USMLE Step 1 Physiology Review 52 08 Bioelectrical Parameters

# USMLE Step 1 Physiology Review 52 08 Bioelectrical Parameters

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### Begin 52 08 Bioelectrical Parameters Transcription

Okay, now for a few questions on bioelectrical parameters.

What are electrical currents carried by in biological systems?

• Currents are carried by ions.

Are currents carried up or down gradients of electrical potential?

• Currents are carried down gradients of electrical potential.

By convention, currents are usually expressed in terms of the flow of what kinds of charges?

• The flow of positive charges.

If the electrical potential remains constant, what happens to the current if the resistance increases?

•  If the resistance increases, the current will decrease.

If resistance remains constant, and the electrical potential increases, what happens to the current?

• The current increases.

Please express current in terms of electrical potential and resistance.

• Current equals electrical potential divided by resistance.

Now, express electrical potential in terms of resistance and current.

• Electrical potential equals current times resistance, or multiplied by resistance.

Student Doctor, please pause the tape and summarize what we have learned about bioelectric properties.

• In biological systems currents are carried by ions.  Currents are carried down gradients of electrical potential.  By convention, currents are usually expressed in terms of the flow of positive charges.  If the electrical flow remains constant, and if the resistance increases, the current will decrease.  If resistance remains constant, and the electrical potential increases, the current increases.  Current, expressed in terms of electrical potential and resistance is as follows: current equals electrical potential divided by resistance.  Electrical potential expressed in terms of resistance and current is as follows: electrical potential equals current times resistance, or multiplied by resistance.

During the propagation of excitation when currents flow outside excitable cells, differences of what develop along the lines of current flow?

• Differences or gradients of electrical potential develop along the lines of current flow.

Why do these gradients of electrical potential develop along the lines of current flow?

• They develop because of small but finite resistance of the extracellular fluids.

What are two examples of excitable cells?

• Nerve cells and Muscle cells.

Charges line up across the cell membrane with mostly which kind of charges inside and which kind of charges outside the cell?

• Charges line up across the cell membrane with negative charges inside and positive charges outside the cell.

Just prior to an action potential, positive charges pool in an area on which side of the membrane?

• On the inside of the membrane.

Student Doctor, please pause the tape and summarize what we have learned about bioelectrical properties since the last summary.

• We started off by talking about gradients of electrical potential developing along the lines of current flow.

During the propagation of excitation when currents flow outside excitable cells, differences or gradients of electrical potential develop along the line of current flow.  These gradients of electrical potential develop along the lines of current flow because of small but finite resistance of the extracellular fluids.  Nerve cells and Muscle cells are excitable.  Charges line up across the cell membrane with negative charges inside and positive charges outside the cell.  Just prior to an action potential, positive charges pool in an area on the inside of the membrane?

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