Biomaterial Database

Depolarizing afterpotentials in myelinated axons of mammalian spinal cord. 1985

A R Blight, and S Someya

Microelectrode recordings were made from 5-10 micron dia axons of adult rat spinal cord in vitro. Action potentials in response to electrical stimulation were recorded intracellularly and electrical characteristics of the axons were examined by injecting current pulses through a bridge circuit. All action potentials larger in amplitude than 80 mV were followed by depolarizing afterpotentials, similar to those recorded in peripheral axons [Barrett and Barrett (1982) J. Physiol., Lond. 323, 117-144]. The afterpotential could be described as the sum of three exponential components, the time constants of which (tau 1, tau 2 and tau 3) were 25.2 +/- 5.6, 3.1 +/- 0.8 and 0.8 +/0 0.3 ms, respectively, at 25 degrees C and a membrane potential of -80 mV. The maximal amplitudes of the afterpotential components, obtained by extrapolating to the peak of the action potential, were 3.8 +/- 1.0, 6.4 +/- 5.2 and 21.7 +/- 9.8 mV, for action potential amplitudes of 102 +/- 11 mV. The amplitude of the longest component of the afterpotential decreased with depolarization and increased with hyperpolarization at the recording site. The amplitude decreased markedly with increase of temperature to physiological levels, in conjunction with the expected decrease in action potential duration. Similar afterpotential components were present in the response of the axon to injected hyperpolarizing current pulses. The observations are consistent with the suggestion [Barrett and Barrett (1982) J. Physiol., Lond. 323, 117-144] that the afterpotential results from charging of the axolemmal capacitance by current passing through the myelin sheath during the action potential. They are inconsistent with a number of calculations of electrical characteristics of peripheral axons derived from voltage clamp experiments in isolated fibers. It is argued that the electrical resistance of the myelin lamellae is relatively low, though within the range calculated for other glial membranes. This suggestion is found more compatible with the available morphological data than the alternative proposal that a leakage pathway under the myelin sheath might be responsible for the afterpotential [Barrett and Barrett (1982) J. Physiol., Lond. 323, 117-144]. The significance of this organization for the function of myelinated axons and the electrical basis of the afterpotential are examined further in the accompanying paper [Blight (1985) Neuroscience 15, 13-31].

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
D011901	Ranvier's Nodes	Regularly spaced gaps in the myelin sheaths of peripheral axons. Ranvier's nodes allow saltatory conduction, that is, jumping of impulses from node to node, which is faster and more energetically favorable than continuous conduction.	Nodes of Ranvier,Nodes, Ranvier's,Ranvier Nodes,Ranviers Nodes
D011919	Rats, Inbred Strains	Genetically identical individuals developed from brother and sister matings which have been carried out for twenty or more generations or by parent x offspring matings carried out with certain restrictions. This also includes animals with a long history of closed colony breeding.	August Rats,Inbred Rat Strains,Inbred Strain of Rat,Inbred Strain of Rats,Inbred Strains of Rats,Rat, Inbred Strain,August Rat,Inbred Rat Strain,Inbred Strain Rat,Inbred Strain Rats,Inbred Strains Rat,Inbred Strains Rats,Rat Inbred Strain,Rat Inbred Strains,Rat Strain, Inbred,Rat Strains, Inbred,Rat, August,Rat, Inbred Strains,Rats Inbred Strain,Rats Inbred Strains,Rats, August,Rats, Inbred Strain,Strain Rat, Inbred,Strain Rats, Inbred,Strain, Inbred Rat,Strains, Inbred Rat
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
D004553	Electric Conductivity	The ability of a substrate to allow the passage of ELECTRONS.	Electrical Conductivity,Conductivity, Electric,Conductivity, Electrical
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
D013116	Spinal Cord	A cylindrical column of tissue that lies within the vertebral canal. It is composed of WHITE MATTER and GRAY MATTER.	Coccygeal Cord,Conus Medullaris,Conus Terminalis,Lumbar Cord,Medulla Spinalis,Myelon,Sacral Cord,Thoracic Cord,Coccygeal Cords,Conus Medullari,Conus Terminali,Cord, Coccygeal,Cord, Lumbar,Cord, Sacral,Cord, Spinal,Cord, Thoracic,Cords, Coccygeal,Cords, Lumbar,Cords, Sacral,Cords, Spinal,Cords, Thoracic,Lumbar Cords,Medulla Spinali,Medullari, Conus,Medullaris, Conus,Myelons,Sacral Cords,Spinal Cords,Spinali, Medulla,Spinalis, Medulla,Terminali, Conus,Terminalis, Conus,Thoracic Cords