AN3.1-3 | General features of Muscle — Gate Quiz

Correct! Cardiac muscle is involuntary (controlled by the autonomic nervous system and intrinsic pacemakers) whereas skeletal muscle is voluntary (controlled by the somatic nervous system). Both types have striations.

Muscle types: Skeletal — voluntary, striated, multinucleate, peripheral nuclei. Cardiac — involuntary, striated, mono/binucleate, central nuclei, intercalated discs, branching fibres. Smooth — involuntary, non-striated, mononucleate, central nuclei, fusiform cells.

Incorrect. The key difference here is voluntary vs involuntary control. Both cardiac and skeletal muscle have striations. Cardiac muscle has intercalated discs (not skeletal).

Correct! The origin is conventionally the less mobile (fixed) attachment — usually the proximal attachment of the muscle. The insertion is the more mobile attachment — typically the distal end that moves when the muscle contracts. However, these roles can reverse in some activities.

Origin: Less mobile, usually proximal end. Insertion: More mobile, usually distal end. Important exception: reverse action — e.g., biceps brachii can flex the arm towards a fixed forearm (when doing chin-ups, the origin moves). The terms are conventional, not absolute.

Incorrect. Origin = less mobile, fixed attachment (usually proximal). Insertion = more mobile attachment (usually distal). In reverse muscle action, the insertion becomes fixed and the origin moves.

Correct! Pennate muscles (fibres angled like a feather) can pack more muscle fibres into the same volume compared to parallel-fibre muscles, giving them a greater physiological cross-sectional area (PCSA) and therefore greater force/power generation. They sacrifice range of movement for power.

Muscle architecture: Parallel (fusiform) = longer fibres, greater range of movement and speed. Pennate (unipennate, bipennate, multipennate) = more fibres per volume, greater PCSA, greater force. Quadriceps = large bipennate component. Sartorius = longest parallel-fibre muscle in the body.

Incorrect. Pennate muscles generate more force (power) than parallel-fibre muscles of similar size. Parallel fibres (fusiform) allow greater range of movement and speed.

Correct! An aponeurosis is a flat, sheet-like tendinous structure connecting a wide muscle to bone or another structure. Examples: palmar aponeurosis, plantar aponeurosis, aponeurosis of external oblique muscle.

Tendons = cord-like fibrous tissue (muscle to bone). Aponeuroses = flat sheet-like tendinous structures (broad muscle to bone/fascia). Ligaments = fibrous tissue bone-to-bone. Retinacula = thick bands of deep fascia holding tendons in place. Examples of aponeuroses: palmar, plantar, bicipital, external oblique.

Incorrect. A flat sheet-like tendinous structure = aponeurosis. A cord-like tendinous structure = tendon. Ligament connects bone to bone. Fascia is a broader connective tissue sheet.

Correct! A low innervation ratio (few muscle fibres per motor nerve fibre) allows for fine, precise motor control. The extraocular muscles have ratios as low as 3–6 fibres per motor unit, enabling minute adjustments of eye position. Large postural muscles have ratios of hundreds to thousands.

Motor unit: one alpha motor neurone + all muscle fibres it innervates. Innervation ratio: Low (3–10) = precision — extraocular muscles, intrinsic hand muscles. High (100–2000) = force — gastrocnemius, quadriceps. Graded force is achieved by recruiting more motor units (spatial summation) and increasing firing rate (temporal summation).

Incorrect. Low innervation ratio = fine precision. High innervation ratio = greater force but less precision. Extraocular muscles need precision, not power.

Correct! Isometric contraction produces force without change in muscle length (the joint does not move). The term 'isometric' means 'same measure' (equal length). Examples: holding an object still, pressing against an immovable wall, quadriceps setting.

Muscle contractions: Isometric (static) — length unchanged, force produced. Isotonic concentric — muscle shortens, joint moves. Isotonic eccentric — muscle lengthens while contracting, controls movement against gravity (walking downstairs, lowering weight). Eccentric contractions generate highest forces and cause most DOMS.

Incorrect. Isometric = muscle contracts without shortening/lengthening (no joint movement). Isotonic concentric = muscle shortens while contracting (lifts a weight). Isotonic eccentric = muscle lengthens while contracting (lowering a weight).

Correct! Arterioles and blood vessel walls contain smooth (visceral) muscle in the tunica media. Smooth muscle is involuntary, non-striated, and controlled by the autonomic nervous system and local mediators. Its contraction increases peripheral vascular resistance, contributing to hypertension.

Smooth muscle locations: Blood vessels (tunica media), gut wall, urinary bladder, uterus, iris/ciliary body, arrector pili. Properties: involuntary, slow contraction, sustained tone, less fatigable, can regenerate. Importance in hypertension: arteriolar smooth muscle tone ↑ → peripheral resistance ↑ → BP ↑.

Incorrect. Blood vessel walls contain smooth muscle in the tunica media. Smooth muscle is involuntary and non-striated. Cardiac muscle is only in the heart.

Correct! Biceps brachii has two heads of origin: (1) Long head — from the supraglenoid tubercle of the scapula (tendon passes through the shoulder joint); (2) Short head — from the coracoid process of the scapula (with coracobrachialis). Both heads join to form a single muscle belly.

Biceps brachii: Two origins — Long head (supraglenoid tubercle; intracapsular, extrasynovial tendon through the shoulder joint) + Short head (coracoid process with coracobrachialis). One insertion — radial tuberosity (supination) + bicipital aponeurosis (forearm fascia). Long head tendinitis is common in overhead athletes.

Incorrect. Biceps has two tendons of origin: long head (supraglenoid tubercle) and short head (coracoid process). They unite distally into one belly → one tendon of insertion at the radial tuberosity.

Correct! Type I (slow-twitch, oxidative) fibres are designed for prolonged endurance activities. They are rich in mitochondria, myoglobin (red fibres), and fatigue-resistant. Postural muscles (e.g., soleus, paraspinal) are predominantly Type I.

Muscle fibre types: Type I (slow oxidative, red) — fatigue-resistant, endurance, posture (soleus, paraspinals). Type IIA (fast oxidative-glycolytic) — intermediate. Type IIB (fast glycolytic, white) — power, sprint, fast, easily fatigued. Training can shift IIB → IIA (endurance training).

Incorrect. Type I (slow-twitch) = endurance, posture, fatigue-resistant, red colour. Type II (fast-twitch) = power, speed, sprint, fatigue easily, white/pale colour.

Correct! The antagonist is the muscle that opposes the action of the agonist (prime mover). When biceps (agonist) contracts to flex the elbow, triceps (antagonist) must relax to allow smooth, controlled movement (reciprocal inhibition).

Muscle roles: Agonist (prime mover) — produces the movement. Antagonist — opposes the agonist; relaxes via reciprocal inhibition. Synergist — assists agonist, eliminates unwanted motion. Fixator — stabilizes the origin bone. All roles are context-dependent; a muscle can be agonist in one movement and antagonist in another.

Incorrect. Agonist (prime mover) = performs the action (biceps in elbow flexion). Antagonist = opposes the action (triceps). Synergist = assists the agonist. Fixator = stabilizes the origin.