Which of the following terms are NOT used interchangeably? muscle tension - muscle force in vivo - in the body / the living muscle cell - muscle fiber motor unit - motor neuro

The correct answer is "motor unit - motor neuron".

Explanation:

Motor unit and motor neuron are related terms, however they could not be used interchangeably because a motor unit is not comprised only of a motor neuron. A motor unit is made of a motor neuron, skeletal muscle fibers and neuron's axonal terminals. Therefore motor unit is a more broadly term, and is referred to the units that coordinate the contractions of single muscles.