Question

1. What is the duration of the action potential and the amplitude?

2. how are increasingly stronger stimuli transmitted by action potential along an axon?

3. compare the extracellular ion concentrations to their respective intracellular concentrations determine the magnitude of the differences between intracellular and extracellular concentrations for each ion

Answer 1

1. Action potential duration varies depending upon the type of nerve, in a typical neuron the duration is about 1ms, in skeletal muscle the duration is about 2 to 5 ms, while in cardiac cells it is about 200 to 400 ms.

Action potential do not vary in amplitude, they are all or nothing events, sine either they occur fully or they do not occur at all.

2. As an action potential travels down a axon there is a change in the polarity across the membrane of the axon, sodium channels open at the begining of an action potential, and sodium ions move into the axon causing depolarization, these positive ions triggers the channels next to them, which lets even more positive ions, this continues down a axon in one direction only to the axon terminal, than it signals other neurons.

Large diameter axons have larger conduction velocity, which means they are able to send signals faster.this is because there is more space available so less resistance is there for ion flow. The other factor which speed up an action potential is the presence of myelin sheath, these sheath form an insulating cover and prevents scatering of ions thereby increasing the speed

3. Resting membrane potential is determined by the presence of uneven distribution of ion intracellularly and extracellularly. In a neuron sodium and chloride ions are found outside the cell in large concentration while they are found in small quantity inside the cell and more potassium ions are present inside the cell than outside the cell, these concentration gradient provide the potential energy to drive the formation of membrane potential

The intracellular concentration for sodium ion is about 15 mM and extracellular concentration is about 142 mM.

The intracellular concentration for potassium is about 150 mM and extracellular concentration is 4 mM.

The intracellular concentration for chlorine is about 5mM and extracellular concentration is about 120mM

The intracellular concentration for calcium is about 0.0001mM and extracellular concentration of about 1 mM.