Locomotor system ; muscles

📌 Introduction to Muscle Tissue
🖇 Definition
Muscle = group of contractile fibers responsible for movement, controlled by nervous stimuli.
Types:
1. Skeletal muscle: voluntary, striated, multinucleated, controlled by somatic NS.
2. Cardiac muscle: involuntary, striated, branched fibers forming functional syncytium, single nucleus, controlled by autonomic NS.
3. Smooth muscle: involuntary, non-striated, spindle-shaped, single nucleus, found in viscera & blood vessels, controlled by autonomic NS.
🚨 Clinical Importance
Skeletal muscle injury → movement limitation.
Cardiac muscle → myocardial infarction risk.
Smooth muscle → spasms in intestines, uterus, vessels.
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📌 Skeletal (Striated) Muscle
🟠 Attachments
Origin: fixed end.
Insertion: movable end.
Action: contraction pulls insertion toward origin → movement at joint.
🟣 Parts
Muscle belly: red, fleshy, contractile.
Tendon: white, fibrous, non-contractile → connects muscle to bone.
Tendon: rounded, cord-like.
Aponeurosis: flat, sheet-like.
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📌 Classification of Skeletal Muscles
🖇 According to Fiber Arrangement
🔹 Parallel to line of pull:
Quadrilateral (e.g., Pronator quadratus)
Strap-like (e.g., Sartorius)
Strap with intersections (e.g., Rectus abdominis)
Fusiform (e.g., Biceps brachii)
🔹 Pennate (Feather-like): fibers oblique to tendon
Unipennate: one side (e.g., Flexor pollicis longus)
Bipennate: both sides (e.g., Dorsal interossei)
Circumpennate: around central tendon (e.g., Tibialis anterior)
Multipennate: many bipennate units (e.g., Deltoid)
🔹 Oblique but non-pennate:
Triangular (e.g., Temporalis)
Spiral (e.g., Supinator)
Cruciate/X-shaped (e.g., Masseter)
🟠 According to Number of Heads or Bellies
Biceps: 2 heads (e.g., Biceps brachii)
Triceps: 3 heads (e.g., Triceps brachii)
Quadriceps: 4 heads (e.g., Quadriceps femoris)
Digastric: 2 bellies with intermediate tendon.
🟣 According to Action
Prime mover (Agonist): main muscle causing movement (e.g., Brachialis → elbow flexion).
Antagonist: opposes action (e.g., Triceps).
Synergist: steadies movement & removes unwanted motion (e.g., Wrist extensors).
Fixator: stabilizes origin or joint (e.g., Scapular muscles during grip).
🟠 Example – Firm Grip Coordination:
Prime movers: digital flexors.
Antagonists: digital extensors.
Synergists: wrist extensors.
Fixators: scapular & shoulder muscles.
🟣 According to Number of Joints Acted Upon
Uni-articular: one joint (e.g., Brachialis).
Bi-articular: two joints (e.g., Sartorius).
Multi-articular: more than two (e.g., finger flexors & extensors).
🚨 Clinical Importance
Tendon rupture → loss of muscle function.
Muscle strain → micro-tears in fibers.
Bi-articular muscles → more prone to injury due to stretching across two joints.