Prerequisites（预备知识）：Musclar Cells

Muscular System

The muscular system is one of the most important systems in the human body. It is responsible for producing movement, maintaining posture, generating heat, and stabilizing joints. The muscular system is composed of three different types of muscles: skeletal, smooth, and cardiac.

Skeletal muscles are attached to bones by tendons and are responsible for voluntary movement. They are made up of long, cylindrical fibers that are striated and contain multiple nuclei. Smooth muscles, on the other hand, are found in the walls of organs and blood vessels and are responsible for involuntary movements such as digestion and blood flow. They are not striated and have a single nucleus. Cardiac muscles make up the walls of the heart and are responsible for pumping blood throughout the body. They are striated like skeletal muscles but are involuntary like smooth muscles.

Muscles are composed of individual muscle fibers that contract and relax in response to nerve impulses. When a muscle contracts, it shortens and pulls on the bone to which it is attached, producing movement. Muscles work in pairs, with one muscle contracting while the other relaxes to produce smooth, coordinated movements.

The muscular system is essential for overall health and wellness. Regular exercise helps to strengthen and maintain muscle mass, which in turn helps to prevent injury, improve posture, and maintain a healthy weight. Proper nutrition is also important for muscle health, as muscles require protein and other nutrients to function properly.

肌肉系统

肌肉系统是人体最重要的系统之一。,它负责产生运动、保持姿势、产生热量和稳定关节。肌肉系统由三种不同类型的肌肉组成：骨骼肌、平滑肌和心肌。

骨骼肌通过肌腱附着在骨骼上，负责随意运动。它们由长而圆柱形的纤维组成，这些纤维有条纹并包含多个核。,另一方面，平滑肌存在于器官和血管壁中，负责消化和血液流动等不自主运动。,它们没有横纹，只有一个核。,心肌构成心脏的壁，负责将血液泵送到全身。它们像骨骼肌一样有横纹，但像平滑肌一样是非自愿的。

肌肉由响应神经冲动而收缩和放松的单个肌纤维组成。,当肌肉收缩时，它会缩短并拉动它所附着的骨骼，从而产生运动。肌肉成对工作，一块肌肉收缩，另一块肌肉放松，以产生平稳、协调的运动。

肌肉系统对于整体健康至关重要。定期锻炼有助于增强和保持肌肉质量，进而有助于防止受伤、改善姿势和保持健康的体重。,适当的营养对肌肉健康也很重要，因为肌肉需要蛋白质和其他营养物质才能正常运作。

Muscle contraction and locomotion 

Muscle contraction and locomotion are closely related concepts in the field of physiology. Muscle contraction is the process by which muscle fibers generate tension and produce movement. Locomotion is the act of moving from one place to another, typically using muscles to propel the body.

Muscle Contraction:

Muscle contraction involves a complex interaction between proteins within the muscle fibers. Two key proteins involved in muscle contraction are actin and myosin. Actin is a thin protein filament that forms the backbone of muscle fibers, while myosin is a thicker protein filament that interacts with actin to generate tension.

When a muscle fiber receives a signal from a nerve, calcium ions are released into the muscle cell. These calcium ions then bind to a protein called troponin, which causes a change in the position of tropomyosin, another protein involved in muscle contraction. This change in position exposes binding sites on the actin filaments, allowing myosin to bind and generate tension. This process is known as the sliding filament theory.

Muscle contraction can be either isotonic or isometric. Isotonic contractions generate tension and produce movement, while isometric contractions generate tension without producing movement. An example of an isotonic contraction is when a person lifts a weight, while an example of an isometric contraction is when a person holds a weight in a fixed position.

Locomotion:

Locomotion involves the coordinated movement of the body using muscle contractions. There are two main types of locomotion: terrestrial and aquatic. Terrestrial locomotion is movement on land, while aquatic locomotion is movement in water.

Terrestrial locomotion involves a complex interplay between the musculoskeletal system and the nervous system. Muscles must contract in a coordinated manner to produce movement, while the nervous system must provide feedback to ensure that the body maintains balance and stability.

Aquatic locomotion also involves complex interactions between muscles and the environment. Fish, for example, use their fins to generate propulsion and move through water. The movement of the fins creates vortices in the water, which propel the fish forward.

In summary, muscle contraction and locomotion are closely related concepts in the field of physiology. Muscle contraction is the process by which muscle fibers generate tension and produce movement, while locomotion is the act of moving from one place to another using muscles to propel the body.

肌肉收缩和运动

肌肉收缩和运动是生理学领域密切相关的概念。,肌肉收缩是肌肉纤维产生张力并产生运动的过程。,运动是从一个地方移动到另一个地方的行为，通常使用肌肉来推动身体。

肌肉收缩：

肌肉收缩涉及肌肉纤维内蛋白质之间复杂的相互作用。参与肌肉收缩的两种关键蛋白质是肌动蛋白和肌球蛋白。肌动蛋白是形成肌肉纤维骨架的细蛋白丝，而肌球蛋白是较粗的蛋白丝，可与肌动蛋白相互作用产生张力。

当肌肉纤维接收到来自神经的信号时，钙离子就会释放到肌肉细胞中。然后这些钙离子与一种叫做肌钙蛋白的蛋白质结合，导致原肌球蛋白的位置发生变化，原肌球蛋白是另一种参与肌肉收缩的蛋白质。,这种位置变化暴露了肌动蛋白丝上的结合位点，使肌球蛋白结合并产生张力。这个过程被称为滑动丝理论。

肌肉收缩可以是等张的或等长的。等张收缩产生张力并产生运动，而等长收缩产生张力而不产生运动。,等张收缩的一个例子是当一个人举起重物时，而等长收缩的一个例子是当一个人将重物保持在固定位置时。

运动：

运动涉及使用肌肉收缩的身体协调运动。,有两种主要的运动类型：陆生和水生。,陆地运动是在陆地上运动，而水上运动是在水中运动。

地面运动涉及肌肉骨骼系统和神经系统之间复杂的相互作用。,肌肉必须以协调的方式收缩才能产生运动，而神经系统必须提供反馈以确保身体保持平衡和稳定。

水生运动还涉及肌肉与环境之间复杂的相互作用。,例如，鱼使用鳍产生推进力并在水中移动。,鳍的运动在水中产生漩涡，推动鱼前进。

总之，肌肉收缩和运动是生理学领域密切相关的概念。,肌肉收缩是肌肉纤维产生张力并产生运动的过程，而运动是使用肌肉推动身体从一个地方移动到另一个地方的行为。

                                               Cardiac Muscle Tissue

Link：https://courses.lumenlearning.com/boundless-ap/chapter/cardiac-muscle-tissue/

Microscopic Anatomy

Cardiac muscle appears striated due to the presence of sarcomeres, the highly-organized basic functional unit of muscle tissue.

Key Points

• Cardiac muscle, composed of the contractile cells of the heart, has a striated appearance due to alternating thick and thin filaments composed of myosin and actin.

• Actin and myosin are contractile protein filaments, with actin making up thin filaments, and myosin contributing to thick filaments. Together, they are considered myofibrils.

• Myosin and actin adenosine triphosphate ( ATP ) binding allows for muscle contraction. It is regulated by action potentials and calcium concentrations.

• Adherens junctions, gap junctions, and desmosomes are intercalated discs that connect cardiac muscle cells. Gap junctions specifically allow for the transmission of action potentials within cells.

Key Terms

• intercalated discs: Junctions that connect cardiomyocytes together, some of which transmit electrical impulses between cells.

• sarcomere: The basic unit of contractile muscle which contains myosin and actin, the two proteins that slide past one another to cause a muscle contraction.

Muscle Contraction and Actin-Myosin Interactions: Skeletal muscle contracts following activation by an action potential. Binding of Acetylcholine at the motor end plate leads to intracellular calcium release and interactions between myofibrils, eliciting contraction.

The Sarcomere: A single sarcomere unit with all functional areas labeled, including thick and thin filaments, Z lines, H zone, I bands, and A band.

Key Medical Terms

Cytoskeleton:

The cytoskeleton is a complex network of protein filaments and tubules that provides structural support and helps maintain the shape of cells. It also plays a crucial role in cell division, cell movement, and intracellular transport.

There are three main types of protein filaments that make up the cytoskeleton: microfilaments, intermediate filaments, and microtubules. Microfilaments are the thinnest filaments, composed of actin proteins, and are involved in cell contraction and movement. Intermediate filaments are thicker and provide mechanical support to cells. They are composed of various proteins, depending on the type of cell. Microtubules are the largest filaments, composed of tubulin proteins, and are involved in cell division and intracellular transport.

The cytoskeleton is responsible for maintaining the shape and structure of cells. It helps cells resist external forces and maintain their shape under various conditions. For example, the cytoskeleton of red blood cells helps them maintain their shape as they pass through narrow blood vessels.

The cytoskeleton is also involved in cell division, specifically in the formation of the spindle apparatus. The spindle apparatus is composed of microtubules and helps separate the chromosomes during cell division.

The cytoskeleton is also essential for cell movement. It provides structural support to cells as they move and helps them change shape. For example, the cytoskeleton of muscle cells helps them contract and generate movement.

In summary, the cytoskeleton is a complex network of protein filaments and tubules that provides structural support, helps maintain the shape of cells, and is involved in cell division, intracellular transport, and cell movement.

细胞骨架是由蛋白质丝和小管组成的复杂网络，可提供结构支持并帮助维持细胞的形状。它还在细胞分裂、细胞运动和细胞内运输中起着至关重要的作用。

构成细胞骨架的蛋白质丝主要有三种类型：微丝、中间丝和微管。,微丝是最细的丝，由肌动蛋白组成，参与细胞收缩和运动。中间丝较粗，为细胞提供机械支撑。,它们由各种蛋白质组成，具体取决于细胞的类型。,微管是最大的细丝，由微管蛋白组成，参与细胞分裂和细胞内运输。

细胞骨架负责维持细胞的形状和结构。,它帮助细胞抵抗外力并在各种条件下保持其形状。例如，红细胞的细胞骨架帮助它们在通过狭窄的血管时保持其形状。

细胞骨架还参与细胞分裂，特别是纺锤体的形成。,纺锤体由微管组成，有助于在细胞分裂过程中分离染色体。

细胞骨架对于细胞运动也是必不可少的。,它在细胞移动时为细胞提供结构支持并帮助它们改变形状。,例如，肌肉细胞的细胞骨架帮助它们收缩并产生运动。

总之，细胞骨架是由蛋白质丝和小管组成的复杂网络，提供结构支持，帮助维持细胞形状，并参与细胞分裂、细胞内运输和细胞运动。

Actin，myosin & tubulin：

Actin, myosin, and tubulin are all protein filaments that play important roles in cellular processes.

Actin and myosin are involved in muscle contraction, as well as other cellular processes such as cell movement and division, as mentioned in the previous answer. Actin is a thin protein filament that forms the backbone of muscle fibers, while myosin is a thicker protein filament that interacts with actin to generate tension and movement.

Tubulin, on the other hand, is the protein that makes up microtubules, which are the largest filaments in the cytoskeleton. Microtubules are involved in cell division, intracellular transport, and cell movement. They provide structural support to cells and help maintain their shape, and also help in the organization of cellular structures such as the mitotic spindle during cell division.

Tubulin is composed of two subunits, alpha-tubulin and beta-tubulin. These subunits combine to form a tubulin dimer, which then assembles into a tubulin filament. The tubulin filaments form the backbone of microtubules, which are dynamic structures that can grow, shrink, and reorganize as needed.

While actin and myosin are involved in muscle contraction and cell movement, tubulin and microtubules play important roles in many cellular processes beyond that. Together, these protein filaments contribute to the structural integrity of cells and their ability to respond to their environment.

肌动蛋白、肌球蛋白和微管蛋白都是在细胞过程中发挥重要作用的蛋白质丝。

如上一个答案所述，肌动蛋白和肌球蛋白参与肌肉收缩以及其他细胞过程，例如细胞运动和分裂。,肌动蛋白是一种形成肌肉纤维骨架的细蛋白丝，而肌球蛋白是一种较粗的蛋白丝，它与肌动蛋白相互作用以产生张力和运动。

另一方面，微管蛋白是构成微管的蛋白质，微管是细胞骨架中最大的细丝。,微管参与细胞分裂、细胞内运输和细胞运动。它们为细胞提供结构支持并帮助维持其形状，还有助于组织细胞结构，例如细胞分裂期间的有丝分裂纺锤体。

微管蛋白由两个亚基组成，α-微管蛋白和β-微管蛋白。,这些亚基结合形成微管蛋白二聚体，然后组装成微管蛋白丝。,微管蛋白丝形成微管的骨架，微管是动态结构，可以根据需要生长、收缩和重组。

虽然肌动蛋白和肌球蛋白参与肌肉收缩和细胞运动，但微管蛋白和微管在除此之外的许多细胞过程中发挥着重要作用。这些蛋白丝共同有助于细胞的结构完整性及其对环境的反应能力。

Somatic and autonomic nervous system

The nervous system is responsible for controlling and coordinating all the activities of the body. It can be divided into two main parts: the central nervous system (CNS) and the peripheral nervous system (PNS). The PNS is further divided into two main divisions: the somatic nervous system (SNS) and the autonomic nervous system (ANS).

The somatic nervous system is responsible for the voluntary movements of the body. It controls the skeletal muscles and the sensory receptors that detect touch, pain, temperature, and other sensory information. The somatic nervous system is under conscious control, and its actions are usually performed in response to external stimuli.

The autonomic nervous system, on the other hand, is responsible for the involuntary functions of the body, such as breathing, heart rate, and digestion. It regulates the internal organs, glands, and smooth muscles of the body, and is divided into two branches: the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS).

The sympathetic nervous system is responsible for the "fight or flight" response, which prepares the body for physical activity and stressful situations. It increases heart rate, dilates the pupils, and redirects blood flow to the muscles and away from the digestive system.

The parasympathetic nervous system, on the other hand, is responsible for the "rest and digest" response. It slows heart rate, constricts the pupils, and stimulates digestion and other functions that help the body conserve energy.

Overall, the somatic and autonomic nervous systems work together to maintain the proper functioning of the body, ensuring that all organs and systems work in harmony to maintain homeostasis.

躯体和自主神经系统

神经系统负责控制和协调身体的所有活动。,它可以分为两个主要部分：中枢神经系统（CNS）和周围神经系统（PNS）。 PNS 进一步分为两个主要部分：躯体神经系统 (SNS) 和自主神经系统 (ANS)。

躯体神经系统负责身体的自主运动。,它控制骨骼肌和检测触觉、疼痛、温度和其他感觉信息的感觉感受器。,躯体神经系统处于有意识的控制之下，其动作通常是对外部刺激作出反应而进行的。

另一方面，自主神经系统负责身体的非自愿功能，例如呼吸、心率和消化。,它调节身体的内脏、腺体和平滑肌，分为两个分支：交感神经系统（SNS）和副交感神经系统（PNS）。

交感神经系统负责“战斗或逃跑”反应，使身体为身体活动和压力情况做好准备。,它会增加心率，扩大瞳孔，并重新引导血液流向肌肉并远离消化系统。

另一方面，副交感神经系统负责“休息和消化”反应。,它会减慢心率、收缩瞳孔并刺激消化和其他有助于身体保存能量的功能。

总的来说，躯体神经系统和自主神经系统协同工作以维持身体的正常功能，确保所有器官和系统协调工作以维持体内平衡。