action potential

Question 1

explain how a membrane potential is established?

Answer 1

• K+ Is high inside the cell relative to outside
• Na+ is high on the outside relative to inside
• 3 Na+ in pumped into the cell and 2 K+ are pumped out using a sodium potassium pump
• K+ has to move via active transport as the concentration is high inside the cell using ATP
• K+ moves out of the cell down the concentration gradient through K+ channels leaving behind negatively charged ions
• inside of cell becomes negatively charged giving us a electrochemical gradient leading to potential difference

Question 2

explain how a action potential is generated?

Answer 2

• depolarisation shifts the membrane potential
• depolarisation Na+ channel open and Na+ moves into the cell so the membrane potential becomes positive then the resting potential
• repolarisation- membrane potential returns to resting potential
• K+ leaves the cell
• around 40+ Mv Na channels begint to close
• the K+ cells begin to open
• hyperpolarisation- membrane potential is more negative than the resting potential
• returns to normal -70Mv

Question 3

describe the difference between neuronal cardiac action potentials?

Answer 3

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