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The reversal of the resting membrane potential such that the inside of the cell becomes more positive


This reversal is due to changes in membrane permeability

At RMP the membrane is more permeable to K+ than it is to Na+
To generate an AP the membrane becomes more permeable to Na+
To end the AP (so a new one can be generated) the membrane again becomes more permeable to K+


Permeability changes are due to

The opening of protien ion channels in the membrane


Chemically gated ion channels

Open or close when a chemical binds to a protien receptor that is part of the ion channel

Ex: Ach (Acetylcholine) is a neurotransmitter that causes Na+ channels to open


Voltage gated ion channel

Open or close in response to voltage changes
(membrane becoming more positive or negative)


Both channel types are

Highly specific for what ion is allowed to pass through


The ion will move into or out of the cell based on

It's concentration gradient (always down)


In nerve and skeletal tissue

An excitatory stimulus (chemical binding or voltage change) will cause Na+ channels to open

Occurs at RMP, the cell is polarized



Na+ will Move down its concentration gradient into the cell (Na+ influx)
Na+ brings its positive charge with it, creating intracellular positivity

When Na+ channels close influx stops


At about the same time that Na+ channels close

K+ channels open



K+ will move down its concentration gradient out of the cell (K+ eflux)
K+ takes its positive charge with it creating intracellular negativity



A brief period when excess K+ leaves the cell and the membrane temporarily becomes more negative than it was at rest


AP trace

Represents the voltage across the cell membrane
Measured by comparing the charge of the ICF to the ECF

Technique is called "patch clamping"
Branch of science is called "electrophysiology"


Full AP

1. Cell is at RMP, then receives an excitatory stimulus
2. Voltage opens some Na+ channels; allowing Na+ influx and the cell gradually becomes more positive/less negative
3. Voltage allows many Na+ channels to open; allowing an increase in Na+ influx creating a steep incline (spike potential)
4. Na+ channels close and K+ channels open, allowing K+ eflux; the cell becomes more negative/less positive
5. Excess K+ eflux
6. The Na+/K+ pump begins to actively pull K+ back into the cell to restore RMP


Excitation Contraction Coupling

1. Na+ influx through the voltage gated channels on the motor neuron initiates an AP
2. The AP cause Ca+2 influx through voltage gated channels in the terminal end of the motor neuron
3. Ca+2 causes vesicles filled with Ach to fuse to the plasma membrane of the motor neuron. Ach is released by exocytosis into the Neuromuscular Junction (NmJ)
4. Ach binds to its receptor on the sarcolemma
5. Ach binding cause chemically gated Na+ channels to open; Na+ influx; depolarization of the sarcolemma and AP production
6. The AP travels down the T Tubule
7. Voltage causes Ca+2 release from the lateral sacs. Ca+2 binds to TnC after diffusing in the sarcomere and the sliding filament theory takes place
8. The AP originally generated at 5 also travels across the sarcolemma causing voltage gated ion channels to open. AP are generated that travel down distal T Tubules can all the events of 7 take place.
9. To end AP generation on the muscle a chemical called Ach-esterase in the NmJ breaks down and deactivates the Ach


Muscle contraction is the summation of

Many APs (all phases)


There are _______ chemically and voltage gated channels on the sarcolemma.


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