0308 membrane resting and action potential Flashcards
• Define a membrane potential • Explain the uneven distribution of ions across the cell membrane how it is maintained • Describe an action potential and recognise its components • Explain the role of the Na+ channel in the initiation of the AP • Explain how K+ channels are central for repolarisation • Outline the Hodgkin‐Huxley cycle • Summarise the mechanisms behind the absolute and relative refractory periods • Explain how different ion channels may influence the shape of the actio
What is a potential difference? What causes a potential difference
A potential difference is a separation of charge across a cell membrane (measure in Volts, or realistically mV). It is caused by unequal concentrations of positively and negatively charged ions across a membrane
What does the leakiness of a membrane quantify
The leakiness of a membrane describes the permeability of ions across a membrane. It describes how easily an ion can cross 1cm2 of membrane
What does the NERNST equation measure
The NERNST equation is used to calculate the equilbrium potential or Ex of an ion (potential difference at equilibrium)
What is the resting membrane potential? What value is it usually at
The RMP is the potential difference integrating the potential difference of all ions across a membrane. It is usually -60 to -70mV
What transporters maintain the RMP? What is the mechanism by which it does this (describe the process)
Na/K ATPase. It pumps 3 Na+ and 2K+ against their electrochemical gradients using ATP
What does the Goldman Equation measure
The goldman equation measures the resting membrane potential
What is an action potential? List the 3 stages of an AP
An action potential is a sudden change in RMP from -70mV to +20mV. It is the depolarisation, repolarisation and hyperpolarisation of a memrbane
List some cells that would experience action potentials
Neurons, Muscles cells (skeletal, cardiac, smooth) and Pancreatic Beta cells
What is the name of the transporters than play a key role (initiation and process) during an Action Potential
Voltage-gated channels (usually Na and K)
What is the membrane potential value at which both Na+ and K+ voltage gated channels open
About -55mV
Describe depolarisation
A drop in membrane potential to -55mV opens Na voltage gated channels. Na flows into the cell. This reduces the potential difference and depolarizes the membrane potential (Hodgkin - Huxley cycle). As the membrane depolarizes the Na channels inactivate, contributing to the stabilisation of membrane potential
Describe repolarisation
A drop in membrane potential to -55mV slowly opens K voltage gated channels. K flows out of cell, counteracting the actions of depolarisation and repolarises the cell.
Describe hyperpolarisation
As K+ voltage gated channels are slow to close, there is still efflux of K+ ions after RMP is reached (-60mV to -70mV). This causes the RMP to drop below that value
What is the Hodgkin-Huxley Cycle
Describes the process Na ions influx into cell due to depolarisation, causing more depolarisation and causing more influx of ions. Consequently, the upstroke of an AP is very explosive
What is the absolute and relative refractory period
The absolute refractory period is when a second AP cannot initiated (basically from depolarisation to repolarisation). Relative refractory period is when a stronger stimulus is requried for AP (basically during hyperpolarisation)
