Preflexes
Encyclopedia
Preflexes are the latent capacities in the musculoskeletal system
that auto-stabilize movements through the use of the nonlinear visco-elastic
properties of muscles
when they contract
. The term "preflex" for such a zero-delay, intrinsic feedback loop was coined by Loeb. Unlike stabilization methods using neurons such as reflexes and higher brain control
, it happens with minimal time delay. Its chief disadvantage is that it works only to stabilize the main movements of the musculoskeletal system.
, for example, consists of at least seven segments with different bone attachments and neural control. Within each muscle segment, there exists a complex internal structure that goes down to one in which each muscle unit consists of a tendon, aponeurosis
, and a fascicle
of active contractile and passive elements. Another source of variation is in the internal architecture of the fiber orientation relative to a muscle’s line of action, for example, as found in pennate
muscles. The complexities of the different visco-elastic length- and velocity-force relationships of these subparts provides the opportunity for the adaptive selection of structurally complex muscle biocomposites with highly task-tuned nonlinear visco-elastic length- velocity- force relationships. This nature of muscles to be composite structures thus provides the adaptive opportunity for evolution to modify the visco-elastic reactions of the musculoskeletal system so they counteract perturbations without the need for spinal or higher levels of control.
like many other bipedal birds walk
upon rough ground. When a guineafowl's leg steps into a hole (a common disruption against which evolution has tuned the nonlinear visco-elastic properties of its musculoskeletal system), a momentarily uncommanded velocity and length change in the muscles that span its leg joints occurs. This length/velocity discrepancy interacts with the nonlinear length and velocity-force relationships that have evolved in response to such a disruption with the result that the leg extends further into the hole, and thus keeps the bird’s body stable and upright.
leg, not neurally mediated spinal reflexes, that stabilize its wiping movements at irritants when the leg movement is instigated.
up from a squat position, and the leg muscles act to provide a minimal time delay against perturbations from the vertical .
Musculoskeletal system
A musculoskeletal system is an organ system that gives animals the ability to move using the muscular and skeletal systems...
that auto-stabilize movements through the use of the nonlinear visco-elastic
Viscoelasticity
Viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. Viscous materials, like honey, resist shear flow and strain linearly with time when a stress is applied. Elastic materials strain instantaneously when stretched and just...
properties of muscles
Skeletal muscle
Skeletal muscle is a form of striated muscle tissue existing under control of the somatic nervous system- i.e. it is voluntarily controlled. It is one of three major muscle types, the others being cardiac and smooth muscle...
when they contract
Muscle contraction
Muscle fiber generates tension through the action of actin and myosin cross-bridge cycling. While under tension, the muscle may lengthen, shorten, or remain the same...
. The term "preflex" for such a zero-delay, intrinsic feedback loop was coined by Loeb. Unlike stabilization methods using neurons such as reflexes and higher brain control
Motor coordination
thumb|right|Motor coordination is shown in this animated sequence by [[Eadweard Muybridge]] of himself throwing a diskMotor coordination is the combination of body movements created with the kinematic and kinetic parameters that result in intended actions. Such movements usually smoothly and...
, it happens with minimal time delay. Its chief disadvantage is that it works only to stabilize the main movements of the musculoskeletal system.
Visco-elastic correction
Muscles possess nonlinear visco-elastic properties when they contract. This property can autocorrect movements when a muscle is forced to change its length, and at a velocity different to that with which it was originally commanded. Such automatic correction is useful when a commanded action is perturbated, for example, if a step goes into a hole as this causes the foot to unexpectedly stretch down. The nonlinear visco-elastic properties of muscles interact with these perturbation induced velocity and length differences such that they counteract directly, as they happen, the effects upon the body of the perturbation.Evolutionary opportunity
Muscles contain many different systems on which the evolutionary selection of preflex stabilization can operate. The deltoid muscleDeltoid muscle
In human anatomy, the deltoid muscle is the muscle forming the rounded contour of the shoulder. Anatomically, it appears to be made up of three distinct sets of fibers though electromyography suggests that it consists of at least seven groups that can be independently coordinated by the central...
, for example, consists of at least seven segments with different bone attachments and neural control. Within each muscle segment, there exists a complex internal structure that goes down to one in which each muscle unit consists of a tendon, aponeurosis
Aponeurosis
Aponeuroses are layers of flat broad tendons. They have a shiny, whitish-silvery color, are histologically similar to tendons, and are very sparingly supplied with blood vessels and nerves. When dissected, aponeuroses are papery, and peel off by sections...
, and a fascicle
Muscle fascicle
In anatomy, a fascicle is a bundle of skeletal muscle fibers surrounded by perimysium, a type of connective tissue.Specialized muscle fibers in the heart that transmit electrical impulses from the Atrioventricular Node to the Purkinje Fibers are fascicles, also referred to as bundle branches...
of active contractile and passive elements. Another source of variation is in the internal architecture of the fiber orientation relative to a muscle’s line of action, for example, as found in pennate
Pennate
Pennate is used to mean "winged", "feathered" or simply "shaped like a wing". The latter definition is sometimes used to describe plant leaf morphology .Pennate diatoms are bilaterally symmetrical, and belong to the order Pennales....
muscles. The complexities of the different visco-elastic length- and velocity-force relationships of these subparts provides the opportunity for the adaptive selection of structurally complex muscle biocomposites with highly task-tuned nonlinear visco-elastic length- velocity- force relationships. This nature of muscles to be composite structures thus provides the adaptive opportunity for evolution to modify the visco-elastic reactions of the musculoskeletal system so they counteract perturbations without the need for spinal or higher levels of control.
Leg step recovery
Helmeted GuineafowlHelmeted Guineafowl
The Helmeted Guineafowl is the best known of the guineafowl bird family, Numididae, and the only member of the genus Numida...
like many other bipedal birds walk
WALK
WALK may refer to:*WALK , a radio station licensed to East Patchogue, New York, United States*WALK-FM, a radio station licensed to Patchogue, New York, United States...
upon rough ground. When a guineafowl's leg steps into a hole (a common disruption against which evolution has tuned the nonlinear visco-elastic properties of its musculoskeletal system), a momentarily uncommanded velocity and length change in the muscles that span its leg joints occurs. This length/velocity discrepancy interacts with the nonlinear length and velocity-force relationships that have evolved in response to such a disruption with the result that the leg extends further into the hole, and thus keeps the bird’s body stable and upright.
Leg wiping
It is the intrinsic musculoskeletal properties of a frog’sFrog
Frogs are amphibians in the order Anura , formerly referred to as Salientia . Most frogs are characterized by a short body, webbed digits , protruding eyes and the absence of a tail...
leg, not neurally mediated spinal reflexes, that stabilize its wiping movements at irritants when the leg movement is instigated.
Squat jumps
A human example of a preflex stabilization occurs when a person explosively jumpsJumping
Jumping or leaping is a form of locomotion or movement in which an organism or non-living mechanical system propels itself through the air along a ballistic trajectory...
up from a squat position, and the leg muscles act to provide a minimal time delay against perturbations from the vertical .