| Golgi tendon organ | |
|---|---|
 Labeled diagram of Golgi tendon organ from the humanAchilles tendon. | |
| Details | |
| System | Musculoskeletal system |
| Location | Skeletal muscle |
| Identifiers | |
| Latin | organum sensorium tendinis |
| TH | H3.03.00.0.00024 |
| Anatomical terms of microanatomy | |
TheGolgi tendon organ (GTO) (also known asGolgi organ,tendon organ,neurotendinous organ orneurotendinous spindle) is a skeletal musclestretch receptorproprioceptor. It is situated at the interface between amuscle and itstendon known as themusculotendinous junction.[1] It senses muscle tension (whereasmuscle spindles are responsible for detecting muscle length and changes in muscle length). It is innervated bytype Ib sensory nerve fibers.[2]
It represents the sensory leg of theGolgi tendon reflexarc.
The Golgi tendon organ is one of severaleponymous terms named after the Italian physicianCamillo Golgi.
The body of the Golgi tendon organ is made up of braided strands ofcollagen (intrafusal fasciculi) that are less compact than elsewhere in thetendon and are encapsulated.[3] The capsule is connected inseries (along a single path) with a group ofmuscle fibers (10-20 fibers[4]) at one end, and merge into the tendon proper at the other. Each capsule is about1mm long, has adiameter of about0.1 mm.[5][6]
One or more fast-conductingtype Ib sensory nerve fibers penetrate the capsule and lose theirmedullary[clarification needed] sheaths, branch, intertwine with the collagen fibers, and terminate as flattened leaf-like endings between the collagen strands (see figure).[5][6]
When the muscle generates force, the sensory terminals of the Ib afferent axons are compressed and become deformed which causes the opening of stretch-sensitivecation channels, depolarizing the axon and causing it to firenerve impulses. The action potential frequency encodes theforce being developed by the muscle fibers associated with the Golgi tendon organ. The average level of activity in a tendon organ population is representative of the whole muscle force.[5][8]
The Ib sensoryfeedback generatesstretch reflexes and supraspinal responses which control muscle contraction. Ib afferentssynapse withinterneurons in the spinal cord that also project to the brain cerebellum and cerebral cortex. TheGolgi tendon 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.[8][9]
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.[10] The switch to autogenic excitation is a form of positive feedback.[11]
The ascending orafferent pathways to thecerebellum are the dorsal and ventralspinocerebellar tracts. They are involved in the cerebellar regulation ofmovement.[citation needed]
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 theclasp-knife reflex, which protected the muscle and tendons from excessive force.[citation needed] However, the underlying premise was shown to be incorrect by James Houk and Elwood Henneman in 1967.[12]
This article incorporates text in thepublic domain frompage 1061 of the 20th edition ofGray's Anatomy(1918)
Media related toGolgi tendon organ at Wikimedia Commons
