Anatomy and Physiology: Chapter 10 - Muscle Tissue

Overview

• Muscle tissue is a primary tissue, one of the main tissues discussed earlier in the course.
• Three main types of muscle tissue:
  • Skeletal Muscle: Voluntary, moves the body by pulling on bones.
  • Cardiac Muscle: Involuntary, found in the heart.
  • Smooth Muscle: Involuntary, found in hollow organs.
• Focus of Chapter 10: Skeletal Muscle

Functions of Skeletal Muscle

• Movement of the body.
• Maintaining posture and body position.
• Supporting soft tissues.
• Guarding entrances and exits of the body.
• Maintaining body temperature.
• Storing nutrients.

Structure of Skeletal Muscle

1. Connective Tissue Layers

   • Epimysium: Outermost layer, surrounds the entire muscle.
   • Perimysium: Middle layer, surrounds muscle fiber bundles (fascicles).
   • Endomysium: Innermost layer, surrounds individual muscle fibers.

2. Muscle Fiber Organization

   • Muscle fibers = Muscle cells; cells are long and large.
   • Fascicles: Bundles of muscle fibers.
   • Tendons and Aponeuroses: Formed by collagen fibers from all three connective tissue layers, attach muscles to bone.

Anatomy of Skeletal Muscle Fibers

• Contain extensive vascular networks for oxygen supply.
• Multinucleated and striated.
• Sarcolemma: Cell membrane.
• Sarcoplasm: Cytoplasm of muscle fibers.
• T-tubules: Transmit action potentials into cell interior.
• Sarcoplasmic Reticulum (SR): Similar to ER, stores calcium, forms triads with T-tubules.

Myofilaments

• Thin Filaments (Actin): Contain proteins such as F-actin, nebulin, tropomyosin, and troponin.
• Thick Filaments (Myosin): Contain myosin molecules with head and tail structure.

Contraction Mechanism: Sliding Filament Theory

• Sarcomere: Smallest functional unit of a muscle fiber.
• During contraction:
  • H bands and I bands narrow.
  • Zones of overlap widen.
  • Z lines move closer together.
  • A band width remains constant.

Neuromuscular Junction

• Motor neurons release neurotransmitter (acetylcholine) to initiate muscle contraction.
• Action potential travels down neuron, releases ACH, opening sodium channels, leading to depolarization and muscle contraction.

Muscle Contraction Steps

1. Action potential reaches synaptic terminal.
2. Release of acetylcholine into the synaptic cleft.
3. Sodium influx causes depolarization.
4. Action potential spreads via T-tubules.
5. Calcium released from SR binds to troponin.
6. Tropomyosin shifts, exposing active sites.
7. Myosin heads bind to actin (cross-bridge formation).
8. Power stroke occurs, contracting the muscle.

Types of Muscle Contractions

• Isotonic Contractions: Muscle changes length (concentric - shortening, eccentric - lengthening).
• Isometric Contractions: Muscle tension without changing length.

Muscle Tone

• Normal tension and firmness of the muscle at rest.

Energy and Muscle Performance

• ATP: Primary energy source for muscle contraction.
• Types of muscle fibers:
  • Fast Fibers: Quick contractions, fatigue quickly.
  • Slow Fibers: Slow to contract, high endurance.
  • Intermediate Fibers: Characteristics between fast and slow.

Effects of Aging

• Decrease in muscle size, elasticity, and recovery ability.

Other Muscle Tissue Types

• Cardiac Muscle: Involuntary, striated, found in the heart, controlled by pacemakers.
• Smooth Muscle: Involuntary, non-striated, found in walls of hollow organs.