Neuromuscular Physiology
concentration difference of ions across a selectively permeable membrane
Membrane Potential
Begins with a sudden change from the normal resting negative membrane potential to a positive potential and ends vice-versa
Action Potential
Resting membrane potential before the action potential begins. "Polarized stage"
Resting Stage
Rise of the potential in the positive direction caused by Sodium inflow
Depolarization
Re-established of the normal negative RMP
Repolarization
An overshoot of the RMP towards negativity
Hyperpolarization
RMP large nerve fibers
-90 mV
RMP of small nerve fibers
-70 Mv
When the membrane potential becomes less negativ, it activates the activation gate causing sodium ions to pour inward
Activation in NA Channels
In NA CHANNELS, during activation the membrane potential becomes less negative
Depolarization
In K CHANNELS, during Resting stage the gate of the potassium channel is closed and potassium ions are prevented from passing through
Repolarization
threshold needed in initiation of the action potential
-65 mV
required sudden size in initiation of the action potential
15 to 30 mV
any initial rise in the membrane potential will lead to a positive feedback cycle that would open the sodium channels
Initiation of the action potential
an action potential elicited at any one point on an excitable membrane usually excites adjacent portions of the membrane
Propagation of the action potential
The depolarization process travels over the entire membrane if conditions are right but it does not travel at all if the conditions are not right
All or none principle
The potential remains near the peak of the potential for many milliseconds before repolarization begin
Plateau
seen in large fibers
Myelinated Fibers
seen in small fibers
Unmyelinated fibers
central core
Axon