查看Ch15 Sensory Transduction的源代码

=== 耳蜗是由三根平行的、充满液体的管子组成的螺旋形 ===

<b style=color:#0ae>The cochlea is a spiral of three parallel, fluid-filled tubes</b>

The auditory portion of the inner ear is mainly the cochlea, a tubular structure that is ~35 mm long and is coiled 2.5 times into a snail shape about the size of a large pea (Fig. 15-20). Counting its stereovilli, the cochlea has a million moving parts, which makes it the most complex mechanical apparatus in the body.

内耳的听觉部分主要是耳蜗，耳蜗是一种管状结构，<b style=color:#0b0>长约 35mm</b>，盘绕 2.5 次，呈蜗牛形，大约有<b style=color:#f80>大豌豆大小</b>（图 15-20）。算上它的立体绒毛，耳蜗有 100 万个活动部件，这使其成为人体中最复杂的机械装置。

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<b style=color:#0cf>【注】</b> 耳蜗是一个螺旋状的结构，有点像微型海螺，由前庭膜 (Reissner's membrane) 和基底膜 (basilar membrane) 分割为 3 部分，最上部的前庭阶 (scala vestibuli) ，中间的中阶 (scala media) 和下面的鼓阶 (scala tympani) 。基底膜横穿了整条耳蜗的，在它上部的柯蒂氏器 (organ of corti) ，主要包括有内侧毛细胞 (inner hair cells) 和外侧毛细胞 (outer hair cells)。


The cut through the cochlea in the lower left drawing in Figure 15-20 reveals five cross sections of the spiral. We see that in each cross section, two membranes divide the cochlea into three fluid-filled compartments. On one side is the compartment called the scala vestibuli (see Fig. 15-20, right side), which begins at its large end near the oval window— where vibrations enter the inner ear. Reissner’s membrane separates the scala vestibuli from the middle compartment, the scala media. The other boundary of the scala media is the basilar membrane, on which rides the organ of Corti and its hair cells. Below the basilar membrane is the scala tympani, which terminates at its basal or large end at the round window. Both the oval and round windows look into the middle ear (see Fig. 15-19B).

图 15-20 中左下角图中穿过耳蜗的切口显示了螺旋线的五个横截面。我们看到，在每个横截面中，两个膜将耳蜗分成三个充满液体的隔室。一侧是称为前庭阶的隔室（见图 15-20，右侧），它从靠近椭圆形窗口的大端开始——振动进入内耳。前庭膜 (Reissner's membrane) 将前庭与中间隔室（中阶）隔开。中阶的另一个边界是基底膜，其上覆盖着 Corti 器官及其毛细胞。基底膜下方是鼓膜，其终止于圆窗的基端或大端。椭圆形和圆形窗口都可以看到中耳（见图 15-19B）。

Both the scala vestibuli and scala tympani are lined by a network of fibrocytes and filled with perilymph (see pp. 372–373). Like its counterpart in the vestibular system, this perilymph is akin to CSF (i.e., low [K+], high [Na+]). Along the lengths of scala vestibuli and scala tympani, the two perilymphs communicate through the leaky interstitial fluid spaces between the fibrocytes. At the apex of the cochlea, the two perilymphs communicate through a small opening called the helicotrema. Cochlear perilymph communicates with vestibular perilymph through a wide passage at the base of the scala vestibuli (see Fig. 15-17B), and it communicates with the CSF through the cochlear aqueduct.

前庭阶和鼓阶都由纤维细胞网络衬垫，并充满外淋巴液（见第 372-373 页）。与前庭系统中的对应物一样，这种外淋巴液类似于脑脊液 (CSF, Cerebrospinal Fluid) （即低 [K+]、高 [Na+]）。沿着前庭阶和鼓阶的长度，两个外淋巴液通过纤维细胞之间渗漏的间质液空间进行交流。在<b style=color:#f80>耳蜗的顶端</b>，<b style=color:#0b0>两个外淋巴液通过一个称为螺旋线的小开口进行交流</b>。<b style=color:#f80>耳蜗外淋巴液</b>通过前庭阶底部的宽通道与前庭外淋巴液相通（见图 15-17B），并通过<b style=color:#f80>耳蜗导水管</b>与脑脊液 (CSF, Cerebrospinal Fluid) 相通。

<b style=color:#0cf>【注】</b> 有两种类型的外淋巴液：前庭阶 (scala vestibuli) 外淋巴液和鼓阶 (scala tympani) 外淋巴液。前庭阶中的外淋巴液来自穿过半外淋巴屏障 (hemto-perilymphatic barrier) 的血浆（更接近），而鼓阶的外淋巴液来自脑脊液（更接近）。两者的成分都类似于脑脊液 （CSF）：富含钠 （140mM），钾 （5mM） 和钙 （1.2mM） 不足。


The scala media is filled with endolymph. Like its vestibular counterpart—with which it communicates through the ductus reuniens (see Fig. 15-17B)—auditory endolymph is extremely rich in K+. Unlike vestibular endolymph, which has the same voltage as the perilymph, auditory endolymph has a voltage of +80 mV relative to the perilymph (see Fig. 15-20, right side). This endocochlear potential, which is the highest transepithelial voltage in the body, is the main driving force for sensory transduction in both inner and outer hair cells. Moreover, loss of the endocochlear potential is a frequent cause of hearing loss. A highly vascularized tissue called the stria vascularis secretes the K+ into the scala media, and the resulting K+ gradient between endolymph and perilymph generates the strong endocochlear potential.

中阶充满内淋巴液。就像它的前庭对应物一样——它通过连合管 (ductus reuniens) 与之交流（见图 15-17B）——听觉内淋巴液富含 K+。与具有<b style=color:#0b0>与外淋巴液相同电位</b>的<b style=color:#f80>前庭内淋巴液</b>不同，<b style=color:#f80>听觉内淋巴液</b><b style=color:#0b0>相对于外淋巴液的电压为 +80 mV</b>（见图 15-20，右侧）。这种耳蜗电位是体内最高的跨上皮电压，是内毛细胞和外毛细胞感觉转导的主要驱动力。此外，<b style=color:#f80>耳蜗内电位</b>的<b style=color:#0b0>丧失</b>是<b style=color:#e00>听力损失</b>的常见原因。一种称为血管纹的高度血管化组织将 K+ 分泌到中阶中，由此产生的内淋巴液和外淋巴液之间的 K+ 梯度产生强的耳蜗电位。


The stria vascularis is functionally a two-layered epithelium (Fig. 15-21). Marginal cells separate endolymph from a very small intrastrial compartment inside the stria vascularis, and basal cells separate the intrastrial compartment from the interstitial fluid of the spiral ligament, which is contiguous with perilymph. Gap junctions connect one side of the basal cells to intermediate cells and the other side of the basal cells to fibrocytes of the spiral ligament. This architecture is essential for generation of the endocochlear potential.

血管纹在功能上是一个两层上皮（图 15-21）。边缘细胞将内淋巴液与血管纹内一个非常小的心房内隔室分开，基底细胞将心室内隔室与螺旋韧带的间质液分开，螺旋韧带与外淋巴液相邻。间隙连接将基底细胞的一侧连接到中间细胞，将基底细胞的另一侧连接到螺旋韧带的纤维细胞。这种结构对于耳蜗电位的产生至关重要。

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The fibrocytes are endowed with K+ uptake mechanisms that maintain a high [K+]i in the intermediate cells. The KCNJ10 K+ channel of the intermediate cells generates the endocochlear potential. The K+ equilibrium potential of these cells is extremely negative because of the combination of their very high [K+]i and the very low [K+] of the intrastrial fluid. Finally, the marginal cells support the endocochlear potential by mopping up the K+ from the intrastrial fluid— keeping the intrastrial [K+] very low—and depositing the K+ in the endolymph through a KCNQ1 K+ channel.

纤维细胞具有 K+ 摄取机制，可在中间细胞中维持高 [K+]i。中间细胞的 KCNJ10 K+ 通道产生耳蜗电位。这些细胞的 K+ 平衡电位是极负的，因为它们的 [K+]i 非常高，而室内液的 [K+] 非常低。最后，边缘细胞通过从房内液中清除 K+（保持房内 [K+] 非常低）并通过 KCNQ1 K+ 通道将 K+ 沉积在内淋巴液中来支持耳蜗内电位。

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