What are muscle stretch reflexes called? Muscle spindle reflexes: clinical stretch reflex and flexion reflex
Skeletal muscles are made up of bundles muscle fibers. Muscle fibers can contract, relax, or lengthen.
Muscle fibers contract under the influence of an electrical impulse coming from the nerve. One muscle fiber always contracts fully, producing a fixed force. The force developed by the entire muscle is determined by the number of fibers involved in this action by the nervous system.
Connective tissues
The connective tissues in the musculoskeletal system are ligaments, tendons and fascia. Ligaments are attached at both ends to the bones of the joint, tendons attach muscles to bones, and fascia envelops muscle groups and bundles of muscle fibers.
Ligaments and tendons contain large amounts of collagen protein, which gives them rigidity. Ligaments and tendons practically do not stretch; excessive stress on these tissues can lead to injury. Fascia is an elastic connective tissue (contains the protein elastin), and stretching it increases flexibility. Most flexibility exercises focus on stretching the fascia.
Stretch mechanism
When stretching, the muscle fibers are first stretched, and then the collagen fibers are aligned in the direction of the pulling force. connective tissue. This allows the fibers to be aligned in the direction of stretch, allowing stretching exercises to restore healthy tissue structure.
When a muscle is stretched, some of the muscle fibers are stretched, while others remain in their original state. The length of a muscle is determined by the number of stretched fibers (similar to how the length and strength of a compressed muscle is determined by the number of compressed fibers). The more stretched fibers, the longer the stretched muscle.
Stretch reflex
In the thickness of the muscles there are neuromuscular spindles - nerve endings that respond to muscle lengthening. The spindles are parallel to the muscle fibers and stretch with them. At the same time, they record both the change in muscle length and the rate of this change.
When a muscle lengthens strongly or abruptly, a signal from the spindles triggers a protective stretch reflex—the muscle spontaneously contracts in an attempt to prevent lengthening.
The stretch reflex has static and dynamic components. The static component remains the entire time the muscle is stretched. The dynamic component is the response to the rate of change in muscle length, it can be very strong when the muscle is sharply lengthened and decreases when the rate of muscle lengthening decreases.
One of the purposes of holding a stretch pose for a period of time is to allow the muscle spindles to adapt to the new length of the muscle by decreasing the intensity of their signals in the new position.
Elongation reaction
When a muscle contracts, it creates tension on the tendon to which it is attached. The Golgi tendon organ, a type of nerve ending that is located at the junction of muscle fibers and tendons, responds to this. The tendon organ responds to the magnitude of the tension force that occurs (static effect) and to the rate of change of this force (dynamic effect: a sharp tension causes a strong signal).
When the signal from the tendon organ exceeds a certain threshold, a protective lengthening reaction occurs - a sharp spontaneous relaxation of the entire muscle.
The second reason for holding a stretch pose for some time is to allow a lengthening response to occur, which helps the muscle relax (overcoming the contraction reflex).
Mutual inhibition
In relation to the movement performed, muscles can be classified into one of four types:
- Agonists- cause movement.
- Antagonists- cause the opposite movement; are responsible for returning to the initial position of the body.
- Synergists- correct the action of the agonist muscle to ensure the desired direction of the resulting force.
- Stabilizers- support the rest of the body while performing the movement.
Agonists and antagonists are usually found on opposite sides of the joint (eg biceps and triceps), and synergists are on the same side as the agonists, next to them. When large agonist muscles work, nearby smaller muscles are often involved as synergists.
Contraction of an agonist muscle can lead to reflex relaxation of its antagonist. This phenomenon is called mutual inhibition.
Mutual inhibition does not occur with all movements. Sometimes a co-compression phenomenon occurs. For example, when squats, they contract like muscles abdominals, and their antagonists are the back extensors.
Stretching exercises are easier to perform with relaxed rather than contracted muscles. To do this, you can use the effect of mutual inhibition (when it occurs) - causing the antagonist muscles to relax by contracting the agonists. It is also advisable to relax the synergists of the muscle you are stretching. For example, when stretching the calf muscle, you should bend your foot, squeezing the muscles on the front surface of the shin. On the other side, calf muscle is a hamstring synergist, so it is advisable to relax that too. To do this, you need to straighten your leg, thereby squeezing the antagonist of the hamstring - quadriceps muscle hips.
Let's look at some simple examples of the functioning of the motor analyzer with the participation of muscle spindles and Golgi receptors. In the formation of the myotatic reflex, or muscle stretch reflex (Fig. 15.5), afferent neurons take part, forming perforated muscles in the muscle spindles.
Rice. 15.5.
A In the initial “given” state, a small load (/) is held by the extrafusal fibers of the muscle in the nerve fibers that form the afferent endings. Only rare spontaneous action potentials are recorded. B.With an increase in the mass of the load (2 > 1), the muscle with muscle spindles is stretched. In afferent fibers, the frequency of action potentials increases, which arrive through synaptic contacts to a-motoneurons (shown by an arrow in the direction from the muscle spindle) and excite them. From α-motoneurons, action potentials are sent to extrafusal muscle fibers (arrows towards the muscle) and through synaptic contacts cause muscle contraction.IN. The muscle contraction did not occur to the specified length. Elimination of the “error” is carried out with the help of fusimotor gamma neurons, which form motor endings on the intrafusal muscle fibers of the spindles G.The muscle returns to its predetermined length
primary afferent endings, and motor neurons, which provide motor innervation to extrafusal muscle fibers. When a muscle is stretched, the muscle spindles are also stretched, which is accompanied by an increase in the frequency of action potentials in afferent fibers. Since afferent neurons are synaptically connected in the central nervous system with a-motoneurons, the frequency of action potentials in the latter also increases. Propagating along efferent fibers, action potentials through synaptic endings cause contraction - shortening the length of the muscle. Reducing the tensile effect on intrafusal fibers reduces the frequency of action potentials in afferent nerve fibers, and the system returns to a state close to its original state. However full recovery This system does not provide the original length. The system cannot determine the remaining small difference between the initial length of the muscle (before stretching) and the length after the reflex contraction (this is called an error). This would require a feedback link, i.e. a motor neuron with unlimitedly high sensitivity. The so-called fusimotor system, which includes intrafusal muscle fibers and fusimotor (y) motoneurons, which form motor synapses on intrafusal muscle fibers, contributes to the return of muscles to their original “given” length. Activation of this system by action potentials from the motor centers of the analyzer causes contraction of the terminal sections of the spindle and thereby stretching of the central non-contractile section where the afferent primary endings are located. This will lead to an additional increase in the frequency of action potentials in the afferent neuron, which will be perceived by the a-motoneuron with subsequent sending of efferent action potentials to the synaptic endings of the extrafusal fibers. As a result of this, additional contraction will occur in the muscle and the original length will be achieved.
From the above, it becomes clear that the myotatic reflex serves to maintain a constant muscle length when the load acting on it changes. This mechanism in animals, as, apparently, in humans, is carried out without conscious control and plays a decisive role in maintaining posture. Responsible for the position of the body in space extensor muscles must have a certain specified length and, in opposition to the force of gravity, keep the animal’s limbs in a straightened state.
Golgi tendon receptors are connected to muscle fibers in series (not in parallel, like muscle spindles), so they must respond to changes in muscle tension, not length. It was found that through inhibitory interneurons, afferent impulses from Golgi receptors influence a-motoneurons, reducing their level of activity. This, for example, may manifest itself in a decrease in the frequency of action potentials sent to the synapses of extrafusal muscle fibers, which prevents excessive muscle tension. It is also assumed that signaling of muscle tension by tendon receptors to a-motoneurons helps correct inaccuracies in the regulation of muscle length by myotatic reflexes.
Muscle spindles and Golgi tendon organs are involved in the implementation of stretch reflexes that occur in response to a sharp stretch of the muscle. In this case, stimulation of muscle receptors causes a reflex contraction of both this and synergistic muscles. In Fig. Figure 13–5 shows reflex arcs of stretch reflexes, both monosynaptic (I) and polysynaptic (II).
Rice.13 –5 .Reflexessprainsmonosynaptic(I, from muscle spindles, leads to contraction of the same muscle) Andpolysynaptic(II)
Monosynapticarc. I-proprioceptive nerve fibers extending from the muscle spindle enter the dorsal root of the spinal cord and are immediately sent to the anterior horn, where they form synapses with -motoneurons that send signals to the muscle.
Polysynapticarc additionally includes an interneuron. In Fig. Figure 13–5(II) shows the arc of the inhibitory reflex that occurs when the Golgi tendon receptors are stretched.
DynamicAndstaticreflexessprains. There are dynamic and static components of the stretch reflex.
Dynamicreflexsprains occurs when a muscle suddenly and rapidly lengthens, resulting in an equally rapid contraction. It's obvious that functionreflexdirectedagainstunexpectedchangesVlengthmuscles,because themuscleis declining,overcomingstretching.
Staticreflexsprains. The dynamic stretch reflex occurs in a split second. After the muscle is stretched to its new length, a weak static stretch reflex follows. Its importance lies in the fact that it continues as long as the muscle length is changed. Hence,functionstaticreflexsprainsAlsodirectedagainststrength,callingexcessoriginallengthmuscles.
Signals to skeletal muscles from the spinal cord are typically discrete in nature (eg, increase intensity over a few milliseconds, change intensity level, decrease force of contraction, etc.). The fact that normally even the fastest movements are carried out smoothly is precisely due to the presence of dynamic and static components of stretch reflexes. In other words, dynamicAndstaticComponentsreflexsprains-regulatorssmoothnessabbreviations.
Participation of muscle spindles in voluntary movements
Signals from the motor cortex and other areas of the brain arriving at the ‑motoneurons of the spinal cord simultaneously excite the ‑motoneurons (the phenomenon of coactivation of – and ‑motoneurons). 31% of efferents to skeletal muscles are type A nerve fibers. As a result ateveryonemuscularreductionis happeningsimultaneousreductionAndextra–AndintrafusalMV.
-The efferent system is activated by impulses coming from the bulboreticular activating formation of the brain stem, and indirectly by impulses entering the bulboreticular activating formation from the cerebellum, basal ganglia, and cerebral cortex. This is because the bulboreticular activating formation is directly associated with antigravity contractions, and antigravity muscles have the highest concentration of muscle spindles. That's why–efferentdampingmechanismespeciallymanifests itselfintimewalkingAndrunning.
OtherimportantfunctionsystemsmuscularspindleisVstabilizationprovisionsbodyintimetensemuscularactivities. The physiological mechanism of this effect is that during dynamic work (simultaneously with contraction of flexor muscle groups), the stretch reflexes of the extensor group muscles are enhanced. Any increased contraction on one side of the joint is dampened by increased stretch reflexes on the other side. As a result, stabilization of the joint position is achieved.
When muscle spindle length changes suddenly, the primary ending (but not the secondary) is stimulated especially powerfully. This excess excitation of the primary ending is called dynamic response, which means that the primary ending is extremely active in response to the high rate of change in spindle length. Even when the spindle length increases by only a fraction of a micrometer and this increase occurs within a fraction of a second, the primary receptor transmits an enormous number of additional impulses along the large sensory nerve fibers with a diameter of 17 microns, but only as long as the length actually increases. Once the increase in length stops, this additional increase in pulse discharge returns to a much lower level than the static discharge still present in the response.
Vice versa, when the spindle shortens the exact opposite change in signal occurs. Thus, the primary ending sends extremely strong, positive or negative, signals to the spinal cord, informing it of any change in the length of the muscle spindle.
Regulating the intensity of static and dynamic responses by gamma motor neurons. Gamma motor nerves to the muscle spindle can be divided into two types: gamma dynamic (gamma-d) and gamma static (gamma-s). The first of them excite mainly intrafusal fibers with a nuclear bag, and the second excite mainly intrafusal fibers with a nuclear chain. When gamma-d fibers excite fibers with a nuclear bursa, the dynamic response of the muscle spindle becomes extremely enhanced, while the static response is almost unchanged.
Vice versa, gamma-s stimulation fibers that excite nuclear chain muscle fibers enhance the static response while having only a minor effect on the dynamic response.
Continuous discharge of muscle spindles under normal conditions. Normally, especially against the background of some degree of excitation of gamma efferent fibers, impulses constantly arise in the sensory nerve fibers of the muscle spindles. Stretching the muscle spindles increases the firing rate, while shortening the spindles decreases it. Thus, spindles can send positive signals to the spinal cord, i.e. an increased number of impulses, indicating muscle stretching, or negative signals, i.e. the number of impulses is below normal, which indicates a lack of muscle stretching.
Muscle stretch reflex
The simplest manifestation muscle spindle functions is a muscle stretch reflex. Whenever a muscle is suddenly stretched, stimulation of the spindles causes a reflex contraction of the large muscle fibers of the stretched muscle and its closely associated synergistic muscles.
Neural circuit of the stretch reflex. The figure shows the basic outline of the muscle spindle stretch reflex. Proprioceptive nerve fiber type 1a from the muscle spindle is seen to enter the dorsal root of the spinal cord. A branch of this fiber then goes directly to the anterior horn of the gray matter of the spinal cord and synapses with the anterior motor neurons, which send motor nerve fibers to the same muscle from which the muscle spindle fibers originate. Thus, there is a monosynaptic pathway that allows the reflex signal to return with the shortest delay back to the muscle after excitation of the spindle. Most type II fibers from the muscle spindles terminate on many gray matter interneurons, and their axons carry signals to delayed anterior motor neurons or perform other functions.
Stretch reflex (syn. R. myostatic nrk) - the general name of P., manifested by contraction skeletal muscle in response to its passive or active stretching.
Large medical dictionary. 2000 .
See what “stretch reflex” is in other dictionaries:
See stretch reflex. Source: Medical Dictionary... Medical terms
A reflex that causes a muscle to contract in response to stretching. Source: Medical Dictionary... Medical terms
STRETCH REFLEX, MUSCLE STRETCH REFLEX- (myotatic reflex) a reflex that causes muscle contraction in response to its stretching... Explanatory dictionary of medicine
A reflex that occurs in response to a brief stretch of the quadriceps femoris muscle by a light blow to its tendon below the patella, in which there is a sudden contraction of the quadriceps femoris muscle; as a result, the lower leg extends (reflex... Medical terms
I Reflex (lat. reflexus turned back, reflected) is a reaction of the body that ensures the emergence, change or cessation of the functional activity of organs, tissues or the whole organism, carried out with the participation of the central nervous... ... Medical encyclopedia
KNEE REFLEX- (patellar reflex) a reflex that occurs in response to a short-term stretch of the quadriceps femoris muscle with a light blow to its tendon below the patella, in which a sudden contraction of the quadriceps femoris muscle is observed; as a result, shin... ... Explanatory dictionary of medicine
- (nrk) see Stretch reflex... Large medical dictionary
Stretch reflex- – reflex contraction of a muscle in response to tension in the tendon of this muscle. Such reflexes are essential in the processes of maintaining posture. Synonyms: Myotactic reflex, Postural reflex... Encyclopedic Dictionary of Psychology and Pedagogy
FOLDING KNIFE REFLEX- Reaction observed in the limbs of animals in which the brain has been removed. If you apply pressure to a limb, resistance will increase due to the stretch reflex, which contracts the muscles. If, however, you provide enough...
STRETCHES, REFLEX- Reflex contraction of a muscle in response to tension in the tendon of the responding muscle. Such reflexes are important in maintaining posture. Also called the myotactic reflex... Explanatory dictionary of psychology
