OCR Biology-Action Potentials

lauren3105

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Does anybody understand the concept of action potentials? I really can't get my head around it

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Changing Skies

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(Original post by lauren3105)
Does anybody understand the concept of action potentials? I really can't get my head around it

Moved this to the biology section for you

can you be more specific on what you are struggling to understand?

I can try my best to help.

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jiazheng0620

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Action potential or nerve impulses
Occurs only in nerve cells or muscle cells

3 parts -
1. Depolarization
2. Repolarization
3. Hyperpolarization

1. Sodium ions rush in through sodium channel. Membrane potential (MP) becomes less positive. If threshold is reached, sodium voltage gated channels open and more Na+ rushes in creating a spike of MP
2. This stimulates the K+voltage gated channels to open. K+ diffuses out, MP becomes less positive.
3. It can be lowered to an extend below the resting membrane potential due to the delay for K+voltage gated channel to close.

The influx of the NA+ mabe due to external stimulus or adjacent influx of NA+
Action potential transfers along the axon membrane.

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lauren3105

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(Original post by jiazheng0620)
Action potential or nerve impulses
Occurs only in nerve cells or muscle cells

3 parts -
1. Depolarization
2. Repolarization
3. Hyperpolarization

1. Sodium ions rush in through sodium channel. Membrane potential (MP) becomes less positive. If threshold is reached, sodium voltage gated channels open and more Na+ rushes in creating a spike of MP
2. This stimulates the K+voltage gated channels to open. K+ diffuses out, MP becomes less positive.
3. It can be lowered to an extend below the resting membrane potential due to the delay for K+voltage gated channel to close.

The influx of the NA+ mabe due to external stimulus or adjacent influx of NA+
Action potential transfers along the axon membrane.

this is great,thanks!

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lauren3105

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(Original post by Changing Skies)
Moved this to the biology section for you

can you be more specific on what you are struggling to understand?

I can try my best to help.

Posted from TSR Mobile

i think i'm alright with it now, thanks though!

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lauren3105

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(Original post by Changing Skies)
Moved this to the biology section for you

can you be more specific on what you are struggling to understand?

I can try my best to help.

Posted from TSR Mobile

Actually i'm still a bit confused with these things...how a resting potential is established and maintained, how the action potential is generated and the role of neurotransmitters in the transmission of action potentials

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Dynamo123

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(Original post by lauren3105)
Actually i'm still a bit confused with these things...how a resting potential is established and maintained, how the action potential is generated and the role of neurotransmitters in the transmission of action potentials

There are two main factors that contribute to establishment of a resting membrane potential (RMP):
1. The electrical gradient for K+. We have a value of potential for each ion, called the Nernst potential. Just remember that this compares the concentration of ions inside and outside the membrane and determines the potential gradient based on the concentration ratio.
2. The activity of the Na/K pump that pumps three Na out and two K in the cell.

Now consider we have an RMP of -88__-90 mV for a large nerve fiber. This is determined by the Nernst potential for K, which is nearly -96 mV and the potential generated by Na/K pump, which is nearly 8 mV. Adding these up you get -96 +8 = -88 mV, which is the RMP.

Thus these two factors are responsible for establishing and maintaining the RMP.

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Revenged

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(Original post by lauren3105)
how the action potential is generated and the role of neurotransmitters in the transmission of action potentials

take a sensory neurone.

it is activated by a stimulus (e.g. heat)

this activates a receptor ('heat receptors', i think called VR1 receptors).

theses receptor are ion channels (for example) and there activation (if enough heat) generates an action potential at the end (e.g due to influx of sodium ions).

once one is activated the depolarisation rapidly spreads down.

once the end of the nerve is reached there is a gap, called a synapse.

at a synapse there is neurotransmitter released. neurotransmitters regulate synaptic transfer.

they can be exciatory or inhibitory and there are various mechanism of action.

Acetylcholine is the simpliest, as once it is released it binds to receptors on the post-synaptic membrane.

(nictonic) acetylcholine receptors are simple ion channels and when activated they cause depolarisation in the post-synaptic channel.

this causes the 'depolarisation' of the neurone after the synapse.

HTH

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