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 Sublingual Glands
- These are the smallest of the three paired salivary glands and the most deeply situated.
- They are almond-shaped and lie in the floor of the mouth between the mandible and the genioglossus muscle.
- The paired glands unite to form a horseshoe-shaped glandular mass around the lingual frenulum.
- Numerous small ducts (10 to 12) open into the floor of the mouth.
- Sometimes one of the ducts opens into the submandibular duct.
- The nerves the accompany the submandibular and sublingual glands are derived from the lingual and chorda tympani nerves and from the sympathetic nerves.
- The parasympathetic secretomotor fibres are from the submandibular ganglion.
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BONES OF THE CRANIUM
Occipital (1)
Frontal (1)
Sphenoid (1)
Ethmoid (1)
Parietal (2)
Temporal (2)
BONES OF THE FACE
Mandible (1)
Vomer (1)
Maxillae (2)
Zygomae (2)
Lacrimal (2)
Nasal (2)
Inferior nasal conchae (2)
Palatine (2)
Nerves of the Palate
- The sensory nerves of the palate, which are branches of the pterygopalatine ganglion, are the greater and lesser palatine nerves.
- They accompany the arteries through the greater and lesser palatine foramina, respectively.
- The greater palatine nerve supplies the gingivae, mucous membrane, and glands of the hard palate.
- The lesser palatine nerve supplies the soft palate.
- Another branch of the pterygopalatine ganglion, the nasopalatine nerve, emerges from the incisive foramen and supplies the mucous membrane of the anterior part of the hard palate.
Vessels of the Palate
- The palate has a rich blood supply from branches of the maxillary artery.
Muscles of the Soft Palate
The Levator Veli Palatini (Levator Palati)
- Superior attachment: cartilage of the auditory tube and petrous part of temporal bone.
- Inferior attachment: palatine aponeurosis.
- Innervation: pharyngeal branch of vagus via pharyngeal plexus.
- This cylindrical muscle runs inferoanteriorly, spreading out in the soft palate, where it attaches to the superior surface of the palatine aponeurosis.
- It elevates the soft palate, drawing it superiorly and posteriorly.
- It also opens the auditory tube to equalise air pressure in the middle ear and pharynx.
The Tensor Veli Palatini (Tensor Palati)
- Superior attachment: scaphoid fossa of medial pterygoid plate, spine of sphenoid bone, and cartilage of auditory tube.
- Inferior attachment: palatine aponeurosis.
- Innervation: medial pterygoid nerve (a branch of the mandibular nerve).
- This thin, triangular muscle passes inferiorly, and hooks around the hamulus of the medial pterygoid plate.
- It then inserts into the palatine aponeurosis.
- This muscle tenses the soft palate by using the hamulus as a pulley.
- It also pulls the membranous portion of the auditory tube open to equalise air pressure of the middle ear and pharynx.
The Palatoglossus Muscle
- Superior attachment: palatine aponeurosis.
- Inferior attachment: side of tongue.
- Innervation: cranial part of accessory nerve (CN XI) through the pharyngeal branch of vagus (CN X) via the pharyngeal plexus.
- This muscle, covered by mucous membrane, forms the palatoglossal arch.
- The palatoglossus elevates the posterior part of the tongue and draws the soft palate inferiorly onto the tongue.
- Superior attachment: hard palatThe Palatopharyngeus Musclee and palatine aponeurosis.
- Inferior attachment: lateral wall of pharynx.
- Innervation: cranial part of accessory nerve (CN XI) through the pharyngeal branch of vagus (CN X) via the pharyngeal plexus.
- This thin, flat muscle is covered with mucous membrane to form the palatopharyngeal arch.
- It passes posteroinferiorly in this arch.
- This muscle tenses the soft palate and pulls the walls of the pharynx superiorly, anteriorly and medially during swallowing.
The Musculus Uvulae
- Superior attachment: posterior nasal spine and palatine aponeurosis.
- Inferior attachment: mucosa of uvula.
- Innervation: cranial part of accessory through the pharyngeal branch of vagus, via the pharyngeal plexus.
- It passes posteriorly on each side of the median plane and inserts into the mucosa of the uvula.
- When the muscle contracts, it shortens the uvula and pulls it superiorly.
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.
Muscles Around the Eyelids
- The function of the eyelid (L. palpebrae) is to protect the eye from injury and excessive light. It also keeps the cornea moist.
The Orbicularis Oculi Muscle
- This is the sphincter muscle of the eye.
- Its fibres sweep in concentric circles around the orbital margin and eyelids.
- It narrows the eye and helps the flow of tears from the lacrimal sac.
- This muscle has 3 parts: (1) a thick orbital part for closing the eyes to protect then from light and dust; (2) a thin palpebral part for closing the eyelids lightly to keep the cornea from drying; and (3) a lacrimal part for drawing the eyelids and lacrimal punta medially.
- When all three parts of the orbicularis oculi contract, the eyes are firmly closed and the adjacent skin becomes wrinkled.
- The zygomatic branch of the facial nerve (CN VII) supplies it.
The Levator Palpebrae Superioris Muscle
- This muscle raises the upper eyelid to open the palpebral fissure.
- It is supplied by the oculomotor nerve (CN III).