Muscle and Tendon Anatomy Quiz

Tendon

• Connects muscle to bone via fibrous connective tissue.
• Composed of collagen and elastin for tensile strength and elasticity.
• Smaller tendons can withstand greater forces; crucial for injury prevention.

Muscle

• Composed of parallel muscle fibers running in the same direction.
• Rich blood and nerve supply leading to effective oxygenation.

Epimysium

• Connective tissue layer under the fascia that envelops the entire muscle.

Perimysium

• Connective tissue that surrounds bundles of muscle fibers, known as fascicles.

Endomysium

• Connective tissue layer encasing individual muscle fibers.

Fascicles

• Bundles of muscle fibers that produce steady force.

Muscle Fiber

• Individual muscle cell containing multiple nuclei.
• Formed from bundles of myofibrils, measuring 50-100 microns.

Myoblasts

• Embryonic stem cells that fuse to create skeletal muscle.
• Result in multinucleate structures called myotubes, differentiating into muscle fibers.

Myofibril

• Composed of actin and myosin filaments arranged in long bundles.
• Main cellular component, comprising 80% of muscle cell volume.

Sarcomere

• Basic contractile unit of muscle, extending from Z line to Z line.
• Responsible for force generation during muscle contraction, measuring 2.2 microns.

Sarcolemma

• The cell membrane that surrounds a muscle fiber.

Sarcomere Structure

• Key components:
  • Z Line: outer boundary.
  • M Line: center point.
  • I Band: contains thin actin filaments.
  • A Band: consists of thick myosin filaments with some overlap with actin.
  • H Zone: area containing only myosin filaments.

Myosin

• Thick filament measuring 1.6 microns; essential for muscle contraction.

Actin

• Thin filament measuring 1 micron; plays a vital role in muscle movement.

Structural Proteins

• Help maintain and organize muscle structure. Key proteins include:
  • Titin: connects Z line to M line, provides elasticity.
  • Z-line proteins (e.g., alpha-actinin) and M-line proteins (e.g., myomesin).

Contractile Proteins

• Generate force during contraction. Main proteins include actin, myosin, tropomyosin, and the troponin complex.

Nebulin

• A structural protein that stabilizes actin filaments and helps regulate their length during muscle development.

Titin

• Large protein connecting M-line to Z-line; provides elasticity and stabilizes myosin.

M-line

• Central region of the sarcomere anchoring myosin filaments.

Cross Section Through Sarcomere

• I-band: shows only thin actin filaments.
• H-band: shows only thick myosin filaments.
• A band: region where both filament types overlap.

Actin:Myosin Interaction

• Maximum force generation occurs with optimal filament overlap; three myosins surround one actin filament.

I-band

• Light band consisting exclusively of thin filaments, shortens during contraction.

A-band

• Dark band dominated by myosin with minor overlap of actin; its length remains unchanged during contraction.

H-zone

• Central area of A-band, only containing myosin filaments, which reduces in size during muscle contraction.

T-tubule

• Transverse tubules that facilitate rapid depolarization of muscle cells via plasma membrane invaginations.

Signaling System

• Involves T-tubules and terminal cisternae for effective muscle contraction signaling.

Terminal Cisternae

• Expanded areas of the sarcoplasmic reticulum, surrounding T-tubules, essential for calcium storage and release.

Sarcoplasmic Reticulum

• Organelles in muscle fibers responsible for calcium storage and release upon motor neuron stimulation.

Triads

• Structural arrangements made by a T-tubule and two terminal cisternae, crucial for efficient signaling within the sarcomere.