NEET MDS Lessons
Anatomy
-> Most of the facial skeleton is formed by nine bones: four paired (nasal, zygomatic, maxilla, and palatine) and one unpaired (mandible).
-> The calvaria of the new-born infant is large compared with the relatively small fascial skeleton.
-> This results from the small size of the jaws and the almost complete absence of the maxillary and other paranasal sinuses in the new-born skull.
-> These sinuses form large spaces in the adult facial skeleton. As the teeth and sinuses develop during infancy and childhood, the facial bones enlarge.
-> The growth of the maxillae between the ages of 6 and 12 years accounts for the vertical elongation of the child’s face.
The Nasal Bones
-> These bones may be felt easily because they form the bridge of the nose.
-> The right and left nasal bones articulate with each other at the internasal suture.
-> They also articulate with the frontal bones, the maxillae, and the ethmoid bones.
-> The mobility of the anteroinferior portion of the nose, supported only by cartilages, serves as a partial protection against injure (e.g., a punch in the nose). However, a hard blow to the anterosuperior bony portion of the nose may fracture the nasal bones (broken nose).
-> Often the bones are displaced sideways and/or posteriorly.
The Maxillae
-> The skeleton of the face between the mouth and the eyes is formed by the two maxillae.
-> They surround the anterior nasal apertures and are united in the medial plane at the intermaxillary suture to form the maxilla (upper jaw).
-> This suture is also visible in the hard palate, where the palatine processes of the maxillae unite.
-> Each adult maxilla consists of: a hollow body that contains a large maxillary sinus; a zygomatic process that articulates with its mate on the other side to form most of the hard palate; and alveolar processes that form sockets for the maxillary (upper) teeth.
-> The maxillae also articulate with the vomer, lacrimal, sphenoid, and palatine bones.
-> The body of the maxilla has a nasal surface that contributes to the lateral wall of the nasal cavity; an orbital surface that forms most of the floor of the orbit; an infratemporal surface that forms the anterior wall of the infratemporal fossa; and an anterior surface that faces partly anteriorly and partly anterolaterally and is covered buy facial muscles.
-> The relatively large infraorbital foramen, which faces inferomedially, is located about 1 cm inferior to the infraorbital margin; it transmits the infraorbital nerve and vessels.
-> The incisive fossa is a shallow concavity overlying the roots of the incisor teeth, just a shallow concavity overlying the roots of the incisor teeth, just inferior to the nasal cavity. This fossa is the injection site for anaesthesia of the maxillary incisor teeth.
-> If infected maxillary teeth are removed, the bone of the alveolar processes of the maxillae begins to be reabsorbed. As a result, the maxilla becomes smaller and the shape of the face changes.
-> Owing to absorption of the alveolar processes, there is a marked reduction in the height of the lower face, which produces deep creases in the facial skin that pass posteriorly from the corners of the mouth.
The Mandible
-> This is a U-shaped bone and forms the skeleton of the lower jaw and the inferior part of the face. It is the largest and strongest facial bone.
-> The mandibular (lower) teeth project superiorly from their sockets in the alveolar processes.
-> The mandible (L. mandere, to masticate) consists of two parts: a horizontal part called the body, and two vertical oblong parts, called rami.
-> Each ramus ascends almost vertically from the posterior aspect of the body.
-> The superior part of the ramus has two processes: a posterior condylar process with a head or condyle and a neck, and a sharp anterior coronoid process.
-> The condylar process is separated from the coronoid process by the mandibular notch, which forms the concave superior border of the mandible.
-> Viewed from the superior aspect, the mandible is horseshoe-shaped, whereas each half is L-shaped when viewed laterally.
-> The rami and body meet posteriorly at the angle of the mandible.
-> Inferior to the second premolar tooth on each side of the mandible is a mental foramen (L. mentum, chin) for transmission of the mental vessels and the mental nerve.
-> In the anatomical position, the rami of the mandible are almost vertical, except in infants and in edentulous (toothless) adults.
-> On the internal aspect of the ramus, there is a large mandibular foramen.
-> It is the oblong entrance to the mandibular canal that transmits the inferior alveolar vessels and nerve to the roots of the mandibular teeth.
-> Branches of these vessels and the mental nerve emerge from the mandibular canal at the mental foramen.
-> Running inferiorly and slightly anteriorly on the internal surface of the mandible from the mandibular foramen is a small mylohyoid groove (sulcus), which indicates the course taken by the mylohyoid nerve and vessels.
-> These structures arise from the inferior alveolar nerve and vessels, just before they enter the mandibular foramen.
-> The internal surface of the mandible is divided into two areas by the mylohyoid line, which commences posterior to the third molar tooth. -> Just superior to the anterior end of the mylohyoid line are two small, sharp mental spines (genial tubercles), which serve as attachments for the genioglssus muscles.
The Zygomatic Bones
-> The prominences of the cheeks (L. mala), the anterolateral rims and much of the infraorbital margins of the orbits, are formed by the zygomatic bones (malar bones, cheekbones).
-> They articulate with the frontal, maxilla, sphenoid, and temporal bones.
-> The frontal process of the zygomatic bone passes superiorly, where it forms the lateral border of the orbit (eye socket) and articulates with the frontal bone at the lateral edge of the supraorbital margin.
-> The zygomatic bones articulate medially with the greater wings of the sphenoid bone. The site of their articulation may be observed on the lateral wall of the orbit.
-> On the anterolateral aspect of the zygomatic bone near the infraorbital margin is a small zygomaticofacial foramen for the nerve and vessels of the same name.
-> The posterior surface of the zygomatic bone near the base of its frontal process is pierced by a small zygomaticotemporal foramen for the nerve of the same name.
-> The zygomaticofacial and zygomaticotemporal nerves, leaving the orbit through the previously named foramina, enter the zygomatic bone through small zygomaticoorbital foramina that pierces it orbital surface.
-> The temporal process of the zygomatic bone unites with the zygomatic process of the temporal bone to form the zygomatic arch.
-> This arch can be easily palpated on the side of the head, posterior to the zygomatic prominence (malar eminence) at the inferior boundary of the temporal fossa (temple).
-> The zygomatic arches form one of the useful landmarks for determining the location of the pterion. These arches are especially prominent in emaciated persons.
-> A horizontal plane passing medially from the zygomatic arch separates the temporal fossa superiorly from the infratemporal fossa inferiorly.
Other Bones
There are several other, very important bones in the skull, including the palatine bone, ethmoid bone, vomer, inferior concha and the ossicles of the ear (malleus, incus and stapes). These, however, are covered to greater detail where they are relevant in the head (e.g., ethmoid bone with the orbit and nasal cavity).
The Orbital Vessels
- The orbital contents are supplied chiefly by the ophthalmic artery.
- The infraorbital artery, the continuation of the maxillary, also contributes blood to this region.
- Venous drainage is through the superior orbital fissure to enter the cavernous sinus.
The Ophthalmic Artery
- This artery arises from the internal carotid artery as it emerges from the cavernous sinus.
- It passes through the optic foramen within the dural sheath of the optic nerve and runs anteriorly, close to the superomedial wall of the orbit.
The Central Artery of the Retina
- This is the one of the smallest but most important branches of the ophthalmic artery.
- It arises inferior to the optic nerve until it approaches the eyeball.
- It then pierces the optic nerve and runs within it to emerge through the optic disc.
- The central artery of the retina spreads over the internal surface of the retina and supplies it.
The Ophthalmic Veins
The Superior Ophthalmic Vein
- The superior ophthalmic vein anastomoses with the facial vein.
- It has no valves and blood can flow in either direction.
- It crosses superior to the optic nerve, passes through the superior orbital fissure and ends in the cavernous sinus.
The Inferior Ophthalmic Vein
- This begins as a plexus on the floor of the orbit.
- It communicates with the inferior orbital fissure with the pterygoid plexus, crosses inferior to the optic nerve, and ends in either the superior ophthalmic vein or the cavernous sinus.
A. Anatomic position-erect body position with the arms at the sides and the palms upward
B. Plane or section
1. Definition-imaginary flat surface formed by an extension through an axis
2. Median plane-a vertical plane. that divides a body into right and left halves
3. Sagittal plane
- Any plane parallel to the median plane
- Divides the body into right and left portions
4. Frontal plane
- Vertical plane that forms at right angles to the sagittal plane
- Divides the body into anterior and posterior sections
- Synonymous with the term coronal plane
5. Transverse plane
- Horizontal plane that forms at right angles to the sagittal and frontal planes
- Divides the body into upper and lower portions
- Synonymous with the term horizontal plane
C. Relative positions
1. Anterior
- Nearest the abdominal surface and the front of the body
- Synonymous with the term ventral
- In referring to hands and forearms, the terms palmar and Volar are used
2. Posterior
- Back of the body
- Synonymous with the term dorsal
3. Superior
- Upper or higher
- Synonymous with the term cranial (head)
4. Inferior
- Below or lower
- Synonymous with the term caudal (tail)
- In referring to the top of the foot and the sole of the foot. the terms dorsal and plantar are used respectively
5. Medial-near to the median plane
6. Lateral-farther away from the median plane
7. Proximal-near the source or attachment
8. Distal-away from the source or. attachment
9. Superficial-near the surface
10. Deep-away from the surface
11. Afferent-conducting toward a structure
12. Efferent-conducting away from a structure
Mylohyoid Muscle
- Origin: Mylohyoid line of the mandible.
- Insertion: Median raphe and body of the hyoid bone.
- Nerve Supply: Nerve to mylohyoid (branch of the trigeminal nerve, CN V3).
- Arterial Supply: Sublingual branch of the lingual artery and submental branch of the facial artery.
- Action: Elevates the hyoid bone, base of the tongue, and floor of the mouth; depresses the mandible.
The Superior Roof of the Orbit
- The superior wall or roof of the orbit is formed almost completely by the orbital plate of the frontal bone.
- Posteriorly, the superior wall is formed by the lesser wing of the sphenoid bone.
- The roof of the orbit is thin, translucent, and gently arched. This plate of bone separates the orbital cavity and the anterior cranial fossa.
- The optic canal is located in the posterior part of the roof.
The Nose
- The nose is the superior part of the respiratory tract and contains the peripheral organ of smell.
- It is divided into right and left nasal cavities by the nasal septum.
- The nasal cavity is divided into the olfactory area and the respiratory area.
Nerves of the Face
Innervation of the Muscles of Facial Expression
The Facial Nerve (CN VII)
- The seventh cranial nerve supplies the superficial muscle of the neck (platysma), the muscles of facial expression, the auricular muscles and the scalp muscles.
- CN VII is the sole motor supply to the muscles of facial expression.
- The facial nerve emerges from the skull though the stylomastoid foramen.
- Almost immediately, it enters the parotid gland. It runs superficially in this gland before giving rise to its five terminal branches: temporal, zygomatic, buccal, marginal mandibular, and cervical.
- These nerve emerge from the superior, anterior and inferior margins of the gland and spread out like the abducted digits of the hand to supply the muscles of facial expression.
- The temporal branches of CN VII cross the zygomatic arch to supply all the superficial facial muscles superior to it, including the orbital and forehead muscles.
- The zygomatic branch of CN VII passes transversely over the zygomatic bone to supply the muscles in the zygomatic, orbital and infraorbital regions.
- The buccal branches of CN VII pass horizontally, external to the masseter muscle, to supply the buccinator and the muscles of the upper lip.
- The marginal mandibular branch of CN VII supplies the muscles of the lower lip and chin.
- The cervical branch of CN VII supplies the platysma and the superficial muscles of the neck.