Skeletal muscle is the type of muscle that is attached to bones and helps move the skeleton. The muscular system is responsible for moving the body and includes both skeletal muscles and smooth muscles. Skeletal muscles are voluntary, meaning they can be controlled by the brain, while smooth muscles are involuntary and not under conscious control.
Muscle cells, or myocytes, are elongated and have multiple nuclei. Muscle tissue is made up of many myocytes arranged in parallel bundles called fibers. Muscle contraction occurs when myocytes contract and shorten, pulling on tendons that attach the muscle to bone.
The strength of a muscle contraction depends on the number of myocytes contracting at once, as well as the amount of tension each cell produces. Muscle cells produce tension by converting chemical energy into mechanical energy. This process is known as muscle contraction.
Muscle contraction occurs when the filaments within myocytes slide past each other. The two main types of filaments are myosin and actin. Myosin filaments have a head that can bind to actin, causing the filament to slide. Actin filaments are anchored in place and do not move.
Muscle contraction starts with a signal from the brain that is transmitted through nerves to the muscles. This signal triggers the release of a chemical called calcium from storage sites within the muscle cell. Calcium binds to proteins that cover the myosin heads, exposing them so they can bind to actin.
Voluntary, smooth muscle, and cardiac muscle are three examples of different types of muscular tissue. Muscle is made up of protein filaments called myosin and actin. These filaments slide past one another to cause a contraction that transforms both the length and form of the cell. The fundamental function of muscles is to generate both motion and force.
Muscle tissue is found in various forms throughout the human body. Voluntary muscle tissue, which is also known as skeletal muscle tissue, is responsible for generating movements of the skeleton. Smooth muscle tissue makes up the walls of hollow organs and is responsible for involuntary movements, such as peristalsis. Cardiac muscle tissue is only found in the heart and is responsible for pumping blood throughout the body.
All three types of muscle tissue are made up of protein filaments, myosin, and actin. These filaments slide past each other to generate a contraction that changes both the length and form of the cell. Muscle contractions are generated by nerve impulses that cause the release of calcium ions from storage sites within the cell.
The calcium ions then bind to the protein troponin, which triggers a conformational change in the protein tropomyosin. This change exposes the binding sites on the actin filament, which allows the myosin filaments to bind. The myosin filaments then use ATP to generate a power stroke that pulls the actin filaments towards the center of the cell.
The primary role of muscle tissue is to generate both motion and force. Muscle tissue can generate force by contracting, which results in movement of either the entire muscle or attached structures. Muscle tissue can also generate force by maintaining tension, which stabilizes structures and prevents them from moving. In order for muscle tissue to generate force, it must first be stimulated by a nerve impulse.
This impulse causes the release of calcium ions, which then binds to troponin and triggers a conformational change in tropomyosin. This exposes the binding sites on actin, which allows myosin to bind. The myosin filaments then use ATP to generate a power stroke that pulls the actin filaments towards the center of the cell.
Muscle tissue is capable of generating a wide range of force depending on the needs of the body. For example, skeletal muscle tissue is capable of generating enough force to move the entire skeleton, whereas smooth muscle tissue is only capable of generating enough force to move organs and maintain tension in structures such as blood vessels. Cardiac muscle tissue is capable of generating enough force to pump blood throughout the body.
Muscle tissue is an active tissue, meaning that it requires energy to maintain its contractile function. This energy comes from ATP, which is produced by the breakdown of glucose in the cells. Muscle tissue can store a small amount of ATP, but this is quickly used up during muscle contraction. For this reason, muscle tissue must continuously produce ATP in order to maintain its contractile function.
Muscle tissue can produce ATP through aerobic or anaerobic metabolism. Aerobic metabolism uses oxygen to produce ATP, while anaerobic metabolism does not use oxygen. Muscle tissue primarily uses aerobic metabolism to produce ATP; however, anaerobic metabolism can be used when oxygen is not available, such as during strenuous exercise.
Skeletal muscle is made up of myofibrils, which are composed of thick and thin filaments. The sarcolemma limits the overlapping of the myosin and actin, giving skeletal muscles their distinctive striations. Skeletal muscles cover the majority of the skeleton and provide form and movement.
They are also the site of most heat production in the body, due to their high metabolic rate. Muscle contraction is achieved by the sliding filament theory, whereby the myofilaments slide past each other, resulting in the shortening of the muscle fibre. This requires energy in the form of ATP, which is produced by oxidative phosphorylation within the mitochondria.
Muscle contraction can be described in terms of force, velocity and work/power. Muscle force is a measure of the amount of tension that a muscle can generate, while velocity is a measure of how fast this tension can be generated. Work and power are measures of how much mechanical work a muscle can perform (expressed in joules) and how rapidly this work can be performed (expressed in watts), respectively.
Muscle fatigue is the inability of a muscle to generate the required force for a given task and is caused by the depletion of ATP within the muscle fibre. Muscle endurance is the ability of a muscle to sustain repeated contractions over time and is related to the capacity of the muscle to resist fatigue. The type I (slow twitch) fibres are more resistant to fatigue than type II (fast twitch) fibres, due to their greater oxidative capacity.
Skeletal muscles are innervated by motor neurons that originate in the spinal cord. Motor unit recruitment is the process by which motor units are brought into action in order to achieve the required level of force. Low-force tasks require only a few motor units to be recruited, while high-force tasks require the recruitment of many motor units.
Muscle spindles are proprioceptive sensors that are located within skeletal muscles and help to regulate muscle contraction. Golgi tendon organs are also proprioceptive sensors that are located at the junction of muscle and tendon and help to protect the muscle from damage by inhibiting muscle contraction when force exceeds a certain threshold.