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The Axial Skeleton.docx

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University of Toronto St. George
William Huggon

The Axial Skeleton- pgs 211-242 7.1- the 80 bones of the longitudinal axis make up the axial skeleton • Axial skeleton forms the longitudinal axis of the body • Axial components 1. The skull (8 cranial bones and 14 facial bones) 2. Bones associated with the skull (6 auditory ossicles and the hyoid bone) 3. The vertebral column (24 vertebrae, the sacrum and the coccyx) 4. the thoracic cage (the sternum and 24 ribs) • The axial provides a framework that supports and protects the brain, the spinal cord, and the organs in the ventral body cavities’. • Also provides an extensive surface area for the attachment of muscles that (1) adjust the position of the head, neck and trunk; (2) perform respiratory movements; and (3) stabilize or position parts of the appendicular skeleton, which supports the limbs. 7.2 The skull is composed of 8 cranial bones and 14 facial bones • The bones of the skull protect the brain and guard the entrances to the digestive and respiratory systems. • 22 bones: 8 form the cranium and 14 associated with the face • 7 other bones associated with the skull: six auditory ossicles are situated within the temporal bones, and the hyoid bones is connected to the inferior surface of the temporal bones by a pair of ligaments. • 8 cranial bones: occipital, bones, frontal bone, sphenoid, ethmoid, and the paired parietal and temporal bones. • Together, the cranial bones enclose the cranial cavity, a fluid filled chamber that cushions and supports the brain. Blood vessels, nerves and membranes that stabilize the position the brain are attached to the inner surface of the cranium • Outer surface provides an extensive area for the attachment of muscle that move the eyes jaws and head. • A joint between the occipital bone and the first vertebra of the neck stabilizes the positions of the brain and spinal cord, while the joints between the vertebrae of the neck permit a wide range of head movements. • FACIAL BONES protect and support the entrances to the digestive and respiratory tracts. The superficial facial bones provide area for the attachment of muscles that control facial expressions and assist in manipulating food. • The deeper facial bones help separate the oral and nasal cavities, increase the surface area of the nasal cavities or help form the nasal septum, which sub-divides the nasal cavity. • Several bones contain air filled chambers called SINUS. • 2 main function of sinus: (1) makes the bone lighter, (2)the mucous membrane lining them produces mucus that moistens and cleans the air in and adjacent to the sinus. • Joint forms where 2 bones interconnect • Where the mandible contacts the cranium, the connection between the skull and bones of adults are immovable joints called SUTURES. • At the sutures, bones are tied firmly together with dense fibrous connective tissue. 4 major sutures. 1. Lambdoid suture: (L shaped). This stuture separates the occipital bone from the two parietal bones. One or more sutural bones may present along the lambdoid stuture. 2. Coronal Suture: attaches the frontal bone to the parietal bone of either side. A cut through the body that parallels the coronal suture produces a coronal section or frontal section 3. Sagittal stuture: the sagittal stuture extends from the lambdoid suture between the parietal bones. A cut along the midline of the suture produces a midsaggital section; a slice that parallels the sagittal suture produces a parasagittal section 4. Squamous suture: on each side of the skull forms the boundary between the temporal bone and the parietal bone of that side. *INDIVIDUAL BONES OF THE SKULL- prof summarized in the slides, it’s the exact same stuff for function, articulations, landmarks, etc. 7.3- Foramina and fissures of the skull serve as passageways for nerves and vessels - table 7.1 in the textbook. 7.4- An orbital complex contains each eye, and the nasal complex encloses the nasal cavities. Orbital Complexes • The orbits are the bony recesses that contain the eyes • Each orbit is formed by the 8 bones of the orbital complex • The frontal bone forms the roof, and the maxilla provides most of the orbital floor. • The orbital rim and the first portion of the medial wall are formed by the maxilla, the lacrimal bone, and the lateral mass of the ethmoid. • The lateral mass articulates with the sphenoid and small process of the palatine bone. • Several prominent foramina and fissures penetrate the sphenoid or lie between it and the maxilla. Laterally, the sphenoid and maxilla articulate with the zygomatic bone, which forms the lateral wall and rim of the orbit. Nasal complex • Includes the bones that enclose the nasal cavities and the paransal sinuses, air filled chambers connected to the nasal cavities. • The sphenoid, ethmoid, frontal bone, palatine bone and maxillae contain the paranasal sinuses • The paranasal sinuses lighten the skull bones and provide an extensive area of mucous epithelium • The mucous secretions are released into the nasal cavities. The ciliated epithelium passes the mucus back toward the throat, where it is eventually swallowed or expelled by coughing. Incoming air is humidified and warmed as it flows across this thick carpet of mucus. Foreign particulate matters, such as dust or microorganisms, becomes trapped in thie sticky mucus and is then swallowed or expelled. This mechanism helps protect the more delicate portions of the respiratory tract. 7.5 Frontanelles are non-ossified areas between cranial bones that allow for brain growth. • the largest fibrous areas between the cranial bones are known as FONTANELLES • the anterior fontanelle is the largest fontanelle. It lies at the intersection of the frontal, sagittal and coronal sutures in the anterior portion of the skull---soft spot for newborns! Composed of fibrous connective tissues and covers major blood vessel, and the anterior fontanelle pulses as the heart beats. • the occipital fontanelle is at the junction between the lambdoid and sagittal sutures • the sphenoidal fontanelles are at the junctions between the squamous sutures and the coronal sutures • the mastoid fontanelles are at the junctions between the squamous sutures and the lambdoid sutures. 7.6- the vertebral column has 4 spinal curves • rest of the axial skeleton consists of the vertebral column, ribs, and sternum • the adult vertebral column consists of 26 bones: the vertebrae(24), the sacrum, the coccyx • the vertebrae provide a column of support, bearing of weight of the head, neck, and trunk and ultimately transferring the weight to the appendicular skeleton of the lower limbs. Spinal curvature • vertebral column is not straight and rigid • 4 spinal curves- cervical curve, thoracic curve, lumbar curve, and sacral curve • Infants- C shape results from thoracic and sacral curves. These are called primary curves because they appear late in fetal development or accommodation curves because they accommodate the thoracic and abdominopelvic viscera. –present at birth • The secondary curves, do not appear until several months after birth. These curves are also called compensation curves because they help shift the weight to permit an upright posture. The cervical curve d
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