Appendicular Skeleton, Articulations, and Body Movements

The Appendicular Skeleton

Overview of the Appendicular Skeleton

The appendicular skeleton consists of the bones that form the limbs and the girdles that attach them to the axial skeleton. It is essential for movement and manipulation of the environment.

• Pectoral girdle: Attaches the upper limbs to the axial skeleton.

• Pelvic girdle: Attaches the lower limbs to the axial skeleton and supports body weight.

• Upper and lower limbs: Include bones of the arms, forearms, hands, thighs, legs, and feet.

The Pectoral Girdle

Structure and Function

The pectoral girdle is a paired structure composed of the clavicle and scapula. It provides attachment points for muscles and allows for a wide range of motion in the upper limbs.

• Clavicle (collarbone): Anterior bone that articulates with the sternum and scapula.

• Scapula (shoulder blade): Posterior bone that provides attachment for arm and chest muscles.

• Function: Attaches upper limbs to the axial skeleton and allows for flexibility and mobility.

The Upper Limb

Bones of the Upper Limb

The upper limb is specialized for mobility and manipulation. It consists of the arm, forearm, and hand.

• Arm (brachium): Contains the humerus.

• Forearm (antebrachium): Contains the radius and ulna.

• Hand (manus): Includes the carpus (wrist), metacarpals (palm), and phalanges (fingers).

• Each finger has three phalanges except the thumb, which has two.

The Pelvic Girdle

Structure and Function

The pelvic girdle, also known as the hip girdle, is formed by two coxal bones, the sacrum, and the coccyx. It is larger and more robust than the pectoral girdle, reflecting its role in weight bearing and locomotion.

• Coxal bones (ossa coxae): Each formed by the fusion of the ilium, ischium, and pubis.

• Sacrum and coccyx: Complete the pelvic ring.

• Function: Attaches lower limbs to the axial skeleton and supports the weight of the upper body.

Comparing Male and Female Pelves

The male and female pelves differ in structure to accommodate childbirth in females. The female pelvis is broader, lighter, and has a wider pelvic arch.

• Male pelvis: Narrower, heavier, and with a smaller pelvic arch (90° or less).

• Female pelvis: Wider, lighter, and with a larger pelvic arch (100° or more).

The Lower Limb

Bones of the Lower Limb

The lower limb is adapted for weight bearing and locomotion. It consists of the thigh, leg, and foot.

• Thigh: Contains the femur, the heaviest and strongest bone in the body.

• Leg: Contains the tibia (shinbone) and fibula.

• Patella: The kneecap, protects the knee joint.

• Foot: Includes tarsals, metatarsals, and phalanges. Each toe has three phalanges except the great toe, which has two.

• Body weight is concentrated on the calcaneus (heel bone) and talus.

Arches of the Foot

The foot has three main arches that help distribute body weight and provide leverage during walking.

• Medial longitudinal arch

• Lateral longitudinal arch

• Transverse arch

• Function: Redistribute weight between the heel and metatarsals, providing shock absorption and flexibility.

Articulations and Body Movements

Functions of Joints

Joints, or articulations, connect bones and allow for movement and flexibility in the skeletal system.

• Hold bones together

• Permit movement

Classification of Joints

Joints are classified by their function (degree of movement) and structure (type of tissue connecting bones).

• Functional classification (based on movement):

  • Synarthroses: Immovable (mostly axial skeleton)

  • Amphiarthroses: Slightly movable (mostly axial skeleton)

  • Diarthroses: Freely movable (limbs)

• Structural classification (based on material and presence of joint cavity):

  • Fibrous: Bones joined by fibrous tissue; mostly synarthrotic (e.g., sutures, syndesmoses)

  • Cartilaginous: Bones joined by cartilage; mostly amphiarthrotic (e.g., symphyses, synchondroses)

  • Synovial: Bones separated by a fluid-filled cavity; all are diarthrotic

Types of Synovial Joints and Movements

Synovial joints allow for a wide range of movements, including flexion, extension, abduction, adduction, rotation, and circumduction.

• Flexion: Decreases the angle between bones

• Extension: Increases the angle between bones

• Abduction: Movement away from the midline

• Adduction: Movement toward the midline

• Rotation: Movement around a longitudinal axis

• Circumduction: Circular movement combining flexion, extension, abduction, and adduction

Additional info: Synovial joints are further classified by shape (e.g., hinge, ball-and-socket, pivot) and allow for the greatest range of motion in the body.