Graded potential

graded potential

A graded potential is a small, local change in a cell’s membrane voltage caused by a stimulus.

Graded potentials have an impact on whether if the cell

becomes positive enough (reaches threshold) to trigger an action potential — basically, they determine whether the neuron will “fire” or not.

1. A stimulus binds to receptors on a sensory neuron, opening ion channels, changing the activity of cell proteins channels (they seek to maintain electrical and concenrational balance) and thus cause a change in the VOLTAGE of the cell.

2. This lowers the voltage of the cell and thus depolarizes the cell, creating a generator potential, which travels down the axon of the sensory neuron.

2. When the signal reaches a synapse, it triggers the release of a neurotransmitter. The neurotransmitter binds to receptors on the next neuron, opening its ion channels, changing the activity of cell proteins channels, changing the influx and outflux ions eventually reaching a low enough voltage to and create a postsynaptic potential.

3. This process repeats through the neural pathway until it reaches a motor neuron, which connects to a muscle at the neuromuscular junction. There, a strong end plate potential is produced in the muscle cell membrane.

4. The end plate potential causes the muscle cell to contract.

(in the case of non potassium ions which is more often not the case) Stimulus → opens ion channels→ changes membrane potential →membrane potential reaches threshold → action potential travels down the axon → neurotransmitter release

1. Stimulus → opens ion channels on the neuron’s membrane.

2. Ion movement → changes membrane potential (because ions moving in/out changes the charge inside).

   • The intermediate about proteins is mostly the pumps and channels maintaining ion balance, but that’s ongoing background work — it’s not the main driver of the immediate voltage change.

3. If the membrane potential reaches threshold, an action potential is triggered.

4. The action potential travels down the axon (not just a passive flow; it’s an active, self-propagating wave).

5. When it reaches the axon terminal, it causes neurotransmitter release into the synapse.

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How an Action Potential Begins

1. Stimulus causes a graded potential
   – A stimulus (like light, touch, or neurotransmitter) opens some ion channels.
   – Ions move in or out, slightly changing the membrane voltage (the graded potential).

2. Graded potentials add up
   – If enough positive charge enters (depolarization), the membrane potential becomes less negative.
   – If this depolarization reaches a certain level (around –55 mV, called the threshold), it triggers the next step.

3. Voltage-gated sodium (Na⁺) channels open
   – Once threshold is reached, these special channels open automatically.
   – Na⁺ rushes in, making the inside of the cell very positive.
   – This sudden large change = action potential.

4. The action potential propagates
   – The depolarization at one spot triggers nearby voltage-gated channels to open.
   – This repeats along the axon, actively regenerating the signal — not just letting it fade.

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🧠 In short:

• Graded potentials are small and can fade (passive).

• Action potentials are large, self-propagating, and active — once they start, they keep going until the end of the axon.

one axon depolarizes→ → that leads to fresh voltage gated channels to open and depolarize one by one

1. At one small section of the axon, the membrane depolarizes (Na⁺ channels open → Na⁺ rushes in).

2. That makes the inside of that section positive.

3. The positive charge spreads slightly to the next section of the axon.

4. That next section’s voltage-gated (the receptor reacts to change in the voltage/charge on the outer membrane!) Na⁺ channels open, starting depolarization there.

5. This repeats all the way down the axon — like a wave moving through a single neuron.

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So yes — it’s all happening in one neuron, but the signal keeps activating fresh channels further down its own axon, so the electrical signal doesn’t fade.