Masseter and temporal muscles
These two muscles are located more superficially and play a crucial role in closing the jaws.
- Masseter muscle proper (m. masseter)
The muscle originates from the zygomatic arch (arcus zygomaticus). Its insertion site is the external surface of the mandibular ramus, as well as a specialized bony formation — the masseteric tuberosity (tuberositas masseterica). Function: The main action consists of powerful elevation of the mandible. In addition, the superficial bundles of this muscle are capable of protrusion (moving the jaw forward). Blood supply: The muscle is nourished by branches of the masseteric artery (a. masseterica) and facial artery (a. facialis).
- Temporalis muscle (m. temporalis)
This extensive muscle originates within the temporal fossa (fossa temporalis). Its muscle fibers converge inferiorly and insert into the coronoid process of the mandible (proc. coronoideus). Function: Like m. masseter, the temporalis muscle elevates the mandible. At the same time, its posterior bundles perform the movement opposite to protrusion — retraction, i.e., pulling the protracted jaw backward. Blood supply: Provided by the deep temporal arteries (aa. temporales profundi) and superficial temporal artery (a. temporalis superficialis).
Pterygoid muscles
The pterygoid muscles are located in the deeper layers of the facial skeleton and are responsible for both elevation and complex lateral movements of the jaw.
- Medial pterygoid muscle (m. pterygoideus medialis)
The origin (origo) for this muscle serves as the pterygoid fossa (fossa pterygoidea). From here, the fibers head towards their insertion site — the pterygoid tuberosity (tuberositas pterygoidea) on the mandible. Function: The main task of the muscle is elevation of the mandible. Blood supply: Provided by numerous branches of the maxillary artery (a. maxillaris).
- Lateral pterygoid muscle (m. pterygoideus lateralis)
This muscle has the most complex insertion site. It originates from the roof of the infratemporal fossa (fossa infratemporalis) and the lateral plate of the pterygoid process. Its fixation site (insertio) is unique: the fibers blend directly into the capsule and articular disc of the TMJ (temporomandibular joint), and also attach to the neck of the condyle. Function: With bilateral contraction, the muscle moves the jaw forward (protrusion). With unilateral contraction, laterotrusion is ensured — displacement of the jaw to the opposite side. Blood supply: Like the medial muscle, it receives blood from branches of the maxillary artery (a. maxillaris).
Systematization of functions (Biomechanics)
For better memorization, let us classify the functions of the muscles of mastication by the type of movement performed:
- Elevation of the mandible (closing the mouth): provided by three of the four muscles — m. masseter, m. temporalis, and m. pterygoideus medialis.
- Protrusion (forward movement): lateral pterygoid muscle (m. pterygoideus lateralis), as well as the superficial bundles of the masseter muscle (m. masseter).
- Retrusion (backward displacement): exclusively the posterior bundles of the temporalis muscle (m. temporalis).
- Laterotrusion (lateral displacement): lateral pterygoid muscle (m. pterygoideus lateralis).
Briefly: answers to topical questions
Which muscles depress the mandible?
Depression of the mandible is carried out by several muscles acting as antagonists to the jaw elevators. The following take part in this process:
- Mylohyoid muscle — forms the floor of the oral cavity.
- Geniohyoid muscle.
- Digastric muscle — both anterior and posterior bellies participate.
- Stylohyoid muscle.
- Lateral pterygoid muscle.
For effective mouth opening, the hyoid bone must be rigidly fixed by the musculature located inferior to it.
What specific motor branches does the mandibular nerve give off to the muscles of mastication?
To the muscles of mastication, the mandibular nerve (n. mandibularis) gives off three main motor branches. These include:
- Masseteric nerve (n. massetericus).
- Deep temporal nerves (nn. temporales profundi).
- Medial and lateral pterygoid nerves (n. pterygoideus medialis et lateralis).
These branches depart from the mixed mandibular nerve after its exit from the skull through the foramen ovale.
Which fasciae cover the muscles of mastication?
From the cited sources, it is confirmed that:
- Masseteric fascia (fascia masseterica) originates from the zygomatic arch and covers the masseter muscle (m. masseter); posteriorly it continues into the parotid fascia, and anteriorly into the buccopharyngeal fascia.
- Temporal fascia (fascia temporalis) covers the temporalis muscle (m. temporalis), attaches superiorly to the superior temporal line, inferiorly to the zygomatic arch, and splits into superficial and deep layers.
Class and exam questions
Which muscles elevate the mandible?
Three muscles are responsible for jaw elevation: masseter (m. masseter), temporalis (m. temporalis), and medial pterygoid (m. pterygoideus medialis).
Which muscle blends into the TMJ capsule and disc?
The lateral pterygoid muscle (m. pterygoideus lateralis) blends into the capsule and articular disc of the temporomandibular joint.
What is protrusion and which muscles perform it?
Protrusion is the forward movement of the mandible. It is performed by the lateral pterygoid muscle and the superficial bundles of the masseter muscle.
Where do the pterygoid muscles receive blood from?
Both the medial and lateral pterygoid muscles are supplied with blood by branches of the maxillary artery (a. maxillaris).
What else to study on this topic
- Anatomy of the temporal fossa (fossa temporalis) and infratemporal fossa (fossa infratemporalis)
- Structure of the temporomandibular joint (TMJ) and its articular disc
- Branching of the maxillary artery (a. maxillaris) and its role in facial blood supply
- Topography and branches of the mandibular nerve (V3)
- Bony landmarks of the mandible: coronoid process, condyle, and tuberosities
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