The Skeletal System
MaKayla K. Friend
Daytona College, Ormond Beach
The skeletal system includes the skull, vertebral column, thoracic cage, pectoral and pelvic girdle, and the upper and lower limbs. The skeletal system is made up of two different regions, the axial skeleton and the appendicular skeleton (see Figure 1, Appendix A) The average baby is born with 270 bones which fuse together as they age and decrease to about 206 bones by late teens, early twenties. The skeletal system provides support, protection, production, storage
CITATION Sal15 l 1033 (Saladin, 2015).
The most complex part of the skeleton is the skull. The average skull consists of 22 bones which are connected by sutures; eight cranial bones and 14 facial bones. Cranial bones enclose the brain and compose the cranium, a rigid structure with a foramen magnum that allows the spinal cord to come in contact with the brain. The cranial bones include one frontal, two parietal, two temporal, one occipital, one sphenoid, and one ethmoid (see Figure 2, Appendix A) CITATION Sal15 l 1033 (Saladin, 2015).
The frontal bone is the bone that forms the forehead and is anterior to the calvaria (skullcap). It covers about one third of the roof of the cranial cavity, forms the anterior wall and contains the frontal sinus. The supraorbital margin is a ridge that is deep to the eyebrows and contains a supraorbital foramen which provides a passageway for veins, nerve and arteries CITATION Sal15 l 1033 (Saladin, 2015).
The parietal bone is posterior to the frontal bone and paired, left and right, which form most of the cranial roof and sides of the cranium. It is bordered by four sutures: coronal, lambdoid, sagittal, and squamous (see Figure 3, Appendix A) CITATION Sal15 l 1033 (Saladin, 2015).
The temporal bone makes up the lateral wall and portions of the floor of the cranial cavity. The temporal bone is paired and has an intricate shape that can be described by separating into four parts: the squamous part, tympanic part, mastoid part, and petrous part (see Figure 3, Appendix A) CITATION Sal15 l 1033 (Saladin, 2015).
The squamous part contains two parts: the zygomatic process, which forms the cheek bone, and the mandibular fossa, which is where the mandibular and the cranium articulate.
The tympanic part borders the opening of the ear canal. The styloid process, describe as a “pointed spine”, is on the inferior surface and runs attachment for the muscles of the hyoid bone, pharynx, and the tongue CITATION Sal15 l 1033 (Saladin, 2015).
The mastoid part comprises the mastoid process, the lump you feel behind the ear, which is complete with minor air sinuses. The mastoid notch is a groove that is medial to the mastoid process and is the basis of the digastric muscle, which opens the mouth.
The petrous part is on the cranial floor and separates the cranial fossa from the posterior fossa. On its posteromedial surface there is an opening called the internal acoustic meatus that allows route of the vestibulocochlear nerve, transporting signals from the inner ear to the brain for balance and hearing. The inferior surface of the petrous part has two foramina: the carotid canal and the jugular foramen. These foramina have major blood vessels that pass through them. The carotid canal is a passageway that provides a large blood supply to the brain. Blood then drains through the jugular foramen into the jugular vein of the neck CITATION Sal15 l 1033 (Saladin, 2015).
The occipital bone is an unpaired bone that forms the rear and base of the skull. It structures the foramen magnum, which is where the cranial cavity encounters the spinal cord. At each end of the occipital condyle, which is on both sides of the foramen magnum, there is a hypoglossal canal. The hypoglossal nerve passes through the canal and innervates the muscle of the tongue. The external occipital protuberance attaches the nuchal ligament, and this ligament holds the skull and vertebral column together. The superior nuchal line can be palpated on the superior border of the neck. This line provides attachment to the skull for back and neck muscles. The inferior nuchal line delivers attachment for many of the deep neck muscles and cannot be palpated CITATION Sal15 l 1033 (Saladin, 2015).
The Sphenoid Bone
The sphenoid bone has a thick body and with extended greater and lesser wings. About half of the cranial fossa is formed by the greater wing, also the lateral surface of the cranium. The posterior wall of the orbit is formed by the lesser wing and contains the optic canal. The optical canal allows passage of the ophthalmic artery and optic nerve. The anterior clinoid process