why does na+ enter the cell during action potential?

Expert Solution

Because sodium is a positively charged ion, it will change the relative voltage immediately inside the cell relative to immediately outside. The resting potential is the state of the membrane at a voltage of -70 mV, so the sodium cation entering the cell will cause it to become less negative.

When the cell is at rest, and the ion channels are closed (except for leakage channels which randomly open), ions are distributed across the membrane in a very predictable way. The concentration of Na+ outside the cell is 10 times greater than the concentration inside. Also, the concentration of K+ inside the cell is greater than outside. The cytosol contains a high concentration of anions, in the form of phosphate ions and negatively charged proteins. Large anions are a component of the inner cell membrane, including specialized phospholipids and proteins associated with the inner leaflet of the membrane (leaflet is a term used for one side of the lipid bilayer membrane). The negative charge is localized in the large anions.

With the ions distributed across the membrane at these concentrations, the difference in charge is measured at -70 mV, the value described as the resting membrane potential.

Leakage channels allow Na+ to slowly move into the cell or K+ to slowly move out, and the Na+/K+ pump restores them. This may appear to be a waste of energy, but each has a role in maintaining the membrane potential.

Action potential starts with a channel opening for Na+ in the membrane. Because the concentration of Na+ is higher outside the cell than inside the cell by a factor of 10, ions will rush into the cell that are driven largely by the concentration gradient. Because sodium is a positively charged ion, it will change the relative voltage immediately inside the cell relative to immediately outside. The resting potential is the state of the membrane at a voltage of -70 mV, so the sodium cation entering the cell will cause it to become less negative. This is known as depolarization, meaning the membrane potential moves toward zero.

gladiator answered 2 years ago

1. During an Action potential, Na+ enters the cell and causes the membrane voltage to become...

1. During an Action potential, Na+ enters the cell and causes the membrane voltage to become less negative. This process is called______________. 2. During Resting Membrane Potential of a cell, Na+ is more concentrated __________ whereas K+ is more concentrated ____________. 3. At the beginning of Repolarization, ______ channels close and ______ channels open. 4. What is the name of the muscle fiber organelle that is continuous with the sarcolemma and transmits an action potential through the inside of a...

Define an action potential. How are the Na+, K+, and Ca+ ions involved in an action...

Define an action potential. How are the Na+, K+, and Ca+ ions involved in an action potential? How does the myelin speed up its transmission? Define a neurotransmitter. Where are they stored and how do they relay an action potential message from one cell to the next? Define threshold. How do neurotransmitters bring target cells toward or away from threshold. What happens to the response of the target cell if threshold is not reached? What happens if threshold is reached?...

An action potential is a. a reversal of the Na+ and K+ concentrations inside and outside...

An action potential is a. a reversal of the Na+ and K+ concentrations inside and outside the neuron. b. the same size and shape at the beginning and the end of the axon. c. initiated by inhibitory post synaptic graded potentials. d. transmitted to the distal end of a neuron and cause release of neurotransmitter. e. Both b and d are correct 2. Axonal transport refers to: a. the release of neurotransmitter molecules into the synaptic cleft. b. the use...

Match the stage in the action potential with its voltage Na+ influx K+ outflux Na+ channels...

Match the stage in the action potential with its voltage Na+ influx K+ outflux Na+ channels close Na+/K+ ATPase pump Rest Potential A.-85 mV B.-90 mv to -85 mV C.-55 mv to +30 mV D.+30 mV to -90 mV E.+30 mV

In a conduction cell like an SA node action potential, what role does calcium play?

Assume a cell with the following conditions. K+ Equilibrium Potential = -81 mV Na+ Equilibrium Potential...

Assume a cell with the following conditions. K+ Equilibrium Potential = -81 mV Na+ Equilibrium Potential = +58 mV The plasma membrane of the cell is permeable only to K+ The membrane potential is constant over time Which of the following statements is/are correct? a. The cell must expend energy to maintain a K+ concentration gradient. b. The membrane potential is -70mV. c. The rate of K+ exiting the cell is equal to the rate of K+ entering the cell....

At equilibrium potential for potassium: a) The NA+/K+ pump is pumping out of the cell? b)...

At equilibrium potential for potassium: a) The NA+/K+ pump is pumping out of the cell? b) Leak channels for potassium are closed? c) There is no current measured ? d) There an un-equal amounts of potassium ions moving across the membrane depending on the concentration difference? e) There is no potassium ions moving across the membrane?

Why does the action potential spread in only one direction (toward the axon terminal)?

Explain how an action potential when fired spreads to the rest of the axon.Why does the action potential spread in only one direction (toward the axon terminal)?Explain why action potentials are conducted more quickly and effectively (in terms of energy used) in myelinated cells than in unmyelinated cells.

Describe the sequence of steps for an action potential of one neuronal cell leads to the...

Describe the sequence of steps for an action potential of one neuronal cell leads to the action potential in a postsynaptic cell.

Describe in detail the action potential of an SA nodal cell of the heart. Be sure...

Describe in detail the action potential of an SA nodal cell of the heart. Be sure to names the phases, include the main types of membrane proteins involved, how they are opened, the movements of ions, and the changes in membrane potential. Explain how this type of action potential is different from that seen in a skeletal muscle cell and why the difference(s) are significant.

Question