Golgi tendon organ
The Golgi tendon organ (GTO) (also called Golgi organ, tendon organ, neurotendinous organ or neurotendinous spindle) is a proprioceptive sensory receptor organ that senses changes in muscle tension. It lies at the origins and insertion of skeletal muscle fibers into the tendons of skeletal muscle. It provides the sensory component of the Golgi tendon reflex.
|Golgi tendon organ|
Labeled diagram of Golgi tendon organ from the human Achilles tendon.
|Latin||Organum sensorium tendinis|
|Anatomical terms of microanatomy|
The Golgi organ is not to be confused with the Golgi apparatus, which is an organelle in the eukaryotic cell, or the Golgi stain, which is a histologic stain for neuron cell bodies. All of these are named after the Italian physician Camillo Golgi.
The body of the organ is made up of braided strands of collagen (intrafusal fasciculi) that are less compact than elsewhere in the tendon and are encapsulated. The capsule is connected in series with a group of muscle fibers (10-20 fibers) at one end, and merge into the tendon proper at the other. Each capsule is about 1 mm long, has a diameter of about 0.1 mm, and is perforated by one or more afferent type Ib sensory nerve fibers (Aɑ fiber), which are large (12-20 μm) myelinated axons that can conduct nerve impulses very rapidly. Inside the capsule, the afferent fibers lose their medullary sheaths, branch, intertwine with the collagen fibers, and terminate as flattened leaf-like endings between the collagen strands (see figure).
When the muscle generates force, the sensory terminals are compressed. This stretching deforms the terminals of the Ib afferent axon, opening stretch-sensitive cation channels. As a result, the Ib axon is depolarized and fires nerve impulses that are propagated to the spinal cord. The action potential frequency signals the force being developed by 10-20 extrafusal muscle fibers in the muscle. Average level of activity in a tendon organ population is representative of the whole muscle force.
The Ib sensory feedback generates spinal reflexes and supraspinal responses which control muscle contraction. Ib afferents synapse with interneurons that are within the spinal cord that also project to the brain cerebellum and cerebral cortex. The autogenic inhibition reflex assists in regulating muscle contraction force. It is associated with the Ib. Tendon organs signal muscle force through the entire physiological range, not only at high strain.
During locomotion, Ib input excites rather than inhibits motoneurons of the receptor-bearing muscles, and it affects the timing of the transitions between the stance and swing phases of locomotion. The switch to autogenic excitation is a form of positive feedback.
Until 1967 it was believed that Golgi tendon organs had a high threshold, only becoming active at high muscle forces. Consequently, it was thought that tendon organ input caused "weightlifting failure" through the clasp-knife reflex, which protected the muscle and tendons from excessive force. However, the underlying premise was shown to be incorrect by James Houk and Elwood Henneman in 1967.
- Moore JC: The Golgi Tendon Organ: A Review and Update; American Journal of Occupational Therapy, April 1984 vol. 38 no. 4 227-236
- Mancall, Elliott L; Brock, David G, eds. (2011). "Chapter 2 - Overview of the Microstructure of the Nervous System". Gray’s Clinical Neuroanatomy: The Anatomic Basis for Clinical Neuroscience. Elsevier Saunders. p. 29. ISBN 978-1-4160-4705-6.
- Purves et al (2018), Mechanoreceptors Specialized for Proprioception, pp. 201-202
- Pearson & Gordon (2013), 35-3 Golgi Tendon Organs, p. 800
- Saladin (2018), The Tendon Reflex, p. 498-499
- 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. INVERSE STRETCH REFLEX, pp. 162-163. ISBN 978-0-07-160567-0.
- Prochazka, A.; Gorassini, M. (1998). "Ensemble firing of muscle afferents recorded during normal locomotion in cats". Journal of Physiology. 507 (1): 293–304. doi:10.1111/j.1469-7793.1998.293bu.x. PMC 2230769. PMID 9490855.
- Stephens, J. A.; Reinking, R. M.; Stuart, D. G. (1975). "Tendon organs of cat medial gastrocnemius: responses to active and passive forces as a function of muscle length". Journal of Neurophysiology. 38 (5): 1217–1231. PMID 1177014.
- Conway, B. A.; Hultborn, H.; Kiehn, O. (1987). "Proprioceptive input resets central locomotor rhythm in the spinal cat". Experimental Brain Research. 68 (3): 643–656. doi:10.1007/BF00249807. PMID 3691733.
- Prochazka, A.; Gillard, D.; Bennett, D. J. (1997). "Positive Force Feedback Control of Muscles". J Neurophysiol. 77 (6): 3226–3236. PMID 9212270.
- Houk, J.; Henneman, E. (1967). "Responses of Golgi tendon organs to active contractions of the soleus muscle of the cat". Journal of Neurophysiology. 30 (3): 466–481. doi:10.1152/jn.1922.214.171.1246. PMID 6037588.
- 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.
- Purves, Dale; Augustine, George J; Fitzpatrick, David; Hall, William C; Lamantia, Anthony Samuel; Mooney, Richard D; Platt, Michael L; White, Leonard E, eds. (2018). "Chapter 9 - The Somatosensory System: Touch and Proprioception". Neuroscience (6th ed.). Sinauer Associates. ISBN 9781605353807.
- 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 State of America: McGraw-Hill. ISBN 978-0-07-139011-8.
|Wikimedia Commons has media related to Golgi tendon organ.|