Excitability of Tissues and Membrane Potential
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Questions and Answers

What mechanism allows for faster impulse conduction in myelinated nerve fibers?

  • Electrical synaptic transmission
  • Chemical synaptic transmission
  • Continuous conduction along the membrane
  • Saltatory conduction (correct)

What is the primary reason for the slower propagation of impulses in unmyelinated fibers?

  • The presence of thick axonal membranes
  • Increased ion concentration in the extracellular fluid
  • The absence of nodes of Ranvier (correct)
  • Only parts of the axonal membrane depolarize

During which period can a second stimulus not produce another action potential regardless of its strength?

  • Threshold potential
  • Resting membrane potential
  • Absolute refractory period (correct)
  • Relative refractory period

What is required for an action potential to be generated during the relative refractory period?

<p>Suprathreshold stimulus (B)</p> Signup and view all the answers

What is one of the main functions of myelin in nerve fibers?

<p>To facilitate saltatory conduction by insulating the axon (C)</p> Signup and view all the answers

What primarily influences the movement of potassium ions (K+) out of the cell at resting membrane potential?

<p>Concentration gradient favoring K+ exiting (D)</p> Signup and view all the answers

Which factor does NOT contribute to the movements of ions across the cellular membrane?

<p>Cellular energy levels (D)</p> Signup and view all the answers

What is the primary reason for the relative negativity of the intracellular space at resting membrane potential?

<p>Presence of anions in the intracellular fluid (B)</p> Signup and view all the answers

What effect does the sodium-potassium pump have on ion concentration in a resting cell?

<p>It maintains higher intracellular potassium and lower sodium. (D)</p> Signup and view all the answers

How does the electrical gradient influence potassium ion movement?

<p>It attracts potassium ions back into the cell. (C)</p> Signup and view all the answers

What characterizes the resting membrane potential (RMP) of a typical neuron?

<p>Negative inside relative to outside (A)</p> Signup and view all the answers

What happens during the equilibrium potential for an ion?

<p>Rates of ion entry and exit balance out. (D)</p> Signup and view all the answers

What is the primary change in membrane potential during the depolarization phase?

<p>The inside becomes less negative, reaching a positive potential. (C)</p> Signup and view all the answers

What ion movement causes depolarization in excitable membranes?

<p>Sodium ions influx into the cell. (C)</p> Signup and view all the answers

What must be reached for an action potential to occur?

<p>The depolarization threshold. (D)</p> Signup and view all the answers

What characterizes the 'all or nothing' principle regarding action potentials?

<p>Action potentials are either triggered fully or not at all. (B)</p> Signup and view all the answers

What is observed during repolarization?

<p>The membrane potential returns to a negative value after depolarization. (A)</p> Signup and view all the answers

What occurs during hyperpolarization?

<p>The membrane potential exceeds -80mV. (A)</p> Signup and view all the answers

What causes the efflux of potassium ions during repolarization?

<p>Closure of sodium channels and opening of potassium channels. (C)</p> Signup and view all the answers

During the rapid phase of depolarization, which stage does the membrane potential reach 0mV?

<p>Stage 2 (D)</p> Signup and view all the answers

What happens to the charges on either side of the membrane during depolarization?

<p>The inside becomes positive while the outside becomes negative. (D)</p> Signup and view all the answers

What occurs during the repolarization phase of an action potential?

<p>K+ ions efflux out of the cell (C)</p> Signup and view all the answers

Which statement best describes hyperpolarization?

<p>It results in a more negative charge inside the cell than the resting potential. (C)</p> Signup and view all the answers

What is the firing level (FL) in the action potential process?

<p>The level of membrane potential where action potential is generated (A)</p> Signup and view all the answers

What happens immediately after the spike potential of an action potential?

<p>Na+ channels close (B)</p> Signup and view all the answers

How does the ion distribution at resting potential differ from during action potential?

<p>Inside the cell, Na+ concentration is higher than K+ concentration (D)</p> Signup and view all the answers

During which phase does the action potential reach peak potential?

<p>Depolarization phase (D)</p> Signup and view all the answers

What role do K+ channels play during the action potential process?

<p>They help in repolarizing the membrane after spike potential. (D)</p> Signup and view all the answers

What is overshoot in the context of action potential?

<p>The segment of action potential between zero and peak potential. (C)</p> Signup and view all the answers

What triggers the generation of an action potential?

<p>The influx of Na+ ions after reaching the firing level (D)</p> Signup and view all the answers

Flashcards

Saltatory Conduction

A faster method of nerve impulse propagation in myelinated fibers, where impulses jump between the Nodes of Ranvier.

Nodes of Ranvier

Gaps in the myelin sheath of a nerve fiber where depolarization occurs during saltatory conduction.

Absolute Refractory Period (ARP)

The time after an action potential where no stimulus, no matter how strong, can trigger another action potential due to sodium channels being open.

Relative Refractory Period

The time after the absolute refractory period where a stronger-than-usual stimulus is required to trigger an action potential.

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Refractory Period

The period after an action potential where the excitable cell cannot produce another action potential.

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High Selectivity

The ability of a membrane to preferentially allow certain molecules to pass through.

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Concentration Gradient

Difference in concentration of ions across the cell membrane.

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Electrical Gradient

Difference in electrical charge across the cell membrane. positive ions repelled (+) attracted (-)

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Sodium-Potassium Pump

A protein that actively transports sodium out and potassium into the cell.

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Membrane Potential

The voltage difference across a cell's membrane when a cell is at rest.

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Equilibrium Potential

The membrane potential at which the rate of the ion leaving the cell is equal to the rate of the ion entering the cell.

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Resting Membrane Potential (RMP)

The membrane potential of a cell when not stimulated.

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Action Potential

A momentary reversal in electrical potential across a cell membrane, triggered by a stimulus, occurring in excitable cells like neurons and muscles. It's an 'all-or-nothing' event.

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Depolarization

A change in membrane potential from negative to positive, with the inside of the cell becoming less negative.

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Repolarization

Restoration of a polarized state, where the inside of the cell returns to its negative resting membrane potential.

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Threshold

The critical level of stimulation needed to trigger an action potential.

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Resting Membrane Potential

The electrical potential difference across a cell membrane when it is not actively firing.

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Extracellular Recording

Measurement of electrical activity outside the cell.

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Intracellular Recording

Measurement of electrical activity within the cell

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Voltage-Gated Sodium Channels

Protein channels in the membrane that open and close in response to changes in membrane potential; crucial for depolarization.

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Sodium Influx

Movement of sodium ions into a cell due to a difference in concentration; crucial in initiating and propagating an action potential.

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Resting Membrane Potential

The electrical potential difference across the cell membrane when a neuron/cell is not transmitting an impulse.

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Action Potential Depolarization

The rapid change in membrane potential, making it more positive, during an action potential.

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Action Potential Repolarization

The rapid return of the membrane potential to its resting state, restoring negative charge inside.

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Hyperpolarization

A temporary, more negative membrane potential than resting potential after repolarization.

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Afterpotential

The membrane potential change after repolarizing and before returning to RMP.

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K+ Ion Channels

Channels that allow potassium ions to flow across the cell membrane.

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Firing Level (FL)

The membrane potential threshold that must be reached for an action potential to be initiated.

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Sodium Ion Influx

The movement of sodium ions from outside to inside the cell.

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Potassium Ion Efflux

The movement of potassium ions from inside to outside the cell.

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Study Notes

Excitability of Tissues

  • Complex animals consist of four tissue types: epithelial, connective, muscle, and nervous.
  • Nerve and muscle tissues are excitable tissues, responding to stimuli by generating and transmitting signals, unlike other tissue types which can only respond to stimuli.
  • Excitability involves changes in electrical states within the cell, ultimately causing action potentials that can be propagated.
  • Cells have intracellular and extracellular compartments separated by a plasma membrane.
  • This membrane is selectively permeable, controlling which molecules pass through.
  • Factors like ion charge, size, and polarity impact the movement of ions across the membrane.

Membrane Potential

  • Concentration gradients and electrical gradients influence ion movement.
  • For example, potassium ions (K+) have a higher concentration inside the cell.
  • The electrical gradient attracts K+ back into the cell due to the negative intracellular charge.
  • These opposing forces achieve equilibrium at an equilibrium potential—a balance between concentration and electrical gradients.
  • Nernst equation calculates equilibrium potential for a particular ion.

Action Potential

  • Action potential is an electrical impulse in nerve and muscle cells.
  • It starts as a depolarization, changing the membrane's electrical potential from negative to positive.
  • This is then followed by repolarization, restoring the negative potential.
  • Action potentials are triggered when a stimulus reaches a threshold voltage.
  • These are "all-or-nothing" events: if a stimulus doesn't reach this threshold value, no action potential is generated; reaching or exceeding the threshold always triggers a full response.

Factors Affecting Nerve Excitability

  • Temperature: warmer temperatures increase excitability.
  • Pressure
  • Blood supply and oxygenation: reduced supply lowers excitability.

Compound Action Potential

  • It's an aggregate of many neuronal action potentials.
  • Nerve impulses generate a compound action potential in mixed nerves, rather than a single action potential.
  • This means a compound waveform may be observed from mixed nerve stimulation.

Neuron Structure

  • A neuron is the fundamental unit of the nervous system.
  • Parts of a neuron include dendrites, cell body, axon, axon hillock, and axon terminals.
  • Dendrites receive signals from other neurons.
  • The cell body contains the nucleus and other essential organelles.
  • The axon transmits signals away from the cell body.
  • Axon terminals release neurotransmitters at synapses.
  • Different nerve types vary based on axon diameter and myelination, affecting conduction speed.
  • Myelinated vs Unmyelinated fibers

Action Potential Propagation

  • Ion channels (voltage-gated) that open and close in response to changes in membrane potential are crucial for transmitting the action potential.
  • The action potential is propagated in one direction.
  • Two types of propagation exist: electrotonic (unmyelinated) and saltatory (myelinated).
  • The myelin sheath, a fatty insulation layer, is important in saltatory propagation, as it speeds up the transmission process by "jumping" between gaps in the myelin called Nodes of Ranvier.

Refractory Period

  • A period in which the neuron cannot generate another action potential.
  • Two parts exist:
    • Absolute Refractory Period (ARP)
    • Relative Refractory Period (RRP, or relative refractory period)

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Related Documents

PHS203: Exitable Tissues & Autonomic Systems PDF

Description

Explore the concepts of tissue excitability and membrane potential in complex animals. This quiz covers the four tissue types, the role of nerve and muscle tissues, and the factors influencing ion movement across membranes. Test your knowledge on the mechanisms behind action potentials and electrical gradients!

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