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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 1st year Anterior fontanel – closes near end of 2nd 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 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 25th 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 – 1st 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 of the 7th rib Floating ribs – last 2 rib pairs; no attachment to the sternum
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Rib Structure Long, slender shaft which curves around the chest and slopes downward Head – enlarged area on posterior end that articulates with own vertebra and next higher vertebra Tubercle – small knoblike process that articulates with transverse process of vertebra Costal cartilages – hyaline cartilage
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Sternum Breastbone Develops in 3 parts:
Manubrium – articulates with clavicles at clavicular notches Body – fuses to manubrium at middle age at the sternal angle Xiphoid process – begins as cartilage, slowly ossifies, and fuses to the body at middle age Red bone marrow in sternum produces RBCs into adulthood
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Pectoral Girdle Made of 2 clavicles and 2 scapulae
Supports upper limbs Provides attachment for muscles that move the upper limbs
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Clavicles Slender, rodlike bones with elongated S shapes
Located at base of the neck and run horizontally between the sternum and the shoulders Sternal ends – articulate with the manubrium Acromial ends – articulate with the scapulae Brace the scapulae, holding the shoulders in place Structurally weak
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Scapulae Broad, triangular bones located on either side of the upper back Spine – divides posterior surface Supraspinous fossa – area above the spine Infraspinous fossa – area below the spine 2 processes at the head: Acromion process – forms tip of the shoulder and articulates with the clavicle Coracoid process – curves anteriorly and inferiorly to the clavicle Glenoid cavity – between the acromion and coracoid processes; articulates with the head of the humerus
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Upper Limb Bones Bones form the framework of the arm, forearm, and hand Bones function as levers for muscle contraction Includes: Humerus (2) Radius (2) Ulna (2) Carpals (16) Metacarpals (10) Phalanges (28)
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Humerus Long bone that extends from scapula to the elbow
Head fits into glenoid cavity of scapula Greater tubercle – on leteral side Lesser tubercle – on anterior side Surgical neck – tapering region below head and tubercles (common fracture site) Deltoid tuberosity – V shaped rough area near the middle of the shaft on the lateral side attachment for the deltoid muscle
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Humerus Bone Features continued…
Coronoid fossa – process where the elbow bends: receives the ulna Capitulum – articulates with the radius Olecranon fossa – on posterior surface, receives the olecranon process of the ulna when the elbow straightens Trochlea – articulates with the ulna Epicondyles – attachments for elbow muscles and ligaments
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Radius On thumb side of forearm Shorter than the ulna
Extends from the elbow to the wrist and crosses over the ulna when hand is turned over at the wrist Head is thick and disk-like; articulates with the capitulum of the humerus and radial notch of the ulna Radial tuberosity – process just below the head; attachment for the biceps Styloid process – attachment for wrist ligaments at the distal end
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Ulna Longer than the radius Overlaps end of humerus posteriorly
Trochlear notch – at proximal end, wrench-like opening that articulates with the trochlea of the humerus Olecranon process – above the trochlear notch; attachment for triceps that straightens the upper limb at the elbow; fits into olecranon fossa Coronoid process – below trochlear notch, fits into coronoid fossa when elbow bends Styloid process – at distal end provides attachment for wrist ligaments
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Wrist Wrist consists of carpals bound in 2 rows of 4 bones each
Articulate with radius and ulna proximally and metacarpals distally Carpal bones are: Pisiform Triquetrum Lunate Scaphoid Hamate Capitate Trapezoid Trapezium
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Metacarpals Form the palm of the hand 5 per hand
Long bones with rounded distal ends (knuckles) Articulate with carpals and phalanges Lateral metacarpal is the most freely moveable Numbered 1-5, starting at the thumb
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Phalanges Finger bones 3 per finger (proximal, middle, and distal)
2 in thumb – no middle phalanx
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Pelvic Girdle Consists of 2 coxae
Coxae articulate with each other anteriorly and the sacrum posteriorly Pelvis – formed by the sacrum, coccyx, and pelvic girdle Girdle supports the trunk of the body, provides attachments for lower limb muscles, protects the bladder, distal end of the large intestine, and internal reproductive organs Body weight is transmitted through the pelvic girdle to the lower limbs
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Os Coxae Each coxa develops from 3 parts:
Ilium Ishium Pubis Acetabulum – cup-shaped cavity where the 3 parts of coxa fuse
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Ilium Largest and most superior portion of the coxa
Flares outward and forms the prominence of the hip Iliac crest – margin of the ilium Iliac fossa – smooth, concave surface on anterior aspect of the ilium Sacroiliac joint – where ilium and sacrum join Anterior superior iliac spine – found lateral to the groin, provides attachments for ligaments and muscles Posterior superior iliac spine – on posterior border
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Ischium Forms lowest portion of the coxa L-shaped
Ischial tuberosity – rough surface that points down and back; supports body weight when sitting Ischial spine – sharp projection above ischial tuberosity, near the junction between the ilium and the ischium Area between ischial spines is the shortest diameter of the pelvic outlet; felt during vaginal exams
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Pubis Anterior portion of coxa
Symphysis pubis – fibrocartilage joint between the 2 pubic bones Pubic arch – angle between pubic bones Obturator foramen – largest opening in the body Formed between ischium and pubis Covered and nearly closed by obturator membrane
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Male vs. Female Pelvis Male Pelvis: Female Pelvis Heavier bone
More evidence of muscle attachments Female Pelvis Iliac bones are more flared Broader hips Greater angle of pubic arch Greater distance between ischial spines and tuberosities Shorter, flatter sacral curvature More delicate bones
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Lower Limb Bones Femur (2) Patella (2) Tibia (2) Fibula (2)
Tarsals (7/foot) Metatarsals (5/foot) Phalanges (14/foot)
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Femur Bone Features Thigh bone Longest bone in body
Extends from hip to knee Head of femur – large and rounded; projects medially into acetabulum of coxal bone Fovea capitis – pit on head of femur that marks ligament attachment Greater trochanter and lesser trochanter – attachments for muscles of buttocks and lower limbs Linea aspera – longitudinal crest on posterior surface in middle third of shaft Lateral and medial condyles – articulate with tibia
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Patella Articulates with the femur on distal anterior surface Kneecap
Flat sesamoid bone located in a tendon that passes anteriorly over the knee Controls the angle at which the tendon continues toward the tibia functions in lever actions
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Tibia Bone Features Shin bone
Larger of 2 leg bones; located on the medial side Medial and lateral condyles – on proximal end, articulate with condyles of femur Tibial tuberosity – below condyles on anterior surface; attachment of patellar ligament Anterior crest – extends downward from tuberosity; site of CT attachments Medial malleolus – inner ankle Articulates with fibula and talus on distal end
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Fibula Bone Features Long, slender bone located on the lateral side of the tibia Articulates with the tibia just below the lateral condyle Lateral malleolus – distal end that forms the outer ankle
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Bones of the Foot Tarsus – consists of 7 tarsal bones
Talus – tarsal bone that can move freely where it joins the tibia and fibula ankle Other tarsals are bound firmly together to support the talus Calcaneus – largest tarsal bone; heel bone Located below the talus and projects backward Helps support weight of the body
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Metatarsals Numbered 1-5 beginning on the medial side
Ball of the foot formed by the distal ends Longitudinal arch extends from the heel to the toe; provides a stable, springy base for the body Transverse arch stretches across the foot If tissues that bind the metatarsals weaken fallen arches (flat feet)
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Phalanges Shorter, but otherwise similar to fingers
3 bones per toe, except 2 in the great toe
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