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Spinal Cord as part of the Nervous System plus Grey & White matter Already know the reflex arc A few more parts to add Gray and White Matter of the CNS (GROSS ANATOMY OF THE CNS) Gray matter: gray-colored Where neuron cell bodies are clustered White matter: white-colored Where millions of axons are running between different part of CNS, in bundles of “tracts” Remember, tracts are in CNS, vs nerves in PNS White is from the myelin sheaths Usual pattern of gray/white in CNS White exterior to gray __________________ Gray surrounds hollow central cavity ______________________________ Two regions with additional gray called “cortex” ______________ Cerebrum: “cerebral cortex” Cerebellum: “cerebellar cortex” (pic from Marieb lab book p 263) Gray/White in spinal cord Hollow central cavity (“central canal”) Gray matter surrounds cavity White matter surrounds gray matter (white: ascending and descending tracts of axons) “H” shaped on cross section Dorsal half of “H”: cell bodies of interneurons Ventral half of “H”: cell bodies of motor neurons No cortex Same pattern Dorsal (posterior) white gray Central canal_____ Ventral (anterior) Spinal cord cross section Grey Matter vs White Matter 1. Grey matter is made up of nerve cell bodies while white matter is made up of fibers. 2. Unlike the white matter, the neurons of grey matter do NOT have extended axons. 3. Grey matter occupies 40 percent of the brain, while white matter fills 60 percent of the brain. 4. Grey matter has this color because of the grey nuclei that comprises the cells. Myelin is responsible for the white appearance of the white matter. 5. Grey matter has NO myelin sheath, while white matter is myelinated. 6. Processing is concluded in the grey matter, while white matter allows communication to and from grey matter areas, and between the grey matter and the other parts of the body. Basic neuronal organization Anterior view Coronal section of cerebrum Cross sections of spinal cord and brains stem Note gray matter (brown) and white matter (tan) Reflex arc and information processing are shown