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Skeletal System
Axial Skeleton
The Axial Skeleton
• Eighty bones segregated into three regions– Skull– Vertebral column– Bony thorax
Bones of the Axial Skeleton
Figure 7.1
The Skull
• The skull=the cranium and facial bones – Cranium – protects the brain and is the site of
attachment for head and neck muscles• Eight cranial bones – two parietal, two temporal,
frontal, occipital, sphenoid, and ethmoid
– Facial bones• Supply the framework of the face, the sense organs,
and the teeth• Provide openings for the passage of air and food• Anchor the facial muscles of expression
Frontal Bone & Major Markings
Figure 7.2a
Parietal Bones and Major Associated Sutures
• Four sutures mark the articulations of the parietal bones – Coronal suture – between parietal and frontal
bones– Sagittal suture – where right and left parietal
bones meet – Lambdoid suture – between parietal and occipital
bones– Squamosal or squamous suture – between parietal
and temporal bones
Major Sutures
Figure 7.3a
Occipital Bone & Major Markings
Figure 7.2b
Temporal Bones
Figure 7.5
Temporal Bone & Major Markings
Figure 7.3a
(a)
External acoustic meatus
Mastoid process
Styloid process
Zygomatic process
Temporal bone
Sphenoid Bone
• Butterfly-shaped bone that spans the width of the middle cranial fossa (depression)
• Forms the central wedge that articulates with all other cranial bones
Sphenoid Bone
Figure 7.6a
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
Ethmoid Bone
Figure 7.7
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
Mandible and Its Markings
Figure 7.8a
Maxillary Bones
• Medially fused bones that make up the upper jaw and the central portion of the facial skeleton
Zygomatic Bones
• Irregularly shaped bones (cheekbones) that form the prominences of the cheeks and the inferolateral margins of the orbits
Anterior Aspects of the Skull
Figure 7.2a(a)
Parietal bone
Nasal bone
Sphenoid bone(greater wing)Temporal bone
Ethmoid bone
Lacrimal bone
Zygomatic bone
Maxilla
Mandible
Mentalforamen
Frontal bone
Glabella
Middle nasal conchaPerpendicular plate
Inferior nasal concha
Vomer bone
Ethmoidbone
Hyoid Bone
• Not actually part of the skull– lies just inferior to the mandible in the anterior
neck• Only bone of the body that does not articulate
directly with another bone
• Attachment point for neck muscles that raise and lower the larynx during swallowing and speech
THORACIC CAGE
Bony Thorax (Thoracic Cage)
• The thoracic cage is composed of– the thoracic vertebrae dorsally, – the ribs laterally, – and the sternum and costal cartilages anteriorly
Bony Thorax (Thoracic Cage)
• Functions– Forms a protective cage around the heart, lungs,
and great blood vessels
– Supports the shoulder girdles and upper limbs
– Provides attachment for many neck, back, chest, and shoulder muscles
– Uses intercostal muscles to lift and depress the thorax during breathing
Bony Thorax (Thoracic Cage)
Figure 7.19a
Sternum (Breastbone)
• A dagger-shaped, flat bone that lies in the anterior midline of the thorax
• Anatomical landmarks include– the jugular (suprasternal) notch, – the manubrium, – the sternal angle, – the xiphoid process – and the xiphisternal joint
Ribs
• There are twelve pair of ribs forming the flaring sides of the thoracic cage
• All ribs attach posteriorly to the thoracic vertebrae
• The superior 7 pair (true, or vertebrosternal ribs) attach directly to the sternum via costal cartilages
Ribs (continued)
• Ribs 8-12 (false, or vertebrocondral ribs) attach indirectly to the sternum via costal cartilage
– Ribs 11-12 (floating, or vertebral ribs) have no anterior attachment
Structure of a Typical True Rib
• Bowed, flat bone consisting of a head, neck, tubercle, and shaft
Figure 7.20a
Structure of a Typical True Rib
Figure 7.20b
Vertebral Column
Vertebral Column
• Formed from 26 irregular bones (vertebrae) connected in such a way that a flexible curved structure results– Cervical vertebrae – 7 bones of the neck– Thoracic vertebrae – 12 bones of the torso– Lumbar vertebrae – 5 bones of the lower back– Sacrum – 5 fused bones inferior to the lumbar
vertebrae that articulates with the hip bones– Coccyx-4 fused bones that make up the “tailbone”
Vertebral Curvature
• Spine has an sinusoid (or “s”) shape due to curvature– Concave (posteriorly)=cervical and lumbar– Convex (posteriorly)=thoracic and sacral– Allows it to act like a spring when walking upright• Provides flexibility and resiliency
• At birth, spine curved out like 4 legged animals
Vertebral Column
Figure 7.13
Intervertebral Discs
• Act as shock absorper
• Cushion-like pad composed of two parts– Nucleus pulposus:• inner gelatinous center • gives the disc its elasticity and compressibility
– Annulus fibrosus:• surrounds the nucleus pulposus with a collar composed of
collagen and fibrocartilage
Intervertebral Discs
• As one gets older, discs become thinner & more rigid– Causes slight decrease in height– More herniated discs occur– Return to baby curvature of spine (“hump”)
• Herniated Disc (slipped disc):– Nucleus pulposus bulges out past annulus fibrosus– Painful if presses on spinal cord or nerve
Regional Characteristics of Vertebrae
Table 7.2.1
General Structure of Vertebrae
Figure 7.15
Regional Characteristics of Vertebrae
Table 7.2.2
Cervical
• “neck”
• Atlas & Axis (1st 2 vertebra)– Modified to rotate• No intervertebral disc between them
• Atlas “carries” skull (like Atlas of Greek mythology carries the world)– Articulating surfaces allow head to move up and down (“yes”)
• Altas rotates around dens of axis– Rotates head side to side (“no”)
Thoracic Vertebrae
Figure 7.17b
Thoracic and Lumbar Vertebra
• Thoracic:– Attach to ribs– Larger spines for muscle attachments
• Lumbar:– “lower back”– Thicker and well connected for support & stability
Lumbar Vertebrae
Figure 7.17c
Sacrum and Coccyx
• Sacrum:– Bones fuse as develop– Makes up posterior of pelvis
• Coccyx:– “tailbone”– Bones fuse as develop
Sacrum and Coccyx: Anterior View
Figure 7.18a