Muscles of mastication

During mastication

Mastication

Mastication or chewing is the process by which food is crushed and ground by teeth. It is the first step of digestion and it increases the surface area of foods to allow more efficient break down by enzymes. During the mastication process, the food is positioned between the teeth for grinding by...

, four muscles of mastication are responsible for adduction

Adduction

Adduction is a movement which brings a part of the anatomy closer to the middle sagittal plane of the body. It is opposed to abduction.-Upper limb:* of arm at shoulder ** Subscapularis** Teres major** Pectoralis major** Infraspinatus...

 and lateral motion of the jaw. Other muscles, usually associated with the hyoid such as the sternohyomastoid, are responsible for opening the jaw.

Muscles

• The masseter
• The temporalis (the sphenomandibularis
  Sphenomandibularis
  The Sphenomandibularis is a muscle attaching to the sphenoid bone and the mandible. It is a muscle of mastication.Unlike most of the muscles of the human body, which had been categorized several centuries ago, Sphenomandibularis was discovered in the mid-1990s at the University of Maryland at...
  
   is considered a part of the temporalis by some sources, and a distinct muscle by others)
• The medial pterygoid
  Medial pterygoid muscle
  The medial pterygoid , is a thick, quadrilateral muscle of mastication.The mandibular branch of the fifth cranial nerve, the trigeminal nerve, innervates the medial pterygoid muscle.-Origin and insertion:...
  
  
• The lateral pterygoid

Each of these primary muscles of mastication is paired, with each side of the mandible possessing one of the four.

Innervation and embryological origin

Unlike most of the other facial muscles, which are innervated by the facial nerve

Facial nerve

The facial nerve is the seventh of twelve paired cranial nerves. It emerges from the brainstem between the pons and the medulla, and controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue and oral cavity...

 (or CN VII), the muscles of mastication are all innervated by the trigeminal nerve

Trigeminal nerve

The trigeminal nerve contains both sensory and motor fibres. It is responsible for sensation in the face and certain motor functions such as biting, chewing, and swallowing. Sensory information from the face and body is processed by parallel pathways in the central nervous system...

 (or CN V). More specifically, they are innervated by the mandibular branch

Mandibular nerve

The mandibular nerve is the largest of the three branches of the trigeminal nerve.-Roots:It is made up of two roots:* a large sensory root proceeding from the inferior angle of the trigeminal ganglion....

, or V₃

Mandibular nerve

The mandibular nerve is the largest of the three branches of the trigeminal nerve.-Roots:It is made up of two roots:* a large sensory root proceeding from the inferior angle of the trigeminal ganglion....

. This is a testament to their shared embryological origin from the first branchial arch

Branchial arch

In the development of vertebrate animals, the pharyngeal arches are anlage for a multitude of structures. In humans, they develop during the fourth week in utero as a series of mesodermal outpouchings on the left and right sides of the developing pharynx...

.

The muscles of facial expression, on the other hand, derive from the second branchial arch.

Origin and insertion

In humans, the mandible, or lower jaw, is connected to the temporal bone

Temporal bone

The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebrum.The temporal bone supports that part of the face known as the temple.-Parts:The temporal bone consists of four parts:* Squama temporalis...

 of the skull via the temporomandibular joint

Temporomandibular joint

The temporomandibular joint is the joint of the jaw and is frequently referred to as TMJ. There are two TMJs, one on either side, working in unison. The name is derived from the two bones which form the joint: the upper temporal bone which is part of the cranium , and the lower jaw bone called the...

, an extremely complex joint which permits movement in all planes. The muscles of mastication originate on the skull and insert into the mandible, thereby allowing for jaw movements during contraction.

Function

The mandible is the only bone that moves during mastication and other activities, such as talking.

While these four muscles are the primary participants in mastication, other muscles are usually if not always helping the process, such as those of the tongue and the cheeks.