7 The Skeleton: Part A

The skeleton accounts of 20% of body mass Introduction The skeleton accounts of 20% of body mass There are 206 bones in the human skeleton Ligaments –band of fibrous tissue that connects bones Divisions of the Skeleton Axial Skeleton and Appendicular

Contains of 80 bones that collectively form the axis of the body trunk The Axial Skeleton Contains of 80 bones that collectively form the axis of the body trunk Protect the brain and spinal cord and organs within the thoracic cavity Three major regions of the axial skeleton Skull Vertebral column Thoracic cage Hyoid

Cranium Skull Facial bones Clavicle Thoracic cage Scapula (ribs and sternum) Scapula Sternum Rib Humerus Vertebra Vertebral column Radius Ulna Sacrum Carpals Phalanges Metacarpals Femur Patella Tibia Fibula Tarsals Metatarsals (a) Anterior view Phalanges Figure 7.1a

General Characteristics The Skull General Characteristics Composed of: cranial and facial bones Cranial bones enclose and protect the brain Facial bones form the framework of the face, contain cavities for special sense organs, provide openings for food & air, secure teeth, anchor facial muscles Most bones of the skull are: paired

Bones of cranium (cranial vault) Coronal suture Squamous suture Lambdoid suture Facial bones (a) Cranial and facial divisions of the skull Figure 7.2a

Major Sutures of the Skull Four sutures mark the articulations of parietal bones with frontal, occipital, and temporal bones: Coronal (frontal) suture—between parietal bones and frontal bone Sagittal suture—between right and left parietal bones Lambdoid suture—between parietal bones and occipital bone Squamous suture—between parietal and temporal bones on each side of skull

Coronal suture Lambdoid suture Squamous suture Frontal bone Sphenoid bone (greater wing) Parietal bone Temporal bone Lambdoid suture Squamous suture Occipital bone (a) External anatomy of the right side of the skull Figure 7.5a

Sagittal suture Parietal bone Lambdoid suture Occipital bone Superior nuchal line External occipital protuberance Occipital condyle (b) Posterior view Figure 7.4b

Calvaria – Cranial vault “skull cap” The Skull Calvaria – Cranial vault “skull cap” Cranial Base (floor) of the skull is divided into three regions: Anterior cranial fossa-accommodates the frontal lobes of brain Middle cranial fossa- accomodates the temporal lobes Posterior cranial fossa-deepest region houses cerebellum

(b) Superior view of the cranial fossae Anterior cranial fossa Middle cranial fossa Posterior cranial fossa (b) Superior view of the cranial fossae Figure 7.2b

Four pair of cavities within the skull bones called: paranasal sinuses The four pair are: Sphenoid Ethmoid Maxillary Frontal Each cavity is lined with mucous membranes that form mucus, which drains into the nasal cavity

Frontal sinus Frontal sinus Ethmoidal air cells (sinus) Ethmoidal Sphenoid sinus Sphenoid sinus Maxillary sinus Maxillary sinus (a) Anterior aspect (b) Medial aspect Figure 7.15

The Orbits Composed of: Cranial and facial bones; 7 bones in each orbit –frontal, sphenoid, zygomatic, maxilla, palatine, lacrimal, and ethmoid

• Lesser wing of sphenoid bone Superior orbital fissure Roof of orbit Supraorbital notch Optic canal • Lesser wing of sphenoid bone • Orbital plate of frontal bone Medial wall • Sphenoid body Lateral wall of orbit • Orbital plate of ethmoid bone • Zygomatic process of frontal bone • Frontal process of maxilla • Greater wing of sphenoid bone • Lacrimal bone • Orbital surface of zygomatic bone Nasal bone Floor of orbit Inferior orbital fissure Infraorbital groove • Orbital process of palatine bone Zygomatic bone • Orbital surface of maxillary bone Infraorbital foramen • Zygomatic bone (b) Contribution of each of the seven bones forming the right orbit Figure 7.13a

The Nasal Cavity The roof, superior/lateral walls and superior portion of the nasal septum are formed by: the ethmoid bone The floor is formed anteriorly by the palatine processes of the maxillae and the palatine bones The cavity is divided into right and left halves by the nasal septum

(perpendicular plate) Palatine bone (horizontal plate) Frontal sinus Superior nasal concha Ethmoid bone Middle nasal concha Inferior nasal concha Nasal bone Sphenoid bone Maxillary bone (palatine process) Palatine bone (perpendicular plate) Palatine bone (horizontal plate) Figure 7.14a

The Nasal Cavity Nasal conchae- on the lateral walls: formed by the superior and middle nasal conchae of ethmoid bone The conchae and septum are lined with a mucus secreting mucosa that moistens & warms air, helps cleanse it of debris Cribriform plate –porous superior surface of ethmoid for passage of olfactory fibers (smell)

Crista galli Olfactory foramina Cribriform plate Perpendicular plate Middle nasal concha Figure 7.10

General Characteristics The Vertebral Column General Characteristics Contains 33 vertebrae, some of which are fused in adults Intervertebral discs- Inner part Nucleus pulposus- gelatinous nucleus that gives the disc its elasticity and compressibility

The Vertebral Column Outer part Anulus fibrosus- Outer collar composed of collagen and fibrocartilage Herniated disc – usually involves rupture of the anulus fibrosus followed by protrusion of the spongy nucleus pulposus through the anulus

Intervertebral disc Anulus fibrosus Nucleus pulposus Median section of three vertebrae, illustrating the composition of the discs and the ligaments Figure 7.17a

(c) Superior view of a herniated intervertebral disc Spinal cord Herniated portion of disc Anulus fibrosus of disc Nucleus pulposus of disc (c) Superior view of a herniated intervertebral disc Figure 7.17c

Vertebral Column: Curvatures Increase the resilience and flexibility of the spine Four normal curvatures Two primary curvatures- Thoracic and sacral Born with primary curvatures Two secondary curvatures- Cervical and lumbar Develop after birth

Figure 7.37

The Appendicular Skeleton Characteristics Includes: The upper and lower limbs and their girdles (pectoral and pelvic girdle)

Comparison of Male and Female Pelves The true pelvis is: the region inferior to the pelvic brim containing pelvic organs The pubic angle is 80-90 degrees in females and 50-60 degrees in males The acetabula are: smaller and farther apart in females and larger and closer together in males

Animation: Rotatable pelvis Base of sacrum Iliac crest Sacroiliac joint Iliac fossa Anterior superior iliac spine Sacral promontory Coxal bone (os coxae or hip bone) Anterior inferior iliac spine llium Sacrum Pubic bone Pelvic brim Coccyx Acetabulum Pubic tubercle Ischium Pubic crest Pubic symphysis Pubic arch PLAY Animation: Rotatable pelvis Figure 7.29

Table 7.4

Table 7.4

Frontal bone Glabella Parietal bone Frontonasal suture Supraorbital foramen (notch) Squamous part of frontal bone Supraorbital margin Nasal bone Superior orbital fissure Sphenoid bone (greater wing) Optic canal Temporal bone Inferior orbital fissure Ethmoid bone Lacrimal bone Middle nasal concha Zygomatic bone Ethmoid bone Infraorbital foramen Perpendicular plate Maxilla Inferior nasal concha Mandible Vomer Mental foramen (a) Anterior view Mandibular symphysis Figure 7.4a

Intermaxillary suture Hard palate Palatine bone (horizontal plate) (palatine process) Incisive fossa Intermaxillary suture Hard palate Palatine bone (horizontal plate) Median palatine suture Infraorbital foramen Maxilla Zygomatic bone Sphenoid bone (greater wing) Temporal bone (zygomatic process) Foramen ovale Vomer Foramen spinosum Foramen lacerum Mandibular fossa Carotid canal External acoustic meatus Styloid process Stylomastoid foramen Mastoid process Temporal bone (petrous part) Jugular foramen Occipital condyle Pharyngeal tubercle of basilar region of the occipital bone Inferior nuchal line Parietal bone Superior nuchal line External occipital crest External occipital protuberance Foramen magnum (a) Inferior view of the skull (mandible removed) Figure 7.6a