6B Neurons Flashcards
Define resting potential
The voltage across the membrane at rest -70mv
What is the state of the neurone cell membrane at rest
polarised
What is the resting potential created and maintained by
sodium potassium pumps
What do sodium potassium pumps do
move sodium ions out but the membrane is not permeable to them so the sodium ions can’t diffuse back in this is called a sodium ion electrochemical gradient
What is a sodium potassium pump permeable to
potassium ions so potassium ions moves in and out
What does a stimulus do to the neurone cell membrane
they excite the neurone cell membrane causing Na + channels to open the membrane becomes more permeable to Na + so Na + ions diffuse into the neurone down the sodium ion electrochemical gradient
What is depolarisation
When the potential difference reaches threshold -55mv more Na + channels open and Na + ions diffuse rapidly in
What is repolarisation
at a potential difference of +30 mv the sodium ion channels close and potassium ion channels open the membrane is more permeable to potassium so potassium ions diffuse out of the neurone down the potassium ion concentration gradient the membrane starts to go back to its resting potential
What is hyperpolarisation
potassium channels are slow to close so there is a slight overshoot where too many potassium ions diffuse out the neurone so the potential difference is more negative than the resting potential
What happens during resting potential
all the channels are reset and the membrane returns to its resting potential
What happens when an action potential occurs
some of the sodium ions diffuse sideways this causes sodium ion channels in the next region to open and sodium ions diffuse into that part
This causes a wave of depolarisation to travel along the neurone
The wave moves away from the part of the refractory period because they can’t fire an action potential
What happens during the refractory period
ion channels are recovering and can’t be opened it acts as a time delay between action potentials meaning action potentials don’t ovelap, there is a limit to the frequency of electrical impulses and they are unidirectional
What is the all or nothing principle
once a threshold is reached an action potential will always fire with the same change in voltage no matter the size of the stimulus
A bigger stimulus won’t cause a bigger action potential but is will cause them to fire more frequently
How does myelination affect the speed of conduct of action potentials
Myelin sheath is an electric insulator
Myelinated neurons have nodes of ranvier where sodium ions channels are found
Depolarisation only happens at the nodes
The neurons cytoplasm conducts enough electrical charge to depolarise the next node so the impulse just from node to node- salatatory conduction which is really fast
In non myelinated neurons the impulse travels as a wave along the whole axon membrane this is slower than salatory conduction a
How does axon diameter affect the speed of conduct of action potentials
Actions potential are conducted quicker along axons with bigger diameters because there is less resistance to the flow of ions depolarisation reach other parts of the cell membrane quicker
How does temperature affect the speed of conduct of action potential
As temperature increases speed of conduction increases as ions have more kinetic energy so move faster after 40 degrees c the proteins begin to denature and speed decreases
