Nerve, Muscle, Synapse Lecture 3 Flashcards
What is the definition of resting membrane potential
Steady-state condition determined by relative permeability of membrane to K+ and Na+
What happens when ion-selective channels in the membrane are opened?
Disrupts Resting membrane potential
What are the two main types of ion channels associated with Action Potentials (in addition to Leak channels)
1) Voltage-gated ion channels 2) Ligand-gated ion channels
An action potential is generated due to activity of _____\_and _________\_. Opening these channels results in ion flow and membrane potential changes
An action potential is generated due to activity of voltage-gated Na+ channels and Voltage-gated K+ channels. Opening these channels results in ion flow and membrane potential changes
What is an action potential in terms of Resting Membrane Potential?
A large change in membrane potential from -70mV to +30mV and back to resting over a period of a few ms
How are afferents activated?
- Specific sensor for muscle stretch (stretch reflex) or other sensory stimuli results in increased opening of specialized Na+ receptors. entry of Na+ into afferent fiber and depolarization of afferent neuron
What is the threshold?
- ~-50mV
- Threshold for opening of voltage-gated Na+ channels (increase permeabilty to Na+) and an action potential
What opens voltage-gated Na+ channels?
Membrane depolarization
Depolarization removes ______ = allows ____ to flow into the cell
Depolarization removes Activation gate = allows Na+ to flow into the cell
Once activation gate is removed (via depolarization) the influx of Na+ brings the membrane potential closer to _______
Na+ equilibrium potential (+55mV) = gets to ~+30mV
The open conformation of voltage-gated ion channels only lasts a few ms. What closes the channel?
Inactivation gate
Following inactivation gate closing Na+gate, ______ results in the opening of voltage-gated K+ channel and repolarization. What happens here?
Depolarization
K+ rushes out of the cell
What is the after-hyperpolarization phase?
The permeability to K+ is greater in this phase than in resting = the voltage gated K+ channels are still open = K+ coming into the cell
What is happening at each numbered even on the Action Potential graph?
- Resting membrane potential. Voltage-gated Na+ channels are int he resting state and voltage-gated K+ channels are closed
- Stimulus causes depolarization to threshold
- Voltage-gated Na+ channel activation gates are open
- Voltage-gated K+ channels are open, Na+ channels are inactivating
- Na+ channels are in resting state but Voltage-gated K+ channels remain open
- Return to resting membrane potential. Voltage-gated Na+ channels are in resting state and voltage-gated K+ channels are closed
What are the two types of refractory periods?
- Absolute refractory period
- Relative refractory period
What is the difference between an Absolute Refractory Period and a Relative Refractory Period?
Which points on the AP graph are Absolute Refractory and which are Relative?
- Absolute: impossible to fire another AP in response to ANY stimulus no matter how strong because the voltage-gated Na+ channels are either already open or are inactivated (via inactivation gate)
- Points 3 and 4 on the AP graph are ABSOLUTE
- Relative: Possible, but difficult, to fire another AP
- Voltage-gated K+ channels are still open = low chances that we’ll have greater permeability to Na+ than K+
- Point 5 (relative refractory period)
