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Anatomy of the Nose and Olfactory Nerve

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Anatomy of the Nose and Olfactory Nerve Neuroanatomy block-Anatomy-Lecture 12 Editing file Objectives At the end of the lecture, students should be able to: ● Describe the boundaries and functions of the nose and nasal cavity. ● Describe the nasal conchae and meati. ● Demonstrate the openings in each meatus. ● Describe the arterial supply and innervation of the nose. ● Describe the paranasal sinuses and their functions ● Describe the clinical significances of the nose and nasal cavity. Color guide ● Only in boys slides in Green ● Only in girls slides in Purple ● important in Red ● Notes in Grey Only in boys slide The Nose Humidification of the ● The external (anterior) nares or nostrils lead to to the Respiration: inspired air: Mucous nasal cavity. Breathing 6 1 ● Formed above by bony skeleton. ● Formed below by plates of hyaline cartilage Reception of secretions from Olfaction: Smell Functions the paranasal Nasal Cavity 5 2 sinuses and nasolacrimal ● It is a large air filled space above and behind the nose in the duct. middle of the face. ● Each cavity is the continuation of one of the two nostrils. Warming the ● It communicates with nasopharynx posteriorly. 4 3 inspired air: ● It consists of Vestibule, Respiratory, and Olfactory regions. Filtration of dust submucous venous ● It extends from nostrils anteriorly to turbinate (choanae) plexus. posteriorly.(in both slides) Divisions of Nasal Cavity: Vestibule region: Respiratory region: Olfactory Region - The area surrounding the external opening to the nasal cavity. - The largest region. - Located at the apex of the - Lined by modified skin, provided with hairs - Lined with mucous that is continuous nasal cavity. and Sebaceous glands to filter the incoming with that of Nasal Sinuses, Lacrimal sac, - It is lined by olfactory cells air. (Exocrine glands in the skin that secrete Conjunctiva, and Nasopharynx. with olfactory receptors. an oily or waxy matter called sebum to lubricate and waterproof the skin and hairs.) 3 Only in girls slide Nasal Cavity mucosa Respiratory mucosa Nasal (Olfactory) mucosa ● It is thick, ciliated highly vascular and contains mucous glands goblet cells ● It is delicate and contains olfactory nerve cells. ● It lines the lower part of the nasal cavity. ● It is present in the upper part of nasal cavity: (From skin of vestibule to the superior concha). ○ Roof ● It functions to moisten, clean and warm the inspired air ○ On the lateral wall, it lines the upper surface of the ● The air is moistened by the secretion of numerous serous glands superior concha and the sphenoethmoidal recess. ● It is cleaned by the removal of the dust particles via ciliary ○ On the medial wall, it lines the superior part of the action of the columnar ciliated epithelium that covers the nasal septum. mucosa. ● The air is warmed by a submucous venous plexus. 4 Nasal Cavity : It is divided into right and left parts by nasal septum Each part has Floor Roof Medial wall Lateral wall It is formed by: it is formed by: The nasal septum Marked by three projections The nasal (upper) surface of -Body of sphenoid Vertical plate of ethmoid. 1. Superior concha. 2. Middle concha. 3. Inferior concha. the hard (bony) palate: (Posteriorly). Vomer. they Function :to increase the surface area of the nasal cavity to increases the amount of -Palatine process of maxilla -Cribriform plate of ethmoid Septal Cartilage. inspired air They also disrupt the fast, laminar flow of the air, making it slow and turbulent. The air spends longer in the nasal cavity, so that it can be humidified. (Anteriorly). (Middle). -Frontal bone -Horizontal plate of the (Anteriorly). They project into the nasal cavity, creating four pathways for the air to flow: 1.Spheno-ethmoidal recess: opening of sphenoid air sinus palatine (Posteriorly). - Nasal bone (Anteriorly). 2. Superior meatus: receives openings of posterior ethmoidal sinuses. 3. Middle meatus. Contain: (bulla ethmoidalis) for opening of middle ethmoidal sinus Hiatus semilunaris for openings of maxillary sinus, Infundibulum opening of Frontonasal duct that drains the frontal sinus and anterior ethmoidal sinus. 4. Inferior meatus: receives opening of nasolacrimal duct. 5 Nasal Cavity Nerve supply Arterial supply Venous drainage Lymph drainage ● Nerves of smell: Olfactory Nerves (Cr 1). The nasal cavity receives blood from: ● Venous plexus in ● Submandibular & ● Nerves of general sensation: Ophthalmic ● Internal carotid branches: Anterior and submucosa formed by ● Upper deep cervical and Maxillary divisions of Trigeminal Posterior Ethmoidal (ophthalmic). veins accompanying the nodes. nerve (Cr 5). ● External carotid branches: arteries ● The anterior part is supplied by: 1. Sphenopalatine artery (Maxillary). ● They drain into the Anterior Ethmoidal nerve. 2. Superior labial (Facial). pterygoid venous plexus ● The posterior part is supplied by 3. Greater palatine artery & facial vein or branches of the pterygopalatine 4. Lateral nasal arteries cavernous sinus. ganglion: ● Applied anatomy :The most common site 1. Nasopalatine for epistaxis is at the anterior & inferior 2. Nasal. part of nasal septum (Little’s area) 3. Palatine. because of the rich arterial anastomosis. 6 Paranasal Sinuses Definition Functions Clinical significance 1. Inflammation ● They are a group of four paired air-filled spaces 1. (Lighten the skull weight). ● The paranasal sinuses are joined to the that surround the nasal cavity. 2. Increasing resonance of the voice nasal cavity via small orifices called ostia ● They are lined with respiratory epithelium (Amplify the sound as we speak). These become blocked easily by allergic mucoperiosteum (ciliated pseudostratified 3. Providing a buffer against facial inflammation or by swelling in the nasal columnar epithelium). trauma. lining that occurs with a cold If this ● Open in the lateral wall of the nasal cavity 4. Insulating sensitive structures like happens, normal drainage of mucus ● Divided into subgroups that are named according dental roots and eyes from rapid within the sinuses is disrupted, and to the bones within which the sinuses located: temperature change in the nasal sinusitis may occur. cavity. ● Because the maxillary posterior teeth are 1. The Maxillary Sinuses: the largest of the 5. Humidifying and heating of inhaled close to the maxillary sinus, this can also paranasal sinuses, located under the eyes, in the air because of slow air turnover in cause clinical problems if any disease maxillary bones. this region. processes are present, such as an 2. The Frontal Sinuses: superior to the eyes, in the infection in any of these teeth frontal bone, which forms the hard part of the 2. Cancer forehead. ● Malignancies of the paranasal sinuses 3. The Ethmoidal Sinuses: formed from several comprise approximately 0 2 of all discrete air cells within the ethmoid bone malignancies between the nose and the eyes. ● About 80 of these malignancies arise in 4. The Sphenoidal Sinuses: in the sphenoid bone. the maxillary sinus, tumors of the sphenoid and frontal sinuses are extremely rare. ● Carcinomas are more frequent than sarcomas. 7 Olfactory nerve ● The first and shortest cranial nerve, it is the nerve that transmits special sensory information to have a sense of smell. ● it is one of two cranial nerves that do not emerge from the brainstem. ● Elderly people usually have less sensation of smell probably because of progressive reduction in number of olfactory cells. Olfactory pathway: it is important to note that the olfactory nerve is made up of multiple nerve fibers/rootlets coming from the receptors cells. The pathway can be summarized as follows: olfactory receptor cells, olfactory nerves, olfactory bulb, olfactory tract, olfactory striae, olfactory cortex The only sensory pathway which reaches the cerebral cortex without passing through the Thalamus. 1 Olfactory receptors 2 Mitral cells of olfactory bulb ● 1st order neuron ● they are specialized, ciliated nerve ● 2nd neuron cells that lie in the olfactory ● In the cranial cavity, the fibres enter the epithelium olfactory bulb, which lies in the olfactory ● Once the axon penetrates through groove, within the anterior cranial fossa. the basement membrane, it joins ● Preliminary processing of olfactory other non-myelinated processes to information is within the olfactory bulb form the fila olfactoria.(bundles of which contains interneurons and large olfactory axons) Mitral cells. ● The axons of these bipolar cells ● The olfactory nerve fibres synapse with 12-20 fibers from the ture the mitral cells, forming collections olfactory nerve fibers which pass known as synaptic glomeruli. through the cribriform plate of ● From the glomeruli, second order nerves ethmoid (in the roof of the nasal then pass posteriorly into the olfactory cavity) and then join the olfactory tract bulb. 8 Olfactory nerve 3 Olfactory tract 4 Olfactory STRIAE ● The olfactory tract runs inferiorly to ● Medial root (Medial stria): ❖ the frontal lobe crosses midline through anterior ● Each tract divides into 2 roots at the commissure and joins the uncrossed anterior perforated substance olfactory bulb lateral root of the opposite ● Posterior and anterior to the optic side. ❖ chiasm, the olfactory tract on both It connects olfactory centers of 2 cerebral sides splits into medial and lateral hemispheres, so each olfactory centre olfactory striae. receives smell sensation from both halves of nasal cavity. ❖ Lateral root (Lateral stria): ❖ Carries olfactory fibers to end in cortex of the Uncus & adjacent Hippocampal gyrus (center of smell).
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