MUSCLES OF MASTICATION

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INTRODUCTION

Mastication is defined as the process of chewing food in preparation for swallowing and digestion. Four pairs of muscles in the mandible make chewing movements possible.

These muscles along with accessory ones together are termed as ‘MUSCLES OF MASTICATION’.

These muscles can be divided into:

Basic muscles:

-Lateral pterygoid

-Medial pterygoid

-Temporalis

-Masseter

Accessory muscles:

-Buccinator

-Digastric muscle (anterior belly)

-Mylohyoid

-Geniohyoid

-Orbicularis oris

DEVELOPMENT

  • The basic muscles of mastication develop from the mesenchyme of the first branchial arch.
  • So they receive all their innervations from the mandibular branch of the trigeminal nerve, all from the anterior division except the medial pterygoid which gets its nerve supply from the main trunk.
  • Also they originate from the same origin from temporal and infra-temporal fossa of the skull and are inserted in the mandible.

MOVEMENTS OF MANDIBLE

  • Movements that the mandible can undergo are:

1. Depression: as in opening the mouth.

2. Elevation: as in closing the mouth.

3. Protraction: horizontal movement of the mandible anteriorly.

4. Retraction: horizontal movement of the mandible posteriorly.

5. Rotation: the anterior tip of the mandible is “slewed” from side to side.

  • These movements of mandible are performed by various muscles involved in it. So, functionally, the muscles of mastication are classified as:

Jaw elevators:

Masseter

Temporalis

Medial pterygoid

Upper head of lateral pterygoid

Jaw depressors:

Lower head of lateral pterygoid

Anterior digastric

Geniohyoid

Mylohyoid

 

TEMPORALIS

  • It is the largest among all the masticatory muscles and is a fan shape muscle.
  • Origin; from the inferior temporal line , floor of the temporal fossa and from the overlaying temporal fascia.
  • Insertion; anterior and medial tip of the coroniod process.
  • It has been divided into 2 heads:

–     Deep head (anterior, middle and posterior fibers)

–     Superficial head (much smaller)

  • Action:

–     Elevation (anterior fibers)

–     Retraction (posterior fibers)

  • Nerve supply:

–     Anterior division of the mandibular nerve

(by 2 deep temporal nerves)

  • Its action is done by;
  • The anterior fibers during function act vertically and elevate the mandible.
  • The posterior fibers diverge and become horizontal and  retract the mandible.
  • Blood supply; from the maxillary artery (one of 2 termination of external carotid artery).

MASSETER

  • It consist of 2 overlapping heads:
  • The origin of the whole muscle is mainly from the zygomatic process, in which:

-The superficial head arises from the lower border of the zygomatic arch.

-The deep head arises from the inner surface of the zygomatic arch.

  • Insertion of both the heads is into the outer surface of the ramus of the mandible.
  • The superficial head passes downwards and backwards to insert into the lower half of the lateral surface of the ramus.