Physiology of Musculoskeletal System Lecture 5

Musculoskeletal System

• The musculoskeletal system consists of bones, muscles, and joints that work together to provide support, protection, and movement to the body.

Functions of Bones

• Support of the body
• Protection of soft organs
• Movement due to attached skeletal muscles
• Storage of minerals and fats
• Blood cell formation

Joints

• Types of joints:
  • Fibrous joints: connect bones without allowing any movement (e.g., bones of skull and pelvis)
  • Cartilaginous joints: allow for limited movement (e.g., spine or ribs)
  • Synovial joints: allow for more movement (e.g., cavities between bones filled with synovial fluid)

Properties of Muscle Tissue

• Excitability: capacity of muscle to respond to a stimulus
• Contractility: ability of a muscle to shorten and generate pulling force
• Elasticity: ability of muscle to recoil to original resting length after stretched
• Extensibility: muscle can be stretched back to its original length

Muscle Fibers

• Each skeletal muscle is a separate organ composed of hundreds to thousands of muscle fibers
• Sarcolemma: the plasma membrane of a muscle cell
• Transverse (T) tubules: tiny invaginations of the sarcolemma that tunnel in from the surface toward the center of each muscle fiber
• Sarcoplasm: the cytoplasm of a muscle fiber

Thin and Thick Filaments

• Myofibrils: the contractile organelles of skeletal muscle
• Thin filaments: composed mostly of the protein actin
• Thick filaments: composed mostly of the protein myosin
• Both are directly involved in the contractile process

Sarcomeres

• The filaments inside a myofibril do not extend the entire length of a muscle fiber
• Instead, they are arranged in compartments called sarcomeres, which are the basic functional units of a myofibril
• Z discs: narrow, plate-shaped regions of dense protein material that separate one sarcomere from the next

Sliding Filament Mechanism

• Muscle contraction is a folding process, somewhat like closing an accordion
• Skeletal muscle shortens during contraction because the thick and thin filaments slide past one another
• The model describing this process is known as the sliding filament mechanism

Neuromuscular Junction

• Region where the motor neuron stimulates the muscle fiber
• The neuromuscular junction is formed by:
  • End of motor neuron axon (axon terminal)
  • The motor end plate of a muscle (specific part of the sarcolemma that contains ACh receptors)