The Golgi tendon organ (GTO) (also called Golgi organ, tendon organ, neurotendinous organ or neurotendinous spindle) is a

proprioceptor Proprioception ( ) is the sense of self-movement, force, and body position. Proprioception is mediated by proprioceptors, a type of sensory receptor, located within muscles, tendons, and joints. Most animals possess multiple subtypes of propri ...

– a type of

sensory receptor Sensory neurons, also known as afferent neurons, are neurons in the nervous system, that convert a specific type of stimulus, via their receptors, into action potentials or graded receptor potentials. This process is called sensory transduc ...

that senses changes in

muscle tension In physiology, medicine, and anatomy, muscle tone (residual muscle tension or tonus) is the continuous and passive partial contraction of the muscles, or the muscle's resistance to passive stretch during resting state.O’Sullivan, S. B. (2007) ...

. It lies at the interface between a

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

and its

tendon A tendon or sinew is a tough band of fibrous connective tissue, dense fibrous connective tissue that connects skeletal muscle, muscle to bone. It sends the mechanical forces of muscle contraction to the skeletal system, while withstanding tensi ...

known as the

musculotendinous junction Skeletal muscle (commonly referred to as muscle) is one of the three types of vertebrate muscle tissue, the others being cardiac muscle and smooth muscle. They are part of the voluntary muscular system and typically are attached by tendons to bo ...

also known as the

myotendinous junction Skeletal muscle (commonly referred to as muscle) is one of the three types of vertebrate muscle tissue, the others being cardiac muscle and smooth muscle. They are part of the voluntary muscular system and typically are attached by tendons to ...

. It provides the sensory component of the

Golgi tendon reflex The Golgi tendon reflex (also called inverse stretch reflex, autogenic inhibition, tendon reflex) 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-in ...

. The Golgi tendon organ is one of several eponymous terms named after the Italian physician

Camillo Golgi Camillo Golgi (; 7 July 184321 January 1926) was an Italian biologist and pathologist known for his works on the central nervous system. He studied medicine at the University of Pavia (where he later spent most of his professional career) bet ...

Structure

The body of the Golgi tendon organ is made up of braided strands of

collagen Collagen () is the main structural protein in the extracellular matrix of the connective tissues of many animals. It is the most abundant protein in mammals, making up 25% to 35% of protein content. Amino acids are bound together to form a trip ...

(intrafusal fasciculi) that are less compact than elsewhere in the

and are encapsulated. The capsule is connected in

series Series may refer to: People with the name * Caroline Series (born 1951), English mathematician, daughter of George Series * George Series (1920–1995), English physicist Arts, entertainment, and media Music * Series, the ordered sets used i ...

(along a single path) with a group of

muscle fibers Skeletal muscle (commonly referred to as muscle) is one of the three types of vertebrate muscle tissue, the others being cardiac muscle and smooth muscle. They are part of the somatic nervous system, voluntary muscular system and typically are a ...

() at one end, and merge into the tendon proper at the other. Each capsule is about long, has a

diameter In geometry, a diameter of a circle is any straight line segment that passes through the centre of the circle and whose endpoints lie on the circle. It can also be defined as the longest Chord (geometry), chord of the circle. Both definitions a ...

of about , and is perforated by one or more afferent type Ib sensory nerve fibers ( Aɑ fiber), which are large 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).

Function

When the muscle generates force, the sensory terminals are compressed. This stretching deforms the terminals of the Ib afferent axon, opening stretch-sensitive

cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

channels. As a result, the Ib axon is depolarized and fires

nerve impulses An action potential (also known as a nerve impulse or "spike" when in a neuron) is a series of quick changes in voltage across a cell membrane. An action potential occurs when the membrane potential of a specific cell rapidly rises and falls. ...

that are propagated to the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...

. The action potential frequency signals the

force In physics, a force is an influence that can cause an Physical object, object to change its velocity unless counterbalanced by other forces. In mechanics, force makes ideas like 'pushing' or 'pulling' mathematically precise. Because the Magnitu ...

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 Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause and effect that forms a circuit or loop. The system can then be said to ''feed back'' into itself. The notion of cause-and-effect has to be handle ...

generates

stretch reflex The stretch reflex (myotatic reflex), or more accurately ''muscle stretch reflex'', 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 ...

es and supraspinal responses which control muscle contraction. Ib afferents

synapse In the nervous system, a synapse is a structure that allows a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or a target effector cell. Synapses can be classified as either chemical or electrical, depending o ...

with

interneuron Interneurons (also called internuncial neurons, association neurons, connector neurons, or intermediate neurons) are neurons that are not specifically motor neurons or sensory neurons. Interneurons are the central nodes of neural circuits, enab ...

s in the spinal cord that also project to the brain cerebellum and cerebral cortex. The

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. The ascending or afferent pathways to the

cerebellum The cerebellum (: cerebella or cerebellums; Latin for 'little brain') is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as it or eve ...

are the dorsal and ventral

spinocerebellar tract The spinocerebellar tracts are nerve tracts originating in the spinal cord and terminating in the same side (ipsilateral) of the cerebellum. The two main tracts are the dorsal spinocerebellar tract, and the ventral spinocerebellar tract. Both of ...

s. They are involved in the cerebellar regulation of

movement Movement may refer to: Generic uses * Movement (clockwork), the internal mechanism of a timepiece * Movement (sign language), a hand movement when signing * Motion, commonly referred to as movement * Movement (music), a division of a larger co ...

History

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.

Footnotes

Sources

Other sources

* * *

External links

* {{DEFAULTSORT:Golgi tendon organ Somatosensory system Neurophysiology Nervous tissue cells Proprioception Anatomy named for one who described it