Golgi tendon reflex

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The Golgi tendon reflex [1] (also called inverse stretch reflex, autogenic inhibition, [2] tendon reflex [3] ) is an inhibitory effect on the muscle resulting from the muscle tension stimulating Golgi tendon organs (GTO) of the muscle, and hence it is self-induced. The reflex arc is a negative feedback mechanism preventing too much tension on the muscle and tendon. When the tension is extreme, the inhibition can be so great it overcomes the excitatory effects on the muscle's alpha motoneurons causing the muscle to suddenly relax. [1] This reflex is also called the inverse myotatic reflex, [4] because it is the inverse of the stretch reflex.

Contents

GTOs' inhibitory effects come from their reflex arcs: the Ib sensory fibers that are sent through the dorsal root into the spinal cord to synapse on Ib inhibitory interneurons that in turn terminate directly on the motor neurons that innervate the same muscle. The fibers also make direct excitatory synapses onto motoneurons that innervate the antagonist muscle. [2] Note that the disynaptic reflex pathway does not always have inhibitory effects: under certain conditions, GTO stimulation can result in motoneuron excitation. [5]

Besides protecting against too much tension on the muscle and tendon, the tendon reflex may help spread muscle load throughout the muscle fibers, thereby preventing damage to isolated fibers. [1] [3] Whereas the stretch reflex regulates muscle length, the tendon reflex helps regulate muscle force. [2] It helps maintain steady levels of tension and stable joints to counteract effects that reduce muscle force (such as fatigue). [6] Because the Ib inhibitory interneurons receive convergent multisensory inputs and descending pathways, they may allow fine control of muscle forces, [5] and may be better at protective functions. [6] Also, because the Ib fibers connect widely with the motoneurons innervating muscles working on different joints, the Golgi tendon reflex forms part of reflex networks that control movements of the whole limb. [5]

Protective function, autogenic inhibition, and others

The Golgi tendon reflex operates as a protective feedback mechanism to control the tension of an active muscle by causing relaxation before the tendon tension becomes high enough to cause damage. [7] First, as a load is placed on the muscle, the afferent neuron from the Golgi tendon organ fires into the central nervous system. Second, the motor neuron from the spinal cord is inhibited via an IPSP and muscle relaxes.

Because the Ib inhibitory interneurons receive convergent descending pathways and multisensory inputs—including cutaneous receptors, muscle spindles, and joint receptors, they can provide better protection, such as when the joint receptors are signaling joint hyperextension or hyperflexion. [6]

Autogenic inhibition refers to a reduction in excitability of a contracting or stretched muscle, that in the past has been solely attributed to the increased inhibitory input arising from Golgi tendon organs (GTOs) within the same muscle. It was first thought GTOs only had protective function which was to prevent muscles from damages because of the assumptions that they always inhibited motoneurons and that they fired only under high tension. But it is now known that GTOs signal muscle tension continuously providing precise information about muscle force, that the reflex pathway has multisensory inputs that may allow precise control of muscle forces for fine activities, and that Ib fibers connect widely with motoneurons innervating muscles acting on different joints, which when complemented with their reflex pathways, are part of reflex networks that control movements of the whole limbs. [5]

The reduced efferent (motor) drive to the muscle by way of autogenic inhibition is a factor historically believed to assist target muscle elongation, although current literature casts doubt on this hypothesis. [8]

Protective steps

With muscle tension, a Golgi tendon reflex operates as follows:

  1. As tension is applied to a tendon, the Golgi tendon organ (sensor) is stimulated (depolarized)
  2. Nerve impulses (action potentials) arise and propagate along sensory fiber Ib into the spinal cord
  3. Within the spinal cord (integrating center), sensory fiber Ib synapses with and activates (via glutamate) an inhibitory interneuron
  4. The inhibitory interneuron releases the neurotransmitter glycine that inhibits (hyperpolarizes) the α motor neuron
  5. As a consequence fewer nerve impulses are generated in the α motor neuron
  6. The muscle relaxes and excess tension is relieved

Flexibilities

The output of the Ib inhibitory interneurons are flexible because they receive inputs from golgi tendon organs, muscle spindles, cutaneous receptors, joint receptors, and different descending pathways. The multiple sensory/control inputs may allow fine motor activities, such as grasping a delicate object, in which other senses may guide force control. [5] In addition, stimulating GTO doesn't always inhibit motor neurons, because during activities such as walking, the Ib inhibitory interneurons are inhibited, and Ib excitatory interneurons stimulate the motoneurons. [9]

Contrast to stretch reflex

The stretch reflex operates as a feedback mechanism to control muscle length by causing muscle contraction. In contrast, the tendon reflex operates as a negative feedback mechanism to control muscle tension. Although the tendon reflex is less sensitive than the stretch reflex, it can override the stretch reflex when tension is great, for example, causing a person to drop a very heavy weight. Like the stretch reflex, the tendon reflex is ipsilateral. The sensory receptors for this reflex are called tendon Golgi receptors, which lie within a tendon near its junction with a muscle. In contrast to muscle spindles, which are sensitive to changes in muscle length, tendon organs detect and respond to changes in muscle tension that are caused by muscular contraction, but not passive stretch.

Pathology

Upper motor neuron lesions which damage the descending pathways down to the spinal cord may cause increase in muscle tone, partly because alpha motoneurons respond more to muscle spindle afferent inputs. This causes increased resistance to passive movement (that the patient doesn't initiate), called spasticity, which is associated with another neurological sign, the clasp-knife response, in which the spastic muscle initially resists passive movement strongly, and then suddenly yields—like the motion of a pocketknife. The increased initial resistance comes from the stretch reflex hyperactivity, and the sudden collapse may involve the Golgi tendon reflex. [10] The response is also known as the lengthening reaction because of the spastic muscle's reaction to lengthening. [2]

See also

Related Research Articles

Motor neuron Nerve cell sending impulse to muscle

A motor neuron is a neuron whose cell body is located in the motor cortex, brainstem or the spinal cord, and whose axon (fiber) projects to the spinal cord or outside of the spinal cord to directly or indirectly control effector organs, mainly muscles and glands. There are two types of motor neuron – upper motor neurons and lower motor neurons. Axons from upper motor neurons synapse onto interneurons in the spinal cord and occasionally directly onto lower motor neurons. The axons from the lower motor neurons are efferent nerve fibers that carry signals from the spinal cord to the effectors. Types of lower motor neurons are alpha motor neurons, beta motor neurons, and gamma motor neurons.

Trigeminal nerve Cranial nerve responsible for sensory perception and motor functions of the face

The trigeminal nerve (the fifth cranial nerve, or simply CN V) is a nerve responsible for sensation in the face and motor functions such as biting and chewing; it is the most complex of the cranial nerves. Its name ("trigeminal" = tri-, or three, and - geminus, or twin: thrice-twinned) derives from each of the two nerves (one on each side of the pons) having three major branches: the ophthalmic nerve (V1), the maxillary nerve (V2), and the mandibular nerve (V3). The ophthalmic and maxillary nerves are purely sensory, whereas the mandibular nerve supplies motor as well as sensory (or "cutaneous") functions. Adding to the complexity of this nerve is that autonomic nerve fibers as well as special sensory fibers (taste) are contained within it.

In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous movement in response to a stimulus. A reflex is made possible by neural pathways called reflex arcs which can act on an impulse before that impulse reaches the brain. The reflex is then an automatic response to a stimulus that does not receive or need conscious thought.

Somatic nervous system Part of the peripheral nervous system

The somatic nervous system (SNS), or voluntary nervous system is the part of the peripheral nervous system associated with the voluntary control of body movements via skeletal muscles.

Muscle spindle Innervated muscle structure involved in reflex actions and proprioception

Muscle spindles are stretch receptors within the body of a skeletal muscle that primarily detect changes in the length of the muscle. They convey length information to the central nervous system via afferent nerve fibers. This information can be processed by the brain as proprioception. The responses of muscle spindles to changes in length also play an important role in regulating the contraction of muscles, for example, by activating motor neurons via the stretch reflex to resist muscle stretch.

Grey column

The grey column refers to a somewhat ridge-shaped mass of grey matter in the spinal cord. This presents as three columns: the anterior grey column, the posterior grey column, and the lateral grey column, all of which are visible in cross-section of the spinal cord.

Reflex arc

A reflex arc is a neural pathway that controls a reflex. In vertebrates, most sensory neurons do not pass directly into the brain, but synapse in the spinal cord. This allows for faster reflex actions to occur by activating spinal motor neurons without the delay of routing signals through the brain. The brain will receive the sensory input while the reflex is being carried out and the analysis of the signal takes place after the reflex action.

A mechanoreceptor, also called mechanoceptor, is a sensory receptor that responds to mechanical pressure or distortion. Mechanoreceptors are innervated by sensory neurons that convert mechanical pressure into electrical signals that, in animals, are sent to the central nervous system.

Nuclear chain fiber Specialized sensory organ within a muscle

A nuclear chain fiber is a specialized sensory organ contained within a muscle. Nuclear chain fibers are intrafusal fibers that, along with nuclear bag fibers, make up the muscle spindle responsible for the detection of changes in muscle length.

Type Ia sensory fiber type of afferent nerve fiber

A type Ia sensory fiber, or a primary afferent fiber is a type of afferent nerve fiber. It is the sensory fiber of a stretch receptor called the muscle spindle found in muscles, which constantly monitors the rate at which a muscle stretch changes. The information carried by type Ia fibers contributes to the sense of proprioception.

Upper motor neuron

Upper motor neurons (UMNs) is a term introduced by William Gowers in 1886. They are found in the cerebral cortex and brainstem and carry information down to activate interneurons and lower motor neurons, which in turn directly signal muscles to contract or relax. UMNs in the cerebral cortex are the main source of voluntary movement.

Gamma motor neuron

A gamma motor neuron, also called gamma motoneuron, or fusimotor neuron, is a type of lower motor neuron that takes part in the process of muscle contraction, and represents about 30% of (Aγ) fibers going to the muscle. Like alpha motor neurons, their cell bodies are located in the anterior grey column of the spinal cord. They receive input from the reticular formation of the pons in the brainstem. Their axons are smaller than those of the alpha motor neurons, with a diameter of only 5 μm. Unlike the alpha motor neurons, gamma motor neurons do not directly adjust the lengthening or shortening of muscles. However, their role is important in keeping muscle spindles taut, thereby allowing the continued firing of alpha neurons, leading to muscle contraction. These neurons also play a role in adjusting the sensitivity of muscle spindles.

Vestibulospinal tract

The vestibulospinal tract is a neural tract in the central nervous system. Specifically, it is a component of the extrapyramidal system and is classified as a component of the medial pathway. Like other descending motor pathways, the vestibulospinal fibers of the tract relay information from nuclei to motor neurons. The vestibular nuclei receive information through the vestibulocochlear nerve about changes in the orientation of the head. The nuclei relay motor commands through the vestibulospinal tract. The function of these motor commands is to alter muscle tone, extend, and change the position of the limbs and head with the goal of supporting posture and maintaining balance of the body and head.

Stretch reflex

The stretch reflex, or more accurately "muscle stretch reflex", is a muscle contraction in response to stretching within the muscle. The reflex functions to maintain the muscle at a constant length. The term deep tendon reflex is often wrongfully used by many health workers and students to refer to this reflex. "Tendons have little to do with the response, other than being responsible for mechanically transmitting the sudden stretch from the reflex hammer to the muscle spindle. In addition, some muscles with stretch reflexes have no tendons ".

Alpha motor neuron

Alpha (α) motor neurons (also called alpha motoneurons), are large, multipolar lower motor neurons of the brainstem and spinal cord. They innervate extrafusal muscle fibers of skeletal muscle and are directly responsible for initiating their contraction. Alpha motor neurons are distinct from gamma motor neurons, which innervate intrafusal muscle fibers of muscle spindles.

The triceps reflex, a deep tendon reflex, is a reflex as it elicits involuntary contraction of the triceps brachii muscle. It is initiated by the Cervical spinal nerve 7 nerve root. The reflex is tested as part of the neurological examination to assess the sensory and motor pathways within the C7 and C8 spinal nerves.

Clasp-knife response refers to a Golgi tendon reflex with a rapid decrease in resistance when attempting to flex a joint, usually during a neurological examination. It is one of the characteristic responses of an upper motor neuron lesion. It gets its name from the resemblance between the motion of the limb and the sudden closing of a claspknife after sufficient pressure is applied.

Group A nerve fibers are one of the three classes of nerve fiber as generally classified by Erlanger and Gasser. The other two classes are the group B nerve fibers, and the group C nerve fibers. Group A are heavily myelinated, group B are moderately myelinated, and group C are unmyelinated.

Spinal interneuron

A spinal interneuron, found in the spinal cord, relays signals between (afferent) sensory neurons, and (efferent) motor neurons. Different classes of spinal interneurons are involved in the process of sensory-motor integration. Most interneurons are found in the grey column, a region of grey matter in the spinal cord.

Golgi tendon organ Proprioceptive sensory receptor organ that senses changes in muscle tension

The Golgi tendon organ (GTO) is a proprioceptor – a type of sensory receptor that senses changes in muscle tension. It lies at the interface between a muscle and its tendon known as the musculotendinous junction also known as the myotendinous junction. It provides the sensory component of the Golgi tendon reflex.

References

  1. 1 2 3 Hall & Guyton (2006) , Golgi Tendon Reflex, pp. 679–680
  2. 1 2 3 4 Barrett et al (2010) , INVERSE STRETCH REFLEX, pp. 162–163
  3. 1 2 Saladin (2018) , The Tendon Reflex, pp. 498–499
  4. ↑ Michael-Titus, Adina T; Revest, Patricia; Shortland, Peter, eds. (2010). "Chapter 9 - Descending Pathways and Cerebellum". Systems of The Body: The Nervous System – Basic Science and Clinical Conditions (2nd ed.). Churchill Livingstone. Golgi tendon organs, p. 166. ISBN   9780702033735.
  5. 1 2 3 4 5 Pearson & Gordon (2013) , Convergence of Inputs on Ib Interneurons Increases the Flexibility of Reflex Responses, p. 799
  6. 1 2 3 Purves et al (2018a) , The Spinal Cord Circuitry Underlying the Regulation of Muscle Force, pp. 370–371
  7. ↑ Tortora, Gerard (2011). Principles of anatomy and physiology. Hoboken, N.J: Wiley. ISBN   9780470646083.
  8. ↑ Sharman MJ, Cresswell AG, Riek S (2006). "Proprioceptive neuromuscular facilitation stretching : mechanisms and clinical implications". Sports Med. 36 (11): 929–39. doi:10.2165/00007256-200636110-00002. PMID   17052131. S2CID   3123371.
  9. ↑ Pearson & Gordon (2013) , Figure 35–7 The reflex actions of Ib afferent fibers from Golgi tendon organs, p. 801
  10. ↑ Purves et al (2018b) , Box 17D Muscle Tone, p. 404

Other references

  • Barrett, Kim E; Boitano, Scott; Barman, Susan M; Brooks, Heddwen L (2010). "Chapter 9 – Reflexes". Ganong's Review of Medical Physiology (23rd ed.). McGraw-Hill. ISBN   978-0-07-160567-0.
  • Hall, JE; Guyton, AC (2006). "Chapter 54 - Motor Functions of the Spinal Cord; the Cord Reflexes". Textbook of medical physiology (11th ed.). St. Louis, Mo: Elsevier Saunders. pp.  673–684. ISBN   0-7216-0240-1.
  • Pearson, Keir G; Gordon, James E (2013). "35 - Spinal Reflexes". In Kandel, Eric R; Schwartz, James H; Jessell, Thomas M; Siegelbaum, Steven A; Hudspeth, AJ (eds.). Principles of Neural Science (5th ed.). United States: McGraw-Hill. ISBN   978-0-07-139011-8.
  • Purves, Dale; Augustine, George J; Fitzpatrick, David; Hall, William C; Lamantia, Anthony Samuel; Mooney, Richard D; Platt, Michael L; White, Leonard E, eds. (2018a). "Chapter 16 - Lower Motor Neuron Circuits and Motor Control". Neuroscience (6th ed.). Sinauer Associates. pp. 357–379. ISBN   9781605353807.
  • Purves, Dale; Augustine, George J; Fitzpatrick, David; Hall, William C; Lamantia, Anthony Samuel; Mooney, Richard D; Platt, Michael L; White, Leonard E, eds. (2018b). "Chapter 17 - Upper Motor Neuron Control of the Brainstem and Spinal Cord". Neuroscience (6th ed.). Sinauer Associates. pp. 381–406. ISBN   9781605353807.
  • Saladin, KS (2018). "Chapter 13 - The Spinal Cord, Spinal Nerves, and Somatic Reflexes". Anatomy and Physiology: The Unity of Form and Function (8th ed.). New York: McGraw-Hill. ISBN   978-1-259-27772-6.
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