Introduction to Excitable Tissues
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Introduction to Excitable Tissues

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Questions and Answers

What is the primary factor determining the normal resting membrane potential?

  • The differential in permeability (correct)
  • The total ion concentration
  • The resting potential of other ions
  • The concentration of Na+ inside the cell

    • What is the concentration ratio of potassium ions (K+) inside to outside the cell at resting potential?

  • 1:35
  • 1:0.1
  • 0.1:1
  • 35:1 (correct)

    • What is the Nernst potential corresponding to the potassium ion concentration ratio of 35:1?

  • 61 millivolts
  • -61 millivolts
  • -94 millivolts (correct)
  • 0 millivolts

    • How does the permeability of the potassium channels affect the resting membrane potential?

    <p>It facilitates leakage of potassium ions out of the cell</p> Signup and view all the answers

    Which of the following statements about Na+ concentration is TRUE?

    <p>Na+ inside/outside ratio is 0.1</p> Signup and view all the answers

    What role does the logarithm of the potassium concentration ratio play in calculating the Nernst potential?

    <p>It determines the voltage level of the potential</p> Signup and view all the answers

    What happens to the resting membrane potential if the permeability to potassium decreases?

    <p>Resting potential becomes less negative</p> Signup and view all the answers

    Which channel is primarily responsible for the leakage of potassium ions through the nerve cell membrane?

    <p>Potassium leak channel</p> Signup and view all the answers

    Which type of excitable tissue is not classified as muscle tissue?

    <p>Nerve</p> Signup and view all the answers

    What is the primary reason electrical stimulation is often used in physiology?

    <p>It can be applied at varying durations and amplitudes to mimic natural phenomena.</p> Signup and view all the answers

    Which of the following is classified as a type of stimulus according to its intensity?

    <p>Supramaximal</p> Signup and view all the answers

    What type of stimulus is considered to be below the level needed to produce a response?

    <p>Subthreshold</p> Signup and view all the answers

    Which of the following represents a mechanical stimulus?

    <p>A blow to the eye</p> Signup and view all the answers

    Which of the following types of neurons is NOT mentioned as a functional class?

    <p>Autonomic neurons</p> Signup and view all the answers

    What is defined as any change in the environment that prompts tissue reaction?

    <p>Stimulus</p> Signup and view all the answers

    Which type of stimulus is described as the minimum necessary to generate an action potential?

    <p>Threshold</p> Signup and view all the answers

    What factor primarily determines the magnitude of the Nernst potential for potassium ions?

    <p>The ratio of potassium concentration on both sides of the membrane</p> Signup and view all the answers

    According to the Nernst equation, what happens to the electromotive force (EMF) as the concentration ratio of potassium ions increases?

    <p>The EMF increases logarithmically</p> Signup and view all the answers

    Which of the following ions is permeable through the membrane as described?

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

    What is the effect on the inside of the membrane when potassium ions diffuse outward?

    <p>It becomes more positive due to the loss of negative charges</p> Signup and view all the answers

    In the Nernst equation, what does the variable 'z' represent?

    <p>The electrical charge of the ion</p> Signup and view all the answers

    What is the typical result of achieving a strong concentration gradient for potassium ions?

    <p>It inhibits further potassium ion movement</p> Signup and view all the answers

    What is the consequence of the negative anions remaining behind as potassium ions diffuse outward?

    <p>They contribute to a net negative charge inside</p> Signup and view all the answers

    What generally happens within about 1 millisecond after potassium ions begin to diffuse across the membrane?

    <p>The diffusion potential becomes sufficient to halt further movement</p> Signup and view all the answers

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

    <p>To maintain the resting potential of the cell by transporting sodium and potassium ions</p> Signup and view all the answers

    How many sodium ions are transported out of the cell for every two potassium ions transported in by the sodium-potassium pump?

    <p>Three sodium ions</p> Signup and view all the answers

    What is the net effect on positive ions inside the cell due to the operation of the sodium-potassium pump?

    <p>A net loss of positive ions</p> Signup and view all the answers

    Why is the sodium-potassium pump considered an electrogenic pump?

    <p>It moves more positive charges out than in, contributing to electric potential</p> Signup and view all the answers

    What is the typical concentration of sodium ions outside the cell?

    <p>142 mEq/L</p> Signup and view all the answers

    Which of the following accurately describes the concentration of potassium ions inside the cell?

    <p>140 mEq/L</p> Signup and view all the answers

    What happens to the membrane potential when the sodium-potassium pump operates?

    <p>It becomes more negative due to a net loss of positive ions</p> Signup and view all the answers

    If the sodium-potassium pump stops functioning, what is likely to occur?

    <p>The cell will burst due to increased ion concentration</p> Signup and view all the answers

    What is the resting potential difference in a normal mammalian nerve fiber?

    <p>94 millivolts</p> Signup and view all the answers

    What condition causes the Nernst potential to be positive (+)?

    <p>Positive ion diffusing from inside to outside</p> Signup and view all the answers

    If the concentration of potassium ions inside the membrane is 10 times that outside, what is the calculated Nernst potential inside the membrane?

    <p>−61 millivolts</p> Signup and view all the answers

    What role do sodium ions play in generating the resting potential across a nerve fiber membrane?

    <p>They have a high concentration outside, affecting potential difference.</p> Signup and view all the answers

    What is the resting potential for skeletal muscle as indicated in the data?

    <p>−85 to −95 millivolts</p> Signup and view all the answers

    How does the permeability of the membrane to sodium ions influence the potential inside the fiber?

    <p>Contributes positively to membrane potential</p> Signup and view all the answers

    Which ion concentration is higher inside the nerve fiber according to the data?

    <p>Potassium</p> Signup and view all the answers

    What phenomenon does the diffusion potential across the nerve fiber membrane illustrate?

    <p>Ionic diffusion creates a stable potential difference.</p> Signup and view all the answers

    What is the primary characteristic of the membrane that allows for the establishment of a diffusion potential?

    <p>Selectively permeable property</p> Signup and view all the answers

    Study Notes

    Introduction to Excitable Tissues

    • Excitable tissues are defined as tissues that can respond to stimuli and generate electrical signals, which are essential for communication within the organism.
    • The nervous system requires a specific type of cell called a neuron.
    • The Nervous system is composed of sensory, motor, and mixed neurons, which transmit signals to and from the brain and spinal cord.
    • Muscles (skeletal, cardiac, and smooth), are also excitable tissues involved in movement, contraction, and other bodily functions.

    What is a Stimulus?

    • A stimulus is any change in the environment that causes a reaction in a living tissue.

    Types of Stimuli

    • According to physical nature: Electrical, chemical, mechanical, and thermal stimuli.
    • According to intensity: Subthreshold, threshold, maximal, and supramaximal stimuli.
    • According to Source: Internal and External stimuli

    Subthreshold Stimuli

    • Subthreshold stimuli are not strong enough to trigger an action potential in the nerve fiber.
    • No response is observed.

    Threshold Stimuli

    • Threshold stimuli are the minimum intensity required to trigger an action potential in at least one axon.
    • A small potential change is observed when axons with low thresholds are stimulated.

    Maximal Stimuli

    • Maximal stimuli are strong enough to trigger an action potential in all axons within a nerve fiber.
    • The observed potential change represents the full response of the neuron.

    Supramaximal Stimuli

    • Supramaximal stimuli are even stronger than maximal stimuli but do not produce a larger response.
    • The response reaches a plateau.

    Examples of Stimuli Classification

    • Electrical signals: Used in physiology to evoke responses because they resemble the normal electrical currents involved in nerve transmission. Electrical signals can have their amplitude and duration adjusted for experimental purposes.
    • Mechanical stimuli: Examples include a blow to the eye.
    • Chemical stimuli: Substances like neurotransmitters or hormones can act as stimuli.
    • Thermal stimuli: Heat and cold can also trigger responses in excitable tissues.

    The Role of the Nernst Potential

    • The Nernst potential is a key concept in understanding how electrical gradients are established and maintained across cell membranes.
    • The Nernst potential refers to the electrical potential across a cell membrane that is required to prevent the net movement of a specific ion across it.
    • It is determined by the ratio of the concentrations of the ion on either side of the membrane.
    • The Nernst equation calculates the Nernst potential for any univalent ion at a given temperature.

    Resting Membrane Potential (RMP)

    • Resting membrane potential refers to the electrical potential difference across the membrane of a neuron or muscle cell in its resting, undisturbed state.
    • The RMP is typically negative inside the cell compared to the outside.
    • Various factors contribute to RMP, including the permeability of the membrane to different ions, the concentration gradients of ions across the membrane, and electrogenic pumps.

    Role of the Sodium-Potassium Pump (Na+-K+ Pump)

    • The Na+-K+ pump is an active transport system that plays a crucial role in establishing and maintaining the RMP.
    • The pump actively transports sodium ions out of the cell and potassium ions into the cell.
    • This pump contributes to maintaining the concentration gradients of Na+ and K+ across the membrane, ultimately impacting the RMP.

    Leakage of Potassium Through the Membrane

    • Even in the resting state, potassium ions can leak out of the cell through specialized potassium channels.
    • The permeability of the membrane to potassium ions is higher than that of sodium ions, contributing to the RMP being negative inside the cell.

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    Description

    This quiz covers the fundamental concepts of excitable tissues, including the nervous system and muscles. Learn how these tissues respond to different types of stimuli and their roles in bodily functions. Test your understanding of neurons, types of stimuli, and their classifications.

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