I have tight sternocleidomastoid muscle, plus scalene and painful tmj joint but normal opening. no neurological symptoms. could all this be muscle?

Yes, muscle spasms: It is difficult to make a suggestion without more history but TMJ can cause muscle spasms, but not usually in the SCM and scalenes. The SCM muscle may be spastic by the way you sleep or use it and also may be caused by a virus. Try ibuprofen and if not relieved in 2-3 days see a doctor as there may be something under the muscle causing it.