According to Herrington classification, the decerebrate rigidity is characterized by all except
Correct Answer: Rigidity occurs in all the muscles of the body
Description: In decerebrate rigidity, there is rigidity in extensor muscles of all the four extremities (not all muscles of the body). Decerebration Complete transection of the brain stem between the superior and inferior colliculi permits the brain stem pathways to function independently of their input from higher brain structures. This is called a mid-collilcular decerebration. This lesion interrupts all input from the coex (coicospinal and coicobulbar tracts) and red nucleus (rubbrospinal tract), primarily to distal muscles of the extremities. The excitatory and inhibitory reticulospinal pathways (primarily to postural extensor muscles) remain intact. The dominance of drive from ascending sensory pathways to the excitatory reticulospinal pathway leads to hyperactivity in extensor muscles in all four extremities which are called decerebrate rigidity . The excitatory input from the reticulospinal pathway activates Y-motor neurons which indirectly activate alpha-motor neurons ( la spindle afferent activity ). This is called the gamma loop. REf: Ganong&;s review of Medical Physiology 25th edition Pgno: 241, 242
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