Muscles – Notes (Updated & Easy)

Muscles are specialized tissues responsible for movement in animals. They are made of muscle fibers formed from actin and myosin protein filaments. Muscles show a property known as contractility – the ability to shorten and generate force.

Types of Muscles in Vertebrates

Vertebrates have three types of muscle tissues:

Comparison of Muscle Types

Property	Smooth Muscles	Cardiac Muscles	Skeletal Muscles
Appearance	Unstriated	Striated (faint)	Striated (strong)
Cell shape	Spindle-shaped	Branched	Long cylindrical fibers
No. of nuclei	Single per cell	Single (central)	Multiple (peripheral)
Control	Involuntary	Involuntary	Voluntary
Speed of contraction	Slow	Intermediate	Fast
Location	Hollow organs (stomach, intestine)	Heart	Attached to bones
Intercalated discs	Absent	Present	Absent
Fatigue	Does not fatigue easily	Never fatigues	Fatigues quickly
Function	Movement of substances	Pumps blood	Movement of body

1. Smooth Muscles

Also called visceral muscles.
Non-striated and involuntary.
Found in walls of hollow organs: stomach, intestines, urinary bladder, blood vessels, uterus.
Controlled by autonomic nervous system and hormones.
Slow and sustained contractions (peristalsis in intestines).

Latest Information:
- Smooth muscles can divide and regenerate to some extent.
- They respond to hormones like oxytocin (uterus) and adrenaline (blood vessels).

2. Cardiac Muscles

Found only in the heart.
Striated, branched, involuntary.
Cells connected by intercalated discs → allow synchronized contractions.
Myogenic (contract on their own without nerve stimulation).
Rich in mitochondria to produce large amounts of ATP.
Never fatigues.

Latest Information:
- Controlled by Sinoatrial Node (SA Node) – the natural pacemaker.
- Heart contractions are modulated by autonomic nervous system and calcium ions (Ca⁺⁺).

3. Skeletal Muscles

Also called voluntary muscles or striated muscles.
Attached to bones via tendons.
Multi-nucleated long cylindrical fibers.
Under voluntary control by somatic nervous system.
Show rapid contraction but quick fatigue.

Latest Information:
Function in posture, movement, speaking, facial expressions.
Require ATP + calcium ions for contraction.
Can increase in size due to hypertrophy (exercise).
Satellite cells help in repair of skeletal muscles.

Latest Scientific Additions

✔ Muscles store glycogen as quick energy fuel.
✔ Creatine phosphate provides instant ATP during rapid activity.
✔ Muscle fatigue is caused by lactic acid accumulation during anaerobic respiration.
✔ Myoglobin stores oxygen in muscle fibers.
✔ Aging causes sarcopenia – loss of skeletal muscle mass.

Q1. Smooth muscles are primarily found in:
A) Heart
B) Bones
C) Stomach
D) Biceps
✅ Answer: C
💡 Explanation: Smooth muscles line hollow organs like the stomach and intestines.

Q2. Cardiac muscle fibers are connected by:
A) Desmosomes only
B) Intercalated discs
C) Gap junctions only
D) Sarcomeres
✅ Answer: B
💡 Explanation: Intercalated discs contain gap junctions and desmosomes for synchronized heart contraction.

Q3. Which muscle type is voluntary?
A) Smooth
B) Cardiac
C) Skeletal
D) All three
✅ Answer: C
💡 Explanation: Skeletal muscles are controlled by the somatic nervous system (under conscious control).

Q4. The basic contractile unit of a skeletal muscle is:
A) Myofibril
B) Sarcomere
C) Sarcolemma
D) T-tubule
✅ Answer: B
💡 Explanation: The sarcomere (Z-line to Z-line) is the functional unit where actin-myosin sliding occurs.

Q5. Which proteins form the thin and thick filaments in muscle?
A) Actin and myosin
B) Keratin and collagen
C) Tubulin and dynein
D) Actin and tropomyosin
✅ Answer: A
💡 Explanation: Actin is thin filament and myosin is thick filament responsible for contraction.

Q6. Which ion is essential for muscle contraction initiation?
A) Na+
B) K+
C) Ca2+
D) Mg2+
✅ Answer: C
💡 Explanation: Calcium ions bind to troponin, allowing actin-myosin interaction.

Q7. Smooth muscle contraction is usually:
A) Rapid and fatigable
B) Slow and sustained
C) Voluntary
D) Dependent on sarcomeres
✅ Answer: B
💡 Explanation: Smooth muscle contracts slowly and can sustain tone for long periods.

Q8. The pacemaker of the heart is the:
A) AV node
B) SA node
C) Purkinje fibers
D) Bundle of His
✅ Answer: B
💡 Explanation: The sinoatrial (SA) node generates the heartbeat rhythm.

Q9. Which muscle contains intercalated discs?
A) Skeletal
B) Smooth
C) Cardiac
D) All muscles
✅ Answer: C
💡 Explanation: Intercalated discs are unique to cardiac muscle for electrical coupling.

Q10. The plasma membrane of a muscle fiber is called:
A) Sarcoplasm
B) Sarcolemma
C) Endomysium
D) Epimysium
✅ Answer: B
💡 Explanation: Sarcolemma is the cell membrane of muscle fibers.

Q11. Multi-nucleated muscle fibers are typical of:
A) Cardiac muscle
B) Smooth muscle
C) Skeletal muscle
D) Neural tissue
✅ Answer: C
💡 Explanation: Skeletal muscle fibers fuse during development, forming many nuclei per fiber.

Q12. Myoglobin in muscle cells:
A) Stores glycogen
B) Stores oxygen
C) Produces ATP
D) Breaks down lactic acid
✅ Answer: B
💡 Explanation: Myoglobin binds and stores oxygen inside muscle fibers.

Q13. Which band contains only thin filaments in the sarcomere?
A) A band
B) I band
C) H zone
D) M line
✅ Answer: B
💡 Explanation: The I band is the region with only actin (thin) filaments.

Q14. The sliding filament theory was proposed to explain:
A) Muscle development
B) Muscle contraction mechanism
C) Muscle energy metabolism
D) Nervous control of muscles
✅ Answer: B
💡 Explanation: It explains how actin and myosin slide past each other to shorten sarcomeres.

Q15. The neurotransmitter at the neuromuscular junction is:
A) Dopamine
B) Norepinephrine
C) Acetylcholine
D) Serotonin
✅ Answer: C
💡 Explanation: Acetylcholine is released from motor neuron terminals to trigger muscle contraction.

Q16. ATP role in muscle contraction:
A) Provides structural support
B) Breaks actin filaments
C) Releases myosin head from actin and powers the power stroke
D) Produces Ca2+
✅ Answer: C
💡 Explanation: ATP binding and hydrolysis allow cross-bridge cycling and detachment of myosin.

Q17. Which muscle type shows striations?
A) Smooth only
B) Cardiac and skeletal
C) Skeletal only
D) Cardiac only
✅ Answer: B
💡 Explanation: Both cardiac and skeletal muscles have sarcomeres producing visible striations.

Q18. Satellite cells are important for:
A) Heart rhythm
B) Smooth muscle contraction
C) Repair and regeneration of skeletal muscle
D) Producing neurotransmitters
✅ Answer: C
💡 Explanation: Satellite cells are muscle stem cells that help repair skeletal muscle after injury.

Q19. Which structure transmits action potentials deep into a muscle fiber?
A) Sarcoplasmic reticulum
B) T-tubules (transverse tubules)
C) Mitochondria
D) Golgi apparatus
✅ Answer: B
💡 Explanation: T-tubules conduct nerve impulses into the fiber interior to trigger Ca2+ release.

Q20. The sarcoplasmic reticulum stores:
A) Sodium
B) Potassium
C) Calcium
D) ATP
✅ Answer: C
💡 Explanation: SR stores Ca2+ and releases it for contraction.

Q21. A motor unit consists of:
A) One muscle fiber and many neurons
B) One neuron and many muscle fibers
C) Many neurons and many muscles
D) One sarcomere and one motor neuron
✅ Answer: B
💡 Explanation: A motor neuron plus all the muscle fibers it innervates form a motor unit.

Q22. Isometric contraction means:
A) Muscle length changes, tension constant
B) Muscle length unchanged, tension increases
C) Rapid twitch
D) Eccentric contraction only
✅ Answer: B
💡 Explanation: In isometric contraction tension increases but muscle length does not change.

Q23. Which fuel is used first during short, intense muscle activity?
A) Fatty acids
B) Glycogen and creatine phosphate
C) Protein
D) Oxygen from myoglobin
✅ Answer: B
💡 Explanation: Creatine phosphate and glycogen supply ATP quickly during intense exercise.

Q24. Lactic acid in muscles is produced during:
A) Aerobic respiration
B) Anaerobic respiration
C) Photosynthesis
D) Fermentation in plants only
✅ Answer: B
💡 Explanation: Under low oxygen, muscles convert pyruvate to lactate causing lactic acid buildup.

Q25. Which muscle type regenerates best?
A) Skeletal (limited)
B) Cardiac (very limited)
C) Smooth (relatively good)
D) All regenerate equally
✅ Answer: C
💡 Explanation: Smooth muscle cells can divide and regenerate better than cardiac and skeletal.

Q26. The endomysium surrounds:
A) Whole muscle
B) Fascicle
C) Individual muscle fiber
D) Tendon
✅ Answer: C
💡 Explanation: Endomysium is connective tissue around each muscle fiber.

Q27. Contraction speed fastest to slowest:
A) Cardiac > Smooth > Skeletal
B) Skeletal > Cardiac > Smooth
C) Smooth > Skeletal > Cardiac
D) Cardiac > Skeletal > Smooth
✅ Answer: B
💡 Explanation: Skeletal contracts fastest, cardiac intermediate, smooth slowest.

Q28. Which plays main role in muscle fatigue?
A) Depletion of creatine phosphate only
B) Accumulation of lactic acid and ion imbalance
C) Excess ATP
D) Increased O2
✅ Answer: B
💡 Explanation: Lactic acid and ionic changes reduce muscle performance and cause fatigue.

Q29. A twitch is:
A) Sustained muscle contraction
B) Single contractile response to a single stimulus
C) Voluntary contraction
D) Reflex only
✅ Answer: B
💡 Explanation: A twitch is the short response of a muscle fiber to one action potential.

Q30. Rigor mortis occurs because:
A) Excess ATP
B) Lack of Ca2+
C) Lack of ATP causing myosin to remain bound to actin
D) Nerve stimulation after death
✅ Answer: C
💡 Explanation: Without ATP, cross-bridges cannot detach, causing stiffness after death.

Q31. The A band in sarcomere contains:
A) Only actin
B) Only myosin
C) Both actin and myosin overlapping
D) Z-line
✅ Answer: C
💡 Explanation: A band includes overlapping thick (myosin) and thin (actin) filaments.

Q32. Hypertrophy in muscles means:
A) Increase in number of muscle fibers
B) Decrease in fiber size
C) Increase in size (diameter) of muscle fibers
D) Cell death
✅ Answer: C
💡 Explanation: Hypertrophy is growth by enlargement of existing muscle fibers, often from exercise.

Q33. Which structure anchors thin filaments in the sarcomere?
A) M line
B) Z line
C) T-tubule
D) Sarcolemma
✅ Answer: B
💡 Explanation: Z lines mark the boundary of sarcomeres and anchor actin filaments.

Q34. Troponin and tropomyosin regulate contraction by:
A) Blocking myosin binding sites on actin until Ca2+ binds
B) Producing ATP
C) Forming sarcomeres
D) Pumping Ca2+ into SR
✅ Answer: A
💡 Explanation: Tropomyosin blocks binding; Ca2+ binding to troponin shifts it to allow contraction.

Q35. Oxidative (slow) muscle fibers are rich in:
A) Glycogen only
B) Mitochondria and myoglobin
C) Fat only
D) Sarcomeres only
✅ Answer: B
💡 Explanation: Slow oxidative fibers have many mitochondria and myoglobin for endurance.

Q36. Fast glycolytic fibers are best for:
A) Endurance running
B) Slow posture
C) Short bursts of power and speed
D) Heart contractions
✅ Answer: C
💡 Explanation: Fast glycolytic fibers generate quick force but fatigue fast.

Q37. Recruitment in muscles refers to:
A) Replacing dead fibers
B) Activating more motor units to increase force
C) Muscle atrophy
D) Protein synthesis only
✅ Answer: B
💡 Explanation: Stronger contraction needs activation of more motor units (recruitment).

Q38. The neuromuscular junction is:
A) Junction between two muscles
B) Synapse between motor neuron and muscle fiber
C) Connection between heart cells
D) Part of sarcomere
✅ Answer: B
💡 Explanation: It is where the motor neuron communicates with the muscle fiber using ACh.

Q39. Duchenne muscular dystrophy is caused by:
A) Bacterial infection
B) Mutation in dystrophin gene
C) Vitamin deficiency
D) Excessive exercise
✅ Answer: B
💡 Explanation: DMD is an X-linked mutation leading to loss of dystrophin and muscle degeneration.

Q40. Which muscle types are involuntary?
A) Smooth and cardiac
B) Skeletal and cardiac
C) Smooth and skeletal
D) All are voluntary
✅ Answer: A
💡 Explanation: Smooth and cardiac are controlled without conscious effort.

Q41. Endurance training increases:
A) Number of motor neurons
B) Mitochondria and capillary density in muscle
C) Myosin gene mutations
D) Number of sarcomeres only
✅ Answer: B
💡 Explanation: Endurance exercise increases mitochondria and blood supply for aerobic metabolism.

Q42. Creatine phosphate in muscle cells:
A) Stores O2
B) Transfers phosphate to ADP to quickly form ATP
C) Breaks down proteins
D) Is hormone regulating contraction
✅ Answer: B
💡 Explanation: Creatine phosphate donates phosphate to ADP to rapidly regenerate ATP.

Q43. Which layer surrounds a fascicle (bundle of muscle fibers)?
A) Epimysium
B) Perimysium
C) Endomysium
D) Sarcolemma
✅ Answer: B
💡 Explanation: Perimysium wraps groups of muscle fibers into fascicles.

Q44. An eccentric contraction is when:
A) Muscle shortens while generating force
B) Muscle lengthens under load
C) No change in length but tension increases
D) Muscle is electrically silent
✅ Answer: B
💡 Explanation: Eccentric contraction involves controlled lengthening (e.g., lowering a weight).

Q45. Which organelle provides most ATP in muscle cells?
A) Ribosome
B) Lysosome
C) Mitochondria
D) Golgi apparatus
✅ Answer: C
💡 Explanation: Mitochondria carry out oxidative phosphorylation to make ATP.

Q46. Which statement about cardiac muscle is correct?
A) It is voluntary and uni-nucleated with no branching
B) It has intercalated discs and is myogenic
C) It regenerates rapidly like smooth muscle
D) Contains many nuclei per cell like skeletal muscle
✅ Answer: B
💡 Explanation: Cardiac muscle is myogenic and has intercalated discs for coordinated contraction.

Q47. The term “motor end plate” refers to:
A) The sarcomere end
B) The specialized region of the muscle membrane at the neuromuscular junction
C) The T-tubule end
D) The terminal cisternae of SR
✅ Answer: B
💡 Explanation: Motor end plate has ACh receptors to receive signals from motor neurons.

Q48. Which of the following increases during muscle contraction?
A) I band length
B) Sarcomere length
C) Overlap between actin and myosin
D) H zone width
✅ Answer: C
💡 Explanation: During contraction, actin and myosin overlap more, shortening the sarcomere.

Q49. Which hormone causes uterine smooth muscle contraction in labor?
A) Insulin
B) Oxytocin
C) Thyroxine
D) Adrenaline
✅ Answer: B
💡 Explanation: Oxytocin stimulates uterine smooth muscle contractions during childbirth.

Q50. Which fiber type is fatigue-resistant and rich in capillaries?
A) Fast glycolytic
B) Slow oxidative
C) Fast oxidative-glycolytic
D) White fibers only
✅ Answer: B
💡 Explanation: Slow oxidative fibers are adapted for long-duration contractions and endurance.

Q51. Which enzyme breaks down acetylcholine at the neuromuscular junction?
A) Acetylcholinesterase
B) ATPase
C) Kinase
D) Phosphatase
✅ Answer: A
💡 Explanation: Acetylcholinesterase degrades ACh to stop the signal and allow relaxation.

Q52. Which structure aligns thick filaments in the center of the sarcomere?
A) Z line
B) M line
C) I band
D) T-tubule
✅ Answer: B
💡 Explanation: M line holds myosin (thick) filaments in place.

Q53. During muscle contraction, which band disappears or shortens most?
A) A band
B) I band
C) M line
D) Z line
✅ Answer: B
💡 Explanation: I band (thin filament-only region) shortens as filaments overlap.

Q54. Which change increases muscle tone?
A) Reduced motor unit activity
B) Increased motor unit spontaneous activity
C) Loss of neuromuscular junction
D) Decreased blood flow
✅ Answer: B
💡 Explanation: Continuous low-level activation of motor units maintains muscle tone.

Q55. ATP is produced aerobically in muscle mainly from:
A) Glycolysis only
B) Beta-oxidation and TCA cycle in mitochondria
C) Lactic acid fermentation
D) Direct sunlight
✅ Answer: B
💡 Explanation: Aerobic ATP comes from oxidation of glucose and fatty acids in mitochondria.

Q56. What causes tetanus in voluntary muscles?
A) Single stimulus
B) Repeated high-frequency stimuli causing sustained contraction
C) Lack of ATP
D) Dehydration
✅ Answer: B
💡 Explanation: High-frequency action potentials cause summation and tetanic contraction.

Q57. Which ion pump helps restore ion gradients after contraction?
A) Ca2+-ATPase in SR and Na+/K+ pump in membrane
B) H+-ATPase only
C) Cl- channel only
D) ATP synthase only
✅ Answer: A
💡 Explanation: Ca2+-ATPase pumps Ca2+ back into SR and Na+/K+ pump restores membrane potential.

Q58. Which disorder involves immune attack on acetylcholine receptors?
A) Muscular dystrophy
B) Myasthenia gravis
C) ALS
D) Parkinson’s disease
✅ Answer: B
💡 Explanation: Myasthenia gravis causes muscle weakness due to antibodies against ACh receptors.

Q59. Which practice increases muscle strength?
A) Endurance (long-distance) training only
B) Resistance (weight) training causing hypertrophy
C) Only stretching
D) Sleeping more
✅ Answer: B
💡 Explanation: Resistance training stimulates muscle fiber hypertrophy and strength gain.

Q60. Fast oxidative-glycolytic fibers combine:
A) High speed and high fatigue resistance
B) Low speed and low endurance
C) High speed and moderate fatigue resistance
D) Slow speed and no mitochondria
✅ Answer: C
💡 Explanation: They can use both aerobic and anaerobic metabolism for medium endurance and power.

Q61. Which connective tissue surrounds the whole muscle?
A) Endomysium
B) Perimysium
C) Epimysium
D) Endoneurium
✅ Answer: C
💡 Explanation: Epimysium is the outer connective tissue layer around the entire muscle.

Q62. Which is NOT a function of skeletal muscle?
A) Movement
B) Heat production
C) Pumping blood directly
D) Posture maintenance
✅ Answer: C
💡 Explanation: Hearts pump blood; skeletal muscle assists venous return but does not pump blood directly.

Q63. How does tetanus toxin affect muscles?
A) Blocks ACh release causing paralysis
B) Enhances ACh release causing spastic paralysis
C) Damages myosin
D) Reduces Ca2+ release
✅ Answer: B
💡 Explanation: Tetanus toxin blocks inhibitory neurons leading to excessive ACh release and spasticity.

Q64. Muscle atrophy is caused by:
A) Increased exercise
B) Disuse or denervation
C) Hypertrophy
D) Increased protein synthesis
✅ Answer: B
💡 Explanation: Lack of use or nerve supply causes shrinkage (atrophy) of muscle fibers.

Q65. Which structure stores calcium in muscle fibers?
A) Mitochondria
B) Sarcoplasmic reticulum
C) Nucleus
D) Golgi complex
✅ Answer: B
💡 Explanation: SR holds and releases Ca2+ necessary for contraction.

Q66. A single motor neuron controlling few muscle fibers results in:
A) Fine control (e.g., eye muscles)
B) No control
C) Strong but coarse movement (e.g., thigh)
D) Fatigue
✅ Answer: A
💡 Explanation: Small motor units allow precise movements.

Q67. Muscle cramps are often caused by:
A) Overhydration only
B) Electrolyte imbalance and fatigue
C) High ATP only
D) Increased myoglobin
✅ Answer: B
💡 Explanation: Electrolyte loss and fatigue can trigger involuntary painful contractions.

Q68. The primary cause of oxygen debt after exercise is:
A) Too much oxygen used during rest
B) Repaying stores of O2 and removing lactic acid
C) Loss of blood volume
D) Increased myoglobin levels
✅ Answer: B
💡 Explanation: Oxygen debt restores ATP/creatine phosphate and converts lactate back to pyruvate/glucose.

Q69. Which band remains constant in length during contraction?
A) I band
B) A band
C) H zone
D) Z line
✅ Answer: B
💡 Explanation: A band (thick filament length) stays the same while overlap increases.

Q70. Which process increases during muscle growth (hypertrophy)?
A) Number of muscle fibers dramatically increases
B) Size (protein content) of muscle fibers increases
C) Nuclei disappear
D) Muscle turns into fat
✅ Answer: B
💡 Explanation: Hypertrophy increases myofibril number and protein content in existing fibers.


Short Questions (50) — Easy English answers

Q: Define muscle.
Ans: Muscle is a soft tissue that can contract and produce movement or force.
Q: Name three types of muscles in vertebrates.
Ans: Smooth, cardiac, and skeletal muscles.
Q: What proteins are essential for muscle contraction?
Ans: Actin (thin filament) and myosin (thick filament).
Q: What is a sarcomere?
Ans: The sarcomere is the basic contractile unit of a muscle fiber, between two Z lines.
Q: What is the sarcolemma?
Ans: Sarcolemma is the cell membrane of a muscle fiber.
Q: What stores calcium in muscle cells?
Ans: The sarcoplasmic reticulum stores calcium.
Q: What ion triggers muscle contraction?
Ans: Calcium ions (Ca2+).
Q: What is the role of ATP in contraction?
Ans: ATP powers cross-bridge cycling and detaches myosin from actin.
Q: What is a motor unit?
Ans: A motor unit is one motor neuron and all the muscle fibers it controls.
Q: Define muscle tone.
Ans: Muscle tone is the steady, low-level contraction that keeps muscles ready and maintains posture.
Q: What is a neuromuscular junction?
Ans: It is the synapse where a motor neuron communicates with a muscle fiber using ACh.
Q: Name the heart’s pacemaker.
Ans: The SA (sinoatrial) node.
Q: What are intercalated discs?
Ans: Specialized cell junctions between cardiac muscle cells allowing electrical and mechanical connection.
Q: What is myoglobin?
Ans: A protein in muscle that stores and carries oxygen.
Q: What is hypertrophy?
Ans: Increase in muscle fiber size due to exercise or load.
Q: What is atrophy?
Ans: Decrease in muscle size from disuse or disease.
Q: Give one function of smooth muscle.
Ans: To move substances through hollow organs (e.g., peristalsis in intestines).
Q: Give one function of skeletal muscle.
Ans: To move bones and produce voluntary movements.
Q: Give one function of cardiac muscle.
Ans: To pump blood throughout the body.
Q: What is creatine phosphate used for?
Ans: To quickly regenerate ATP during short bursts of activity.
Q: What causes muscle fatigue?
Ans: Lactic acid accumulation, ion imbalance, and depletion of energy reserves.
Q: What is a twitch?
Ans: A single, brief contraction of a muscle fiber in response to one stimulus.
Q: What is tetanus (physiology)?
Ans: A sustained muscle contraction from repeated high-frequency stimulation.
Q: What substance breaks down acetylcholine?
Ans: Acetylcholinesterase.
Q: What are satellite cells?
Ans: Muscle stem cells that aid in skeletal muscle repair.
Q: What does the I band contain?
Ans: Only thin (actin) filaments.
Q: What does the A band contain?
Ans: Overlapping thick (myosin) and thin (actin) filaments.
Q: What is the M line?
Ans: The center of the sarcomere that holds thick filaments together.
Q: What is eccentric contraction?
Ans: Muscle lengthening while under tension (e.g., lowering a weight).
Q: What is concentric contraction?
Ans: Muscle shortening while generating force (e.g., lifting a weight).
Q: Name a disease of skeletal muscle.
Ans: Muscular dystrophy (e.g., Duchenne’s dystrophy).
Q: What is myasthenia gravis?
Ans: An autoimmune disease causing weakness by blocking ACh receptors.
Q: What does the perimysium surround?
Ans: A fascicle (bundle) of muscle fibers.
Q: What does the epimysium surround?
Ans: The whole muscle.
Q: What causes rigor mortis?
Ans: Lack of ATP after death causing cross-bridges to remain attached.
Q: What is oxidative metabolism in muscle?
Ans: Aerobic production of ATP using mitochondria, oxygen, and fuels.
Q: What are fast-twitch fibers best for?
Ans: Quick, powerful movements but they fatigue quickly.
Q: What are slow-twitch fibers best for?
Ans: Endurance and long-lasting contractions.
Q: What is the role of tropomyosin?
Ans: It blocks myosin binding sites on actin when Ca2+ is low.
Q: What is the role of troponin?
Ans: Troponin binds Ca2+ and moves tropomyosin to allow contraction.
Q: How does endurance training affect muscle?
Ans: It increases mitochondria, capillaries, and aerobic capacity.
Q: How does resistance training affect muscle?
Ans: It increases muscle fiber size (hypertrophy) and strength.
Q: Why is calcium removed from cytoplasm after contraction?
Ans: To stop contraction and allow muscle relaxation.
Q: What role do mitochondria play in muscle?
Ans: They produce ATP through aerobic respiration.
Q: Name one clinical test of muscle function.
Ans: Electromyography (EMG) measures electrical activity in muscles.
Q: How is smooth muscle controlled?
Ans: By the autonomic nervous system, hormones, and local factors.
Q: Why does cardiac muscle not fatigue easily?
Ans: Because it has many mitochondria and a constant blood supply.
Q: What is DOMS?
Ans: Delayed onset muscle soreness after unfamiliar or intense exercise.
Q: What does “myogenic” mean?
Ans: Originating within the muscle itself (e.g., heartbeat from SA node).
Q: What is a fascicle?
Ans: A bundle of muscle fibers surrounded by perimysium.