Muscles Contract When The Central Nervous System

Contractility of ASM requires an increased levels of intracellular Ca2+. When surface receptors are not activated, Ca2+ levels are low. Upon activation of these cell surface receptors by contractile agonists e.g. acetylcholine, serotonin and histamine, intracellular Ca2+ increases causing a contraction (9). Smooth muscle cell contraction is controlled by both receptor and mechanical activation of proteins actin and myosin and also changes to membrane potential.

Muscle contraction can be understood as the consequence of a process of transmission of action potentials from one neuron to another. A chemical called acetylcholine is the neurotransmitter released from the presynaptic neuron. As the postsynaptic cells on the muscle cell membrane receive the acetylcholine, the channels for the cations sodium and potassium are opened. These cations produce a net depolarization of the cell membrane and this electrical signal travels along the muscle fibers. Through the movement of calcium ions, the muscle action potential is taken into actual muscle contraction with the interaction of two types of proteins, actin and myosin.

-Sarcoplasmic Reticulum (SR) then releases Calcium which binds to troponin in the thin filament, exposing myosin-binding sites;

These muscles are under control of will. These muscles are controlled by the central nervous system. i.e. Coraco brachialis muscle. This is found in the upper part of the arm and flexes the shoulder joint.

Smooth muscle contraction occurs when calcium is present in the smooth muscle cell and binds onto calmodulin to activate myosin light chain kinase (Wilson et al., 2002). Phosphorylation of myosin light chains result in myosin ATPase activity thus cross-bridge cycling occurs causing the muscle to contract (Horowitz et al., 1996). There are two known models of excitation and contraction in smooth muscle, electromechanical coupling (EMC) and pharmomechanical coupling

How is contraction ended? Ach is released and binds to receptors on the motor end plate, then an action potential is produced which releases Ca+. The Ca+ binds to troponin, then myosin binds to actin to form crossbridges. The myosin pulls the actin then releases from actin and ADP is bound to the myosin.

These muscle tissue cells specialised to contract and move parts of the body. It is also capable of responding to stimuli. There are three types of muscle in the body such as: skeletal, cardiac and smooth. Each muscle is created of muscle fibers that are capable of contracting and returning back to original state-relaxation. Contraction causes movement of the skeleton, soft tissue, blood or specific material. Skeletal muscle is attached to the bones of the skeleton. Some facial muscles are attached to the skin. They have direct control over them through nervous impulses from our brain sending messages to the muscle. Contractions can vary to produce fast, powerful movements. These muscles also have the ability to stretch and contract to return to original shape. Cardiac muscles are found in the chambers of the heart such as the atria and ventricles. It is under the control of the automatic nervous system; however, even without nervous input contractions can occur. It is completely different to all the other muscles. Smooth muscles are also known as involuntary due to our inability to control its movement. This muscle is usually found in the walls of hollow organs

For muscle to contract, actin and myosin filaments need to slide past each other, causing the sarcomere to shorten in length . Each myosin filament has a protruding bulbous head, which can bind with the binding sites on the

Figure 1. The muscle-derived electric organ lacks sarcomeres. Electron micrographs of a regions of control muscle fiber (A) and an electrocyte (B).

Myofibrils are made up of long proteins that include myosin, titin, and actin while other proteins bind them together. These proteins are arranged into thin and thick filaments that are repetitive along the myofibril in sectors known as sarcomeres. The sliding of actin and myosin filaments along each other is when the muscle is contracting. Dark A-bands and light I-bands reappear along myofibrils. The alignment of myofibrils causes an appearance of the cell to look banded or striated. A myofibril is made up of lots of sarcomeres. As the sarcomeres contract individually the muscle cells and myofibrils shorten in length. The longitudinal section of skeletal muscle exhibits a unique pattern of alternating light and dark bands. The dark staining, A-bands possess a pale region in the middle called the H-zone. In the middle of the H-zone the M-line is found, that displays filamentous structures that can join the thick filaments. The light-staining bands also known as I-bands are divided by thin Z-line. These striated patterns appear because of the presence of myofibrils in the sarcoplasm (IUPUI, 2016).

Actin and Myosin proteins serve the primary role of producing muscle contraction. Myosin molecules will create pressure in the skeletal muscle, where ATP hydrolysis causes Myosin to bind to Actin. A conformational change of the molecule then result in Myosin being

As stated by (Muscles, 2015) “If a muscle cell fires an action potential, which is as a result of the motor neuron command. Then it causes the release of calcium ions, which are released from the sarcoplasmic reticulum” Sarcoplasmic reticulum is a specialised type of smooth ER that regulates the calcium ion concentration in the cytoplasm of striated muscle cells (Sarcoplasmic Reticulum Cell Biology, 2015).

There are three main types of muscles skeletal, cardiac, and smooth muscles. Most of them contract every time we move. Many muscles must contract to move the bone they are attached to or to provide resistance. In this essay I will talk about the different ways muscles contract.

One of this filament is called myosin. Myosin exists as a filament inside of the eukaryotic cells which are a motor molecule responsible for a number of interactions, such as contractions muscles and movement. The head and the tail domain are mostly composed of myosin molecules and converts ATP (adenosine triphosphate), a molecule that cells use in order to work and live, into mechanical energy (energy of work). This will then create force and movement. The filamentous actin is bound by the head domain and uses ATP hydrolysis to "walk" along the filament and to create force and towards the end. The tail domain generally mediates interaction with other myosin subunits and/or cargo molecules. This will result in an expansion and contraction movement. It works closely with a globular protein called actin that polymerises to create actin

Both of these muscles expand and contract as they have complex structures so it is essential how they do this. The cardiac muscle needs the contractions to occur in order to pump blood out of the atria and into the ventricles and round the circulatory system so the structure of this muscle shows the systole of the heart. The contractions of the skeletal muscle also depend on its structure. The binding and releasing of two strands of sarcomere is how the repeated pattern of contractions occurs. ATP is used to prepare myosin for binding to allow the contractions to happen. The skeletal and cardiac muscle also both has elasticity. The elasticity is used to restore the muscles back to their original lengths which enable them to resume back to their original length once they have contracted and been stretched.