Anatomy of olfactory system


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Anatomy of olfactory system

  1. 1.  Oldest sensory modalities in the phylogenetic history of mammals Olfactorysystem detects food and influences social and sexual behavior
  2. 2. 3 cell types, basal, supporting, and olfactory receptor cells Basalcells are stem cells that give rise to the olfactory receptor cells continuous turnover unique to the olfactory system receptorcells are actually bipolar neurons, each possessing a thin dendritic rod that contains specialized cilia extending from the olfactory vesicle and a long central process that forms the fila olfactoria
  3. 3. olfactory nerve (I) Olfactory bulb Olfactory tract Optic nerve (II) Optic chiasma Optic tract Oculomotor nerve (III) Trochlear nerve (IV) Trigeminal nerve (V) Abducens nerve (VI) Cerebellum MedullaTable 14.3 (1 of 12)
  4. 4.  small unmyelinated axons of the olfactory receptor cells form the fine fibers of the first cranial nerve travel centrally toward the ipsilateral olfactory bulb to make contact with the second-order neurons cribriform plate of the ethmoid bone, separated at the midline by the crista galli, contains multiple small foramina through which the olfactory nerve fibers, or fila olfactoria, traverse
  5. 5.  lies inferior to the basal frontal lobe The layers (from outside toward the center of the bulb) are differentiated as follows: • Glomerular layer • External plexiform layer • Mitral cell layer • Internal plexiform layer • Granule cell layer
  6. 6.  Medial fibers of the tract contact the anterior olfactory nucleus and the septal area. Some fibers project to the contralateral olfactory bulb via the anterior commissure. Lateral fibers contact third-order neurons in the primary olfactory cortex (prepyriform and entorhinal areas) directly
  7. 7.  Third-order neurons send projections to the dorsomedial nucleus of the thalamus, the basal forebrain, and the limbic system
  8. 8.  Pyriform lobe includes the olfactory tract, the uncus, and the anterior part of the parahippocampal gyrus is known as the entorhinal area the secondary olfactory cortex The prepyriform and the periamygdaloid areas of the temporal lobe represent the primary olfactory cortex.
  9. 9.  Communications with superior and inferior salivary nuclei are important in reflex salivation . Patient with olfactory impairment c/o loss of taste [every thing feels like mud.]
  10. 10.  Loss of smell sensation –patient miss olfactory danger signals. olfactory deficits - two types 1-conductive 2-sensorineural 1-interfernce of an odour in contact 2-dysfunction of receptor/central connections
  11. 11.  ensure nasal passages are open stimuli should be non irritant examine each nostril separately occluding the other one with eyes closed ask the patient whether smells something or not if yes identify the substance repeat the test in other nostril
  12. 12.  the side that might be abnormal should be examined first perception of an odour –continuty of olfactory pathway identification of an odour – intact cortical functions
  13. 13.  Anosmia - Absence of smell sensation Hyposmia - Decreased sensation Dysosmia - Defect in sense of smell Cacosmia - Sensation of a bad or foul smell Parosmia - Sensation of smell in the absence of appropriate stimulus
  14. 14.  URTI Head trauma Nasal and sinus disease Idiopathic • These Four are most Common Causes
  15. 15. Others- Olfactory groove meningioma Frontal Lobe tumor Sellar /Parasellar tumor Vitamin deficiency (B6,B12,A) Parkinsons Disease Kallmans Synddrome Psychiatric conditions Cadmium Toxicity Cocaine Abuse
  16. 16.  Kallmann syndrome (ie, hypogonadism with anosmia) Foster Kennedy syndrome (ie, papilledema, unilateral anosmia, and optic atrophy usually associated with an olfactory groove meningioma). Cranio cerebral Trauma – Results in damage of olfactory nerve at the cribriform plate of ethmoid
  17. 17.  Purely Motor Nerve Origin - Two nuclei from the medulla lies beneath the floor of the fourth ventricle under the medial aspect of the hypoglossal trigone Axons emerge in the sulcus between the pyramid and the inferior olive as many rootlets
  18. 18.  Runsinferior to the tongue - innervates the tongue muscles Facial nerve (VII) Vestibulocochlear nerve (VIII) Glossopharyngeal nerve (IX) Vagus nerve (X) Accessory nerve (XI) Hypoglossal nerve (XII) Table 14.3 (12 of 12)
  19. 19.  rootletsof this nerve are collected into two bundles, which perforate the dura mater separately, opposite the hypoglossal canal in the occipital bone The nerve descends almost vertically to a point corresponding with the angle of the mandible
  20. 20.  It descends through the neck at the level of the angle of mandible, here it lies beneath the carotid sheath It runs forward above the hyoid bone and divides into number of fibers supplying the tongue Branches of the hypoglossal nerve are • Meningial • Descending • thyrohyoid • Muscular
  21. 21. Its branches of communication are, Vagus. First and second cervical nerves. Sympathetic. Lingual
  22. 22.  Tounge has extrinsic – paired muscles Genioglossus Styloglossus Hyoglossus Chondroglossus Intrinsic muscles – Superior and inferior longitudinales, transversus, verticalis Extrinsic mucles help in Protrusion and retraction of the tounge, move the tounge up and down Intrinsic muscles help in Change in Length, width and curvature of the dorsal surface, and turn the non protruded tip from side to side
  23. 23.  The centre that regulates the tounge movements – lower portion of precentral gyrus near and within the sylvian fissure The supranuclear fibres run in corticobulbar tract through the genu of the internal capsule and through the cerebral peduncle The supranuclear pathway is crossed
  24. 24.  Examination consists of evaluating1) Strength2)Bulk3)Dextirity of the tongue One has to look for • Weakness • Atrophy • Abnormal movements • Impairment of rapid movements
  25. 25.  Patient is asked to move tongue in and out ,up and down , side to side Best by assessing the strength against pressed cheek In unilateral weakness, the tounge is deviated towards the same side In bilateral weakness, tounge movements may be impaired
  26. 26.  Symptoms- • Unilateral weakness- Speech and swallowing are little affected • Bilateral weakness – First stage of swallowing is impaired • Difficulty in articulation and respiratory difficulty • Supranuclear, Nuclear, infranuclear lesions
  27. 27.  Supranulear Lesions • Causes weakness but no atrophy • Lesions are seen in cotrex, corticobulbar tract, internal capsule, cerebral peduncle and pons Pseudobulbar Palsy • Due to bilateral UMN disease causing bilateral weakness • Hemispheric lesion causes apraxia of tounge movements Extrapyramidal disorders causes slowing of tounge movements
  28. 28.  Nuclear and Infra nuclear lesions – causes weakness + Atrophy In addition to above, Fasciculations are seen in Progressive nuclear disease The disorders include neoplasms, vascular lesions, Motor neuron diseases, Granulomas etc.
  29. 29.  Infra nuclear lesions • Intracranial • Extracranial Intracraniallesions same as nuclear lesions and other causes includes meningitis, SAH, Trauma Extracranial causes- penetrating wounds, carotid aneurysms, infections