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.
These are also called voluntary muscles.. Smooth muscle is involuntary, and is not under conscious control; the muscles in your digestive system are smooth muscles. The cells are individual and are found in sheets instead of long fibers.here skeletal muscle is voluntary, cardiac muscle is autorhythmic (beats involuntarily; generates its own action potentials). 3. Smooth muscle: refers to the muscles that are controlled involuntarily by the brain, like those attached to the base of hair follicles or in the walls of the gastro-intestinal tract.