NEET MDS Lessons
Anatomy
The Cheeks
- The cheeks (L. buccae) form the lateral wall of the vestibule of the oral cavity.
- They have essentially the same structure as the lips with which they are continuous.
- The principal muscular component of the cheeks is the buccinator muscle.
- Superficial to the fascia covering this muscle is the buccal fatpad that gives cheeks their rounded contour, especially in infants.
- The lips and cheeks act as a functional unit (e.g. during sucking, blowing, eating, etc.).
- They act as an oral sphincter in pushing food from the vestibule to the oral cavity proper.
- The tongue and buccinator muscle keep the food between the molar teeth during chewing.
Sensory Nerves of the Cheeks
- These are branches of the maxillary and mandibular nerves.
- They supply the skin of the cheeks and the mucous membrane lining the cheeks.
Histology
Histology is the study of tissues.
A tissue is a group of cells with similar structure and function plus the extracellular substances located between the cells.
There are four basic types of tissues:
- Epitheliums
- Connective tissue
- Muscle tissue
- Nervous tissue
The Nasopharynx
- The nasal part of the pharynx has a respiratory function.
- It lies superior to the soft palate and is a posterior extension of the nasal cavity.
- The nose opens into the nasopharynx via to large posterior apertures called choanae.
- The roof and posterior wall of the nasopharynx form a continuous surface that lies inferior to the body of the sphenoid bone and the basilar part of the occipital bone.
- In the mucous membrane of the roof of the posterior wall of the nasopharynx is a collection of lymphoid tissue, known as the pharyngeal tonsil (commonly known as the adenoids).
- The pharyngeal orifice of the auditory tube is on the lateral wall of the nasopharynx, 1 to 1.5 cm posterior to the inferior concha, and level with the superior border of the palate.
- The orifice is directed inferiorly and has a hood-like tubal elevation over it called the torus of the auditory tube or the torus tubarius (L. torus, swelling).
- Extending inferiorly from the torus is a vertical fold of mucous membrane, known as the salpingopharyngeal fold.
- The collection of lymphoid tissue in the submucosa of the pharynx, posterior to the orifice of the auditory tube, is known as the tubal tonsil.
- Posterior to the torus and the salpingopharyngeal fold, there is a slit-like lateral projection of the pharynx called the pharyngeal recess.
- It extends laterally and posteriorly.
The Muscles of Facial Expression
- These lie in the subcutaneous tissue and are attached to the skin of the face.
- They enable us to move our skin and change our facial expression. They produce their effects by pulling on the skin but do not move the facial skeleton.
- These muscles surround the facial orifices and act as sphincters and dilators.
- All facial muscles receive their innervation from the branches of the facial nerve (CN VII)-temporal, zygomatic, buccal, marginal mandibular, cervical.
The Laryngopharynx
- The laryngeal part of the pharynx lies posterior to the larynx.
- It extends from the superior border of the epiglottis to the inferior border of the cricoid cartilage, where it narrows to become continuous with the oesophagus.
- Posteriorly, the laryngopharynx is related to the bodies of C4 to C6 vertebrae.
- Its posterior and lateral walls are formed by the middle and inferior constrictor muscles, with the palatopharyngeus and stylopharyngeus internally.
- The laryngopharynx communicates with the larynx through the aditus or inlet of the larynx.
- The piriform recess is a small, pear-shaped depression of the laryngopharyngeal cavity on each side of the inlet of the larynx.
The Nasal Mucosa
- Mucosa lines the entire nasal cavities except for the vestibule of the nose.
- The nasal mucosa is firmly bound to the periosteum and perichondrium of the supporting structures of the nose.
- It is continuous with the adjoining cavities to which the nasal cavity communicates (e.g., the nasopharynx and paranasal sinuses).
- The inferior 2/3 of the nasal mucosa is called the respiratory area and air passing over this is warmed and moistened before it passes into the lungs.
- The superior 1/3 is called the olfactory area.
The Olfactory Area of Nasal Mucosa
- This area contains the peripheral organ of smell.
- Sniffing draws air into this area
- Olfactory receptor cells (from the olfactory nerve, CN I, are located in the mucosa of this area in the nose.
Nerves to the Respiratory Area of Nasal Mucosa
- The inferior 2/3 of the nasal mucosa are supplied chiefly by the trigeminal nerve (CN V).
- The mucous membrane of the nasal septum is supplied chiefly by the nasopalatine nerve, a branch of the maxillary nerve (CN V2).
- Its anterior portion is supplied by the anterior ethmoidal nerve (a branch of the nasociliary nerve) which is derived from the ophthalmic nerve (CN V1).
- The lateral walls of the nasal cavity are supplied by branches of the maxillary nerve (CN V2); the greater palatine nerve, and the anterior ethmoidal nerve.
Arteries of the Nasal Mucosa
- The blood supply of the mucosa of the nasal septum is derived mainly from the maxillary artery.
- The sphenopalatine artery, a branch of the maxillary, supplies most of the blood of the nasal mucosa.
- It enters by the sphenopalatine foramen and sends branches to the posterior regions of the lateral wall and to the nasal septum.
- The greater palatine artery, also a branch of the maxillary, passes through the incisive foramen to supply the nasal septum.
- The anterior and posterior ethmoidal arteries, branches of the ophthalmic artery, supply the anterosuperior part of the mucosa of the lateral wall of the nasal cavity and nasal septum.
- Three branches of the facial artery (superior labial, ascending palatine, and lateral nasal) also supply the anterior parts of the nasal mucosa.
Veins of the Nasal Mucosa
- The veins of the nasal mucosa form a venous network of plexus in the connective tissue of the nasal mucosa.
- Some of the veins open into the sphenopalatine vein and drain to the pterygoid plexus.
- Others join the facial and infraorbital veins.
- Some empty into the ophthalmic veins and drain into the cavernous sinus.
The Salivary Glands
- There are three large, paired salivary glands: the parotid, submandibular, and sublingual glands.
- In addition to the main salivary glands, there are numerous small accessory salivary glands scattered over the palate, lips, cheeks, tonsils, and tongue.