Which statement describes a neuroregulin?
◦ Chemical mediator that initiates signals from the anterior horn cell of the spinal card to the axon of motor nerve branches of groups of muscle fibers
◦ Neurotransmitter that provides a means of reporting changes in length, tension, velocity, and tone in muscles
◦ Proteoglycan secreted by neurons, which increases acetylcholine receptors
◦ Mechanoreceptor that lies parallel to muscle fibers and responds to muscle stretching