Introduction to Excitable Tissue

Study Notes

Introduction to Excitable Tissues

Excitable tissues have the unique ability to respond to stimuli, generating electrical signals known as action potentials.
Key examples include muscle and nerve tissues, which are capable of transmitting electrochemical impulses due to their polarized membranes.

Definitions and Importance

Irritability: The capacity of living tissues to respond to both external and internal stimuli.
Excitability: Specialized cells' ability to produce action potentials in response to stimuli.
These properties are essential for functions such as muscle contraction and nerve signal transmission.

Characteristics of Excitable Cell Membranes

Membranes exhibit electrical excitability, allowing transmission of impulses.
Contain various ion channels that can open or close to regulate ion flow (e.g., Na⁺, K⁺).

Resting Membrane Potential

The resting membrane potential is the voltage across a membrane when the cell is not actively sending signals.
It is recorded as less negative (or more positive) inside the cell compared to the outside owing to ion distribution.

Electrical Phenomena in Nerve Cells

Changes in membrane potential can be observed through a cathode ray oscilloscope, revealing upward (less negative) or downward (more negative) deflections.
When electrodes are outside the membrane, the recorded potential is zero, transitioning to a negative value as they enter the cell.

Nernst Equation and Equilibrium Potential

The Nernst equation calculates the equilibrium potential, which prevents the net diffusion of specific ions across the membrane.
Key equilibrium potentials:
- K⁺: approximately -90 mV
- Na⁺: approximately +60 mV
Despite these potentials, the major ions (Na⁺, K⁺, Cl⁻, Ca²⁺) are not in electrochemical equilibrium; rather, they maintain stable concentrations relative to the extracellular environment, a state termed nonequilibrium steady state.

Clinical Example

A case study of a 9-year-old boy who experiences weakness and muscle spasms after physical activity raises questions regarding ionic imbalances, particularly potassium, which is critical to muscle function.

Conclusion

Understanding excitable tissues is foundational for grasping the mechanisms underlying muscle contraction, nerve signal transmission, and the role of ions in maintaining membrane potentials.

Description

This quiz on excitable tissues covers key concepts such as the definition of excitable tissues, the ionic basis of resting membrane potential, and the significance of the Na⁺-K⁺ pump. Designed for second-year medical students, it will reinforce essential knowledge for future studies in physiology and medicine.