Chapter 7 - The Skeletal System The Axial Skeleton PDF

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BIOL 235: Chapter 7 – The Skeletal System: The Axial Skeleton 

Musculoskeletal system: integrated system consisting of the bones, muscles, and joints

7.1: Divisions of the Skeletal System: 

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Axial skeleton: consists of the bones that lie around the longitudinal axis (vertical) of the body - skull: cranium and face; hyoid bone; auditory ossicles; vertebral column; thorax: sternum and ribs Appendicular skeleton: consists of the bones of the upper and lower limbs (extremities or appendages) and the bones forming the girdles that connect the limbs to axial skeleton - pectoral (shoulder) girdles: clavicle and scapula; upper limbs: humerus, ulna, radius, carpals, metacarpals, phalanges; pelvic (hip) girdles: hip, pelvic, or coxal bone; lower limbs: femur, patella, tibia, fibula, tarsals, metatarsals, phalanges

7.2: Types of Bones:  

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Long, short, flat, irregular, and sesamoid Long bones: have greater length than width, and consist of a shaft and variable number of extremities or epiphyses; slightly curved for strength - consist mostly of compact bone tissue in their diaphysis, but have some spongy bone tissue in their epiphyses - femur, tibia, fibula, humerus, ulna, radius, phalanges Short bones: cube-shaped; nearly equal in length and width; mostly spongy tissue with a layer of compact bone - carpal (wrist), tarsal (ankle) Flat bones: thin; two parallel plates of compact bone enclosing a layer of spongy bone - cranial bones, sternum, ribs, scapulae (shoulder bones) Irregular bones: complex shapes and vary in amounts of compact or spongy bone - vertebrae (backbones), hip bones, certain facial bones, calcaneus Sesamoid bones: develop in certain tendons where there is considerable friction, tension, and physical stress - palms, soles - exception is two patellae (kneecaps) Sutural bones: classified by location; small bones located in sutures (joints) between certain cranial bones

7.3: Bone Surface Markings: 

Surface markings: structural features adapted for specific functions - two major types: depression and openings, and processes

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Depression and Openings: Sites allowing the passage of soft tissue (nerves, blood vessels, ligaments, tendons), or formation of joints

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- fissure: narrow slit between adjacent parts of bones which blood vessels or nerves pass - foramen: opening through which blood vessels, nerves, or ligaments pass - fossa: shallow depression - sulcus: furrow along bone surface that accommodates blood vessel, nerve, or tendon - meatus: tubelike opening Processes: Projections or outgrowths on bone that form joints or attachment points for connective tissue, such as ligaments and tendons 1st three: processes that form joints - condyle: large, round protuberance with a smooth articular surface at end of bone - facet: smooth, flat, slightly concave or convex articular surface - head: usually rounded articular projection supported on neck (constricted portion) of bone 2nd seven: processes that form attachment points for connective tissue - crest: prominent ridge or elongated projection - epicondyle: typically roughened projection above condyle - line: long, narrow ridge or border (less prominent than crest) - spinous process: sharp, slender projection - trochanter: very large projection - tubercle: variably sized rounded projection - tuberosity: variably sized projection that has a rough, bumpy surface

7.4: Skull:  

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Skull: bony framework of the head; grouped into two categories, cranial and facial Cranial bones: form the cranial cavity, which encloses and protects the brain - frontal bone, two parietal bones, two temporal bones, the occipital bone, the sphenoid bone, the ethmoid bone Facial bones: form the face - two nasal bones, two maxillae, two zygomatic bones, the mandible, two lacrimal bones, two palatine bones, two inferior nasal conchae, the vomer

Exhibit 7.A: Cranial Bones – Frontal Bone:  

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Frontal bone: forms the forehead (anterior part of cranium), the roofs of the orbit (eye socket), and most of the anterior part of the cranial floor Supraorbital margin: where the frontal bone thickens at the superior border of the orbits (eye sockets) - slightly medial to this margin is the supraorbital foramen: hole near the margin Frontal sinuses: mucous membrane-lined cavity deep to the frontal squama

Exhibit 7.B: Cranial Bones – Parietal Bones: 

Two parietal bones: form the greater portion of the sides and roof of the cranial cavity

Exhibit 7.C: Cranial Bones – Temporal Bones: 

Temporal bones: form the interior lateral aspects of the cranium and part of the cranial floor

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Temporal squama: thin, flat part of the temporal bone that forms the anterior and superior part of the temple Zygomatic process: articulates (forms a joint) with the temporal process of the zygomatic (cheek) bone - projects from inferior portion of temporal squama Zygomatic arch: where the zygomatic process and the temporal process of the zygomatic bone form Mandibular fossa: sockets located on the inferior posterior surface of the zygomatic process of each temporal bone - this and articular tubercle articulate with mandible (jaw) Mastoid process: rounded projection of the mastoid portion of the temporal bone posterior and inferior to the external auditory meatus; serves as attachment for several neck muscles Inner auditory meatus: opening through which the facial (VII) nerve and vestibulocochlear (VIII) pass Styloid process: projects inferiorly from the inferior surface of the temporal bone and serves as point of attachment for muscles and ligament of the tongue and neck

Exhibit 7.D: Cranial Bones – Occipital Bone:   

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Occipital bone: forms the posterior part and most of the base of the cranium Foramen magnum: in the inferior part of the bone; connects with the spinal cord Occipital condyles: oval processes with convex surfaces on either side of the foramen magnum - articulates with depression on first cervical vertebrae forming atlanto-occipital joint (allows you to nod) External occipital protuberance: prominent midline projection on the posterior surface of the bone just above the foramen magnum

Exhibit 7.E: Cranial Bones – Sphenoid Bone: 

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Sphenoid bone: lies at the middle part of the base of the skull - articulates with all other cranial bones, holding them together - forms part of the floor, sidewalls, and rear wall of orbits (eye sockets) Sella turcica: bony, saddle-shaped structure on the superior surface of the body of the sphenoid Optic foramen or canal: where the optic (II) nerve and ophthalmic artery pass into the orbit - found between the body and lesser wing just anterior to the Sella turcica

Exhibit 7.F: Cranial Bones – Ethmoid Bone: 

Ethmoid bone: a delicate bone located in the anterior part of the cranial floor medial to the orbits and is spongelike in appearance - anterior to sphenoid and posterior to nasal bones - forms: part of the anterior portion of the cranial floor, the superior portion of the nasal septum, the medial walls of the orbits, and most of the superior sidewalls of the nasal cavity

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Superior nasal concha and middle nasal concha (turbinate): thin, scroll-shaped projections lateral to the nasal septum found in the lateral masses of the ethmoid bone Conchae: increase vascular and mucous membrane surface area in the nasal cavity, warms and moistens inhaled air, causes inhaled air to swirl and many inhaled particles become trapped in the mucus that lines the nasal cavity

Exhibit 7.G: Facial Bones – Nasal, Lacrimal, Palatine, Inferior Nasal Conchae, Vomer, Maxillae, Zygomatic, and Mandible: 

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Nasal bones: (2) small, flattened, rectangular-shaped bones that form the bridge of the nose - protect the upper entry to the nasal cavity and provide attachment for a couple of thin muscles of facial expression Lacrimal bones: (2) thin and roughly resemble a fingernail in size and shape (smallest of the face) - posterior and lateral to the nasal bones, form a part of medial wall of each orbit Palatine bones: (2) form the posterior portion of the hard palate, part of the floor and later wall of the nasal cavity, and a small portion of the floors of the orbits Inferior nasal conchae: (2) separate bones not part of the ethmoid bone - scroll-like bones that form a part of the inferior lateral wall of the nasal cavity and project into the nasal cavity - increase surface area of nasal cavity, swirls, and filters air Vomer: roughly triangular bone on the floor of the nasal cavity that forms the inferior portion of the bony nasal septum, the partition that divides the nasal cavity into right or left sides Maxillae: (2) bones that form the upper jawbone and articulate with every bone in the face except the mandible (lower jawbone) - forms most of hard palate: bony roof of the mouth that separates nasal cavity from oral cavity - each maxilla contains maxillary sinus that empties into the nasal cavity - infraorbital foramen: an opening in the maxilla inferior to the orbit, which also passage of the infraorbital blood vessels and nerve Zygomatic bones: (2) bones commonly called cheekbones, form the prominences of the cheeks and part of the lateral wall and floor of each orbit - articulate with the frontal, maxilla, sphenoid, and temporal bones - zygomatic arch: where the temporal process of the zygomatic bone articulates with the zygomatic process of the temporal bone Mandible: or lower jawbone, is largest and strongest facial bone - consists of a curved, horizontal portion called the body - and two perpendicular portions called the rami - the two angles are where the body and each ramus means (point of jawline) - each ramus has: condylar processes that are joint with mandibular fossa and articular tubercle forming the temporomandibular joint (TMJ) and coronoid processes: where the temporalis muscle attaches

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- alveolar process: ridgelike arch containing the alveoli (sockets) for the mandibular (lower) teeth Joints called sutures attach most of the skull bones together and are especially noticeable on the outer surface of the skull Nasal septum: consists of bone and cartilage; it is the vertical partition in the naval cavity that divides the left and right sides Orbits: eye sockets (orbital cavity) that holds the eyeball and associated structures - three cranial bones of the orbit are: frontal, sphenoid, and ethmoid - four facial bones of the orbit are: palatine, zygomatic, lacrimal, and maxilla

Unique Features of the Skull: Sutures:  

Suture: an immovable joint that holds most skull bones together in adults; in children they are often moveable and function as important growth centers in the developing skull There are four prominent sutures found in the skull: - coronal suture: unites the frontal bone and both parietal bones - sagittal suture: unites the two parietal bones on the superior midline of skull - lambdoid suture: unites the two parietal bones to the occipital bone - squamous sutures: (2) unite the parietal and temporal bones on the lateral aspects of the skull

Sinus: 

Paranasal sinuses: mucous membrane-lined cavities within certain cranial and facial bones near the nasal cavity - secretions drain from here into the lateral wall of the nasal cavity - skull bones that contain the paranasal sinuses: frontal, sphenoid, ethmoid, and maxillae - allow the skull to increase in size without changing mass of bone, increase surface area of nasal and thus increasing production of mucus for moisture and filtered air, and enhance quality of voice

Fontanels:    

Fontanels: incompletely developed cranial bones (soft spots) They are areas where unossified mesenchyme develops into the dense connective tissues of the skull Eventually replaced with bone by intramembranous ossification Serve as spacers for the neighboring skull bones and provide some flexibility to the fetal skull

7.5: Hyoid Bone:  

Hyoid bone: unique component of the axial skeleton because it does not articulate with any other bone > located in anterior neck between mandible and larynx Suspended from the styloid processes of the temporal bones by ligaments and muscles

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Supports tongue, attaches tongue muscles, neck muscles, and pharynx muscles

7.6: Vertebral Column: 

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Vertebral column: (spine, backbone, spinal column) makes up two fifths of your total height - composed of a series of bone called vertebrae: - forms together with sternum and ribs to make trunk of the body Consists of bone and connective tissue - functions as a strong, flexible rod with elements that can move forward, backwards, sideways, and rotate Adult vertebral column consists of 26 vertebrae: - 7 cervical vertebrae in the neck region - 12 thoracic vertebrae posterior to the thoracic cavity - 5 lumbar vertebrae supporting the lower back - 1 sacrum consisting of 5 fused sacral vertebrae - 1 coccyx consisting of 4 fused coccygeal vertebrae Normal curves: four slight bends in the vertebral column when viewed from the side - cervical and lumbar curves: convex (bulging out) - thoracic and sacral curves: concave (cupping in) - curves increase strength, help maintain balance in upright position, absorb shock during walking, and protect vertebrae from fracture

Intervertebral Discs:  

Intervertebral discs: found between the bodies of adjacent vertebrae from the second cervical vertebrae to the sacrum and account for 25% of the height of the vertebral column Each disc has a nucleus pulposus: inner soft, pulpy, highly elastic substance - discs form strong joints, permit various movements of the vertebral column, and absorb vertical shock

Parts of a Typical Vertebra:     

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Vertebral body: thick, disc-shaped anterior portion and weightbearing part of a vertebra Vertebral arch: formed from two short, thick processes (aka pedicles) that project posteriorly from the body and unite with flat laminae Vertebral foramen: formed by the unity of the vertebral body and arch - contains spinal cord, adipose tissue, areolar connective tissue, blood vessels Vertebral (spinal) canal: formed from all the vertebral foramina Intervertebral foramen: the opening between adjoining vertebrae on both sides of the column that permits the passage of a single spinal nerve carrying information to and from the spinal cord Processes: seven arise from the vertebral arch - transverse processes: extends laterally on each side where a lamina and pedicle join - spinous process: projects posteriorly from the junction of the laminae - superior articular processes: articulate (form joints) with the two inferior articular processes of the vertebra immediately above them

- inferior articular processes: articulate (form joints) with the two superior articular processes of the vertebra immediately below them, and so on Regions of the Vertebral Column: Exhibit 7.H: Vertebral Regions – Cervical Vertebrae: 

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Cervical vertebrae: (C1-C7) at most superior region and smaller than all other vertebrae except those that form the coccyx - there are seven of them total Spinal processes of C2 through C6 are often bifid: they bran into two small projections at the tips Atlas: (C1): first cervical vertebrae inferior to the skull; it is a ring of bone with anterior and posterior arches, as well as large lateral masses - has no body or spinous process - superior articular facets are concave and articulate with occipital condyles to form atlantooccipital joints (which allows you to nod) Axis: (C2): second cervical vertebrae that has a body - dens or odontoid process: projects superiorly through the anterior portion of the vertebral foramen of the atlas - makes a pivot on which the atlas and head rotate; articulation formed between the anterior arch of the atlas and dens of the axis, and between their articular facets is called the atlantoaxial joint - this permits side to side shaking of the head

Exhibit 7.I: Vertebral Regions – Thoracic Vertebrae:     

Thoracic vertebrae: (T1-T12) large and stronger than cervical vertebrae T1-T10: spinous processes are long, laterally flattened, and directed inferiorly T11-T12: spinous processes are shorter, broader, and directed more posteriorly Vertebrocostal joints: articulations between the thoracic vertebrae and ribs; distinguishing features of the thoracic vertebrae Facets and demi-facets: articulation spots for the ribs?

Exhibit 7.J: Vertebral Regions – Lumbar Vertebrae: 

Lumbar vertebrae: (L1-L5): largest and strongest of the unfused bones in the vertebral column because the amount of body weight supported by the vertebrae increases toward inferior end of backbone

Exhibit 7.K: Vertebral Regions – Sacral and Coccygeal Vertebrae: 

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Sacrum: (S1-S5): triangular bone formed by the union of five sacral vertebrae and is positioned at the posterior portion of the pelvic cavity medial to the two hip bones - serves as strong foundation for pelvic girdle Anterior sacral foramina: four pairs that are found at the end of the transverse (ridges) lines that join the sacral vertebrae (foramina are: opening that allows passage of structures)

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Median sacral crest: found at the posterior surface of the sacrum down the middle - it is the fused transverse processes of the sacral vertebrae Posterior sacral foramina: found at posterior surface are four pairs of this - they connect with anterior sacral foramina to allow passage of nerves and blood vessels Sacral canal: continuation of the vertebral cavity Sacral hiatus: the inferior entrance to the vertebral canal from the failure of certain laminae to meet Sacral promontory: is the anteriorly projecting border of the base Sacroiliac joint: where the auricular surfaces and sacral tuberosities on the lateral sides of the sacrum articulate with ilium of each hip bone Lumbosacral joint: where the base of the sacrum articulates with the body of the fifth lumbar vertebra Coccyx: (Co1-Co4): triangular shape and formed by the fusion of four coccygeal vertebrae

7.7: Thorax:   

Thorax: refers to the entire chest region Thoracic cage: skeletal part of the thorax that is a bony enclosure formed by the sternum, ribs, and their costal cartilages, and the bodies of the thoracic vertebrae Encloses and protects organs in the thoracic and superior abdominal cavities, provides support, for upper limb bones, plays a role in breathing

Exhibit 7.L: Thoracic Bones – Sternum:  

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Sternum: or breastbone: flat, narrow bone located in the center of the anterior thoracic wall Consists of three parts: - superior manubrium; middle and largest part body; inferior and smallest part: xyphoid process (provides attachment for some abdominal muscles and organs; makes floor of diaphragm ) Sternal angle: formed by the junction of the manubrium and the body Suprasternal notch: depression on the superior surface of the manubrium Clavicular notches: lateral to the suprasternal notches; articulate with medial ends of the clavicle to form sternoclavicular joints

Exhibit 7.M: Thoracic Bones – Ribs:      

Ribs: twelve pairs (1-12); give structural support to the sides of the thoracic cavity - each rib articulates posteriorly with its corresponding thoracic vertebrae Costal cartilage: hyaline cartilage that attaches true ribs to the sternum; prevents fracture and enhances elasticity True ribs: ribs 1-7 that have costal cartilages and attach directly to t...