Muscle Structure and Function, Muscle Contraction Flashcards
What are the three types of muscle tissue in the body?
Cardiac Muscle
Skeletal Muscle
Smooth Muscle
What are the functions of muscle tissue?
Produces body movements
Stabilizes body positions
Regulates organ volumes (e.g., sphincters)
Moves substances within the body (e.g., blood, food)
Produces heat (e.g., shivering)
What are the properties of muscle tissue?
Excitability: Responds to nerve signals.
Conductivity: Sends electrical signals across the cell.
Contractility: Shortens to generate force.
Extensibility: Stretches without damage.
Elasticity: Returns to its original shape after being stretched.
What are the three connective tissue layers in skeletal muscles?
Epimysium: Surrounds the entire muscle.
Perimysium: Surrounds muscle fibre bundles (fascicles).
Endomysium: Surrounds individual muscle cells (fibres).
What is a motor unit?
A motor unit consists of one motor neuron and all the muscle fibres it innervates.
What is the sarcomere, and why is it important?
The sarcomere is the basic contractile unit of muscle.
It is composed of overlapping thick (myosin) and thin (actin) filaments.
Muscle contraction occurs when these filaments slide past each other.
What are the two types of myofilaments in skeletal muscle?
Thick Filaments: Made of myosin; generates force for contraction.
Thin Filaments: Made of actin, troponin, and tropomyosin; interacts with myosin for contraction.
What are the three major proteins in muscles and their roles?
Contractile Proteins: Actin and Myosin (for contraction).
Regulatory Proteins: Troponin and Tropomyosin (control contraction).
Structural Proteins: Titin, Myomesin, Nebulin, Dystrophin (stabilize and align filaments).
What is the role of the sarcoplasmic reticulum (SR) in muscle contraction?
The SR stores calcium ions (Ca++) in a relaxed muscle.
It releases Ca++ (calcium ions) to trigger muscle contraction.
What are T-tubules, and what do they do?
T-tubules are invaginations of the sarcolemma into the muscle cell.
They carry action potentials deep into the muscle fiber, allowing for uniform contraction.
What are the functions of skeletal muscles?
Produce skeletal movement.
Maintain body position.
Support tissues.
Guard body openings.
Maintain body temperature.
Store nutrient reserves.
Provide proprioception.
What are the components of a triad in muscle fibres?
1 T-tubule and 2 terminal cisternae of the sarcoplasmic reticulum.
This structure is crucial for efficient Ca++ release and muscle contraction.
What are the differences between the A band, I band, and H zone in a sarcomere?
A band: Contains thick (myosin) filaments and areas of overlap with thin filaments.
I band: Contains only thin (actin) filaments.
H zone: Central region with only thick (myosin) filaments.
What is titin, and what is its function?
Titin is a structural protein that anchors thick filaments to the Z disc and M line.
It helps muscles recover after stretching, especially in eccentric contractions.
What is the sliding filament mechanism?
Myosin cross-bridges pull on thin filaments.
Thin filaments slide inward towards the M line.
Z discs move closer, shortening sarcomeres and the muscle fiber.
The thick and thin filaments do not change length.
What are the steps in skeletal muscle contraction?
Nerve impulse triggers ACh release at the synaptic cleft.
ACh binds to sarcolemma receptors, opening Na+ channels.
Na+ influx generates an action potential.
Action potential travels along T-tubules.
Ca++ is released from the terminal cisternae.
Ca++ binds to troponin, exposing actin-binding sites.
Myosin heads attach to actin, beginning the contraction cycle.
What are the steps of the contraction cycle?
Exposure of active sites: Ca++ binds to troponin, moving tropomyosin.
ATP hydrolysis: Myosin heads become energized.
Cross-bridge formation: Myosin binds to actin.
Power stroke: Myosin pulls thin filaments inward.
Detachment: Myosin releases actin after new ATP binds.
What happens during muscle relaxation?
Acetylcholinesterase breaks down ACh.
Ca++ channels close, and Ca++ is actively transported back to the sarcoplasmic reticulum.
Ca++ detaches from troponin.
Tropomyosin recovers actin-binding sites.
Muscle returns to its resting length.
What is the length-tension relationship in muscles?
Optimal length: Maximum overlap of thick and thin filaments produces the greatest tension.
Overstretched muscle: Few cross-bridges form, reducing force.
Overly shortened muscle: Thick filaments collide with Z discs, reducing force.
What are the three sources of ATP in muscle fibres?
Creatine phosphate: Provides energy for ~15 seconds (e.g., 100m dash).
Anaerobic respiration: Glycolysis produces ATP for 30–40 seconds.
Aerobic respiration: Produces ATP for sustained activities longer than 30 seconds.
How does creatine phosphate contribute to ATP production?
Resting muscles store excess ATP as creatine phosphate.
During activity, creatine phosphate donates phosphate to ADP, regenerating ATP.
What happens during anaerobic respiration in muscles?
Glycolysis converts glucose to pyruvate, generating ATP.
Without oxygen, pyruvate converts to lactic acid, which diffuses into the blood.
Supports activity for 30–40 seconds (e.g., 200m race).
What occurs during aerobic respiration in muscles?
Pyruvate enters mitochondria, producing ATP, water, and heat in the presence of oxygen.
Fatty acids and amino acids can also fuel ATP production.
Sustains activity longer than 30 seconds.
What role does calcium (Ca++) play in muscle contraction?
Released from the sarcoplasmic reticulum upon stimulation.
Binds to troponin, shifting tropomyosin to expose actin-binding sites.
Essential for the contraction cycle to begin.
What is the function of acetylcholinesterase (AChE)?
AChE breaks down acetylcholine in the synaptic cleft, stopping muscle stimulation and allowing relaxation.
What is the length-tension curve?
A graph showing the relationship between sarcomere length and tension:
Optimal overlap produces maximum tension (peak of curve).
Overstretching or shortening reduces force production.
