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.
There are two other types. One is smooth muscle, which has no visible striations and it also involuntary. This is found in arteries and the walls of the digestive, urinary, other hollow organs and respiratory tracts and the irises of the eye.