L4 Resting Membrane Potential Flashcards
Describe the four different classes of ions channels?
- Mechanically gated channels
- Voltage gated channels
- Ligand gated channels
- Leaky/Always open channels
Describe mechanically gated channels with example.
Gate opens in response to pressure or mechanical vibration such as sound waves or the pressure of touch, resulting in physical deformation of the receptor. These are usually found in the skin or ear.
Describe voltage gated channels with example.
Gate opens in response to a change in membrane potential specifically when there is depolarization of membrane e.g. Membrane potential of -70mV moves to -30mV. Each channel is specific to one ion. These are in the axon.
Describe ligand gated channels with example.
Channels normally exist in a closed state, ions can’t pass through them, however when a chemical ligand binds to the channel, the gate opens e.g. neurotransmitters like serotonin. Located in plasma membrane
Describe always open/leaky channels with example.
Aka leaky channels- these are specific to an ion and allows for to ions come in and out as they please e.g. sodium, chloride and potassium. These are found in the plasma membrane.
Definition of Resting membrane potential
The resting membrane potential is the potential difference across the cell membrane when the cell, muscle cell or neuron, is at rest (non-excitable state).
How is Resting membrane potential set up?
RMP is set up by 1. The conc. gradients of Na+ and K+ ions and 2. The permeability of the cell membrane to those ions.
Describe the setting up of RMP?
The predominant extracellular ion is Na+ while the predominant intracellular ion is K+.
The cell is more permeable to potassium ion movement than sodium ions’ because neurons have far more potassium leakage channels than sodium leakage channels.
Therefore, potassium diffuses out of the cell along its concentration gradient (high inside to low outside) at a much faster rate than sodium leaks in.
Resultantly, more cations are leaving the cell than are entering and this causes the interior of the cell to be negatively charged relative to the outside of the cell leading to the negative resting membrane potential to be created.
How is resting membrane potential measured?
Measured via the use of microelectrodes that are inserted within the cell.
What is the standard resting membrane potential of a neuron?
The standard RMP of a neuron is -70mV.
That is 70 millivolts more negative than the outside.
How is resting membrane potential maintained?
The actions of the sodium potassium pump help to maintain the resting potential.
Describe the maintainance of the resting membrane potential?
Sodium potassium pumps bring two K+ ions into the cell while removing three Na+ ions per ATP consumed. As more cations are expelled from the cell than taken in, the inside of the cell remains negatively charged relative to the outside.
Why is the cell membrane compared to a capacitor?
Inside of cell is relatively negative to the outside of cell which is relatively positive. Due the bilipid membrane of the celling being fatty it can separate the ions (electrical charges) from the inside of the cell to the outside of the cell.
What is electrochemical potential difference?
The electrical and diffusional (chemical) forces that influence the movement of K+ ions across the membrane.
How does electrochemical potential difference come about?
This arises through the movement of only K+ across the membrane.
Potassium moves along its concentration gradient (high to low), out of the cell, driven by a chemical force which results in the inside of the cell becomes negative relative to the outside, thus creating a charge imbalance and thus setting up an electrical potential.
K+ moves opposing its concentration gradient, via an electrical force, back into the cell due to unlike charges attracting each other and like charges repelling.
