Cell Biology: Ion Movement Across Membranes

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Questions and Answers

What determines the movement of individual ions across a cell membrane?

The net electrochemical driving force. (correct)

The concentration gradient alone.

The electrical gradient alone.

The size of the ion.

What are the two main forces that result in equilibrium across a selectively permeable membrane when considering electrically charged molecules?

The attempt to achieve electroneutrality and the attempt to oppose the concentration gradient.

The attempt to achieve equal concentration and the attempt to maximize the electrical gradient.

The attempt to minimize the concentration gradient and the attempt to minimize the electrical gradient.

The attempt to achieve equal concentration and the attempt to achieve electroneutrality. (correct)

Which of the following is a primary characteristic of leakage channels?

They open and close with changes in membrane potential.

They allow for facilitated transport of large molecules.

They are always open, allowing specific ions to pass according to electrochemical gradients. (correct)

They are closed until a specific stimulus is received.

How do voltage-gated channels respond to changes in their environment?

They open and close in response to changes in the membrane potential. Signup and view all the answers

Based on the provided table, which ion is present in a higher concentration inside the cell compared to the extracellular fluid?

K+ Signup and view all the answers

According to the table, there is a high concentration of which of the following outside the cell?

Glucose Signup and view all the answers

Which of the following best describes the function of ion channels?

To selectively permit the passage of ions across the cell membrane. Signup and view all the answers

If a cell membrane is only permeable to potassium, which statement is most accurate regarding potassium movement?

Potassium movement is determined by the net electrochemical driving force. Signup and view all the answers

What primarily causes the resting membrane potential?

The diffusion of potassium and chloride ions down their concentration gradients. Signup and view all the answers

Why does the outside of the cell membrane develop a net positive charge during the establishment of the resting membrane potential?

Because potassium ions diffuse out of the cell without being replaced by an equal number of positive ions. Signup and view all the answers

What prevents potassium and sodium concentrations from reaching equilibrium across the cell membrane?

The sodium-potassium pump which actively transports ions. Signup and view all the answers

What is the primary factor that limits the outward diffusion of potassium ions during the establishment of resting membrane potential?

The negative charge buildup inside the cell attracting the potassium ions. Signup and view all the answers

Chemically-gated ion channels open when a specific molecule binds to a receptor. What is the term for this type of molecule?

Ligand. Signup and view all the answers

If a cell starts with no potential difference, what process initially generates the resting membrane potential?

The diffusion of potassium and chloride ions along their concentration gradients. Signup and view all the answers

Which statement accurately describes the movement of ions by the sodium-potassium pump?

It pumps three sodium ions out of the cell for every two potassium ions pumped in. Signup and view all the answers

Why can't the large, negatively charged intracellular molecules contribute to the positive charge build up on the outside of the cell during the formation of the resting membrane potential?

Because they are too large to cross the membrane. Signup and view all the answers

What is the relationship between the stimulus amplitude and the graded potential amplitude?

The graded potential amplitude is directly proportional to the stimulus amplitude. Signup and view all the answers

Which of the following refers to a membrane potential becoming more negative than the resting state?

Hyperpolarized Signup and view all the answers

What is the primary ion responsible for increasing membrane permeability during the action potential?

Sodium (Na+) Signup and view all the answers

What is an essential initial event for initiating an action potential?

An adequate (threshold) stimulus. Signup and view all the answers

Which of the following accurately describes a cell membrane in its resting state?

The cell membrane is described as polarized. Signup and view all the answers

What is meant by the term 'repolarization'?

The membrane potential returns to its resting state. Signup and view all the answers

Which of the following best describes the role of graded potentials in initiating action potentials?

Graded potentials cause the changes in membrane potential that lead to the opening of voltage-gated channels. Signup and view all the answers

Where on a neuron does an action potential typically originate?

At the point of adequate threshold stimulus on the axon. Signup and view all the answers

During the initial phase of an action potential, what causes the transmembrane potential to reach zero?

An influx of sodium ions. Signup and view all the answers

What is the primary cause of membrane repolarization following depolarization during an action potential?

Increased potassium permeability and efflux Signup and view all the answers

What event leads to the hyperpolarized state of the membrane following an action potential?

More potassium ions moving out than required to restore resting potential. Signup and view all the answers

What is the typical resting membrane potential of a nerve cell?

-70 mV Signup and view all the answers

What is the role of the sodium-potassium pump after an action potential?

To transport Na+ out of and K+ into the cell. Signup and view all the answers

What happens at the originally stimulated point of the membrane while the action potential propagates to the adjacent region?

The membrane's permeability to sodium decreases as Na+ channels are inactivated. Signup and view all the answers

What is the threshold potential that must be reached in a nerve cell to trigger an action potential?

-55 mV Signup and view all the answers

Which of the following best describes how depolarization propagates along the axonal membrane after initial stimulation?

By a local current acting as a stimulus to adjacent regions. Signup and view all the answers

What is the main characteristic of the synapse that makes nerve transmission unidirectional?

The presence of specific receptors on the post-synaptic membrane. Signup and view all the answers

Which of the following steps is not involved in synaptic transmission?

Sodium ions enter the pre-synaptic neuron, initiating an action potential. Signup and view all the answers

What happens to the amplitude of a compound nerve action potential as stimulus intensity increases?

It increases, as more axons reach their threshold and participate in the action potential. Signup and view all the answers

What is the role of calcium ions in synaptic transmission?

They facilitate the fusion of synaptic vesicles with the pre-synaptic membrane, releasing neurotransmitters. Signup and view all the answers

What is the primary mechanism by which most action potentials are initiated in the body?

A change in membrane potential at the axon hillock. Signup and view all the answers

Which of the following correctly describes the removal of neurotransmitters from the synaptic cleft?

Neurotransmitters can be removed by enzymatic degradation, reuptake into the pre-synaptic terminal, or diffusion. Signup and view all the answers

How does the action potential amplitude vary with stimulus intensity in a compound nerve?

It increases, as more axons are activated. Signup and view all the answers

What is the primary function of a compound nerve?

To provide a coordinated response to a stimulus. Signup and view all the answers

What primarily contributes to the variations in conduction velocity among axons within a nerve?

Differences in axon diameter and the degree of myelination. Signup and view all the answers

How are compound nerve action potentials (CNAPs) recorded?

By placing electrodes on the exterior surface of the nerve. Signup and view all the answers

What does the electrical potential refer to when recording compound action potentials?

The relative voltage at a point in an electric field with respect to reference point. Signup and view all the answers

In the context of extracellular recording, what happens when the active fibers at electrode A are externally electronegative to the fibers at electrode B?

The oscilloscope beam shows an upward deflection. Signup and view all the answers

Why does the recording beam return to zero potential in the diphasic compound action potential?

When the fibers under both electrodes are equally polarized. Signup and view all the answers

When recording a diphasic action potential using external electrodes, what causes the downward deflection of the oscilloscope beam?

When electrode B is depolarized relative to electrode A. Signup and view all the answers

What is indicated by the humps in the falling phase of an action potential recorded from a nerve?

The recruitment of different groups of axons with varying conduction velocities. Signup and view all the answers

What is the direct cause of the difference in potential between two electrodes used to record a compound nerve action potential?

The difference in the polarization states of fibers under the two electrodes. Signup and view all the answers

Study Notes

Nerve Physiology

The body constantly responds to internal and external changes, detected by sensory receptors and communicated via neurons to the central nervous system (CNS).
Neurons are the basic functional units of the nervous system, responsible for transmitting information.
Electrical forces (attraction/repulsion of ions) and concentration gradients drive passive ion transport.
Ions carry charges, positive (cations) and negative (anions). Opposite charges attract, same charges repel.

Electrical Forces and Transport

Some atoms and molecules carry a charge. Charged atoms/molecules are ions.
Positively charged ions repel, and negatively charged ions repel.
Positive and negative ions attract.
Ions in solution are influenced by pressure, concentration, and electrical forces.
Examples, Na+ (sodium) and K+ (potassium) ions interact electrically in solution.

Resting Cell Membrane Potentials

All cells have a resting membrane potential, representing the electrical potential difference across the plasma membrane when not stimulated.
This potential is due to an imbalance of charged particles (ions) across the membrane.
The exterior of the membrane has a net positive charge while the interior has a net negative charge.

Resting Membrane Potential (Cont.)

This potential difference is maintained by the unequal distribution of ions across the membrane, and the membrane's selective permeability to different ions.
Equilibrium is achieved between concentration and electrical gradients.
K+ tends to move out of the cell down its concentration gradient.
Cl- tends to move into the cell down its concentration gradient.
Na+ tends to move into the cell down its concentration gradient, but the membrane is less permeable to Na+ at rest.

Ion Channels and Membrane Potential

Ion channels are embedded in cell membranes, controlling ion movement.
Leakage channels are always open.
Gated channels open or close in response to stimuli (voltage or chemically gated).
Membrane potential is affected by the specific permeability of the membrane to different ions.

Development of Resting Potential

K+ diffuses out of the cell, Cl- diffuses inward.
Na+ cannot diffuse to the interior easily.
Large negatively charged intracellular proteins (A-) cannot diffuse outward.
Sodium-potassium pump (Na+/K+ ATPase) actively transports Na+ out of and K+ into the cell, maintaining concentration gradients.

Excitable Cells

Nerve and muscle cells have special properties: excitability and conductivity.
Their membrane potentials can change in response to stimuli, leading to action potentials.

Graded Potentials

Variable-strength signals.
Amplitude is directly related to the strength of the stimulus.
They can be depolarizing or hyperpolarizing.
Spread short distances.

Action Potentials

Rapid, large changes in membrane potential.
All-or-none phenomenon (either occur completely or not at all, in a fixed strength and duration).
Involve a sequence of specific events leading to depolarization and repolarization.

Action Potential Phases

Depolarization phase: Sodium channels open, causing the influx of sodium ions, making the membrane interior more positive.
Repolarization phase: Sodium channels inactivate, and potassium channels open, resulting in the efflux of potassium ions, returning the membrane to its resting potential.

Refractory Period

Non-responsive period following an action potential.
Absolute refractory period: No new stimulus can trigger another action potential.
Relative refractory period: A supra-threshold stimulus can trigger an action potential

Factors Affecting Conduction Velocity

Axon diameter: Larger diameters have faster conduction.
Myelin sheath: Myelinated fibers are faster due to saltatory conduction (jumping between nodes of Ranvier).
Temperature: Higher temperatures generally increase conduction velocity.

Synapse

Specialized junction between neurons.
Action potentials cause neurotransmitter release into the synapse.
Neurotransmitters bind to receptors on the postsynaptic neuron, triggering a response.
Removal of neurotransmitters is crucial to terminate signaling.

Compound Nerves

Composed of multiple axons, so action potentials observed are graded with stimulus intensity.

Recording Action Potentials

Recording electrodes detect electrical potential differences across the nerve membrane during an action potential.
The resulting tracing is the compound nerve action potential (CNAP), representing the overall electrical activity.

Disease Applications- Multiple Sclerosis

Progressive loss of myelin sheaths of neurons.
Results in impaired nerve impulse transmission.

Disease Applications- Sciatica

Inflammation of the sciatic nerve, leading to pain.
Often caused by disk injury.

Disease Applications- Epilepsy

Abnormally rapid firing of nerve impulses.
Causes seizures.
Treated with drugs like Dilantin to stabilize neuron membranes and control excessive activity.

Experimental Outline

Description of experimental setup and methodology for studying nerve impulses.

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Description

This quiz examines the factors that influence individual ions' movement across cell membranes, focusing on forces that lead to equilibrium in selectively permeable membranes. It highlights key concepts such as leakage channels, voltage-gated channels, and resting membrane potentials. Test your knowledge on ion distribution and their functions within cellular environments.