lecture 4: Neuronal action potential Flashcards
What are **voltage gated **ion channels?
- these channels open in response to a change in membrane potential
- they give the membrane the ability to undergo action potentials
What are 2 important channels involved in the neuronal action potential?
- K+ voltage gated channel
- Na+ voltag gated channel
What are the** 3 states** of the Na+ voltage gated ion channel?
- closed
- open
- inactivated
What are the** 2 states** for K+ voltage gated ion channels?
- they are either
- open or
- closed
Explain the **differences **between Na+ and K+ voltage gated channels
- Na+ channel **responds faster **to changes in membrane voltage (aka depolarisation)
- Na+ channels have an extra feature in their structure called an** inactivation gate** which regulates the influx of Na+
Why is the resting membrane potential closer to the K+ equilibrium potential?
- there are more open K+ chanels than Na+ channels
- also due to the presence of K+ leak channels
What are the different steps for an action potential?
- RMP
- depolarising stimulus reaches threshold
- depolarisation
- peak AP
- repolarisation
- hyperpolarisation
Describe the mechanism of an action potential
- At RMP, all voltage gated channels are closed
- A **depolarising stimulus **(NT binding to receptor) causes membrane to reach **threshold
- at threshold, all Na+ voltage gated channels are open and activated & there is a big depolarisation (influx of Na+)
- At peak AP, the Na+ channel is inactivated, at the same time the K+ channel opens and K+ flows out of cell
- Repolarisation occurs and there is a huge outflow of K+, returning it back to RMP
*further movement of K+ out of cell causes hyperpolarisation (membrane even more neg than RMP) - then K+ gate closes, and membrane returns to RMP
in what direction does the action potential occur across the neuron?
- from the cell body to the axon terminal
What is an absolute refractory period?
- During an action potential, a second stimulus, no matter how strong will not produce a second AP
- this region of the membrane is said to be in in its absolute refractory period
- this occurs when the Na+ are beginning to become inactivated
What is a relative refractory period?
- following the absolute refractory period, there is an interval, in which a** second action potential can be generated** - relative refractory period
- but only if the stimulus is strong/depolarising enough
- it occurs after the period of hyperpolarisation
Where along the axon are there a high density of Na+ voltage gated channels? What is the function of this?
- the nodes of ranvier (gaps between myelin sheath)
- this is to **rapidly propagate **the action potentials in myelinated axons
What is action potenial propagation?
- the action potential in a region of a neuron will produce local currents that repolarize the region next to it, producing another AP at the next site
- the** spread of AP along the neuron**
Explain saltatory conduction of action potentials
***myelin sheath **along axons acts as an insulator, but it has a **low concentration **of voltage gated Na+ channels
* therefore action potentials can only occur at the nodes of ranvier between the myelin sheath
* AP’s **jump from one node to the next **as they propagate along a myelinated fiber
What are examples of Na+ channels antagonist/ blocker drugs?
- TTX - tetradotoxin
- lidocaine
