Muscle and Nerve Physiology and Response to Electric Current Flashcards
What does a motor unit consist of?
One motor neuron and all the muscle fibers it stimulates
Describe the process of neuromuscular transmission
1) an action potential is carried along the alpha motor neuron and releases Ach into the synaptic cleft
2) Ach diffuses across the cleft and binds to nicotnic receptors on the end plate region of the skeletal muscle cell
3) an action potential is initiated in the skeletal muscle cell
Describe what occurs in the muscle cell once the action potential initiates it
1) the AP generated at the motor end plate region spreads along the membrane of the skeletal muscle cell and into the T tubules
2) these T tubules have receptors that connect to the Ca2+ channels
3) contraction of the muscle results from the interaction of the actin and myosin filaments (which can occur once the Ca2+ has been released through channels)
Describe the order in which nerves are depolarized. How does this relate to phase duration?
1) Sensory nerves
2) Motor nerves
3) Pain nerves
4) Muscle fibers
Nerves that take less to stimulate (depolarize) have a short phase duration, whereas those that take longer to stimulate have long phase durations
What must the phase duration be in order to depolarize a muscle fiber?
direct current
In order for a nerve to depolarize what must happen to the intensity stimulus if the duration is decreased?
The intensity will have to increase
Compare and contrast muscle contractions in skeletal and smooth muscle
Skeletal muscle contractions develop quickly but fatigue occurs
Smooth muscle contractions develop slowly and last longer
Compare and contrast ATP in skeletal and smooth muscle contractions
Skeletal muscle contractions use a lot of ATP whereas smooth muscle contractions use less
What is the primary source of calcium in skeletal muscle?
Sarcoplasmic Reticulum
What is the primary source of calcium in smooth muscle?
Extracellular Ca2+ stores
What are spontaneous depolarizations called in smooth muscle?
slow wave contractions
What connects cardiac muscle cells?
gap junctions (electrical current)
What controls cardiac muscle contractions?
The autonomic nervous system, hormones, and other intrinsic factors
Compare and contrast stimulus propagation in physiologically stimulated muscle and electrically stimulated muscle
In physiologically stimulated muscle the stimulus moves in one direction
In electrically stimulated muscle the stimulus propagates in both directions
Which muscle type is activated first physiologically?
Smaller, slow twitch Type I fibers are activated first
Which muscle type is activated first electrically?
Largest diameter Type II muscle fibers are activated first
Should GTOs be electrically stimulated?
No
Are electrically stimulated contractions effective at strengthening muscle fibers weakened by disuse?
Yes
Electrically stimulated contractions are ____ fatiguing, thus ___ rest times are needed between contractions.
more
long
Where is the place in a muscle in which electrical stimulation will produce the greatest contraction with the least amount of electricity? Why?
Over the middle of the muscle belly, because this is where the muscle is the most superficial
How far apart must electrodes be placed in order for a current to form?
2 inches
*Make sure the size of one of your electrodes can fit in the space between the electrodes
Describe monopolar electrode application
One or more small active electrodes are placed over a treatment area and a large dispersive electrode is placed somewhere else on the body
When utilizing monopolar electrode application where should the higher current density be?
Under the one electrode over the treatment area
Describe quadripolar electrode application
Two sets of bipolar electrodes; each of which comes from a completely separate channel on the electrical stimulator.
What is the purpose/proposed benefit of the crisscross pattern?
You can treat the area more focally and deeper
The _____the load placed on a muscle, and the ____ force contraction it produces, the more strength that muscle will gain.
greater
higher
How do you increase the force of muscle contraction electrically?
Increase the intensity
What are the 3 Physiologic Responses to Electric Current?
- Thermal
- Chemical
- Physiologic
What are electrical currents used to do?
Produce muscle contractions and modify pain impulses
When would you use muscle re-education over muscle strengthening?
When someone has a decent quality contraction, but require more cueing
How does electrical current activate the receptor cites on nonexcitable cells?
It stimulates the cellular changes that occur naturally with chemical molecular stimulation
Denervated muscle must be stimulated via what type of current?
Continuous direct current
Stimulation of denervated muscle must last more than __ ms
10
When stimulating denervated what must the ratio of stimulus to pause be?
1:4 or 1:5
What happens when a muscle membrane receives a second stimulus?
There is an increased mechanical shortening of the muscle fiber, due to the superimposing of one twitch contraction on another. This can lead to tetanus
What common stimulant can block the affect of TENS?
Caffeine blocks the nicotinic receptors on the effector organ
How does botulinum affect neuromuscular potential transmission?
It inhibits Ca2+ induced vesicle release from presynaptic terminals and degeneration of the terminals
How does lidocaine and other local anesthetics affect neuromuscular potential transmission?
It prevents the generation and transmission of action potentials by blocking Na+ channels
What neurons are the first to be blocked by lidocaine?
Small-diameter neurons that transmit pain information are the first to be blocked
Myasthenia Gravis is a pathology characterized by a lack of what type of receptor? What does this result in?
ACh
Therefore, muscles are not able to contract as well, and when they do they fatigue quickly. This means that they will be greatly impacted by the use of TENS
What is multiple sclerosis?
The demyelination of nerves in the CNS
How are nerves in the CNS demyelinated?
By autoimmune factors or scarring/sclerosis on the myelin of the nerves
What is the result of multiple sclerosis?
There is slow or absent conduction of impulses
Can you use e-stim on patients who are on blood thinners? Why or why not?
No, because their potential for bleeding is higher
Can you use e-stim on patients who with sickle cell anemia or hemophiliacs? Why or why not?
No, because it may cause clot deformation
What is one of the most important things to do when preparing a patient for electrical stimulation?
assess sensation
