What is the name of the muscle that extends from the sphenoid bone to the mandible?

RRB Nsg. Superintendent-20 July 2019 (Shift-3rd)

Applied Anatomy

Easy

Appeared in: RRB Nsg. Superintendent-20 July 2019 (Shift-3rd)

Explanation

The pterygoid muscles are a pair of muscles of mastication located in the infratemporal fossa of the skull.
The lateral pterygoid muscle has two heads, both of which originate from the sphenoid bone (the greater wing and the lateral pterygoid plate).
The medial pterygoid muscle also originates from the sphenoid bone (medial surface of the lateral pterygoid plate).
Both muscles insert onto the mandible, fulfilling the criteria described in the question.
Their primary function involves complex jaw movements required for chewing, including protrusion and side-to-side grinding.

Option B: The Masseter muscle is a powerful muscle of mastication, but it originates from the zygomatic arch (cheekbone), not the sphenoid bone.
Option C: The Sternocleidomastoid is a large muscle in the neck responsible for head and neck movement. It does not attach to either the sphenoid bone or the mandible.
Option D: The Trapezius is a large, superficial muscle of the upper back and neck. It is involved in moving the scapula and has no direct connection to the sphenoid bone or mandible.

Visual 1: Diagram - A lateral view of the skull showing the muscles of mastication. This visual should clearly label the Pterygoid (medial and lateral), Masseter, and Temporalis muscles, along with their origin (e.g., sphenoid bone, zygomatic arch) and insertion (mandible) points.
Visual 2: Infographic - A simplified chart comparing the four muscles of mastication (Masseter, Temporalis, Medial Pterygoid, Lateral Pterygoid) by their origin, insertion, action, and nerve supply (Mandibular nerve - CN V3).

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Anatomy of the muscles of mastication, specifically their origin and insertion points as background academic context rather than a clinical decision trigger.
Understanding the anatomy of the pterygoid muscles is crucial for diagnosing and managing Temporomandibular Joint (TMJ) disorders. Spasm or dysfunction of the lateral pterygoid is a common cause of jaw pain, clicking, and limited mouth opening.
Knowledge of this anatomy is essential for dental professionals, especially when administering an inferior alveolar nerve block for dental procedures on the lower teeth. The needle passes near the medial pterygoid muscle, and incorrect technique can lead to a hematoma or trismus (difficulty opening the jaw).
What if the patient presents with jaw deviation to the left side upon opening their mouth? This could indicate weakness or paralysis of the right lateral pterygoid muscle, as the functioning left muscle pulls the jaw towards the weakened side.

How to Approach the Question

First, identify the key anatomical structures mentioned in the question stem: the origin ('from the sphenoid bone') and the insertion ('to the mandible').
This is a factual recall question about musculoskeletal anatomy. Access your knowledge of the major muscles of the head and neck.
Systematically evaluate each option based on its known origin and insertion points.
Eliminate options that clearly do not connect the sphenoid bone and mandible. Sternocleidomastoid and Trapezius are neck and back muscles, respectively, and can be quickly ruled out.
Differentiate between the remaining muscles of mastication (Pterygoid and Masseter). Recall that the Masseter originates from the zygomatic arch.
Conclude that the Pterygoid muscles are the ones that originate from the sphenoid bone and insert on the mandible.

Concept Tested & Keywords

Concept Tested: Anatomy of the muscles of mastication, specifically their origin and insertion points.
Stem keywords: muscle, sphenoid bone, mandible
Lead-in keywords: name
Negative lead-in flag: false

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