How do nerves work Flashcards
What are the 2 ways of sending a signal in the body?
Chemical (slow)
– Short distance (e.g. synapse)
– Long distance (e.g. hormones)
Electrical (fast)
– Graded potentials – short distance
– Action potentials - long distance
Why do we need a propagating signal – action potential?
because…
– Signal decays over 2-3mm
– But nerves can be long >1m
Eletrical potential accrosss membrane is due to…
– Permeability to key ions
– Concentration gradients for key ions
– Gradients maintained by active transporters
All cells have a resting membrane potential but with nerves they have the potential to change that.
What is a Sodium Potassium Pump?
Uses ATP
Transports Na+ out of the cell
Transports K+ into the cell
Ratio: 3Na+ out for every 2K+ in
Helps maintains concentration gradients
Balance at equilibrium potential of potassium ions?
Chemical gradient trying to pull K+ ions out of the cell and then an eletrical gradient trying to pull K+ ions into the cell.
hence this causes a Balance at equilibrium potential.
What is the Nernst equation?
Nernst equation: – Equilibrium potential for K+ = -90mV
What will the resting membrane potential be closer to outve sodium and potasium.
RMP will be nearer K+ equilibrium potential
as Membrane is much less permeable to Na+
What is Hodgkin’s Cycle process?
Threshold depolarisation
Na+ Channel opens up
Increase Na+ permability
Na+ Moves into cells
Depolarisation
What do local anesthetic do?
Local anesthetic block the sodium channels so depolarisation cant start
What is the Action potential propagation?
Local current flow to adjacent area
Raises potential to threshold
Voltage gated Na+ channels open
+ve feedback
Propagation along axon
Why do action potentials only go in 1 Direction?
due to refractory period
What are the 2 Refractory Periods ?
Absolute refractory period
Na+ channels not in their resting configuration
An action potential cannot occur
Relative refractory period
The K+ channels are open
Membrane is hyperpolarised
An action potential can occur but it requires a larger stimulus
What insultes the nerve?
Myelin sheath
What are the exposed axons ?
Node of Ranvier
Local currents flow node to node
