The resting membrane potential Flashcards
Outline what a membrane potential is, how it may be measured and the range of values found
All cells have an electrical potential difference (voltage) across their plasma membrane. This membrane potential provides the basis of signalling in the nervous system as well as in many other types of cells.
Nerve Cells have resting potentials in the range of -70
Smooth Muscle Cells have resting potentials of around -50 mV
Cardiac and Skeletal muscle cells have the largest resting potentials of -80 to -90mV
SA node resting potential is around -60 mV
How does selective permeability of cell membranes arise?
The cell membrane is selectively permeable to different ions, the permeability of the membrane to ions occurs by way of channel proteins.
How is the resting membrane set up?
The resting membrane potential depends on the type and concentration of ion channels present, as these will dictate the cell’s permeability.
Most cells rely on K channels. K moves down its concentration gradient outside of the cell, leaving a higher concentration of negative anions within the cell. These do not follow K out as they cannot pass through the cell membrane.
What is an equilibrium potential and how would you measure it?
The equilibrium potential of an ion is the membrane potential at which there is no net movement of the ion across the membrane. This is measured by the Nernst equation.
Explain depolarisation and hyperpolarisation. How do they occur?
Depolarisation: membrane potential decreases in size, however must meet threshold to generate AP. The cell becomes less negative inside, usually through the movement of Na
Hyperpolarisation: membrane potential increases in size, below that of RMP. Cell interior becomes more negative, usually through opening of Cl or K channels
How can ion channel changes lead to membrane potential changes and cell signalling?
The RMP is a dynamic equilibrium of numerous ions with multiple ion channel types contributing to the voltage. Thus a change in just one type of channel can influence the overall RMP. Changes in membrane potential can reach threshold level and be propagated between cells or along an axon by way of an action potential.
What is the difference between fast and slow synaptic transmission?
Fast Synaptic Transmission
In fast synaptic transmission, the receptor protein is also an ion channel.
The binding of transmitter causes the channel to open.
Slow Synaptic Transmission
In slow synaptic transmission the receptor protein and ion channel are separate proteins. They may be linked either by G-Proteins or intracellular messengers.
What are ligand gated channels?
Ligand gated channels are ion channels which open in response to a messenger binding
How do ligand gated channels give rise to synaptic potentials?
There are two types of synapses, excitatory or inhibitory. Excitatory synapses depolarise the membrane in response to a ligand and generate an excitatory post synaptic potential. Inhibitory synapses hyperpolarise the membrane in response to a ligand, generating an inhibitory post synaptic potential.
What is an action potential and what are its characteristics?
An action potential is a change in voltage across a membrane. It:
(o) Depends on ionic gradients across membrane (E)
(o) Only occurs if threshold level is reached
(o) Is an all or nothing response
(o) Is propagated without loss of amplitude
The influx of Na channels moves the membrane potential towards E(Na)
If the permeability of a particular ion was increased, what would happen to the RMP relative to that ion?
Any increase in permeability of an ion will move the membrane potential closer to the equilibrium potential for that ion. This is calculated through the Nernst equation.
Explain and contrast the Absolute and Relative Refractory periods
In the Absolute Refractory Period all of the Na channels are inactive and a second action potential cannot be initiated. In the Relative Refractory Period, Na channels are recovering and becoming active again, therefore becoming more excitable. In this period it is possible to generate another action potential.
What is neural accommodation?
the ability of nerve tissue to adjust to a constant source and intensity of stimulation so that some change in either intensity or duration of the stimulus is necessary to elicit a response beyond the initial reaction. Accommodation is probably caused by reduced sodium ion permeability, which results in an increased threshold intensity and subsequent stabilization of the resting membrane potential.
Explain the difference between hydrophobic and hydrophilic pathways of local anaesthetics
Local anaesthetics work by blocking Na channels and therefore stopping depolarisation and action potential formation. Hydrophobic agents can enter the bilayer and inactivate the channel, whilst hydrophilic agents can only act on open channels from outside of the membrane. Therefore they are use dependent. LA act first on small myelinated, then unmyelinated then large myelinated axons.
Explain membrane capacitance and resistance
Capacitance is the ability to store charge and is a property of the lipid bilayer. Membrane resistance is the obstruction of the movement of charge/ ions across the membrane due to the membrane getting in the way. The more channels open, the less resistance.
