The Axial Skeleton I

Transcription

1 Anatomy lecture 2

2 The Axial Skeleton I

3 Morphological Classification of the Bones According to shape, bones of the body can be classified into: a. Long bones: Have greater length than width. Each consists of shaft (body) and two ends, proximal and distal. Examples: humerus, femur, radius, ulna, tibia, fibula, metacarpal, metatarsal, and phalanges. b. Short bones: They are nearly equal in length and width; example: carpal bones. c. Irregular bones: Have complex shapes; examples: hip bone, vertebrae, calcaneus, and certain bones of the face.

4 d. Flat bones: These are thin bones; examples: cranial bones, sternum, ribs and scapula. e. Sesamoid bones: These bones develop in certain tendons. Their shapes like a sesame seed. The largest sesamoid bone is the patella. Except the patella, sesamoid bones measured only few millimeters

5 The Skull Consists of two groups of bone, the cranial bones and the facial bones. The cranial bones form the cranial cavity, which encloses and protects the brain. The facial bones form the bone of the face.

6 Cranial Bones Are singles except two of them are pairs: 1- Frontal Bones Parietal Bones Occipital Bone Temporal Bones Sphenoid Bone Ethmoid Bone. -1

7 a. Frontal bone (fig. 1 & 5) Forms the forehead, and most of the floor of the anterior cranial fossa and roof of orbital cavities. It contains the two frontal air sinuses. b. Parietal bones (fig. 2, 4 & 6) Form the greater part of the roof and sides of the skull. They articulate anteriorly with the frontal bone forming the coronal suture, posteriorly with the occipital bone forming the lambdoid suture, and in the midline with each other

8 Figure 1 Anterior view of skull.

9 The sagittal suture meets anteriorly the coronal suture in the brigma, and posteriorly the lambdoid suture in the lambda. In newborn child, the bones of the skull in the regions of the brigma and lambda are separated by unossified membranous intervals called the anterior and posterior fontanelles, respectively (fig. 3). The anterior fontanelle is diamond in shape, closed by 18 months of age. The posterior fontanelle is triangular in shape, closed by the end of the third month after birth.

10 Figure 2 Superior view of skull.

11 Figure 3 Fontanelle.

12 c. Occipital bone (fig. 4 & 5) Forms the posterior part and the greater part of base of cranium. It has the following parts: i. basilar part (the anterior part); ii. lateral parts; and iii. squamous part (the posterior part). The four parts surround the largest foramen in body, the foramen magnum. The squamous part presents roughened elevations on its outer and inner surfaces called the external and internal occipital protuberance, respectively).

13 The superior nuchal lines, one on each side, are transverse ridges that run laterally from the external occipital protuberance. These lines form the boundaries between occipit and back of neck. The inferior nuchal lines lie little below and parallel to superior nuchal lines. At the base of the skull, the margin of foramen magnum is overlapped anteriorly on each side by kidney-shaped occipital condyles, which articulates with superior articular facet of the atlas vertebra, forming the atlanto-occipital joint.

14 Figure 4 Posterior view of skull.

15 Figure 5 Cranial fossae.

16 d. Temporal bones (fig. 5 & 6) Form part of base and lateral wall of the cranium. Each temporal bone has the following parts: i. Squamous part: Forms part of the lateral wall and the base of the skull. ii. Mastoid part: Lies behind and below squamous part. The mastoid process projects downward from this part, behind and below the external auditory meatus. It contains several mastoid air cells.

17 Figure 6 Lateral view of skull.

18 iii. Petrous part: Lies at the base of the skull between sphenoid and occipital bones. This part houses the middle and internal ear. It is pyramidal in shape, its apex directed medially and the base laterally. iv. Tympanic plate: Lies at the base of the skull behind the mandibular fossa. v. Styloid process: Is a slender process, about 2.5 cm in length that projects downwards from base of skull immediately behind the middle of the tympanic plate. Stylomastoid foramen: Lies on base of skull, between styloid and mastoid process.

19 e. Sphenoid bone (fig. 5) Forms the middle part of base of cranium. It has the following parts: (1) The body in the middle. (2) The greater and lesser wings on each side. (3) The pterygoid processes below. The body contains the two sphenoidal air sinuses. The two wings are separated by the superior orbital fissure, which transmits the branches of ophthalmic nerve (frontal, nasociliary, and lacrimal nerves), oculomotor nerve, trochlear nerve, abducent nerve, and ophthalmic veins.

20 f. Ethmoid bone Lies anteriorly in median area, between orbital cavities. It has the following parts: (1) The horizontal plate (fig. 5): Forms part of roof of nasal cavity. It has several foramena for passage of olfactory nerves. (2) The perpendicular plate. (3) The two lateral mass (one on each side): Each lateral mass contains three groups of ethmoidal air cells: anterior, middle, and posterior ethmoidal air sinuses.

21 Cranial Fossae 1. Anterior cranial fossa (fig. 5): This fossa contains the frontal lobes of the two cerebral hemispheres of the brain. The floor of this fossa has a median and two lateral portions. a. Median portion: It is formed anteriorly by horizontal plate of ethmoid bone, and posteriorly by anterior part of body of sphenoid bone. b. Lateral portions: Each is mainly formed by frontal bone; whereas the small posterior part is formed by lesser wing of sphenoid bone.

22 2. Middle cranial fossa (fig. 5): It is deeper than the anterior. It contains the temporal lobes of cerebral hemispheres of brain. The floor of this fossa has a median and two lateral portions. a. Median portion: o It is formed by body of sphenoid bone. o Anteriorly there is a shallow sulcus termed sulcus chiasmaticus.

23 o The sulcus leads on each side to optic canal. o Behind this sulcus the upper surface of body of sphenoid is shaped like a Turkish saddle and hence called sella turcica. o The sella turcica presents a deep depression called the hypophysial fossa, which contains hypophysis cerebri (pituitary gland). o Behind this fossa, a plate of bone projects upward to form dorsum sellae.

24 b. Lateral portions: Each is formed anteriorly by greater wing of sphenoid bone; posteriorly by anterior surface of petrous part of temporal bone; and laterally by squamous part of temporal bone, which is wedged between greater wing and petrous. The greater wing of sphenoid is pierced by: (1)Foramen rotundum: Transmits the maxillary nerve. (2) Foramen ovale: Transmits the mandibular nerve, and accessory meningeal artery. (3) Foramen spinosum: Transmits the middle meningeal artery.

25 The foramen lacerum is an irregular space between apex of petrous part of temporal bone and body of the sphenoid. It is closed in the living persons by cartilage.

26 3. Posterior cranial fossa: It is deeper than the middle fossa, occupied by hind brain (cerebellum, pons, and medulla oblongata), and the cerebellum. The floor of this fossa is formed mainly by occipital bone, but the small anterolateral part is formed on each side by posterior surface of petrous; and the lateral part by the mastoid bone.

27 The posterior surface of the petrous presents near its center the internal acoustic meatus. It transmits the motor and sensory roots of the facial nerve, and the vestibulocochlear nerve. The jugular foramen is situated between petrous and occipital bone immediately below internal acoustic meatus. It transmits internal jugular vein and the glossopharyngeal, vagus, and accessory nerves.

28 Paranasal Sinuses These are cavities lined by mucous membrane, and open into the nasal cavities. They are found in the interior of: (1)Frontal bone frontal air sinuses (fig. 8). (2) Maxillary bone maxillary air sinus (fig. 7). (3) Ethmoid bone The anterior, middle, and posterior ethmoidal air sinuses (fig. 7). (4) Sphenoid bone sphenoidal air sinuses (fig. 8). Besides producing mucous, the function of paranasal sinuses is to act as resonators to voice; they also reduce the weight of skull.

29 Figure 7 The maxillary and ethmoidal air sinuses.

30 They open into nasal cavity through relatively small apertures. Thus secretions produced by these sinuses drain into nasal cavity. When the apertures of the sinuses are blocked, or they become filled with fluid, the quality of the voice is markedly changed. Infection of paranasal sinuses (sinusitis) is a common complication of nasal infections.

31 Figure 8 The frontal and sphenoidal air sinuses.

32 Facial Bones Are paired except two of them are single: 1- Maxillary Bones Zygomatic Bones Nasal Bones Lacrimal Bones Palatine Bones Inferior nasal conchae Vomer Bone Mandible. -1

33 B. The Facial Bones a. Maxillary bones or maxillae (fig. 1) Form the upper jawbone. Each maxillary bone has a body and four processes: (1) Upper (frontal) process: Projects upward and articulates with frontal bone. (2) Lateral (zygomatic) process: Articulates with zygomatic bone. (3) Lower (alveolar) process: possesses sixteen sockets for roots of upper (maxillary) teeth.

34 (4) The posterior (palatine) process (fig. 9): Articulates with horizontal plate of the palatine bone to form bony or hard palate, which forms anterior part of base of skull; floor of nasal cavity; and roof of mouth cavity. The maxillary bone is responsible for elongation of face between ages of 6 12 years. Each maxillary bone contains one maxillary air sinus.

35 Figure 9 Inferior view of the skull.

36 b. Zygomatic bones (fig. 1) Form the prominences and bony part of cheeks. It has two processes: (1)The upper (frontal) process: Articulates with zygomatic process of frontal bone. (2) The posterior (temporal) process: Articulates with zygomatic process of the temporal bone forming zygomatic arch. c. Nasal bones (fig. 1) Articulate anteriorly with each other in midline, and posteriorly with the frontal process of maxillary bone. Their lower border is free, to which lateral nasal cartilage is attached.

37 d. Lacrimal bone (fig. 1) lies behind frontal processes of maxillary bones. Forms part of medial wall of orbital cavity. e. Palatine bones (fig. 9) Form the posterior part of hard palate. It also form part of lateral wall and floor of nasal cavity. f. Inferior nasal conches (fig. 8) Are shelves of bone that project downward from corresponding lateral wall of nasal cavity. g. Vomer bone (fig. 9) Forms posterior part of nasal septum, which divides nasal cavity into right and left halves.

38 h. Mandible (fig. 10) Consist of an anterior horizontal part called body and a posterior vertical part termed ramus. 1. The body: o Is horse-shoe shaped. o Anteriorly the external surface in the midline is marked by a faint ridge, indicates line of fusion of the two halves of fetal bone, the symphysis menti. o The mental foramen lies on external surface of body usually midpoint between upper and lower borders. o It transmits mental nerve and vessels.

39 o The upper border of the body is called alveolar process, which exhibits 16 sockets for lower (mandibular) teeth. o The internal surface of the body is marked by an oblique ridge, the mylohyoid line. o The fossa below mylohyoid line is called submandibular fossa for submandibular salivary gland. o The fossa above mylohyoid line is termed sublingual fossa for sublingual salivary gland.

40 Figure 10 The mandible.

41 2. The ramus: o Is quadrilateral. o Its posterior border meets lower border at angle of mandible. o Its upper border presents two processes separated by a wide notch called mandibular notch. o The anterior process is called coronoid process. o The posterior process is called condylar process, which has an expanded upper part, the head of mandible, and a constricted lower part, the neck of mandible.

42 o The medial surface exhibits a little above its center an irregular foramen, the mandibular foramen. o The foramen leads into a bony canal termed the mandibular canal. o The canal runs below sockets of teeth. o The mandibular foramen transmits inferior alveolar nerve and vessels. o The mandibular foramen is obscured by a thin triangular process, the lingula.