Entry 7

Anosmia

  The sense of smell is regulated by cranial nerve I, olfactory n. The cell bodies of olfactory receptor neurons are located in the olfactory organ; located in the roof of the nasal cavity and along the nasal septum and medial wall of the superior nasal concha. These neurons are both receptors and conductors, and the apical surfaces of the neurons are covered in fine olfactory cilia, bathed by a film of watery mucus secreted by the olfactory glands of the epithelium.

Anosmia is simply the loss of smell, just like hearing loss occurs with growing older, so does smell. Sometimes the loss of smell is associated with upper respiratory infections, sinus disease, and head trauma. A severe head trauma the olfactory bulbs may be torn away from the olfactory nerves or some olfactory nerve fibers may be torn as the pass through a fractured cribriform plate. If these bundles are torn a complete loss of smell will occur. Anosmia may also be a clue to a fracture of the cranial base and cerebrospinal fluid rhinorrhea. http://en.wikipedia.org/wiki/Anosmia

Acoustic Neuroma

 Cranial nerve VIII, vestibulocochlear nerve, regulates the special sensations of hearing and equilibrium and motion. CN VIII emerges from the junction of the medulla and pons continuing through the internal acoustic meatus and then separates into the vestibular nerve and cochlear nerves. The peripheral processes of the vestibular neurons extend to the utricle and saccule; to the cristae of the ampullae of the semicircular ducts. The peripheral processes of the cochlear neurons extend to the spiral organ for the sense of hearing.

            Acoustic neuroma is a slow growing benign tumor of the Schwann cells. These cells wrap around neurons creating a myelin shealth, a conductive platform for impulses to travel down. The tumor begins in the vestibular nerve while it is in the internal acoustic meatus. The early symptom is usually hearing loss; Dysequilibrium and tinnitus can also occur but only in 70% of patients. Treatment options range from simple observation to surgery and possibly stereotactic radiosurgery.
http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001782/

Olfactory Hallucinations

            Cranial nerve I, olfactory nerve, as stated previously in this entry, regulates the sense of smell. CN I emerges from the forebrain, but unlike the other cranial nerves, it consists of a collection of many sensory nerve fibers that extend to the olfactory bulb; passing through the many openings of the Cribriform plate of the Ethmoid bone. These tracts divide into the lateral and medial olfactory striae. The lateral olfactory stria terminates in the piriform cortex of the anterior part of the temporal lobe. The medial stria prjects through the anterior commissure to olfactory structures.

Olfactory hallucinations might be the result of lesions in the temporal lobe of the cerebral hemisphere. These lesions could cause irritation to the lateral olfactory area, which could cause temporal lobe epilepsy, or “uncinate fits”. Characterized by imaginary disagreeable odors and involuntary movements of the lips and tongue. This disorder was one of the symptoms of the patient on the latest House episode. Treatment of these lesions is still in the infancy stages.
http://en.wikipedia.org/wiki/Phantosmia