Muscular system Flashcards | Easy Notecards
Actin/Thin myofilament. attach to Z Myosin/Thick myofilament. in the center of . Describe the relationship between myofibrils and muscle cells. myofibrils are. Muscle Fiber (cell). Muscle Fiber. (with many nuclei). Myofibril. Sarcomere. Thin Filament (actin) Relationships: Bunch of Fascicles = Relationships: Bunch of Sarcomeres = Myofibril; Sarcomere = Bunch of Myofilaments (Actin + Myosin). There are two types of myofilaments in myofibrils: thick myofilaments and thin Drawing showing relationship between sarcoplasmic reticulum and a transverse .
Myofibrils are composed mainly of actin and myosin proteins. Some other types of proteins are also present in myofibrils. These proteins are organized into thick and thin long filaments called myofilaments.
Thin myofilaments consist primarily of actin protein while thick filaments consist of myosin protein. These two types of myofilaments run through the length of the myofibril in sections called sarcomeres.
Myofibrils comprise of repeating sections of sarcomeres. These sarcomeres appear as alternating dark and light bands under the microscope and are responsible for muscle contractions.
Muscle fibers and myofibrils are responsible for muscle contractions.
Both types are tubular in shape. Both types are arranged in parallel inside the muscle. Myofibrils are the basic units of muscle fibers. One muscle fiber contains hundreds of myofibrils. Myofibril vs Muscle Fiber Myofibril is a basic rod-like unit of a muscle fiber. Muscle Fiber is a tubular shaped cell of the muscle. Composition Myofibril is composed of two types of myofilaments called thin and thick filaments.
Muscle Fiber is composed of numerous myofibrils. The protein complex composed of actin and myosin is sometimes referred to as "actinomyosin". In striated muscle, such as skeletal and cardiac musclethe actin and myosin filaments each have a specific and constant length on the order of a few micrometers, far less than the length of the elongated muscle cell a few millimeters in the case of human skeletal muscle cells.
The filaments are organized into repeated subunits along the length of the myofibril.
Difference Between Myofibril and Muscle Fiber | Myofibril vs Muscle Fiber
These subunits are called sarcomeres. The muscle cell is nearly filled with myofibrils running parallel to each other on the long axis of the cell. The sarcomeric subunits of one myofibril are in nearly perfect alignment with those of the myofibrils next to it.
This alignment gives rise to certain optical properties which cause the cell to appear striped or striated. In smooth muscle cells, this alignment is absent, hence there are no apparent striations and the cells are called smooth. Each sarcomere is delimited by two very dark colored bands called Z-discs or Z-lines from the German zwischen meaning between.
These Z-discs are dense protein discs that do not easily allow the passage of light. The T-tubule is present in this area.
Difference Between Myofibril and Muscle Fiber
The area between the Z-discs is further divided into two lighter colored bands at either end called the I-bands, and a darker, grayish band in the middle called the A band.
The I bands appear lighter because these regions of the sarcomere mainly contain the thin actin filaments, whose smaller diameter allows the passage of light between them.
However, these tubules DO NOT open into the interior of the muscle cell; they pass completely through and open somewhere else on the sarcolemma i. A muscle fiber is excited via a motor nerve that generates an action potential that spreads along the surface membrane sarcolemma and the transverse tubular system into the deeper parts of the muscle fiber.
Sarcoplasmic reticulum SR membranes in close proximity to a T-tubule. The membrane of the SR is well-equipped to handle calcium: In addition, the membrane has special openings, or "gates", for calcium.
In a relaxed muscle, these gates are closed and calcium cannot pass through the membrane. So, the calcium remains in the SR.
This, as you will see, is a key step in muscle contraction. Myofibrils are composed of 2 types of myofilaments: In skeletal muscle, these myofilaments are arranged in a very regular, precise pattern: In a side view, thin myofilaments can be seen above and below each thick myofilament. Myofibril cross-section showing arrangement of thick and thin myofilaments. Image from Widrick et al. Tskhovrebova and Trinick Muscle structure Each myofibril is composed of many subunits lined up end-to-end.
In each sarcomere, thin myofilaments extend in from each end. Thick myofilaments are found in the middle of the sarcomere and do not extend to the ends. Because of this arrangement, when skeletal muscle is viewed with a microscope, the ends of a sarcomere where only thin myofilaments are found appear lighter than the central section which is dark because of the presence of the thick myofilaments. Thus, a myofibril has alternating light and dark areas because each consists of many sarcomeres lined up end-to-end.
The Z-LINE is where adjacent sarcomeres come together and the thin myofilaments of adjacent sarcomeres overlap slightly. Thus, a sarcomere can be defined as the area between Z-lines.
Used by permission of John W.