Body systems: Muscular

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Body systems: Muscular

The Muscular System: A Tour

Types of Muscles that you will encountor:There are three types of muscles in the body: smooth muscles, cardiac muscles, and skeletal muscles. Smooth muscles line walls of hallow organs, the digestive track and blood vessels, where it helps move substances. The smooth muscle contraction is relatively slow and involentary. Cardiac muscles are responsible for the contractions of the heart. Cardiac muscles are involentary and generates its own stimuli to initiate a muscle contraction. While cardiac muscle also consists of striations, the main characteristic is the presence of intercalated disks. Skeletal mucles are attached mainly to bones but also to some other organs (such as the eyes). Skeletal muscles are responsible for movement and do so by means of volentary signals. Skeletal muscles are banded together and are also called striated muscles.

Things to be aware of: muscle contractionsMuscles are composed of two major protein filaments: a thick filament composed of the protein myosin and a thin filament composed of the protein actin. Muscle contraction occurs when these filaments slide over one another in a series of repetitive events. Myosin is a motor protein that generates the force in a muscle contraction much like the stroke of an oar. It consists of a head and a tail region. Together, the tails of approximately three hundred myosin molecules form the shaft of the thick filament. The myosin heads of these molecules project outward toward the thin filaments like the oars of a rowboat. Actin is a spherical protein that forms, among other things, the thin filament in muscle cells. Thin filaments are composed of two long chains of these actin molecules that are twisted around one another. Each actin molecule has a myosin-binding site where a myosin head can bind. So how do the thick and thin filaments generate muscle contraction? The attraction between the myosin head and the myosin-binding site of actin are strong enough that the bond can form spontaneously. Once the two proteins are bound, the myosin protein undergoes a conformational change, or a change in protein shape, that 'cocks' the head. Like the oar stroke of a rower, the movement of the myosin head causes the thin filament to move.This is where the Z disc comes into play. Without the anchoring the Z disc provides, the thick filaments would simply slide past the thin filaments in opposite directions. By anchoring the thin filaments in place, movement generated by the myosin heads instead causes the muscle cell to contract and, by extension, cause our body to move. The binding between actin and myosin is so strong that the body must use control mechanisms to prevent unwanted muscle contractions. There are two main proteins that regulate actin and myosin interactions: tropomyosin and troponin. Tropomyosin is a long strand that loops around the actin chains in the thin filament. By covering the myosin-binding sites of the actin molecules, tropomyosin prevents muscle contraction.

10 Important muscles That you will see:1. orbicularis oris2. pectoralis major3. satorius4. extensor digitorum longus5. rectus femoris6. biceps brachii7. deltoid8. heart9. calf10. gluteaus maximus

Flexors and extendorsOur next stop is how flexors and extensors work:Together, they bend and straighten the body's joints to create motion and activate other muscle groups, generating muscle activity -- which is another way to say working out. Flexors work to bend a joint. You may recognize a common exercise term right in the word "flex." When you flex your muscles, your flexors contract and pull on the bone, creating a bending movement of the joint. Extensors serve the opposite purpose -- extending and straightening joints. In a bicep curl, the extensor muscles contract as the fist is let down from the shoulder. The same occurs with walking or running, as hip extensors contract and pull the thigh back to the anatomical position.

To look out for: Muscle FatiqueMuscle fatigue, or physical fatigue, is the decline in ability of a muscle to generate force. It can be a result of vigorous exercise but abnormal fatigue may be caused by barriers to or interference with the different stages of muscle contraction. There are two main causes of muscle fatigue. The limitations of a nerve’s ability to generate a sustained signal (neural fatigue) and the reduced ability of the muscle fiber to contract (metabolic fatigue).

Know what you're looking at: ligaments, tendons, muscles Ligaments and tendons are fibrous bands of connective tissue that attach to bone. Ligaments connect two or more bones together and help stabilize joints. Tendons attach muscle to bone. Tendons vary in size and are somewhat elastic and attach bones to muscles.

Things you may see: all or none responseThe property of cardiac muscle in which stimulation from a single myocyte travels to the atrium and ventricle before contracting, resulting in a coherent and co-ordinated pump activity.

Extra Things You May See:1. acetylcholine - Acetylcholine is one of many neurotransmitters in the autonomic nervous system (ANS). It acts on both the peripheral nervous system (PNS) and central nervous system (CNS) and is the only neurotransmitter used in the motor division of the somatic nervous system. 2. belly - A muscle belly is basically the sum of all the muscle fibers in any given muscle.3. cholinesterase - In biochemistry, cholinesterase is a family of enzymes that catalyze the hydrolysis of the neurotransmitter acetylcholine into choline and acetic acid, a reaction necessary to allow a cholinergic neuron to return to its resting state after activation.4. Muscle Fiber - A cylindrical, multinucleate cell composed of numerous myofibrils that contracts when stimulated.5. A myofibril (also known as a muscle fibril) is a basic rod-like unit of a muscle. Muscles are composed of tubular cells called myocytes, also known as muscle fibers, and these cells in turn contain many chains of myofibrils.6. Myology - Is the study of the muscular system, including the study of the structure, function, and diseases of muscle.


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