PSL300H1 Lecture Notes - Lecture 3: Myelin, London Academy Of Music And Dramatic Art, Exocytosis
Document Summary
Node of ranvier: high density na channels at node (100-2000 per micron sq. , density so high it squeezes any other channels, no voltage gated channels so no after-hyperpolarization, when diameter increased, internodal distance can be larger. Unmeylinated axons: lots of current leakage, slows down conductance velocity, majority of axons are unmeylinated, do have some insulation: schwann cell and oligodendrocyte engulf the cell (no winding) Vesicle release: trigger for exocytosis is always ca2+ ions, how do they get in, bouton membrane contains ca++ channels which open when depolarized by ap currents, ap depolarizes the bouton membrane -> reaches threshold for opening voltage gated. Ca++ channels (-50mv: ca++ diffuses into bouton, and triggers cascade of reactions which result in vesicle excocytosis (kiss and run type or full fusion, normally vesicles are docked in preparation for fusion. Electronic synapse: adjacent membranes are 35 a apart, gap junction bridged by connexins which allow small ions and depolarization.
