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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