Muscle Physiology- Pt 1 Quiz

Membrane Potential

• The membrane potential is the difference in electrical potential between the interior and exterior of a biological cell.
• It exists across the membrane of all cells and is dependent on the electrical potential of different ions and the permeability of those ions.

Resting Potential

• The resting potential is the membrane potential of non-excitable cells or excitable cells that lack excitation.
• It is approximately -70 millivolts, but can range between -40 to -90 millivolts.
• The -70 millivolt charge refers to the inside of the cell being 70 millivolts more negative than the outside of the cell.
• The diffusion of potassium has a larger impact on the resting potential in comparison to sodium.

Ion Movement and Diffusion Potential

• Diffusion potential is the charge (potential difference) generated by ions (charge molecules) moving down their concentration gradient.
• Uncharged molecules use the concentration gradient for their driving force of movement.
• Charged molecules use the concentration gradient in combination with electrical charges for their driving force of movement.
• The diffusion potential is dependent on the concentration gradient and the permeability of the membrane.

Equilibrium Potential

• Equilibrium potential stops ion movement as it is the diffusion potential that balances the tendency of ion diffusion down its concentration gradient.

Ion Channels and Pumps

• Potassium leak channels allow for potassium diffusion out of the cell, resulting in an increased negative charge within the cell.
• Sodium leak channels allow for the diffusion of sodium into the cell, causing an increased positive charge within the cell.
• The sodium-potassium pump transports 3 sodium ions out of the cell and 2 potassium ions into the cell, maintaining the negative internal charge of the cell.

Action Potential

• An action potential is the rapid change in membrane potential that spreads along a nerve fiber membrane until it reaches the nerve fiber's end.
• Each action potential starts with a rapid change from the membrane's normal negative resting membrane potential to a positive membrane potential.

Stages of Action Potential

• Step 1: Resting Stage - The membrane is at a resting membrane potential of approximately -70 millivolts.
• Step 2: Threshold - The membrane reaches a membrane potential of -55 millivolts, achieving threshold.
• Step 3: Depolarization - The influx of sodium ions into the cell results in an increased positive charge within the cell.
• Step 4: Repolarization - The voltage gated sodium channels close, resulting in an increased negative charge within the cell.
• Step 5: Hyperpolarization - The membrane potential goes below the resting membrane potential before eventually returning back to it.

Refractory Periods

• Absolute Refractory Period - The time period throughout the entire action potential, excluding the hyperpolarization stage, during which another action potential cannot start.
• Relative Refractory Period - The time period during the hyperpolarization stage when an action potential is difficult to achieve, but not impossible.

This quiz covers the concept of diffusion potential, which is generated by ions moving down their concentration gradient, affecting the electrical charge inside and outside cell membranes.