Biophysics

1. The threshold potential is reached, causing time and voltage sensitive sodium channels to open, causing Na+ influx.

2. Time and voltage dependant calcuium channels opne more slowly, causing efflux of K+, repolarising the membrane. 

3. The conducatnce is proportional to the number of ion channels open.

4. Increased K+ conductance causes an undershoot of the resting otential, leading to hyperpolarisation and the formation of a relative refractory period, where action potential propagation is inhibited (the absolute refractory period is during the depolarisation, where it is impossible for a new action potential to be formed). 

• Cl channels are not voltage dependant.
• The resting potential is maintained by sodium:potassium pumps. 
• Using conductance instead of permeability in the constant field equation is preferred as you don't have to use radiation to measure the conductance.
  
• A the start and end of the action potential, K+ conductance is highest and at the peak of the action potential Na+ conductance is highest.
• Conductance (g) is the inverse of resistance

Membrance capacitance

• The membrane can store charge and so is a capacitor.
• The charge in a membrane is proportional to the potential across it, with the proportionality constant being the capacitance: Q = E CM
• CM = A*gamma/d
• gamma = dielectric constant   d = membrane thickness  A = membrane area

Conduction velocity

• This is the speed at which the action potential travels.
• It is related to the space and time constant.
•                   The time constant is increased (spread slowed down) by depositing some…