Tendon reflex

Tendon reflex (or T-reflex) is a feedback mechanism that controls increasing muscle tension by causing muscle relaxation before tension force becomes so great it may damage the muscle.

In a neurologic exam, deep tendon reflexes are scored from 0-4.^[1]

Function

The sensory receptor that detects change in tension is the golgi tendon which lie within tendon. It causes the muscle to relax via a polysynaptic reflex in order to decrease tension in the tendons. Another motor neuron sends efferent impulse to its antagonistic muscle, causing it to contract.

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 feedback mechanism to control muscle tension by causing muscle relaxation before muscle force becomes so great that tendons might be torn. Although the tendon reflex is less sensitive than the stretch reflex, it can override the stretch reflex when tension is great, making you drop a very heavy weight, for example. 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 passive stretch or muscular contraction.

Steps

A tendon reflex operates as follows:

1. As the tension applied to a tendon increases, the Golgi tendon organ (sensory receptor) is stimulated (depolarized to threshold).
2. Nerve impulses (action potentials) arise and propagate into the spinal cord along a sensory neuron.
3. Within the spinal cord (integrating center), the sensory neuron activates an inhibitory interneuron that makes a synapse with a motor neuron.
4. The inhibitory neurotransmitter inhibits (hyperpolarizes) the motor neuron, which then generates fewer nerve impulses.
5. The muscle relaxes and relieves excess tension.

Pathology

The clasp-knife response is a stretch reflex with a rapid decrease in resistance when attempting to flex a joint. However, it is actually thought to be caused by the tendon reflex of the antagonistic muscle of that joint, which gets extended ^[2]. It is one of the characteristic responses of a upper motor neurone lesion.

References

1. ^ "Deep Tendon Reflexes of the Lower Extremities". http://www.meddean.luc.edu/lumen/Meded/medicine/pulmonar/PD/pstep56.htm. 
2. ^ musom.marshall.edu - SPINAL REFLEXES

See also

• Reflex action
• Reflex arc
• Muscle spindle
• H-reflex
• Motor control
• Stretch Reflex

External links

• Tendon reflex at Dorland's Medical Dictionary
• MeSH Reflex,+Tendon
• Tendon+reflex at eMedicine Dictionary