Temporalis- Propeties (Revision)
The temporalis muscle appears as a broad and radiating muscle located on the lateral side of the head. The majority of this muscle arises from the temporal fossa and deep to the surface of the temporal fascia. Fibres converge as they descend, forming a tendon, this passes deep to the zygomatic arch and inserted into the anterior border of the coronoid process. The temporalis runs through the large opening just behind the eye (zygomatic arch). The larger the arch, the larger the temporalis muscle passing through the arch.
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The temporalis has the following action:
- Elevation of the mandible
- Retraction of the mandible
- Crushing of food between the molars
The posterior temporalis helps retract the mandible. The posterior temporalis is the thinnest and weakest. The posterior fibres are horizontal and fulfil the requirement of mandibular retraction.
The anterior temporalis is the thickest and strongest and therefore provides the required force of elevation against resistance. The muscle is the most prominent when a person eats varying hardness of foods and objects.
The temporalis muscle receives innervations from the deep temporal branch of the mandibular division of the trigeminal nerve. Two or three deep temporal nerves then ascend deep to the temporalis muscle.
The temporalis’ evolutionary role is to aid in grabbing prey with canine teeth, hence the temporalis’ strength is greatest when the mandible is open about 20mm. In humans as well as other carnivores the temporalis muscle is the strongest and most efficient muscle in mastication. The ratio of neuron to muscle fibre is 1:900.
The temporal fascia covers the temporal muscle, which is covered laterally by auricularis anterior and superior, by the galea aponeurotica, and part of obicularis oculi.
Damage to the trigeminal nerve causes the patient to experience symptoms, like headache and migraines.
Less advanced forms have a larger temporalis muscle reflecting their more herbivorous diet. Very large temporalis muscles may even require attachment to the sagittal crest, a long narrow ridge running down the apex of the skull between the two parietal bones.