How Nerves Work 2
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How do neurones send electrical signals?
• Action potentials: transmit signals over long distances • Graded potentials: decide when an action potential should be fired • Resting membrane potential: keeps cell ready to respond
What is the resting membrane potential
-70mV
What is the equilibrium potential?
The membrane potential at which the electrical gradient is exactly equal and opposite to the concentration gradient
What equation predicts the equilibrium potential for a single ion species?
The Nernst equation
Why are bananas dangerous?
Bananas contain high [K] • Reduction in concentration gradient • This sustains a smaller electrical gradient at equilibrium • RMP is reduced as the cell depolarises • Stresses the importance of the blood brain barrier
What can an increase in [K] lead to?
Hyperkalaemia which leads to ventricular fibrillation
How is the blood brain barrier protective?
• Capillaries of the brain are especially tight • Due to astrocytes and tight junctions between endothelial cells • This protects the brain from changes in plasma [K]
What has the biggest effect of the resting membrane potential?
Leaky potassium channels
What equation predicts the equilibrium potential generated by several ions?
The Goldman equation
Why is the resting membrane potential nearer -70mV than -90mV?
• Other leaky channels, Na and Cl especially • Eletrogenic nature of the Na/K • Large intracellular -ve charged molecules
When does the cell hyperpolarise?
When there is an increase in negative charge within the cell
When does the cell depolarise?
When there is an increase in positive charge within the cell