Human Skeletal System: Joints, Skull Foramina, and Thorax

Human Skeletal System: Key Structures and Functions

Types of Synovial Joints

• Plane Joints

  Characterized by flat surfaces on one bone meeting with flat surfaces of another, allowing for slipping and gliding movement with no axial rotation. Common examples include the carpal bones of the wrist.

• Hinge Joints

  A cylindrical projection of one bone fits into a trough-shaped surface of another bone. These joints permit flexion and extension, like the elbow joint (specifically, the olecranon process of the ulna).

• Pivot Joints

  A rounded projection of one bone fits into a rounded depression or sleeve of another bone, often held together by ligaments. They allow for uniaxial movement, such as the rotation of the odontoid process of C2 (axis) within the anterior arch of the atlas (C1). Another example is the proximal radioulnar joint, enabling pronation and supination of the ulna and radius.

• Condyloid Joints

  An oval-shaped projection fits into an oval-shaped depression of another bone. These joints allow for biaxial movement (flexion/extension and abduction/adduction). Examples include the radiocarpal joints (wrist) and metacarpophalangeal joints (e.g., the 2nd metacarpal articulating with the proximal phalanx), allowing flexion and extension.

• Saddle Joints

  Both articulating bones have concave and convex surfaces, resembling a saddle. This unique shape allows for biaxial movement with a greater range of motion than condyloid joints. The prime example is the carpometacarpal joint of the thumb.

• Ball and Socket Joints

  A spherical head of one bone articulates with a cup-like depression of another bone. These are multiaxial joints, offering the greatest range of motion (flexion/extension, abduction/adduction, rotation). Examples include the coxal (hip) and glenohumeral (shoulder) joints.

Cranial Anatomy and Features

Zygomatic Arch Formation

The zygomatic arch is formed by the zygomatic process of the temporal bone and the temporal process of the zygomatic bone.

Major Cranial Sutures

• Coronal Suture: Separates the frontal and parietal bones.
• Sagittal Suture: The location where the two parietal bones conjoin.
• Lambdoid Suture: The location where the occipital and parietal bones conjoin.
• Squamous Suture: A suture on the lateral side of the head (each side), separating the temporal and parietal bones.

Key Foramina of the Skull

• Foramen Rotundum: Transmits the Trigeminal nerve (V2: maxillary division).
• Foramen Lacerum: No significant structures pass directly through it; it is largely filled with cartilage.
• Foramen Ovale: Transmits the Trigeminal nerve (V3: mandibular division).
• Foramen Spinosum: Transmits the Middle Meningeal Artery.
• Hypoglossal Canal: Transmits the Hypoglossal nerve (XII).
• Optic Canal: Transmits the Optic nerve (II).
• Internal Acoustic Meatus: Transmits the Facial nerve (VII) and the Vestibulocochlear nerve (VIII).

Other Important Bone Processes

• Palatine Bone: Sphenoidal process.
• Temporal Bone: Mastoid process.
• Ethmoid Bone: Uncinate process.

Bones Forming the Ocular Orbits

The ocular orbits (eye sockets) are formed by seven bones: frontal, sphenoid, zygomatic, maxilla, palatine, lacrimal, and ethmoid.

Osseous Hard Palate and Paranasal Sinuses

• Osseous Hard Palate Formation

  Formed by the palatine process of the maxilla and the horizontal plate of the palatine bone.

• Paranasal Sinuses and Locations

  These air-filled cavities lighten the skull and resonate sound. They include:

  • Frontal Sinuses: Located in the forehead.
  • Maxillary Sinuses: Located in the cheeks; pressure in these sinuses can cause pain.
  • Ethmoid Sinuses: Located between the eyes.
  • Sphenoid Sinuses: Located in the center of the skull; cannot be palpated externally.

Vertebral Column and Thoracic Cage

Curvatures of the Vertebral Column

The human vertebral column exhibits natural curvatures:

• Cervical Curvature: 7 vertebrae, located in the neck.
• Thoracic Curvature: 12 vertebrae, located in the upper back.
• Lumbar Curvature: 5 vertebrae, located in the lower back.
• Sacrum: A large, fused bone composed of 5 segments.
• Coccyx: The tailbone, typically composed of 3-5 fused segments.

Composition and Function of the Thoracic Cage

The thoracic cage is comprised of the thoracic vertebrae, ribs, and sternum. Its primary functions include:

• Providing protection for vital organs such as the lungs, heart, and major blood vessels.
• Offering attachment points for muscles of the back, chest, and upper limbs.
• Facilitating the mechanics of breathing.

Ribs 1-10 articulate anteriorly with the sternum (directly or indirectly via costal cartilage). There are also 2 floating ribs (ribs 11 and 12) that do not articulate with the sternum anteriorly.

Scapula and Clavicle Connection

The scapula (shoulder blade) and clavicle (collarbone) connect at the acromial end of the clavicle and the acromion process of the scapula, forming the acromioclavicular joint.