Anatomy & Physiology Study Guide: The Skeletal and Muscular Systems (Chapters 5 & 6)

The Skeletal System

Overview and Functions of the Skeletal System

The skeletal system provides the structural framework for the human body, protects vital organs, and facilitates movement. It is composed of bones, cartilage, ligaments, and joints.

• Types of Bones: Bones are classified by shape: long, short, flat, and irregular.

• Functions: Support, protection, movement, mineral storage (especially calcium and phosphorus), and blood cell formation (hematopoiesis).

• Major Divisions: The skeleton is divided into the axial skeleton (skull, vertebral column, rib cage) and the appendicular skeleton (limbs and girdles).

• Joints: Articulations between bones that allow for movement and flexibility.

Example: The femur is a long bone that supports body weight and enables leg movement.

Bone Structure and Growth

Bones are dynamic organs that grow and remodel throughout life. They consist of compact and spongy bone tissue.

• Compact Bone: Dense and strong, forms the outer layer of bones.

• Spongy Bone: Porous and lightweight, found at the ends of long bones and inside flat bones.

• Bone Marrow: Red marrow produces blood cells; yellow marrow stores fat.

• Ossification: The process of bone formation from cartilage or fibrous membranes.

Example: During childhood, long bones lengthen at the epiphyseal (growth) plates.

Major Bones and Landmarks

Understanding the location and function of major bones is essential for identifying body regions and movements.

• Skull: Protects the brain and forms the structure of the face.

• Vertebral Column: Supports the body and protects the spinal cord.

• Rib Cage: Protects the heart and lungs.

• Upper Limb Bones: Humerus, radius, ulna, carpals, metacarpals, phalanges.

• Lower Limb Bones: Femur, tibia, fibula, tarsals, metatarsals, phalanges.

• Girdles: Pectoral (shoulder) and pelvic girdles attach limbs to the axial skeleton.

Example: The scapula (shoulder blade) is part of the pectoral girdle.

Joints and Movements

Joints are classified by their structure and the type of movement they allow.

• Fibrous Joints: Immovable (e.g., sutures of the skull).

• Cartilaginous Joints: Slightly movable (e.g., intervertebral discs).

• Synovial Joints: Freely movable (e.g., knee, shoulder).

Example: The elbow is a hinge joint allowing flexion and extension.

The Muscular System

Overview and Functions of Muscles

The muscular system enables movement, maintains posture, and produces heat. Muscles are classified as skeletal, cardiac, or smooth.

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

• Cardiac Muscle: Involuntary, striated, found only in the heart.

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

Example: The biceps brachii is a skeletal muscle responsible for flexing the forearm.

Muscle Structure and Contraction

Muscle fibers contract in response to nerve impulses, using energy from ATP.

• Muscle Fiber Anatomy: Each muscle fiber contains myofibrils made of actin and myosin filaments.

• Sliding Filament Theory: Muscle contraction occurs when myosin heads pull actin filaments inward.

• ATP: Provides the energy required for muscle contraction.

Equation:

$\text{ATP} \rightarrow \text{ADP} + \text{P}_i + \text{energy}$

Example: During exercise, muscles use stored ATP and generate more through cellular respiration.

Muscle Actions and Interactions

Muscles work in groups to produce coordinated movements. They are classified by their roles in movement.

• Prime Mover (Agonist): Main muscle responsible for a movement.

• Antagonist: Opposes the action of the prime mover.

• Synergist: Assists the prime mover.

• Fixator: Stabilizes the origin of the prime mover.

Example: In elbow flexion, the biceps brachii is the prime mover, and the triceps brachii is the antagonist.

Major Skeletal Muscles and Their Functions

Identifying major muscles and their actions is essential for understanding body movements.

• Facial Muscles: Control expressions and movements of the face.

• Neck Muscles: Support the head and enable movement.

• Trunk Muscles: Maintain posture and protect internal organs.

• Upper Limb Muscles: Enable movement of the arms and hands.

• Lower Limb Muscles: Enable movement of the legs and feet.

Example: The quadriceps femoris group extends the knee.

Muscle Terminology

Understanding muscle terminology helps in identifying muscle actions and locations.

Term	Meaning
ab-	away from
ad-	toward
hyper-	over, above
inter-	between
iso-	same, equal
tetra-	four
sy- / syn-	together
myo-	muscle

Example: The term abductor refers to a muscle that moves a limb away from the midline.

Additional info:

• Muscle contraction is regulated by calcium ions and the nervous system.

• Muscle fatigue occurs when ATP reserves are depleted and lactic acid accumulates.