CH8 – Joints

Structural Types of Joints

Joints, also known as articulations, are connections between bones that allow for movement and provide mechanical support. They are classified based on their structure and the type of tissue that connects the bones.

• Fibrous Joints: Bones are joined by dense connective tissue; little to no movement. Examples: Sutures (skull), syndesmoses (between radius and ulna), gomphoses (teeth in sockets).

• Cartilaginous Joints: Bones are joined by cartilage; allow more movement than fibrous joints but less than synovial joints. Examples: Synchondroses (epiphyseal plates), symphyses (pubic symphysis).

• Synovial Joints: Bones are separated by a fluid-filled joint cavity; highly movable. Examples: Shoulder, knee, hip joints.

Joint Classifications by Function

Joints are also classified by the amount of movement they allow:

• Synarthroses: Immovable joints (e.g., sutures of the skull).

• Amphiarthroses: Slightly movable joints (e.g., symphysis pubis).

• Diarthroses: Freely movable joints (all synovial joints).

Types of Synovial Joints

Synovial joints are further classified by the shapes of their articulating surfaces and the movements they allow:

• Multiaxial: Movement in multiple axes (e.g., ball-and-socket joints like the shoulder).

• Nonaxial: Gliding movements only (e.g., intercarpal joints).

• Uniaxial: Movement in one axis (e.g., hinge joints like the elbow).

• Biaxial: Movement in two axes (e.g., saddle joints like the thumb).

Common Joint Types

• Synchondroses: Cartilaginous joints where bones are united by hyaline cartilage.

• Suture: Immovable fibrous joints found only in the skull.

• Gomphosis: Peg-in-socket fibrous joint (e.g., teeth in alveolar sockets).

• Syndesmosis: Fibrous joint with bones connected by a ligament (e.g., distal tibiofibular joint).

• Symphysis: Cartilaginous joint where bones are united by fibrocartilage (e.g., intervertebral discs).

Common Movements at Joints

Joints allow for a variety of movements, which are essential for daily activities and locomotion:

• Abduction: Movement away from the midline of the body.

• Adduction: Movement toward the midline of the body.

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

• Flexion: Decreasing the angle between two bones.

• Extension: Increasing the angle between two bones.

CH7 – The Skeleton: Appendicular Skeleton

Axial & Appendicular Skeleton

The human skeleton is divided into two main parts: the axial skeleton (central core) and the appendicular skeleton (limbs and girdles). Understanding the differences and being able to classify bones is essential for anatomy studies.

• Axial Skeleton: Includes the skull, vertebral column, and thoracic cage.

• Appendicular Skeleton: Includes the pectoral girdle, pelvic girdle, and limbs.

Example: The femur is part of the appendicular skeleton, while the sternum is part of the axial skeleton.

Bone Identification and Features

Students should be able to identify bones and their features on diagrams and real bones, regardless of orientation. Key bones and features include:

• Scapula: Shoulder blade; features include the spine, acromion, and glenoid cavity.

• Clavicle: Collarbone; features include the sternal and acromial ends.

• Humerus: Upper arm bone; features include the head, greater tubercle, and medial/lateral epicondyles.

• Radius: Lateral bone of the forearm; features include the head, neck, and styloid process.

• Ulna: Medial bone of the forearm; features include the olecranon, coronoid process, and styloid process.

• Carpals: Wrist bones; eight small bones arranged in two rows.

• Metacarpals: Bones of the palm; numbered I-V from thumb to little finger.

• Phalanges: Finger bones; each finger has three (proximal, middle, distal) except the thumb (two).

• Pelvis: Hip bones; features include the ilium, ischium, and pubis.

• Femur: Thigh bone; features include the head, neck, greater/lesser trochanters, and condyles.

• Patella: Kneecap; a sesamoid bone in the quadriceps tendon.

• Tibia: Medial bone of the lower leg; features include the medial/lateral condyles and tibial tuberosity.

• Fibula: Lateral bone of the lower leg; features include the head and lateral malleolus.

• Tarsals: Ankle bones; seven bones including the talus and calcaneus.

• Metatarsals: Foot bones; numbered I-V from big toe to little toe.

• Phalanges (foot): Toe bones; similar arrangement to fingers.

• Feet: Ability to identify bones and features in various orientations.

Example: On a diagram, the humerus can be identified by its rounded head and the presence of the greater and lesser tubercles.

Orientation and Positioning

It is important to be able to identify bones and their features regardless of whether the bone is shown from the left or right side, or in different orientations. This skill is essential for practical exams and clinical applications.

• Practice identifying bones and features on both diagrams and real bones.

• Be familiar with anatomical terms of direction: medial, lateral, proximal, distal, anterior, posterior.

Example: The radius is lateral to the ulna in the anatomical position.