White matter
The ratio between axon diameter and that of the total nerve fiber (axon and myelin) is 0.6–0.7, a ratio that is well maintained regardless of the axon caliber. The length of the myelin sheath along the axon is approximately 1 mm in the PNS. Between two adjacent myelin segments, there are approximately 1-μm-long gaps called nodes of Ranvier (Figure 1A and E). At the nodes, the axon is exposed to the extracellular space. In contrast, among the myelinated nerve fibers, axons are mostly covered by myelin sheaths, and transmembrane currents can only occur at the nodes of Ranvier where the axonal membrane is exposed. An axon (from Greek ἄξων axōn, áxōn), axis also known as a nerve, fibre is a, long slender projection of a nerve, cell or, neuron that typically conducts electrical impulses away from the'neuron s cell. Body the function of the axon is to transmit information to different, neurons muscles and. glands Axons make contact with other cells—usually other neurons but sometimes muscle or gland cells—at junctions called synapses. At a synapse, the membrane of the axon closely adjoins the membrane of the target cell, and special molecular structures serve to transmit electrical or electrochemical signals across the gap. Anatomy. The cerebrum is a large, folded mass of nervous tissue that makes up the majority of the human brain. Many ridges of cerebral tissue, called gyri (singular: gyrus), extend from the surface of the cerebrum and are bordered by grooves in the cerebrum.... Click to read more below. The cerebrum is the most superior and anterior of the brain’s major regions. It is the seat of reason, planning, memory, and sensory integration. All conscious thought originates in the cerebrum and can influence the subconscious functions of the lower regions of the White matter is composed of bundles of myelinated nerve cell projections (or axons), which connect various grey matter areas (the locations of nerve cell bodies) of the brain to each other, and carry nerve impulses between neurons. Myelin acts as an insulator, increasing the speed of transmission of all nerve signals. Men have more white matter than females both in volume and in length of myelinated axons. At the age of 20, the total length of myelinated fibers in males is 176,000 km while that of a female is 149,000 km. The white matter is white because of the fatty substance (myelin) that surrounds the nerve fibers (axons). This myelin is found in almost all long nerve fibers, and acts as an electrical insulation. Men have more white matter than females both in volume and in length of myelinated axons. At the age of 20, the total length of myelinated fibers in males is 176,000 km while that of a female is 149,000 km. 1 Gray matter located on the surface of the brain is called cortex (e.g., cortex of the cerebral hemispheres, cortex of the cerebellum). 2  Masses of gray matter located deeper in the brain are called nuclei .(e.g., brainstem nuclei, nuclei of the thalamus). Pyramidal cells are the efferent (long-axon) cells of the cerebral cortex. The name refers to the shape of the cell body as seen in standard sections perpendicular to the cortical surface. The apex of the pyramid points toward Schwann cells make myelin in the peripheral nervous system (PNS: nerves) and oligodendrocytes in the central nervous system (CNS: brain and spinal cord). In the PNS, one Schwann cell forms a single myelin sheath (Figure 1A). In contrast, among the myelinated nerve fibers, axons are mostly covered by myelin sheaths, and transmembrane currents can only occur at the nodes of Ranvier where the axonal membrane is exposed. White matter is a component of the central nervous system, in the brain and superficial spinal cord, and consists mostly of glial cells and myelinated axons that transmit signals from one region of the cerebrum to another and between the cerebrum and lower brain centers. Men have more white matter than females both in volume and in length of myelinated axons. At the age of 20, the total length of myelinated fibers in males is 176,000 km while that of a female is 149,000 km. 1 Medullary body: 2  the 'white matter' of the cerebrum; consists of myelinated axons. 3  types of axons include: 4  commissural fibers-conduct impulses between cerebral hemispheres (and form the corpus callosum). 5  projection fibers-conduct impulses in & out of the cerebral hemispheres. Like the brain, the spinal cord consists of gray matter and white matter. The gray matter (cell bodies & synapses) of the cord is located centrally & is surrounded by white matter (myelinated axons). Schwann cells: these cells provide the myelin that covers neurons in the peripheral nervous system. Larger neurons are covered in a myelin sheath. Myelin is high in lipid and serves the same purpose as insulation around electrical wires. Myelinated axons conduct nerve impulses faster. These cells form the substance of the brain, spinal cord, and peripheral nervous system. The brain is composed of the basic units of the cerebral hemispheres, brainstem, and cerebellum. The cerebral hemispheres can be further categorized by structure and function.
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Myelinated axons that extend between the cerebral hemispheres are called