Educational resource developed at the Veterinary Anatomy Section, ICAR-Indian Veterinary Research Institute (ICAR-IVRI), Bareilly.
📝 STANDARD DESCRIPTION:
Three types of muscle tissue:
1. Skeletal (Voluntary, Striated) Muscle
• Attached to bone via tendons.
• Striated under microscope (sarcomeres visible).
• Multinucleate fibres (peripheral nuclei).
• Voluntary control — somatic nerves.
• Fatigues quickly under load.
2. Cardiac Muscle
• Found only in heart.
• Striated.
• Single central nucleus.
• Intercalated discs — gap junctions allow synchronised contraction.
• Involuntary; auto-rhythmic.
3. Smooth (Visceral, Unstriated) Muscle
• In walls of viscera, blood vessels, ducts.
• Spindle-shaped cells, single central nucleus.
• No striations.
• Involuntary; slow, sustained contractions.
📚 DETAILED DESCRIPTION:
MYOLOGY — STUDY OF MUSCLES
Muscles are the only contractile tissue in the body. Their excitability + contractility produce all body movement, propel blood, push food, expel urine, and warm us.
I. SKELETAL MUSCLE:
• Forms the 'flesh' (~40% of body mass).
• Each fibre is a long, cylindrical, multinucleate cell.
• Sarcomeres (functional units) made of actin+myosin filaments → striations.
• Innervation: somatic motor neurons; one neuromuscular junction per fibre.
• Energy: glycolysis + oxidative phosphorylation.
• Two main fibre types: Type I (red, slow-twitch, oxidative) = postural; Type II (white, fast-twitch, glycolytic) = phasic.
II. CARDIAC MUSCLE:
• Branched cells joined end-to-end at intercalated discs (with gap junctions + desmosomes).
• Acts as a functional syncytium — wave of contraction spreads from cell to cell.
• Auto-rhythmic — sinoatrial (SA) node sets pace.
• Innervation: autonomic (modulating, not initiating).
III. SMOOTH MUSCLE:
• Two types: visceral (single-unit) — spreads excitation via gap junctions (gut, ureter, uterus); multi-unit — each cell innervated separately (iris, ductus deferens).
• No striations because actin/myosin not arranged in sarcomeres.
• Slow, prolonged tonic contractions; less ATP per contraction.
STRUCTURE OF A SKELETAL MUSCLE (Whole organ):
• Epimysium — outer connective tissue covering of whole muscle.
• Perimysium — surrounds fascicles (bundles of fibres).
• Endomysium — surrounds individual fibres.
• These connective tissues converge at the ends to form the tendon.
PARTS OF A MUSCLE:
• Origin — usually fixed (proximal) attachment.
• Insertion — usually movable (distal) attachment.
• Belly (venter) — fleshy contractile portion.
• Tendon (proximal) — at origin (usually short, broad).
• Tendon (distal) — at insertion (usually long, cord-like).
// COMPARATIVE ANALYSIS
| HORSE |
Very high % Type IIb 'fast-twitch' fibres in gluteal/locomotor muscles → bursts of sprint speed. |
| CATTLE |
Higher proportion of Type I oxidative fibres → endurance grazing. |
| BIRD |
Pectoralis: red 'dark meat' (oxidative) in flying birds vs white 'breast meat' (glycolytic) in chickens — chickens fly very little. |
CLINICAL RELEVANCE
Muscle biopsy — for diagnosis of muscular dystrophies, myositis, polysaccharide storage myopathy (PSSM in horses). Rhabdomyolysis ('tying up' in horses) — muscle damage releases myoglobin → kidney damage.
