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KIN 3600

Lec 16

Functions of nervous system -Sensory -Motor -Inhibitory
What is electro-chemical equilibrium in a resting cell? When the electrical & chemical force are equal in quantity. -Electrical ions pulling in & chemical pushing ions out
What happens when we stimulate cell / gets disturbed? -Na+ gates open -Make cell membrane less negative -Results is overboard & becomes positive charge inside the cell (+30mV) -Na+ wants to get in equilibrium but the Na+ gates close before it can reach it -->Reversal potential
Electrical Activity of Neurons What is sodium/potassium pump -ATP energy spent
Action Potential & its ionic bases -Sodium gates closes preventing further influx -30mV -Cell is positive so it is pushing K+ out (0mV) -Cell becomes more negative and goes back to -70mV -Too much K+ gets out so it becomes hyperpolarized (-75mV) -K+ going back in (-70mV )
1 nerve impulse 1 Action Potential
Na+ & K+ are voltage regulated gates -Open & Closes based off voltage
Na+ & K+ pumps chemically regulated
What causes negativity in the cell? Responsible ions: K+ outflux -Cell regains normal negativity
What ions cause hyper-polarization Outflux of K+ -Why – membrane permeability is still higher than normal
Absolute refractory period cell cannot be stimulated regardless of how strong -Time elapsed from beginning of stimulation during which another action potential cannot be generated in the cell regardless if stimulus strength.
Relative refractory period cell may be stimulated if stronger than normal stimulation will trigger a reaction
Characteristics of AP -ALL-or-none principle -Stimulation threshold -Hyper/Hypo polarization
ALL-or-none principle -ALL way up or ALL way down -Stimulus intensity large enough to initiate AP it will trigger – even if you make it higher --->AP will be the same size
Stimulation threshold -Causes trigger AP -Can change depend on what you’re doing
Hyperpolarization -Cell is polarized more than normal (-75mv) -Drops membrane potential -Less excitable -Need intense stimulus to get AP
Hypo-polarized -Drop membrane potential -Polarized less than normal -Easily excitable
Thicker fibers faster propagation
Thinner fibers Slower propagation
Saltatory Conduction -Myelinated is 25x faster than regular conduction in fibers of same diameter (1msec – 130msec) -Myelination lowers energy expenditure
Larger diameter of an axon greater is the propagation velocity
Schwan Cells (PNS) -1mL -Warp around nerve fibers • Shiny white because myelination • Look like sausage links
Nodes of Ranvier Gaps between Schwan cell • Only area that is exposed • AP inly happen here • Hopping from node to node
Lower energy expenditure Fewer Na+ & K+ ions are exchanged during propagation of AP
Multiple Sclerosis Demyelination of axons -Delays of transmission
Transmission of information through the nervous system – coding the stimulus intensity Frequency of action potential
Created by: rmart11