Muscles of the Head and Neck Posterior
The muscular system of the head and neck is defined by two movements: One is the relatively fine movements of the muscles activating the sensory organs of the head; the other is by the grosser movements of the neck muscles, which allow those senses to be properly targeted. The neck muscles are responsible for the bulk of gross motor movement in the muscular system of the head and neck. They move the head in every direction, pulling the skull and jaw against the shoulders, spine, and scapula. These neck muscles are often paired. One such typical bifurcated strap-like muscle in the back of the neck connects the base of the skull to several vertebrae. These muscle pairs bend the head toward the chest and pull it erect, or turn the face to one side or the other. Additionally, some muscles of the neck aid in facial expressions, or help to open the mouth. Finer musculature dominates the head, including muscles that give the face its infinite expressiveness (a smile uses 17 muscles, a frown uses 43), including muscles over the top of the cranium. However, the muscular systems of the tongue and eyes are most significant. An extensive complement of tightly interlaced muscles allows the tongue a range of complex movements for chewing, sucking, and swallowing, as well as the vital function of making sounds to produce speech. Of these, four extrinsic muscle sets (connecting the tongue to the surrounding bones) move the tongue in virtually any direction, with fine shape changes (such as for speech) the province of four intrinsic tongue muscles. As for the eye, six extrinsic eye muscles that provide movement in eight different directions, constantly and at tremendous speed, actuate movement. Dilation of the pupil and focusing of the eye, too, is controlled by intrinsic muscles. Even the ear takes part in the muscular system of the head and neck. In fact, the smallest muscle of the skeleton is the stapedius, which measures 1/20th of an inch. It is the activator of the stirrup that sends vibrations from the eardrum to the inner ear.