L10 Nerve Conduction

Nervous System Overview

Nerve Impulses and Neurones:Nerve impulses are electrochemical signals that travel along neurones. Sensory neurones detect external stimuli, conveying this information to the central nervous system, while motor neurones transmit impulses to effectors (muscles or glands) to induce movement or secretion. Intermediate (or relay) neurones connect sensory and motor neurones, enabling reflex actions without direct brain involvement.

Key Components of Neurones:Neurones consist of a cell body that contains the nucleus, dendrites that receive and integrate signals, and an axon that transmits impulses away from the cell body. Myelin sheaths insulate the axon and enhance impulse speed, and nodes of Ranvier facilitate rapid conduction through saltatory transmission.

Impulse Transmission:In myelinated neurones, impulses jump from one node of Ranvier to another, dramatically increasing the speed of transmission compared to non-myelinated neurones, which transmit more slowly as impulses propagate uniformly along the axon.

Role of Sodium and Potassium Ions:Sodium (Na+) and potassium (K+) ions are crucial for generating and propagating electrical impulses in neurones. The rapid influx of Na+ during depolarization alters the membrane potential, whereas K+ outflow during repolarization restores the resting membrane potential, maintaining the neurone’s excitability.

Resting and Action Potential

Resting Potential:The resting potential of a neurone is typically maintained at -70mV, primarily by the sodium-potassium pump, which actively transports sodium ions out of the neurone and potassium ions into it. This gradient is vital for the neurone's readiness to fire an action potential.

Action Potential Process:An action potential is initiated when neurotransmitters bind to receptors, triggering the membrane potential to reach a threshold of -55mV. This results in depolarization to about +40mV, followed by subsequent repolarization and a phase of hyperpolarization before stabilizing at resting potential.

Heart Activity and ECG

ECG Basics:An ECG traces the electrical activity of the heart, highlighting key events in the cardiac cycle: the P wave corresponds with atrial depolarization, the QRS complex marks ventricular depolarization, and the T wave is for ventricular repolarization. ECGs are essential for monitoring heart health and diagnosing arrhythmias.

Calculating Heart Rate:Heart rate can be determined by counting the number of R waves in an ECG rhythm strip. The duration of small boxes on the ECG grid can be used to find time intervals, giving health practitioners insight into the heart's rhythm and rate.

Summary and Review

Action Potential Graph Analysis:Analysis of action potential graphs allows for understanding the interplay of sodium and potassium channels during the action potential phases. This knowledge is critical for comprehending how signals propagate along neurones and how various external factors can influence these physiological processes.