Musculoskeletal System Overview

Musculoskeletal System

• The musculoskeletal system is comprised of two systems: the skeletal and muscular systems.
• The skeletal system forms the body's bony framework.
• Two types of bone tissue exist: compact and cancellous bone; compact bone is the hardest connective tissue.
• Bone tissue is composed of microscopic structures called Haversian systems.
• Haversian systems consist of: Haversian canal, lamellae, lacunae, and canaliculi.
• The Haversian canal is a central canal for blood vessels, nerves, and lymphatic vessels.
• Lamellae are concentric plates of bone.
• Lacunae are small spaces between lamellae containing lymph and bone cells (osteocytes).
• Canaliculi are small channels radiating from the Haversian canal to lacunae, supplying nourishment to osteocytes.
• Interstitial lamellae fill spaces between Haversian systems.
• Compact bone differs from cancellous bone in its density; compact bone has Haversian systems, while cancellous bone does not.
• Cancellous bone contains osteocytes in small numbers forming trabeculae, providing a sponge-like appearance.
• Red bone marrow is always present in cancellous bone, filling spaces between trabeculae and producing red blood cells, white blood cells, and platelets.

Bone

• Compact bone is denser than cancellous bone.
• Haversian systems are not present in cancellous bone.
• Osteocytes in cancellous bone form trabeculae, giving it a sponge-like appearance.
• In children, all marrow is red.
• In adults, some marrow is yellow. Red bone marrow produces erythrocytes, leukocytes, and thrombocytes.
• Periosteum covers the outer surface of bone, providing attachment for muscle tendons and ligaments.
• Osteocytes within the bone deposit new bone material.
• Deeper layers have osteoblasts producing new bone.
• Periosteum is not found on the articular surface of bones; hyaline cartilage replaces periosteum in these areas.

Bone Development

• Bone develops from cartilage (long and irregular bones) and membranes (flat bones).
• Long bones have diaphysis, medullary canal, epiphyses, and compact bone surrounding cancellous bone and red marrow.
• Ossification is the conversion of tissue to bone by osteoblasts.
• Osteoblasts become osteocytes when established within lacunae.

Functions of Skeletal System

• Provides support for the body and protection for organs (Cranial, Thoracic, and Pelvic).
• Enables joint formation for movement.
• Provides attachment points for muscles.
• Produces blood cells in red bone marrow in cancellous bone.
• Stores calcium salts.

Axial Skeleton

• Composed of the skull, vertebral column, ribs, and sternum.

Appendicular Skeleton

• Composed of the shoulder girdle, pelvic girdle, and the upper and lower limbs.

Fontanelles

• Joints of the skull are immovable and joined by sutures.
• At birth, fontanelles are not fully formed.
• Fontanelles consist of membranes.
• Anterior and posterior fontanelles close at specific times.

Joints

• Joints can be fibrous (fixed), cartilaginous (slightly moveable), or synovial (freely moveable).
• Synovial joints include ball-and-socket, hinge, gliding, pivot, condyloid, and saddle.
• Synovial joints contain a synovial membrane and fluid.

Muscular System

• All movements require mechanisms.
• Muscular tissue provides movement.
• Muscles consist of elongated cells (several types noted).
  • Cardiac (specialised, non-voluntary)
  • Striated (skeletal or voluntary, powerful)
  • Smooth (unstriped, visceral or involuntary. Not under voluntary control, e.g., vascular muscles)
• Primary function of skeletal muscles is movement.
• Muscles maintain posture and produce heat.
• Skeletal muscle accounts for 40-50% of body weight.

Muscle Structure and Function

• Muscles act in coordinated groups that work together.

• Important groups of muscles includes:

  • Prime movers: Initiate and maintain movement.
  • Antagonists: Resist and reverse prime mover action, and decelerate movement.
  • Synergistic: Cancel out unwanted movements.

• Muscles have connective tissues (epimysium, perimysium, endomysium) for attachment and support.

• Muscles consist of repeating units called sarcomeres, for contraction.

• Sarcomeres contain thin (actin) and thick (myosin) filaments that slide over one another.

• Muscle contraction is initiated by nerve impulses.

• Nerve impulses trigger the release of acetylcholine at the neuromuscular junction.

• Acetylcholine causes calcium release, and leads to muscle contraction.

• Nerves to muscle leave spinal column and terminate at neuromuscular junctions or muscle end plates.

• Muscles are composed of elastic tissues, transmitting the force of contraction to bones.

• Nerves supply sensory and motor information. Sensory information is relayed to positions via proprioceptors. Motor nerves cause muscle contraction.