查看Ch15 Sensory Transduction的源代码

=== 耳石器官（球囊和椭圆囊）检测头部的方向和线性加速度 ===

<b style=color:#0ae>The otolithic organs (saccule and utricle) detect the orientation and linear acceleration of the head</b>

The otolithic organs are a pair of relatively large chambers— the saccule and the utricle—near the center of the labyrinth (see Fig. 15-17B). These otolithic organs as well as the semicircular canals are (1) lined by epithelial cells, (2) filled with endolymph, (3) surrounded by perilymph, and (4) encased in the temporal bone. Within the epithelium, specialized vestibular dark cells secrete K+ and are responsible for the high [K+] of the endolymph. The mechanism of K+ secretion is similar to that by the stria vascularis in the auditory system (see p. 378).

耳石器官是一对相对较大的腔室——球囊和椭圆囊——靠近迷路中心（见图 15-17B）。这些耳石器官以及半规管 （1） 由上皮细胞排列，（2） 充满内淋巴，（3） 被外淋巴包围，以及 （4） 包裹在颞骨中。在上皮细胞内，专门的前庭暗细胞分泌 K+，并负责内淋巴液的高 [K+]。K+ 分泌的机制与听觉系统中血管纹的分泌机制相似（见第 378 页）。

The saccule and utricle each have a sensory epithelium called the macula, which contains the hair cells that lie among a bed of supporting cells. The stereovilli project into the gelatinous otolithic membrane, a mass of mucopolysaccharides that is studded with otoliths or otoconia (Fig. 15-18A, B). Otoconia are crystals of calcium carbonate, 1 to 5 μm in diameter, that give the otolithic membrane a higher density than the surrounding endolymph. With either a change in the angle of the head or a linear acceleration, the inertia of the otoconia causes the otolithic membrane to move slightly, deflecting the stereovilli.

球囊和椭圆囊各有一个称为黄斑的感觉上皮，其中包含位于支持细胞床中的毛细胞。立体绒毛投射到凝胶状耳石膜中，这是一团粘多糖，上面布满耳石或耳石（图 15-18A、B）。耳石颗粒是直径为 1 至 5 μm 的碳酸钙晶体，使耳石膜的密度高于周围的内淋巴液。随着头部角度的变化或线性加速度，耳石的惯性导致耳石膜轻微移动，使立体绒毛偏转。


The macula is vertically oriented (in the sagittal plane) within the saccule and horizontally oriented within the utricle when the head is tilted down by ~25 degrees, as during walking. Recall that hair cells are depolarized or hyperpolarized when stereovilli bend toward or away from the kinocilium, respectively (see Fig. 15-16). In the saccule, the kinocilia point away from a curving reversal line that divides the macula into two regions (see Fig. 15-18D). In the utricle, the kinocilia point toward the reversal line. The hair cells of the saccule and utricle respond well to changes in head angle and to acceleration of the sort that is experienced as a car or an elevator starts or stops. Of course, the head can tilt or experience acceleration in many directions. Indeed, the orientations of hair cells of the saccule and utricle covers a full range of directions. Any tilt or linear acceleration of the head will enhance the stimulation of some hair cells, reduce the stimulation of others, and have no effect on the rest.

当头部向下倾斜约 25 度时，黄斑在球囊内垂直定向（在矢状面上），在椭圆囊内水平定向，就像在行走时一样。回想一下，当立体绒毛分别朝向或远离纤毛弯曲时，毛细胞会去极化或超极化（见图 15-16）。在球囊中，金纤毛指向远离将黄斑分成两个区域的弯曲反转线（见图 15-18D）。在椭圆囊中，金纤毛指向反转线。球囊和椭圆囊的毛细胞对头部角度的变化和汽车或电梯启动或停止时所经历的那种加速度反应良好。当然，头部可以向多个方向倾斜或经历加速度。事实上，球囊和椭圆囊的毛细胞方向涵盖了所有方向。头部的任何倾斜或线性加速度都会增强对某些毛细胞的刺激，减少对其他毛细胞的刺激，而对其余毛细胞没有影响。

[[文件:Physiology-ch15-18.png]]

Each hair cell synapses on the ending of a primary sensory axon that is part of the vestibular nerve, which in turn is a branch of the vestibulocochlear nerve (CN VIII). The cell bodies of these sensory neurons are located in Scarpa’s ganglion within the temporal bone. The dendrites project to multiple hair cells, which increases the signal-to-noise ratio. The axons project to the ipsilateral vestibular nucleus in the brainstem. N15-6 Because the saccule and utricle are paired structures (one on each side of the head), the CNS can simultaneously use information encoded by the full population of otolithic hair cells and unambiguously interpret any angle of tilt or linear acceleration. The push-pull arrangement of increased/decreased activity within each macula (for hair cells of opposite orientation) and between maculae on either side of the head enhances the fidelity of the signal.

每个毛细胞突触位于初级感觉轴突的末端，该轴突是前庭神经的一部分，而前庭神经又是前庭耳蜗神经 （CN VIII） 的一个分支。这些感觉神经元的细胞体位于颞骨内的 Scarpa 神经节中。树突投射到多个毛细胞上，这增加了信噪比。轴突投射到脑干的同侧前庭核[N15-6]。因为球囊和椭圆囊是成对的结构（头部两侧各一个），所以 CNS 可以同时使用由整个耳石毛细胞群编码的信息，并明确解释任何倾斜角度或线性加速度。每个黄斑内（对于相反方向的毛细胞）和头部两侧黄斑之间活动增加/减少的推拉排列增强了信号的保真度。

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