Week 34 / Muscle, Joints & Bones -6 Flashcards
Q: What are the characteristics of skeletal muscle?
A: Skeletal muscle:
Makes up 40-50% of total body weight
Voluntary control
Primarily responsible for movement of bones and body parts
Stabilizes body positions
Q: What are the characteristics of cardiac muscle?
A: Cardiac muscle:
Found only in the heart
Involuntary control
Develops pressure for arterial blood flow
the Special Characteristics of Muscle:
Q: What is excitability in muscle tissue?
Q: What is contractility in muscle tissue?
Q: What is extensibility in muscle tissue?
Q: What is elasticity in muscle tissue?
A: Excitability (responsiveness or irritability) is the ability of muscle tissue to receive and respond to stimuli.
A: Contractility is the ability of muscle tissue to shorten when stimulated.
A: Extensibility is the ability of muscle tissue to be stretched.
A: Elasticity is the ability of muscle tissue to recoil to its resting length after being stretched.
Q: What are the characteristics of smooth muscle?
A: Smooth muscle:
Located in the walls of hollow organs and tubes
Regulates movement of blood, food, air, and urine through respective systems
Controls contractions that maintain tube diameters, such as in blood vessels, the gastrointestinal tract, and respiratory airways
Q: How does skeletal muscle help in maintaining posture and body position?
A: Skeletal muscles help maintain posture and body position by holding the head still when reading a book or balancing body weight when walking.
Q: What is the role of skeletal muscle in producing movement?
A: Skeletal muscles are responsible for producing movement, such as moving the arm or breathing, as well as coordinating complex movements like swimming or piano playing.
Q: How do skeletal muscles support soft tissues?
A: Skeletal muscles form the abdominal wall and pelvic floor cavity, supporting the weight of visceral organs and protecting internal tissues from injury.
Q: How do skeletal muscles guard body entrances and exits?
A: Skeletal muscles control the openings of the digestive and urinary tracts, giving us voluntary control over functions like swallowing, defecating, and urinating.
Q: How do skeletal muscles help in maintaining body temperature?
A: Skeletal muscles release heat during contraction, which helps maintain body temperature within a normal range for proper functioning.
Q: How do skeletal muscles store nutrients?
A: Skeletal muscles store contractile proteins, and when broken down, the amino acids are released into circulation. These amino acids can be used by the liver to synthesize glucose or provide energy.
Q: What is the endomysium in skeletal muscles?
A: The endomysium is a loose connective tissue that surrounds individual muscle fibers. It contains blood vessels, nerves, and satellite cells (embryonic stem cells involved in muscle tissue repair).
Q: What happens to the collagen fibers in all three connective tissue layers?
A: The collagen fibers of the epimysium, perimysium, and endomysium come together at each end of the muscle to form a tendon, which connects the muscle to the bone.
Q: What is the function of perimysium?
A: The perimysium surrounds a group of muscle fibers (a fascicle) with collagen and elastic fibers. It contains blood vessels and nerves that supply the muscle fibers.
Q: What is the role of epimysium?
A: The epimysium is dense irregular connective tissue that surrounds the entire muscle. It separates the muscle from surrounding tissues and organs and is connected to the deep fascia.
Q: What is the role of motor neurons in muscle contraction?
A: Motor neurons stimulate muscle fibers to contract. Their axons branch to ensure each muscle fiber is innervated, forming a neuromuscular junction (also called myoneural junction).
Q: What is the neuromuscular junction?
A: The neuromuscular junction is the synapse or connection point where a motor neuron communicates with a muscle fiber to stimulate contraction.
Q: How do capillary beds supply muscles with nutrients?
A: Capillary beds surround muscle fibers and provide the muscles with oxygen, nutrients, and help carry away metabolic waste produced during muscle contraction. Muscles require a large amount of energy, and the extensive vascular network ensures these needs are met.
Q: What is the sarcolemma?
A: The sarcolemma is the cell membrane of a muscle fiber. It surrounds the sarcoplasm (the cytoplasm of the muscle fiber) and contains organelles, including an abundance of myoglobin (an oxygen-binding protein).
Q: What are transverse tubules (T-tubules) in muscle fibers?
A: T-tubules are narrow tubes that extend into the sarcoplasm at right angles to the surface of the muscle fiber. They are filled with extracellular fluid and help transmit signals deep into the muscle fiber.
Q: What are the two types of myofilaments in muscle fibers?
A: The two types of myofilaments are:
Actin filaments (thin filaments)
Myosin filaments (thick filaments)
Q: What are myofibrils and what role do they play in muscle contraction?
A: Myofibrils are cylindrical structures within muscle fibers, composed of bundles of protein filaments (myofilaments). When the myofibrils shorten, the muscle contracts.
Q: What is the sarcomere?
A: The sarcomere is the functional unit of a muscle fiber, composed of repeating patterns of thick and thin filaments that allow muscle contraction.
Q: What are thick filaments made of, and where are they located?
A: Thick filaments are made of myosin and run the entire length of the A band.
Q: What are thin filaments made of, and where are they located?
A: Thin filaments are made of actin, and they run the length of the I band and extend partway into the A band.
Q: What is the structure of actin filaments?
A: Actin filaments are made of two strands of fibrous (F) actin forming a double helix, extending the length of the myofilament and attached at the sarcomere.
Q: What is the H zone in a sarcomere?
A: The H zone is the lighter midregion where thick and thin filaments do not overlap.
Q: What is the M line, and what is its function?
A: The M line is a line of the protein myomesin that holds adjacent thick filaments together.
Q: What is the function of the Z disc in a sarcomere?
A: The Z disc is a coin-shaped sheet of proteins that:
Anchors thin filaments
Connects myofibrils to one another
Q: What are G actin monomers, and what is their function?
A: G actin monomers are the individual units of F actin. Each G actin has an active site that can bind myosin during muscle contraction.
Q: What is tropomyosin, and what is its function?
A: Tropomyosin is an elongated protein that winds along the groove of the F actin double helix. It helps block the myosin-binding sites on actin when the muscle is relaxed.
Q: What is troponin, and what are its three subunits?
A: Troponin is a regulatory protein made up of three subunits:
Tn-I: Binds to actin
Tn-T: Binds to tropomyosin
Tn-C: Binds to calcium ions
Q: How does the tropomyosin-troponin complex regulate muscle contraction?
A: When calcium binds to Tn-C, troponin changes shape, moving tropomyosin away from actin’s active sites, allowing myosin to bind and muscle contraction to occur.
Q: What is the structure of thick myosin filaments?
A: Thick filaments are made of many elongated myosin molecules, shaped like golf clubs.
Q: What are the components of a myosin molecule?
A: A myosin molecule consists of:
Two heavy myosin molecules wound together to form a rod portion (parallel to the filament).
Two heads that extend laterally.
Q: What are the three key functions of myosin heads?
A:
Bind to active sites on actin to form cross-bridges.
Attach to the rod portion by a hinge region that can bend and straighten during contraction.
Have ATPase activity to break down ATP, releasing energy for contraction.
Q: What is the function of ATPase activity in myosin heads?
A: ATPase breaks down ATP, releasing energy that helps bend the hinge region of myosin, allowing muscle contraction.
Q: What is the sarcoplasmic reticulum (SR) in muscle cells?
A: It’s an elaborate smooth endoplasmic reticulum that surrounds each myofibril and runs longitudinally.
Q: What are terminal cisternae in the SR?
A: They are chambers of the SR found on either side of the T-tubules.
Q: What is a muscle triad composed of?
A: One T-tubule + two terminal cisternae = a triad.
Q: What does the SR do when the muscle is not contracting?
A: It stores Ca²⁺ ions.
Q: What happens to calcium when the muscle is stimulated?
A: The SR releases Ca²⁺ into the sarcoplasm.
Q: What happens to calcium after contraction?
A: Ca²⁺ pumps in the SR membrane actively pump calcium back into the SR.
Q: What forms when a motor neuron axon reaches a muscle fiber?
A: A neuromuscular junction is formed between the axon ending and the muscle fiber.
Q: What stimulates skeletal muscles?
A: Somatic motor neurons stimulate skeletal muscles.
Q: What is the neuromuscular junction (NMJ)?
A: A functional connection between a nerve fiber and a muscle cell.
Q: What neurotransmitter is released at the NMJ?
A: Acetylcholine (ACh).
Q: What is the synaptic knob?
A: The swollen end of the axon terminal; it contains ACh.
Q: What is the motor end plate?
A: The highly folded region of the sarcolemma next to the synaptic knob; it contains ACh receptors and AChE.
Q: What does acetylcholinesterase (AChE) do?
A: It breaks down ACh, leading to muscle relaxation.
Q: What is the synaptic cleft?
A: A tiny gap between the synaptic knob and the muscle fiber’s sarcolemma.
Q: What are the four main stages of muscle contraction and relaxation?
A:
Excitation
Excitation-contraction coupling
Contraction
Relaxation
Q: What happens during the Excitation phase?
A: Nerve action potentials lead to action potentials in the muscle fiber.
Q: What occurs in Excitation-contraction coupling?
A: Action potentials on the sarcolemma activate the myofilaments.
Q: What defines the Contraction phase?
A: The shortening of the muscle fiber due to filament interaction.
Q: What happens during Relaxation?
A: The muscle returns to resting length after contraction ends.
Q: What does the Sliding Filament Theory explain?
A: It explains how thick and thin filaments interact during muscle contraction.
Q: What triggers the start of the sliding filament process?
A: The release of calcium ions (Ca²⁺) from the sarcoplasmic reticulum (SR).
Q: What does calcium bind to after being released?
A: Troponin.
Q: What happens when calcium binds to troponin?
A: Troponin changes shape and moves tropomyosin, exposing actin’s active site.
Q: What forms once the actin active site is exposed?
A: The myosin head binds to actin, forming a cross-bridge.
Q: What does the myosin head do after forming a cross-bridge?
A: It bends toward the H zone, pulling actin inward.
Q: What causes sarcomeres, muscle fibers, and muscles to shorten?
A: The shortening of H zones and the sliding of filaments inward.
Q: What role does ATP play in this process?
A: ATP allows the myosin head to release from actin, breaking the cross-bridge and resetting the cycle.
Muscle Contraction Summary (Slide 28 of 55):
Q: What initiates muscle contraction?
Q: What neurotransmitter is released at the NMJ?
Q: What does ACh bind to on the muscle membrane?
Q: What happens when ACh binds to nAChRs?
Q: Where does the action potential travel next?
Q: What does the action potential trigger in the muscle fiber?
Q: What does calcium bind to after being released?
Q: What happens after calcium binds to troponin?
Q: What happens when the myosin heads bind to actin?
Q: What role does ATP play in muscle contraction?
Q: When do muscles stop contracting?
A: A nerve impulse reaches the neuromuscular junction (NMJ).
A: Acetylcholine (ACh).
A: Nicotinic receptors (nAChRs).
A: Na⁺ ions enter the muscle cell, generating an action potential in the sarcolemma.
A: Down the T-tubules.
A: The sarcoplasmic reticulum (SR) releases Ca²⁺.
A: Troponin.
A: The troponin-tropomyosin complex moves, exposing binding sites on actin.
A: They create a power stroke, pulling actin filaments inward.
A: ATP detaches myosin heads from actin and energizes them for another contraction cycle.
A: When action potentials cease, calcium is reabsorbed, and contraction stops.
What are the steps of muscle contraction?
Nerve impulse reaches NMJ
* Acetylcholine (ACh) is released from motor neuron
* ACh binds with Nicotinic receptors (nAChR) in the muscle
membrane to allow Na+ ions to enter
* Na+ influx will generate an action potential in the sarcolemma
* Action potential travels down T tubule
* Sarcoplasmic reticulum releases calcium
* Calcium binds with troponin to move the troponin, tropomyosin
complex
* Binding sites in the actin filament are exposed
* Myosin head attach to binding sites and create a power stroke
* ATP detaches myosin heads and energizes them for another
contraction
* When action potentials cease the muscle stop contracting
Q: What does hydrolysis of ATP by myosin do?
A: It energizes the cross-bridges, providing energy for force generation.
Q: How does ATP affect calcium levels during muscle relaxation?
A: ATP energizes Ca²⁺ pumps in the SR, actively transporting Ca²⁺ back in and lowering cytosolic Ca²⁺.
Q: What is the role of ATP binding to myosin?
A: It dissociates cross-bridges that are bound to actin, allowing muscle relaxation.
Q: What pump does ATP fuel to maintain membrane potential?
A: The Na⁺/K⁺ pump in the sarcolemma, which maintains the resting membrane potential.
Q: What provides the immediate energy source for muscle contraction?
A: ATP.
Q: What are the three sources of ATP for muscle contraction?
A:
Creatine phosphate (CP)
Aerobic respiration
Anaerobic respiration (Glycolysis)
Q: Which ATP source is the fastest but yields only 1 ATP per reaction?
A: Creatine phosphate.
Q: What is the most efficient ATP source and how many ATP does it produce per glucose?
A: Aerobic respiration, yielding 36 ATP per glucose.
Q: Which ATP source occurs without oxygen and produces lactic acid?
A: Anaerobic respiration (Glycolysis).
Q: What is the direct phosphorylation mechanism for ATP production?
A: It involves the coupled reaction of creatine phosphate (CP) and ADP.
Energy source: CP
Oxygen use: None
Products: 1 ATP per CP, creatine
Duration: 15 seconds
Q: What is the anaerobic mechanism for ATP production?
A: It involves glycolysis, breaking down glucose into pyruvic acid or lactic acid.
Energy source: Glucose
Oxygen use: None
Products: 2 ATP per glucose, lactic acid
Duration: 30-60 seconds
Q: What is the aerobic mechanism for ATP production?
A: It involves aerobic respiration in the mitochondria.
Energy source: Glucose, pyruvic acid, fatty acids, amino acids
Oxygen use: Required
Products: 36 ATP per glucose, CO₂, H₂O
Duration: Hours
Q: What are the three factors that influence velocity and duration of muscle contraction?
A:
Muscle fiber type
Load
Recruitment
Q: How are skeletal muscle fibers classified?
A: Skeletal muscle fibers are classified according to:
Speed of contraction: Slow or fast, based on ATPase activity and motor neuron electrical patterns.
Metabolic pathways for ATP synthesis: Oxidative or glycolytic fibers.
Q: What are slow oxidative fibers?
not needed
A:
Slow-twitch fibers.
Contract slowly and are resistant to fatigue.
Use aerobic respiration (oxidative) for ATP production.
Best suited for endurance activities (e.g., marathon running).
Q: What are fast oxidative fibers?
not needed
A:
Fast-twitch fibers.
Contract quickly but also have some resistance to fatigue.
Use both aerobic and anaerobic metabolism for ATP production.
Suitable for activities requiring moderate endurance and power (e.g., sprinting).
Q: What are fast glycolytic fibers?
not needed
A:
Fast-twitch fibers that contract rapidly and produce high power.
Use anaerobic glycolysis to generate ATP, leading to quick fatigue.
Best suited for short bursts of activity (e.g., weightlifting).
Q: What are the metabolic characteristics of Slow Oxidative Fibers?
A:
Speed of Contraction: Slow
Myosin ATPase Activity: Slow
Primary Pathway for ATP Synthesis: Aerobic
Myoglobin Content: High
Glycogen Stores: Low
Recruitment Order: First
Rate of Fatigue: Slow (fatigue-resistant)
Activities Best Suited For: Endurance-type activities (e.g., running a marathon, maintaining posture)
Q: What are the metabolic characteristics of Fast Oxidative Fibers?
A:
Speed of Contraction: Fast
Myosin ATPase Activity: Fast
Primary Pathway for ATP Synthesis: Aerobic (some anaerobic glycolysis)
Myoglobin Content: High
Glycogen Stores: Intermediate
Recruitment Order: Second
Rate of Fatigue: Intermediate (moderately fatigue-resistant)
Activities Best Suited For: Sprinting, walking
Q: What are the metabolic characteristics of Fast Glycolytic Fibers?
A:
Speed of Contraction: Fast
Myosin ATPase Activity: Fast
Primary Pathway for ATP Synthesis: Anaerobic glycolysis
Myoglobin Content: Low
Glycogen Stores: High
Recruitment Order: Third
Rate of Fatigue: Fast (fatigable)
Activities Best Suited For: Short-term intense or powerful movements (e.g., hitting a baseball)
Q: What are the structural characteristics of Slow Oxidative Fibers?
A:
Color: Red
Fiber Diameter: Small
Mitochondria: Many
Capillaries: Many
Q: What are the structural characteristics of Fast Oxidative Fibers?
A:
Color: Red to pink
Fiber Diameter: Intermediate
Mitochondria: Many
Capillaries: Many
Q: What are the structural characteristics of Fast Glycolytic Fibers?
A:
Color: White (pale)
Fiber Diameter: Large
Mitochondria: Few
Capillaries: Few
Q: How does an increase in load affect muscle contraction?
A:
Latent Period: Increases
Contraction Speed: Decreases
Duration of Contraction: Decreases
Explanation:
With a heavier load, the muscle does not shorten as much, and the contraction duration is shorter.
The contraction is also slower due to the increased resistance.
What are the phases of a muscle twitch and what happens in each?
A:
Latent Period (2 msec delay):
No visible contraction or tension development.
Excitation-contraction coupling is occurring.
Contraction Phase:
External tension develops as the muscle shortens.
Fast twitch fibers contract in about 10 msec, while slow twitch fibers take about 100 msec.
Relaxation Phase:
Tension decreases and the muscle returns to its resting length.
Calcium is pumped back into the sarcoplasmic reticulum (SR).
Q: What is a motor unit?
A: A motor unit is a motor neuron and all the muscle fibers it supplies.
Q: How does the number of muscle fibers per motor unit vary?
A: The number of muscle fibers per motor unit can vary based on the function of the muscle.
Q: Which muscles have small motor units?
A: Muscles that control fine movements, like those in the fingers and eyes, have small motor units.
Q: Which muscles have large motor units?
A: Large weight-bearing muscles, like those in the thighs and hips, have large motor units.
Q: What is the motor unit ratio for back muscles?
Q: What is the motor unit ratio for finger muscles?
Q: What is the motor unit ratio for eye muscles?
A: The motor unit ratio for back muscles is 1:100 (1 motor neuron controls 100 muscle fibers).
A: The motor unit ratio for finger muscles is 1:10 (1 motor neuron controls 10 muscle fibers).
A: The motor unit ratio for eye muscles is 1:1 (1 motor neuron controls 1 muscle fiber).
Q: What are the characteristics of smooth muscle cells?
A: Smooth muscle cells are not striated, smaller than skeletal muscle fibers, spindle-shaped with a single central nucleus, and have more actin than myosin.
Q: Why do smooth muscle cells lack striations?
A: Smooth muscle cells lack striations because their actin and myosin are not arranged as symmetrically as in skeletal muscle, and they do not have sarcomeres.
Q: How is smooth muscle arranged in the walls of hollow organs?
A: Smooth muscle is grouped into sheets in the walls of hollow organs, consisting of a longitudinal layer (muscle fibers running parallel to the organ’s long axis) and a circular layer (muscle fibers running around the circumference of the organ).
Q: What are caveolae in smooth muscle?
A: Caveolae are indentations in the sarcolemma of smooth muscle cells that may act like T-tubules.
Q: What is the function of dense bodies in smooth muscle?
A: Dense bodies, instead of Z disks, are used in smooth muscle to anchor actin filaments and have non-contractile intermediate filaments for structural support.
Q: What is the role of the longitudinal and circular layers of smooth muscle?
A: Both the longitudinal and circular layers of smooth muscle participate in peristalsis, which is the rhythmic contraction and relaxation that moves substances through the organ.
: What is the difference between visceral (unitary) and multiunit smooth muscle?
A:
Visceral (unitary) smooth muscle: Impulses spread through gap junctions, causing the whole sheet of muscle to contract as a unit. Found in walls of small arteries, veins, and hollow viscera (e.g., stomach, intestines, urinary bladder). It is often autorhythmic.
Multiunit smooth muscle: Cells or groups of cells act as independent units. Found in walls of large arteries, large airways in the lungs, arrector pili muscles of hair follicles, and internal eye muscles.
Q: How is smooth muscle innervated?
A: Smooth muscle is innervated by the autonomic nervous system (ANS).
Q: How does smooth muscle contraction occur?
A: Smooth muscle contraction occurs when actin and myosin interact through the sliding filament mechanism. The final trigger for contraction is an increase in intracellular Ca²⁺, which is released from the SR and extracellular space. Ca²⁺ binds to calmodulin, activating myosin light chain kinase (MLCK), which then phosphorylates myosin cross-bridges, allowing them to interact with actin and produce shortening. Smooth muscle relaxes when Ca²⁺ levels drop.
Q: What is the role of Ca²⁺ in smooth muscle contraction?
A: Ca²⁺ binds to calmodulin, which activates myosin light chain kinase (MLCK). MLCK then phosphorylates myosin cross-bridges, enabling them to interact with actin and produce contraction. Relaxation occurs when intracellular Ca²⁺ levels decrease.
Q: What are the characteristics of cardiac muscle?
A: Cardiac muscle is involuntary and found only in the heart wall. It has striated, branched short fibers with a single, central nucleus in each fiber. The fibers are connected by intercalated discs, which are thickened cell membranes, and gap junctions that allow the spread of action potentials. ATP is generated by abundant mitochondria and by lactic acid when oxygen is insufficient.
Q: How do cardiac muscle fibers communicate?
A: Cardiac muscle fibers are connected by intercalated discs, which include gap junctions. These gap junctions allow the spread of action potentials, enabling coordinated contraction of the heart muscle.
Q: Does cardiac muscle require nerve stimulation to contract?
A: No, cardiac muscle does not require nerve stimulation. It has its own intrinsic pacemaker and conduction system within the cardiac muscle that initiates contraction. This ability is known as auto-rhythmicity.
Q: What is the role of intercalated discs in cardiac muscle?
A: Intercalated discs contain gap junctions, which transmit action potentials from one muscle cell to the next. This ensures coordinated contraction of the heart muscle.
Q: What connective tissue components are present in skeletal, cardiac, and smooth muscle?
A:
Skeletal muscle: Epimysium, perimysium, and endomysium
Cardiac muscle: Endomysium attached to fibrous skeleton of the heart
Smooth muscle: Endomysium
Q: What is the presence of myofibrils composed of sarcomeres in skeletal, cardiac, and smooth muscle?
A:
Skeletal muscle: Yes, with two T-tubules at A-junctions
Cardiac muscle: Yes, but myofibrils are of irregular thickness
Smooth muscle: No, but actin and myosin filaments are present throughout; dense bodies anchor actin filaments
Q: What is the presence of T tubules and the site of invagination in skeletal, cardiac, and smooth muscle?
A:
Skeletal muscle: Yes, with T-tubules at the A-junctions
Cardiac muscle: Yes, with one T-tubule in each sarcomere at the Z disc; larger diameter than skeletal muscle T-tubules
Smooth muscle: No, only caveolae
Q: What is the presence of elaborate sarcoplasmic reticulum in skeletal, cardiac, and smooth muscle?
A:
Skeletal muscle: Yes
Cardiac muscle: Less than skeletal muscle (1-8% of cell volume); scant terminal cisternae
Smooth muscle: Equivalent to cardiac muscle (1-8% of cell volume); some SR contacts the sarcolemma
Q: What is the presence of gap junctions in skeletal, cardiac, and smooth muscle?
A:
Skeletal muscle: Yes
Cardiac muscle: Yes, at intercalated discs
Smooth muscle: Not in single-unit muscle; yes in multiunit muscle
Q: How is contraction regulated in skeletal, cardiac, and smooth muscle?
A:
Skeletal muscle: Voluntary via axon terminals of the somatic nervous system
Cardiac muscle: Involuntary; intrinsic system regulation; also autonomic nervous system controls; hormones; stretch
Smooth muscle: Involuntary; autonomic nerves, hormones, local chemicals; stretch
Q: Where is calcium regulation located in skeletal, cardiac, and smooth muscle?
A:
Skeletal muscle: Troponin on actin-containing thin filaments
Cardiac muscle: Troponin on actin-containing thin filaments
Smooth muscle: Calmodulin in the cytosol
: Do skeletal, cardiac, and smooth muscles have pacemaker(s)?
A:
Skeletal muscle: No
Cardiac muscle: Yes
Smooth muscle: Yes (in single-unit muscle only)
Q: How is contraction influenced by the nervous system in skeletal, cardiac, and smooth muscle?
A:
Skeletal muscle: Excitation
Cardiac muscle: Excitation or inhibition
Smooth muscle: Excitation or inhibition
Q: What is the speed of contraction in skeletal, cardiac, and smooth muscle?
A:
Skeletal muscle: Slow to fast
Cardiac muscle: Slow
Smooth muscle: Very slow
Q: How does skeletal, cardiac, and smooth muscle respond to stretch?
A:
Skeletal muscle: No
Cardiac muscle: Contractile strength increases with degree of stretch (to a point)
Smooth muscle: Contractile strength increases with degree of stretch
Q: What type of respiration do skeletal, cardiac, and smooth muscles rely on?
A:
Skeletal muscle: Aerobic and anaerobic
Cardiac muscle: Aerobic
Smooth muscle: Mainly aerobic
