The Human Skeleton. Divisions of the Skeleton Axial skeleton – skull, vertebrae, and bony thorax Appendicular skeleton – bones of the arms and legs, including

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Text of The Human Skeleton. Divisions of the Skeleton Axial skeleton – skull, vertebrae, and bony...

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  • The Human Skeleton
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  • Divisions of the Skeleton Axial skeleton skull, vertebrae, and bony thorax Appendicular skeleton bones of the arms and legs, including their associated girdles
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  • The Skull Consists of 22 bones interlocked along sutures (all except the mandible) 8 bones make up the cranium 13 bones make up the facial skeleton Mandible = lower jawbone; only movable bone held to the cranium by ligaments Orbit of the eye is formed by cranial and facial bones
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  • The Cranium Encloses and protects the brain Surface provides attachments for muscles involved in chewing and head movements
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  • Sinuses Air-filled cavities of the cranium Lined with mucous membranes All connected by passageways to the nasal cavity Function to reduce the weight of the skull and increase voice intensity and resonance
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  • Cranial Bones Frontal bone Parietal bones (2) Occipital bone Temporal bones (2) Sphenoid bone Ethmoid bone
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  • Frontal Bone Features Supraorbital foramen Frontal sinuses Develops in 2 parts that grow together by 5-6 years old
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  • Parietal Bone Features Sagittal suture Coronal suture
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  • Occipital Bone Features Lambdoidal suture Foramen magnum Occipital condyles
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  • Temporal Bone Features Squamosal suture temporal to parietal External auditory meatus Mandibular fossae joint with mandible Mastoid process neck muscle attachment Styloid process below EAM, anchors muscles of tongue and pharynx Zygomatic process helps form cheek prominence
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  • Sphenoid Bone Features Wedged between several other bones in anterior portion of the cranium 2 winglike structures extend laterally toward each side of the skull Sella turcica houses pituitary gland Sphenoidal sinuses
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  • Ethmoid Bone Features Located in front of the sphenoid bone Consists of 2 masses on each side of the nasal cavity Cribriform plates join the 2 parts of the ethmoid bone Perpendicular plate form most of nasal septum Superior and middle nasal conchae support mucous membranes of the nose Ethmoid sinuses Crista galli triangular process that projects upward from the cribriform plates; place of attachment for membranes around the brain
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  • Facial Skeleton 13 immovable bones + the mandible Provides attachments for muscles for facial expressions and jaw movements
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  • Bones of the Facial Skeleton Maxillary bones (2) Palatine bones (2) Zygomatic bones (2) Lacrimal bones (2) Nasal bones (2) Vomer bone Inferior nasal conchae (2) Mandible
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  • Maxillary Bone Features Form upper jaw All other immovable facial bones articulate with them Hard palate Sockets of upper teeth Maxillary sinuses Palatine processes where the maxillary bones meet
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  • Palatine Bone Features L-shaped bones behind the maxillae Posterior hard palate
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  • Zygomatic Bone Processes Prominences of the cheeks Temporal processes
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  • Lacrimal Bone Features Thin, scalelike bones between the ethmoid bone and maxillae in the medial walls of the orbits Groove in anterior portion provides pathway for tears to the nasal cavity
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  • Nasal Bone Features Form the bridge of the nose
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  • Vomer Bone Features Joins perpendicular plate of ethmoid bone to form the nasal septum
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  • Inferior Nasal Conchae Features Scroll-shaped bones attached to lateral walls of the nasal cavity Support mucous membranes of the nose
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  • Mandible Features Ramus attachment for large chewing muscles Mandibular condyle articulates with mandibular fossae of temporal bones Alveolar border houses lower tooth sockets Mandibular foramen carries nerves and blood vessels to the lower teeth; dental injection site Mental foramen carries branches of nerves and blood vessels of the mandibular foramen
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  • Review of Fontanels Fontanels = membranous areas where the skull is incompletely developed; soft spots Permit some movement during childbirth Eventually close as bones grow together Posterior fontanel closes at 2 months Sphenoid fontanel closes at 3 months Mastoid fontanel closes near end of 1 st year Anterior fontanel closes near end of 2 nd year
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  • Other Infantile Skull Features Relatively small face Prominent forehead Large orbits Small jaw Small nasal cavity Sinuses are incompletely formed Frontal bone is in 2 parts Thin skull bones, but not easily fractured
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  • The Vertebral Column Extends from the skull to the pelvis Forms the vertical axis of the skeleton Composed of vertebrae, intervertebral disks, and ligaments
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  • Functions of the Vertebral Column Supports the head and trunk Permits movement Protects the spinal cord which passes through the vertebral canal
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  • Development of the Vertebral Column Consists of 33 bones at infancy 5 fuse to form the sacrum 4 fuse to form the coccyx 26 bones are found in the adult vertebral column
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  • Curvatures of the Vertebral Column Primary curvatures are anteriorly concave Thoracic curvature Pelvic curvature Secondary curvatures are anteriorly convex Cervical curvature Lumbar curvature Cervical curvature develops when a baby begins to hold up its head Lumbar curvature develops when a child begins to stand
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  • Typical Vertebra Body thick, drum-shaped, anterior portion of bone Intervertebral disks cushion and soften forces caused by movements Pedicles 2 short stalks that project posteriorly from each vertebral body Laminae 2 plates that arise from pedicles to fuse and form the spinous process Transverse processes between the pedicles and laminae; project laterally and posteriorly
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  • Typical Vertebra continued Vertebral arch formed by the pedicles, laminae, and spinous process; around the vertebral foramen Vertebral foramen opening through which the spinal cord passes Intervertebral foramina passageways for spinal nerves; between adjacent vertebrae
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  • Cervical Vertebrae 7 vertebrae Make up the neck region Smallest vertebrae Denser bone tissues than the other regions Distinctive because they have transverse foramina (passageways for arteries leading to the brain) Spinous processes are uniquely forked (C2-C6) C7 = vertebrae prominens; spinous process is longer and protrudes beyond the other cervical vertebrae
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  • Atlas C1 Supports the head Has no body or spine Consists of a bony ring with 2 transverse processes Facets kidney-shaped areas on the superior surface that articulate with the occipital condyles
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  • Axis C2 Dens toothlike process that projects upward and lies in the ring of the atlas As the head is turned from side to side, the atlas pivots around the dens.
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  • Thoracic Vertebrae 12 in number Larger than cervical vertebrae Long, pointed spinous process which slopes downward Facets on sides of vertebral body articulate with the ribs Bodies of the vertebrae increase in size from T3 down can bear an increasing load of body weight
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  • Lumbar Vertebrae 5 in number Located in the small of the back Larger, stronger, and support more weight than the others Transverse processes project posteriorly at sharp angles Short, thick spinous processes are nearly horizontal
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  • Sacrum Triangular structure at the base of the vertebral column 5 vertebrae fuse to form the sacrum between 18-30 years of age Fused spinous processes form a ridge of tubercles called the median sacral crest Dorsal sacral foramina openings to the sides of the tubercles through which nerves and blood vessels pass Sacral canal formed from vertebral foramina and opens at the sacral hiatus
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  • Coccyx Tailbone Lowest part of the vertebral column Made of 4 vertebrae that fuse by the 25 th year Acts as a shock absorber when sitting
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  • Vertebral Column Disorders Ruptured/herniated disk outer layers of the intervertebral disk are broken and the central mass of the disk is squeezed out from extra pressure, pressing on the spinal cord and spinal nerves pain, numbness, loss of muscular function
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  • Curvature Disorders of the Spine Kyphosis hunchback; exaggerated thoracic curvature Scoliosis abnormal lateral curvature Lordosis swayback; exaggerated lumbar curvature
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  • Thoracic Cage Includes ribs, thoracic vertebrae, sternum, and costal cartilages Supports the shoulder girdle and upper limbs Protects viscera Plays a role in breathing
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  • Ribs 12 pair one pair for each vertebra True ribs 1 st 7 rib pairs; join the sternum directly by costal cartilages False ribs bottom 5 rib pairs; do not join the sternum directly Cartilages of the upper 3 false ribs join the cartilage