Neuronal Communication Flashcards
How does resting potential work
The carrier protein in the cell surface membrane of the neurone has a high affinity for sodium ions inside the cell. Therefore, 3 sodium ions bind to it.
An ATP is hydrolysed to ADP and a phosphate group. The phosphate group binds to the carrier protein. This causes the shape of the carrier protein to change and it opens facing outside rather than inside. The protein has a low affinity for sodium ions outside the cell therefore these three ions detach themselves and are lost. However, this protein molecule has a high affinity for potassium ions. Therefore, two potassium ions bind to the protein. The phosphate group detaches itself from the protein. The protein switches back to facing inside the cell. The protein has a low affinity for potassium ions inside the cell. The two potassium ions leave the protein.
What is generator potential
The bigger the stimulus, the more voltage gated channels that are opened, the more potentials that are formed.
When the sum of generator potentials formed pass a threshold, a nerve impulse is generated.
Analogy: a fly sitting on my arm
I wouldn’t notice it because not many potentials are being send. However, if I also see the fly then there are enough impulses, for me to swat the fly away (the response).
How is the threshold surpassed in a generator potential
When several impulses are send through a neurone
Or when several neurones send an impulse
What occurs at a polarised state
3 sodium ions out and 2 potassium in the neurone cell. Therefore, it is more negative inside that it is outside the cell.
The stages of an action potential
The membrane is resting. It is at a polarised state, with the inside of the cell being -60mV to the outside.
A threshold generator potential causes voltage-gated sodium channels to open. This causes sodium ions to flood in.
This depolarises the membrane. This means that the inside is less negative compared to outside. Eventually it reaches a threshold of -50mV.
As more sodium ions diffuse into the cell, this stimulates more sodium ions to enter due to more voltage-gated channels being opened. This is a positive feedback.
As more sodium ions enter the cell, the potential difference across the membrane eventually reaches +40mV. This when the inside of the cell is positive compared to outside.
The sodium channels close. The potassium channels open.
Potassium ions diffuse out of the cell bringing the potential difference back to negative inside the cell- repolarisation.
The potential difference overshoots slightly making the cell hyperpolarised.
The original potential difference is restored, and ions are moved back to the correct sides of the membrane by the sodium/potassium pumps.
What is the ALL OR NOTHING LAW
This states that the nerve impulse is NOT affected by the strength of the generator potential. The impulse either occurs or not.
What does depolarised mean
When the inside of the cell is less negative compared to outside. This is caused by sodium ions flooding into the cell.
What does repolarisation mean
This is when inside of the cell becomes negative again compared to outside the cell. This occurs when potassium ions diffuse out the cell.
What does hyper-polarisation mean
This is when it is very negative inside and very positive outside. There is a large negative potential difference.
What does absolute refractory periods mean
This is the period where stimulus cannot be fired because an impulse is being processed. As this period progresses, it becomes easier to fire another stimulus.
This is when sodium channels are not open.
What is relative refractory period
This is when another action potential can be produced but only if the stimulus is greater than the threshold stimulus.
The potassium ions are still open through repolarisation and hyperpolarisation.
What do photoreceptors do
They detect light
What do chemoreceptors do
They detect chemicals
What do mechanoreceptors do
Detect mechanical strain or stretching (the ears detect the sound by this method)
What do proprioceptors do
Detect body position
