Term
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Definition
| A geletin-like substance that fills spaces between and inside the myofibrils. As the cytoplasm of the muscle fiber, (the fluid part), it primarily contains dissolved proteins, minerals, fats, necessary organelles and a large quantity of stored glycogen and myoglobin, which serves as an oxygen binding compound that's similar to hemoglobin in red blood cells. |
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Term
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Definition
| Also known as transverse tubules. Extensions of the Plasmalemma housed in the sarcoplasm. These pass laterally through the muscle fiber and are interconnected as they pass through the myofibrils, allowing nerve impulses to rapidly transmit to individual myofibrils after being received by the plasmalemma. These also provide paths from the outside to the inside of the fiber, allowing substances to enter and wastes to leave. |
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Term
| Sarcoplasm Reticulum (SR) |
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Definition
| A longitudinal network of tubules that parallel the myofibrils and loop around them within the muscle fiber. It stores calcium, which is essential for muscle contraction. |
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Term
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Definition
| Small fibers made up of contractile elements of sacromeres, (basic contractile elements of skeletal muscle). They appear as long strands of sacromeres under electron microscopes. Several hundred to several thousand can be found within each muscle fiber. |
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Term
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Definition
| The basic functional unit of a myofibril and the basic contractile unit of muscle. They are joined end to end at the Z-disk, and includes several elements between each pair. Also includes the rest of the A-Band outside of the H-Zone and a second I-Band. |
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Term
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Definition
| Part of the sacromeres between the Z-Disks. The light zone, made up only of thin filaments composed primarily of actin. |
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Term
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Definition
| Part of the sacromeres between the Z-Disks. The dark zone, which contains both thick and thin filaments. |
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Term
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Definition
| Part of the sacromeres between the Z-Disks. Found in the middle of the A-Band, made up only of thick filaments and composed primarily of myosin. |
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Term
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Definition
| Part of the sacromeres between the Z-Disks. Found in the middle of the H-Zone. Composed of proteins that serve as the attachment site for thick filaments. Assists in stabilizing sacromere structure. |
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Term
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Definition
| Appears on each side of the sacromere. They are composed of proteins and provide points of attachments and stability for thin filaments alongside titin and nebulin. |
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Term
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Definition
| The collective term for a single a-motor neuron and the muscle fibers it directly signals to communicate between the nervous and muscular systems. |
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Term
| Excitation-Contraction Coupling |
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Definition
| The sequence of events that triggers muscle fibers to contract. It begins when a motor nerve is excited, leading to contraction of the muscle fibers as the end result. |
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Term
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Definition
| The tilting of the myosin head that drags the thin filament towards the center of the sacromere, which is caused by a conformational change in the cross-bridge once they bind with actin. |
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Term
| Principle of Orderly Recruitment |
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Definition
| The idea that motor units are generally activated on the basis of a fixed order of fiber recruitment, where motor units within a muscle appear to be ranked. Essentially, the first muscle fiber is always used for big or small tasks, but the larger the task, the more muscle fibers need to be activated, typically in the same order every time. |
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Term
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Definition
| A term referring to the process by which the tension of a motor unit can vary from that of a twitch to that of a tetanus by increasing the frequency of stimulation in that motor unit. Essentially, the tension of a motor unit can differ depending on how often the unit is used, from being able to only use minimal effort to its physical peak, likely somewhere in between. |
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