The third and fourth one definitely
Answer:
motor unit
The impulses that initiate muscle contraction originates in the. brain or spinal cord. A group of muscle cells stimulated by a single motor neuron is known as a. motor unit
A single motor neuron, however, can innervate many muscle fibers. The combination of an individual motor neuron and all of the muscle fibers that it innervates is called a motor unit. The number of fibers innervated by a motor unit is called its innervation ratio.
Answer:
A cell is a mass of cytoplasm that is bound externally by a cell membrane. Usually microscopic in size, cells are the smallest structural units of living matter and compose all living things. Now put that into your own words.
Explanation: