- Each tendon organ is innervated by a single afferent axon! Function : Golgi tendon organs are sensitive to changes in tension. The stretch reflex: - This is the simplest of all reflexes. - For the muscle spindle afferents (Ia), the stretch induces a brisk increase in their rate of discharge (=increased firing rate). - It is mediated by a monosynaptic excitatory synapse between primary afferent fibres (Ia) from muscle spindles and alpha-motor neurons innervating the same muscle and motor neurons innervating synergist muscles. Step 1: Stretch induces the firing of spindle fibre afferents. Step 2a: Action potential is carried along the fibre and results in release of neurotransmitter at the afferent and alpha-motor neuron synapse (Monosynaptic pathway). The delay, which is introduced by a single synapse, is between 0.5 to 0.8 msec. Step 2b: Action potential is carried along the afferent fibre and results in release of neurotransmitter at the alpha motor neuron and an inhibitory interneuron synapse (Disynaptic pathway). Step 3a: The action of the Neurotransmitter is excitatory and the alpha motor neuron is excited. This results in action potentials
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