查看Ch15.4 Sensor Transduction - Pain的源代码

== 肌梭感知骨骼肌纤维长度的变化，而高尔基肌腱器官测量肌肉的力量 ==
<b style=color:#0ae>Muscle spindles sense changes in the length of skeletal muscle fibers, whereas Golgi tendon organs gauge the muscle’s force</b>

The somatic sensory receptors described thus far provide information about the external environment. However, the body also needs detailed information about itself to know where each of its parts is in space, whether it is moving, and if so, in which direction and how fast. Proprioception provides this sense of self and serves two main purposes. First, knowledge of the positions of our limbs as they move helps us judge the identity of external objects. It is much easier to recognize an object if you can actively palpate it than if it is placed passively into your hand so that your skin is stimulated but you are not allowed to personally guide your fingers around it. Second, proprioceptive information is essential for accurately guiding many movements, especially while they are being learned.

到目前为止描述的躯体感觉受体提供关于外部环境的信息。然而，身体亦需要有关自身的详细信息，以了解它的每个部分在空间中的位置，它是否在移动，如果是，则向哪个方向移动，以及移动的速度。本体感觉提供了这种自我意识，并有两个主要目的。首先，了解我们四肢移动时的位置有助于我们判断外部物体的特征。如果您可以主动触诊一个物体，则比将其被动放在手中以刺激您的皮肤但不允许亲自引导手指绕过它要容易得多。其次，本体感觉信息对于准确指导许多动作至关重要，尤其是在学习它们时。


Skeletal muscles, which mediate voluntary movement, have two mechanosensitive proprioceptors: the muscle spindles (or stretch receptors) and Golgi tendon organs (Fig. 15-30). Muscle spindles measure the length and rate of stretch of the muscles, whereas the Golgi tendon organs gauge the force generated by a muscle by measuring the tension in its tendon. Together, they provide a full description of the dynamic state of each muscle. The different sensitivities of the spindle and the tendon organ are due partly to their structures but also to their placement: spindles are located in modified muscle fibers called intrafusal muscle fibers, which are aligned in parallel with the “ordinary” forcegenerating or extrafusal skeletal muscle fibers. On the other hand, Golgi tendon organs are aligned in series with the extrafusal fibers.

介导自主运动的骨骼肌有两个机械敏感的本体感受器：肌梭（或拉伸受体）和高尔基肌腱器官（图 15-30）。<b style=color:#f80>肌肉梭 (muscle spindles)</b>测量肌肉的长度和拉伸率，而<b style=color:#f80>高尔基肌腱器官 (Golgi tendon organs)</b>通过测量肌腱的张力来测量肌肉产生的力。它们共同提供了每块肌肉的动态状态的完整描述。纺锤体和肌腱器官的不同敏感性部分是由于它们的结构，但也是由于它们的位置：纺锤体位于称为导流内肌纤维的改良肌纤维中，它们与“普通”产生力或导流外骨骼肌纤维平行排列。另一方面，高尔基体肌腱器官与融合纤维串联排列。

[[文件:Ch15-30.png]]


The Golgi tendon organ consists of bare nerve endings of group Ib axons (see Table 12-1). These endings intimately invest an encapsulated collagen matrix and usually sit at the junction between skeletal muscle fibers and the tendon. When tension develops in the muscle as a result of either passive stretch or active contraction, the collagen fibers tend to squeeze and distort the mechanosensitive nerve endings, triggering them to fire action potentials.

高尔基体肌腱器官由 Ib 组轴突的裸露神经末梢组成（见表 12-1）。这些末端紧密地投入了一个封装的胶原蛋白基质，通常位于骨骼肌纤维和肌腱之间的交界处。当肌肉因被动拉伸或主动收缩而产生紧张时，胶原纤维往往会挤压和扭曲机械敏感的神经末梢，触发它们激发动作电位。

[[文件:Table-12-1.png]]


The mammalian muscle spindle is a complex of modified skeletal muscle fibers (intrafusal fibers) combined with both afferent and efferent innervation. The spindle does not contribute significant force generation to the muscle but serves a purely sensory function. A simplified summary of the muscle spindle is that it contains two kinds of intrafusal muscle fibers (bag and chain), with two kinds of sensory endings entwined about them (the primary and secondary endings). The different viscoelastic properties of the muscle fibers make them differentially sensitive to the consequences of muscle stretch. Because the primary sensory endings of group Ia axons coil around and strongly innervate individual bag muscle fibers (in addition to chain fibers), they are very sensitive to the dynamics of muscle length (i.e., changes in its length). The secondary sensory endings of group II axons mainly innervate the chain fibers and most accurately transduce the static length of the muscle; in other words, they are slowly adapting receptors. The discharge rate of afferent neurons increases when the whole muscle—and therefore the spindle—is stretched. ENaC and ASIC2 channels may contribute to the stretch sensitivity of the sensory nerve terminals in muscle spindles.

哺乳动物肌梭是改良骨骼肌纤维（导静脉内纤维）与传入神经支配和传出神经支配相结合的复合物。纺锤体不会对肌肉产生显着的力，但提供纯粹的感觉功能。肌肉梭的简化总结是它包含两种导静脉内肌纤维（袋和链），两种感觉末梢缠绕着它们（初级和次级末梢）。肌肉纤维的不同粘弹性特性使它们对肌肉拉伸的后果具有不同的敏感性。因为 Ia 组轴突的初级感觉末梢盘绕并强烈支配单个袋肌纤维（除了链纤维），所以它们对肌肉长度的动力学（即其长度的变化）非常敏感。II 组轴突的次级感觉末梢主要支配链纤维，最准确地转导肌肉的静态长度;换句话说，它们正在慢慢适应受体。当整个肌肉（以及纺锤体）被拉伸时，传入神经元的放电率会增加。ENaC 和 ASIC2 通道可能有助于肌肉梭感觉神经末梢的拉伸敏感性。


What is the function of the motor innervation of the muscle spindle? Consider what happens when the α motor neurons stimulate the force-generating extrafusal fibers and the muscle contracts. The spindle, connected in parallel to the extrafusal fibers, quickly tends to go slack, which makes it insensitive to further changes in length. To avoid this situation and to continue to maintain control over the sensitivity of the spindle, γ motor neurons cause the intrafusal muscle fibers to contract in parallel with the extrafusal fibers. This ability of the spindle’s intrafusal fibers to change their length as necessary greatly increases the range of lengths over which the spindle can work. It also means that the sensory responses of the spindle depend not only on the length of the whole muscle in which the spindle sits but also on the contractile state of its own intrafusal muscle fibers. Presumably, the ambiguity in this code is sorted out centrally by circuits that simultaneously keep track of the spindle’s sensory output and the activity of its motor nerve supply.

肌梭的运动神经支配有什么作用？考虑一下当 α 运动神经元刺激产生力的 EFFUSAL 纤维并且肌肉收缩时会发生什么。与纺纱外纤维并联的纺锤体很快就会变得松弛，这使得它对长度的进一步变化不敏感。为了避免这种情况并继续保持对纺锤体敏感性的控制，γ 运动神经元导致导膜内肌纤维与导膜外纤维平行收缩。纺锤体的导膜内纤维根据需要改变其长度的这种能力大大增加了纺锤体可以工作的长度范围。这也意味着纺锤体的感觉反应不仅取决于纺锤体所在的整块肌肉的长度，还取决于其自身导神经内肌纤维的收缩状态。据推测，这段代码中的歧义是由电路集中整理出来的，这些电路同时跟踪纺锤体的感觉输出和运动神经供应的活动。


In addition to the muscle receptors, various mechanoreceptors are found in the connective tissues of joints, especially within the capsules and ligaments. Many resemble Ruffini, Golgi, and Pacini end organs; others are free nerve endings. They respond to changes in the angle, direction, and velocity of movement in a joint. Most are rapidly adapting, which means that sensory information about a moving joint is rich. Nerves encoding the resting position of a joint are few. We are nevertheless quite good at judging the position of a joint, even with our eyes closed. It seems that information from joint receptors is combined with that from muscle spindles and Golgi tendon organs, and probably from cutaneous receptors as well, to estimate joint angle. Removal of one source of information can be compensated by use of the other sources. When an arthritic hip is replaced with a steel and plastic one, patients are still able to tell the angle between their thigh and their pelvis, even though all hip joint mechanoreceptors are long gone.

除了肌肉受体外，在<b style=color:#0b0>关节的结缔组织中还发现了各种机械感受器</b>，尤其是在关节囊和韧带内。许多类似于 Ruffini、Golgi 和 Pacini 终末器官；其他是游离神经末梢。它们对关节运动的角度、方向和速度的变化做出反应。大多数都在快速适应，这意味着关于活动关节的感觉信息非常丰富。编码关节静止位置的神经很少。尽管如此，我们还是很擅长判断关节的位置，即使我们闭着眼睛也是如此。似乎来自关节受体的信息与来自肌肉梭和高尔基肌腱器官的信息相结合，也可能来自皮肤受体的信息相结合，以估计关节角度。删除一个信息来源可以通过使用其他来源来补偿。当关节炎髋关节被钢制和塑料髋关节取代时，即使所有的髋关节机械感受器早已消失，患者仍然能够分辨出大腿和骨盆之间的角度。

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