Comparative Vertebrate Physiology
Action potentials
Neuron anatomy and signaling
Action potential
DepolarizationRepolarizationHyperpolarization
Action potential Phases
Resting membrane potential Depolarization Repolarization Hyperpolarization
Nernst equation Measures equilibrium potential Depends on:
absolute temperature valence ratio of concentration gradients
Ex =RTzF
In[X]I[X]II
Nernst equation
If [K]o = 0.01M and [K]I = 0.1M
Ex =0.058z
log[X]I[X]II
Ex =0.0581
log0.010.1
=−58mV
Action potential Hodgkin and Huxley theory
Resting membrane potential
Action potential Resting membrane potential
Action potential Hodgkin and Huxley theory
Depolarization: rising phase Na+ (5,000x)
Action potential Hodgkin and Huxley theory
Repolarization : falling phase K+ (10x)
Action potential Hodgkin and Huxley theory
Hyperpolarization
Membrane permeability
Protein gates Types
Chemical Occur between neurons
Voltage Occur within neurons
Voltage gates
Refractory period Absolute
Na+ activation gate open
Relative Na+ activation gate closed
Channel toxins TTX (tetradotoxin)
Japanese puffer fish decreases Na+conductance increases K+conductance
Channel toxins TEA (tetraethylammonium)
Synthetic organic compound increases Na+conductance decreases K+conductance
Channel toxins
Threshold An all-or-none event
Threshold
Factors effecting Magnitude Duration
Excitation curve
Volts
Milliseconds
1
1
2
2
3
3
4
4 5X
Chronaxie
A
B
C
Rheobase
Impulse conduction
Impulse conduction
Schwann cell secrete myelin
Conduction velocity
Mylenated: 15 - 40 msec-1
Unmylenated: 0.4 - 0.5 msec-1