Physiology of Peripheral Nerves I - Angelfire PDF
Preview Physiology of Peripheral Nerves I - Angelfire
PPhhyyssiioollooggyy ooff PPeerriipphheerraall NNeerrvveess II Amelyn R. Rafael, MD © TTrraannssppoorrtt ooff IIoonnss aanndd MMoolleeccuulleess tthhrroouugghh tthhee cceellll mmeemmbbrraannee • DIFFUSION (Passive transport) • ACTIVE TRANSPORT DDIIFFFFUUSSIIOONN • Means random molecular movement of substances molecule by molecule either through intermolecular spaces in the membrane or in combination with a carrier protein • The energy that causes diffusion is the energy of the normal kinetic motion of matter – the continual movement of molecules among one another in liquids, or in gases DDiiffffuussiioonn ssuubbttyyppeess • 1. Simple diffusion – molecular kinetic movement of molecules or ions • Occurs through a membrane opening or through intermolecular spaces without the necessity of binding with carrier proteins in the membrane • The rate of diffusion is determined by the amount of substance available, by the velocity of kinetic motion, and by the number of openings in the cell membrane through which the molecules can move SSiimmppllee ddiiffffuussiioonn • Occur through the cell membrane by two pathways: • Through the interstices of the lipid bilayer • The rate of diffusion of lipid soluble substances is directly related to their lipid solubility • Through watery channels in some of the transport proteins PPrrootteeiinn cchhaannnneellss • Distinguished by 2 important characteristics: • Selective permeability • Gating • Voltage gating • Chemical gating • Ex. acetylcholine SSeelleeccttiivvee ppeerrmmeeaabbiilliittyy • Results from the characteristic of the channel itself: diameter, shape, and the nature of the electrical changes along its inside surfaces ex. Sodium channels GGaattiinngg • Provides a means for controlling the permeability of the channels • Gate-like extensions of the transport molecule • Can close over the opening of the channel or can be lifted away from the opening by a conformational change in the shape of the protein molecule itself VVoollttaaggee ggaattiinngg • The molecular conformation of the gate responds to the electrical potential across the cell membrane • Sodium channels • The inner surfaces are strongly negatively charged – postulated to pull small dehydrated sodium ions into these channels • Specifically selective for the passage of sodium ions
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