Neuroscience Grade 2: Excitable Tissues

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Questions and Answers

What is the primary characteristic that distinguishes excitable tissues from non-excitable tissues?

They can produce electrical signals. (correct)

They can grow indefinitely.

They possess more cells.

They are more durable.

Which of the following best defines irritability in living tissues?

Ability to consume energy efficiently.

Ability to reproduce quickly.

Ability to respond to stimuli. (correct)

Ability to conduct electrical impulses.

What role does the Na⁺-K⁺ pump play in excitable tissues?

It increases the permeability of cell membranes.

It maintains the resting membrane potential. (correct)

It generates electrical signals directly.

It enhances muscle contraction rates.

What is one consequence of a malfunctioning Na⁺-K⁺ pump in excitable cells?

Loss of ability to respond to stimuli. Signup and view all the answers

Which ion channels are essential for generating an action potential in excitable tissues?

Sodium and Potassium channels. Signup and view all the answers

How do excitable tissues differ in response to stimuli compared to non-excitable tissues?

Excitable tissues produce action potentials. Signup and view all the answers

Which scenario indicates a potential issue with the excitability of muscle tissue?

A lack of muscle coordination. Signup and view all the answers

What distinguishes neurons from other excitable cells in the body?

Their specialized role in impulse transmission. Signup and view all the answers

What is the typical resting membrane potential of a large nerve fiber?

-90 mv Signup and view all the answers

Which ion is primarily responsible for the negative charge inside the cell at resting membrane potential?

K⁺ Signup and view all the answers

What does the Na⁺-K⁺ pump do regarding ion movement?

Pumps 3 Na⁺ ions out for every 2 K⁺ ions in Signup and view all the answers

How does the permeability of the membrane affect the resting membrane potential?

It affects the equilibrium potential of ions Signup and view all the answers

What contributes approximately 20% to the resting membrane potential?

Na⁺-K⁺ ion pump Signup and view all the answers

Which of the following factors leads to a negative resting membrane potential?

Accumulation of negatively charged proteins inside Signup and view all the answers

What is the primary charge inside the cell at resting membrane potential?

Negative Signup and view all the answers

Which ions are predominantly affected by the Na⁺-K⁺ pump?

Na⁺ and K⁺ Signup and view all the answers

What effect do Barbiturates and Benzodiazepines have on Cl- channels?

They increase the duration of Cl- channel opening. Signup and view all the answers

How does high intracellular concentration of Cl- ions affect neuronal excitability?

It leads to hyperpolarization, making it more difficult to depolarize. Signup and view all the answers

What characteristic distinguishes excitable tissues from non-excitable tissues?

Excitable tissues can undergo dramatic changes in membrane potential when stimulated. Signup and view all the answers

What is the primary role of Cl- channels in relation to cell excitability?

They influence cell excitability by altering membrane resistance. Signup and view all the answers

What happens to the input resistance of a cell that is described as 'leaky'?

It becomes low, making it difficult to change membrane potential. Signup and view all the answers

Which of the following conditions can ion channel dysfunction contribute to?

Ataxias and paralyses. Signup and view all the answers

What is the effect of low resting membrane potential on excitable tissues?

It reduces the excitability of the tissue. Signup and view all the answers

What happens to the membrane potential of excitable cells during stimulation?

It becomes less negative over milliseconds. Signup and view all the answers

Which condition is NOT related to mutations of ion channels?

Hypertension Signup and view all the answers

What effect does a modern western diet have on the sodium-potassium ratio in the body?

Creates an unnatural sodium-potassium ratio Signup and view all the answers

Which of the following mechanisms is primarily responsible for the circadian firing cycles of SCN neurones?

Change in resting membrane potential (RMP) Signup and view all the answers

How does an excess of table salt impact nerve cells?

Inhibits sodium-potassium pump function Signup and view all the answers

Which of the following processes is directly influenced by melatonin secretion?

Sleep cycles Signup and view all the answers

What does an upward deflection on a calibrated cathode ray oscilloscope indicate about the nerve cell membrane?

The inside of the membrane has become less negative. Signup and view all the answers

Which of the following correctly describes the resting membrane potential?

It is the potential recorded when the electrode passes inside the membrane. Signup and view all the answers

What is the Nernst potential for K+ ions?

-90 mv Signup and view all the answers

Why do Na+ ions tend to move into the cell while K+ ions move out?

Due to the concentration gradient across the cell membrane. Signup and view all the answers

What does the term 'membrane potential' refer to?

The separation of electric charges across the membrane. Signup and view all the answers

Which equation is used to determine the equilibrium potential for ions?

Nernst equation Signup and view all the answers

Which statement about the permeability of the nerve cell membrane is true concerning K+ and Na+ ions?

The membrane is about 100 times more permeable to K+ ions than to Na+ ions. Signup and view all the answers

What effect does permeability to K+ ions have on the membrane potential when K+ ions move?

It results in hyperpolarization of the membrane. Signup and view all the answers

Study Notes

Course Information

University: University of Baghdad
College: College of Medicine
Academic Year: 2022-2023
Module: NS (presumably Neuroscience)
Grade: 2
Lecture Title: Introduction to the excitable tissue
Speaker: Dr. Hanan Luay
Date: 4/10/2022

Objectives

Define excitable tissues
Identify the ionic basis of the resting membrane potential.
Describe the importance of the Na+-K+ pump.

What is Irritability?

All living tissues have the ability to respond to stimuli (internal or external).

What is Excitability?

Specialized cells respond to stimuli by producing electrical signals (action potentials) at the membrane.

Excitable Tissues

Muscles and nerves are excitable tissues
Excitability is due to electrical phenomena, enabling them to transmit electrochemical impulses (polarized)
Neurons (nerve cells) are specialized for receiving, integrating, and transmitting nerve impulses.

Neuron Structure

Cell body: central part of the neuron
Dendrites: branched extensions receiving signals
Myelin sheath: insulating layer encasing the axon
Axon: long extension carrying signals
Axon terminals: ends of the axon, transmitting signals to other neurons

Case Study (Patient)

A 9-year-old boy presented with difficulty moving arms and legs after a soccer game.
Weakness developed 10 minutes after the game, preventing him from standing for around 30 minutes.
He complained of weakness after consuming bananas and experienced frequent muscle spasms.

Membrane Properties

Excitable membranes have electrical excitability and can transmit impulses along the membrane.
They contain ion channels that allow selective ion flow across the membrane.

Micropipettes and Channels

Micropipettes are used to study cell ion channels.

Electrical Phenomena of Nerve Cells

The cathode ray oscilloscope is used to measure membrane potential changes
Upward deflection signifies that the inside of the membrane's potential is less negative (or more positive) relative to the outside.
Downward deflection indicates that the inside of the cell's potential becomes more negative.

Resting Membrane Potential

The membrane potential when there is no action potential occurring
Measured as zero when electrodes are outside the membrane; more negative when inside the membrane
Maintained at a stable voltage due to ion channels and active transport.

Nernest Equation

Determines the potential level across the membrane preventing net diffusion of an ion.

Equilibrium Potential

Potential necessary to prevent net ion diffusion because of ion concentration differences between intracellular and extracellular environments.
Potassium equilibrium potential is around -90 mV; sodium equilibrium potential is around +60 mV

Role of the Na+-K+ Pump

The Na+-K+ pump's role is to actively transport sodium ions out of the cell and potassium ions into the cell.
This contributes to the negative resting membrane potential, primarily by creating a difference in ion concentration across the membrane in the cell. (3 sodium ions out, 2 potassium ions in per ATP molecule).

Factors influencing overall membrane potential

Overall membrane resistance
Presence of ion channels (e.g., chloride channels)

Difference between Excitable and Non-Excitable Tissues

Non-excitable cells (e.g., epithelial, adipose cells) don't dramatically alter their membrane potential, unlike excitable cells where membrane potential changes significantly with stimulation over short periods.

Ion Channel Diseases

Mutations involving ion channels are linked to diseases such as ataxias, paralysis, epilepsy, and deafness
Also linked to other conditions like hereditary epilepsy, and hemiplegic migraines.
Diseases like idiopathic ventricular fibrillation may also be related to these mutations
Sodium-potassium pumps can be affected by illnesses impacting nerve cell resting potential.

Circadian Rhythm

Biological processes like neuronal firing frequency, and melatonin secretion (affecting sleep) are influenced by a 24-hour, daily or cyclic cycle.
Circadian rhythms involve alterations in resting membrane potential, often influenced by calcium- and potassium-channel activity.

Reference

Textbook of Medical Physiology (Guyton and Hall, 2006)

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Description

Explore the fundamental concepts of excitable tissues in this quiz. You will learn about the ionic basis of membrane potentials, the role of the Na+-K+ pump, and the nature of muscle and nerve cells. Test your understanding and define key terms associated with irritable and excitable cells.