Skeletal System Lecture Notes PDF

Lec. 2 The Skeletal System By: Dr. Farah Talib The skeletal system consists of the bony skeleton and the related skeletal muscles. The functions of the skeletal system are support, protection and motion of different parts of the body. The bony skeleton can be subdivided into: 1. The axi...

Lec. 2 The Skeletal System By: Dr. Farah Talib The skeletal system consists of the bony skeleton and the related skeletal muscles. The functions of the skeletal system are support, protection and motion of different parts of the body. The bony skeleton can be subdivided into: 1. The axial skeleton that includes the skull and the vertebral column, within the cavities of these bony structures lie the parts of the central nervous system (the brain within the cranium and the spinal cord within the vertebral column). The skull is composed of membranous bony parts; frontal bone, parietal bone, temporal bone, occipital bone, the maxilla and the zygomatic bone. Theses bones are tightly joined to each other by suture lines. The brain is contained within the cranial cavity, so that the two cerebral hemispheres can be subdivided into lobes according to the overlying bony parts.  The base of the skull contains foramina and apertures from which the cranial nerves and veins emerge, and arteries perforate to supply different parts of the intracranial structures. The largest foramen in the base of skull is the foramen magnum, through which the spinal cord emerges in continuation with the medulla oblongata. The orbital cavities within the skull are two in number that lodge the eye globe and the attached periocular muscles. The optic nerve enters the cranium through the superior orbital fissure. The nasal cavity is located in the central and anterior portion of the skull opening posteriorly to the pharynx, while the paranasal sinuses are blind cavities located within the maxilla, frontal bones, ethmoid bones and sphenoid parts of the temporal bone.  The base of skull articulates with the C1 (atlas) vertebra by two articular faucets known as the occipital condyles, the underlying C2 (axis) vertebra articulates with C1 in a fashion permitting rotatory movement of the skull. Cervical vertebra are 7 in number, thoracic vertebra are 12, the lateral spines articulate with corresponding ribs on both sides, lumbar vertebra are five, sacral vertebra are five fused vertebra, articulating downwards with four fused coccygeal vertebra. Vertebra are stacked over each other separated by the intervertebral discs and articulate with each other by articular faucets leaving a space between the vertebral body and vertebral pedicles that forms the vertebral canal lodging the spinal cord along its length. The spinal cord gives rise to spinal nerves emerging from the intervertebral space, forming two roots; motor anterior root and sensory posterior root. 2. The appendicular skeleton that comprises the hip and the shoulder joints (girdles), with the attached bony structures of the upper and the lower limbs. The shoulder girdle is composed of the scapula to which articulates the humerus and the clavicle at the lateral portions. The clavicle articulates medially with the manubrium sternii. The bone of the arm is the humerus and the forearm is formed by two bones; the medial ulna articulating with the humerus forming the elbow joint, and the lateral radius. Both bones participate in forming the wrist joint together with the small bones of the wrist (scaphoid, lunate, triquetrum, pisiform, trapezium, trapezoid, capitate and hamate), that in turn articulate distally with the five metacarpal bones of the hand.  The pelvis is composed of three bones united to each other; ileum, acetabulum and pubis. The bony pelvis protects the internal visceral organs and gives rise to the hip joint through the acetabulum to which the femoral head articulates. The long femur is the only bone of the thigh, the distal dilated condyles give rise to the articular surfaces to which the tibia of the leg is articulated, while the fibula articulates only to the tibia, and both bones dilate distally to form the articular condyles of the ankle joint. The talus and calcaneus are the two bones forming the ankle joint, articulating on the other side with the small bones of the foot (navicular, cuboid and three cuneiform bones), that in turn give rise to the metatarsal bones. 3. The visceral skeleton that includes the lower jaw and parts of the upper jaw, the hyoid bone, the ribs and sternum. The latter two together form the thoracic cage. Within the thoracic cage lie the lungs, the heart and the great vessels and the other anatomical structures of the mediastinum, protecting these structures from injury.. The ribs articulate with the vertebra posteriorly and with the costal cartilages anteriorly that in turn articulate with the sternum. This pattern provides resilience to the contractile movement of the anatomical structures lying within the thoracic cage during respiration and contraction of the heart.