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Macula of utricle

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Macula of utricle

Macula of utricle
illustration of otolith organs showing detail of utricle, otoconia, endolymph, cupula, macula, hair cell filaments, and saccular nerve
Details
Latin macula utriculi
Identifiers
Gray's p.1051
Dorlands
/Elsevier
m_01/12509297
Anatomical terminology

The portion of the utricle which is lodged in the recess forms a sort of pouch or cul-de-sac, the floor and anterior wall of which are thickened, and form the macula of utricle (or utricular macula), which receives the utricular filaments of the vestibulocochlear nerve.

The macula of utricle allows a person to perceive changes in longitudinal acceleration (in horizontal directions only).

Layers

The macula consists of three layers.

The bottom layer is made of sensory hair cells which are embedded in bottom of a gelatinous layer. Each hair cells consists of 40 to 70 steriocilia and a kinocilium, which lies in the middle of the steriocilia and is the most important receptor.

On top of this layer lie calcium carbonate crystals called statoconia or otoliths. The otoliths are relatively heavy, providing weight to the membrane as well as inertia. This allows for a greater sense of gravity and motion.

The gelatinous layer and the statoconia together are referred to as the otolithic membrane, where the tips of the stereocilia and kinocilium are embedded. When the head is tilted such that gravity pulls on the statoconia the gelatinous layer is pulled in the same direction also causing the sensory hairs to bend.

Signals

Unbent and at rest hairs in the macula have a base rate of depolarization of 90-100 action potentials a second. The brain suppresses this, and we ignore it and know that our body is stabilized. If the head moves or the body accelerates or decelerates, then bending occurs.

Depending on the direction of bending, the hair cells will either be excited or inhibited resulting in either an increase or decrease in firing frequency of the hair cells.

The macula is also sensitive to linear acceleration as the inertia possessed by the statoconia can also shift the gelatinous layer during increases and decreases in linear velocity.

External links

  • http://www.neurophys.wisc.edu/h&b/textbook/chap-7.html#Obj2

This article incorporates text from a public domain edition of Gray's Anatomy.


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