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Biological Sciences
Connie Soros

1 Lecture 5 The Skeletal System: Axial Division (based on chapters 6, 7 and 8) Introduction • The skeleton is divided into 2 portions: the axial skeleton and the appendicular skeleton It is a rigid framework of 206 bones , muscles and organs are attached by tendons and ligaments o Bones act as levers (with joints acting as pivots) when muscles contract and move body The Axial Skeleton: - composed of bones along the central axis of the body – 80 bones Divided into three regions: Skull Vertebral column Thoracic cage Functions of the axial skeleton: Framework that supports and protects organs in the dorsal and ventral body cavities Protects special sense organs for taste, smell, hearing, balance, and vision Attachment sites for muscles that: Adjust the posture of the head, neck, and trunk Move the thoracic cage for respiration Stabilize the appendicular skeleton The Skull and Associated Bones Cranial and Facial Subdivisions of the Skull The skull consists of Face: 14 individual bones Cranium: 8 individual bones Associated bones: 7 individual bones (auditory ossicles – 3 per ear and hyoid bone) Cranial bones – form cranium, encase and protect brain (8 bones) Frontal bone – (1) forehead Parietal bones – (2) either side of the top of head Temporal bones - (2) temples on either side of the head Occipital bone – (1) back of head o Sphenoid bone – (1) butterfly shaped, keystone of skull, unites cranial and facial bones and base of cranium o Ethmoid bone – (1) between obits/walls, floor of cranium, part of nasal cavity and nasal septum Facial bones – form bone framework of oral cavity and jaw (14 bones) Nasal bones - (2) base of nose, cartilage forms the flexible portion Lacrimal bones – (2) (lacrima =tear), encloses tear duct and drains tears into nasal cavity Vomer - (1) means plowshare (looks like part of a plow from the front), inferior part of nasal septum Maxilla – (2) the largest of the facial bones, together form the upper jaw, articulate with all other facial bones except mandible, oral margins form the alveolar processes that contain the upper teeth Mandible – (1) forms the entire lower jaw, teeth are supported by the mandibular body, articulates with the temporal bone (tempomandibular joint) for jaw movements when talking or eating, high mobility but makes it easy to dislocate the jaw Zygomatic bones – (2) cheek bones © 2012 Pearson Education, Inc. 2 Inferior Nasal Conchae – (2) one on each side of nasal septum, along with the nasal conchae of the ethmoid bone, they create turbulence in inhaled air (slows air movement and provides additional time for warming, humidification and dust removal before air reaches more delicate portions of the respiratory tract0 Palatine bones – (2) form inferior portions of the hard palate, part of nasal cavity and eye orbit Associated Bones Auditory ossicles – 6 bones in middle ear (ear bones), smallest bones in the body, transmit sound impulses; 2 malleus, 2 incus, 2 stapes Hyoid Bone – only bone that does not articulate with any other bone, above the larynx (voice box) below mandible (jawbone) supports the tongue, aids in swallowing The Vertebral Column The adult vertebral column is made up of 26 bones: 24 vertebrae 7 cervical vertebrae – cervical curve 12 thoracic vertebrae – thoracic curve 5 lumbar vertebrae – lumbar curve 1 sacrum (5 fused vertebrae) – sacral curve 1 coccyx (3-5 fused vertebrae) These curves, along with muscle attachment to the various vertebral processes, help to maintain balance Functions of the vertebral column Encloses and protects the spinal cord Supports the skull Supports the weight of the head, neck, and trunk Transfers weight to the lower limbs Helps maintain the upright position of the body Curves of the spine act like a spring to absorb muscle shock (without snapping) Vertebral Processes of a Typical Vertebra Vertebral body Vertebral foramen Spinous process Transverse process (superior articular and inferior articular) Transverse foramen Intervertebral Joints Function in shock absorbance Inferior articular facet articulates with superior articular facet and they come together in facet joints Between bodies of vertebrae are intervertebral discs Nucleus pulposis –gel-like pad in center (mostly water) o Anulus fibrosis – surrounds nucleus pulposis, fibrocartilage with collagen fibers attach to the vertebrae Spinal nerves run through vertebral foramen and intervertebral foramen where the spinal nerves emerge as they branch off the spinal cord The Thoracic Cage © 2012 Pearson Education, Inc. 3 The thoracic cage has two functions: It protects the heart, lungs, thymus, and other structures within the cavity It serves as the attachment site for muscles involved in: Respiration Positioning the vertebral column Movements of the pectoral girdle and upper limb The Thoracic Cage The Thoracic Cage Sternum (3 bones) Manubrium Body
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