Resting Potentials and Active Potentials

A Resting Neurone

• When a neurone is not transmitting an action potential it is said to be at rest.
• It is actively transporting ions across its plasma membrane.
• Sodium/pottasium ion pumps use ATP to pump 3 sodium ions out for every 2 potasiums in.
• Plasma membrane is more permeable to pottasium ions than sodium ions so many diffuse out again.
• Interior of the cell is a negative potential compared to the outside.
• The cell mambrane is said to be polarised.
• Potential difference across the cell mambrane is -60mV.
• This is called the resting potential. 

An Action Potential

• At rest the gated sodium ion channels are kept closed.
• the sodium/pottasium ion pump uses ATP to actively transport three sodium ions out for every 2 pottasium ions brought into the axon.
• A few pottasium ions diffuse back out as some pottasium channels open
• If some of the sodium ions channels are opened then sodium ions will quickly diffuse down their concentration gradient into the cell from the surrounding tissue fluid.
• Causes a depolarisation of the membrane.
• Generator region of the receptor cells the gated channels are open due to an energy change in the environment.
• E.g. pressure change.
• The gates further along the neurone are opened by changes in the potential difference across the membrane.
• These are called voltage-gated channels.
• Channels respond to depolarisations of the membrane.

All or Nothing

• Generator potentials in the sensory receptor are depolarisations of the cell membrane.
• A small depolarisation will have…