length contraction

Examples of length contraction in the following topics:

• Length Contraction

  • Let's look at the results with the aether again.If we have a rod of length $L_0$ in the primed frame what it is length in the unprimed frame.
  • We have define the length to be the extent of an object measured at a particular time.

• Length Contraction

  • Objects that are moving undergo a length contraction along the dimension of motion; this effect is only significant at relativistic speeds.
  • Length contraction is the physical phenomenon of a decrease in length detected by an observer of objects that travel at any non-zero velocity relative to that observer.
  • Length contraction arises due to the fact that the speed of light in a vacuum is constant in any frame of reference.
  • Consequently, the length of the ruler will appear to be shorter in your frame of reference (the phenomenon of length contraction occurred).
  • The effect of length contraction is negligible at everyday speeds and can be ignored for all regular purposes.

• Types of Muscle Contractions: Isotonic and Isometric

  • Muscle contractions are defined by changes in the length of the muscle during contraction.
  • Several types of muscle contractions occur and are defined by the changes in the length of the muscle during contraction.
  • Isotonic contractions maintain constant tension in the muscle as the muscle changes length.
  • In contrast to isotonic contractions, isometric contractions generate force without changing the length of the muscle, common in the muscles of the hand and forearm responsible for grip.
  • In both instances, cross-bridge cycling is maintaining tension in the muscle; the sarcomere, muscle fibers, and muscle are not changing length.

• Force of Muscle Contraction

  • The force a muscle generates is dependent on its length and shortening velocity.
  • The force a muscle generates is dependent on the length of the muscle and its shortening velocity.
  • When a sarcomere contracts, myosin heads attach to actin to form cross-bridges.
  • If the muscle is over-contracted, the potential for further contraction is reduced, which in turn reduces the amount of force produced.
  • The force-velocity relationship in muscle relates the speed at which a muscle changes length with the force of this contraction and the resultant power output (force x velocity = power).

• Interactions of Skeletal Muscles

  • Skeletal muscle contractions can be grouped based on the length and frequency of contraction.
  • The time between the stimulus and the initiation of contraction is termed the latent period, which is followed by the contraction period.
  • At peak contraction the muscle relaxes and returns to its resting position.
  • After contraction the muscle relaxes back to a resting level of tension.
  • If the frequency of these contractions increases to the point where maximum tension is generated and no relaxation is observed then the contraction is termed a tetanus.

• Velocity and Duration of Muscle Contraction

  • Skeletal muscle contractions can be broadly separated into twitch and tetanic contractions.
  • In a twitch contraction, a short burst of stimulation causes the muscle to contract, but the duration is so brief that the muscle begins relaxing before reaching peak force.
  • The force-velocity relationship in muscle relates the speed at which a muscle changes length to the force of this contraction and the resultant power output (force x velocity = power).
  • Twitch contractions are short in duration.
  • Tetanic contractions, which are long in duration, reach peak force and plateau.

• Skeletal Muscle Fibers

  • Myocytes can be incredibly large, with diameters of up to 100 micrometers and lengths of up to 30 centimeters.
  • The sarcolemma of myocytes contains numerous invaginations (pits) called transverse tubules which are usually perpendicular to the length of the myocyte.
  • Transverse tubules play an important role in supplying the myocyte with Ca+ ions, which are key for muscle contraction.
  • These myoblasts asre located to the periphery of the myocyte and flattened so as not to impact myocyte contraction.
  • Myofibrils run parallel to the myocyte and typically run for its entire length, attaching to the sarcolemma at either end.

• Sliding Filament Model of Contraction

  • Movement often requires the contraction of a skeletal muscle, as can be observed when the bicep muscle in the arm contracts, drawing the forearm up towards the trunk.
  • The sliding filament model describes the process used by muscles to contract.
  • The region between two neighboring, parallel I-bands is known as the A-band and contains the entire length of single myosin myofilaments.
  • Their elasticity provides the underpinning of muscle contraction.
  • The A-band remains constant throughout as the length of the myosin myofilaments does not change.

• Volume Expansion

  • Substances expand or contract when their temperature changes, with expansion or contraction occurring in all directions.
  • The volumetric thermal expansion coefficient is the most basic thermal expansion coefficient. illustrates that, in general, substances expand or contract when their temperature changes, with expansion or contraction occurring in all directions.
  • To derive the relationship, let's take a cube of steel that has sides of length L.
  • (a) Area increases because both length and width increase.

• Hypotonia and Hypertonia

  • Effects of hypertonia include spasticity dystonia (a state of prolonged muscle contractions) and rigidity (a state of muscle stiffness and decreased flexibility).
  • Spastic hypertonia is the general condition of muscle spasms caused by random contractions of the muscles, and is typical in cerebral palsy and spinal cord injuries; it can also occur from stroke.
  • Dystonic hypertonia is the resistance to passive stretching in muscles, and the return of limbs to fixed positions after contraction.
  • Hypotonia is the state of reduced muscle tone and tension, resulting in lessened ability to generate force from muscle contractions.
  • A muscle spindle, with γ motor neurons, sensory fibers and proprioceptor that detect the amount and rate of change of length in a muscle.