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…