Musculoskeletal System Notes

Musculoskeletal System

Introduction

• The musculoskeletal system consists of the muscular and skeletal systems.
• Its primary function is to provide support and enable movement.

Skeletal System

Functions:

• Support: Provides the structural framework for the body.
• Protection: Protects internal organs from injury.
• Movement: Enables body movement through muscle attachment and leverage.
• Blood cell production: Bone marrow is responsible for hematopoiesis.
• Calcium and phosphate storage & regulation: Bones store and release these minerals to maintain homeostasis.
• Number of bones: Adults have 206 bones, while newborns have approximately 300 (which fuse together during growth).

Axial vs. Appendicular Skeleton

• Axial Skeleton: Bones along the body’s long axis.
  • Skull
  • Laryngeal skeleton
  • Vertebral column
  • Thoracic/rib cage
• Appendicular Skeleton: Bones that form the upper and lower limbs/extremities.
  • Shoulder and pelvic girdles

Types of Bones

• Long
• Short
• Flat
• Irregular

Long Bones

• Examples: Fibula, tibia, metacarpals, humerus, ulna, radius, femur, metatarsals, phalanges.
• Shape: Cylindrical and longer than they are wide.
• Function: Act as levers for movement when muscles contract.

Short Bones

• Examples: Talus (ankle), scaphoid (wrist).
• Shape: Cube-like, with approximately equal length, width, and thickness.
• Function: Provide stability, support, and limited motion.

Flat Bones

• Examples: Cranial bones, scapulae (shoulder blades), sternum (breastbone), ribs.
• Shape: Typically thin and often curved.
• Function: Serve as attachment points for muscles and protect internal organs.

Irregular Bones

• Examples: Vertebrae, pelvis, many facial bones.
• Shape: Complex shapes that do not fit into other categories.
• Function: Support and protect the spinal cord (vertebrae), provide structure for facial features and sinuses.

Bone Structure

• Compact Bone: Outer layer, rigid and dense.
• Spongy Bone: Inner layer, porous.

Bone Marrow

• Red Bone Marrow: Produces blood cells and platelets; found in spongy bone.
• Yellow Bone Marrow: Stores energy as fat.
• Location of red marrow in adults: Bones of the skull, sternum, ribs, clavicle, pelvic bones, and vertebral column.
• Children have more red bone marrow than adults due to their higher metabolic rate and growth requirements.

Joints & Ligaments

• Joint: Place where bones meet.
• Specialized connective tissue (cartilage).
• Ligament: Connects bones with each other; made of dense regular connective tissue.

Types of Joints

• Ball and Socket
• Hinge
• Pivot

Ball and Socket Joint

• Structure: Rounded head of one bone (ball) fits into the concave articulation (socket) of the adjacent bone.
• Examples: Hip joint (femoral head and acetabulum), shoulder joint (head of humerus and scapula).
• Range of motion: Greatest range of motion, allowing multiple rotational movements.
• Dislocation risk: Easier to dislocate due to the wide range of motion.

Hinge Joint

• Structure: Convex end of one bone articulates with the concave end of the adjoining bone.
• Movement: Allows for bending and straightening along a single axis (uniaxial joint).
• Examples: Elbow, knee, ankle, interphalangeal joints (fingers and toes).

Pivot Joint

• Movement: Restricts movement to a single plane.
• Structure: A rounded portion of a bone is enclosed within a ring formed partially by the articulation with another bone and partially by a ligament. The bone rotates within this ring.
• Examples: Atlantoaxial joint (between C1 and C2 vertebrae).

Skeletal System Diseases

Arthritis

• Definition: Inflammation of the joints.
• Signs and symptoms: significant joint pain, along with swelling, stiffness, and reduced joint mobility.
• Causes:
  • Degenerative: Osteoarthritis (reduction of cartilage).
  • Autoimmune: Rheumatoid arthritis.
• Forms: There are more than 100 different forms of arthritis.
• Other causes: Aging, damage to articular cartilage, bacterial or viral infections, or unknown (possibly genetic) causes.

Osteoporosis

• Definition: Disease in which bones become weak due to a decrease in bone mass.
• Mechanism: The rate of bone resorption exceeds the rate of bone formation.
• Causes:
  • Change in hormone levels
  • Vitamin D/calcium deficiency
• Risk factors:
  • Age (>70 years)
  • Sex (women)
  • Genetics
  • History of falls
  • Physical inactivity
  • Low muscle mass and strength
  • Low body weight
  • Smoking
  • High alcohol intake
  • Inadequate energy or protein intake

Muscular System

Functions:

• Movement
• Maintain posture
• Blood circulation
• Number of muscles: Approximately 640 skeletal muscles + all smooth muscles.

Types of Muscle

• Cardiac muscle
• Skeletal muscle (striated)
• Smooth muscle

Skeletal Muscle

• Structure: Composed of thousands of cells called muscle fibers (elongated shape).
• Components: Muscle tissue includes surrounding connective tissues, blood vessels, and nerves.

Tendons vs. Ligaments

• Tendon: Connects muscle to bone.
• Ligament: Connects bone to bone.

Skeletal Muscle Movement

• Mechanism: The nervous system stimulates skeletal muscles to contract.
• Muscles can only pull bones, not push them.
• Muscle contraction requires ATP (energy).
• Antagonistic pairs: Muscles work in opposition (e.g., biceps and triceps).
• Immovable vs. Movable bone: When a muscle contracts, one end is connected to an immovable bone (anchor), while the other end is connected to a movable bone.

Skeletal Muscle Structure

• Muscle Fiber: A muscle cell.
• Myofibrils: Rod-like organelles of muscle cells that consist of different proteins and aid in contraction.
• Sarcolemma: Muscle fiber membrane.
• Nuclei: Muscle fibers are multinucleated; nuclei lie beneath the membrane.
• Mitochondria: Fibers contain many mitochondria (energy-producing organelles).

Why Muscle Fibers Contain Many Mitochondria

• Muscle cells need energy to do mechanical work and respond quickly.
• High number of mitochondria ensures sufficient energy supply.

Myofibrils & Sarcomeres

• Myofibrils contain contractile units called sarcomeres.
• Main proteins in sarcomeres: actin and myosin.
• Sarcomeres are the reason why striated (skeletal) muscle has a banded pattern.

Sarcomere Function

• Muscle tissue is able to shorten (contract) because each sarcomere gets shorter.
• The entire muscle gets shorter because sarcomeres are connected to each other.
• Muscle pulls on a tendon connected to a bone, causing movement.

Muscular System Diseases

Tendinitis

• Definition: Inflammation (or irritation) of the tendons.
• Causes: Overuse, bad posture, and sometimes infection.
• Risk factors: Age & engaging in some sports.
• Treatment: Rest, pain relievers & physical therapy.
• Severe cases may require surgery if a tendon ruptures.
• Symptoms: Pain and tenderness just outside a joint.
• Common locations: Shoulders, elbows, wrists, knees, and heels.
• Examples:
  • Tennis elbow (lateral epicondylitis): Pain on the outside of the elbow.
  • Golfer's elbow (medial epicondylitis): Pain on the inside of the elbow.
  • Pitcher's shoulder
  • Swimmer's shoulder
  • Jumper's knee

Muscular Dystrophy (MD)

• Definition: Weakness and loss of muscle mass.
• Nature: Group of genetic diseases that cause progressive weakness and loss of muscle mass.
• Causes: Genetic mutations that interfere with the production of proteins needed to form healthy muscle.
• Risk factors: Family history of MD, sex (males).
• Treatment: Exercise & mobility aids.
• Types: Many kinds; the most common is Duchenne Muscular Dystrophy (more prevalent in boys).
• Gower's Sign: Using hands to push on legs to stand.
• Duchenne Muscular Dystrophy progression: Weakness, especially of pelvic girdle muscles; marked lordosis; enlarged calves; severe crippling deformities and contractures.

Muscle Strains

• Definition: Tearing of the muscle fibers (part or all).
• Location: Can happen to the muscle or to the tendon.
• Causes: Injuries.
• Risk factors: Poor flexibility, improper warm-up, poor footwear, overexertion.
• Treatment: Rest, ice, pain relievers.
• Initial treatment: Rest, ice, compression, and elevation.
• Injuries range from overstretching to partial or complete tears.
• Common locations: Lower back and hamstrings.