Biomaterial Database

Myelin sheath thickness and conduction latency groups in the cat optic nerve. 1978

B Freeman

In many animals, the optic nerve has multiple conduction latency groups of fibres yet displays a unimodal frequency distribution of fibre sizes. An attempt has been made to resolve this discrepancy in the cat. Examination of teased preparations of fixed cat optic nerve fibres by polarizing interference light microscopy indicated that a fibre's size may change abruptly along its length. Furthermore, the diameters of single nerve fibres followed for distances of up to 30 mum in serial transverse sections of cat optic nerve showed variations of up to 100% of a fibre's average diameter over that distance. On the other hand, the myelin sheath thickness of these fibres appeared to be relatively constant along any one fibre. A population of cat optic nerve fibres which had a unimodal axon diameter frequency distribution was found to have a myelin sheath thickness frequency distribution with five modes. These modes have been interpreted as indicating the existence of five groups of fibres in the cat optic nerve. Four of these groups may be related to four negative peaks seen in the antidromic compound action potential recorded at the margin of the cat optic disc following stimulation of the optic chiasm. The fifth myelin thickness group appears to represent the slowly conducting fibres which do not make an obvious contribution to the antidromic compound action potential. It is concluded that for the cat optic nerve, the conduction latency groups seen in the compound action potential may be more directly correlated with the frequency distribution of fixed nerve myelin thickness than with the frequency distribution of fixed nerve fibre diameter.

UI	MeSH Term	Description	Entries
D009186	Myelin Sheath	The lipid-rich sheath surrounding AXONS in both the CENTRAL NERVOUS SYSTEMS and PERIPHERAL NERVOUS SYSTEM. The myelin sheath is an electrical insulator and allows faster and more energetically efficient conduction of impulses. The sheath is formed by the cell membranes of glial cells (SCHWANN CELLS in the peripheral and OLIGODENDROGLIA in the central nervous system). Deterioration of the sheath in DEMYELINATING DISEASES is a serious clinical problem.	Myelin,Myelin Sheaths,Sheath, Myelin,Sheaths, Myelin
D009413	Nerve Fibers, Myelinated	A class of nerve fibers as defined by their structure, specifically the nerve sheath arrangement. The AXONS of the myelinated nerve fibers are completely encased in a MYELIN SHEATH. They are fibers of relatively large and varied diameters. Their NEURAL CONDUCTION rates are faster than those of the unmyelinated nerve fibers (NERVE FIBERS, UNMYELINATED). Myelinated nerve fibers are present in somatic and autonomic nerves.	A Fibers,B Fibers,Fiber, Myelinated Nerve,Fibers, Myelinated Nerve,Myelinated Nerve Fiber,Myelinated Nerve Fibers,Nerve Fiber, Myelinated
D009431	Neural Conduction	The propagation of the NERVE IMPULSE along the nerve away from the site of an excitation stimulus.	Nerve Conduction,Conduction, Nerve,Conduction, Neural,Conductions, Nerve,Conductions, Neural,Nerve Conductions,Neural Conductions
D009897	Optic Chiasm	The X-shaped structure formed by the meeting of the two optic nerves. At the optic chiasm the fibers from the medial part of each retina cross to project to the other side of the brain while the lateral retinal fibers continue on the same side. As a result each half of the brain receives information about the contralateral visual field from both eyes.	Chiasma Opticum,Optic Chiasma,Optic Decussation,Chiasm, Optic,Chiasma Opticums,Chiasma, Optic,Chiasmas, Optic,Chiasms, Optic,Decussation, Optic,Decussations, Optic,Optic Chiasmas,Optic Chiasms,Optic Decussations,Opticum, Chiasma,Opticums, Chiasma
D009898	Optic Disk	The portion of the optic nerve seen in the fundus with the ophthalmoscope. It is formed by the meeting of all the retinal ganglion cell axons as they enter the optic nerve.	Blind Spot,Optic Disc,Optic Nerve Head,Optic Papilla,Blind Spots,Disc, Optic,Disk, Optic,Head, Optic Nerve,Nerve Head, Optic,Optic Discs,Optic Disks,Optic Nerve Heads,Optic Papillas,Papilla, Optic,Papillas, Optic,Spot, Blind
D009900	Optic Nerve	The 2nd cranial nerve which conveys visual information from the RETINA to the brain. The nerve carries the axons of the RETINAL GANGLION CELLS which sort at the OPTIC CHIASM and continue via the OPTIC TRACTS to the brain. The largest projection is to the lateral geniculate nuclei; other targets include the SUPERIOR COLLICULI and the SUPRACHIASMATIC NUCLEI. Though known as the second cranial nerve, it is considered part of the CENTRAL NERVOUS SYSTEM.	Cranial Nerve II,Second Cranial Nerve,Nervus Opticus,Cranial Nerve, Second,Cranial Nerves, Second,Nerve, Optic,Nerve, Second Cranial,Nerves, Optic,Nerves, Second Cranial,Optic Nerves,Second Cranial Nerves
D002415	Cats	The domestic cat, Felis catus, of the carnivore family FELIDAE, comprising over 30 different breeds. The domestic cat is descended primarily from the wild cat of Africa and extreme southwestern Asia. Though probably present in towns in Palestine as long ago as 7000 years, actual domestication occurred in Egypt about 4000 years ago. (From Walker's Mammals of the World, 6th ed, p801)	Felis catus,Felis domesticus,Domestic Cats,Felis domestica,Felis sylvestris catus,Cat,Cat, Domestic,Cats, Domestic,Domestic Cat
D000200	Action Potentials	Abrupt changes in the membrane potential that sweep along the CELL MEMBRANE of excitable cells in response to excitation stimuli.	Spike Potentials,Nerve Impulses,Action Potential,Impulse, Nerve,Impulses, Nerve,Nerve Impulse,Potential, Action,Potential, Spike,Potentials, Action,Potentials, Spike,Spike Potential
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D001369	Axons	Nerve fibers that are capable of rapidly conducting impulses away from the neuron cell body.	Axon