures develop from the neuroectoderm, a region of the dorsal midline ectoderm that folds in upon itself to form a neural tube. The spinal cord retains a tube-like structure, while the brain undergoes massive proliferation, expanding and folding to form the cerebrum and brainstem. The olfactory bulb and tract, in addition to the retina and optic nerve are embryologically derived from the CNS and are thus parts of the telencephalon and diencephalon, respectively.
Structurally, the CNS is encased in bone. The brain lies within the skull, and the spinal cord lies within the vertebral column. The CNS is covered and protected by the meninges, a three-layered sheath formed by the tough outer dura mater, the middle arachnoid mater, and the inner pia mater. Contained between the arachnoid and pia mater is the cerebrospinal fluid.
Functionally, the CNS receives sensory afferents from the body, processes that information, and elicits output through efferent neurons and hormonal release.
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