electric potentials

• Membrane potential (mV) is the potential difference between the inside and outside of a cell
• Measured in millivolts, 1 mV = 0.001 V or 1x10-3 V
• All cells have an electrical potential (voltage) difference across their plasma membrane
• Animal cells have negative membrane potentials at rest that range from –20 to – 90 mV
• Cardiac and skeletal muscle cells have resting potentials of – 80 to – 90 mV
• Nerve cells have resting potentials in the range of – 50 to – 75 mV
• Depolarization is a decrease in the size of the membrane potential from its normal value
• Cell interior becomes less negative, e.g. a change from – 70 mV to – 50 mV
• Hyperpolarization is an increase in the size of the membrane potential from its normal value
• Cell interior becomes more negative, e.g. a change from – 70 mV to – 90 mV
• Substances diffuse from an area of high concentration to an area of low concentration
• Ions in solution are charged and exert electrostatic forces on each other, even across a membrane
• Setting up the resting potential is dependent on concentration gradients
• K+ diffusion gradient and electrical gradient are involved in setting up the resting potential
• Equilibrium potential is a balance of diffusional and electrical forces
• The Nernst equation allows you to calculate the membrane potential at which ions will be in equilibrium
• You can use the Nernst equation for any ion to calculate equilibrium potential
• Membrane potentials arise as a result of selective ionic permeability
• Changing membrane ion permeability will change the membrane potential
• Equilibrium potentials for physiological ions: K+: -90 mV, Ca2+: +120 mV, Na+: +70 mV, Cl-: -70 mV
• Channels can open and close in a process termed gating
• Different channels are gated by different stimuli, such as ligand gating, voltage gating, and mechanical gating
• Synaptic connections occur between nerve cell - nerve cell, nerve cell - muscle cell, nerve cell - gland cell, sensory cell - nerve cell
• Excitatory transmitters open ligand-gated channels causing membrane depolarization
• Inhibitory transmitters open ligand-gated channels causing hyperpolarization
• Electrogenic pumps like Na/K-ATPase can alter membrane excitability
• Active transport of ions is responsible for the entire membrane potential, setting up and maintaining ionic gradients
• A method of depolarizing the membrane potential rapidly
• A way of repolarizing (bringing back to rest) the membrane potential
• The ability to generate another action potential soon after
• A mechanism where the action potential can travel along the cell from one end to the other without loss of amplitude
• These events need to occur with minimal energy expenditure
• If the conductance (permeability) to any ion is increased, the membrane potential (Vm) will move closer to the equilibrium potential for that ion
• The conductance of the membrane to a particular ion is dependent on the number of channels for the ion that are open
• The amount of ions that move to produce a relatively large change in the membrane potential is very small
• Axon diameter (µm) and the increase in [Na+] required to produce a 100 mV depolarization
• Effect of reducing extracellular [Na+] and its impact on membrane potential
• The peak of the action potential changes in a manner parallel to the changes in ENa
• Supporting experimental evidence that Na+ is responsible for AP depolarization
• Voltage clamp technique and its role in measuring membrane currents over time at a set membrane potential