University:
Kentucky State University
Course:
BIO 301 | Human Anatomy
Academic year:

2019
Views:

334

Pages:

22
Author:

Arielle Armstrong

Gray and White Matter in CNS White matter myelinated processes (white in color) Gray matter nerve cell bodies, dendrites, axon terminals, bundles of unmyelinated axons and neuroglia (gray color) Nuclei masses of nerve cell bodies inside the CNS SHEET NOTE #1 >> gray and white matters are found in the central nervous system >> the reason behind their colors is their contents mentioned in the previous table. >> the assembly of the nerve cells bodies in shape of masses through white matter is called: NUCLEI , & this is exclusively found in the central nervous system : 1)spinal cord 2)brain . Gray and White Matter in CNS In the spinal cord: gray matter forms an H-shaped inner core surrounded by white matter In the brain: a thin outer shell of gray matter covers the surface & also is found in clusters embedded in white matter called nuclei inside the SHEET NOTE #2 >> the previous slide talks about the difference in gray matter’s shape and features between spinal cord and brain >> in the brain the distribution of the gray matter is exactly the opposite in the spinal cord >> in the brain we will find the gray matter making the outer shell of the brain which is called cerebral cortex . >> as u can see in the picture there is Gray mass embedded in the white matter We call it nuclei ( its defined in the previous Sheet ). PNS Nerves Bundles of axons Ganglia Masses (ovoid structures) of nerve cell bodies inside the PNS In PNS cell bodies also are found in some sensory organs e.g., olfactory mucosa • Peripheral nerves consist of axons from motor neurons (in the spinal cord), sensory neurons and autonomic neurons (in ganglia). • Ganglia which can be either sensory or autonomic, contain neuronal cell bodies and their satellite cells and are surrounded by connective tissue continuous with that of nerves. SHEET NOTE #3 >> PNS = peripheral nervous system. >> in PNS we don’t say white or gray matters instead we have GANGLIA & PERIPHRAL.N >> ganglia is same as nuclei in CNS its assembly of nerve cell bodies making masses in shape of (ovoid structure ). >> assembly of bundles of axons in PNS is called peripheral nerves >> olfactory mucosa is responsible of smelling >> peripheral nerves which consist of axons are mostly mixed ( not always) like being sensory and autonomic at the same time . SHEET NOTE #4 >> in P.N axons that form motor neurons their cell bodies are found in the spinal cord when cell bodies of axons that form sensory neurons are found in ganglia . Peripheral Nerves Connective tissue coverings of peripheral nerves: • Epineurium: is a thick, outermost layer of dense irregular CT surrounds the whole nerve (whole fascicles) • Perineurium: surrounds each single fascicle consists of 2-6 layers flat fibrocytes with their edges sealed together by tight junctions make up blood-nerve barrier. • Endoneurium: Thin CT layer (reticular fibers, scattered fibroblasts, and capillaries).Immediately around external lamina of Schwann cell. So, Sheet Note #5 Fibrocytes = Blood nerve barrier ( to protect nerve in infection and foreign body in fascicles) Endoneurium  external lamina  schwann cell  single nerve fiber ( axon) • Myelinat ion A multilayered lipid and protein covering called the myelin sheath and produced by Schwann cells and oligodendrocytes surrounds the axons of most neurons • The sheath electrically insulates the axon and increases the speed of nerve impulse conduction. Sheet Note #6 Product by oligodendrocytes (CNC ) schwann cells (PNC) Myelinat ion • Node of Ranvier: periodic gap in the insulating sheath (myelin) on the axon of certain neurons that serves to facilitate the rapid conduction of action potential by saltatory conduction. Sheet Note #7 Saltatory conduction  jumping Myelination in the CNS • Oligodendrocytes myelinate axons in the CNS • Broad, flat cell processes wrap about CNS axons, but the cell bodies do not surround the axons (No neurolemma) • Difficult to regrowth after injury is due to the lack of a neurolemma Myelination in PNS ● • ● Schwann cells myelinate (wrap around) axons in the PNS • Schwann cell cytoplasm & nucleus forms outermost layer of neurolemma with inner portion being the myelin sheath • Compact cords of proliferated Schwann cells guide growing axons that are repairing themselves Sheet Note #8 ● Myelination in CNS V.S PNS (differences) ● First they differ in glial cell type ]oligodendrocyte in CNS , Schwann cells in PNS[ ● Second ,the way how myelin is formed]in CNS only the processes wrap around different segment in different axons , in PNS the whole cell wrap around single segment in the axon [ ● Which means that no glial cells around CNS axons therefore no Neuorolemma ● NOTE:A myelinated axon in PNS is surrounded by neurolemma while in CNS there is no neurolemma Myelination of large-diameter PNS axons Sheet Note #9 ● In PNS ,large diameter axons are always myelinated - Schwann cells produce myelin● When this happen ,multilayers of myelin pushes the cytoplasm to peripheral ,and the Schwann cells remain around the axon as neurolemma ● Because all axons in PNS have neurolemma, they are suspected to have high ability to regrow and regenerate after injury HOW? Schwann cells in PNS axons proliferate (mitosis) , surround the injured part and stimulate axon’s repair ● While in CNS ,with no neurolemma its difficult to regrow after injury ● Remember :nerve cells( neurons ) are fully differentiated cells while neuroglial cells have the ability to grow in mitosis .

Gray and White Matter in CNS

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