Unit 1.4d (i) Flashcards
What is a nerve impulse?
It’s a signal that’s transmitted along a nerve fibre
What speed do nerve impulses travel at?
120 m/s
What is membrane potential?
It’s the mixture of + and - ions and molecules in and outside of the cell creating a charge across its membrane
What is the membrane charge referred to as?
Voltage
What’s the resting membrane potential?
It’s when there’s no net flow of ions across the membrane apart from the 3Na+ out, 2K+ in (it’s normal state)
What allows K+ ions to leak out of the cell?
Potassium channels inside the neurons membrane
When K+ ions leak out of cell what happens to the charge?
The outside of the cell develops a positive charge
How are nerve impulses transmitted?
A change in the neurons membrane potential
What is depolarisation?
The reduction of the negative charge within the cell
What is the determining factor as to whether a nerve impulse will occur?
When there is a wave of depolarisation from the original resting membrane potential
What happens if the drop in charge reaches -55mV?
The nerve signal is carried along the axon
What is action potential?
The temporary reversal of the membrane potential (the inside become positive then returns to resting membrane potential)
Why would happen if -55mV was not reached?
There no action potential, so no nerve signal
What happens to the membrane when it returns to resting membrane potential?
The membrane is repolarised
What triggers depolarisation?
Neurotransmitter
What are neurotransmitters?
Chemicals that transmit signals across synapses
What’s a synapse
Gap between 2 neurons
How do neurotransmitters initiate responses in the next neuron?
They bind to transmembrane receptor proteins found on the surface of the neuron in the synapse
What type of receptor are those that are found on the surface of the neuron that neurotransmitters bind to?
Ligand-gated ion channels
When do the ligand-gated ion channels open?
When a neurotransmitter binds to it
How does the ligand-ion channel opening cause the initial depolarisation of the membrane?
Because Na+ ion can now enter into the cell
Do Na+ ions entering the cell move up or down the electrochemical gradient?
Down
What happens as more Na+ ions move into the cell?
More voltage-gated ions begin to open until action potential is reached.
Which order do these 4 steps - that represent how a change in charge causes more channels to open along the axon towards the next neuron - go in?
- Depolarisation moves along axon
- Voltage gated channels along axon open
- An area depolarises
- Behind action potential the axon membrane is repolarised
Why is resting membrane potential reestablished after the wave of depolarisation?
In preparation for the next nerve impulse
Why do the voltage-gated Na+ ion channels close?
When the voltage reaches a critically high level
What opens when the voltage gated Na+ channels close?
The voltage gated K+ ion channels
Where do the K+ ions go when there voltage gated channels open?
The K+ ions move out of the cell to restore the resting membrane potential
What happens to all the channels when the resting membrane potential is restored?
The K+ channels close close and the Na+ channels return to their original configurations
What does the Na+/K+ do?
Continues its normal operation to restore and reset the ion gradient
Once the action potential reaches the end of the neuron what happens?
A vesicle don’t neurotransmitters fuses with the membrane
Once fused with the membrane what does the vesicle containing the neurotransmitter do?
It releases the neurotransmitter into the synapse and it diffuses across to the target cell
What triggers the wave of depolarisation in the next neuron?
The neurotransmitter diffusing to the target cell
