Week 3 Flashcards
*What are passive electrical properties?
Neurons conduct current through ions, unlikes wires that use electricity
Voltage decays over distance, described using space constant - distance travelled, and time constant - speed of travel
*Describe Action Potentials (AP) in terms of conduction ?
APs amplify signals as passive conduction is insufficient
Generated by Na+ and K+ voltage-gated channels (Na+ influx = depolarisation, K+ = repolarisation)
They travel unidirectionally due to refractory period.
- Factors of Conduction velocity?
Depends on Space and time constant, Velocity∝λ/τ.
Increased axon diameter (less axial resistance) and myelination (enables saltatory conduction) enhances velocity
*Effect of Myelination?
Myelin increases conduction efficiency and speed, due to saltatory conduction = jumping
Demyelination (e.g., in Multiple Sclerosis) reduces signal amplitude/strength and increases latency.
Neuron Types and their conduction speed?
Motor neurons (alpha): Large, myelinated, fast.
Sensory neurons (beta/delta): Intermediate speed.
Pain neurons (C fibers): Small, unmyelinated, slow.
*Points about Sodium-Potassium Pump?
Maintains resting membrane potential (-70 mV) by exchanging Na⁺ (out) and K⁺ (in) ensuring the electrochemical gradient required for APs.
Na⁺ channels open rapidly, initiating APs.
K⁺ channels open slower, restoring the resting potential.
This timing difference ensures AP propagation.
*Process of Sodium-Potassium Pump?
1) Actively transports 3 Na⁺ out and 2 K⁺ in using ATP.
Maintains high Na⁺ concentration outside and high K⁺ inside the cell.
Creates a negative resting membrane potential (~-70 mV).
2) A stimulus depolarizes the membrane, reducing the negative resting potential.
Once the threshold (~-55 mV) is reached, voltage-gated Na⁺ channels open.
Na⁺ rushes into the cell, making the inside positive and generating the action potential (AP).
Repolarization:
3) After a short delay, voltage-gated K⁺ channels open, allowing K⁺ to leave the cell.
This restores the negative membrane potential.
Refractory Period:
4) Na⁺ channels close and deactivate, ensuring the AP travels in one direction.
K⁺ outflow continues briefly, creating a temporary hyperpolarization.
Resetting Gradients:
5) The Na⁺/K⁺ pump restores ion concentrations to their resting state.
This prepares the neuron for the next action potential.
Stimulation of Nerves?
Reversal of electrical gradient (depolarization) triggers APs.
Used to measure conduction velocity by stimulating at multiple sites.
Conduction travels in both directions along the nerve because the stimulation bypasses the natural directional control of the nervous system
Muscle contraction mechanism ?
*Motor units?
Made of alpha motor neuron and the associated muscle fibres
Force output depends on motor unit recruitment and firing frequency.
Precision is influenced by motor unit numbers; smaller units offer better control (e.g., eye muscles).
What is an EMG?
Electromyography
Measures electrical activity in muscles via surface or needle electrodes.
EMG signals correlate with muscle force but vary with fiber type and contraction type.
Types and Causes of muscle fatigue?
High-frequency fatigue (rapid recovery, transmission failure).
Low-frequency fatigue (longer recovery, calcium release issues).
Biochemical changes, neural contributions (e.g., central fatigue), and reduced calcium release, however Neural control adjusts via mechanisms like “muscle wisdom” to maintain performance.
Strength and training in early lifters?
Early strength gains from training arise from improved neural drive rather than muscle growth.
Electrical vs. voluntary training?
Differs in effectiveness, favoring voluntary efforts.
(check for more)
*Measurement methods for muscle contraction?
Electromyography(EMG):
Measures electrical activity in muscles via surface or needle electrodes, vary with fiber type and contraction type.
Acoustomyography (AMG): Tracks sound from muscle contractions, sensitive to fatigue.
Ultrasound: Monitors muscle length changes during contraction.
