Lecture 18 : Neurphysiology, The Action Potential Flashcards
What is the [Na+] in ECF?
135-145 mmol /L
What is the [K+] in ICF?
3.5-5 mmol /L
What is a voltage gated ion channel?
A voltage gated ion channel is a class of transmembrane proteins which are activated (opened) via the change of membrane potential near the channel.
What is the resting membrane potential?
Resting membrane potential is static. There is no movement of ions in or out. For most cells this value is usually at -70mV which means it is more - inside the cell than outside.
What is a leak channel?
Channels which constantly remain opening allowing small movement of K+ and Na+. Allows cells to keep a stable resting membrane potential.
What is the first step of action potentials?
The membrane potential undergoes depolarisation to threshold. Roughly -60mV. This changes the shape of voltage gated Na+ channels allowing Na+ to flow into the ICF. ‘Depolarisation to Threshold’
What state are the voltage gated ion channels in before an action potential?
The membrane potential is at resting membrane potential. Leak channels are open but all voltage gated ion channels are closed until a depolarisation to threshold occurs.
What is the second step of creating an action potential?
Sodium channels are now open causing a rapid depolarisation of the membrane potential. Membrane potential becomes +ve, roughly 10+.
What is the third step of creating an action potential?
Once the membrane potential reaches toughly 30+ the voltage gated sodium ion channels close and simultaneously the voltage gated potassium channels open beginning the process of repolarisation.
What is the fourth step of creating an action potential?
Here repolarization occurs as the membrane potential heads back towards the resting membrane potential of -70 mv, however it usually shoots past this in what is called hyperpolarisation going to -90mv.
What is the final step of creating an action potential?
The voltage gated potassium channel closes once RMP is reached.
What are the absolute and relative refractory periods?
The absolute refractory period is where another action potential can not be created. The relative refractory period, another action potential is prohibited but not impossible. The relative refractory period follows the absolute refractory period.
What is the purpose of the axon hillock?
The axon hillock acts as a decision point for whether or not an action potential will be passed down the axon. We can think of this as a hill. The energy has to get over the hill to initiate the action potential. The amount of energy is knows as the initiation threshold.
What is the first step of action potentials travelling down unmyelinated axons?
Initially the first segment will be depolarised to + 30 mv.
What is the second step of action potentials travelling down unmyelinated axons?
As the sodium ions spread away from the voltage gated ion channels in segment one they move towards segment two. This quickly brings the membrane potential of the second segment to threshold.
