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