Comprehensive Study Guide: Skeletal and Muscular Systems in Anatomy & Physiology

• Skeletal System

Bone Shapes and Examples

The human skeleton is composed of bones with various shapes, each adapted for specific functions.

• Long bones: e.g., femur, humerus. Designed for support and movement.

• Short bones: e.g., carpals, tarsals. Provide stability and support with limited movement.

• Flat bones: e.g., sternum, skull. Protect internal organs and provide surfaces for muscle attachment.

• Irregular bones: e.g., vertebrae, pelvis. Complex shapes for specialized functions.

• Sesamoid bones: e.g., patella. Embedded in tendons, reduce friction.

Structure of Bone

Bones have a complex structure that supports their function in the body.

• Diaphysis: Shaft of a long bone, composed mainly of compact bone.

• Medullary cavity: Central cavity containing yellow bone marrow (fat storage).

• Epiphysis: Ends of long bones, contain spongy bone and red marrow.

• Articular cartilage: Hyaline cartilage covering joint surfaces, reduces friction.

• Periosteum: Dense connective tissue covering bone, contains nerves and blood vessels.

• Endosteum: Membrane lining the medullary cavity.

Bone Marrow

Bone marrow is a soft tissue found in the cavities of bones.

• Red bone marrow: Site of hematopoiesis (blood cell formation), found in flat bones and epiphyses of long bones.

• Yellow bone marrow: Stores fat, found in the medullary cavity of long bones.

Composition of Bone

Bones are composed of organic and inorganic materials that provide strength and flexibility.

• Organic matrix: Mainly collagen fibers, provide tensile strength.

• Inorganic salts: Primarily calcium phosphate (hydroxyapatite), provide hardness.

• Calcium phosphate equation:

$Ca_3(PO_4)_2$

• Bone cells: Osteoblasts (build bone), osteocytes (maintain bone), osteoclasts (break down bone).

Microscopic Anatomy of Bone

Bones have a unique microscopic structure that supports their function.

• Compact bone: Organized into osteons (Haversian systems) with central canals, lamellae, and canaliculi.

• Spongy bone: Contains trabeculae, spaces filled with marrow.

Bone Formation (Ossification)

Bone develops through two main processes: intramembranous and endochondral ossification.

• Intramembranous ossification: Bone forms directly from mesenchymal tissue (e.g., flat bones of the skull).

• Endochondral ossification: Bone forms from a cartilage template (e.g., long bones).

• Epiphyseal plate: Growth plate where lengthening occurs during development.

Bone Remodeling and Growth

Bones are constantly remodeled in response to stress and hormonal signals.

• Osteoblasts: Build new bone.

• Osteoclasts: Break down bone tissue.

• Hormonal regulation: Parathyroid hormone (PTH) increases blood calcium by stimulating osteoclasts; calcitonin lowers blood calcium by inhibiting osteoclasts.

Fractures and Bone Healing

Fractures are breaks in bone that heal through a multi-step process.

• Types of fractures: Simple, compound, comminuted, greenstick, spiral, etc.

• Healing steps: Hematoma formation, fibrocartilaginous callus formation, bony callus formation, bone remodeling.

Osteoporosis

Osteoporosis is a condition characterized by decreased bone density and increased fracture risk.

• Causes: Aging, hormonal changes, lack of calcium/vitamin D, sedentary lifestyle.

• Diagnosis: Bone density measurement (DEXA scan).

• Treatment: Medications, calcium/vitamin D supplementation, weight-bearing exercise.

Table: Comparison of Bone Cells

Cell Type	Function	Location
Osteoblast	Bone formation	Bone surface
Osteocyte	Maintains bone tissue	Within bone matrix
Osteoclast	Bone resorption	Bone surface

Joints and Articulations

Classification of Joints

Joints are classified by structure and function.

• Fibrous joints: Bones joined by dense connective tissue; little or no movement (e.g., sutures in skull).

• Cartilaginous joints: Bones joined by cartilage; limited movement (e.g., intervertebral discs).

• Synovial joints: Freely movable joints with a synovial cavity (e.g., shoulder, knee).

Types of Synovial Joints and Movements

Synovial joints allow various types of movement.

• Nonaxial (gliding): e.g., intercarpal joints.

• Uniaxial: e.g., hinge (elbow), pivot (atlas-axis).

• Biaxial: e.g., saddle (thumb), condyloid (wrist).

• Multiaxial: e.g., ball-and-socket (shoulder, hip).

Joint Structure and Function

• Articular cartilage: Covers bone ends, reduces friction.

• Synovial fluid: Lubricates joint.

• Ligaments: Connect bone to bone, stabilize joints.

• Tendons: Connect muscle to bone.

Table: Types of Synovial Joints

Joint Type	Example	Movement
Hinge	Elbow	Flexion/Extension
Ball-and-socket	Shoulder	Multiaxial
Pivot	Atlas-axis	Rotation
Saddle	Thumb	Flexion/Extension, Abduction/Adduction

Muscular System

Types of Muscle Tissue

Muscle tissue is classified into three types, each with distinct structure and function.

• Skeletal muscle: Voluntary, striated, attached to bones for movement.

• Cardiac muscle: Involuntary, striated, found in the heart.

• Smooth muscle: Involuntary, non-striated, found in walls of hollow organs.

Muscle Anatomy

Skeletal muscle is organized into bundles of fibers surrounded by connective tissue.

• Muscle fiber: Single muscle cell.

• Fascicle: Bundle of muscle fibers.

• Endomysium: Surrounds individual fibers.

• Perimysium: Surrounds fascicles.

• Epimysium: Surrounds entire muscle.

Muscle Contraction

Muscle contraction occurs through the sliding filament mechanism.

• Sarcomere: Functional unit of muscle contraction, composed of actin and myosin filaments.

• Sliding filament theory: Myosin heads bind to actin, pulling filaments past each other to shorten the sarcomere.

• ATP: Provides energy for contraction.

$ATP \rightarrow ADP + P_i + \text{energy}$

Neuromuscular Junction

The neuromuscular junction is the site where a motor neuron stimulates a muscle fiber.

• Motor end plate: Region of muscle fiber membrane with receptors for neurotransmitter acetylcholine (ACh).

• Synaptic cleft: Gap between neuron and muscle fiber.

• Action potential: Electrical signal that triggers muscle contraction.

Muscle Metabolism

Muscles generate energy through aerobic and anaerobic pathways.

• Aerobic metabolism: Uses oxygen, produces ATP, CO2, and water.

• Anaerobic metabolism: No oxygen, produces ATP and lactic acid.

• Creatine phosphate (CP): Rapid source of ATP.

Muscle Fatigue and Soreness

Muscle fatigue and soreness result from intense or prolonged activity.

• Fatigue: Decreased ability to contract due to depletion of ATP, accumulation of lactic acid.

• Delayed Onset Muscle Soreness (DOMS): Soreness peaking 24-72 hours after exercise, caused by microtrauma to muscle fibers.

• Muscular atrophy: Decrease in muscle mass due to inactivity or disease.

• Fibromyalgia: Chronic pain disorder affecting muscles and soft tissues.

• Torn muscle: Muscle fibers are damaged, leading to pain and loss of function.

Table: Types of Muscle Contraction

Type	Description	Example
Isotonic	Muscle changes length	Lifting a weight
Isometric	Muscle length remains the same	Holding a plank

Additional info:

• Hormones such as growth hormone, estrogen, testosterone, and thyroid hormone play roles in bone and muscle development.

• Bone density is measured using DEXA scans to diagnose osteoporosis.

• Muscle soreness (DOMS) is not caused by lactic acid but by microscopic damage to muscle fibers.