Graffiti is a highly controversial and polarizing topic, with some people considering it to be a form of artistic expression and others viewing it as nothing more than vandalism. In this essay, we will examine both sides of the argument to determine whether graffiti should be considered art or vandalism.
On one hand, proponents of graffiti argue that it is a legitimate form of art. They point out that graffiti has a long history dating back to ancient civilizations, where it was often used to convey important messages or tell stories. Graffiti can also be seen as a way for artists to express their creativity and share their ideas with the world. Many graffiti artists take great care in planning and executing their works, using a variety of techniques and styles to create visually striking and thought-provoking pieces.
However, those who view graffiti as vandalism argue that it is a destructive and illegal activity that damages public and private property. Graffiti often appears on buildings, trains, and other public structures without the permission of the property owner, and removing it can be costly and time-consuming. Additionally, some graffiti is used to spread hate speech or gang-related messages, which can create a sense of fear and unrest in a community.
In conclusion, the question of whether graffiti is art or vandalism is highly subjective and depends on one's personal beliefs and values. While some may see it as a legitimate form of artistic expression, others view it as a destructive and illegal activity. Ultimately, it is important to respect the rights of property owners and ensure that graffiti is not used to spread hate or cause harm to others.
How Do Muscles Contract: Steps to Muscle Contraction
Cross-bridges can only form where thick and thin filaments overlap, allowing myosin to bind to actin. This is an electrical event, called an action potential, that can be used as a cellular signal. The chemical message, a neurotransmitter called acetylcholine, binds to receptors on the outside of the muscle fiber. In this case, they are not permitted to return to an evenly mixed state. Each skeletal muscle fiber is controlled by a motor neuron, which conducts signals from the brain or spinal cord to the muscle. He loves to teach PTs and OTs ways to save time and money in and out of the clinic, especially when it comes to documentation or continuing education.
It is measured in volts, just like a battery. If there were no gaps, your peer can challenge you with some questions about your explanation. ATP can then attach to myosin, which allows the cross-bridge cycle to start again and further muscle contraction can occur Figure 6. If the sarcomere is shortened, even more, thin filaments begin to overlap with each other—reducing cross-bridge formation even further and producing even less tension. The sliding filament theory of muscle contraction was developed to fit the differences observed in the named bands on the sarcomere at different degrees of muscle contraction and relaxation. Likewise, the more motor units activated, the greater your strength or force can be.
ATP binding causes myosin to release actin, allowing actin and myosin to detach from each other. The motor end plate possesses junctional folds—folds in the sarcolemma that create a large surface area for the neurotransmitter to bind to receptors. These contractions extend from the muscle fiber through connective tissue to pull on bones, causing skeletal movement. After this happens, the newly bound ATP is converted to ADP and inorganic phosphate, Pi. The sarcoplasmic reticulum is a specialized endoplasmic reticulum found in muscle cells. The area of the sarcolemma on the muscle fiber that interacts with the neuron is called the motor end plate. After the power stroke, ADP is released; however, the cross-bridge formed is still in place, and actin and myosin are bound together.
When K+ leaves the cell, obeying its concentration gradient, that effectively leaves a negative charge behind. Once released by the synaptic terminal, ACh diffuses across the synaptic cleft to the motor end plate, where it binds with ACh receptors. Skeletal muscle tissue is composed of cells called muscle fibers. AChE resides in the synaptic cleft, breaking down ACh so that it does not remain bound to ACh receptors, which would cause unwanted extended muscle contraction Figure 6. . Potassium channels continue at 90% conductance.
Was this a good reminder of the basics? In vertebrates, each myofiber responds fully if stimulated. Acetylcholine ACh is a neurotransmitter released by motor neurons that binds to receptors in the motor end plate. Potassium is able to leave the cell through K+ channels that are open 90% of the time, and it does. At the foundation of all movement is the humble muscle cell. This amount of stretching does not usually occur because accessory proteins, internal sensory nerves, and connective tissue oppose extreme stretching. Excitation-contraction coupling Excitation-contraction coupling is the link transduction between the action potential generated in the sarcolemma and the start of a muscle contraction.
As mentioned above, increasing the frequency of action potentials the number of signals per second can increase the force a bit more, because the tropomyosin is flooded with calcium. The action potential moves across the entire cell, creating a wave of depolarization. The whole process is called the mechanism of muscle contraction and it can be summarized in three steps: 1 A message travels from the nervous system to the muscular system, triggering chemical reactions. The depolarization then spreads along the sarcolemma, creating an action potential as sodium channels adjacent to the initial depolarization site detect the change in voltage and open. The enzyme at the binding site on myosin is called ATPase.
However, the transmembrane potential is considerably smaller 0. The ideal length of a sarcomere during the production of maximal tension occurs when thick and thin filaments overlap to the greatest degree. Tropomyosin blocks myosin binding sites on actin molecules, preventing cross-bridge formation and preventing contraction in a muscle without nervous input. The zone of overlap, in which thin filaments and thick filaments occupy the same area, increases as the thin filaments move inward. You can read a textbook, or even study the simplified steps above, but watching it in action is very helpful.
If present, calcium ions bind to troponin, causing conformational changes in troponin that allow tropomyosin to move away from the myosin binding sites on actin. The proteins inside muscle fibers are organized into long chains that can interact with each other, reorganizing to shorten and relax. This diagram shows excitation-contraction coupling in a skeletal muscle contraction. To enable a muscle contraction, tropomyosin must change conformation, uncovering the myosin-binding site on an actin molecule and allowing cross-bridge formation. Regulatory proteins When a muscle is in a resting state, actin and myosin are separated. Myosin has another binding site for ATP at which enzymatic activity hydrolyzes ATP to ADP, releasing an inorganic phosphate molecule and energy.
Once the tropomyosin is removed, a cross-bridge can form between actin and myosin, triggering contraction. Conversely, if the sarcomere is stretched to the point at which thick and thin filaments do not overlap at all, no cross-bridges are formed and no tension is produced. Follow him on YouTube for weekly videos on ways to improve your financial health. The receptors are actually sodium channels that open to allow the passage of Na+ into the cell when they receive neurotransmitter signal. When you are done, ask your peer what terms or steps you missed or did not explain well. This charge gradient is carried by ions, which are differentially distributed across the membrane. The myosin head moves toward the M line, pulling the actin along with it.
This enables the same muscles to move very light objects and very heavy objects. ACh is broken down by the enzyme acetylcholinesterase AChE into acetyl and choline. This entire process shortens the sarcomere, which is functional unit of a muscle cell. What effect would Sarin have on muscle contraction? Communication occurs between nerves and muscles through neurotransmitters. When the nervous system signal reaches the neuromuscular junction a chemical message is released by the motor neuron.
