Why do sarcomeres in series not add force?
Sum of the areas of the each fiber in muscle determines PCSA (physiological cross sectional area), which is proportional to the generated force.Assume two muscles with the same PCSA and same pennations. Lets say muscle A has longer fibers than muscle B. In this case, muscle A has a higher velocity than muscle B. However, they have the identical peak forces. In other words, maximum contraction velocity increases if the fiber length is increased.All muscle fibers are connected to each other. For a muscle containing non-spanning fibers (fibers that do not anchor to tendinous tissue at both ends), you can say that those fibers will contribute to the PCSA. But how are they going to contribute to the total force? The answer is connections between muscle fibers. These connections can transmit force! This implies that skeletal muscle cannot be regarded as an in-series combination of contractile elements. Mechanical load balance of a muscle is much more complicated than its generally assumed to be.
Can someone please explain what a sarcomere is and its components? Also, what does it mean when an ADP or ATP?
A sarcomere is the basic functional unit of striated muscle. In the human body. - The sarcomers are made up fro two types of overlapping structures, thick myosin filaments lying parallel to an another, and thin filaments made up of F-actin and also arranged in parallel. - - - - - - - - - - - - - - - Adenosine triphosphate (ATP) is the energy currency of life and it provides that energy for most biological processes by being converted to ADP (adenosine diphosphate). Since the basic reaction involves a water molecule, ATP + H2O → ADP + Pi this reaction is commonly referred to as the hydrolysis of ATP.
What is the nature of the force that makes a muscle fiber contract? Is it electrostatic?
There are many theories of muscle contraction, but the most accepted one is the ‘sliding filament theory” proposed by Sir Andrew Huxley in 1971. It has stood the test of time. The contraction is not electrostatic in nature, but molecular.Essentially, each muscle fibre is divided into smaller sections called sarcomeres (see about) where contraction occurs. Each sarcomere has two inter digitating molecular filaments: thick filament is made of myosin (shown in red above), and thin filament (blue) is made of actin with regulatory proteins troponin and tropomyosin. In a test tube if you put myosin and actin together, they connect and stay connected, that is what happens after a person dies. However, in vivo, tropomyosin and troponin prevent binding sites on actin and myosin to interact. Myosin molecules forming the thick filament has portions called heads (short red vertical lines in the figure) which can flip up and attach to binding sites on actin molecules.[Here I am going to give you a very simplified explanation, details are given elsewhere on Quora]. When the muscle membrane is depolarized by an action potential, calcium ions are released around the thick and thin filaments. In the presence of Ca++, the regulatory proteins expose the binding sites on actin. The myosin heads quickly bind to actin and form what are called cross bridges. These cross brides are like springs. Once formed, they pull towards the central black line shown in the figure above. That pulls the wavy black lines together generating force on the neighbouring sarcomeres, and ultimately force is passed on to tendons. The cross-bridges act as little molecular springs, when hundreds of them in parallel pull, they exert force. During this pull, thin filaments slide past the thick filaments, giving support to the term “sliding filament theory” of muscle contraction.
What is the exact mechanism that causes soreness?
DOMS (Delayed onset muscle soreness): While it is still not fully understood, scientists believe it is caused by micro breaks and small damage (Microtrauma) in the muscle fiber after eccentric (lengthening) exercises.Quoting Wiki:The mechanism of delayed onset muscle soreness is not completely understood, but the pain is ultimately thought to be a result of microtrauma – mechanical damage at a very small scale – to the muscles being exercised.DOMS was first described in 1902 by Theodore Hough,[3] who concluded that this kind of soreness is "fundamentally the result of ruptures within the muscle".[1]:63 According to this "muscle damage" theory of DOMS, these ruptures are microscopiclesions at the Z-line of the muscle sarcomere.[4] The soreness has been attributed to the increased tension force and muscle lengthening from eccentric exercise.[5] This may cause the actin and myosin cross-bridges to separate prior to relaxation, ultimately causing greater tension on the remaining active motor units.[5] This increases the risk of broadening, smearing, and damage to the sarcomere. When microtrauma occurs to these structures, nociceptors (pain receptors) within muscle connective tissues are stimulated and cause the sensation of pain.[6]Another explanation for the pain associated with DOMS is the "enzyme efflux" theory. Following microtrauma, calcium that is normally stored in the sarcoplasmic reticulum accumulates in the damaged muscles. Cellular respiration is inhibited and ATPneeded to actively transport calcium back into the sarcoplasmic reticulum is also slowed. This accumulation of calcium may activate proteases and phospholipases which in turn break down and degenerate muscle protein.[7] This causes inflammation, and in turn pain due to the accumulation of histamines, prostaglandins, and potassium.[6][8]An earlier theory posited that DOMS is connected to the build-up of lactic acid in the blood, which was thought to continue being produced following exercise. This build-up of lactic acid was thought to be a toxic metabolic waste product that caused the perception of pain at a delayed stage. This theory has been largely rejected, as concentric contractions which also produce lactic acid have been unable to cause DOMS.[4] Additionally, lactic acid is known from multiple studies to return to normal levels within one hour of exercise, and therefore cannot cause the pain that occurs much later.[6]
Which statement correctly describes an activity involved in muscle contraction?
1.Sarcomeres produce actin and myosin. 2.Myofibrils attach to Z lines. 3.Myosin heads attach to sites on actin filaments. 4.ATP causes fascicles to contract muscle fibers. Which structure is composed of the filaments actin and myosin? 1.sarcomere 2.myofibril 3.muscle fiber 4.fascicle Which statement best describes how a muscle moves a bone? 1.Extensors cause the bone to move in both directions. 2.Tendons connect extensors and flexors to move the bone. 3.The muscle pulls on the insertion point on the bone. 4.Flexors cause the bone to move in both directions.
What are the differences/similarities between skeletal and cardiac muscle?
They are both striated. Skeletal Muscle Structure: The cells of skeletal muscles are long fiber-like structures. They contain many nuclei and are subdivided into smaller structures called myofibrils. Myofibrils are composed of 2 kinds of myofilaments. The thin filaments are made of 2 strands of the protein actin and one strand of a regulatory protein coiled together. The thick filaments are staggered arrays of myosin molecules. Units of organization of skeletal muscle. The filaments are organized into structures called sarcomeres. Sarcomeres are constructed in the following manner: Z lines are at the borders of the sarcomere. They align in adjacent myofibrils. I bands are areas near the edge of the sarcomere containing only thin filaments. A bands are regions where thick and thin filaments overlap and correspond to the length of the thick filaments. H zones are areas in the center of the A bands containing only thick filaments. Cardiac Muscle in vertebrates is only found in the heart. It is striated as mentioned before. Differences: The muscles cells are branched, and the junctions between the cells contain intercalated discs that electrically connects all heart muscle cells, allowing coordinated action. Cells can also generate their own action potential.