chapter 12 neuroglia cells + myelination

nervous tissue - neuroglia cells + myelination ONLY

neuroglia cells

supporting cells that protect neuron, help them function

oligodendrocytes (CNS)

myelin sheaths in CNS; speed up signal conduction

ependymal cells (CNS)

central canal of spinal cord, ventricles of brain; secrete cerebrospinal fluid (CSF)

microglia (CNS)

macrophages formed from monocytes (phagocytosis); increased in area on injury (infection, trauma, stroke)

astrocytes (CNS)

largest, most; helps form blood brain barrier (BBB)

schwann cells (PNS)

myelin sheath in PNS; assist in damaged fiber regeneration

satellite cells (PNS)

surround nerve cell bodies in peripheral ganglia; function a bit uncertain (electrical insulation, regulate chemical environment)

myelin sheath

insulating layer around nerve fiber (axon)

formed by oligodendrocytes in CNS and schwann cells in PNS

20% protein, 80% lipid = looks white

PNS (peripheral nervous system)

hundreds of layers wrap axon

neurilemma

covered by basal lamina and endoneurium

CNS (central nervous system)

no neurilemma or endoneurium

neurilemma

thick, outermost coil of myelin sheath in PNS

nodes of Ranvier

gaps between myelin segments

trigger zone

initial segment (before 1st schwann cell) and axon hillock, where signals begin

multiple sclerosis

oligodendrocytes and myelin sheaths in CNS deteriorate

myelin replaced by hardened scar tissue

nerve conduction disrupted (double vision, tremors, numbness, speech defects)

type A fibers (axons)

large diameter, myelinated, high speed (=up to 120m/s)

→ fast sent to skeletal muscles

type B fibers (axons)

medium diameter, myelinated, medium speed (= 3.0m/s to 15.0m/s)

type C fibers (axons)

small diameter, unmyelinated, slow speed (= 0.5m/s to 2.0m/s)

→ slow sent to stomach

nerve regeneration of peripheral nerve

1) cell body (soma) is intact

2) some neurilemma remains intact