Podcast
Questions and Answers
What is required for cross bridge cycling to continue during muscle contraction?
What is required for cross bridge cycling to continue during muscle contraction?
What happens to the troponin complex when Ca2+ is removed from troponin-C?
What happens to the troponin complex when Ca2+ is removed from troponin-C?
How does the frequency of stimulation affect muscle contraction strength?
How does the frequency of stimulation affect muscle contraction strength?
What role do Ca pumps in the SR play during muscle relaxation?
What role do Ca pumps in the SR play during muscle relaxation?
Signup and view all the answers
What effect does recruiting more motor units have during muscle contraction?
What effect does recruiting more motor units have during muscle contraction?
Signup and view all the answers
How does fiber length affect the tension generated during muscle contraction?
How does fiber length affect the tension generated during muscle contraction?
Signup and view all the answers
What primarily determines the speed of contraction in muscle fibers?
What primarily determines the speed of contraction in muscle fibers?
Signup and view all the answers
Which factor increases the latency period prior to muscle contraction?
Which factor increases the latency period prior to muscle contraction?
Signup and view all the answers
Which process is crucial for the reuptake of Ca2+ during muscle relaxation?
Which process is crucial for the reuptake of Ca2+ during muscle relaxation?
Signup and view all the answers
Which fiber type is associated with slow contraction speeds?
Which fiber type is associated with slow contraction speeds?
Signup and view all the answers
What conclusion can be drawn about excessive stretching of muscle fibers?
What conclusion can be drawn about excessive stretching of muscle fibers?
Signup and view all the answers
In a muscle contraction, what effect does a heavier load have on the duration of shortening?
In a muscle contraction, what effect does a heavier load have on the duration of shortening?
Signup and view all the answers
What is the primary role of cross-bridge cycling in muscle contraction?
What is the primary role of cross-bridge cycling in muscle contraction?
Signup and view all the answers
What initiates the release of acetylcholine (ACh) into the neuromuscular junction?
What initiates the release of acetylcholine (ACh) into the neuromuscular junction?
Signup and view all the answers
What occurs after acetylcholine binds to nicotinic receptors on the motor end plate?
What occurs after acetylcholine binds to nicotinic receptors on the motor end plate?
Signup and view all the answers
What part of muscle contraction is directly initiated by the end plate potential (EPP)?
What part of muscle contraction is directly initiated by the end plate potential (EPP)?
Signup and view all the answers
During excitation-contraction coupling, what is the role of Ca2+ that is released from the sarcoplasmic reticulum (SR)?
During excitation-contraction coupling, what is the role of Ca2+ that is released from the sarcoplasmic reticulum (SR)?
Signup and view all the answers
What is the effect of ATP binding to myosin during cross bridge cycling?
What is the effect of ATP binding to myosin during cross bridge cycling?
Signup and view all the answers
What structure at the motor end plate is characterized by a high density of cholinergic receptors?
What structure at the motor end plate is characterized by a high density of cholinergic receptors?
Signup and view all the answers
What type of potential is the end plate potential (EPP)?
What type of potential is the end plate potential (EPP)?
Signup and view all the answers
In cross bridge cycling, what happens after ADP and Pi are released from the myosin head?
In cross bridge cycling, what happens after ADP and Pi are released from the myosin head?
Signup and view all the answers
Study Notes
Muscle Contraction
- Myosin heads will walk along the actin filament, shortening the sarcomere, as long as there is sufficient Ca2+ and ATP available.
Ca2+ and Muscle Contraction
- Sarcoplasmic reticulum (SR) pumps actively remove Ca2+ from the cytosol, returning the troponin complex to its resting shape.
- Tropomyosin returns to its position, blocking the myosin binding sites on the actin filaments.
- Elastic fibers recoil, and the myofibril returns to its resting length.
Muscle Contraction Force and Velocity
- Motor unit: A single motor neuron innervates multiple muscle fibers, and all these fibers contract when the motor neuron transmits an action potential.
-
Graded muscle contraction: Varying the number of motor units recruited allows for controlled muscle contractions.
- The force of contraction depends on the number of myosin cross-bridges attached to actin.
Factors Influencing Cross Bridge Formation
- Frequency of stimulation: Higher frequency of stimulation leads to stronger contractions.
-
Length-tension relationship:
- Muscle fibers at their resting length have a greater capacity for shortening due to optimal overlap between thick and thin filaments.
- Excessive stretch or shortening reduces the ability of myosin heads to bind to actin.
-
Fiber arrangement:
- The physiological cross-sectional area determines muscle fiber arrangement.
-
Properties of the innervating motor neuron:
- Excitability, conduction velocity, and cell diameter influence muscle contraction velocity.
Factors Affecting Contraction Velocity
-
Fiber type:
- The rate of ATP hydrolysis by myosin depends on the myosin isoform.
- Slow fibers (type I) contain MYH7.
- Fast fibers (type II) contain MYH1 (type IIX), MYH2 (type IIA).
- The rate of ATP hydrolysis by myosin depends on the myosin isoform.
-
Rate of Ca2+ reuptake into SR:
- SERCA abundance and isoform determine the rate of Ca2+ reuptake.
-
Rate and economy of ATP transformation:
- Energy substrate and O2 availability determine the efficiency of ATP production.
-
Load:
- The lighter the load, the faster the contraction.
- Greater loads increase the latency period before contraction, reduce shortening distance, and shorten contraction duration.
-
Recruitment:
- Using more motor units for a task increases the force of contraction.
Excitation-Contraction Coupling
- Transmission of an action potential along the sarcolemma initiates the sliding filament model of muscle contraction.
- Ca2+ released from the SR following an action potential binds to Troponin-C.
- This causes a change in the troponin complex shape, moving tropomyosin away to expose the myosin binding sites on actin.
-
Cross Bridge Cycling:
- Cross bridge formation: High-energy myosin attaches to its binding site on actin.
- Power stroke: ADP and Pi are released, and the myosin head pivots and bends, pulling the attached actin filament toward the M-line.
- Cross bridge detachment: ATP attaches to low-energy myosin, detaching it from actin.
- Cocking of the myosin head: Hydrolysis of ATP returns myosin to its high-energy state.
Neuromuscular Junction
-
Acetylcholine (ACh): neurotransmitter released at the neuromuscular junction to initiate muscle fiber depolarization.
- Ca2+ influx into the axon terminal triggers ACh release.
- ACh binds to nicotinic receptors on the motor end plate, causing local depolarization.
- Motor end plate: Specialized region of sarcolemma with high density of cholinergic receptors.
-
End plate potential (EPP): A graded potential generated by the influx of Na+ and efflux of K+ across the motor end plate.
- Summation of multiple miniature EPPs is required to depolarize the sarcolemma past the threshold potential.
- The EPP spreads into the sarcolemma and triggers an action potential, which then leads to Ca2+ release from the SR and muscle contraction.
- Acetylcholinesterase degrades ACh within the synaptic cleft, preventing continued contraction.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
