Examples of concentric contraction in the following topics:
- Isotonic muscle contractions can be either concentric or eccentric.
- A concentric contraction is a type of muscle contraction in which the muscles shorten while generating force, overcoming resistance.
- For example, when lifting a heavy weight a concentric contraction of the biceps would cause the arm to bend at the elbow, lifting the weight towards the shoulder.
- For example a voluntary eccentric contraction would be the controlled lowering of the heavy weight, raised during the above concentric contraction.
- An isotonic concentric contraction results in the muscle shortening, an isotonic eccentric contraction results in the muscle lengthening.
- The gap junctions spread action potentials to support the synchronized contraction of the myocardium.
- In cardiac, skeletal, and some smooth muscle tissue, contraction occurs through a phenomenon known as excitation contraction coupling (ECC).
- The actual mechanical contraction response in cardiac muscle occurs via the sliding filament model of contraction.
- The pathway of contraction can be described in five steps:
- Intracellular calcium is then removed by the sarcoplasmic reticulum, dropping intracellular calcium concentration, returning the troponin complex to its inhibiting position on the active site of actin, and effectively ending contraction as the actin filaments return to their initial position, relaxing the muscle.
- Parallel muscles are characterized by fascicles that run parallel to one another, and contraction of these muscle groups acts as an extension of the contraction of a single muscle fiber.
- Muscle fibers can often exert opposing effects during contraction, such as not pulling in the same direction depending on the location of the muscle fiber.
- Fascicles pull on the tendon at an angle, thus not moving as far at the parallel muscles during a contraction.
- The fibers of the circular or sphincter muscles are arranged concentrically around an opening or recess.
- As the muscle contracts, the opening it circumvents gets smaller.
- Ninety-nine percent or more is deposited in bone and the remainder plays a vital role in nerve conduction, muscle contraction, hormone release and cell signalling.
- The plasma concentration of Ca++ is 2.2 mmol/l and phosphate is 1.0 mmol/l.
- The concentration of Ca++ in the cytoplasm is < 10-6 mmol/l but the concentration of Ca++ in the cell is much higher as calcium is taken up (and is able to be released from) cell organelles.
- It is the ionized calcium concentration that is monitored by the parathyroid gland and if low, parathyroid hormone secretion is increased.
- This leads to disruptions of mechanical stabilization and calcium concentration regulation within the sarcomeres, altering the ability of filaments to bind and cause contraction.
- In affected muscle the tissue becomes disorganized and the concentration of dystrophin (green) is greatly reduced.
- Exercise damages muscles due to eccentric and concentric muscle loading and often results in delayed onset muscle soreness (DOMS).
- Exercise damages muscles due to eccentric and concentric muscle loading.
- Resistance training, and particularly high loading during eccentric contractions, results in delayed onset muscle soreness (DOMS).
- Acute inflammation of the muscle cells, as understood in exercise physiology, can result after induced eccentric and concentric muscle training.
- Damage to the sarcomeres causes aninflux of white blood cells, leading to inflammation, which is itself associated with increased plasma enzyme concentration, myoglobinemia, and abnormal muscle structure and histology.
- Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, particularly the large arteries and small arterioles .
- The mechanism that leads to vasoconstriction results from the increased concentration of calcium (Ca2+ ions) within vascular smooth muscle cells.
- However, the specific mechanisms for generating an increased intracellular concentration of calcium depends on the vasoconstrictor.
- Once elevated, the intracellular calcium concentration is returned to its basal level through a variety of protein pumps and calcium exchangers located on the plasma membrane and sarcoplasmic reticulum.
- This reduction in calcium removes the stimulus necessary for contraction allowing for a return to baseline.
- The blood flow to an active muscle changes depending on the exercise intensity, and contraction frequency and rate.
- Between muscle contractions, intramuscular pressure transiently returns to a level below the venous blood pressure and blood from the capillary system refills the veins until the next contraction.
- Dynamic exercise is characterized by relaxation periods between contractions.
- The blood flow to an active muscle changes depending on the exercise intensity, contraction frequency, contraction-to-relaxation duty cycle, etc.
- Oxygen consumption (VO2) during exercise is best described by the Fick Equation: VO2=Q x (a-vO2 diff), which states that the amount of oxygen consumed is equal to cardiac output (Q) multiplied by the difference between arterial and venous oxygen concentrations.
- Agonist binding thus causes a rise in the intracellular concentration of the second messenger cAMP.
- Adrenaline or noradrenaline are receptor ligands to α1, α2 or βadrenergic receptors (the pathway is shown in ). α1 couples to Gq, which results in increased intracellular Ca2+ which results in smooth muscle contraction. α2, on the other hand, couples to Gi, which causes a decrease of cAMP activity, resulting in smooth muscle contraction. β receptors couple to Gs, and increases intracellular cAMP activity, resulting in heart muscle contraction, smooth muscle relaxation and glycogenolysis.
- Specific actions of the α1 receptor mainly involve smooth muscle contraction.
- Other areas of smooth muscle contraction are as follows:
- Adrenaline and noradrenaline are ligands to α1, α2, or β-adrenergic receptors. α1 receptors couple to Gq, resulting in increased intracellular Ca2+ and causing smooth muscle contraction. α2 receptors couple to Gi, causing a decrease in cAMP activity and resulting in smooth muscle contraction. β receptors couple to Gs, increasing intracellular cAMP activity and resulting in heart muscle contraction, smooth muscle relaxation and glycogenolysis.
- Skeletal muscle contains different fibers which allowing for both rapid short-term and slower, repeatable long-term contractions.
- Slow-twitch fibres are good for endurance activities like maintaining
posture or long distance running which require long term or repeated
- The ATP required for slow-twitch fibre contraction is generated
through aerobic respiration (glycolysis and Krebs cycle) whereby 30 molecules
of ATP are produced from each one of glucose in the presence of oxygen.
- Due to this requirement for large amounts of oxygen slow-twitch fibers are associated with large numbers of blood vessels, mitochondria and
high concentrations of myoglobin, an oxygen binding protein related to hemoglobin
found in the blood, which lends them a red coloration.
- Fast-twitch fibers are good for rapid movements like jumping
or sprinting which require fast muscle contractions of short duration.