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Equine Special Senses - Horse Anatomy (view source)
Revision as of 12:02, 22 November 2012
, 12:02, 22 November 2012→Inner Ear
====Inner Ear====
====Inner Ear====
[[Image:Inner, Membranous Labyrinth.jpg|thumb|right|150px|Inner, Membranous Labyrinth - Copyright David Bainbridge]]
[[Image:Outer, Bony Labyrinth.jpg|thumb|right|150px|Outer, Bony Labyrinth - Copyright David Bainbridge]]
[[Image:Section through a Cochlear Turn.jpg|thumb|right|150px|Section through a Cochlear Turn - Copyright David Bainbridge]]
The inner ear is located within the '''petrous temporal bone'''. The inner ear contains the '''membranous labyrinth''', which is surrounded by the '''bony labyrinth'''. The membranous labyrinth is an interconnected group of fluid-filled membranous sacs. The fluid contained within it is known as '''endolymph'''. It is the movement of the endolymph that stimulates the sensory cells within the membranous wall.
The membranous labyrinth consists of:
*''vestibular labyrinth'': contains the receptor organ involved with balance, containing the '''saccule, utricle''' and the '''semicircular ducts'''. The saccule and utricle contain sensory '''maculae''' within their walls, and there's a sensory '''crista''' within the '''ampullae''' of the semicircular ducts. The maculae and ampullae sense and conduct impulses concerned with balance via the '''vestibular nerve'''. The three semicircular ducts arise from the utricle, and the cochlear duct arises from the saccule.
*''cochlear labyrinth'': contains the organ involved with hearing. It consists of the '''organ of Corti''', within the cochlear duct. The cochlear duct is fluid-filled, the fluid being endolymph. The organ of Corti contains the receptor cells for hearing.
*''ductus reuniens'': this is the duct through which the above two labyrinths communicate
The bony labyrinth consists of:
*''vestibule'': a chamber in the centre of the bony labyrinth, which communicates with both the cochlea and the semicircular canals. The '''oval''' and the '''round windows''' are both located in the lateral wall of the vestibule.
*''semicircular canals'': contain the '''semicircular ducts''', which have arisen from the utricle of the vestibular labyrinth. There are three '''semicircular canals''', corresponding to the three dimensions in which you can move, so they are almost at right angles with each other. Each duct has two '''crura''' (leg-like parts). One crus of each duct has an '''ampulla''', which is an expansion of the duct. Movement of endolymph stimulates receptor cells within the ampullae.
*''cochlea'': forms a spiral around a central hollow core of bone, called the '''modiolus''',which contains the '''cochlear nerve'''. The '''spiral lamina''' projects into the '''spiral canal''', partially bisecting the lumen into two parts, which are called the '''scala tympani''' and the '''scala vestibuli'''. The ''scala media'' (the cochlear duct) is between these two parts. In the horse, the cochlea makes 2.5 turns.
The external ear receives sounds, which cause vibrations of the tympanic membrane. These vibrations move along the ossicles of the middle ear, to be transmitted to the inner ear. The stapes is connected to the oval window, so when the stapes transmits vibrations, this causes movement of '''perilymph''' that is in the inner ear. The movement of the perilymph is transmitted via the '''scala vestibuli''' and the '''scala tympani''', to the '''round window''', where it induces movement of the '''secondary tympanic membrane'''. This results in the movement of the '''endolymph''' of the '''cochlear duct''', causing pressure on the '''tectorial membrane''', which then induces pressure on the sensory hairs, stimulating the receptor cells within the cochlear duct to send impulses to the '''spiral ganglion'''. The axons of the spiral ganglion form part of the '''vestibulocochlear nerve'''.
===Hearing===
===Hearing===
====The Outer and Middle Ear====
====The Outer and Middle Ear====