Skeletal Muscle Part 3 Flashcards
What is a Curare?
- A deadly poison that strongly binds to ACh receptors in skeletal muscle (ACh cant bind)
- Prevents ion channels from opening
- Resistant to degradation by AChE
What can Curare lead to?
- Death by asphyxiation (deprivation of oxygen)
- Curare paste-covered blow darts used to hunt prey
- Low doses previously used in clinical care settings as a muscle relaxant
What is the Antidote for Curare?
AChE inhibitors
AChE inhibitors, or acetylcholinesterase inhibitors, are a class of drugs that block the action of the enzyme acetylcholinesterase (AChE). Acetylcholinesterase is responsible for breaking down acetylcholine, a neurotransmitter involved in the transmission of nerve impulses.
What is Botulism?
- Clostridium Botulinum: an anaerobic bacteria that produces botulinum toxins, a group of neurotoxins that cause muscle paralysis
- C. Botulinum spores can be found on the surface of produce and seafood
- Botulinum toxins prevent ACh release from the axon terminal
- Causes muscle weakness and paralysis
What is Botox?
- A modified form of Botulinum toxins used to treat several medical conditions including cervical dystonia, muscle contractures and pain management
- Botox is also used for cosmetic reasons, to relax the muscles of the face, preventing the formation of wrinkles
- Botox works by temporarily paralyzing or weakening targeted muscles or blocking nerve signals to specific glands
What is the function of the transverse T tubule?
spread the action potential deep within the myofibre so that all myofibrils are affected.
What is a Cross-Bridge Cycle?
the sequence of events that occurs between the time a cross-bridge forms, moves and then is set to repeat the process.
Order of Events
Summary of the Steps involved in Muscle Contraction (1)
6
Summary of the Steps involved in Muscle Contraction (2)
6
Whats is Muscle Tension?
What is Load?
Muscle tension and load are opposing forces
Muscle Tension: the force exerted on an object by a contracting muscle
Load: the force exerted on the muscle by an object (usually its weight)
What does the change in muscle length during a contraction depends on? (5)
- The weight/force of the load
- The amount of force generated by the muscle
- The initial length of the muscle fiber
- The frequency of stimulation
- The number of motor units recruited
What occurs in an “Isotonic, Concentric Contraction”?
muscle tension is greater than the external load, resulting in a decrease in muscle length as the muscle shortens during the contraction.
What occurs in an “Isometric Contraction”?
muscle tension equals the external load, resulting in no change in muscle length during the contraction.
What happens to muscle As load increases…?
- The less the muscle can shorten
- The slower the shortening velocity
- The longer the latent period
Load-Velocity Relationship
As load increases, shortening and lengthening velocity decrease
Frequency-Tension Relationship
- While the action potential in a muscle lasts 1-2 ms, the generated tension can last ≥100 ms
- A second action potential sent before completion of the relaxation period can result in a greater peak tension
- The closer the action potentials (the shorter the interval between stimuli) → the greater the resulting peak tension
Frequency-Tension Relationship
What is Summation?
The increase in muscle tension arising from successive action potential
Frequency-Tension Relationship
What is a Tetanus?
A maintained contraction in response to repetitive stimulation
Frequency-Tension Relationship
Unfused vs Fused
- Unfused → the muscle fiber has time to partially relax between contractions/stimuli
- Fused → the muscle fiber does not have time to relax between contractions/stimuli, resulting in maintained muscle tension
What is the Sequence of motor unit recruitment?
-Motor units are recruited on a rotating basis
Sequence of motor unit recruitment goes from smallest to largest:
- Smallest motor unit contains the fewest and slowest muscle fibers
- Larger motor units contain faster, more powerful muscle fibers
When is Maximum muscle tension reached?
all motor units are recruited and in a state of fused tetanus
What happens to Calcium during a Muscle Twitch?
Ca 2+ release causes troponin to shift
Ca 2+ is pumped back into the SR almost immediately after its release ∴ tropomyosin quickly shifts back
What happens to calcium during a Tetanic contractions?
APs are sent before Ca 2+ has the time to return to the SR ∴ tropomyosin doesn’t shift
Myosin-binding sites are more available on actin -> more time for cross-bridge cycling -> greater muscle tension
What is considered the optimal length (L0)
length at which the fibre develops the greatest isometric force
What are the Three primary factors affecting Force Genaration?
What is Active tension?
The tension generated by active mechanisms (cross- bridge cycling)
What is Passive tension?
- The tension generated when a muscle is stretched beyond its resting length
- Due to elastic elements within the muscle/tendon
- Tension arises in the absence of muscle contraction
