ABSTRACT
Stronger contraction of a muscle results from the firing of more motor neurons, and hence the recruitment of more motor units. The name 'striated muscle' comes from the striped appearance that skeletal muscle has under the microscope. The stripes consist of a number of bands and lines in each myofibril. Each set of bands and lines is a functional unit called a sarcomere. Reflexes are actions that take place automatically in response to some stimulus, and permit immediate actions without the intervention of the brain. The simplest reflex is the monosynaptic stretch reflex. Each muscle contains intrafusal muscle fibers, also called muscle spindles, which are stretch receptors. When a muscle is stretched by contraction of an opposing muscle, the afferent nerve fiber serving each spindle passes information to the spinal cord. Within each muscle are subsets of fibers, which are innervated by a single motor neuron.
