Bones of the Head, Trunk, and Upper Extremities: A Comprehensive Overview
Bones of the Head and Trunk
The human head comprises 22 bones: 8 cranial and 14 facial. These bones enclose and protect the brain.
Cranial Bones
- Frontal
- Parietal (2)
- Temporal (2)
- Occipital
- Ethmoid
- Sphenoid
Facial Bones
- Nasal (2)
- Maxillary (2)
- Zygomatic (2)
- Lacrimal (2)
- Palatine (2)
- Inferior Nasal Conchae (2)
- Vomer
- Mandible
2 Hyoid Bone
The hyoid bone is unique in that it doesn’t articulate with any other bone. Suspended by ligaments and muscles between the mandible and larynx, it supports the tongue and provides attachment points for various muscles.
The Spine
The spine, composed of vertebrae, allows for forward, backward, and sideways rotation. It houses the spinal cord, supports the head, connects with the ribs, and provides attachment points for back muscles. Intervertebral foramina between vertebrae allow passage of nerves. Spinal discs facilitate movement and absorb shock.
Vertebral Composition
A typical vertebra consists of a body and a vertebral arch, which includes pedicles, articular processes, transverse processes, and a spinous process.
4 Cervical Vertebrae
There are seven cervical vertebrae.
- Atlas (C1): Supports the head, lacks a body, articulates with the occipital bone and axis, and has large transverse processes and a vertebral foramen.
- Axis (C2): Features a dens projecting into the atlas’s vertebral foramen, enabling head rotation.
- Typical Cervical Vertebrae (C3-C6): Small bodies, large vertebral arches, bifid spinous processes, and three foramina (vertebral and two transverse).
- Prominent Vertebra (C7): The seventh cervical vertebra, distinguished by its prominent spinous process.
5 Thoracic Vertebrae
Twelve thoracic vertebrae, larger and stronger than cervical vertebrae, possess long, downward-pointing spinous processes. They articulate with the ribs and have limited movement.
6 Lumbar Vertebrae
The five lumbar vertebrae are the largest and strongest in the spine. They have short, thick processes, laterally directed articular processes, and square-shaped spinous processes.
7 The Sacrum
The sacrum forms the pelvic portion of the spine, acting as the base for the pelvic girdle. It sits between the two coxal bones and contains the sacral canal, a continuation of the vertebral canal.
8 Coccyx
The coccyx is formed by the fusion of four atrophied vertebrae. The first coccygeal vertebra articulates with the sacrum.
9 Spinal Curvature
The spine, measuring 73-75 cm in men and 60-65 cm in women, shortens with age due to disc compression. It has two types of curves:
- Anteroposterior Curves: Convex, concave, convex, and concave.
- Lateral Curves: Typically imperceptible. Scoliosis can cause noticeable lateral curvature.
The Shoulder
The shoulder connects the upper extremities to the trunk. It is formed by the clavicle and scapula.
1 Clavicle
The clavicle, articulating with the sternum and acromion, is S-shaped with a fragile area at the curve. The medial end forms the sternoclavicular joint, while the lateral end forms the acromioclavicular joint.
2 Scapula
Located between the 2nd and 7th ribs, the scapula has two surfaces:
- Anterior: Contains the subscapular fossa.
- Posterior: Features the spine, which projects laterally to form the acromion. The supraspinatus and infraspinatus fossae are also present. The glenoid cavity articulates with the humerus. The coracoid process provides attachment for the biceps brachii.
Humerus
The humerus is a long bone with a shaft (diaphysis) and two ends (epiphyses). The proximal end features the head, anatomical neck, greater and lesser tubercles, and surgical neck. The distal end includes the trochlea, capitulum, olecranon fossa, and coronoid fossa.
Radius
Located on the lateral side of the forearm, the radius has a triangular shaft. The proximal end includes the head, neck, and radial tuberosity. The distal end articulates with the carpal bones and features the styloid process and ulnar notch.
Ulna
Located medially in the forearm, the ulna’s proximal end features the olecranon, coronoid process, and trochlear notch. The distal end includes the head and styloid process.
Bones of the Hand
1 Carpal Bones
Eight carpal bones form the wrist: scaphoid, lunate, triquetrum, pisiform, trapezium, trapezoid, capitate, and hamate.
2 Metacarpal Bones
Five metacarpal bones form the palm, articulating with the carpals and phalanges.
3 Phalanges
Each finger has three phalanges (proximal, middle, and distal), except the thumb, which has two.