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manjeet



Number of posts : 1
Location : rohtak,haryana
Occupation : DOCTOR
Educational Qualification : PG FINAL YEAR
Registration date : 2007-04-01

PostSubject: query   Thu Apr 26, 2007 10:11 pm

what is the role of olfactory nerve in sneezing reflex,,


n its reflex arc



thanks
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anandbhaskar



Number of posts : 49
Age : 37
Location : Christian Medical College, Vellore
Occupation : Assistant Professor in Physiology
Educational Qualification : MBBS, MD
Registration date : 2007-01-07

PostSubject: Re: query   Thu Apr 26, 2007 10:15 pm

"The sneeze reflex is similar to the cough reflex, but it differs in several ways. The source of irritation that initiates the sneeze reflex is in the nasal passages instead of in the trachea and bronchi, and the action potentials are conducted along the trigeminal nerves to the medulla, where the reflex is triggered. During the sneeze reflex the uvula and the soft palate are depressed so the air is directed primarily through the nasal passages, although a considerable amount passes through the oral cavity. The rapidly flowing air dislodges particulate matter from the nasal passages and propels it a considerable distance from the nose."

To explain this a bit, the trigeminal nerve acts as the main senory nerve of the head. A simple reflex involves a sensory nerve that received the information and directly stimulates a motor nerve that provides the response. So long as the sensory nerve stimulates the motor nerve you should get the response. Physiology proves more complicated. The pathway may involve intermediary nerve cells which may receive influence from other areas. Thus most people can "supress" a reflex. People who suffer damage to the controling pathways will have "released" or pathologically hyperactive reflexes.

In the case of the sneeze, the sensory nerve cells reside in a ganglion outside of the central nervous system. This is the trigeminal ganglion. The nerve cell then stimulate nerve cells in the spinal trigeminal tract which receives, among other things, the irritative, or nociceptive information.

Now things get complicated.

The information then passes to the nucleus ambiguus to send the motor information to the pharyngeal muscles, to the respiratory centers in the brainstem reticular formation, and to the motor neurons in the spinal cord that trigger the diaphram--the phrenicnerve nuclei and the intercostal muscles.

Information taken from: http://www2b.abc.net.au/science/k2/stn/archives/archive6/newposts/33/topic33292.shtm
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