Nerve Impulse Conduction/Repolarization/Refractory Period

What is a nerve impulse/message ?i i

A nerve impulse is an electrochemical change that happens actoss the neuron membrane .i i

Where does the energy for the impulse transmission come from ?i i

The energy is provided by ATP .i i

When is a neuron at rest ?i i

A neuron is at rest when it does not have an impulse travelling through it .i i

Does the neuron have polarity when at rest ?i i

No .i i

What is polarity ?i i

Polarity is a difference in charge found across the neuron membrane .i i

Describe the charge in and outside of a resting neuron .i i

The neuron has a positive charge on the outside and a negative charge on the inside .i i

What are the 3 main reasons the neuron negative on the inside and positive on the outside ?i i

1. Chlorine ions are found inside the neuron

2. Large negative ions are also found inside the neuron

3. The sodium potassium pump

What is the sodium-potassium pump ?i i

Special proteins in the neuron membrane pump 3 sodium ions out of the neuron while 2 potassium ions are pumped in .i i

What type of transport is used by the sodium potassium pump ?i i

Active transport .i i

What resting membrane potential does a resting neuron typically have ?i i

-70mV .i i

What happens if the membrane potential reaches -55mV ?i i

An action potential occurs .i i

What is -55 mV also called ?i i

The threshold valve .i i

What does action potential mean ?i i

The nerve impulse now travels down the neuron .i i

Why is an action potential called an “all or none” event ?i i

Because it either happens or doesn't happen .i i

Do action potentials have different strengths ?i i

No .i i

What happens to the neuron when -55 mV is reached (3) ?i i

Sodium channels open up in the neuron membrane and sodium rushes into the axon. This changes the polarity of the neuron. It is now negative on the outside and positive on the inside .i i

Where does the membrane potential usually peak ?i i

+35 mV .i i

What happens to the membrane potential reaches +35 mV (2) ?i i

1. It repolarizes (resets itself)

2. Potassium ions open in the membrane so it rushes out of the neuron

What happens to the membrane potential once potassium ions rush out of the neuron (2) ?i i

1. It overshoots the membrane potential to -90 mV

2. The sodium potassium pump helps it return to -70 mV

What is the refractory period ?i i

The refractory period is a short period of time after a nerve impulse where an action potential cannot occur at that location on the neuron .i i

Why does the refractory period happen ?i i

It happens to keep the impulse travelling in the correct direction and prevents it from travelling backwards .i i