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Unformatted text preview: Chapter 12: The sense organs Mechanoreceptors: the inner ear Neuromast cells also present in the inner ear Senses movement in the water or air External ear: present in mammals Middle ear: present in most tetrapods Development of the inner ear: ‘Otic placode’ forms a vesicle that completely separates from the surface ectoderm (just behind pharyngeal arches)-forms an otic pit through evagination on a region just behind the pharyngeal arches- Vesicle elaborates into a complex structure of ducts filled with endolymph : the membranous labyrinth (contains semicircular ducts, utricle, saccule and lagena) Parts of the Inner ear Semicircular ducts : 1 pair in hagfish, 2 pairs in lampreys, and 3 pairs in gnathostomes- part of memb. Labyrinth- sense body (head) movement- Ampulla – a swelling of each duct containing a neuromast organ- We have three because there are three possible planes of movement o Lampreys/hagfish have no real need for them because they are parasites- Ducts are filled with liquid o As the head turns the water stays the same and the cupula, which moves with the head gets pushed This opens an ion channel in the neuromast organ which is found in the semicircular duct Angular acceleration – rotation of the head (pitch, yaw, or roll) is sensed by the crista of the semicircular ducts. Movement of endolymph relative to the neuromast organ pushes on the cupula and deflects the cilia of the hair cells Utricle (dorsal) and Saccule – 2 sacs that form from part of the membranous labyrinth that detects head position Operate similar to the semicircular ducts but...
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This note was uploaded on 08/16/2008 for the course BIOL 276 taught by Professor Johnson during the Spring '07 term at UNC.
- Spring '07