Muscles Of The Head And Neck Review Sheet 13

Muscles of the head and neck are a complex and fascinating group, essential for everything from facial expressions and speech to swallowing and head movements. Understanding their individual functions and how they interact is crucial for students in fields like anatomy, physical therapy, and medicine. This review sheet delves into the major muscles, offering a structured approach to memorization and functional understanding.

I. Muscles of Facial Expression

These muscles are unique because they insert into the skin, allowing for a wide range of emotions. They are all innervated by the facial nerve (CN VII).

• Occipitofrontalis: This muscle has two parts:

  • Frontalis (frontal belly): Located on the forehead, it raises the eyebrows and wrinkles the forehead skin horizontally.
  • Occipitalis (occipital belly): Located at the back of the head, it retracts the scalp.

• Orbicularis Oculi: This muscle surrounds the eye and is responsible for closing the eyelids. It has two parts:

  • Palpebral part: Gently closes the eyelids, as in blinking or sleeping.
  • Orbital part: Tightly closes the eyelids, as in squinting.

• Corrugator Supercilii: Located deep to the frontalis, it draws the eyebrows medially and downwards, creating vertical wrinkles above the nose (as in frowning).

• Nasalis: This muscle is located on the nose and has two parts:

  • Transverse part: Compresses the nostrils.
  • Alar part: Dilates the nostrils.

• Orbicularis Oris: This muscle surrounds the mouth and is responsible for closing and protruding the lips (as in kissing or whistling).

• Zygomaticus Major: This muscle runs from the zygomatic bone to the corner of the mouth and draws the corner of the mouth upwards and laterally (as in smiling).

• Zygomaticus Minor: Located medial to the zygomaticus major, it also elevates the upper lip, contributing to facial expressions.

• Levator Labii Superioris: This muscle elevates the upper lip.

• Depressor Anguli Oris: This muscle runs from the mandible to the corner of the mouth and draws the corner of the mouth downwards (as in frowning).

• Depressor Labii Inferioris: This muscle depresses and everts the lower lip.

• Mentalis: This muscle elevates and protrudes the lower lip, wrinkling the chin skin (as in pouting).

• Buccinator: This muscle forms the muscular component of the cheek. It compresses the cheek against the teeth (as in whistling or chewing) and helps keep food between the teeth. While it aids in chewing, it is considered a muscle of facial expression because it is innervated by the facial nerve.

• Platysma: This broad, thin muscle covers the anterior neck. It tenses the skin of the neck and helps depress the mandible.

II. Muscles of Mastication

These muscles are responsible for chewing. They are all innervated by the mandibular division of the trigeminal nerve (CN V3).

• Masseter: This powerful muscle is located on the lateral aspect of the mandible. It elevates the mandible (closes the jaw).

• Temporalis: This fan-shaped muscle is located on the side of the head. It elevates and retracts the mandible.

• Medial Pterygoid: This muscle is located deep to the mandible. It elevates and protrudes the mandible, and also assists in lateral movements.

• Lateral Pterygoid: This muscle is also located deep to the mandible. It protracts the mandible and assists in lateral movements. It is the only muscle of mastication that opens the jaw.

III. Suprahyoid Muscles

These muscles are located above the hyoid bone and generally elevate the hyoid bone and larynx during swallowing and speech.

• Digastric: This muscle has two bellies:

  • Anterior belly: Originates from the mandible and is innervated by the nerve to mylohyoid (a branch of CN V3).
  • Posterior belly: Originates from the mastoid process of the temporal bone and is innervated by the facial nerve (CN VII). Both bellies elevate the hyoid bone and depress the mandible.

• Stylohyoid: This muscle runs from the styloid process of the temporal bone to the hyoid bone. It elevates and retracts the hyoid bone. Innervated by the facial nerve (CN VII).

• Mylohyoid: This muscle forms the floor of the mouth. It elevates the hyoid bone and the floor of the mouth, and also depresses the mandible. Innervated by the nerve to mylohyoid (a branch of CN V3).

• Geniohyoid: This muscle is located superior to the mylohyoid. It elevates the hyoid bone and depresses the mandible. Innervated by C1 via the hypoglossal nerve (CN XII).

IV. Infrahyoid Muscles

These muscles are located below the hyoid bone and generally depress the hyoid bone and larynx during swallowing and speech. They are also known as the "strap muscles" of the neck. All are innervated by the ansa cervicalis (a loop of nerves from the cervical plexus), except for the thyrohyoid, which is innervated by C1 via the hypoglossal nerve (CN XII).

• Sternohyoid: This muscle runs from the sternum to the hyoid bone. It depresses the hyoid bone.

• Omohyoid: This muscle has two bellies:

  • Superior belly: Runs from the hyoid bone to the intermediate tendon.
  • Inferior belly: Runs from the intermediate tendon to the scapula. Both bellies depress the hyoid bone.

• Sternothyroid: This muscle runs from the sternum to the thyroid cartilage. It depresses the thyroid cartilage.

• Thyrohyoid: This muscle runs from the thyroid cartilage to the hyoid bone. It depresses the hyoid bone and elevates the thyroid cartilage.

V. Muscles of the Anterior Neck

• Sternocleidomastoid (SCM): This large muscle runs from the sternum and clavicle to the mastoid process of the temporal bone. It has several actions:

  • Unilateral contraction: Tilts the head to the same side and rotates the head to the opposite side.
  • Bilateral contraction: Flexes the neck.
  • When the head is fixed: Elevates the sternum and assists in forced inspiration. It is innervated by the spinal accessory nerve (CN XI) and C2-C3 spinal nerves.

• Scalenes (Anterior, Middle, Posterior): These muscles are located on the lateral aspect of the neck, deep to the SCM.

  • Action: Elevate the ribs during forced inspiration. Unilateral contraction bends the neck to the same side.
  • Innervation: Cervical spinal nerves.

VI. Muscles of the Posterior Neck

These muscles are important for extending and rotating the head and neck.

• Trapezius: While primarily a back muscle, the trapezius also acts on the neck. Its upper fibers elevate and rotate the scapula, extend the neck, and laterally flex the neck. It is innervated by the spinal accessory nerve (CN XI) and C3-C4 spinal nerves.

• Splenius Capitis: This muscle is located deep to the trapezius. It extends and rotates the head. Innervated by cervical spinal nerves.

• Splenius Cervicis: Located deep to the splenius capitis, it extends and rotates the neck. Innervated by cervical spinal nerves.

• Semispinalis Capitis: This muscle is located deep in the posterior neck. It extends the head and rotates it to the opposite side. Innervated by cervical spinal nerves.

• Suboccipital Muscles: These are a group of four muscles located deep in the posterior neck, below the occipital bone. They are primarily involved in fine motor control of head movements.

  • Rectus Capitis Posterior Major: Extends the head and rotates it to the same side.
  • Rectus Capitis Posterior Minor: Extends the head.
  • Obliquus Capitis Superior: Extends the head and bends it to the same side.
  • Obliquus Capitis Inferior: Rotates the head to the same side. All suboccipital muscles are innervated by the suboccipital nerve (C1).

VII. Key Concepts for Memorization

• Nerve Supply is King: Mastering the nerve supply to each muscle is crucial. Grouping muscles by their innervation (e.g., all muscles of facial expression are innervated by CN VII) significantly simplifies memorization.
• Action and Location: Connecting a muscle's location to its primary action helps reinforce understanding. For example, muscles located anteriorly tend to flex or depress, while those located posteriorly tend to extend.
• Mnemonics: Create mnemonics to remember lists of muscles. For example, for the infrahyoid muscles (Sternohyoid, Omohyoid, Sternothyroid, Thyrohyoid), you could use "Some Old Scientists Teach Truth."
• Visual Aids: Use diagrams, anatomical models, and online resources to visualize the muscles and their relationships to each other.
• Active Recall: Test yourself frequently using flashcards, practice questions, and by explaining the muscles to someone else.

VIII. Clinical Significance

Understanding the muscles of the head and neck is critical for diagnosing and treating a variety of clinical conditions, including:

• Bell's Palsy: Paralysis of the facial nerve (CN VII) leading to weakness or paralysis of the muscles of facial expression on one side of the face.
• Temporomandibular Joint (TMJ) Disorders: Dysfunction of the TMJ can cause pain and limited movement, often involving the muscles of mastication.
• Torticollis (Wry Neck): A condition in which the sternocleidomastoid muscle is shortened or contracted, causing the head to tilt to one side and rotate to the opposite side.
• Headaches: Tension headaches are often associated with muscle tension in the neck and scalp, involving muscles like the trapezius, splenius capitis, and semispinalis capitis.
• Swallowing Disorders (Dysphagia): Weakness or dysfunction of the suprahyoid and infrahyoid muscles can lead to difficulty swallowing.

IX. Detailed Muscle-by-Muscle Breakdown

To solidify your understanding, let's examine each muscle group with more specific details:

A. Facial Expression:

Muscle	Origin	Insertion	Action	Innervation
Occipitofrontalis	Frontalis: Galea aponeurotica; Occipitalis: Superior nuchal line	Frontalis: Skin of eyebrows; Occipitalis: Galea aponeurotica	Frontalis: Raises eyebrows, wrinkles forehead; Occipitalis: Retracts scalp	CN VII
Orbicularis Oculi	Medial orbital margin, medial palpebral ligament	Skin around the orbit and eyelids	Closes eyelids (gently and tightly)	CN VII
Corrugator Supercilii	Medial end of superciliary arch	Skin of eyebrow	Draws eyebrows medially and downward (frowning)	CN VII
Nasalis	Maxilla	Bridge of nose	Transverse part: Compresses nostrils; Alar part: Dilates nostrils	CN VII
Orbicularis Oris	Muscles surrounding the mouth	Skin and muscles around the mouth	Closes and protrudes lips (kissing, whistling)	CN VII
Zygomaticus Major	Zygomatic bone	Corner of mouth	Draws corner of mouth upward and laterally (smiling)	CN VII
Zygomaticus Minor	Zygomatic bone	Upper lip	Elevates upper lip	CN VII
Levator Labii Superioris	Infraorbital margin of maxilla	Upper lip	Elevates upper lip	CN VII
Depressor Anguli Oris	Mandible (oblique line)	Corner of mouth	Draws corner of mouth downward (frowning)	CN VII
Depressor Labii Inferioris	Mandible (oblique line)	Lower lip	Depresses and everts lower lip	CN VII
Mentalis	Mandible (incisive fossa)	Skin of chin	Elevates and protrudes lower lip, wrinkles chin skin (pouting)	CN VII
Buccinator	Maxilla, mandible (alveolar processes), pterygomandibular raphe	Orbicularis oris	Compresses cheek against teeth (chewing, whistling)	CN VII
Platysma	Fascia of upper chest and shoulder	Mandible, skin of lower face	Tenses skin of neck, depresses mandible	CN VII

B. Mastication:

Muscle	Origin	Insertion	Action	Innervation
Masseter	Zygomatic arch	Mandibular ramus and angle	Elevates mandible (closes jaw)	CN V3
Temporalis	Temporal fossa	Coronoid process of mandible	Elevates and retracts mandible	CN V3
Medial Pterygoid	Medial pterygoid plate of sphenoid bone	Mandibular ramus and angle (medial)	Elevates, protrudes, and laterally moves mandible	CN V3
Lateral Pterygoid	Lateral pterygoid plate of sphenoid bone	Condyle of mandible	Protracts and laterally moves mandible (opens jaw)	CN V3

C. Suprahyoid:

Muscle	Origin	Insertion	Action	Innervation
Digastric	Anterior: Mandible; Posterior: Mastoid process	Hyoid bone	Elevates hyoid bone, depresses mandible	CN V3, CN VII
Stylohyoid	Styloid process	Hyoid bone	Elevates and retracts hyoid bone	CN VII
Mylohyoid	Mylohyoid line of mandible	Hyoid bone	Elevates hyoid bone and floor of mouth, depresses mandible	CN V3
Geniohyoid	Mandible (mental spine)	Hyoid bone	Elevates hyoid bone, depresses mandible	C1 via CN XII

D. Infrahyoid:

Muscle	Origin	Insertion	Action	Innervation
Sternohyoid	Sternum	Hyoid bone	Depresses hyoid bone	Ansa Cervicalis
Omohyoid	Scapula	Hyoid bone	Depresses hyoid bone	Ansa Cervicalis
Sternothyroid	Sternum	Thyroid cartilage	Depresses thyroid cartilage	Ansa Cervicalis
Thyrohyoid	Thyroid cartilage	Hyoid bone	Depresses hyoid bone, elevates thyroid cartilage	C1 via CN XII

E. Anterior & Posterior Neck:

Muscle	Origin	Insertion	Action	Innervation
Sternocleidomastoid	Sternum, clavicle	Mastoid process	Unilateral: Tilts head to same side, rotates to opposite side; Bilateral: Flexes neck	CN XI, C2-C3
Scalenes	Cervical vertebrae	Ribs 1 & 2	Elevates ribs during forced inspiration, bends neck to same side	Cervical spinal nerves
Trapezius	Occipital bone, spinous processes of cervical and thoracic vertebrae	Scapula, clavicle	Elevates/rotates scapula, extends/laterally flexes neck (upper fibers)	CN XI, C3-C4
Splenius Capitis	Spinous processes of cervical and thoracic vertebrae	Occipital bone	Extends and rotates head	Cervical spinal nerves
Splenius Cervicis	Spinous processes of thoracic vertebrae	Cervical vertebrae	Extends and rotates neck	Cervical spinal nerves
Semispinalis Capitis	Transverse processes of cervical and thoracic vertebrae	Occipital bone	Extends head, rotates it to opposite side	Cervical spinal nerves
Suboccipitals	Various (see detailed breakdown above)	Occipital bone, C1, C2	Fine motor control of head movements (extension, rotation, lateral flexion)	Suboccipital nerve (C1)

X. Frequently Asked Questions (FAQ)

• Q: How can I best memorize the origins and insertions of these muscles?

  • A: Focus on the major bony landmarks. Group muscles based on their attachments to specific bones (e.g., hyoid bone, mandible, occipital bone). Use visual aids and mnemonic devices. Repetition and active recall are key.

• Q: What is the significance of the hyoid bone?

  • A: The hyoid bone is unique because it does not articulate with any other bone. It serves as an attachment point for many muscles of the head and neck, playing a crucial role in swallowing and speech.

• Q: Why are the muscles of facial expression innervated by the facial nerve (CN VII)?

  • A: All muscles of facial expression are derived from the second pharyngeal arch during embryonic development, which is innervated by the facial nerve.

• Q: What is the difference between protraction and retraction of the mandible?

  • A: Protraction refers to moving the mandible forward, while retraction refers to moving it backward. The lateral pterygoid muscle is primarily responsible for protraction, while the temporalis muscle assists in retraction.

• Q: How are the suboccipital muscles unique?

  • A: They are deep posterior neck muscles primarily involved in fine motor control of head movements. They are located below the occipital bone and are innervated by the suboccipital nerve (C1). Understanding these muscles is key for treating certain types of headaches and neck pain.

XI. Conclusion

Mastering the muscles of the head and neck requires dedicated study and a systematic approach. By focusing on nerve supply, action, location, and clinical significance, you can build a strong foundation for understanding this complex and vital anatomical region. This review sheet provides a comprehensive overview to guide your learning and prepare you for success in your studies and future clinical practice.