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).
Geniohyoid Muscle
- Origin: Inferior genial tubercles of the mandible.
- Insertion: Anterior surface of the body of the hyoid bone.
- Nerve Supply: Branch of C1 through the hypoglossal nerve (CN XII).
- Arterial Supply: Sublingual branch of the lingual artery.
- Action: Elevates the hyoid bone and depresses the mandible.
Blood Supply to the Head and Neck
- Most arteries in the anterior cervical triangle arise from the common carotid artery or one of the branches of the external carotid artery.
- Most veins in the anterior cervical triangle are tributaries of the large internal jugular vein.
The Common Carotid Arteries
- The right common carotid artery begins at the bifurcation of the brachiocephalic trunk, posterior to the right sternoclavicular joint.
- The left common carotid artery begins arises from the arch of the aorta and ascends into the neck, posterior to the left sternoclavicular joint.
- Each common carotid artery ascends into the neck within the carotid sheath to the level of the superior border of the thyroid cartilage.
- Here it terminates by dividing into the internal and external carotid arteries.
The Internal Carotid Artery
- This is the direct continuation of the common carotid artery and it has no branches in the neck.
- It supplies structures inside the skull.
- The internal carotid arteries are two of the four main arteries that supply blood to the brain.
- Each artery arises from the common carotid at the level of the superior border of the thyroid cartilage.
- It then passes superiorly, almost in a vertical plane, to enter the carotid canal in the petrous part of the temporal bone.
- A plexus of sympathetic fibres accompany it.
- During its course through the neck, the internal carotid artery lies on the longus capitis muscle and the sympathetic trunk.
- The vagus nerve (CN X) lies posterolateral to it.
- The internal carotid artery enters the middle cranial fossa beside the dorsum sellae of the sphenoid bone.
- Within the cranial cavity, the internal carotid artery and its branches supply the hypophysis cerebri (pituitary gland), the orbit, and most of the supratentorial part of the brain.
The External Carotid Arteries
- This vessel begins at the bifurcation of the common carotid, at the level of the superior border of the thyroid cartilage.
- It supplies structures external to the skull.
- The external carotid artery runs posterosuperiorly to the region between the neck of the mandible and the lobule of the auricle.
- It terminates by dividing into two branches, the maxillary and superficial temporal arteries.
- The stems of most of the six branches of the external carotid artery are in the carotid triangle.
The Superior Thyroid Artery
- This is the most inferior of the 3 anterior branches of the external carotid.
- It arises close to the origin of the vessel, just inferior to the greater horn of the hyoid.
- The superior thyroid artery runs anteroinferiorly, deep to the infrahyoid muscles and gives off the superior laryngeal artery. This artery pierces the thyrohyoid membrane in company with the internal laryngeal nerve and supplies the larynx.
The Lingual Artery
- This arises from the external carotid artery as it lies on the middle constrictor muscle of the pharynx.
- It arches superoanteriorly, about 5 mm superior to the tip of the greater horn of the hyoid bone, and then passes deep to the hypoglossal nerve, the stylohyoid muscle, and the posterior belly of digastric muscle.
- It disappears deep to the hyoglossus muscle.
- At the anterior border of this muscle, it turns superiorly and ends by becoming the deep lingual artery.
The Facial Artery
- This arises from the carotid artery either, in common with the lingual artery, or immediately superior to it.
- In the neck the facial artery gives off its important tonsillar branch and branches to the palate and submandibular gland.
- The facial artery then passes superiorly under the cover of the digastric and stylohyoid muscles and the angle of the mandible.
- It loops anteriorly and enters a deep groove in the submandibular gland.
- The facial artery hooks around the inferior border of the mandible and enters the face. Here the pulsation of this artery can be felt (anterior to the masseter muscle).
The Ascending Pharyngeal Artery
- This is the 1st or 2nd branch of the external carotid artery.
- This small vessel ascends on the pharynx, deep to the internal carotid artery.
- It sends branches to the pharynx, prevertebral muscles, middle ear and meninges.
The Occipital Artery
- This arises from the posterior surface of the external carotid near the level of the facial artery.
- It passes posteriorly along the inferior border of the posterior belly of digastric.
- It ends in the posterior part of the scalp.
- During its course, it is superficial to the internal carotid artery and three cranial nerves (CN IX, CN X and CN XI).
The Posterior Auricular Artery
- This is a small posterior branch of the external carotid artery.
- It arises from it at the superior border of the posterior belly of the digastric muscle.
- It ascends posteriorly to the external acoustic meatus and supplies adjacent muscles, the parotid gland, the facial nerve, structures in the temporal bone, the auricle, and the scalp.
The Internal Jugular Vein
- This is usually the largest vein in the neck.
- The internal jugular vein drains blood from the brain and superficial parts of the face and neck.
- Its course corresponds to a line drawn from a point immediately inferior to the external acoustic meatus to the medial end of the clavicle.
- This large vein commences at the jugular foramen in the posterior cranial fossa, as the direct continuation of the sigmoid sinus.
- The dilation at its origin is called the superior bulb of the internal jugular vein.
- From here it runs inferiorly through the neck in the carotid sheath.
- The internal jugular vein leaves the anterior triangle of the neck by passing deep to the SCM muscle.
- Posterior to the sternal end of the clavicle, it unites with the subclavian vein to form the brachiocephalic vein.
- Near its termination is the inferior bulb of the jugular vein contains a bicuspid valve similar to that of the subclavian vein.
- The deep cervical lymph nodes lie along the course of the internal jugular vein, mostly lateral and posterior.
Tributaries of the Internal Jugular Vein
- This large vein is joined at its origin by the: inferior petrosal sinus, the facial, lingual, pharyngeal, superior and middle thyroid veins, and often the occipital vein.
BONE
A rigid form of CT, Consists of matrix and cells
Matrix contains:
organic component 35% collagen fibres
inorganic salts 65% calcium phosphate (58,5%), calcium carbonate (6,5%)
2 types of bone - spongy (concellous)
compact (dense)
Microscopic elements are the same
Spongy bone consists of bars (trabeculae) which branch and unite to form a meshwork
Spaces are filled with bone marrow
Compact bone appears solid but has microscopic spaces
In long bones the shaft is compact bone
And the ends (epiphysis) consists of spongy bone covered with compact bone
Flat bones consists of 2 plates of compact bone with spongy bone in-between
Periosteum covers the bone
Endosteum lines marrow cavity and spaces
These 2 layers play a role in the nutrition of bone tissue
They constantly supply the bone with new osteoblasts for the repair and growth of bone
Microscopically
The basic structural unit of bone is the Haversian system or osteon
An osteon consists of a central Haversian canal
- In which lies vessels nerves and loose CT
- Around the central canal lies rings of lacunae
- A lacuna is a space in the matrix in which lies the osteocyte
- The lacunae are connected through canaliculi which radiate from the lacunae
- In the canaliculi are the processes of the osteocytes
- The canaliculi link up with one another and also with the Haversian canal
- The processes communicate with one another in the canaliculi through gap junctions
- Between two adjacent rows of lacunae lie the lamellae, 5-7µm thick
- In three dimensions the Haversian systems are cylindrical
- The collagen fibres lie in a spiral in the lamellae
- Perpendicular to the Haversian canals are the Volkman's canals
- They link up with the marrow cavity and the Haversian canals
- Some lamellae do not form part of a Haversian system
- They are the:
- Inner circumferential lamellae - around the marrow cavity
- Outer circumferential lamellae - underneath the outer surface of the bone
- Interstitial lamellae - between the osteons
Endosteum
Lines all cavities like marrow spaces, Haversian- and Volkman's canals
Consists of a single layer of squamous osteoprogenitor cells with a thin reticular CT layer underneath it
Continuous with the inner layer of periosteum
Covers the trabeculae of spongy bone
Cells differentiate into osteoblasts (like the cells of the periosteum)
Periosteum
Formed by tough CT
2 layers
Outer fibrous layer: Thickest, Contains collagen fibres,
Some fibres enter the bone - called Sharpey's fibres
Contains blood vessels.
Also fibrocytes and the other cells found in common CT
Inner cellular layer
Flattened cells (continuous with the endosteum)
Can divide and differentiate into osteoprogenitor cells
spindle shaped
little amount of rough EPR
poorly developed Golgi complex
play a prominent role in bone growth and repair
Osteoblasts
Oval in shape, Have thin processes, Rough EPR in one part of the cell (basophilic)
On the other side is the nucleus, Golgi and the centrioles in the middle, Form matrix
Become trapped in the matrix
Osteocytes
Mature cells, Less basophilic than the osteoblasts, Lie trapped in the lacunae, Their processes lie in the canaliculi, Processes communicate with one another through gap junctions, Substances (nutrients, waste products) are passed on from cell to cell
Osteoclasts
Very large, Multinucleate (up to 50), On inner and outer surface of bone, Lie in depressions on the surface called Howships lacunae, The cell surface facing the bone has short irregular processes
Acidophylic
Has many lysosomes, polyribosomes and rough EPR
Lysosomal enzymes are secreted to digest the bone
Resorbs the organic part of bone
Histogenesis
Two types of bone development.
- intramembranous ossification
- endochondral ossification
In both these types of bone development temporary primary bone is deposited which is soon replaced by secondary bone. Primary bone has more osteocytes and the mineral content is lower.
Gross anatomy-study of structures that can be identified with the naked eye; usually involves the use of cadavers
- Microscopic anatomy (histology)-study of cells that compose tissues and organs; involves the use of a microscope to study the details of the species
- Developmental anatomy (embryology)-study of an individual from beginning as a single cell to birth
- Comparative anatomy -comparative study of the animal structure in regard to similar organs or regions
The Parotid Glands
- The parotid glands are the largest of the three pairs of salivary glands.
- Each gland is wedged between the mandible and the sternocleidomastoid muscle and partly covers them.
- The parotid gland is wrapped with a fibrous capsule (parotid fascia) that is continuous with the deep investing fascia of the neck.
- Viewed superficially, the parotid gland is somewhat triangular in shape.
- Its apex is posterior to the angle of the mandible and its base is along the zygomatic arch.
- The parotid gland overlaps the posterior part of the masseter muscle.
- The parotid duct (Stensen's duct) is about 5 cm long and 5 mm in diameter.
- It passes horizontally from the anterior edge of the gland.
- At the anterior border of the masseter muscle, the parotid duct turns medially and pierces the buccinator muscle.
- It enters the oral cavity opposite the second maxillary molar.
Blood Vessels of the Parotid Gland
- This gland is supplied by branches of the external carotid artery.
- The veins from the parotid gland drains into the retromandibular vein, which enters the internal jugular vein.
Lymphatic Drainage of the Parotid Gland
- The lymph vessels of this gland end in the superficial and deep cervical lymph nodes.
Nerves of the Parotid Gland
- These nerves are derived from the auriculotemporal nerve and from the sympathetic and parasympathetic systems.
- The parasympathetic fibres are derived from the glossopharyngeal nerve (CN IX) through the otic ganglion.
- Stimulation of these fibres produces a thin watery (serous) saliva to flow from the parotid duct.
- The sympathetic fibres are derived from the cervical ganglia through the external carotid plexus.
- Stimulation of these fibres produces a thick mucous saliva.
o English: all speech sounds produced by making exhaled air audible
o Two ways of producing sound
at larynx
further up in vocal tract (tongue, lips)
o How to produce sound at larynx
changes in breathing: regulate airstream from lungs to atmosphere by changing movements of vocal folds, pharynx, soft-palate, tongue, lips and jaws
• inhalation: take in greater volume more quickly, abduct folds
• expiration: variable force; use muscles of inhalation to control rate of expiration, adduct
How to vibrate vocal cords
• NOT rhythmic contraction of laryngeal muscles: would be impossible b/c frequenceies of virbration
• Changes in air pressure cause vibrations
o Adduct folds increase in subglottal pressure force folds apart folds sucked back together (Bernouilli effect)
• The vibration of vocal cords disturbs airareas of low pressure (rarefaction) alternating with areas of high pressure (compression)
• Changes in pressure sound at ears
• Sine waves
o Changes in amplitudes: loudness
o Changes in frequency: pitch
o Normal sounds have fundamental frequency, overtones or harmonics
o Mass of folds: critical in voice
Low pitch of lion’s roar: due to massive fibrous pad that forms part of vocal cords
Men: more massive vocal cords
Larger foldsslow vibrationdeeper voice
o Producing vowels and constants
Most vowels are “voiced”: vocal folds produce sounds
Consonants: can be “voiced” (Z) or “non-voiced” (S)
• Use higher regions of vocal tract to control by stopping, restricting airflow from vocal folds; use lips, teethaperiodic sound
o Vocal folds and resonators emphasize and deemphasize certain frequencies
Never hear sounds produced at vocal foldsevery sound changed by passage thru vocal tract: sinuses/resonating chambers
Howling monkeys: large hyoid bonepowerful resonator
o Age-related changes in voice
Infant larynx is smaller, different proportions
• Arytenoids are proportionately larger
• Smaller vocal apparatushigher pitch
• Larynx sits higher easier to breathe thru nose
Abrupt change in larynx at pubertycan’t control voice
Older adult: normal degenerative changes in lamina propria, ossification of thyroid cartilagechanges in fundamental frequency
Lose your voice vocal fold are irritated
• Can’t adduct foldsair escapes
o Singing v. speaking
Singing: greater thoracic pressure and uneven breathing with changes in resonators
o Whispering
Intercartilaginous portions of vocal folds: open to allow air to escapelesser subglottal pressureslittle vibration of foldslittle tonal quality, low volume
o Falsetto
Allowing only part of vocal folds to vibrate
Increase range by training which part of vocal folds to vibrate
o Colds
Mucus secretions add mass to folds—decrease in pitch, can’t adduct folds as well
o Surgeryscars, fibrotic changes can interfere with voice