What is the pinna? The pinna is the only visible part of the ear (the auricle) with its special helical shape. It is the first part of the ear that reacts with sound. The function of the pinna is to act as a kind of funnel which assists in directing the sound further into the ear. Without this funnel the sound waves would take a more direct route into the auditory canal.
Smooth muscle is called involuntary muscle because you can not control this type of muscle movement. These muscles line internal organs, blood vessels, and organs such found in the digestive and reproductive systems. Structurally, these muscle fibers appear non-striated (not striped) when magnified, have one nucleus per cell, and are usually short.
For example, smooth muscles in bronchi, gastrointestinal tract, ureters of kidneys, muscles in uterus(womb.)a â¦ nd smooth muscles in blood vessels. They are all involuntary muscles.That means they are not under your control but under control of autonomic nervous system.