The Human Skeleton
Divisions of the Skeleton
• Axial skeleton – skull, vertebrae, and bony thorax
• Appendicular skeleton – bones of the arms and legs, including their associated girdles
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
The Cranium
• Encloses and protects the brain
• Surface provides attachments for muscles involved in chewing and head movements
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
Cranial Bones• Frontal bone• Parietal bones (2)• Occipital bone• Temporal bones (2)• Sphenoid bone• Ethmoid bone
Frontal Bone Features
• Supraorbital foramen• Frontal sinuses• Develops in 2 parts that grow together by 5-6
years old
Parietal Bone Features
• Sagittal suture• Coronal suture
Occipital Bone Features
• Lambdoidal suture• Foramen magnum• Occipital condyles
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
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
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
Facial Skeleton
• 13 immovable bones + the mandible
• Provides attachments for muscles for facial expressions and jaw movements
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
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
Palatine Bone Features
• L-shaped bones behind the maxillae
• Posterior hard palate
Zygomatic Bone Processes
• Prominences of the cheeks
• Temporal processes
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
Nasal Bone Features
• Form the bridge of the nose
Vomer Bone Features
• Joins perpendicular plate of ethmoid bone to form the nasal septum
Inferior Nasal Conchae Features
• Scroll-shaped bones attached to lateral walls of the nasal cavity
• Support mucous membranes of the nose
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
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
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
The Vertebral Column
• Extends from the skull to the pelvis
• Forms the vertical axis of the skeleton
• Composed of vertebrae, intervertebral disks, and ligaments
Functions of the Vertebral Column
• Supports the head and trunk
• Permits movement
• Protects the spinal cord which passes through the vertebral canal
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
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
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
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
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
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
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.
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
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
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
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
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
Curvature Disorders of the Spine
• Kyphosis – hunchback; exaggerated thoracic curvature
• Scoliosis – abnormal lateral curvature
• Lordosis – swayback; exaggerated lumbar curvature
Thoracic Cage• Includes ribs,
thoracic vertebrae, sternum, and costal cartilages
• Supports the shoulder girdle and upper limbs
• Protects viscera• Plays a role in
breathing
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
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
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
Pectoral Girdle• Made of 2
clavicles and 2 scapulae
• Supports upper limbs
• Provides attachment for muscles that move the upper limbs
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
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
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)
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
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
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
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
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
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
Phalanges
• Finger bones• 3 per finger (proximal,
middle, and distal)• 2 in thumb – no
middle phalanx
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
Os Coxae• Each coxa develops from 3 parts:
– Ilium– Ishium– Pubis
• Acetabulum – cup-shaped cavity where the 3 parts of coxa fuse
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
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
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
Male vs. Female Pelvis
• Male 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
Lower Limb Bones
• Femur (2)• Patella (2)• Tibia (2)• Fibula (2)• Tarsals (7/foot)• Metatarsals (5/foot)• Phalanges (14/foot)
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
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
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
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
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
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)
Phalanges
• Shorter, but otherwise similar to fingers
• 3 bones per toe, except 2 in the great toe