Action Potential and Membrane Permeability Quiz
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Questions and Answers

What happens when a weak stimulus is applied to a nerve trunk?

  • The nerve becomes refractory
  • Only a proportion of the nerve fiber is excited (correct)
  • Excitability is completely lost
  • All nerve fibers are excited simultaneously

    • During the Absolute Refractory Period (A.R.P.), what occurs in the nerve fiber?

  • Excitability is completely lost due to complete depolarization (correct)
  • Excitability gradually increases to normal level
  • Excitability is higher than normal
  • Excitability is depressed below normal level

    • What is the main factor affecting the velocity of conduction in nerve fibers?

  • The strength of the stimulus
  • Presence of myelination
  • The number of nerve fibers excited
  • Type and diameter of the nerve (correct)

    • What is the process called where the nerve impulse jumps from node to node in a myelinated nerve fiber?

    <p>Salutatory conduction</p> Signup and view all the answers

    How does the excitability change during the Relative Refractory Period (R.R.P.)?

    <p>Gradually increases to normal level</p> Signup and view all the answers

    How does stimulation of a nerve affect the propagation of a nerve impulse in an unmyelinated nerve fiber?

    <p>Flow of electrical currents between active and inactive areas affect propagation</p> Signup and view all the answers

    What is the preferred type of stimulus to stimulate a nerve fiber?

    <p>Electrical stimulus</p> Signup and view all the answers

    What is the purpose of the strength duration curve?

    <p>To illustrate the reciprocal relation between strength and duration of stimulus</p> Signup and view all the answers

    What does rheobase refer to in the context of nerve stimulation?

    <p>The minimum strength below which no response occurs despite stimulation duration</p> Signup and view all the answers

    What does chronaxie represent in nerve stimulation?

    <p>The time taken for tissue excitation with double the rheobase strength</p> Signup and view all the answers

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

    <p>-70 mV</p> Signup and view all the answers

    How does the strength duration curve demonstrate the relationship between strength and duration of a stimulus?

    <p>By indicating that greater strength is needed for shorter durations to cause a response</p> Signup and view all the answers

    What is the junction between a nerve and a muscle called?

    <p>Neuromuscular junction</p> Signup and view all the answers

    What is the potential required to trigger the action potential in neuromuscular transmission?

    <p>$-40$ mV</p> Signup and view all the answers

    What happens to acetylcholine after it triggers muscle contraction?

    <p>It is hydrolyzed into choline and acetate</p> Signup and view all the answers

    How do Ca++ ions affect the release of acetylcholine at the neuromuscular junction?

    <p>Increase release of acetylcholine</p> Signup and view all the answers

    What is the continuous state of localized subthreshold depolarization at the motor end plate during rest called?

    <p>End plate potential</p> Signup and view all the answers

    What is the main component of a motor unit?

    <p>One anterior horn cell and its axon</p> Signup and view all the answers

    During the -ve after potential, what happens to the excitability of nerve fibers?

    <p>It increases</p> Signup and view all the answers

    Which type of nerve fiber has the highest velocity of conduction?

    <p>A Fiber</p> Signup and view all the answers

    Which type of nerve fiber has very high excitability?

    <p>A Fiber</p> Signup and view all the answers

    What is responsible for restoring the normal ionic distribution in a nerve fiber after an action potential?

    <p>Membrane pump</p> Signup and view all the answers

    Which type of nerve fiber is involved in proprioception, such as muscle spindle la & Golgi tendon organs?

    <p>A Fiber</p> Signup and view all the answers

    What happens during the +ve after potential in terms of excitability and conduction velocity?

    <p>Both excitability and conduction velocity are depressed</p> Signup and view all the answers

    What is the main cause of the resting membrane potential according to the text?

    <p>High concentration of K+ inside the cell</p> Signup and view all the answers

    Which ion does the cell membrane show high permeability to, contributing to the resting membrane potential?

    <p>K+ ions</p> Signup and view all the answers

    What happens during depolarization of the cell membrane?

    <p>K+ ions influx into the cell</p> Signup and view all the answers

    What is one of the properties of action potential mentioned in the text?

    <p>The magnitude and duration are constant obeying all-or-none law</p> Signup and view all the answers

    What occurs at the end of depolarization during action potential changes?

    <p>Na+ permeability returns to normal</p> Signup and view all the answers

    What is responsible for the movement of Na+ ions into the cell during depolarization?

    <p>Increased permeability to Na+ ions</p> Signup and view all the answers

    Study Notes

    Nerve Stimulation and Action Potential

    • A weak stimulus applied to a nerve trunk will not elicit a response due to the threshold being unmet.
    • During the Absolute Refractory Period (A.R.P.) of a nerve fiber, no stimulus, regardless of strength, can evoke another action potential as the sodium channels are inactivated.

    Nerve Conduction

    • The velocity of nerve conduction is primarily influenced by the diameter of the nerve fiber and the presence of myelin.
    • Saltatory conduction describes the process of impulse propagation in myelinated nerve fibers, where the nerve impulse jumps from one node of Ranvier to the next.

    Nerve Excitability

    • During the Relative Refractory Period (R.R.P.), excitability increases, but a stronger stimulus is needed to trigger an action potential.
    • Stimulation of a nerve fiber in an unmyelinated nerve fiber causes depolarization at the stimulation site, and the impulse travels along the fiber in a continuous wave.

    Stimulus and Strength-Duration Curve

    • Electric stimuli are the preferred type for stimulating nerve fibers.
    • The strength-duration curve displays the relationship between the strength of the stimulus and the duration needed to elicit a nerve fiber's response.
    • Rheobase represents the minimum strength of stimulus required to elicit an action potential regardless of duration.
    • Chronaxie indicates the time needed for a stimulus twice the rheobase to trigger an action potential.

    Resting Membrane Potential and Action Potential

    • The resting membrane potential of a nerve cell is typically around -70 mV, where the inside of the cell is more negative than the outside.
    • The strength-duration curve demonstrates that a strong stimulus with a shorter duration can evoke an action potential while a weak stimulus requires a longer duration.

    Neuromuscular Junction

    • The junction between a nerve and a muscle is called the neuromuscular junction.
    • The potential required to trigger the action potential in neuromuscular transmission is known as the end-plate potential (EPP).
    • Acetylcholine, after triggering muscle contraction, is broken down by acetylcholinesterase (AChE).

    Calcium and Acetylcholine Release

    • Calcium ions (Ca++) play a crucial role in the release of acetylcholine at the neuromuscular junction.

    Motor Unit

    • The motor unit is the functional unit of muscle contraction, consisting of a motor neuron and all the muscle fibers it innervates.
    • During the negative after potential, nerve fibers are hyperpolarized, hence exhibiting reduced excitability.

    Nerve Fiber Types and Properties

    • Type A nerve fibers have the highest velocity of conduction.
    • Type C nerve fibers have very high excitability.
    • The sodium-potassium pump is responsible for restoring normal ionic distribution in a nerve fiber after an action potential.

    Proprioception and Positive After Potential

    • Type Ia and Ib nerve fibers, associated with proprioception, relay information from muscle spindles and Golgi tendon organs.
    • During the positive after potential, nerve fibers become hyperexcitable and experience an increased conduction velocity.

    Resting Membrane Potential and Ion Permeability

    • The resting membrane potential is primarily established by the movement of potassium ions (K+) across the cell membrane, as the membrane is more permeable to K+ than Na+.
    • Depolarization involves the movement of sodium ions (Na+) into the cell, making the inside of the cell less negative.

    Properties of Action Potential

    • One property of action potential is its "all-or-none" nature, meaning it either occurs fully or not at all.
    • Repolarization, marking the end of depolarization, occurs due to the movement of K+ ions out of the cell.
    • The movement of Na+ ions into the cell during depolarization is driven by the sodium-potassium pump and electrochemical gradients.

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    Test your knowledge on action potential, membrane permeability, ionic distribution, and after potentials in neuron physiology.

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