concentric contraction

Examples of concentric contraction in the following topics:

• Types of Muscle Contractions: Isotonic and Isometric

  • 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.

• Mechanism and Contraction Events of Cardiac Muscle Fibers

  • 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.

• Electric Potential in Human

  • As a result, a cell can contain a concentration of a given ion that differs from that which exists outside.
  • No energy is required for this to occur, and therefore ions can only move from areas of higher concentration to those of lower concentration.
  • This involves ion pumps using energy to push an ion from an area of lower concentration to one of higher concentration.
  • When the brain decides on an action, it sends an impulse that cascades to the extremity where a muscle contracts.
  • This impulse is passed through the axon, a long extension of the cell, in the form of an electrical potential created by differing concentrations of sodium and potassium ions on either side of a membrane in the axon.

• Nerve Conduction and Electrocardiograms

  • Free ions will diffuse from a region of high concentration to one of low concentration.
  • Only small fractions of the ions move, so that the cell can fire many hundreds of times without depleting the excess concentrations of Na+ and K+.
  • Just as nerve impulses are transmitted by depolarization and repolarization of an adjacent membrane, the depolarization that causes muscle contraction can also stimulate adjacent muscle cells to depolarize (fire) and contract.
  • The P wave is generated by the depolarization and contraction of the atria as they pump blood into the ventricles.
  • The semipermeable membrane of a cell has different concentrations of ions inside and out.

• Control of Hormone Secretion

  • The physiological activity of a hormone depends largely on its concentration within the circulatory system.
  • The effects of too high or too low a concentration of hormones can be damaging—this level must be tightly controlled.
  • The hormone oxytocin is produced by the posterior pituitary that stimulates and enhances contractions during labor.
  • Oxytocin travels to the uterus through the bloodstream, stimulating the muscles in the uterine wall to contract which in turn increases the activation of the pressure receptors and stimulates further release of oxytocin.
  • The strength of muscle contractions intensifies until the baby is born and the stimulation of the pressure receptors is removed, which stops the release of oxytocin.

• Contractile Vacuoles in Microorganisms

  • Contractile vacuoles absorb excess water and wastes from a microorganism's cell and excrete them into the environment by contracting.
  • In freshwater environments, the concentration of solutes inside the cell is higher than outside the cell.
  • The CV's phases of collecting water (expansion) and expelling water (contraction) are periodical.
  • The contraction of the CV and the expulsion of water from the cell is called systole.
  • In hyperosmotic environments, less water will be expelled and the contraction cycle will be longer.

• Regulatory Proteins

  • Troponin, which regulates the tropomyosin, is activated by calcium, which is kept at extremely low concentrations in the sarcoplasm.
  • Once the tropomyosin is removed, a cross-bridge can form between actin and myosin, triggering contraction.
  • The concentration of calcium within muscle cells is controlled by the sarcoplasmic reticulum, a unique form of endoplasmic reticulum in the sarcoplasm.
  • Muscle contraction ends when calcium ions are pumped back into the sarcoplasmic reticulum, allowing the muscle cell to relax.
  • The outflow of calcium allows the myosin heads access to the actin cross-bridge binding sites, permitting muscle contraction.

• Slow-Twitch and Fast-Twitch Muscle Fibers

  • Skeletal muscle contains different fibers which allow for both rapid short-term contractions and slower, repeatable long-term contractions.
  • Slow-twitch fibers are designed for endurance activities that require long-term, repeated contractions, like maintaining posture or running a long distance.
  • The ATP required for slow-twitch fiber contraction is generated through aerobic respiration (glycolysis and Krebs cycle), whereby 30 molecules of ATP are produced from each glucose molecule in the presence of oxygen.
  • Due to their large oxygen requirements, slow-twitch fibers are associated with large numbers of blood vessels, mitochondria, and high concentrations of myoglobin, an oxygen-binding protein found in the blood that gives muscles their reddish color.
  • Fast-twitch fibers are good for rapid movements like jumping or sprinting that require fast muscle contractions of short duration.

• Forward and Spot Transactions

  • Press concentrated on derivatives as the cause of the bankruptcy, but the fund manager made poor decisions.
  • We discuss CDS contracts in this chapter.
  • Derivatives are a contract, a piece of paper.
  • Contract protects both the bread company and farmers from price fluctuations.
  • Derivatives are contracts, and buyers and sellers exchange the contracts in the derivative markets.

• Adrenergic Neurons and Receptors

  • Agonist binding thus causes a rise in the intracellular concentration of the second messenger cAMP.
  • α1 couples to Gq, which results in increased intracellular Ca2+ that results in smooth muscle contraction.
  • α2, on the other hand, couples to Gi, which causes a decrease of cAMP activity, that results in smooth muscle contraction.
  • Specific actions of the α1-receptor mainly involve smooth muscle contraction.
  • Other areas of smooth muscle contraction are: