5/21/2023 0 Comments Auricula meaning anatomyIf the head moves or the body accelerates or decelerates, then bending occurs. The brain suppresses this, and we ignore it and know that our body is stabilized. Unbent and at rest hairs in the macula have a base rate of depolarization of 90-100 action potentials a second. The effect of this is that, for example, an individual lying down to sleep will continue to detect that they are lying down hours later when they awaken. This signal to the vestibular nerve (which takes it to the brainstem) does not adapt with time. The hair cells convert this pattern of stimulation to nerve signals, and the brain is thus advised of changes in your linear velocity. When you stop at the next light, the macula stops but the otolithic membrane keeps going for a moment, bending the stereocilia forward. The otolithic membrane of the macula utriculi briefly lags behind the rest of the tissues, bends the stereocilia backward, and stimulates the cells. Suppose you are sitting in a car at a stoplight and then begin to move. The inertia of the otolithic membranes is especially important in detecting linear acceleration. The brain interprets head orientation by comparing these inputs to each other and to other input from the eyes and stretch receptors in the neck, thereby detecting whether only the head is tilted or the entire body is tipping. Any orientation of the head causes a combination of stimulation to the utricles and saccules of the two ears. Depending on whether the tilt is in the direction of the kinocilium or not, the resulting hair cell polarisation is excitatory (depolarising) or inhibitory (hyperpolarisation), respectively. These are covered by otoliths which, due to gravity, pull on the stereocilia and tilt them. The utricle contains mechanoreceptors called hair cells that distinguish between degrees of tilting of the head, thanks to their apical stereocilia set-up. The ductus utriculosaccularis comes off of the anterior wall of the utricle and opens into the ductus endolymphaticus. The cavity of the utricle communicates behind with the semicircular ducts by five orifices. Labyrinthine activity responsible for the nystagmus induced by off-vertical axis rotation arises in the otolith organs and couples to the oculomotor system through the velocity storage mechanism. 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. The addition in weight and inertia is vital to the utricle's ability to detect linear acceleration, as described below, and to determine the orientation of the head. The otolithic membrane adds weight to the tops of the hair cells and increases their inertia. This membrane is weighted with calcium carbonate-protein granules called otoliths. The tips of these stereocilia and kinocilium are embedded in a gelatinous layer, which together with the statoconia form the otolithic membrane. The kinocilium is the only sensory aspect of the hair cell and is what causes hair cell polarization. The hair cells are mechanoreceptors which have 40 to 70 stereocilia and only one true cilium called a kinocilium. The broad auricular cartilage has numerous holes (see Figure 1-1), which are traversed by branches arising from the caudal auricular artery.The macula of utricle ( macula acustica utriculi) is a small (2 by 3 mm) thickening lying horizontally on the floor of the utricle where the epithelium contains vestibular hair cells that allow a person to perceive changes in latitudinal acceleration as well as the effects of gravity it receives the utricular filaments of the acoustic nerve. It is the largest cartilage of the external ear. The shape and size of the external ear vary greatly among different breeds of dogs, mainly owing to the auricular cartilage that forms the skeleton of the pinna. The skin covering the auricular cartilage may show breed-specific pigmentation. The skin on the concave surface of the pinna is very tightly connected to the underlying auricular cartilage, accentuating all the auricular prominences (see Figure 1-3). The caudal margin of the pinna exhibits a cutaneous pouch called the marginal pouch (Figure 1-3). The leaf-shaped pinna of the external ear is broad with medial (rostral) and lateral (caudal) margins. The ear is moved by three sets of muscles (rostral, ventral, and caudal) that are innervated by branches of the facial nerve (cranial nerve VII). It is designed to localize and collect sound waves and transmit them to the tympanic membrane (eardrum). Carriage of the pinna is breed-specific in the dog but mostly upright in the cat. The pinna, or auricle, is a highly visible structure.
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