The human skull has only one movable bone.

MP CHO - 2022

Applied Anatomy

Easy

Appeared in: MP CHO - 2022

Explanation

The mandible, which forms the lower jaw, is the only bone in the skull that is not fused to the cranium.
It articulates with the temporal bones on both sides at the temporomandibular joints (TMJ), which are synovial joints.
This unique articulation allows for movements essential for mastication (chewing) and phonation (speech), including depression (opening the mouth), elevation (closing the mouth), protraction (moving jaw forward), and retraction (moving jaw backward).

Option A: The maxilla forms the upper jaw. It is a paired bone that is fused in the midline and is fixed to the base of the cranium, making it immovable.
Option B: The ethmoid bone is a deep, unpaired cranial bone situated at the roof of the nose, between the two orbits. It is a fixed part of the cranium.
Option C: The sphenoid bone is a complex, butterfly-shaped bone that forms part of the floor of the middle cranial fossa. It is considered the 'keystone' of the cranium because it articulates with almost all other cranial bones, but it is immovable.

Visual 1: Diagram - A lateral view of the human skull with the mandible highlighted in a different color to clearly distinguish it from the fused bones of the cranium.
Visual 2: Animation - A short animation demonstrating the range of motion of the mandible at the temporomandibular joint (TMJ), showing elevation, depression, protraction, and retraction movements.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Anatomy of the skull and identification of its movable components as background academic context rather than a clinical decision trigger.
Understanding the mandible's unique mobility is fundamental for assessing patients with facial trauma, jaw pain (trismus), or difficulty chewing. A fractured or dislocated mandible is a medical emergency requiring immediate attention to maintain airway and function.
Nurses often encounter patients with temporomandibular joint disorders (TMD), which can cause significant pain, clicking, popping sounds, and functional limitations. Nursing assessment includes palpating the joint during movement and inquiring about pain during mastication.
What if? If a patient presents with their jaw 'locked' in an open position after a wide yawn, the nurse should suspect an anterior dislocation of the mandible. The priority is to reassure the patient and prepare for a physician to perform a manual reduction of the joint.

How to Approach the Question

First, identify the core concept of the question, which is to find the 'only one movable bone' in the 'human skull'.
This is a direct factual recall question from the subject of anatomy.
Mentally visualize the human skull. Recall that the cranium (braincase) and the upper part of the face are a single, solid unit composed of fused bones.
Consider the function of the jaw. The lower jaw must move to allow for chewing and speaking.
Evaluate the options based on this understanding: The maxilla is the upper jaw (fixed). The ethmoid and sphenoid are deep cranial bones (fixed). The mandible is the lower jaw.
Conclude that the mandible is the only bone listed that is designed for movement, and select it as the correct answer.

Concept Tested & Keywords

Concept Tested: Anatomy of the skull and identification of its movable components.
Stem keywords: human skull, movable bone
Lead-in keywords: only one

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