Download The Skeleton

The Skeleton
Axial Skeleton
 Structured from 80 bones segregated into three
major regions
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The skull
Vertebral column
Bony thorax
 This part of the skeleton supports the head, neck,
and trunk and it protects the brain, spinal cord, and
the organs in the thorax
The Skull
 The skull is the body’s most complex bony structure
 Formed by cranial and facial bones
 The cranial bones or cranium, enclose and protect the
fragile brain and are an attachment site for the head and
neck muscles
 Most skull bones are flat except for the mandible, which
is connected by a freely moving joint
 All bones of the adult skull are connected by interlocking
joints called sutures.
 Major skull sutures are
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Coronal sagittal, squamous, and lambdoid sutures
Cranium
 8 cranial bones: paired parietal, temporal bones,
unpaired frontal, occipital, phenoid and ethmoid
bones
 Frontal bone forms the anterior portion of the
cranium
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The frontal squama is commonly called the forehead
The frontal squama ends at the supraorbital margins, the
thickened margins of the orbits that lie under the eyebrows
Parietal Bones and Major Sutures
 The two large parietal bones are curves, rectangular
bones that form most of the superior and lateral
aspects of the skull
 The 4 largest sutures are:
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Coronal suture, where the parietal bones meet the frontal bone
anteriorly
Sagittal suture, where the right and left parietal bones meet
superiorly at the cranial midline
Lamboid suture, where the parietal bones meet the occipital
bone posteriorly
Squamous suture, where a parietal and temporal bone meet on
the lateral aspect of the skull
Occipital Bone
 Forms most of the skull’s posterior wall and base
 Internally it forms the walls of the posterior cranial
fossa, which supports the cerebellum
 Foramen magnum: is located at the base of the
occipital bone
 Occipital condyles: flank the foramen magnum and
articulate with the first vertebrae
 Hypoglossal canal: a nerve with the same name
passes through
Temporal Bones
 2 temporal bones are best viewed on the lateral skull
surface, they lie inferior to the parietal bones and
meet them at the squamous sutures
 4 major regions:
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Squamous region- contains the zygomatic process and
Zygomatic arch- (cheekbone) formed by the squamous region
and the zygomatic process
Tympanic region- surrounds the external ear canal
Mastoid region- anchoring site for neck muscles
Petrous region- contributes to the cranial base
Sphenoid Bone
 Butterfly-shaped bone that spans the width of the
middle cranial fossa
 Forms the central wedge that articulates with all
other cranial bones
Sphenoid Bone
 Central body: consists of sphenoid sinuses and
hypophyseal fossa
 Greater wings: project laterally from the body
forming, middle cranial fossa, dorsal walls of orbits,
external wall of skull
 Lesser wings: form part of the floor of the anterior
cranial fossa, trough shaped pterygoid processes
project inferiorly
 Optic canals
Ethmoid Bone
 Most deep of the skull bones; lies between the
sphenoid and nasal bones
 Forms most of the bony area between the nasal
cavity and the orbits
 Major landmarks:
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Cribriform plate-form the roof of the nasal cavities
Crista galli- triangular process
Perpendicular plate-forms superior part of the nasal septum
Facial bones
 Fourteen bones of which only the mandible and
vomer are unpaired
 The paired bones are the maxillae, zygomatics,
nasals, lacrimals, palatines, and inferior conchae
 Women’s faces tend to be rounder and less angular
Mandible
 U-shaped, lower jaw bone
 Strongest bone of the face
 Has a body that forms the chin and two upright rami
(branches)
 Major landmarks are: mandibular notch, coronoid
process, mandibular condyle, alveolar margin,
mandibular foramina
Maxillary Bones
 Medially fused bones that make up the upper jaw
and the central portion of the facial skeleton
 Facial keystone bones that articulate with all other
facial bones except the mandible
 Carry the upper teeth
Zygomatic Bones
 Irregularly shaped bones (cheekbones) that form the
prominences of the cheeks and the inferolateral
margins of the orbits
Facial Bones Cont’d
 Nasal bones: thin, rectangular bones fused medially,
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forming the bridge of the nose
Lacrimal bones: contribute to the medial walls of
each orbit frontal bone superiorly
Palatine bones: L-shaped, formed from two bony
plates
Vomer: slender, plow-shaped, lies in the nasal cavity
where it forms part of the nasal sptum
Inferior nasal conchae: thing, curved bones in the
nasal cavity
Orbit Cavity
 Orbits are bony cavities within which the eyes are
firmly encased and cushioned by fatty tissue
Nasal Cavity
 Constructed of bone and hyaline cartilage
 Roof–formed by the cribriformplate of the ethmoid
 Lateral walls –formed by the superior and middle conchaeof
the ethmoid, the perpendicular plate of the palatine, and the
inferior nasal conchae
 Floor–formed by palatine process of the maxillae and palatine
bone
Paranasal Sinuses
 Mucosa-lined, air-filled sacs found in five skull bones
–the frontal, sphenoid, ethmoid, and paired
maxillary bones
 Air enters the paranasal sinuses from the nasal cavity
and mucus drains into the nasal cavity from the
sinuses
 Lighten the skull and enhance the resonance of the
voice
Vertebral Column
 Also called the spine, backbone, or spinal column
 Functions to:
 Protect the spinal cord
 Support the head
 Serve as a point of attachment for the ribs, pelvic girdle,
and muscles
 The vertebral column is curved to varying degrees
in different locations
Curves increase the column strength
 Help maintain balance in the upright position
 Absorb shocks during walking, and help protect the
vertebrae from fracture
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Vertebral Column
 Composed of a series of bones called vertebrae
(Adult=26)
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7 cervical are in the neck region
12 thoracic are posterior to the thoracic cavity
5 lumbar support the lower back
1 sacrum consists of five fused sacral vertebrae
1 coccyx consists of four fused coccygeal vertebrae
 Intervertebral Discs: cushion-like pad composed of
two parts
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Nuclues pulposus and annulus fibrous
Act as shock absorbers during walking, jumping, running
and allow spine to flex and extend
Vertebrae Regions
 Cervical Region
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Cervical vertebrae (C1–C7)
The atlas (C1) is the first cervical vertebra
The axis (C2) is the second cervical vertebra
 Thoracic Region
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Thoracic vertebrae (T1–T12)
Articulate with the ribs
 Lumbar Region
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Lumbar vertebrae (L1–L5)
Provide for the attachment of the large back muscles
 Sacrum
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The sacrum is a triangular bone formed by the union of five sacral vertebrae
(S1–S5)
Serves as a strong foundation for the pelvic girdle
 Coccyx
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The coccyx, like the sacrum, is triangular in shape
It is formed by the fusion of usually four coccygeal vertebrae
Bony Thorax
Thorax
 Sternum
 “Breastbone” located in the center of the thoracic
wall
 Consists of the manubrium, body, xiphoid
process
 Ribs
 Twelve pairs of ribs give structural support to the
sides of the thoracic cavity
 Costal cartilages
 Costal cartilages contribute to the elasticity of the
thoracic cage
Appendicular Skeleton
 Bones of the limbs and their girdles because they are
appended to the axial skeleton that forms the
longitudinal axis of the body.
 Consists of the pectoral girdle, free upper limb,
pelvic girdle, lower limbs
Pectoral (Shoulder) Girdle
 Composed of two bones
 Clavicle—collarbone
 Scapula—shoulder blade
 These bones allow the
upper limb to have
exceptionally free
movement
Scapula
Upper Limb
 Humerus
 Forms the arm
 Single bone
Upper Limb
 The forearm has two bones
 Ulna
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Medial bone in anatomical position
Radius
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Lateral bone in anatomical position
Upper Limb
 The hand
 Carpals—wrist
 Metacarpals—palm
 Phalanges—fingers
Pelvic (Hip) Girdle
 Formed by two coxal (ossa coxae) bones
 Composed of three pairs of fused bones
 Ilium
 Ischium
 Pubis
 The total weight of the upper body rests on the pelvis
 It protects several organs
 Reproductive organs
 Urinary bladder
 Part of the large intestine
The Pelvis
Gender Difference in Pelvis
 The female inlet is larger and more circular
 The female pelvis as a whole is shallower, and the
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bones are lighter and thinner
The female ilia flare more laterally
The female sacrum is shorter and less curved
The female ischial spines are shorter and farther
apart; thus the outlet is larger
The female pubic arch is more rounded because the
angle of the pubic arch is greater
 Male
Female
Lower Limbs
 The thigh has one bone
 Femur
The longest, largest,
strongest bone in the body
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Lower Limb
 The lower leg has two bones
 Tibia
Shinbone
 Larger and medially oriented
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Fibula
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Thin and sticklike
Lower Limb
 The foot
 Tarsals
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Two largest tarsals
 Calcaneus (heelbone)
 Talus
Metatarsals—sole
Phalanges—toes
Arches of the foot
 Bones of the foot are arranged to form three strong
arches
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Two longitudinal
One transverse