- Information
- AI Chat
Excitable Cells - Term 1 Human Body Notes
The Human Body (PY4010)
Kingston University
Recommended for you
Related Studylists
human bodyPreview text
- Explain how the membrane potential is established [K+] is high inside the cell relative to outside [Na+] is low inside the cell relative to outside The Na+/K+ pump allows 3 Na+ out for every 2 K+ in. K+ has to move in via active transport as the concentration is high inside the cell, so using ATP. The Na+/K+ pump sets up a concentration gradient with more K+ inside the cell and more Na+ outside the cell. K+ moves out the cell down its concentration gradient through K+ channels, leaving behind negatively charged anions that it normally associates with. The inside of the cell is more negatively charged. This gives us an electrochemical gradient, so we have a separation of +ve and –ve ions, leading to a potential difference. Membrane potential- Voltage (difference in electrical charge) across the plasma membrane. The Na/K pump establishes a chemical gradient. The K ‘leak’ establishes an electrical gradient.
- Understand how we can calculate equilibrium potentials and membrane potentials Nernst Equation (DO NOT NEED TO LEARN EQUATION): -Used to calculate the equilibrium potential of a specific ion in a cell. -Equilibrium potential is the membrane potential at which the electrical and chemical gradients of a specific ion are balanced. -Ek is the K equilibrium potential. Around -90mV -ENa is the Na equilibrium potential. Around +60mV The Goldman Equation is used to calculate the resting membrane potential of a cell taking into account multiple ion permeabilities.
- Describe how the action potential is generated Action potential occurs when a depolarisation shifts the membrane potential sufficiently. The stimulus needs to cause sufficient depolarisation to raise the voltage above the threshold. The membrane potential does not reach ENa as the Na channels inactivate. Depolarisation- Na channels open. Na+ moves into the cell, so the membrane potential becomes more positive than the resting potential. We need to reach a certain threshold for an action potential to occur, so enough Na+ needs to enter the cell.
Repolarisation- Membrane potential returns to resting potential after depolarisation. K+ leaves the cell. At a certain membrane potential, around +40 mV, the Na+ channels begin to close, and K+ cells begin to open. Hyperpolarisation- Membrane potential is more negative than the resting potential. Then the activity of the Na+/K+ pump returns the resting potential back to normal, around –70 mV. - Describe the differences in neuronal and cardiac action potentials Neuronal: -The action potential spreads across the axon, all the way to the axon terminal. -Resting membrane potential of –70mV, duration 5ms -When the action potential reaches the synapse, the membrane will depolarise. This depolarisation allows the entry of Ca2+ into the nerve terminal. Calcium allows the fusion of synaptic vesicles with the synaptic membrane, which contain neurotransmitters. These are released into the synaptic cleft, and diffuse over to a post synaptic terminal. Cardiac: -Slower than neuronal action potentials. -Stage 1- signal comes in, which results in very rapid depolarisation. Sodium channels open. -Stage 2- plateau. K+ channels open, but some calcium channels are also activated which results in a plateau. -Stage 3- repolarisation. Calcium channels close, potassium channels open. -Stage 4- most sodium and potassium channels are closed. Action potentials are important as they underlie the electrical conduction system, which controls the rhythm of the heart. Resting membrane potential –90mV, duration 300ms
Excitable Cells - Term 1 Human Body Notes
Module: The Human Body (PY4010)
University: Kingston University
