MCAT Biology Ch. 11 The Musculoskeletal System

1. Skeletal
2. Smooth
3. Cardiac

• Functions:
  • Support & movement
  • Propulsion of blood thru veins
  • Thermoregulation (shivering)
• Characteristics:
  • Multinucleated
  • Striated
  • Under voluntary (somatic) control
  • Divided into 2 types of fibers:
    • Red (Slow-Twitch) Fibers - oxidative phosphorylation
    • White (Fast-Twitch) Fibers - anaerobic metabolism

• Located in respiratory, reproductive, cardiovascular, & digestive systems
• Characteristics:
  • Nonstriated
  • Under involuntary (autonomic) control
  • Uninucleated (only 1 nucleus)
  • * Myogenic Activity - contraction w/out any neural input

• Comprises contractile tissue of the heart
• Characteristics:
  • Striated
  • Under involuntary (autonomic) control
  • Can be uni- or binucleated (1 or 2 nuclei)
  • Cells are connected w/ intercalated discs that contain gap junctions
  • * Myogenic Activity - contraction w/out any neural input

• High myoglobin content (red color)
• Derive energy aerobically
• Many mitochondria for oxidative phosphorylation

• Contain much less myoglobin than red fibers (white color)
• Derive energy mostly anaerobically

Cardiac muscle cells are connected by intercalated discs which contain many gap junctions. Gap junctions are connections between the cytoplasm of adjacent cells, allowing for the flow of ions directly between cells. Allows for rapid & coordinated muscle cell depolarization & efficient contraction of cardiac muscle

Basic contractile unit of striated (skeletal) muscle.

• Made of thick (myosin) & thin (actin) filaments

Found on the thin filament & regulate actin-myosin interactions

Sarcomeres attach end to end to become myofibrils

• M-Line - located in middle of sarcomere
• I-Band - contains only thin filaments
• H-Zone - consists of only thick filaments
• A-Band - contains thick filaments in their entirety, including any overlapping area w/ thin filaments. **Only part of sacromere that maintains constant size during contraction!!!

A muscle cells or muscle fiber. Made up of many myofibrils

Surrounds myofibrils, is a calcium-containing modified endoplasmic reticulum

Cell membrane of a myocyte

A system of T-tubules is connected to the sarcolemma & oriented perpendicularly to the myofibrils, allowing incoming signals from nerves to reach all parts of the muscle