The muscles of the head play an important role in maintaining facial expression, eye movement, and mastication. To better understand these muscles, they can be divided into four key groups; the tongue, muscles of facial expression, extra-ocular muscles, and muscles of mastication.
The tongue is composed of intrinsic and extrinsic muscles and is innervated by the hypoglossal nerve. It is responsible for providing both taste and general sensation to the individual.
The muscles of facial expression are located in the subcutaneous tissue and are responsible for controlling movements of the face. These muscles can be divided into three categories; orbital, nasal, and oral. Each of these areas is innervated by the facial nerve.
The orbital muscles of facial expression control movement of the eyelids. These muscles are the orbicularis oculus and corrugator supercilia, receiving motor innervation from the facial nerve. These muscles are important in protecting the cornea from damage.
The nasal muscles of facial expression control movement of the nose, as well as the surrounding skin. The three muscles in this group include nasalis, procerus, and depressor septi nasi, all of which are innervated by the facial nerve.
The oral muscles of facial expression are responsible for the movement of the mouth and lips. These muscles consist of the orbicularis oris and buccinator, both innervated by the facial nerve.
The extra-ocular muscles are located in the orbit and control movement of the eyeball, along with the superior eyelid. This group is composed of the levator palpebrae superioris, superior, inferior, medial and lateral recti muscles, and superior and inferior oblique muscles. The levator palpebrae superioris functions to elevate the upper lid and is innervated by the oculomotor nerve while the others are all innervated by the oculomotor nerve, with the exception of the superior oblique, which is innervated by the trochlear nerve, and the lateral rectus muscle, which is innervated by the abducens nerve.
The muscles of mastication are responsible for movement of the jaw and develop from the first pharyngeal arch. They are the masseters, temporalis, medial pterygoid, and lateral pterygoid muscles, all of which receive motor innervation from the mandibular nerve (CNV3).
Each of the muscles of the head has a distinct purpose and, when functioning normally, contribute to the facial structure and expression and necessary movement of the eyes and jaw.
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