Human Anatomy & Physiology I Dr. Sullivan Unit VIIIa The Axial Skeleton Chapter 8 (Sections )

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1 Human Anatomy & Physiology I Dr. Sullivan Unit VIIIa The Axial Skeleton Chapter 8 (Sections ) I. Divisions of the skeletal system a) An adult human skeleton has 206 named bones b) Most are paired bilaterally (on both left & right) c) There are two principal divisions of the adult skeleton i) The Axial Skeleton: down the center (1) Skull, Spine, Ribs, Sternum ii) ii. The Appendicular Skeleton: the periphery (1) Shoulder, Hip, Upper limb & Lower limb d) ARTICULATE: to form a joint with. II. Bone Surface Markings a) Surface markings are structural features on bones that are adapted for specific functions. b) Can be raised surfaces, holes, depressions, or projections off the bone. c) See Table 8.1 in the text for a list of all the bones of the human body. d) See Table 8.2 in the text for a list of bone surface markings. e) Bones are listed in bold type and their surface markings are listed below each bone in italics III. The Skull a) There are 22 bones in the skull, which rests on the superior end of the vertebral column b) There are two sets of skull bones c) Cranial Bones (8): forms the cranial cavity to protect the brain i) 1 Frontal bone, 2 parietal bones, 2 temporal, 1 occipital, 1 ethmoid, & 1 sphenoid d) Facial Bones (14): forms the face i) 2 Nasal, 2 maxillae, 2 zygomatic, mandible, 2 lacrimal, 2 palantine, 2 inferior nasal conchae, vomer. e) The skull also forms the nasal cavity and orbits. f) The skull is held together by immoveable joints called sutures g) The inner surface of the brain provides attachment sites for three membranes called the meninges, which function to stabilize the position of the brain, blood vessels, and nerves h) The outer surface of the skull has many surface markings for attachment of muscles that move the head and form facial expression. i) The Facial bones form the shape of the face as well as provide protection and support for the entrances of the digestive system and respiratory system and the delicate special sense for hearing, taste, vision, and smell. j) Cranial Bones i) Frontal Bone: forms the forehead at the anterior portion of the cranium, the superior roof of the orbits, and the anterior floor of the cranial cavity (interiorly). (1) Frontal Sinuses: two mucous-membrane lined cavities superior to the orbits (2) Supraorbital foramen: two small holes superior to the orbits for branches of the facial nerve to exit the skull and innervate muscles and skin. ii) Parietal Bones (2): bilateral. Form the greater portion of the sides and roof of the cranial cavity. (1) Sagittal suture: joint between bilateral parietal bones iii) Temporal Bones (2): bilateral. Form the inferior lateral aspects of the cranium and part of the internal cranial floor. (1) Surrounded by the squamous suture (2) contributes to the zygomatic arch via its zygomatic process (3) Provides the Mandibular Fossa for articulation with the mandible to form the temporomandibular joint (TMJ) (4) The temporal bone also contains the mastoid process and styloid process for muscle attachments.

2 (5) External Auditory Meatus: allows for the ear canal to conduct sound waves into the skull. (6) jugular foramen: hole for jugular vein to pass through (7) formamen ovale: hole for mandibular nerve (8) foramen lacerum: hole internal carotid artery iv) Occipital Bone: forms the posterior portion of the cranium. (1) Foramen Magnum: a large hole in the inferior portion of the bone, which allows the brainstem to pass into the spinal canal. (2) Occipital Condyles: Oval processes with convex surfaces for articulation with the atlas, the first vertebra of the neck. (3) External occipital protuberance: a large bump on the occipital bone, just superior to the foramen magnum for attachment of the ligamentum nuchae, which provides stability to the neck and head. (4) Superior & Inferior nuchal lines: two ridges lateral to the external occipital protuberance that provide attachment for muscles of the neck. (5) Foramen Spinosum: hole for the middle meningeal artery v) Sphenoid Bone: lies at the middle part of the base of the skull (1) resembles a butterfly (2) Sella Turcica: a saddle-shaped structure on the superior portion of the sphenoid, which provided protection for the pituitary gland. vi) Ethmoid Bone: a light, sponge-like bone on the midline, in the anterior part of the cranial floor; medial to the orbits; anterior to the sphenoid, posterior to the nasal bones. (1) Cribiform Plate: part of the ethmoid that lies in the inferior floor of the anterior cranial cavity and makes the roof of the nasal cavity. (2) Crista Galli: triangular projection supriorly from the cribiform plate providing attachment for the membrane that covers and supports the brain. (3) Superior & Middle Nasal Conchae: causes turbulence to the air entering the nostrils, resulting in particles being trapped in the mucus as well as moistening and warming the air before it enters the lungs. k) Facial Bones i) Nasal Bones (2): two paired bones meeting at the midline to form part of the bridge of the nose. ii) Maxilla (2): Form the upper jawbone and articulates with every bone of the face except the mandible. (1) Form part of the floor of the orbits, part of the lateral walls of the nasal cavity, and part of the hard palate (roof of the mouth) (2) The maxillae are usually completely fused together by birth (a) Cleft Palate: failure of the maxillary bones to unite before birth. (3) Alveolar Process: arched process for attachment of the upper teeth. (4) Infraorbital foramen: hole for the passage of a branch of the facial nerve iii) Zygomatic Bones (2): forms the prominence of the cheeks. (1) Forms part of the lateral wall of the orbit. iv) Lacrimal Bones (2): thin, fingernail-size bones postero-lateral to the nasal bones (a) Lacrimal Fossa: formed with the maxilla and hold the lacrimal sac for tear production. v) Palatine Bones (2): form the posterior portion of the hard-palate. vi) Inferior Nasal Concha (2): inferior to the middle nasal concha of the ethmoid bone. Separate from the ethmoid bone vii) Vomer: on the floor of the nasal cavity. Part of the nasal septum, which divides the naal cavity into right and left sides. viii) Mandible: the lower jawbone. (1) The largest, strongest facial bone. (2) The only moveable skull bone (other than the auditory ossicles) (3) Consists of a bilateral ramus, body, angle, mandibular condyle, mental foramen, coronoid process, and mandibular notch. (4) Alveolar processes: provide attachment for lower teeth l) Orbits: Seven bones of the skull form each orbit, or eye socket.

3 i) Roof: frontal and sphenoid bones ii) Lateral Wall: zygomatic and sphenoid iii) Floor: maxilla, zygomatic, palatine bones iv) Medial Wall: maxilla, lacrimal, ethmoid, sphenoid bones m) Sutures: immoveable joint in adult skull i) Coronal Suture: unites frontal bone with both parietal bones ii) Sagittal Suture: Unites the two parietal bones in the superior midline iii) Lambdoid Suture: unites the two parietal bones with the occipital bone iv) Squamous Suture (2): unites the parietal bones to the temporal bones n) Fontanelles: areas of the embryonic & newborn skull of fibrous connective tissue that will eventually be replaced by bone after birth. i) Allow for flexibility of the skull to ease childbirth. ii) Anterior fontanel: diamond-shaped junction of the 2 parietal bones and the fontal bone. iii) Posterior fontanel: at the juncture of the 2 parietal bones and the occipital bone. iv) Anterolateral Fontanelles (2): small, irregularly shaped. Located bilaterally between the frontal, parietal, temporal, and sphenoid bones. v) Posterolateral Fontanelles (2): irregularly shaped, located bilaterally at the junction of the parietal, occipital, and temporal bones. o) Hyoid Bone: U-shaped bone that does not articulate with any other bone i) Suspended from the styloid processes of the temporal bones by ligaments and muscles. ii) Located in the anterior neck inferior to the mandible, superior to the larynx (adam s apple) iii) Provides attachments for tongue muscles, neck muscles, and pharyngeal muscles (swallowing) IV. The Vertebral Column a) Also called the spinal column, spine, backbone. b) Consists of a series of bones, each called a vertebra (plural: vertebrae) c) During early development, the total number of vertebrae is 33. i) Then several vertebrae fuse, leaving 26 in the adult. d) The vertebral column is distributed into 5 section: e) The Cervical Spine: the neck i) Contains 7 vertebrae listed as C1-C7 ii) C1 & C2 called the Atlas & Axis f) The Thoracic Spine: the upper and mid back i) Contains 12 vertebrae listed as T1-T12 g) The Lumbar Spine: the lower back i) Contains 5 vertebrae listed as L1-L5 h) The Sacrum: the posterior portion of the pelvis i) Contains 5 fused sacral vertebrae (listed as S1-S5) ii) located median to the posterior hips i) The Coccyx: the tailbone i) Contains four fused coccygeal vertebrae ii) The cervical, thoracic, & lumbar vertebrae are moveable segments of the spine, the sacrum and coccyx are not. j) Movement of the vertebral column: i) Flexion: forward bending ii) Extension: backward bending iii) Right & Left Lateral Flexion: bending to the side iv) Right & Left Rotation: turning to the side k) Normal Curves of the Vertebral Column i) When viewed from the side, the spinal column has a normal S-shaped curved designed for weight-bearing. ii) The curves increase strength, maintain upright balance, absorb shock when walking, and help protect the vertebrae from fracturing. iii) Relative to the anterior, the cervical and lumbar spine have a convex curve called a lordosis. (1) Convex: the bulging part of the curve is toward the anterior.

4 iv) Relative to the anterior, the thoracic and sacral spine have a concave (bulging toward the posterior) curve called a kyphosis. v) Each of these curves can be measured in degrees and they each have specific normal ranges that are best for spinal function. Decreases or increases in the normal curve measurements are called hypo- and hyper- kyphosis or lordosis. (1) i.e.: A decrease in the normal cervical lordosis (aka: a straightened neck), is called a cervical hypolordosis. l) Intervertebral Discs (aka IVD) i) Between the bodies of adjacent vertebrae from C2-S1, there are shock-absorbing discs ii) Composed of a fibrocartilage exterior called the annulus fibrosus and a jelly-like interior called the nucleus pulposus iii) The IVD increase strength, absorb shock, and contribute flexibility for movement m) Structure of a typical vertebra i) The anatomy of vertebrae differ slightly from region to region of the spine. ii) Each Vertebra has a body, sup. & inf. articular facets, vertebral foramen, spinous process, transverse process, sup. and inf. vertebral notches, a vertebral foramen, laminae, & pedicles. (1) The laminae, pedicles, and spinous process form the vertebral arch (2) The foramen formed by the vertebral arch in the center of the vertebra is called the vertebral foramen (3) When all the vertebrae are stacked up to form the spine, the vertebral foramina form the vertebral canal, which is where the spinal cord lives & travels from the brain down through the spine. iii) Superior & Inferior vertebral notches: semi-circular notches in the pedicles that, when lined up with another vertebra, form a full-circle notch called the interverteral foramen (IVF). This allows spinal nerves formed from the spinal cord to exit the vertebral column and travel to all other parts of the body n) The Cervical Region i) The exception to the typical vertebral anatomy is C1, which has lateral masses and an anterior tubercle instead of a body, a posterior turbercle instead of a spinous process, a posterior arch instead of laminae, and an anterior arch instead of pedicles. ii) The cervical region has unique anatomical differences for specific functions (1) C2, or Axis, has a superior process called the odontoid process, or the dens. (a) The dens articulates with the posterior portion of the anterior arch of atlas to form a pivot joint that allows for rotational movement. iii) There are foramen in the bilateral transverse processes of the cervical vertebrae called the transverse foramen for passage of the vertebral artery, which comes from the aorta and travels superiorly to the brainstem area. iv) Bifid Spinous Process: the spinous processes of C2-C6 are split into two v) The vertebral foramen of the cervical vertebrae is wide and triangle-shaped, to allow for a cervical enlargement of the spinal cord in this region. o) The Thoracic Region a. Thoracic vertebrae are larger and stronger than cervical vertebrae b. The spinous processes are longer than those of the cervical region, not bifid, and most are directed inferiorly to allow for the thoracic kyphosis. c. The vertebral foramen is small and circular for a thinning circular spinal cord. d. Thoracic vertebrae articulate with the ribs at the costal facets of the bodies and the transverse facets on the transverse processes. e. The joints formed by ribs & thoracic vertebra are called the vertebrocostal joints p) The Lumbar Region i) The largest and strongest in the vertebral column for maximum weight-bearing ii) The spinous processes are thick & broad, projecting posteriorly. iii) The body of the vertebra lies superior to the spinous process. iv) The vertebral foramen is small and triangular due to the ending of the spinal cord at L1-2.

5 v) The superior articular facets face medially and the inferior articular facets face laterally. q) The Sacrum & Coccyx i) Triangular bone formed by 5 fused sacral vertebra ii) Divided into fused segments called S1-S5. iii) L5 & S1 form a joint called the lumbosacral joint iv) The auricular surfaces articulate with the Ilium of the hip bone, and form the sacroiliac joints. v) The sacrum forms the posterior 1/3 of the pelvis. vi) The sacral ala is formed on either side by the fused transverse processes of the sacral vertebrae. vii) The coccyx is inferior to the sacrum, is triangular, and formed by the fusion of four coccygeal vertebrae V. The Thorax a) The Sternum (breastbone) i) Flat, narrow, located at the center of the anterior chest wall. ii) Articulates bilaterally with the cartilage of the 1 st through 6 th ribs to form sternocostal joints iii) Articulates bilaterally with the left & right clavicles to form the sternoclavicular joints iv) Contains the manubrium, body,sternal angle, suprasternal notch (aka jugular notch), clavicular notches, & xiphoid process. b) The Ribs (12): latin = costa i) The ribs are numbered 1-12 based on the thoracic vertebra they articulate with. ii) Posteriorly, the ribs articulate directly with the vertebrae and anteriorly articulate with the costal cartilage, which eventually articulates with the sternum iii) Ribs 1-7 (true ribs) have their own costal cartilage that articulates directly with the sternum iv) Ribs 8-10 s (false ribs) costal cartilages fuse together with that of the 7 th rib and share its articulation v) The 11 th & 12 th ribs (false ribs) terminate without costal cartilage along the mid-axillary line and do not articulate with the sternum (1) 11 th & 12 th ribs called floating ribs (2) The spaces in between ribs is known as the intercostal spaces and contain intercostal muscles, blood vessels, and nerves (3) The head of the rib is found posteriorly and contains the superior and inferior facets for articulation with the thoracic vertebrae. (4) The tubercle of the rib has an articular portion for articulation with the transverse process of a thoracic vertebra.