" sciatica , bell's palsy , multiple sclerosis " is a nervous disorder ?

Yes, all three are neural disorder. Sciatica is an irritation of the sciatic nerve. The most common cause of sciatica is a slipped intervertebral disc. Multiple sclerosis is a progressive degenerative disease of central neural system, so named because of the many sites in which hardened tissue has replaced the normal myelin sheath of neuron. Bell's palsy occurs due to damage of facial nerve which results in paralysis of the muscles on one side of the face.