How Would A Muscle Cell Differ From Other Types Of Animal Cells

Muscle Cell Definition

A musculus prison cell, known technically as a myocyte, is a specialized animal cell which can shorten its length using a series of motor proteins specially arranged inside the cell. While several associated proteins help, actin and myosin grade thick and thin filaments which slide by each other to contract small units of a muscle cell. These units are called sarcomeres, and many of them run terminate-to-cease inside a larger fiber called a myofibril. A single muscle cell contains many nuclei, which are pressed against the cell membrane. A muscle jail cell is a long jail cell compared to other forms of cells, and many muscle cells connect together to form the long fibers plant in muscle tissue.

Construction of a Muscle Cell

As seen in the image beneath, a muscle cell is a compact bundle of many myofibrils. Each myofibril is made of many sarcomeres bundled together and attached stop-to-end. A specialized form of the endoplasmic reticulum, known as the sarcoplasmic reticulum, extends in and effectually these myofibril bundles. The sarcoplasmic reticulum (SR for short) concentrates a chemical needed for the musculus cells to contract, and is activated past signals from nerve cells. The signals travel through the transverse tubules (T tubules in the motion picture below) after being received from a nerve and activates the SR. Mitochondria are densely packed throughout muscle cells, to provide a constant flow of ATP. The unabridged cell is covered in a specialized prison cell membrane known every bit the sarcolemma. The sarcolemma has special opening which allow nervus impulses to be passed into transverse tubules.

Beneath is a blown upward view of each sarcomere. Each sarcomere is made primarily from thick and thin filaments. Thick filaments are fabricated from repeating units of a protein known as myosin. Myosin has minor heads on it which can bind to an actin filament. Repeating units of the protein actin make up the thin filament. Actin is supported by a number of accompaniment proteins which requite the strands stability and allow the muscle to be controlled by nerve impulses.

The actin filaments are supported on each end by specialized proteins. The CapZ protein holds actin to the Z plate, while tropomodulin connects to the end of each actin filament. Nebulin connects CapZ to tropomodulin, providing a structural framework to hold the actin filaments rigid. Some other large protein, titin, connects the Z plates together and prevents the sarcomere from existence overstretched when it is not contracting. These proteins cannot be seen in the image below.

Actin is covered past ii additional proteins, troponin and tropomyosin. Troponin is the modest yellow ball in the image below, while tropomyosin is the thread-like poly peptide which follows the actin filament. The myosin proteins tin can also be seen. The heads extend upward from a thick fiber fabricated of many myosin tails wound together.

Function of a Musculus Cell

To activate a musculus, the encephalon sends an impulse downwards a nerve. The nervus impulse travels downward the nerve cells to the neuromuscular junction, where a nerve cell meets a musculus cell. The impulse is transferred to the nervus prison cell and travels down specialized canals in the sarcolemma to achieve the transverse tubules. The energy in the transverse tubules causes the SR to release of the Ca²⁺ information technology has built up, flooding the cytoplasm with calcium. The Caⁱⁱ⁺ has a special upshot on the proteins associated with actin.

Troponin, when not in the presence of Ca²⁺, will bind to tropomyosin and cause it to cover the myosin-binding sites on the actin filament. This ways that without Ca^two+ the muscle cell will be relaxed. When Ca²⁺ is introduced into the cytosol, troponin volition release tropomyosin and tropomyosin volition slide out of the way. This allows the myosin heads to attach to the actin filament. Once this happens, myosin can used the energy gained from ATP to crawl along the actin filament. When many sarcomeres are doing this at the same time, the unabridged muscle contract.

While but a small-scale per centum of the heads are attached at any in one case, the many heads and continual apply of ATP ensures a smooth wrinkle. The myosin crawls until it reaches the Z plate, and total contraction has been obtained. The SR is continually removing Ca²⁺ from the cytoplasm, and in one case the concentration falls below a certain level troponin rebinds to tropomyosin, and the muscle releases.

While the above model is a generalized version of what happens in skeletal muscle, like processes control the contractions of both cardiac and smooth muscle. In cardiac musculus, the impulses are in office controlled by pacemaker cells which releases impulses regularly. Smooth musculus is unlike from skeletal muscle in that the actin and myosin filament are not organized in user-friendly bundles. While they are organized differently, smoothen muscle still operates on the functioning of myosin and actin. Smooth muscle can obtain a signal to contract from many sources, including the nervous organisation and environmental cues the cells receive from other parts of the torso.

Quiz

1. Certain heart defects can be inherited genetically. Some of these defects occur because the genetic lawmaking responsible for creating actin or myosin is a mutant variation. Why would this affect the center?
A. Actin and Myosin command contractions in the eye
B. If your muscles don't work, your heart cannot pump enough blood to them
C. The heart needs the ATP released from myosin

Answer to Question #one

A is correct. Actin and myosin control contractions in every muscle. If your genetics contain a version of these proteins which doesn't function properly, musculus contraction in general volition be difficult or impossible. Some variations of the myosin and actin genomes contain varieties that work, but not about as well as the normal variation. These varieties tin can crusade the heart to try to beat out harder to keep up, resulting in an irregular heartbeat and oversized heart.

two. A scientist desire to see what the muscle will do without ATP. He puts a musculus cell in a petri dish, but removes all the ATP from the dish and from the cell. He and so adds Caⁱⁱ⁺ to the cytoplasm. Which of the following will happen?
A. Nothing
B. The myosin will adhere to the actin
C. The musculus will contract

Answer to Question #2

B is correct. In the presence of Ca²⁺ the myosin volition be able to bind to actin. The calcium will release the troponin and shift the tropomyosin, revealing the bounden site for myosin to attach to. However, the myosin needs ATP to swing the heads and crawl along the actin filament. Without this, the myosin will bind to the actin just will not be able to motion or contract the cell at all. Farther, many other cell functions require ATP and the cell will surely perish.

3. In doing scientific exploration, scientists found that an electrical current will stimulate a muscle cell, even if the cell is not in a living animal. Why is this the case?
A. The electricity causes the proteins to bind together
B. The electricity is the same as a nervous impulse
C. The electricity mimics the calcium released during contraction

Answer to Question #3

B is correct. Nerve impulses are nothing more than electrical voltages being carried down the cell membrane. When a muscle jail cell is exposed to certain voltages of electricity, the sarcoplasmic reticulum releases Ca²⁺, the same as if a nervous impulse triggered the contraction.

References

• Lodish, H., Berk, A., Kaiser, C. A., Krieger, One thousand., Scott, M. P., Bretscher, A., . . . Matsudaira, P. (2008). Molecular Cell Biology 6th. ed. New York: W.H. Freeman and Visitor.
• Reece, J. B., Urry, Fifty. A., Cain, Grand. L., Wasserman, Due south. A., Minorsky, P. V., & Jackson, R. B. (2014). Campbell Biology, Tenth Edition (Vol. 1). Boston: Pearson Learning Solutions.
• Blausen.com staff (2014). "Medical gallery of Blausen Medical 2014". WikiJournal of Medicine 1 (2). DOI:x.15347/wjm/2014.010. ISSN 2002-4436.

Source: https://biologydictionary.net/muscle-cell/

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