Muscular System lab Review flash cards

Muscle Tissue Models

Skeletal Muscle Fiber (Whole-Cell) Model

• Connective-tissue sheaths

  • Endomysium: thin areolar C.T. wrapper investing each individual muscle fiber; provides extracellular matrix for capillaries + nerve fibers.

  • Practical link: damage → impaired nutrient exchange during muscular dystrophy.

• Sarcolemma

  • Phospholipid bilayer + associated proteins; conducts the action potential (AP).

  • Voltage change here opens \text{Na}^+ channels → depolarization cascade.

• Neuromuscular Junction (NMJ)

  • Synaptic knob (axon terminal): houses \approx 3000 vesicles of acetylcholine (ACh) per terminal.

  • Synaptic cleft: \approx 20\,\text{nm} extracellular gap filled with basal lamina containing acetylcholinesterase.

  • Motor end plate: specialized sarcolemma region; high density of ACh receptors (ligand-gated \text{Na}^+/\text{K}^+ channels).

  • Clinical tie-in: Curare competitively inhibits these receptors → flaccid paralysis.

• Sarcoplasm: cytoplasm; rich in glycogen granules + myoglobin for O_2 storage (makes red meat red).

• Peripheral nuclei (multinucleated syncytium from myoblast fusion).

• Myofibrils

  • \approx 80\% of cell volume; column-like contractile organelles.

• Sarcomeres

  • Repeating contractile units \bigl(\text{Z line} \rightarrow \text{Z line}\bigr); fundamental force-generating structure.

Myofibril (Sub-Cellular) Model

• Myofibrils: bundles of myofilaments; each \approx 1\,\mu\text{m} in diameter.

• Myofilaments

  • Thick: myosin II; heads exhibit ATPase activity.

  • Thin: actin, tropomyosin, troponin complex.

• Sarcoplasmic Reticulum (SR)

  • Smooth ER derivative storing Ca^{2+}; terminal cisternae flank T-tubules to form triads.

• T-tubules (Transverse tubules)

  • Invaginations of sarcolemma; carry AP into fiber core; trigger Ca^{2+} release.

• Bands & Lines (give striated appearance)

  • A band: dark; length of thick filaments.

  • I band: light; thin filaments only.

  • H zone: central lighter zone in A band; thick only.

  • M line: protein meshwork anchoring thick filaments.

  • Z line (disc): anchors thin filaments; defines sarcomere borders.

  • Sliding-filament theory: during contraction I + H zones shorten, A band unchanged.

• Glycogen granules: on-site glucose reserve for anaerobic glycolysis.

• Mitochondria: numerous, sandwiched between myofibrils; supply ATP.

• Sarcolemma: repeated here to emphasize continuity from cell to myofibril view.

Histology of Muscle Tissue

Skeletal Muscle (Longitudinal & Cross Section)

• Epimysium: dense irregular C.T. around entire muscle.

• Perimysium: surrounds fascicles (10–100 fibers each).

• Endomysium: around single fiber (reiterated for microscopy context).

• Fascicles: visible as bundles; circular in cross section, parallel cylinders in longitudinal.

• Fibers

  • Cylindrical, unbranched, up to 30\,\text{cm} long.

• Peripheral Nuclei: diagnostic of skeletal type.

• Striations: alternating light/dark, correlate with I & A bands.

• Myofibrils: appear as punctate dots in cross section (darker points).

Neuromuscular Junction Slide

• Axon of motor neuron: myelinated until terminal.

• Actual junction: space + specialized membranes; stains as pale zone.

• Associated skeletal muscle fibers: show relation of single axon to multiple fibers (motor unit).

Smooth Muscle (Small Intestine)

• Location: muscularis externa; inner circular & outer longitudinal layers.

• Key features

  • Spindle-shaped (fusiform) cells.

  • Single central nucleus.

  • No striations (actin/myosin arrangement is criss-cross, not sarcomeric).

• Functional note: slow, sustained contractions; autonomic control.

Cardiac Muscle

• Branching fibers forming syncytium.

• Central nuclei, usually one per cell.

• Striations (sarcomeres present).

• Intercalated discs

  • Gap junctions + desmosomes; allow rapid electrical coupling.

  • Clinical: damage during MI interrupts conduction → arrhythmia.

Muscles as Organs – Gross Anatomy

• Laboratory requirement: learn 62 named muscles (see p.41 of manual).

• Groups emphasized for dissection & function questions:

  • Rotator Cuff

  • Supraspinatus

  • Infraspinatus

  • Subscapularis

  • Teres minor

  • Quadriceps Femoris

  • Rectus femoris

  • Vastus lateralis

  • Vastus medialis

  • Vastus intermedius

  • Hamstrings

  • Biceps femoris

  • Semimembranosus

  • Semitendinosus

• Study tip: Associate origin-insertion pairs to predict action; e.g., quadriceps common insertion on tibial tuberosity via patellar ligament → knee extension.

Knee Joint (Supportive Structures)

Remember: although only muscles create movement, passive structures stabilize.

• Lateral meniscus: fibrocartilaginous C-shaped pad; shock absorption.

• Medial meniscus: more firmly attached to tibial collateral ligament → higher tear rate.

• Posterior cruciate ligament (PCL): prevents posterior displacement of tibia.

• Anterior cruciate ligament (ACL): prevents anterior displacement of tibia; common sports injury.

• Fibular (lateral) collateral ligament (LCL): cord-like; resists varus stress.

• Tibial (medial) collateral ligament (MCL): broad; resists valgus stress.

• Transverse ligament: connects anterior horns of menisci; balances load.

Terminology Clarification (Anatomical vs. Lay Language)

• Upper limb

  • Arm (brachium): region between shoulder & elbow.

  • Forearm (antebrachium): elbow to wrist.

• Lower limb

  • Thigh: hip to knee.

  • Leg (crus): knee to ankle.