Understanding Muscular Tissue — Long Answer Questions
Medium Level (Application & Explanation)
Q1. Explain the structure and function of a skeletal muscle fibre and describe how actin and myosin cause muscle contraction.
Answer:
A skeletal muscle fibre is a long, cylindrical cell with many nuclei (multinucleated) and visible striations made by repeating units called sarcomeres. Each sarcomere contains thin actin filaments and thick myosin filaments. The fibres are bundled by connective tissue to form the whole muscle.
During contraction the sliding filament mechanism occurs: myosin heads attach to binding sites on actin and pull the actin filaments inward, shortening the sarcomere.
This process needs ATP for myosin head movement and detachment, and Ca2+ to expose binding sites on actin by altering regulatory proteins.
When many sarcomeres shorten together, the whole muscle contracts, producing force and movement under voluntary control through motor neurons.
Q2. Compare skeletal, cardiac, and smooth muscles in terms of structure, control, and function. Give examples and explain how their structures suit their functions.
Answer:
Skeletal muscle: Striated, multinucleated, attached to bones, under voluntary control. Example: biceps. Structure with sarcomeres and strong, fast contractions suits quick and powerful body movements.
Cardiac muscle: Striated, usually single nucleus, has intercalated discs with gap junctions, involuntary. Example: heart. The discs allow fast, coordinated impulse spread, making rhythmic and continuous pumping possible.
Smooth muscle: Non-striated, single nucleus, involuntary, found in walls of hollow organs like stomach and blood vessels. Its spindle shape and slow, sustained contractions are ideal for moving food (peristalsis) and regulating vessel diameter.
Each muscle’s structure (striation pattern, nuclei, connectivity) directly supports its specific role in the body.
Q3. Describe the sliding filament theory of muscle contraction in simple terms and explain the roles of ATP and calcium ions (Ca2+).
Answer:
The sliding filament theory says muscle contraction happens when thin actin filaments slide past thick myosin filaments, shortening each sarcomere. Myosin has heads that attach to actin, forming cross-bridges, then pull actin inward.
ATP is essential: it binds to the myosin head to release it from actin and provides energy when hydrolysed for the next power stroke. Without ATP, myosin stays attached and causes stiffness.
Ca2+ is released from the sarcoplasmic reticulum when a nerve impulse arrives. Ca2+ binds to regulatory proteins (troponin), causing a shift that exposes binding sites on actin, enabling cross-bridge formation.
After contraction, Ca2+ is pumped back and ATP restores the muscle to a relaxed state. This coordinated ATP–Ca2+ system controls contraction and relaxation.
Q4. Explain how smooth muscle produces movement in the digestive tract. What is peristalsis, and how is it controlled?
Answer:
Smooth muscle lines the walls of the digestive tract and contracts rhythmically and slowly to move food. The muscle layers (circular and longitudinal) alternate contractions to push contents forward.
Peristalsis is the wave-like coordinated contraction and relaxation of smooth muscle that propels food from the oesophagus through the stomach and intestines to the anus. A circular contraction behind the food bolus and relaxation ahead creates the forward movement.
Control is involuntary and mainly through the autonomic nervous system and the enteric nervous system, plus hormones and local chemical signals.
Smooth muscle’s ability for sustained tension and gentle, coordinated waves makes peristalsis efficient for digestion and absorption without conscious effort.
Q5. What causes muscle fatigue, and how can one prevent or reduce it during exercise? Mention biochemical and practical factors.
Answer:
Muscle fatigue happens when muscles cannot maintain force or power. Biochemical causes include ATP depletion, accumulation of metabolic by-products such as lactic acid (C3H6O3), and ionic imbalances (e.g., disrupted Ca2+ handling). Poor oxygen supply pushes muscles to anaerobic metabolism, increasing lactic acid and lowering pH, which impairs enzyme activity.
Practical causes include overuse, inadequate rest, dehydration, and low blood glucose.
Prevention methods: pace exercise and build endurance gradually, ensure proper hydration, eat balanced meals for energy, allow rest and recovery, warm up and cool down, and include breathing for oxygen supply. Adequate sleep and training reduce fatigue by improving muscle efficiency and recovery.
High Complexity (Analytical & Scenario-Based)
Q6. A patient develops an irregular heartbeat (arrhythmia). Explain how the structure of cardiac muscle contributes to normal heart rhythm and how disruption leads to arrhythmia. Discuss possible effects on the body.
Answer:
Cardiac muscle cells are branched and connected by intercalated discs that contain gap junctions. Gap junctions allow rapid electrical impulse spread so heart cells depolarise almost simultaneously, producing a coordinated heartbeat. Pacemaker cells set rhythm and conduct impulses through specialised pathways.
If structural or electrical connections are damaged (by ischemia, scar tissue, ion imbalance, or drug effects), impulse spread is disrupted, causing arrhythmia—beats too fast, too slow, or irregular.
Consequences include reduced cardiac output, poor blood supply to organs, dizziness, shortness of breath, chest pain, or fainting. Severe arrhythmias can cause heart failure or sudden cardiac arrest.
Treatment aims to restore conduction (drugs, pacemakers, ablation) and address the underlying cause to re-establish coordinated contraction.
Q7. Describe what happens when a skeletal muscle is torn (strain). Explain the healing process, possible complications, and why physiotherapy matters for recovery.
Answer:
A torn skeletal muscle fibres occur from overstretching or heavy load. Immediately there is pain, swelling, bleeding into tissue (haematoma), and loss of function.
Healing phases: inflammation (clears debris and recruits repair cells), proliferation (satellite cells — muscle stem cells — divide and fuse to form new fibres), and remodelling (new fibres mature and connective tissue repairs the area). Scar tissue (fibrous connective tissue) may form if damage is extensive.
Complications: excessive scar formation reduces flexibility and strength, repeated injury, and chronic pain.
Physiotherapy helps by controlled exercises, stretching, strengthening, and gradual load increase to align new fibres correctly, prevent contractures, reduce scar stiffness, and restore full function safely.
Q8. Imagine the autonomic nervous system fails to control smooth and cardiac muscles properly. Analyze how this would affect homeostasis and give examples of symptoms and life-threatening outcomes.
Answer:
The autonomic nervous system (ANS) controls involuntary muscles: cardiac muscle (heart rate) and smooth muscle (vessel tone, digestion, airway diameter). ANS failure disrupts these controls, harming homeostasis—the stable internal environment.
Examples: if heart rate regulation fails, blood pressure and tissue perfusion become unstable, causing dizziness, organ ischemia, or shock. Loss of vascular tone leads to dangerous drops in blood pressure.
Digestive smooth muscle failure causes impaired peristalsis, nausea, constipation, malabsorption, and increased infection risk. Airway smooth muscle dysfunction can cause breathing difficulties.
Severe ANS failure can lead to multi-organ dysfunction, inability to maintain body temperature, and can be life-threatening without emergency support to restore circulation and respiration.
Q9. Explain how calcium channel blockers affect muscle function and why they are used to treat high blood pressure. Discuss effects on cardiac and smooth muscle and possible side effects.
Answer:
Calcium channel blockers (CCBs) inhibit Ca2+ entry through voltage-gated calcium channels in cell membranes. In cardiac muscle, reduced Ca2+ lowers contractility and can slow heart rate, decreasing cardiac output. In smooth muscle of blood vessels, lower Ca2+ causes relaxation and vasodilation, reducing peripheral resistance and blood pressure.
They are used to treat hypertension and certain arrhythmias because lowering vascular tone reduces the workload on the heart and improves blood pressure control.
Possible side effects: dizziness (from low blood pressure), swelling of ankles (vasodilation), constipation, and in some people slowed heart rate or worsening heart failure. Monitoring and choosing the right CCB type helps balance benefits and risks.
Q10. Compare how different animals adapt their muscle types for special functions — for instance, insect flight muscles, fish cardiac muscle, and smooth muscle in large animals. Explain structural or functional specialisations.
Answer:
Insect flight muscles often use asynchronous contraction and high-frequency oscillations. Many insects have indirect flight muscles that stretch and deform the thorax to create wing beats far faster than nerve firing rates; they rely on elastic energy storage and calcium-independent mechanisms for speed.
Fish cardiac muscle is adapted to water temperature and oxygen availability; some fish have a single circulatory loop and their heart muscles can function at lower metabolic rates, with special pacemaker properties for different swimming demands.
Smooth muscle in large animals (e.g., elephants) must sustain lo...
