Lecture 2 : Action Potentials Flashcards
Resting membrane potential
- -70mV in a neuron
- All permeable ions contribute to RMP
Eion for the 4 types of ions
How is an action potential generated?
- Resting potential is -70mV (more K+ inside cell, more Na+ outside cell)
- Stimulus causes depolarisation, Na+ voltage gated channels open
- Na+ enters cell, increasing membrane potential to -55mV, which is the THRESHOLD VALUE
- If reached, action potential triggered
- Depolarisation occurs where more Na+ channels open, membrane potential reaches +30mV
- Repolarisation occurs, Voltage gated Na+ channels close, K+ channels open, K+ exits cell, negative membrane potential restored
- Hyperpolarisation occurs because too much K+ leaves, so membrane potential is below resting
- K+ channels close, Na+ channels open to restore resting membrane potential
What is the all or nothing principle
If stimulus is below threshold, no action potential occurs.
What are the 2 gates involved in sodium movement in a neuron?
Activation Gate
- Opens in response to membrane depolarisation (when threshold potential reached)
- Lets Na+ enter neuron before the 2nd depolarisation occurs
Inactivation Gate
- Closes after activation gate opens, even if membrane is still depolarised
- Stops influx of Na+ contributing to repolarisation phase of action potential
What are the 2 types of refractory period?
Absolute refractory period
- During depolarisation and early repolarisation phase
- Na+ channels open or inactivated, another action potential cannot occur
Relative Refractory Period
- Occurs during later repolarisation and hyperpolarisation phase
- Some Na+ channels reset but K+ remains open
Ensure unidirectional action potentials, limits rate of signal transmission
What factors can increase rate of action potentials
Myelination
- Impulses can ‘jump’ between nodes of ranvier in saltatory conduction, less distance for impulse to travel so quicker
- Insulates axon, higher temp, more kinetic energy, quicker rate of movement of ions across membrane
Axon diameter
- Larger diameter, lower resistance to flow of ions
Temperature
- Ion channels open and close faster
