Tapping the quad muscle, you produce a reflexive quadriceps contraction. Ia afferents enter the spinal cord and stimulate its own efferent alpha motor-neuron. Also inhibit the antagonist muscle (i. e. the hamstring) uses a branch (collateral) of the. Collaterals also feed up the dosal-column medial lemniscal system (not shown in same ia afferent fibre diagram) Agonist muscle excited, but the antagonist inhibited. Functions as the first defence in overcoming unexpected muscle stretches (i. e. think of someone pushing you over; you want to contract the same muscle that was stretched by the perturbation); second defence is the vestibular postural reflex. Extraordinarily fast (contraction 30ms after the stretch); voluntary contractions caused by a bone. Record electrical activity of entire muscle because all the individual muscle fibres in the motor tap take 150ms: electromyogram (emg) unit simultaneously send action potentials. Much easier than recording from the nerve: different speeds of stretch summate & reach threshold. Medium = as fast as we can go manually.