Electrotherapy: Nervous System Overview

Study Notes

Overview of the Nervous System and Neuron Function

Nervous system consists of sensory, motor, and interneurons that facilitate communication and processing of information.
Neurons are specialized cells responsible for transmitting signals throughout the body.

Types of Neurons

Sensory Neurons: Transmit sensory information from receptors to the central nervous system (CNS).
Motor Neurons: Convey signals from the CNS to muscles or glands, facilitating movement.
Interneurons: Connect sensory and motor neurons, playing a critical role in reflex arcs and processing information.

Neuron Structure

Components:
- Dendrites: Receive signals from other neurons.
- Axon: Conducts impulses away from the neuron's cell body.
- Myelin Sheath: Insulates axons to speed up signal transmission.

Resting Membrane Potential

Maintains a net positive charge outside and negative charge inside the neuron.
Mechanisms:
- Sodium-potassium pumps move three Na+ ions out for every two K+ ions in.
- Membrane permeability allows K+ to diffuse outward faster than Na+ influx.
- Large negatively charged anions inside the neuron create an imbalance, contributing to the resting potential.

Action Potential

Initiated when a stimulus depolarizes the membrane toward the threshold potential.
If the threshold is met, Na+ channels open, causing rapid depolarization.
Following peak action potential, K+ channels open allowing K+ to exit, leading to hyperpolarization.
The refractory period follows, during which the neuron's ability to fire is temporarily inhibited, restoring the resting potential.

Current Flow

Electric Current: Movement of charged particles; involves both electron and ion flow.
Electron Flow: Moves through electrical conductors between generators and electrodes.
Ion Flow: Occurs in tissues, with negative ions towards the anode and positive ions towards the cathode.

Electrical Impedance

Refers to the resistance to current flow in biological tissues.
Impedance arises from combinations of resistive and capacitive properties of tissues.
High water content in tissues facilitates better conductance and lower impedance.

Types of Electrical Currents

Direct Current (DC): Unidirectional flow; used for iontophoresis and wound care.
Alternating Current (AC): Bidirectional flow, required to change direction at least once per second; frequency measured in hertz (Hz).

Modes of Electrical Currents

Continuous Mode: Steady current flow.
Interrupted or Pulsed Mode: Current flow is periodically interrupted.

Electrical Current Classification by Frequency

Low Frequency Currents: Range 1-1000 Hz; effective for sensory and motor nerve stimulation.
Medium Frequency Currents: Around 1 kHz; requires modulation for nerve stimulation.
High Frequency Currents: Greater than 1 MHz; generally non-stimulatory to sensory and motor nerves.

Current Characteristics

Current Amplitude: Peak distance the wave rises above/below baseline.
Pulse Attributes: Include amplitude, phase duration, pulse duration, and intervals affecting muscle contraction types.

Pulse Frequency

Measured in pulses per second (pps); higher frequencies lead to different contraction types (e.g., twitch vs. tonic contraction).
Low pulse frequency allows for greater resistance than high frequency.

Rise and Decay Times

Rise time: how quickly a pulse reaches maximum amplitude.
Decay time: time taken for the pulse to drop from max to zero.
Significant for understanding nervous tissue excitability during stimulation.

Duty Cycle

Ratio of current ON time to total cycle time; calculated as a percentage.
Affects muscle stimulation patterns, starting low to prevent fatigue, gradually increasing for effectiveness.

Description

This quiz covers the physiological background of electrotherapy, focusing on the nervous system and neuron function. Topics include types of neurons, neuron structure, and resting membrane potential. Test your understanding of these fundamental concepts in neurophysiology.