Download THE AXIAL SKELETON

THE SKELETON
THE SKELETON
• Composed of bones, cartilages, joints, and
ligaments, accounts for about 20% of body
mass (30 pounds in a 160 pound person)
– Bones make up most of the skeleton
– Cartilages occur only in isolated areas
• Nose, parts of the ribs, and the joints
– Ligaments connect bones and reinforce joints,
allowing required movements while restricting
motions in other directions
– Joints, the junction between bones, provide for the
remarkable mobility of the skeleton
Axial Skeleton
• Structured from 80 bones
segregated into three
major regions:
– Skull
– Vertebral column
– Bony thorax
• Supports the head, neck,
and trunk, and protects
the brain, spinal cord, and
organs in the thorax
AXIAL SKELETON
The Skull
• The skull consists of 22 cranial and facial bones that form the
framework of the face, contain cavities for special sense organs,
provide openings for air and food passage, secure the teeth, and
anchor muscles of facial expression
• The cranial bones (cranium) enclose and protect the fragile brain
and furnish a site for attachment of head and neck muscles
• Facial bones:
– Form the framework of the face
– Contain cavities for the special sense organs of sight, taste, and
smell
– Provide openings for air and food passage
– Secure the teeth
– Anchor the facial muscles of expression, which we use to show
our feelings
The Skull
•
Except for the mandible, which
is joined to the skull by a freely
movable joint, most skull bones
are flat bones joined by
interlocking joints called
sutures
– Suture lines have a sawtoothed or serrated
appearance
• Major sutures that
connect cranial bones
are:
– Coronal
– Sagittal
– Squamous
– Lambdoid
EXTERNAL LATERAL SKULL
POSTERIOR SKULL
The Skull
• Most other skull
sutures connect
facial bones and are
named according to
the specific bones
they connect
– Examples:
• Frontonasal suture
• Occipitomastoid suture
ANTERIOR SKULL
POSTERIOR SKULL
Overview of Skull Geography
• The anterior aspect of
the skull is formed by
facial bones, and the
remainder is formed by
a cranium, which is
divided into:
– 1. Cranial vault (calvaria):
• Forms the superior,
lateral, and posterior
aspects of the skull, as
well as the forehead
EXTERNAL LATERAL SKULL
The Skull
• 2. Cranial base (floor)
(a): inferior superficial
view
– Forms the skull’s inferior
aspect
– Internally (b+c):
• (b): superior view of the
floor of cranial cavity
• (c): schematic view of the
cranial cavity floor
• prominent bony ridges
divide the base into three
distinct “steps” or
fossa:
– Anterior cranial fossa
– Middle cranial fossa
– Posterior cranial fossa
INFERIOR SKULL
SUPERIOR SKULL
The Skull
• The cavities of the
skull include:
– Cranial cavity:
• Houses the brain
– Ear cavities
– Nasal cavity
– Orbit cavities:
• House the eyeballs
– Air-filled sinuses:
• Lighten the skull
SKULL CAVITIES
The Skull
• The skull has about 85 named openings
that provide passageways for the spinal
cord, major blood vessels serving the
brain, and the cranial nerves
– Named:
• Foramina
• Canals
• Fissures
Cranium
• Consists of eight strong,
superiorly curved bones
• 1. Frontal bone:
– Forms the anterior cranium
– Most anterior part of the
frontal bone is the vertical
frontal squama (forehead)
– Articulates posteriorly with the
parietal bones via the coronal
suture, extends forward to the
supraorbital margins, and
extends posteriorly to form the
superior wall of the orbits and
most of the anterior cranial
fossa
ANTERIOR SKULL
EXTERNAL LATERAL SKULL
Parietal Bone
• 2. Two large, rectangular
bones on the superior and
lateral aspects of the skull
– Form the bulk of the cranial
vault
• The four largest sutures of
the skull are located where
the parietal bones articulate
with other bones:
– Coronal: parietal bones
meet the frontal anteriorly
– Sagittal: the parietal bones
meet superiorly at the
cranial midline
– Lambdoid: parietal bones
meet the occipital bone
posteriorly
– Squamous: where a
parietal and temporal bone
meet on the lateral aspect of
the skull
POSTERIOR SKULL
EXTERNAL LATERAL SKULL
Occipital Bone
• Articulates with the parietal,
temporal, and sphenoid
bones
• Forms most of the posterior
wall and base of the skull
• The foramen magnum, a
large opening through which
the brain connects to the spinal
cord, is located in the base of
the occipital bone
• Rockerlike occipital
condyles articulate with the
first vertebra of the spinal
column in a way that permits
a nodding movement of the
head
POSTERIOR SKULL
EXTERNAL LATERAL SKULL
Temporal Bone
• Lateral skull surface
• Articulate with the parietal
bones and form the
inferolateral aspects of the
skull and parts of the cranial
floor
• The temporal bone is
characterized by the small,
oval mandibular fossa on the
inferior surface of the
zygomatic process
– It receives the condyle of
the mandible (lower jawbone)
forming the freely movable
temporomandibular joint
EXTERNAL LATERAL SKULL
MID SAGITTAL SKULL
INFERIOR SKULL
Temporal Bone
• Tympanic region
surrounds the external
acoustic meatus
(external ear canal)
• Housed in the petrous
region are the middle
and inner ear cavities,
which contain sensory
receptors for hearing and
balance
TEMPORAL BONE
Temporal Bone
•
•
Jugular foramen: passage of internal
jugular vein and three cranial nerves
Carotid canal: passage of the internal
carotid arteries (both supply 80% of
blood to the brain)
–
•
Closeness to the inner ear cavities
explains why, during excitement or
exertion, we sometimes hear our
rapid pulse as a thundering sound in
the head
Mastoid process: felt as a bump just
posterior to the ear
–
–
Anchoring site for some neck muscles
Full of air cavities (mastoid sinuses: air
cells)
•
•
•
Position adjacent to the middle ear
cavity (high-risk area for infections
spreading from the throat) puts it at risk
for infection itself
Mastoid sinus infection (mastoiditis) is
difficult to treat
Separated from the brain by only a
very thin bony plate
–
Infections may spread to the brain
INFERIOR SKULL
TEMPORAL BONE
TEMPORAL BONE
Sphenoid Bone
• Spans the width of the
middle cranial fossa
(furrow or shallow
depression)
• Keystone of the
cranium because it
articulates with all other
cranial bones
• Pterygoid processes
anchor the pterygoid
muscles which are
important in chewing
• Optic canals: allow
passage of optic nerve
SUPERIOR SKULL
SPHENOID BONE
SPHENOID BONE
Ethmoid Bone
• Lies between the sphenoid
and nasal bones
• Forms most of the bony area
between the nasal cavity and
the orbits
• Superior surface (cribriform
plate) helps form the roof of
the nasal cavities and the
floor of the anterior cranial
fossa
• Olfactory foramina: allows
passage of the olfactory nerve
• Perpendicular plate: forms
superior part of the nasal
septum, which divides the
nasal cavity into right and left
halves
ETHMOID BONE
ETHMOID BONE
Sutural Bones
• Sutural, or Wormian,
bones are groups of
irregularly shaped bones
or bone clusters located
within sutures (most
often in the lambdoid
suture) that vary in
number and are not
present on all skulls
– Formed during fetal
development
– Structurally unimportant
POSTERIOR SKULL
Facial Bones
Mandible
•
•
•
•
•
U-shaped bone
Lower jawbone
Largest, strongest bone of the
face
Body forms the chin
Two upright rami
– Each ramus meets the body
posteriorly at a mandibular angle
– Superior margin of each ramus
are two processes separated by
the mandibular notch
• The anterior coronoid process
is an insertion point for the large
temporalis muscle that elevates
the lower jaw during chewing
• The posterior mandibular
condyle articulates with the
mandibular fossa of the
temporal bone, forming the
temporomandibular joint on the
same side
FACIAL BONES
Mandible
Facial Bones
Mandible
• Mandibular body
anchors the lower
teeth:
– Its superior border, called
the alveolar margin,
contains the sockets
(alveoli) in which the
teeth are embedded
– In the midline of the
mandibular body is a
slight depression, the
mandibular symphysis,
indicating where the two
mandibular bones fused
during infancy
FACIAL BONES
Mandible
ANTERIOR SKULL
Facial Bones
Mandible
• Large mandibular foramina:
– One on the medial surface of
each ramus
– Permit the nerves
responsible for tooth
sensation to pass to the
teeth in the lower jaw
– Dentist inject Novocain into
these foramina to prevent pain
while working on the lower
teeth
• Mental foramina:
– Openings on the lateral
aspects of the mandibular
body
– Allow blood vessels and
nerves to pass to the skin of
the chin and lower lips
FACIAL BONES
Mandible
Facial Bones
Maxillary Bones
• Maxillae (b)
• Form the upper jaw and central
portion of the face
• Articulates with all other facial
bones except the mandible
– Hence the maxillae are
considered the keystone
bones of the facial skeleton
• Maxillae carry the upper
teeth in their alveolar
margins
• Just inferior to the nose the
maxillae meet medially,
forming the pointed anterior
nasal spine at their junction
Facial Bones
Maxillary Bones
Facial Bones
Maxillary Bones
• Palatine processes of
the maxillae project
posteriorly from the
alveolar margins and fuse
medially, forming the
anterior 2/3 of the hard
palate, or bony roof of
the mouth
• Posterior to the teeth is
a midline foramen,
called the incisive fossa
– Serves as a passageway
for blood vessels and
nerves
MID SAGITTAL SKULL
INFERIOR SKULL
Facial Bones
Maxillary Bones
• Frontal processes
extend superiorly to the
frontal bone, forming
part of the lateral
aspects of the bridge of
the nose
• Regions that flank the
nasal cavity laterally
contain the maxillary
sinuses, the largest of
the paranasal sinuses
– They extend from the
orbits to the upper teeth
Facial Bones
Maxillary Bones
SINUSES
Facial Bones
Maxillary Bones
• Laterally, the
maxillae articulates
with the zygomatic
bones via their
zygomatic
processes
ANTERIOR SKULL
EXTERNAL LATERAL SKULL
Facial Bones
Maxillary Bones
• Inferior orbital fissure is
located deep within the orbit at
the junction of the maxilla with
the greater wing of the
sphenoid
– Permits the zygomatic
nerve, the maxillary nerve
(branch of cranial nerve V),
and blood vessels to pass
to the face
• Just below the eye socket on
each side is an infraorbital
foramen that allows the
infraorbital nerve and artery
to reach the face
ANTERIOR SKULL
Facial Bones
Zygomatic Bones
• Commonly called cheek
bones
• They articulate with the
zygomatic process of the
temporal bones posteriorly, the
zygomatic process of the
frontal bone superiorly, and
with the zygomatic processes
of the maxillary bones
anteriorly
• Form the prominences of the
cheeks and parts of the
inferolateral margins of the
orbits
ANTERIOR SKULL
EXTERNAL LATERAL SKULL
Facial Bones
Nasal Bones
• Form the bridge of the
nose
• Articulate with the frontal
bone superiorly, the
maxillary bones laterally,
and the perpendicular
plate of the ethmoid
bones posteriorly
• Inferiorly they attach to
the cartilages that form
most of the skeleton of
the external nose
ANTERIOR SKULL
EXTERNAL LATERAL SKULL
Facial Bones
Lacrimal Bones
• Located in the medial
wall of the orbits
• Articulate with the frontal
bone superiorly, ethmoid
bone posteriorly, and
maxillae anteriorly
• Contains a deep groove
that helps form a
lacrimal fossa
– Houses the lacrimal sac,
part of the passageway
that allows tears to drain
from the eye surface into
the nasal cavity
ANTERIOR SKULL
EXTERNAL LATERAL SKULL
Facial Bones
Palatine Bones
• Consist of bony
plates that complete
the posterior portion
of the hard palate
• Form part of the
posterolateral walls of
the nasal cavity, and
small parts of the
orbits
INFERIOR SKULL
NASAL CAVITY
Facial Bones
Vomer
• Lies in the nasal
cavity, where it
forms part of the
nasal septum
• Plow-shaped
ANTERIOR SKULL
Facial Bones
Inferior Nasal Conchae
• Paired thin, curved
bones in the nasal
cavity
• Project medially from the
lateral walls of the nasal
cavity, just inferior to the
middle nasal conchae of
the ethmoid bone
• Largest of the three pairs
of conchae and, like the
others, they form part of
the lateral walls of the
nasal cavity
ANTERIOR SKULL
NASAL CAVITY
Special Characteristics of the
Orbits and Nasal Cavity
• The orbits are bony cavities
that contain:
– The eyes which are firmly
encased and cushioned by
fatty tissue
– Muscles that move the eyes
– Tear-producing glands
lacrimal glands
– The walls of each orbit are
formed by parts of seven
bones—the frontal, sphenoid,
zygomatic, maxilla, palatine,
lacrimal, and ethmoid bones
– Superior and inferior orbital
fissures
– Optic canals
ORBIT
ORBIT
Facial Bones
Nasal Cavity
• Constructed of bone and
hyaline cartilage
• Roof of the nasal cavity is
formed by the cribriform plate
of the ethmoid
• Lateral walls are largely
shaped by the superior and
middle conchae of the ethmoid
bone, the perpendicular plates
of the palatine bones, and the
inferior nasal conchae
– The depressions under cover
of the conchae on the lateral
walls are called meatuses
(superior, middle, inferior)
NASAL CAVITY
Facial Bones
Nasal Cavity
• It is divided into
right and left parts
by the nasal
septum, which
consists of portions of
the ethmoid bone and
vomer
– A sheet of cartilage
called the septal
cartilage completes
the septum anteriorly
NASAL CAVITY
Nasal Cavity
• Nasal septum and conchae are covered
with a mucus-secreting mucosa that
moistens and warms the entering air
and helps cleanse it of debris
– The scroll-shaped conchae increase the
turbulence of air flowing through the nasal
cavity
• This swirling forces more of the inhaled air into
contact with the warm, damp mucosa and
encourages trapping of airborne particles
(dust, pollen, bacteria) in the sticky mucus
Paranasal Sinuses
•
•
•
•
Five skull bones—frontal, sphenoid, ethmoid, and paired maxillary bones—contain
mucosa-lined, air-filled sinuses that cause them to look rather moth-eaten in an X-ray image
Are air-filled sinuses that cluster around the nasal cavity
– Small openings connect the sinuses to the nasal cavity and act as “two-way streets”
• Air enters the sinuses from the nasal cavity
• Sinus mucosae:
– Forms mucus which drains into the nasal cavity
– Helps to warm and humidify inspired air
Lightens the skull
Enhances resonance of the voice
SINUSES
Hyoid Bone
•
•
•
•
Not really part of the skull
U-shaped
Lies inferior to the mandible in the
anterior neck
– It is the only bone of the
body that does not
articulate directly with any
other bone
• Anchored by the narrow
stylohyoid ligaments to the
styloid processes of the
temporal bones
Acts as a movable base for the
tongue:
– Its body and greater horns are
attachment points for neck
muscles that raise and lower
the larynx during swallowing
and speech
HYOID BONE
THE VERTEBRAL COLUMN
•
General Characteristics:
– The vertebral column consists of
26 irregular bones (vertebrae)
• Separated by intervertebral
discs
– Forms a flexible, curved structure
extending from the skull to the
pelvis
– Surrounds and protects the spinal
cord
– Provides attachment for ribs and
muscles of the neck and back
– Divisions and Curvatures:
• The vertebrae of the spine fall
in five major divisions:
–
–
–
–
7 cervical
12 thoracic
5 lumbar
5 fused vertebrae of the
sacrum
– 4 fused vertebrae of the
coccyx
VERTEBRAL COLUMN
Curvatures
• Right lateral view
• Cervical and lumber
curvatures are concave
(spherically depressed: bowl
like) posteriorly
• Thoracic and sacral
curvatures are convex
(curved sphere like)
posteriorly
• Curvatures of the spine
increase resiliency and
flexibility of the spine
allowing it to function like a
spring rather than as a rigid
rod
VERTEBRAL COLUMN
Homeostatic Imbalance
•
•
There are several types of abnormal spinal curvatures caused by:
– Congenital (present at birth)
– Disease
– Poor posture
– Unequal muscle pull on the spine
Scoliosis: twisted disease
– Abnormal lateral curvature that occurs most often in the thoracic region
– Quite common during late childhood, particularly in girls, for some
unknown reason
– Sever cases result from abnormal vertebral structure, lower limbs of
unequal length, or muscle paralysis
– If muscles on one side of the body are nonfunctional, those of the
opposite side exert an unopposed pull on the spine and force it out
of alignment
– Treated (with braces or surgery) before growth ends
• Prevents permanent deformity and breathing difficulties due to
compressed lung
Homeostatic Imbalance
• Kyphosis: hunchback
– Dorsally exaggerated thoracic curvature
– Common in aged individuals because of osteoporosis (loss of
bone mass), but may also reflect tuberculosis of the spine,
rickets, or osteomalacia (vitamin D deficiency, loss of calcium
salts)
• Lordosis: swayback
– Accentuated lumbar curvature
– Can result from spinal tuberculosis or osteomalacia
– Temporary lordosis common in people with:
– Pot bellies
– Pregnant woman
• In an attempt to preserve their center of gravity, these individuals
automatically throw back their shoulders, accentuating their lumbar
curvature
Ligaments
•
The vertebral column cannot
possibly stand upright by itself
– It must be held in place by an
elaborate system of cablelike
supports
• Straplike ligaments and the trunk
muscles assume this role
– Ligaments: band of regular
fibrous tissue that connects
bones
•
The major supporting ligaments
of the spine are the anterior and
posterior longitudinal
ligaments, which run as
continuous bands down the front
(anterior) and back (posterior)
surfaces of the spine from the
neck to the sacrum
VERTEBRAL DISC
Ligaments
•
Anterior ligament:
–
–
–
•
Strongly attached to both the bony
vertebrae and the disc
Broad and strong
Along with its supporting role, it
prevents hyperextension of the spine
(bending too far backward)
Posterior ligament:
–
–
–
–
Attaches only to discs
Narrow and relatively weak
Resists hyperflexion of the spine
(bending too sharply forward)
However:
•
The ligamentum flavum, which contains
elastic connective tissue, is especially
strong
–
•
Stretches on bending forward and
recoils when we resume an erect
posture
Short ligaments connect each
vertebra to those immediately above
and below
VERTEBRAL DISC
Intervertebral Discs
•
Cushionlike pads:
– Composed of two parts:
• Inner gelatinous nucleus pulposus
– Acts like a rubber ball, giving
the disc its elasticity and
compressibility
• Annulus fibrosus:
– Surrounds the nucleus pulposus
– Strong collar composed of
collagen fibers superficially and
internally fibrocartilage
– Limits the expansion of the
nucleus pulposus when the spine
is compressed
– Holds together successive
vertebrae and resists tension
in the spine
– Act as shock absorbers and allow the
spine to flex, extend, and bend laterally
• At points of compression, the discs
flatten and bulge out a bit between
the vertebrae
– Flattened somewhat during the course of the
day, so we are always a few centimeters
shorter at night than when we awake in the
morning
VERTEBRAL DISC
Homeostatic Imbalance
• Severe or sudden physical trauma to the spine—for example, from
bending forward while lifting a heavy object—may result in
herniation of one or more discs
– Herinated (prolapsed) disc:
• Slipped disc
• Usually involves rupture of the annulus fibrosus followed by protrusion of the
spongy nucleus through the annulus
– If protrusion presses on the spinal cord or on spinal nerves exiting from the cord,
numbness or excruciating pain may result
• Treatment:
–
–
–
–
Moderate exercise
Heat therapy
Painkillers
Surgical removal followed by a bone graft to fuse the adjoining
vertebrae
– Partial vaporization with a laser
• Outpatient procedure
VERTEBRAL DISC
General Structure of Vertebrae
•
Each vertebra consists of an
anterior body (centrum) and a
posterior vertebral arch
– Disc-shaped body is the
weight-bearing region
– Together, the body and
vertebral arch enclose an
opening called the vertebral
foramen
• Successive vertebral
foramina of the
articulated vertebrae
form the long vertebral
canal, through which
the spinal cord passes
General Structure of Vertebrae
• The vertebral arch
consists of two pedicles
and two laminae, which
collectively give rise to
several projections
– Pedicles (little feet):
• Short bony pillars
projecting posteriorly from
the vertebral body
• Form the sides of the arch
– Laminae:
• Flattened plates that fuse
in the median plane
• Complete the arch
posteriorly
General Structure of Vertebrae
• The pedicles have
notches on their
superior and inferior
borders, providing lateral
openings between
adjacent vertebrae called
intervertebral foramen
– Provide openings for the
passage of spinal nerves
General Structure of Vertebrae
• Seven processes project from
the vertebral arch
– Spinous process (1): median
posterior projection arising at
the junction of the two laminae
• Attachments sites for muscles
that move the vertebral
column and for ligaments that
stabilize it
– Transverse processes (2):
extends laterally from each
side of the vertebral arch
• Attachments sites for muscles
that move the vertebral
column and for ligaments that
stabilize it
THORACIC VERTEBRAE
General Structure of Vertebrae
– Paired superior and inferior
articular processes (2):
• Protrude superiorly and
inferiorly, respectively, from
the pedicle-lamina junctions
• The smooth joint surfaces
of the articular processes,
called facets (little faces),
are covered with hyaline
cartilage
• The inferior articular
processes of each vertebra
form movable joints with
the superior articular
processes of the vertebra
immediately below
– Thus, successive
vertebrae join both at their
bodies and at their
articular processes
THORACIC VERTEBRAE
VERTEBRA
Cervical Vertebrae
• Smallest vertebrae
• Identified as C1-C7
• They typically have:
– An oval body: wider from side to side than in the
anteroposterior dimension
– Except in C7, the spinous process is short, projects
directly back, and is bifid (split at its tip)
– Vertebral foramen is large and generally triangular
– Each transverse process contains a transverse
foramen through which the vertebral arteries pass
to service the brain
Cervical Vertebrae
• The spinous process of
C7 is not bifid and is
much larger than those of
the other cervical
vertebrae
– Its spinous process is
visible through the skin
– Used as a landmark for
counting the vertebrae and
is called the vertebra
prominens (prominent
vertebra)
CERVICAL VERTEBRAE
Cervical Vertebrae
•
The first two cervical vertebrae are
unusual
–
Atlas and Axis
•
•
•
Have no intervertebral disc between
them
Have special functions
Atlas (C1) has no body or spinous
process
–
–
Essentially, it is a ring of bone
consisting of anterior and posterior
arches and a lateral mass on each side
Each lateral mass has articular facets
on its superior and inferior surfaces
•
The superior articular facets articulate
with the occipital condyles of the skull
–
–
–
They carry the skull just as Atlas
supported the heavens in greek
mythology
These joints allow you to nod “YES”
The inferior articular surfaces form
joints with the axis below (inferiorly)
Cervical Vertebrae
• Axis (C2) has a body,
spine, and other typical
vertebral processes
– Not as special as the atlas
– Its only unusual feature is
the knoblike dens (tooth),
or odontoid process,
projecting superiorly from
its body
• Acts as a pivot for the
rotation of the atlas
– Hence, this joint allows
you to rotate your
head from side to side
to indicate “NO”
CERVICAL VERTEBRAE
Thoracic Vertebrae
•
•
•
•
•
12 thoracic vertebrae (T1-T12)
All articulate with ribs
Gradually transition between
cervical structure at the top, and
lumbar structure toward the
bottom
Thoracic vertebrae have a roughly
heart-shaped body
Typically bears (demifacets: halffacets), on each side, one at the
superior edge and the other at the
inferior edge
– The demifacets articuale with
the ribs
•
•
Circular vertebral foramen
Spinous process is long and
points sharply downward
THORACIC VERTEBRAE
Lumbar Vertebrae
• 5 Lumbar vertebrae (L1-L5)
• Receives the most stress
• The enhanced weightbearing function is reflected
in their sturdier structure
• Large vertebrae that have
kidney-shaped bodies
• Triangular vertebral foramen
• Short, thick pedicles and
laminae
• Short, flat, hatchet-shaped
spinous processes
LUMBAR VERTEBRAE
Sacrum
• Forms the posterior wall of
the pelvis
• It is formed by five, fused
vertebrae in adults, and
articulates with the fifth lumbar
vertebra superiorly, the coccyx
inferiorly, and the hip bones
laterally via the sacroiliac joint
• The vertebral canal continues
through the sacrum, often
ending at a large external
opening, the sacral hiatus
• Body’s center of gravity
SACRUM/COCCYX VERTEBRAE
Coccyx
• The coccyx (tailbone) is
a small bone consisting of
four, fused vertebrae that
articulate superiorly with
the sacrum
• Except for the slight
support it affords the
pelvic organs, it is a
nearly useless bone
• Occasionally, a baby is
born with an unusually
long coccyx
– Snipped off
SACRUM/COCCYX VERTEBRAE
THE BONY THORAX
•
The bony thorax (thoracic cage)
–
Consists of the thoracic vertebrae dorsally, the ribs laterally, and the sternum and costal
cartilages anteriorly
•
–
–
–
Costal cartilage secure the ribs to the sternum
It forms a protective cage around the organs of the thoracic cavity, and provides support for
the shoulder girdles (pectoral) and upper limbs
Provides attachment points for many muscles of the neck, back, chest, and shoulders
Intercostal spaces between the ribs are occupied by the intercostal muscles, which lift
and depress the thorax during breathing
BONY THORAX
Sternum
•
•
The sternum (breastbone) lies in the anterior midline of the thorax
Is a flat bone resulting from the fusion of three bones: the manubrium,
body, and xiphoid process
• The manubrium (superior portion) articulates with the clavicles and the first two pairs of
ribs
• The body (midportion) articulates with the cartilage of ribs two through seven
• The xiphoid process (inferior portion) forms the inferior end, articulating only with the
body
– Serves as an attachment point for some abdominal muscles
BONY THORAX
Ribs
• The sides of the thoracic cage
are formed by twelve pairs of
ribs that attach posteriorly to
the thoracic vertebrae and
curve inferiorly toward the
anterior body surface
• The superior seven pairs of
ribs are called true, or
vertebrosternal, ribs
– They attach directly to the
sternum via individual costal
cartilages
• The lower five pairs of ribs are
called false ribs
– They either attach indirectly to
the sternum or lack a sternal
attachment entirely
BONY THORAX
Rib
•
•
•
A typical rib is a bowed flat bone
Bulk of a rib is simply called the shaft
Wedged shaped head articulates
with the vertebral bodies by two
facets:
–
–
•
•
•
One joins the body of the samenumbered thoracic vertebra
The other articulates with the body
of the vertebra immediately superior
Neck is the constricted portion of the
rib just beyond the head
Knoblike tubercle articulates with
the transverse process of the samenumbered thoracic vertebra
Costal cartilages provide secure but
flexible rib attachments to the
sternum
TRUE RIB
Appendicular Skeleton
• Bones of the limbs
and their girdles
– They are appended to
the axial skeleton that
forms the longitudinal
axis of the body
• Pectoral girdles
attach the upper limbs
to the body trunk
• Pelvic girdle secures
the lower limbs
APPENDICULAR SKELETON
Pectoral Girdle
• The pectoral (shoulder) girdle consists
of the clavicle, which joins the sternum
anteriorly, and the scapula, which is
attached to the posterior thorax and
vertebrae via muscular attachments
• The pectoral girdles are very light and have a
high degree of mobility due to the openness of
the shoulder joint and the free movement of the
scapula across the thorax
Pectoral Girdle
•
•
The paired pectoral girdles and their
associated muscles form your shoulders
Although the term girdle usually signifies a
beltlike structure encircling the body, a
single pectoral girdle, or even the pair, does
not quite satisfy this description
– Anteriorly, the medial end of each
clavicle joins the sternum; the distal
ends of the clavicles meet the
scapulae laterally
• However, the scapulae fail to
complete the ring posteriorly,
because their medial borders do
not join each other or the axial
skeleton
• Instead, the scapulae are
attached to the thorax and
vertebral column only by the
muscles that cover their
surfaces
PECTORAL GIRDLE
Pectoral Girdle
• The mobility is due to the
following factors:
– 1. Only the clavicle attaches
to the axial skeleton, the
scapula can move quite freely
across the thorax, allowing the
arm to move with it
– 2. The socket of the
shoulder joint (the scapula’s
glenoid cavity) is shallow and
poorly reinforced, so it does
not restrict the movement of
the humerus (arm bone)
• Although this arrangement
is good for flexibility, it is
bad for stability
• Shoulder dislocations are
fairly common
PECTORAL GIRDLE
Clavicle
• The clavicles (collarbones)
extend horizontally across the
thorax (a)
• Articulating medially with the
axial skeleton (sternum), and
laterally with the scapula,
bracing the arms and scapulae
laterally
• (b+c):Each clavicle is cone
shaped at its medial sternal
end, which attaches to the
sternal manubrium, and
flattened at its lateral
acromial end, which
articulates with the scapula
PECTORAL GIRDLE
Clavicle
• Anchors many muscles
in the shoulder region
• Braces and holds the
scapulae and arms out
laterally, away from the
narrower superior part of
the thorax
– This bracing function
becomes obvious when a
clavicle is fractured: the
entire shoulder region
collapses medially
APPENDICULAR SKELETON
Clavicle
• Not very strong and are
likely to fracture
• Example:
– When a person uses
outstretched arms to break
a fall
• The curves in the clavicle
ensure that it usually
fractures anteriorly
(outward)
• If it were to collapse
posteriorly (inward),
bone splinters would
damage the subclavian
artery, which passes just
deep to the clavicle to
serve the upper limb
PECTORAL GIRDLE
Scapulae
•
The scapulae (shoulder blades) are
thin, triangular flat bones that lie on the
dorsal surface of the ribcage between
ribs 2 + 7
–
•
Derived from words Spade/Shovel
Each scapula has three borders:
–
Superior border:
•
–
Medial (vertebral) border:
•
–
Parallels the vertebral column
Lateral (axillary) border:
•
•
•
Shortest, sharpest
Thick
Abuts the armpit and ends superiorly in
a small, shallow fossa (glenoid cavity)
Articulating with the humerus via
the glenoid cavity, and the clavicle
via the acromion forming the
shoulder joint
Scapula
SCAPULA
Scapula
• Like all triangle, the
scapula has three
corners or angles
– Superior scapular border
meets the medial at the
superior angle
– Superior scapular border
meets the lateral border at
the lateral angle
– The medial and lateral
borders join at the inferior
angle
• The inferior angle moves
extensively as the arm is
raised and lowered
PECTORAL GIRDLE
SCAPULA
Scapula
• The anterior, or costal,
surface is concave
(depression) and relatively
featureless
• Posterior surface bears a
prominent spine that is easily
felt through the skin
– Spine ends laterally in an
enlarged, roughened
triangular projection called
the acromion (point of
shoulder)
• Acromion articulates with
the acromial end of the
clavicle, forming the
acromioclavicular joint
PECTORAL GIRDLE
Scapula
Scapula
• Projecting anteriorly from
the superior scapular
border is the coracoid
(beadlike) process
– Looks like a little bend
finger
– Anchors the biceps
muscle of the arm
– Bounded by the
suprascapular notch (a
nerve passage) medially
and by the glenoid cavity
laterally
Scapula
Scapula
Scapula
• Several large fossae
appear on both sides of
the scapula and are
named according to
location:
– Infraspinous fossa:
inferior to the spine
– Supraspinous fossa:
superior to the spine
– Subscapular fossa:
shallow concavity formed
by the entire anterior
scapular surface
Scapula
Scapula
Upper Limb
• 30 separate bones form the bony
framework of each upper limb
• Each of these bones may be described
regionally as a bone of the arm
(anatomically is the part of the upper limb
between the shoulder and elbow),
forearm, or hand
Arm: Humerus
• Sole bone of the arm
• Typical long bone
• Largest, longest bone
of the upper limb
• Articulates with the
scapula at the shoulder
and with the radius and
ulna (forearm bones) at
the elbow
APPENDICULAR SKELETON
Humerus
•
Proximal end is its smooth,
hemispherical head
– Fits into the glenoid cavity of
the scapula in a manner that
allows the arm to hang freely at
one’s side
•
•
Tubercles (greater, inter, lesser)
are sites where muscles attach
Distal to the tubercles is the
surgical neck
– Named because it is the most
frequently fractured part of the
humerus
– Midway down the shaft on its
lateral side is the deltoid
tuberosity
• Attachment site for the deltoid
muscle of the shoulder
HUMERUS ARM
HUMERUS
Humerus
•
Distal end are two condyles
– Medial trochlea (pulley):
• Articulates with the ulna
– Lateral capitulum (ball-like):
• Articulates with the radius
•
Condyle pair (medial trochlea and
lateral capitulum) are flanked by
the medial and lateral
epicondyles:
– Muscle attachment
– Directly above these epicondyles
are the supracondylar ridges
• Ulnar nerve runs behind the
medial epicondyle and is
responsible for the painful,
tingling sensation you
experience when you hit your
“funny bone” (medial
epicondyle of the humerus)
HUMERUS ARM
Humerus
• Superior to the trochlea on the
anterior surface is the
coronoid fossa
– Posterior surface is the deeper
olecranon fossa
– These two depressions
allow the corresponding
processes of the ulna to
move freely when the elbow
is flexed and extended
• Small radial fossa, lateral to
the coronoid fossa, receives
the head of the radius when
the elbow is flexed
HUMERUS ARM
Forearm
• The forearm is
the region
between the
elbow and wrist
• It consist of two
bones, the ulna
and the radius
FOREARM BONES
Ulna
•
The ulna:
– Proximal end forms the elbow joint
with the humerus
– Distal end forms joints with the wrist
• Articulates with the bones of the
wrist via a cartilage disc at the
distal end
– It articulates with the radius both
proximally and distally at small
radioulnar joints
– Ulna and radius are connected along
their entire length by a flexible
interosseous membrane
– In the anatomical position, the radius
lies laterally (on the thumb side) and
the ulna medially
• However, when you rotate your
forearm so that the palm faces
posteriorly (a movement called
pronation), the distal end of the
radius crosses over the ulna and
the two bones form an X
FOREARM BONES
Ulna
•
•
Main responsibility for forming the elbow
joint with the humerus
Proximally bears two prominent
processes
•
•
–
–
•
•
Olecranon process (elbow):
Coronoid process
Separated by a deep concavity: trochlear
notch
Together these two processes grip the
trochlea of the humerus, forming a hinge
joint that allows the forearm to be bent upon
the arm (flexed), then straightened again
(extended)
On the lateral side of the coronoid
process is a small depression, the radial
notch, where the ulna articulates with the
head of the radius
Distally the ulna ends in a knoblike head:
–
–
–
Separated from the bones of the wrist by a
disc of fibrocartilage
Plays no role in hand movement
Medial to the head is a styloid process,
from which a ligament runs to the wrist
FOREARM BONES
Radius
•
Head is shaped like the head of a nail
–
–
–
•
While the ulna contributes more
heavily to the elbow joint, the radius
is the major forearm bone
contributing to the wrist joint
–
•
Superior surface of this head is
concave, and it articulates with the
capitulum of the humerus
Medially, the head articulates with the
radial notch of the ulna
Inferior to the head is the rough
radial tuberosity, which anchors the
biceps muscle of the arm
When the radius moves, the hand
moves with it
It articulates with the carpels of the
wrist and the ulna medially at the
distal end
FOREARM BONES
RADIUS/ULNA
HOMEOSTATIC IMBALANCE
• Colle’s fracture is a
break in the distal end
of the radius
• Common fracture
when a falling
person attempts to
break his or her fall
with outstretched
hands
FOREARM BONES
Hand
• Skeleton of the hand includes the bones
of:
– The carpus (wrist)
– The metacarpus (palm)
– The phalanges (bones of the fingers)
Carpus
•
The carpus (wrist) consists of eight
marble-size short bones (carpals),
arranged in two irregular rows of four
bones each, closely united by
ligaments:
–
–
Gliding movements occur between
these bones
Quite flexible
•
Proximal row (lateral to medial):
–
–
–
–
•
Distal row (lateral to medial):
–
–
–
–
•
Scaphoid: articulates with the radius to
form the wrist
Lunate: articulates with the radius to
form the wrist
Triquetral
Pisiform Trapezium
Trapezium
Trapezoid
Capitate
Hamate
Sally left the party to take Cathy home
HAND BONES
HOMEOSTATIC IMBALANCE
• The carpus is concave anteriorly and a
ligament roofs over this concavity, forming
the notorious carpal tunnel
– Besides the median nerve (which supplies the lateral
side of the hand), several long muscle tendons crowd
into this tunnel
– Overuse and inflammation of the tendons cause them
to swell, compressing the median nerve, which
causes numbness of the areas served
• Carpal tunnel syndrome
Metacarpus (Palm)
• Radiate from the wrist like
spokes to form the palm of the
hand
• Not named but numbered
– 1 to 5 from thumb to little
finger
• Bases articulate with the
carpals proximally and each
other medially and laterally
• Bulbous heads articulate
with the proximal phalanges
of the fingers
– When you clench your fist,
the heads of the
metacarpals become
prominent as your knuckles
HAND BONES
Phalanges
• Fingers (digits)
• Numbered from 1 to 5
beginning with the thumb
(pollex)
– There are 14 phalanges
(miniature bones) of the
fingers:
• Thumb (pollex) is digit 1,
and has two phalanges
• The other fingers (digits),
numbered 2-5 have three
phalanges each
– Distal
– Middle
– Proximal
HAND BONES
HAND BONES
PELVIC (HIP) GIRDLE
• Attaches the lower limbs to the axial skeleton
• Transmits the weight of the upper body to the
lower limbs
• Supports the visceral organs of the pelvis
• Whereas the pectoral girdle is sparingly
attached to the thoracic cage, the pelvic girdle
is secured to the axial skeleton by some of
the strongest ligaments in the body
• Lacks the mobility of the pectoral girdle but is far
more stable
PELVIC (HIP) GIRDLE
• It is formed by a pair
of coxal bones, each
consisting of three
fused bones; the
ischium, ilium, and
pubis
• Each coxal bone
unites with its
partner anteriorly
and with the sacrum
posteriorly
BONY PELVIS
PELVIC (HIP) GIRDLE
• At the point of fusion of the
ilium, ischium, and pubis is a
deep hemispherical socket
called the acetabulum on the
lateral surface of the pelvis
– The acetabulum receives the
head of the femur, or thigh
bone, at this hip joint
• The deep, basinlike structure
formed by the hip bones,
together with the sacrum
and coccyx, is called the
bony pelvis
BONY PELVIS
ILIUM
• (b): Lateral view of right hip
• (c): medial view of right hip
• Large flaring bone that forms
the superior region of the coxal
bone
– It consists of a body and a
superior winglike portion
called the ala
• When you rest your hands
on your hips, you are
resting them on the
thickened superior margins
of the alae, the tubercle of
the iliac crests
ILIUM
ILIUM
•
•
•
•
(b): lateral right
(c): medial right
Each iliac crest ends anteriorly in the
blunt anterior superior iliac spine and
posteriorly in the sharp posterior
superior iliac spine
– Anterior superior iliac
spine is easily felt
through the skin and is
visible in thin people
– Posterior superior iliac
spine is revealed by a
skin dimple in the
sacral region
• Located below these are the
less prominent anterior and
posterior inferior iliac spines
All of these spines are attachment
points for the muscles of the trunk,
hip, and thigh
ILIUM
ILIUM
• Inferior to the
posterior inferior iliac
spine, the ilium
indents deeply to form
the greater sciatic
notch, through which
the thick cordlike
sciatic nerve passes
to enter the thigh
ILIUM
ILIUM
• Internal surface of the
iliac ala exhibits a
concavity called the iliac
fossa
• It articulates with the
sacrum, forming the
sacroiliac joint, and also
with the ischium and
pubis anteriorly
– Weight of the body is
transmitted from the
spine to the pelvis
through the sacroiliac
joints
BONY PELVIS
Ischium
• (b): lateral right
• (c): medial right
• The ischium forms the
posteroinferior portion of
the coxa (hip bone)
• Roughly L-shaped or arcshaped
• It has a thicker, superior
body adjoining the ilium
and a thinner, inferior
ramus
– Joins the pubis anteriorly
Ischium
Ischium
•
•
(b): lateral right / (c): medial right
Three important markings:
•
Ischial spine:
– Projects medially into the pelvic
cavity and serves as a point of
attachment of the sacrospinous
ligament from the sacrum
Lesser sciatic notch:
– Inferior to the ischial spine
– A number of nerves and blood
vessels pass through this notch to
supply the anogenital area
Ischial tuberosity:
– Inferior surface of the ischial body
– Rough and thickened
– When we sit, our weight is borne
entirely by the ischial tuberosities
• Strongest parts of the hip
bones
•
•
Ischium
Ischium
• A massive ligament runs from the sacrum
to each ischial tuberosity
– This sacrotuberous ligament (not
illustrated) helps hold the pelvis
together
Pubis
•
The pubic bones form the
anterior portion of the coxae
– They are joined by a fibrocartilage
disc, forming the midline pubic
symphysis joint
•
•
In the anatomical position, it
lies nearly horizontally and the
urinary bladder rests upon it
As the two rami of the pubic
bone run laterally to join with
the body and ramus of the
ischium, they define a large
opening in the hip bone, the
obturator foramen through which
a few blood vessels and nerves
pass
– Although it is large, it is nearly
closed by a fibrous membrane in
life
Pubis
• Inferior to the pubic
symphysis joint, the
inferior pubic rami angle
laterally, forming an
inverted V-shaped arch
called the pubic arch
– The acuteness of the
pubic arch helps to
differentiate the male and
female pelvis
– More acute in the males
– Less than 90O (50O-60O)
• Females: 80O – 90O
Pubis
Pelvic Structure and Childbearing
• The female pelvis is modified for
childbearing. It tends to be wider,
shallower, lighter, and rounder than the
male pelvis
– Not only accommodates a growing fetus,
but it must be large enough to allow the
infant’s relatively large head to exit at birth
Pelvic Structure and Childbearing
•
Pelvic brim:
– Continuous oval ridge that runs from
the pubic crest through the arcuate line
and sacral promontory
– Separates: false and true pelvis
• The false (greater) pelvis
superior to the pelvic brim
– Really part of the abdomen
and helps support the
abdominal viscera
– Does not restrict child birth
• The true (lesser) pelvis inferior
to the pelvic brim
– Almost entirely surrounded
by bone
– Its dimensions (inlet and
outlet) are critical to the
uncomplicated delivery of a
baby
– Carefully measured by an
obstetrician
Pelvic Brim
Pelvic Inlet/Outlet
• Pelvic Inlet is the Pelvic
Brim
– Widest dimension is from
right to left along the frontal
plane
– As labor begins, an
infant’s head typically
enters the inlet:
• Forehead facing one
ilium and the occiput
(back part of the skull)
facing the other ilium
– A sacral promontory that
is particularly large can
impair the infant’s entry
into the true pelvis
Pelvic Inlet/Outlet
• Pelvic Outlet:
– Is the inferior margin of the true pelvis
• Bounded anteriorly by the pubic arch, laterally by the ischia,
and posteriorly by the sacrum and coccyx
– Both the coccyx and the ischial spines protrude into the outlet
opening
» A sharply angled coccyx or unusually large ischial spines
can interfere with delivery
• Generally, after the baby’s head passes through the inlet,
it rotates so that the forehead faces posteriorly and the
occiput anteriorly
– Thus, during birth, the infant’s head makes a quarter turn
to follow the widest dimensions of the true pelvis
Pelvic Structure and Childbearing
•
•
Female:
–
–
–
–
–
Tilted forward
Adapted for childbearing
True pelvis defines the birth canal
Cavity of true pelvis is broad, shallow, and
has a greater capacity
Bone thickness:
•
•
•
•
–
–
–
Broader: 80-90O
More rounded
Wider
Shorter
Sacral curvature is accentuated
Coccyx:
•
•
More movable
straighter
Tilted less forward
Adapted for support of a heavier build and
stronger muscles
Cavity of the true pelvis is narrow and deep
Bone thickness:
•
•
•
•
–
–
More acute: 50-60O
Sacrum:
•
•
•
–
Larger
Closer
Pubic arch/angle:
•
–
Greater
Heavier
Thicker
Markings more prominent
Acetabula:
•
•
Sacrum:
•
•
•
–
Smaller
Farther apart
Pubic arch/angle:
•
•
–
–
–
Acetabula:
•
•
–
Less
Lighter
Thinner
Smoother
Male:
Narrow
Longer
Sacral promontory more ventral
Coccyx:
•
•
Less movable
Curves ventrally
HIP BONE
Thigh
• Is the region between the hip and
knee
• It has one bone, the femur
• The femur is the largest, longest,
and strongest bone in the body
–It articulates proximally with the hip
via a ball-like head, and distally with
the knee at the lateral and medial
condyles
Femur
• The ball-like head of the
femur has a small central pit
called the fovea capitis
– The short ligament of the
head of the femur
(ligamentum teres) runs
from this pit to the
acetabulum, where it helps
secure the femur
• The ball-like head is carried
on a neck that angles laterally
to join the shaft
– The neck is the weakest
part of the femur and is
often fractured, an injury
commonly called a
broken hip
THIGH BONE
Femur
• At the junction of
the shaft and neck
are the lateral
greater trochanter
and posteromedial
lesser trochanter
– These projections
serve as sites of
attachment for
thigh and buttock
muscles
Femur
• Distally , the femur broadens
and ends in the wheel-like
lateral and medial condyles,
which articulate with the
tibia of the leg
– Medial and lateral epicondyles
(sites of muscle attachment)
flank the condyles superiorly
• The smooth patellar surface,
between the condyles on the
anterior femoral surface,
articulates with the patella,
or kneecap
Patella
• Is a triangular sesamoid
(short bones embedded
in tendons) bone
enclosed in the
(quadriceps) tendon
that secures the
anterior thigh muscles
to the tibia
– It protects the knee joint
anteriorly and improves
the leverage of the thigh
muscles acting across
the knee
KNEE BONE
THIGH BONE
FEMUR
LOWER LIMB
•
•
•
Leg: The leg is the region between the
knee and ankle. It has two bones, the
tibia and fibula
• These two bones are connected
by an interosseous membrane
and articulate with each other both
proximally and distally
– But unlike the joints
between the radius and ulna
of the forearm, the
tibiofibular joints of the
leg allow essentially NO
movement
The medial tibia articulates proximally
with the femur to form the modified hinge
joint of the knee and distally with the talus
bone of the foot at the ankle
The fibula, by contrast, does not
contribute to the knee joint and merely
helps stabilize the ankle joint
TIBIA/FIBULA
Tibia
•
•
•
•
The tibia (shinbone) receives the
weight of the body from the femur and
transmits it to the foot
It is second only to the femur in size
and strength
At its broad proximal end are the
concave medial and lateral
condyles, which look like two huge
checkers lying side by side
– These are separated by an
irregular projection, the
intercondylar eminence
– The tibial condyles articulate
with the corresponding
condyles of the femur
Inferior to the condyles, the tibia’s
anterior surface displays the rough
tibial tuberosity, to which the patellar
ligament attaches
Tibia
• Shaft is triangular in
cross section
– Its anterior border is the
sharp anterior crest
• Neither this crest nor the
tibia’s medial surface is
covered by muscles, so
they can be felt just
deep to the skin along
their entire length
– The anguish of a
“bumped” shin is an
experience familiar to
nearly everyone
Tibia
• Distally the tibia is flat
where it articulates with
the talus bone of the
foot
– Medial to that joint surface
is an inferior projection, the
medial malleolus, which
forms the medial bulge of
the ankle
– The fibular notch, on the
lateral surface of the
tibia, participates in the
distal tibiofibular joint
Fibula
• Is a sticklike, nonweight-bearing bone
• It has expanded ends that
articulate proximally via
the head and distally via
the lateral malleolus with
the lateral aspects of the
tibia
– The lateral malleolus
forms the conspicuous
lateral ankle bulge and
articulates with the talus
TIBIA/FIBULA
HOMEOSTATIC IMBALANCE
• Pott’s fracture
occurs at the distal
end of the fibula, the
tibia, or both
– Common sports
injury
TIBIA/FIBULA
TIBIA/FIBULA
Foot
• Skeleton of the foot includes the bones of
the:
– Tarsus
– Metatarsus
– Phalanges (toe bones)
• Two important functions:
• 1. Supports our body weight
• 2. Acts as a lever to propel the body
forward when we walk and run
Tarsus
•
•
Consists of seven tarsal bones
that make up the posterior half of
the foot
Body weight is carried primarily
by the two largest, most
posterior tarsals
– Talus: ankle
• Articulates with the tibia and fibula
superiorly
– Calcaneus: heel bone
• Forms the heel of the foot and
carries the talus on its superior
surface
• The thick calcaneal (Achilles)
tendon of the calf muscles
attaches to the posterior surface
of the calcaneus
• The part of the calcaneus that
touches the ground is the tuber
calcanei
FOOT BONES
Tarsus
• Tarsal bones:
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Posterior Talus
Inferior Calcaneus
Lateral Cuboid
Medial Navicular
Anterior medial cunieform
Anterior intermediate
cunieform
– Anterior lateral cunieform
• The cuboid and
cunieform bones
articulate with the
metatarsal bones
anteriorly
FOOT BONES
Metatarsus
• The metatarsus consists of five
small, long bones called
metatarsal bones which
number 1 to 5 beginning on
the medial (great toe) side of
the foot
• First metatarsal is short and
thick and plays an important
role in supporting body
weight
• Distally, where the metatarsals
articulate with the proximal
phalanges of the toes, the
enlarged head of the first
metatarsal forms the “ball” of
the foot
FOOT BONES
Phalanges (Toes)
• There are 14 phalanges
of the toes:
• Smaller than those of the
fingers and thus are less
nimble
• There are three
phalanges in each digit
except for the great toe
(hallux)
– The great big toe (hallux)
is digit 1 and has two
phalanges
– The other toes,
numbered 2-5, have three
phalanges each
FOOT BONES
Arches of the Foot
• A segmented structure can
hold up weight ONLY if it is
arched
• Foot has three arches: account
for its awesome strength
– Two longitudinal:
• Medial arch
• Lateral arch
– One transverse arch
• The arches of the foot are
maintained by:
– Interlocking shapes of the foot
bones
– Strong ligaments
– Pull of some tendons during
muscle activity
FOOT ARCHES
Arches of the Foot
• Ligaments and muscle tendons provide
a certain amount of springiness
• Arches give or stretch slightly when
weight is applied to the foot and spring
back when the weight is removed,
which makes walking and running more
economical in terms of energy use than
would otherwise be the case
Arches of the Foot
• If you examine your wet
footprint, you will see that the
medial margin from the heel to
the head of the first
metatarsal leaves no print
– This is because the MEDIAL
LONGITUDINAL ARCH
curves well above the
ground
– The talus is the keystone of
this arch, which originates
at the calcaneus, rises to
the talus, and then
descends to the three
medial metatarsals
FOOT ARCHES
FOOT BONES
Arches of the Foot
• Lateral longitudinal
arch:
– Is very low
– It elevates the lateral part
of the foot just enough to
redistribute some of the
weight to the calcaneus
and the head of the fifth (5)
metatarsal (to the ends of
the arch)
• Cuboid is the keystone
bone of this arch
FOOT ARCHES
FOOT BONES
Arches of the Foot
• The two longitudinal
arches (medial and
lateral) serve as pillars
for the transverse arch,
which runs obliquely
from one side of the
foot to the other,
following the line of the
joints between the tarsals
and metatarsals
Arches of the Foot
• Together, the arches
of the foot form a
half-dome that
distributes about
half our standing
and walking weight
to the heel bones
and half to the
heads of the
metatarsals
HOMEOSTATIC IMBALANCE
• Standing immobile for extended periods
places excessive strain on the tendons
and ligaments of the feet (because
muscles are inactive) and can result in
fallen arches, or “flat feet,” particularly if
one is overweight
• Running on hard surfaces can also
cause arches to fall unless one wears
shoes that give proper arch support
DEVELOPMENTAL ASPECTS
OF
THE SKELETON
• Membrane bones of the skull begin to ossify late in the
second month of development
• At birth, skull bones are connected by fontanels,
unossified remnants of fibrous membranes
• Changes in cranial-facial proportions and fusion of bones
occur throughout childhood
– At birth, the cranium is much larger than the face, and several
bones are still unfused
– By nine months, the cranium is half the adult size due to rapid
brain growth
– By age 8-9, the cranium has reached almost adult proportions
– Between ages 6-13, the jaws, cheekbones, and nose become
more prominent, due to expansion of the nose, paranasal
sinuses, and development of permanent teeth
FETAL SKULL
DEVELOPMENTAL ASPECTS
OF
THE SKELETON
• Curvatures of the Spine
– The primary curvatures (thoracic and sacral
curvatures) are convex posteriorly and are
present at birth
– The secondary curvatures (cervical and
lumbar curvatures) are convex anteriorly and
are associated with the child’s development
– The secondary curvatures result from
reshaping the intervertebral disc
DEVELOPMENTAL ASPECTS
OF
THE SKELETON
• Changes in body height and proportion
occur throughout childhood
– At birth, the head and trunk are roughly 1 ½
times the length of the lower limbs
– The lower limbs grow more rapidly than the
trunk, and by age 10, the head and trunk are
about the same length as the lower limbs
– During puberty, the female pelvis widens and
the male skeleton becomes more robust
GROWTH RATES
DEVELOPMENTAL ASPECTS
OF
THE SKELETON
• Effects of age on the skeleton
– The intervertebral discs become thinner, less
hydrated, and less elastic
– The thorax becomes more rigid, due to
calcification of the costal cartilages
– All bones lose bone mass
HOMEOSTATIC IMBALANCE
• Cleft Palate:
– Condition in which the right and left halves of
the palate fail to fuse medially
• Dysplasia of the hip:
– Acetabulum forms incompletely or the
ligaments of the hip joint are loose, so the
head of the femur slips out of its socket