Muscular System
Muscular System Study Guide
Learning Objectives
Define and pronounce key terms and anatomic terms in this chapter.
Locate and identify the muscles of the head and neck on a diagram, skull, and patient.
Describe the origin, insertion, action, and innervation of each muscle of the head and neck.
Discuss the processes of mastication, speech, and swallowing concerning anatomic considerations involving the muscles of the head and neck.
Discuss the pathology associated with the muscles of the head and neck.
Correctly complete the review questions and activities for this chapter.
Integrate an understanding of the muscles of the head and neck into clinical dental practice.
Key Terms
Action: Movement accomplished by a muscle when muscle fibers contract.
Facial paralysis (puh-ral-i-sis): Loss of the action of facial muscles.
Insertion: End of the muscle attached to a more movable structure.
Muscle: Body tissue that shortens under neural control, causing soft tissue and bony structures to move.
Muscular system: System that includes skeletal muscle tissue.
Origin: End of muscle attached to the least movable structure.
Muscular System Overview
The muscular system includes skeletal muscle tissue that shortens under neural control, causing soft tissue and bony structures of the body to move. Each muscle is attached at both ends of these moving structures, categorized by its role in movement:
Origin: Attached to the least movable structure.
Insertion: Attached to the more movable structure where the movement occurs.
Action: The specific type of movement accomplished when the muscle fibers contract.
Innervation: Specific nerves supplying each muscle, further elaboration available in Chapter 8.
Blood Supply: Discussed further in Chapter 6; artery supply is regional unlike innervation.
Head and Neck Muscles
Understanding the location and action of skeletal muscles of the head and neck is crucial for dental examinations, as their positions can affect the placement of structures such as bones, nerves, blood vessels, and lymph nodes. Additionally, these muscles can malfunction, contributing to temporomandibular joint disorders, occlusal trauma, and certain nervous system diseases.
Muscle Groups
The muscles of the head and neck are divided into six main groups:
Cervical Muscles
Muscles of Facial Expression
Muscles of Mastication
Hyoid Muscles
Muscles of the Tongue
Muscles of the Pharynx
Not covered in this chapter are muscle groups of the ears, eyes, and nose, but they can be referenced elsewhere.
Cervical Muscles
Sternocleidomastoid Muscle (SCM)
Origin: Medial part of the clavicle and superior lateral surfaces of the sternum.
Insertion: Mastoid process of the temporal bone and the lateral half of the superior nuchal line of the occipital bone.
Action: Unilateral contraction results in head and neck bending to the same side and face rotation to the opposite side; bilateral contraction leads to neck flexion and head extension at the skull.
Innervation: Eleventh cranial or accessory nerve.
Trapezius Muscle
Origin: External surface of the occipital bone and posterior midline of the cervical and thoracic regions.
Insertion: Lateral third of the clavicle and parts of the scapula.
Action: Cervical fibers act to lift the clavicle and scapula (shrugging shoulders).
Innervation: Eleventh cranial or accessory nerve, third and fourth cervical nerves.
Muscles of Facial Expression
These paired muscles are located within the superficial fascia of the facial tissue.
Origin and Insertion: Most originate from the surface of the skull bone and insert into the dermis of the skin.
Action: They cause movement of the skin to produce facial expressions, often creating wrinkles.
Innervation: All muscles are innervated by the seventh cranial or facial nerve.
Major Muscles of Facial Expression
Epicranial Muscle:
Organs: Frontalis originates from the epicranial aponeurosis, occipitalis from the occipital and temporal bones; inserts on the skin of the eyebrow.
Action: Raises eyebrows and scalp (surprise).
Orbicularis Oculi Muscle:
Origin: Orbital rim, frontal bone, and maxilla.
Action: Closes eyelids, squints, and protects the eye.
Orbicularis Oris Muscle:
Origin: Encircles the mouth without bony attachments.
Action: Controls mouth closing and shapes lip movements during speech.
Clinical Considerations with Cervical Muscle Pathology
Malfunction of cervical muscles can result in abnormal head and neck positioning, which may affect dental treatment.
Conditions can arise from trauma or chronic muscle stress.
Clinical Significance of Facial Expression Muscles
Damage to the facial nerve can lead to unilateral facial paralysis presenting challenges in communication and facial expressions, impacting dental treatment.
Muscles of Mastication
Masseter Muscle:
Origin: Zygomatic arch; Insertion: Angle of the mandible; Action: Elevates the mandible during jaw closure; Innervated by the masseteric nerve.
Temporalis Muscle:
Origin: Temporal fossa; Insertion: Coronoid process of the mandible; Action: Elevates and retracts the mandible; Innervated by the deep temporal nerves.
Medial Pterygoid Muscle:
Origin: Pterygoid fossa; Insertion: Medial surface of the mandibular ramus; Action: Elevates mandible; Innervated by the medial pterygoid nerve.
Lateral Pterygoid Muscle:
Origin: Infratemporal surface; Insertion: Neck of the mandibular condyle; Action: Protrudes and depresses the mandible; Innervated by the lateral pterygoid nerve.
Actions of the Muscles of Mastication
The muscles work collectively to facilitate jaw movements for chewing, including elevation, depression, protrusion, retraction, and lateral deviation. Innervation occurs via branches of the mandible from the trigeminal nerve.
Hyoid Muscles
The hyoid bone serves as an anchor point for various muscles aiding in mastication and swallowing. Muscles are grouped as either suprahyoid or infrahyoid.
Actions and Innervation
Suprahyoid muscles elevate the hyoid and assist during swallowing; infrahyoid muscles depress the hyoid.
Suprahyoid Muscle Examples
Digastric Muscle: Depresses mandible; Innervation: Mylohyoid nerve (anterior belly) and posterior digastric nerve (posterior belly).
Mylohyoid Muscle: Forms floor of the mouth; Innervation: Mylohyoid nerve.
Muscles of the Tongue
Comprised of intrinsic and extrinsic muscles that allow for diverse tongue movements essential for mastication, speech, and swallowing.
Intrinsic Muscles
Alter the tongue's shape; innervated by the hypoglossal nerve.
Extrinsic Muscles
Move the tongue in and out of the mouth; also innervated by the hypoglossal nerve.
Muscles of Pharynx
Involved in swallowing and speech; include the stylopharyngeus and pharyngeal constrictors.
Actions and Innervation
Involved in elevating the pharynx; innervated primarily by the vagus nerve.
Muscles of the Soft Palate
Important for swallowing and sound production.
Key Muscles
Palatoglossus: Elevates and arches tongue; Palatopharyngeus: Moves the palate.