Resting Membrane Potential and Excitable Tissues

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Questions and Answers

Which cation is primarily found in intracellular fluid (ICF)?

K (correct)

What is the typical resting membrane potential (RMP) of a nerve fiber?

+70 mV

-70 mV (correct)

0 mV

-90 mV

Which mechanism contributes to the development of the resting membrane potential?

Active transport of calcium

Selectively permeable membrane (correct)

Water diffusion

Endocytosis of ions

Which ion is primarily responsible for the negative charge on the inner surface of the nerve fiber during rest?

Potassium (K) Signup and view all the answers

What percentage of total body fluids do body fluids constitute?

40% Signup and view all the answers

Which statement regarding interstitial fluid is correct?

It accounts for nearly 10 L. Signup and view all the answers

What is the effect of the Na-K pump on resting membrane potential?

It helps maintain the unequal distribution of ions. Signup and view all the answers

How does the permeability of a cell membrane for K+ ions compare to that for Na+ ions?

The membrane is more permeable to K+. Signup and view all the answers

What is the primary function of the sodium-potassium pump?

To maintain the balance of sodium and potassium ions across the cell membrane Signup and view all the answers

How many sodium ions are released outside the cell during a full cycle of the sodium-potassium pump?

3 Signup and view all the answers

Which statement accurately describes the structure of the sodium-potassium pump?

It has specific binding sites for sodium and potassium ions Signup and view all the answers

What role does acetylcholine play at the motor end plate?

It activates sodium and potassium ion channels Signup and view all the answers

During depolarization in an action potential, what primarily happens to the ion channels?

Sodium channels open, allowing Na+ to enter the cell Signup and view all the answers

What is a sarcomere?

The functional unit of skeletal muscle composed of filaments Signup and view all the answers

What occurs during the phase of repolarization in an action potential?

Resting membrane potential is restored Signup and view all the answers

What is the function of the cholinesterase enzyme at the neuromuscular junction?

To hydrolyze acetylcholine into choline and acetic acid Signup and view all the answers

Study Notes

Resting Membrane Potential (RMP)

The main cation in intracellular fluid (ICF) is potassium (K+).
The total body fluids constitute about 60% of the body weight.
The ICF volume is approximately 14-15 liters.
Interstitial fluid is found in the spaces between cells, not inside them, and is about 10 liters.

Excitable Tissues

Nerves, muscles, and some glands are excitable tissues as their plasma membranes can respond to stimuli.
During rest, the inner surface of a nerve fiber is negatively charged compared to the outer surface, which is positively charged.

Resting Membrane Potential

RMP is the potential difference between the inner and outer surfaces of the cell membrane while the cell is at rest.
This difference is measured in millivolts (mV).
RMP is typically -70 mV in nerve fibers, meaning the inside is negative relative to the outside.
RMP in skeletal muscle fibers is -90 mV.

Causes of Resting Membrane Potential

Unequal distribution of ions: There is a higher concentration of K+ ions inside the cell and Na+ ions outside the cell.
Selective permeability of the cell membrane: The cell membrane is more permeable to K+ ions than Na+ ions, allowing more K+ to leak out of the cell.
Sodium-potassium pump: This active transport system continuously pumps 3 Na+ ions out of the cell and 2 K+ ions into the cell, maintaining the concentration gradients.

Sodium-Potassium Pump (Na+-K+ pump)

The Na+-K+ pump is a large protein molecule located in the cell membrane.
It has an ATP-binding site, allowing it to split ATP to obtain energy.
The pump has 3 binding sites for Na+ on the inner surface of the membrane and 2 binding sites for K+ on the outer surface.

Mechanism of Na+-K+ pump

When all binding sites are occupied, the carrier molecule undergoes a conformational change.
This change allows the pump to split ATP, releasing 3 Na+ ions to the outside and 2 K+ ions to the inside of the cell.

Action Potential (AP)

AP is the electrical change in RMP caused by an effective stimulus.
AP involves phases of:
- Depolarization: The membrane potential becomes less negative as Na+ ions rush into the cell.
- Repolarization: The membrane potential becomes more negative again as K+ ions move out of the cell.
- Redistribution of ions: The Na+-K+ pump restores the original ionic concentration gradients.

Skeletal Muscle Innervation

The motor end plate (MEP) is the region of muscle fiber that receives the signal from a motor neuron.
The MEP is postsynaptic and contains several components:
- Junctional folds: These increase the surface area of the MEP, enhancing its ability to receive signals.
- Cholinergic receptors: These receptors bind acetylcholine (Ach) and act as ion channels, allowing Na+ and K+ to pass through.
- Cholinesterase enzyme: This enzyme hydrolyzes Ach into choline and acetic acid, terminating the signal.
- Sarcomere: The functional unit of muscle, is the distance between two adjacent Z lines or discs.
- Thick filaments: Composed of myosin.

Motor Neuron Components

Axon terminal (presynaptic): This contains vesicles filled with Ach, as well as mitochondria to provide ATP.

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Description

This quiz explores the concepts of resting membrane potential (RMP) and the properties of excitable tissues such as nerves and muscles. It covers key details including ionic composition, voltage measurements, and physiological significance of RMP. Test your understanding of these fundamental topics in cellular physiology.