Appendicular Skeleton: Structure, Function, and Key Joints

스터디 가이드 - 스마트 노트

자료에 맞춘 맞춤형 노트, 핵심 정의, 예시, 맥락을 확장해 제공합니다.

Appendicular Skeleton Overview

Divisions of the Skeletal System

The human skeleton is divided into two main parts: the axial skeleton and the appendicular skeleton. The appendicular skeleton consists of 126 bones and is primarily responsible for movement and manipulation of the environment.

Axial Skeleton: Composed of 80 bones, protects vital organs such as the brain, spinal cord, heart, and lungs.
Appendicular Skeleton: Includes bones of the upper and lower limbs, pectoral girdle, and pelvic girdle. It facilitates locomotion and manipulation.

Diagram of axial and appendicular skeleton

Components of the Appendicular Skeleton

Upper Limbs: Pectoral girdle, upper arm (humerus), forearm (radius and ulna), and hand (carpals, metacarpals, phalanges).
Lower Limbs: Pelvic girdle, upper leg (femur), lower leg (tibia and fibula), and foot (tarsals, metatarsals, phalanges).

Labeled diagram of appendicular skeleton

Pectoral (Shoulder) Girdle

Structure and Function

The pectoral girdle attaches the upper limbs to the axial skeleton and allows for extensive mobility. It consists of the clavicle and scapula, stabilized by muscles and ligaments.

Clavicle: S-shaped bone on the anterior side of the shoulder.
Scapula: Flat, triangular bone on the posterior side, attached to ribs by muscles and tendons.
Joints: Sternoclavicular, acromioclavicular, and glenohumeral joints provide mobility and stability.

Pectoral girdle and clavicle anatomy Scapula anatomy

Glenohumeral (Shoulder) Joint

The glenohumeral joint is a ball-and-socket joint with the largest range of motion in the body.

Articulation: Head of humerus fits into the shallow glenoid cavity of the scapula.
Glenoid Labrum: Fibrocartilage deepens the cavity for stability.
Support: Ligaments, muscles (especially rotator cuff), and bursae provide structural support and reduce friction.

Shoulder joint anatomy

Bones and Joints of the Upper Limb

Major Bones

Humerus: Long bone of the upper arm.
Radius: Located on the thumb side of the forearm.
Ulna: Located on the pinky side of the forearm.

Forearm bones and joints Humerus anatomy

Key Joints

Glenohumeral Joint: Allows wide range of motion.
Proximal Radioulnar Joint (Elbow): Allows forearm rotation.
Distal Radioulnar Joint (Wrist): Allows pronation and supination.
Interosseous Membrane: Maintains forearm integrity.

Elbow joint anatomy

Muscles of the Upper Limb

Muscles that move the arm cross the shoulder joint and are classified by their location and function.

Flexion: Biceps brachii, brachialis, brachioradialis.
Extension: Triceps brachii, anconeus.
Pronation: Pronator teres, pronator quadratus.
Supination: Supinator.

Muscles of the upper arm Muscles of the forearm Muscles of the wrist, hand, and fingers Intrinsic muscles of the hand

Bones and Joints of the Lower Limb

Pelvic (Hip) Girdle

The pelvic girdle provides a stable base for the lower limbs and supports the weight of the upper body.

Structure: Consists of the sacrum and two coxal bones (each fused from ilium, ischium, and pubis).
Acetabulum: Deep socket for the head of the femur, providing stability.
Function: Weight-bearing, transmits weight, supports pelvic organs.

Hip joint and acetabulum Pelvic girdle anatomy Hip bone anatomy

Bones of the Lower Limb

Femur: Longest and heaviest bone in the body.
Tibia: Larger, weight-bearing bone of the lower leg.
Fibula: Smaller, stabilizing bone of the lower leg.
Patella: Largest sesamoid bone, stabilizes knee joint.

Lower limb anatomy

Knee Joint

The knee joint is a hinge joint formed by the distal femur, patella, and proximal tibia.

Menisci: Medial and lateral fibrocartilage discs provide padding and stability.
Ligaments: Anterior and posterior cruciate ligaments, collateral ligaments, and transverse ligament stabilize the joint.

Knee joint anatomy Ligaments of the knee joint

Bones of the Foot

Tarsals: Includes talus (articulates with tibia and fibula) and calcaneus (heel bone).
Metatarsals: Form the framework of the foot.
Phalanges: Allow flexion and extension of toes.
Arches: Medial, lateral, and transverse arches distribute weight and provide leverage.

Bones of the foot

Ankle and Foot Joints

Talocrural (Ankle) Joint: Uniaxial hinge joint between talus and distal tibia/fibula, allows dorsiflexion and plantar flexion.
Subtalar Joint: Between talus and calcaneus, allows inversion and eversion.
Ligaments: Provide stability and prevent abnormal movements.
Intrinsic Muscles: Support arches and move toes.

Ankle and foot ligaments Intrinsic muscles of the feet

Ossification of Appendicular Bones

Bone Development

Most girdle and limb bones develop by endochondral ossification, except the clavicle.

Endochondral Ossification: Process where cartilage is replaced by bone tissue.
Clavicle: Develops by intramembranous ossification.

Summary Table: Major Bones of the Appendicular Skeleton

Region	Main Bones	Key Joints
Upper Limb	Clavicle, Scapula, Humerus, Radius, Ulna, Carpals, Metacarpals, Phalanges	Shoulder (glenohumeral), Elbow, Wrist
Lower Limb	Pelvic girdle, Femur, Tibia, Fibula, Patella, Tarsals, Metatarsals, Phalanges	Hip, Knee, Ankle

Additional info:

Lower limb bones are larger and stronger than upper limb bones due to their weight-bearing function.
Both the shoulder and hip joints are multiaxial ball-and-socket joints, but the hip joint is deeper and more stable.
Muscles of the lower limb are larger and more powerful to support movement and posture.