W1:EMG lab Flashcards
What is the size of motor units like?
Vary in size.
Small motor unit - generate less force
Large motor unit - generate more force
What is an EMG?
En electromyograph measures the electrical activity of skeletal muscle (muscle fibres) as rest and during contraction.
What can be analysed from an EMG?
The timing of contraction and relaxation
The pattern of motor neuron recruitment
Amplitude - which reflexes strength/force of muscle contraction
What are the two different methods of recoding an EMG?
Surface EMG - electrodes are placed on the skin surface
Intramuscular EMG - needle electrodes are inserted into the muscle through the skin
What are the features of a surface EMG?
Non-invasive
May be affected by adipose tissue
Restricted to superficial muscles
Cannot discriminate between the activity of adjacent muscles.
Limited use in clinical situations
What are the features of an intramuscular EMG?
Invasive
Can analyse the activity of a single motor unit (localised)
Produces consistent and accurate information for diagnostic purposes
What is the organisation of skeletal muscle?
Muscle - surrounded by epimysium
Muscle fascicle - surrounded by perimysium
Muscle fibres - surrounded by endomysium
Muscle fibres are the same as muscle cells and are made of muscle filaments (actin and myosin)
What happens to electrical activity in the muscle as the force of contraction is increased?
Amplitude on the EMG increases
Force of contraction increasing indicates more muscle fibres are being recruited indicates the involvement of more motor units.
More electrical activity underpins more mechanical contraction.
How do muscles work together to control movement around a joint?
Agonists - primary mover - concentric contraction
Antagonists - oppose movement - often by eccentric contraction when the muscle is under pressure.
These act as an antagonist pair to control movement, ensure it is coordinated.
What is meant by coactivation of muscles?
The contraction of an agonist muscle leads to minor activity in the antagonist muscle.
This is meant to help stabilse the joint during isotonic contractions
What is meant by muscle fatgiue?
The inability to maintain force during muscle contraction.
Repeated stimulation of a skeletal muscle fibre leads to decrease tnesion in that fibre (even in the presence of stimulation)
Is reversible after periods of short rest
What are the key features of muscle fatigue?
Decreased force of contraction
Decreased force of/slower relaxation
Decrease in number of active cross birdges
Decreased velocity of muscle shortening
insufficient oxygen for muscle contraction
Slower production of force
Reversible with a short period of rest
What are the key features of muscle damage?
Damage to muscle fibres
Unable to contract - no engagement is cross bridge cycles
Recovery may last a few days
What are some psychological causes of muscel fatigue?
Loss of central drive or motivation to complete a task
Change in the perceived psychological effort to complete a physical task.
What is the basic process of muscle contraction?
Initiation and conduction of an action potential along a nerve.
Release of the neurotransmitter acetylcholine (ACh), into the synaptic cleft.
Acetylcholine (ACh) binds to receptors on the motor endplate.
Depolarization of the motor endplate.
Depolarization of the muscle cell membrane.
Release of Ca2+ from the sarcoplasmic reticulum.
Crossbridge cycling (requires the presence of ATP and Ca2+).
Muscle contraction.
What are some of the physiological events that can cause muscle fatigue?
Failure of action potential to reach the skeletal muscle
Impaired initiation or conduction of action potentials along the muscle
Impaired release or reuptake of Ca2+ for cross bridge formation.
Depletion of energy sources in crossbrdige formation (ATP depletion)
In an individual undergoing strenuous exercise, what factor is likley to make their muscles suffer from fatigue first?
Loss of central drive
Due to experience of sore muscles and disorganised muscles
THis may be due to lack of ATP and accumulation of lactic acid but it is the central drive that will cause to stop before the physiological limits are reached.
What physiological factors can influence central drive?
Low blood glucose
Accumulation of lactic acid
Dehydration
Increased core body temperature
Altered blood elcetrolytes
Cerebral hypoxia.
What are the features of botox adminstration in clinc?
Adminstration is considered safe in a clincal setting
Is given in minute doses to treat muscle spasms.
Is given in small doses in the cosmetic injury.
What are the potential complications of the botulinum toxin?
Is relatively toxic
Can cause unintended paralysis if injected into the wrong muscle.
What must be done prior to taking an EMG recording?
Remove jewelry from the volunteers wrist
Lightl abrade the areas where the electrodes are to be placed with alochol wipes and allow to dry.
What is the basic set up of an EMG?
Green earth strap connected to a band around the wrist.
Electrodes placed in pairs along the muscles of interest (one negative and one positive electrode)
What is a basic definition of myasthenia gravis?
Autoimmune disease in which antibodies block or destroy nicotinic ACh receptors at the NMJ
What is a basic definition of motor neuron disease?
Motor abilities are affected due to progressive loss of motor neurons
