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.
Muscles are classified as either voluntary or involuntary and as either striated or smooth. From this we get three types of muscles: smooth (involuntary) muscle, skeletal (voluntary) muscle and. cardiac (involuntary) muscle. 1) Voluntary skeletal muscle is under conscious control. Each fiber is an enormous. 2) Cardiac muscle is similar to skeletal muscle, but is not under conscious control.