Athena Vale
The human body is a complex system that involves a multitude of reflexes and mechanisms to function. One such reflex is the Golgi tendon reflex, which is responsible for muscle relaxation. This reflex operates as a protective feedback mechanism to prevent potential damage to the muscles by controlling muscle tension. When a load is placed on a muscle, it triggers a response in the afferent neuron from the Golgi tendon organ, leading to the inhibition of the motor neuron from the spinal cord and subsequent muscle relaxation. This reflex is particularly important in maintaining the body's overall balance and stability, ensuring that muscles do not contract simultaneously and causing a person to, for instance, drop a heavy weight. Understanding the intricacies of reflexes like the Golgi tendon reflex provides valuable insights into the body's ability to self-regulate and protect itself from potential harm.
| Characteristics | Values |
|---|---|
| Reflex Name | Golgi tendon reflex |
| Type | Tendon reflex |
| Function | Protective feedback mechanism to control the tension of an active muscle |
| Sensory Receptors | Tendon Golgi receptors |
| Response | Muscle relaxation |
| Other Characteristics | Operates as a negative feedback mechanism, less sensitive than the stretch reflex, overrides the stretch reflex when tension is high |
| Related Reflexes | Stretch reflex, Myotatic reflex, Deep tendon reflex |
| Related Terms | Autogenic inhibition, Ib inhibitory interneurons, IPSP, Clonus |
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Golgi tendon reflex
The Golgi tendon reflex is a protective feedback mechanism that controls muscle tension and prevents damage to the muscle and tendon. It is mediated by the Golgi tendon organs (GTOs), which act as muscle tension receptors. GTOs continuously signal muscle tension, providing precise information about muscle force. This reflex helps regulate muscle force and maintain steady levels of tension to prevent damage caused by high tension.
When tension is applied to a tendon, the GTO is stimulated, and nerve impulses (action potentials) are generated and propagated along the sensory fiber Ib into the spinal cord. Within the spinal cord, the sensory fiber Ib synapses with and activates an inhibitory interneuron, which releases the neurotransmitter glycine, inhibiting the α motor neuron. As a result, fewer nerve impulses are generated in the α motor neuron, leading to muscle relaxation. This process is known as autogenic inhibition, which refers to a reduction in the excitability of a contracting or stretched muscle.
The Golgi tendon reflex is less sensitive than the stretch reflex, which operates as a feedback mechanism to control muscle length by causing muscle contraction. However, the tendon reflex can override the stretch reflex when tension is high, such as when a person drops a heavy weight. The tendon reflex helps spread muscle load across muscle fibers, preventing damage to isolated fibers.
The Golgi tendon reflex is associated with the clasp-knife response, a neurological sign where a spastic muscle initially resists passive movement strongly and then suddenly yields, similar to the motion of a pocketknife. The sudden collapse may involve the Golgi tendon reflex, providing a protective mechanism to prevent muscle damage.
The tendon reflex, or Golgi tendon reflex, is a crucial protective mechanism that ensures muscle tension remains within safe limits, preventing potential damage to muscles, tendons, and associated structures. By regulating muscle force and maintaining steady tension, this reflex contributes to the overall stability and functionality of the musculoskeletal system.
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Stretch reflex
The stretch reflex, also known as the muscle stretch reflex or myotatic reflex, is a neural reflex involving a receptor and effector neurone, which can be either phasic or tonic. It is a muscle contraction in response to stretching a muscle. The function of the reflex is generally thought to be maintaining the muscle at a constant length but the response is often coordinated across multiple muscles and even joints.
The older term deep tendon reflex is now criticised as misleading. Tendons have little to do with the response, and some muscles with stretch reflexes have no tendons. Rather, muscle spindles detect a stretch and convey the information to the central nervous system. As an example of a spinal reflex, it results in a fast response that involves an afferent signal into the spinal cord and an efferent signal out to the muscle. The stretch reflex can be a monosynaptic reflex which provides automatic regulation of skeletal muscle length, whereby the signal entering the spinal cord arises from a change in muscle length or velocity.
The patellar reflex (knee jerk) is an example of the stretch reflex and it is used to determine the sensitivity of the stretch reflex. Reflexes can be tested as part of a neurological examination, often if there is an injury to the central nervous system. To test the reflex, the muscle should be in a neutral position. The muscle being tested needs to be flexed for the clinician to locate the tendon. After the muscle is relaxed, the clinician strikes the tendon. The response should be contraction of the muscle. If this is the knee jerk reflex, the clinician should observe a kick.
The stretch reflex has both phasic and tonic components. A tonic stretch reflex is one in which a stimulus produces a prolonged asynchronous discharge of motor neurons causing sustained muscle contraction for the maintenance or alteration of posture. In contrast, a phasic stretch reflex consists of a synchronous motor neuron discharge caused by brief stimulation of muscle spindles or their afferent nerve pathways. The tendon jerk is a phasic stretch reflex. The active contraction provoked in a muscle by continuous stretch is a tonic reflex and is the basis of muscle ‘tone’.
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Myotatic reflex
The myotatic reflex, also known as the muscle stretch reflex, is a reflex mechanism that helps regulate muscle tone and response to stretching. It is a type of stretch reflex, causing muscle contraction after the muscle is stretched. This reflex is used for body posture and movement and does not rely on cerebral input for function.
The myotatic reflex is a spinal reflex that results in a fast response. It involves an afferent signal into the spinal cord and an efferent signal out to the muscle. The reflex is initiated when a mechanical stretch is detected by a fusiform-shaped microstructure called the muscle spindle, which is located within the muscle belly. The muscle spindle consists of an outer connective tissue sheath containing spiral threads, intrafusal specialized muscle fibres, and nerve endings. The intrafusal fibres are parallel with the extrafusal muscle fibres, allowing them to stretch and contract together.
When a muscle is stretched, the nerve endings of the spindle are depolarized, producing a burst of impulses in the sensory fibres. These sensory fibres directly activate the large (alpha) motor neuron in the spinal cord. The alpha motor neuron then discharges impulses through its axon, causing a contraction of the extrafusal muscle fibres of the same muscle. This results in a reflex muscle contraction, as seen in the patellar reflex or "knee-jerk" reflex.
The patellar reflex is the most reliable myotatic reflex and is often used to determine the sensitivity of the stretch reflex. To test this reflex, the patient should be relaxed and the pelvic limb held in a slightly flexed position. The clinician then briskly taps the patellar ligament with a pleximeter, evoking a reflex arc that causes a sudden extension of the stifle.
The myotatic reflex helps to maintain an upright posture by detecting postural muscle group stretch and reflexively correcting in cases of leaning or postural instability. It also helps resist changes in muscle length, which is useful when trying to maintain the position of a limb during purposeful work.
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Tonic stretch reflex
The stretch reflex is a neural reflex that involves a receptor and effector neurone, which can be either phasic or tonic. The tonic stretch reflex is a stimulus that produces a prolonged asynchronous discharge of motor neurons, resulting in sustained muscle contraction for the maintenance or alteration of posture. This is in contrast to the phasic stretch reflex, which involves a synchronous motor neuron discharge caused by brief stimulation of muscle spindles or their afferent nerve pathways.
The tonic stretch reflex is a biological biomarker of deficits in motor control. It is the joint angle or muscle length at which muscle activation begins. In spasticity, the tonic stretch reflex threshold abnormally lies inside the biomechanical joint range. This can be determined by measuring the Dynamic Stretch Reflex Thresholds (DSRTs) by stretching the resting muscle at different velocities.
The tonic stretch reflex is also referred to as the myotatic reflex, which is a muscle contraction in response to stretching a muscle. This reflex is generally thought to maintain the muscle at a constant length, but the response is often coordinated across multiple muscles and even joints. The stretch reflex has the shortest latency of all spinal reflexes, including the Golgi tendon reflex and reflexes mediated by pain and cutaneous receptors.
The patellar reflex (knee jerk) is an example of the stretch reflex and is used to determine the sensitivity of the reflex. To test the reflex, the muscle should be in a neutral position and flexed so that the clinician can locate the tendon. After the muscle is relaxed, the clinician strikes the tendon, and the response should be a contraction of the muscle.
The tonic stretch reflex is a protective mechanism that helps to control muscle tension and prevent damage. It involves the activation of gamma motor neurons, which adjust the length of the intrafusal muscle fibers to maintain tension on the spindle during the range of motion of the limb. This reflex is important for maintaining posture and muscle tone, and it can be enhanced by the Jendrassik maneuver.
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Muscle spindle
The muscle spindle consists of a group of fine muscle fibres, called intrafusal muscle fibres, which are 4–10 mm long. Their central portions are not contractile. The connective tissue capsule encloses two different types of intrafusal fibres: nuclear chain intrafusal fibres and nuclear bag fibres. The former has a set of aligned nuclei in the centre, while the latter has a clump of nuclei randomly arrayed in a bag-like structure in the centre of the intrafusal fibre. Typically, a spindle has two to three nuclear bag fibres and about five nuclear chain fibres.
There are two distinct types of afferent sensory fibre endings: large myelinated nerves termed Ia or primary afferents and medium myelinated nerves termed II or secondary afferents. The former surrounds the central portion of all of the intrafusal muscle fibres, forming a coiled structure called the annulospiral ring. Stretching this nerve ending activates stretch-activated channels in its surface that depolarize the neuron and therefore increase its firing rate. The latter ends adjacent to the central regions of the static bag and chain fibres. These fibres send information by stretch-sensitive mechanically-gated ion channels of the axons.
The motor part of the spindle is provided by motor neurons: up to a dozen gamma motor neurons, also known as fusimotor neurons. These activate the muscle fibres within the spindle. Gamma motor neurons supply only muscle fibres within the spindle, whereas beta motor neurons supply muscle fibres both within and outside of the spindle. Activation of the neurons causes a contraction and stiffening of the end parts of the muscle spindle muscle fibres.
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Frequently asked questions
The tendon reflex, also known as the Golgi tendon reflex, is a negative feedback mechanism that controls muscle tension. It is less sensitive than the stretch reflex but can override it when tension is high. When a load is placed on the muscle, the afferent neuron from the Golgi tendon organ fires into the central nervous system, inhibiting the motor neuron from the spinal cord and causing the muscle to relax.
The stretch reflex, also known as the muscle stretch reflex, is a feedback mechanism that controls muscle length by causing muscle contraction in response to stretching. An example of this reflex is the patellar reflex (knee jerk). When a muscle is stretched, the muscle spindle is activated, sending an impulse to the motor neuron, which then causes the muscle to contract.
The tendon reflex acts as a protective mechanism to prevent muscles from damage by controlling muscle tension. It helps to maintain muscle tension within a safe range, ensuring that it does not become too high and cause injury. This reflex also allows for precise control of muscle forces, enabling fine movements and activities.
