Babinski reflex and corticospinal tract lesion

Stretch ReflexAgonist muscleAntagonistmuscle+-+MonosynapticServes to maintain the muscle toneFeedback system keeping the muscles around a set lengthIt involves a contraction that takes place when the muscle gets stretched.Mechanism: When the muscle is stretched, this results in the stretching of the intrafusal muscle fibersin the muscle spindle. As a result, the Ia endings are stretched and increase their firing rate. They makeexcitatory connections onto the alpha MN innervating the same muscle and also onto those innervatingsynergistic muscles. Thus, the muscle contracts and its length is reduced.Ia fibers can also synapse onto inhibitory interneurons and cause the relaxation of the antagonistmuscles. (polysynaptic component)13Flexion Withdrawal ReflexPolysynaptic--Protective ReflexThe limb is quickly withdrawn froma painful stimulus,usually by thesimultaneous contraction of allflexor muscles in the limbExtensormusclepainFlexormuscleMechanism: When there is a painful stimulus, the sensorysignal excites the motor neurons that innervate flexormuscles of the stimulated limb and inhibits MN thatinnervate the extensor muscles of the limb (reciprocalinnervation)Also, the reflex can produce an opposite effect in thecontralateral limb to enhance postural support. (crossextensionreflex)FlexormuscleExtensormuscle14