Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
64 Cards in this Set
- Front
- Back
What is a muscle twitch?
|
A muscle twitch is the response of a muscle to a single, brief threshold stimulus
|
|
What sets off a muscle twitch?
|
A muscle AP
|
|
Is a muscle twitch a slow or fast mechanical response? How long does it last?
|
Slow mechanical response lasting 10-200 msec
|
|
From fast to start, which 3 muscles twitch quickly that we looked at?
|
1. Extraocular muscle
2. Gastrocnemius 3. Soleus |
|
What is the latent period?
|
The latent period is very brief and begins the moment muscle is stimulated
|
|
What happens during the latent period?
|
It is the time when excitation-contraction coupling occurs and slack is taken up in muscle
|
|
What is the contraction period?
|
The contraction period is the time when the muscle shortens and develops tension
|
|
What is the relaxation period?
|
The relaxation period is the time when calcium is pumped back into the SR and muscles lose tension
|
|
If a muscle could only twitch, contractions would be what?
|
Weak and jerky
|
|
Muscle responses are graded by what two things?
|
1. Change in frequency of stimulation
2. Change in strength of stimulus |
|
A single stimulus results in what?
|
A single brief weak contraction
|
|
In order to for a wave summation and tetanus to occur, what must happen?
|
Increase in frequency of stimulus and neurons fire a volley of APs
|
|
What is the effect of increasing frequency of stimulus?
|
Calcium becomes more available from SR and the muscle does not have time to relax between stimuli and twitches summate
|
|
Low stimulation frequency causes what kind of tetanus?
|
Unfused (incomplete) tetanus
|
|
High stimulation frequency causes what kind of tetanus?
|
Fused (complete) tetanus
|
|
What is recruitment?
|
Recruitment is multiple motor unit summation
|
|
As stimulus strength increases, what occurs?
|
Muscle contracts more vigorously
|
|
Why does the muscle contract more vigorously when stimulus strength increases?
|
Increases due to recruitment of motor units thus more and more muscle fibers are being stimulated
|
|
What is a motor unit?
|
A motor unit is a motor neuron and all the muscle fibers it innervates
|
|
A sustained tetanic contraction results from what?
|
Increasing the frequency of stimulus
|
|
What is the net result of weak stimulus strength recruiting motor units?
|
Stimulus strength eventually recruits the maximum number of motor units
|
|
How many fibers are in one motor unit?
|
4 to several hundred
|
|
Where are fibers in a motor unit located?
|
Located throughout the muscle
|
|
When a motor neuron fires APs, what occurs in a motor unit?
|
ALL fibers in its unit contract in unison
|
|
Small motor units in muscles control what? Examples?
|
Fine movements like in eyes or fingers
|
|
Large motor units in muscles control what? Examples?
|
Large weight-bearing muscles like in thighs and hips
|
|
What is spastic paralysis?
|
Muscle stays contracted
|
|
What is flaccid paralysis?
|
Muscle stays relaxed
|
|
What is Acetylcholinesterase?
|
It is an enzyme that breaks down ACh
|
|
Where does AChE naturally occur?
|
It naturally occurs at the motor end plate
|
|
What is the normal way a muscle relaxes when a neuron stops firing?
|
AChE degrades ACh
|
|
When AChE degrades ACh, what happens?
|
It turns off EPPs, muscle APs, and muscle contraction
|
|
As long as ACh stays bound, what will happen?
|
Channels stay open and EPPs continue (stays contraction)
|
|
What are AChE inhibitors?
|
Toxic chemicals in nerve gases and pesticides
|
|
What do AChE inhibitors cause?
|
Inhibit the action of AChE and prevent ACh breakdown
|
|
What is the effect on muscle contraction when AChE inhibitors interfere?
|
Muscle stays contracted. Unable to relax
|
|
What is Myasthenia Gravis?
|
Autoimmune disease
|
|
What does myasthenia gravis do?
|
The immune system destroys 80% of cholinergic receptors at motor end plate
|
|
What is the effect of myasthenia gravis?
|
Muscle contractions become weak and brief
|
|
What are some symptoms of myasthenia gravis?
|
Droopy eyelids, profound muscle weakness
|
|
How might a myasthenia patient be helped by taking AChE inhibitors?
|
Inhibitor would prolong the action of ACh on the remaining channels so contractions can last
|
|
When 80% of cholinergic receptors are destroyed, EPPs may not be what?
|
EPP may not be large enough to set off muscle AP or muscle contraction
|
|
What is the most potent toxin known?
|
Botulinum Toxin (Botox)
|
|
What is botulinum toxin? What does it act on and cause?
|
It is a neurotoxin that acts on motor neuron to prevent secretion of ACh.
|
|
What is the effect of the botulinum toxin on muscle contraction?
|
Muscle stays relaxed. Unable to contract.
|
|
What are three medical uses for the botulinum toxin?
|
1. Relax muscles causing crossed eyes
2. Relieve muscle spasms in stroke victims 3. Paralyze facial muscles to reduce wrinkles |
|
What is the Tetanus toxin? What does disease does it cause?
|
Tetanus is a neurotoxin that causes the disease Tetanus (lockjaw)
|
|
How does the Tetanus toxin travel through the body?
|
Tetanus travels up motor neurons and enters the CNS
|
|
What does the tetanus toxin cause?
|
It inhibits inhibitory interneurons and causes massive contractions in opposing muscles
|
|
Where does black widow spider venom act?
|
Acts at the NMJ
|
|
What does black widow spider venom enhance?
|
Enhances ACh secretion from motor neuron
|
|
What is the effect of black widow spider venom on muscle contraction?
|
Muscle stays contracted, unable relax
|
|
Black widow spider venom particularly affects what kind of motor neurons that secrete ACh?
|
It particularly affects parasympathetic motor neurons to contract smooth muscle in digestive organs
|
|
What is the result of being bit by a black widow spider?
|
Massive abdominal cramps
|
|
What is Curare?
|
It is a poison from the tubocurarine plant
|
|
Where does Curare act?
|
Curare acts at NMJ
|
|
Curare is used by who and for what?
|
Used by South American Indians for blow-dart poison
|
|
What does curare do?
|
Curare blocks cholinergic receptors on motor end plate and ACh cannot bind
|
|
What is the effect of curare on muscle contraction?
|
Muscle stays relaxed, unable to contract
|
|
What are two medical uses of curare?
|
1. Relax muscles during anesthesia and intubation
2. Relief of abdominal muscles after black widow spider bite |
|
What is hypocalcemia?
|
Low blood calcium (ECF)
|
|
What does hypocalcemia cause?
|
Causes muscle spasms
|
|
What are the muscle spasms caused by hypocalcemia called?
|
Hypocalcemic tetany
|
|
How does LOW calcium cause INCREASED muscle contraction?
|
Motor neurons become more excitable and spontaneously fires APs that set off muscle contraction
|