Question

Multi unit muscle fibres are found in the:

• A. Ciliary and iris of eyes
• B. Arrector pilli of dermis
• C. Wall of large blood vessels
• D. All of the above

Answer 1

The correct option is D All of the above

• Multi-unit smooth cells can be found in the in the trachea, the large elastic arteries, the iris of the eye, in the lungs, erectile tissues of hair follicles ( Arrector pili of the dermis) and the vas deferens in the male genital tract.
• The response of the whole muscle depends on upon the number of motor units active, the frequency of discharge in the fibers and the relative amount of excitatory and inhibitory input.
• Multi-unit smooth muscle activity can be initiated by hormones, but it is not much affected by rapidly stretching the muscle.
• Hence the correct option is D.