L3: Neural signaling

How are action potentials propagated?

Can action potential be initiated if the threshold potential is not reached?

no

Define depolarization

Occurs when the potential difference between the two sides of the membrane is decreased (membrane potential gets less negative)

Mechanism of depolarization during an action potential using voltage gated sodium channels

• When the threshold potential (-55mV) is reached, additional voltage-gated sodium channels open

• This allows sodium (Na+) to move into the neuron through facilitated diffusion

Define repolarization

Occurs when the potential difference between the two sides of the membrane increases again (the inside of the cell becomes more negative relative to the outside)

Mechanism for repolarization during an action potential using voltage gated potassium channels

• At about +30mV, voltage-gates potassium channels open

• This allows potassium (K+) to move out of the neuron through facilitated diffusion

Describe the movement of sodium ions in a local current

• Voltage-gated Na+ channeles open

• This causes local depolarization

• the positive change spreads to nearby regions, triggering the next section of membrane

Explain how the movement of sodium ions propagates an action potential along an axon

• When voltage-gates Na+ channels open, Na+ rushes into the axon, causing depolarization

• The influx of Na+ creates a local; current that spreads to adjacent sections of the axon

• The local depolarization opens Na+ channels in the next region

• In this way, Na+ movement propagates the action potential along the axon in one direction

Outline the cause and consequences of the refractory period after depolarization

Cause

• After depolarization, voltage-gated Na+ channels become inactivated and cannot reopen immediately

Consequence

• The neuron cannot fire another action potential or requires a strange stimulus

• This ensures the action potential travels in one direction and limits the maximum firing frequency of the neuron