VG Na+ Channel does what
- opens quickly
- inactivates quickly
- drives rapid reversal of membrane potential
VG K+ Channel what does it do:
- opens slowly
- Stays open longer
- drives repolarization and after - hyperpolarization
The Characteristic Phases of the AP
Opening/closing of voltage gated ion channels
Depolarization involves
A 30x increase in Na+ conductance
Repolarization involves
A decrease in gNa and a delayed increases in gk
What is Conductance
Movement of charge per unit space
The VG Na+ Channel has two gates:
- A voltage dependent activation gate
- A voltage-dependent time-delayed inactivation gate
AP move down the axon
Without decrement
Local Na+ currents spread longitudinally via:
Electronic conduction and depolarize adjacent particles
The innactivation gate
Prevents AP from traveling backwards
After an AP is triggered
Neurons enter a refractory period
During the absolute refractory Periods
No AP can be triggered because the voltage-gated Na+ channels are in an inactivated state
It is generally harder to generate a new AP during the relative refractory period because:
The membrane is hyperpolarized
Signal Conduction can Occur by:
- Passive spread (electronic)
- action Potentials (AP)
- Saltatory conduction
- chemical and electronically synapses
Axonal Conditions
- combination of electronic current flow and APs
- electronic current flow is much faster than APs
- electronic current flow is graded and can only travel short distances
Factors Affecting Conduction Speed: 1. The Length Constant (lambda)
- the decay of Vm with distance in described by the length constant: lambda
Factors Affecting Conduction Speed: 2. The Time Constant (T)
Membrane voltage changes are reduced by high membrane capacitance and resistance
Factors Affecting Speed of Propagation: 1. Axon myelination
- the axon of some neurons are wrapped with myelin
- Myelination increases speed of propagation
- Segmented myelination leads to fast saltatory conduction of APs
Myelination prevents ions from leaking out through:
a membrane as the charge spreads
Charge spreads until it reaches the:
Node of Ranvier, which is packed with Na+ and K+ channels
Factors Affecting Speed of Propagation: 2. Axon Diameter
Increased axonal diameter reduces longitudinal resistance (RI), thereby increasing the length constant and conduction velocity
