EW

lecture 1 muscle terms and disorders

Mechanics of Skeletal-Muscle–Driven Movement

• Skeletal muscles create movement by exerting force on tendons, which in turn pull on bones (or sometimes on other muscles).
• Tendons are continuous with the connective-tissue wrappings of the muscle (epimysium, perimysium, endomysium) and usually merge with the periosteum of bone.
• Not every tendon inserts directly on the articulating bones of a joint; insertions can occur distal to the joint line.
• Sarcomere shortening → whole-muscle shortening of ≈ 30\% at maximal contraction; partial contractions are under voluntary neural control.

Origin vs. Insertion

• Origin ("O")
• Classically defined as the attachment on the stationary bone during the movement being described.
• Usually (but not always) the more proximal attachment.
• Insertion ("I")
• Attachment on the bone that moves.
• Usually the distal attachment.
• Caveat: Some books redefine origin/insertion based on which end moves for a given action. In this course the traditional O = fixed (proximal), I = distal convention is retained regardless of action.
• Example cases
• Biceps brachii
– Long head originates on the supraglenoid tubercle of the scapula.
– Short head originates on the coracoid process.
– Insertion: radial tuberosity (with minor ulnar attachment) ➜ elbow flexion.
• Triceps brachii
– Three heads originate on scapula + humerus.
– Insertion: olecranon of ulna ➜ elbow extension.
• Serratus anterior ("hugging/boxer’s muscle")
– Textbook O: ribs 1–8/9; I: vertebral border & inferior angle of scapula.
– When scapula is free ➜ protracts scapula (hug/punch).
– When scapula fixed ➜ elevates ribs for deep breathing.

Lever Systems in the Body

• A lever = rigid bar that pivots about a fulcrum to move a load with an applied effort.
• Effort (E): muscular force applied.
• Fulcrum (F): pivot point (joint).
• Load (L): weight or resistance moved (body part + any external object).
• Symbol variation in different texts: E ≈ Force/Work, F ≈ Pivot/Axis, L ≈ Load/Weight/Resistance.
• Three lever classes (det. by relative positions of E-F-L)

  1. First-class (F between E and L) — e.g.
    • Scissors analogy.
    • Atlanto-occipital joint: posterior neck muscles (E) pull skull (L) over joint (F) to nod head posteriorly.
  2. Second-class (L between F and E)
    • Wheelbarrow analogy.
    • Plantar flexion when standing on tip-toe: ball of foot = F, body weight = L, gastrocnemius/soleus pull on calcaneus = E.
  3. Third-class (E between F and L) — most common in body.
    • Biceps curl: elbow = F, biceps pull on radius = E, hand + forearm = L.

Fascicle (Fasciculi) Arrangement & Functional Consequences

• Fibers bundled in parallel fascicles; pattern → power vs. ROM trade-off.
• Patterns
• Parallel: fibers run parallel to tendon (ex: sartorius).
• Fusiform: spindle-shaped with central belly (ex: biceps brachii).
• Circular: concentric rings; control openings (orbicularis oculi/oris).
• Triangular (convergent): broad origin, narrow insertion (pectoralis major).
• Pennate (fiber angle to tendon)
– Unipennate (extensor digitorum longus).
– Bipennate (rectus femoris).
– Multipennate (deltoid) — several short fascicles converging on multiple tendinous slips that then converge to a single tendon.

Functional Group Terminology

• Agonist (Prime Mover): provides major force for a specific movement.
• Synergist: assists agonist, adds extra force, reduces undesirable motion.
• Antagonist: opposes or reverses a particular movement.
• Example set at elbow
• Biceps brachii = agonist for flexion.
• Brachialis = synergist for flexion.
• Triceps brachii = antagonist to flexion (agonist for extension; anconeus = its synergist).

Naming Muscles (lecture reviewed in separate file)

• Common bases for names
• Location (temporalis, tibialis anterior).
• Shape (deltoid = triangular).
• Size (gluteus maximus/minimus, adductor longus/brevis).
• Fiber direction (rectus = straight, oblique = angled).
• Number of origins (biceps = 2, triceps = 3, quadriceps = 4).
• Origin & insertion (sternocleidomastoid).
• Action (flexor, extensor, adductor).
• Students advised to master terminology before lab model identification.

Survey of Major Muscle Groups (highlighted points only)

• Facial-expression muscles lie within the superficial fascia; originate on skull fascia/bone & insert on skin ➜ move skin rather than joints.
• Extra-ocular muscles
• Recti (sup., inf., med., lat.) = straight pulls.
• Obliques (sup., inf.) = angled pulls.
• Levator palpebrae superioris elevates upper eyelid (important in vision unit).
• Mastication: temporalis & masseter are key closers of mandible; several deeper pterygoid muscles omitted from lab list.
• Speech & swallowing, pelvic floor, intrinsic hand/foot muscles: many exist but not required for current practical — tables provided for enrichment.

Intrinsic Foot-Muscle Note

• Arches maintained by tendons + plantar intrinsic muscles.
• Regular barefoot/minimal-shoe time strengthens these muscles; constant arch-support can weaken them.
• Flat-foot (pes planus) may improve with targeted strengthening if ligamentous stretch not irreversible.

Common Musculoskeletal Injuries & Disorders

• Running Injuries (esp. knee)
• Often involve ligaments (ACL, PCL, MCL, LCL), menisci, or surrounding tendons (quadriceps, hamstrings, gastrocnemius, popliteus, plantaris, adductors).
• Contributing factors: poor training technique, biomechanical issues in foot/hip/back, excess body mass.
• Initial management — PRICE protocol:
\text{P} = \text{Protection},\; \text{R} = \text{Rest},\; \text{I} = \text{Ice},\; \text{C} = \text{Compression},\; \text{E} = \text{Elevation}
• Medications: NSAIDs (aspirin, ibuprofen) > acetaminophen; corticosteroid injections if severe; surgery for structural tears.
• Key advice: respect healing times of tendons/ligaments (slower than muscle) — avoid premature high-intensity return.
• Compartment Syndrome
• Muscle groups wrapped in dense fascia (compartments) — prominent in limbs.
• Internal bleeding/edema within a compartment → pressure ↑ → compromised blood flow & nerve function → severe pain & potential neuromuscular damage.
• Emergency treatment: fasciotomy (surgical fascia release) plus source-of-bleeding repair to prevent irreversible injury.
• Plantar Fasciitis
• Inflammation/tearing of plantar aponeurosis (runs calcaneus ➜ toes).
• Sharp heel or sole pain, often sudden after overuse.
• Therapy:
– Rest + controlled stretching to avoid tendon healing in shortened state (foot tends to plantar-flex during sleep).
– Ice/heat, weight reduction, orthotic devices maintaining ankle dorsiflexion, NSAIDs; steroid injections or surgery if refractory.

Ethical / Practical Considerations Discussed

• Balancing exercise enthusiasm with injury prevention: rest is ethically important for long-term musculoskeletal health.
• Surgery vs. conservative care: decision must weigh risks, healing time, and likelihood of full functional recovery.
• Barefoot/minimalist footwear debate: Encouraging natural strengthening vs. foot-protection needs — individualized approach recommended.

Connections to Earlier Coursework

• Prior knowledge of joint structure (Chapter 9) underpins understanding of lever fulcrums & running injuries.
• Familiarity with connective-tissue organization (epimysium → endomysium) clarifies origin/insertion, compartment syndrome, plantar aponeurosis.
• Muscle-naming lecture prerequisite for efficient lab identification, echoing anatomical terminology foundations from first weeks.

Key Numerical / Statistical Mentions

• Whole-muscle max shortening ≈ 30\% of resting length.

Study Tips From Instructor

• Master naming terminology before tackling model lists.
• Stick to official lab list for exam prep; extra tables are for enrichment.
• Use lever diagrams to visualize origin–insertion placements and resulting movement class.