Excitable Tissues Overview

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Questions and Answers

What primarily influences the movement of K+ ions out of the cell?

Solubility of K+ ions

Electrical gradient

Sodium-Potassium pump activity

Concentration gradient (correct)

What is the effect of a negative intracellular charge on K+ ions?

It repels K+ ions from entering the cell.

It prevents any ion movement across the membrane.

It has no effect on K+ ion movement.

It attracts K+ ions back towards the intracellular space. (correct)

What condition describes the resting membrane potential (RMP) of a cell?

Intracellular space is positive.

Extracellular fluid is anionic.

Sodium concentration is higher inside the cell.

Intracellular space is negative. (correct)

Which of the following correctly describes the role of the sodium-potassium pump?

It helps maintain the concentration gradients of Na+ and K+ ions. Signup and view all the answers

What causes the unequal distribution of ions across the membrane?

Active transport mechanisms. Signup and view all the answers

What occurs at the equilibrium potential for ions?

Conc.gradient and electrochemical gradient rates are equal. Signup and view all the answers

Which factor can affect the movements of ions across the cellular membrane?

Concentration gradient and electrical gradient. Signup and view all the answers

Why do K+ ions tend to exit the cell according to the concentration gradient?

Because intracellular K+ levels are significantly higher. Signup and view all the answers

What occurs immediately after the removal of the stimulating electrode from a resting cell?

K+ ions rush out of the cell Signup and view all the answers

During the depolarization phase of an action potential, what happens to the sodium ions?

They influx into the cell Signup and view all the answers

What defines the firing level (FL) in relation to membrane potential?

The initial threshold for action potential generation Signup and view all the answers

What is the term for the period after the peak potential during which the inside of the cell becomes more negative than the resting membrane potential?

After hyperpolarization Signup and view all the answers

What is the primary ion responsible for the repolarization phase of an action potential?

Potassium (K+) Signup and view all the answers

How does the ion distribution inside and outside the cell change after the action potential?

Low Na+ concentration and high K+ outside Signup and view all the answers

What characterizes the overshoot portion of the action potential?

Voltage peaks between zero and peak potential Signup and view all the answers

What occurs during the propagation of an action potential?

Transmission occurs in a wave-like fashion Signup and view all the answers

What does orthodromic impulse refer to in nerve conduction?

Propagation away from the axon terminal Signup and view all the answers

Which of the following best describes an antidromic impulse?

It occurs in the opposite direction of normal propagation. Signup and view all the answers

What is the mechanism of nerve impulse conduction in unmyelinated neurons?

Impulses are conducted in the form of action potential waves. Signup and view all the answers

Which of the following is NOT a characteristic of orthodromic impulses?

They move towards the soma. Signup and view all the answers

What role do Na+ ions play in the mechanism of nerve impulse conduction?

They open additional Na+ channels after entry. Signup and view all the answers

Which statement accurately reflects the nature of electrotonic conduction?

It involves local current flow in unmyelinated neurons. Signup and view all the answers

In what scenario would an antidromic impulse be most likely to occur?

Due to external electrical stimulation. Signup and view all the answers

Which best describes the conduction speed in unmyelinated neurons compared to myelinated ones?

Slower than in myelinated neurons. Signup and view all the answers

What is required for a subthreshold stimulus to elicit an action potential?

It must be stronger than a normal stimulus. Signup and view all the answers

During which period is a stimulus that previously failed to elicit a response likely to succeed?

Supernormal period Signup and view all the answers

Which of the following factors contributes to supernormality?

Availability of fast Na+ channels Signup and view all the answers

What occurs during the late subnormal period following the supernormal period?

The threshold current returns to baseline levels. Signup and view all the answers

What type of stimulus is classified as suprathreshold?

A stimulus stronger than threshold stimuli Signup and view all the answers

How does the proximity of the membrane potential (Em) to threshold affect excitability during the supernormal period?

It allows for easier depolarization to threshold. Signup and view all the answers

What characterizes the subnormal period of excitability?

Only larger stimuli can produce action potentials. Signup and view all the answers

What leads to the formation of compound action potentials?

Multiple stimuli. Signup and view all the answers

What determines when the resting membrane potential will equal the equilibrium potential for a particular ion?

The rate at which the ion crosses the membrane Signup and view all the answers

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

To maintain the resting membrane potential by actively transporting Na+ and K+ against their gradients Signup and view all the answers

Which of the following correctly describes how the resting membrane potential (RMP) is altered?

By altering the permeability of the membrane to various ions Signup and view all the answers

What is the Nernst Equation used for?

To calculate the value of the equilibrium potential for a specific ion Signup and view all the answers

What occurs when the threshold stimulus is applied?

The action potential is generated Signup and view all the answers

How many sodium ions are exported for every ATP molecule used by the sodium-potassium pump?

Three sodium ions Signup and view all the answers

Which method is used to measure resting membrane potential?

Intracellular recording method with two electrodes Signup and view all the answers

What happens to potassium ions during the operation of the sodium-potassium pump?

Potassium ions move into the cell against their gradient Signup and view all the answers

What initiates the action potential in excitable membranes?

A critical level of stimulus is reached Signup and view all the answers

During the depolarization phase, what happens to the inside of the cell membrane?

It experiences a positive charge Signup and view all the answers

What is the result when the sodium ion channels open during depolarization?

Sodium ions rush into the cell, causing a reversal of charge Signup and view all the answers

What is hyperpolarization during the repolarization phase?

A temporary increase in negative charge beyond resting potential Signup and view all the answers

What is the all-or-nothing principle in relation to action potentials?

Once the threshold is met, an action potential occurs or does not occur at all Signup and view all the answers

What causes repolarization to occur following the peak of action potential?

Opening of voltage-gated potassium channels Signup and view all the answers

What is the initial stage of depolarization?

From -70 mV to -55 mV Signup and view all the answers

What describes the phase of repolarization following the action potential?

Rapid return of membrane potential from positive to negative Signup and view all the answers

Study Notes

Exitable Tissues

Complex animals have four primary tissue types: epithelial, connective, muscle, and nervous.
Nerve and muscle tissues respond to stimuli (chemical, electrical, mechanical) and generate transmittable signals (action potential), classifying them as excitable tissues.
Cells have intracellular and extracellular compartments separated by the cell plasma membrane.
The cell membrane is semi-permeable, regulating the passage of molecules.
Factors affecting movement across membranes include electrical charge, molar mass, and polarity.
Ions (e.g., K+, Na+, Cl-) require specific channels for movement due to membrane structure.

Factors Mediating Ion Movement

Concentration gradient: drives ions from high to low concentration.
Electrical gradient: attracts opposite charges and repels like charges.
Active transport: requires energy to move ions against their gradient (e.g., sodium-potassium pump).
K+ ions, due to their concentration gradient, tend to exit the cell, but the electrical gradient also attracts them back. The equilibrium between these opposing forces determines the equilibrium potential (EK) for K+.

Membrane Potential

Membrane potential (Vm): difference in electrical potential across the cell membrane.
Resting membrane potential (RMP): the electrical potential difference across the membrane when the cell is at rest (typically around -70mV).
Equilibrium potential: the membrane potential at which the net movement of an ion is zero. This occurs when the concentration gradient's drive to move ions is balanced by the electrical gradient's opposing force.

Action Potential

Action potential: a rapid, transient change in membrane potential.
Depolarization: membrane becomes more positive (inside becomes more positive).
Repolarization: the membrane restores its negative potential.
Voltage-gated channels play a critical role in generating and transmitting action potentials. These channels open and close in response to changes in membrane potential.
Threshold stimulus: the minimum stimulus needed to trigger an action potential.
All-or-none response: an action potential either occurs completely or not at all; the size and shape are consistent.
Refractory period: after the action potential occurs, the cell is temporarily unable to respond to another stimulus.

Propagation of Action Potentials

Propagation of action potentials: action potentials spread along the nerve or muscle fiber.
Orthodromic: the action potential travels in the normal direction of the impulse.
Antidromic: the action potential travels in the opposite direction of the impulse.
Electrotonic conduction: local current flow in unmyelinated axons.
Saltatory conduction: action potentials "jump" between nodes of Ranvier in myelinated axons, resulting in faster conduction.
Myelin: fatty substance surrounding the axon in myelinated fibers, increasing the speed of impulse transmission.
Nodes of Ranvier: gaps in the myelin sheath where action potential generation occurs.

Refractory Period

Absolute refractory period: cell cannot respond to any stimulus, because Na+ channels are inactivated.
Relative refractory period: cell can respond to a very strong stimulus, because K+ channels are open.
Supernormal period: a period after absolute refractory period where the threshold for a stimulus is reduced (i.e. excitability is increased).
Subnormal period: a period after supernormal period where the threshold for a stimulus is increased (excitability is decreased).

Compound Action Potential

Compound action potential (CAP): the combined action potentials of multiple nerve fibers.
CAP is affected by factors including stimulation intensity, temperature, blood supply, oxygen supply, and presence of pressure.

Nerve Cells (Neuron)

Neurons: primary structural and functional units of nerve tissue.
Parts of a neuron include dendrites, cell body, axon, axon terminals and the synapse.
Dendrites: receive signals from other neurons.
Cell body: contains the nucleus and other organelles.
Axon: transmits signals away from the cell body.
Axon terminals: transmit signals to other neurons or target cells.
Myelinated versus unmyelinated: based on presence of myelin sheath.
Types of nerves (A, B, C): differentiated by size and speed of transmission.

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Description

Explore the primary tissue types, focusing on excitable tissues like nerve and muscle. Understand how these tissues respond to stimuli and the mechanisms governing ion movement across cell membranes. This quiz will cover key concepts such as concentration gradients and active transport.