The difference in electrical potential between the intracellular fluid (ICF) and the extracellular fluid (ECF)
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What are the mechanisms that maintain the membrane potential and what's its value?
The Na/K pump and leak channels.
-70mV
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What is the Na/K pump?
A protein pump that pumps 3 Na ions out of the cell for every K ion pumped into the cell. important for setting up the concentration gradient. Uses active transport
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What is the equilibrium potential?
The membrane potential in which there is no net movement of ion across the membrane.
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Explain the Equilibrium potential for K+
As K is pumped into the cell, the concentration gradient of K in the ICF increases. this causes K to leave the cell via leak channels but as it does this, attached anions cannot pass through the channels thus making the inside of the membrane more negativ
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Explain the Equilibrium potential for Na+
As Na is pumped out of the cell, the concentration gradient of Na in the ECF increases, This causes Na to enter the cell via leak channels leaving behind its attached anions. This makes the membrane potential inside more positive. +60mV
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Can these equilibrium potentials be reached?
No because these processes happen simultaneously in opposite directions so they cancel each other out
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How can you calculate the Equilibrium potential?
Using the Nernst Equation
E ion = (RT/zF) X log {[ion out]/[ion in]}
E ion is the equilibrium potential for the ion
R is the gas constant
T is the absolute temperature
z is the valency of the ion
F is Faradays constant
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Define action potential
A change in the membrane potential which results in the inside of the membrane becoming more positive than the outside.
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How is the action potential reached?
The membrane must be permeable to Na+ ions, the membrane must pass the threshold potential and it will reach +55mV.
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What are the types of voltage-gated Na channels?
1. Open- means gates are open
2. Closed but capable of opening- means only the activation gate is closed/used
3. Closed and incapable of opening- means both the activation and inactivation gate are closed.
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What is a graded potential?
Local changes in the membrane which vary in size. Usually dissipate over short distances
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What is the Refractory period?
Describes the point in time after the action potential when it is not possible for the same stimulus to create another action potential.
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What does the refractory period do?
Ensures the action potential can only go one way.
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What are the 2 types of Refractory period?
1. Absolute- not possible to generate AP no matter how long the triggering event, Na channels are closed/incapable of opening.
2. Relative- happens during hyperpolarisation, AP can only be generated due to a large triggering event. Some Na channels are ca
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What happens during the depolarisation period?
Membrane potential becomes LESS negative, -70mV to -60mV
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What happens during the hyperpolarisation period?
Membrane potential becomes MORE negative, -70mV to -80mV
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What is Contiguous conduction?
Conduction of an AP in one direction, this is usually slow but can be seen up through an increase in axon diameter and myelination
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What is Saltatory conduction?
Conduction of an AP though jumps/leaps. The AP cannot pass through the myelin and so must 'jump' to each Node of Ranvier to conduct the signal.
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What is a synapse?
The junction between neurones.
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Where does the AP leave from and where is it received?
Leaves from the presynaptic membrane, travels across the synaptic cleft and is received by receptors on the postsynaptic membrane
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What are the types of synapses?
1.Electrical, physical connections between neurones where gap junctions form a pore, bidirectional, fast and unregulated.
2. Chemical, no physical contact, neurotransmitters
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What are the 2 types of neurotransmitters and what effect can they cause?
1. Excitatory, creating an excitatory postsynaptic potential (EPSP) which makes an AP more likely to occur.
2. Inhibitory, creating an inhibitory postsynaptic potential (IPSP) which makes an AP less likely to occur.
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What is Summation?
The input of all Action potentials
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What are the types of summation?
1. Spatial - when many EPSP from multiple presynaptic inputs occur, combine to trigger an AP
2. Temporal - when one EPSP from one presynaptic input happens close enough to trigger an AP.
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What are the mechanisms that maintain the membrane potential and what's its value?
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