Lecture 11 Notes — Myology: Head & Neck (ANAT1005)

Etymology and Key Terms

  • Useful word roots and technical terms referenced in the module:
    • Intrinsic (E = ‘within, part of’)
    • Extrinsic (E = ‘outside, external but related’)
    • Intra (L = ‘within, inside’)
    • Extra (L = ‘outside, more, beyond, besides’)
    • Inter (L = ‘between, among’)
    • Oblique (L) = angled/diagonal
    • Rect- (L) = straight
    • Scalene (G) = uneven (e.g., Scalene triangle)
    • Orbi- (L) = ring
    • -cula/-icle (L) = little (orbicularis = little ring)
    • Ipsi- (L) = self/same
    • Contra- (L) = against/opposition
    • Zygo- (L) = yoke (not yolk!)
    • Masticat- (L) = chew
    • Sterno- (G) = breastbone
    • Cleido- (G) = key
    • Clavi- (L) = key (clavicle = little key)
    • Masto- (G) = breast/mound
    • -oid (G) = form, shaped-like
    • Capit-/caput- (L) = head
    • Colli (L) = neck (as in “collar”)
    • Hyo- (G) = ‘U’ shaped (also ‘Y’ shaped)
    • Pharynx (G) = throat
    • Larynx (G) = windpipe/throat
  • Blue text in the slides indicates terms seen in previous lists.

Learning Outcomes

  • By the end of the module, you should be able to:
    • Identify and describe the major muscles (including origins and insertions) of:
    • Facial expression
    • Extrinsic eye muscles
    • Mastication
    • Neck (superior anterior & deep vertebral)
    • Relate the structure of these muscles to their function
    • Describe the action of these muscles
  • Specific categories:
    • 1. Facial Expression
    • 2. Extrinsic Eye
    • 3. Mastication (chewing)
    • 4. Neck (superficial anterior & deep vertebral)

Classification and Scope of the Head & Neck Muscles

  • Classification of muscles of the head & neck:
    1) Facial Expression (CN VII)
    2) Extrinsic eye muscles
    3) Mastication (CN V)
    4) Superficial anterior neck
    5) Deep neck muscles of the vertebral column
  • Next lecture: Posterior neck (and back)
  • Not in this course: Muscles of the tongue; muscles of the pharynx/larynx
  • Also not in this module: Intrinsic eye muscles; muscles of the middle ear (tiny, associated with vision and hearing)

Contents / Scope of the Module

  • 1. Muscles of Facial Expression
    • A. Facial muscles near the mouth
    • B. Facial muscles near the eye
  • 2. Extrinsic Eye Muscles
    • A. Identifying the extrinsic eye muscles
    • B. Eye movements
  • 3. Muscles of Mastication
  • 4. Anterolateral muscles neck
  • 5. Deep Neck Muscles of the Vertebral Column

Skeletal Muscles and Basic Anatomy

  • Skeletal muscles are categorized as axial or appendicular:
    • Axial: Stabilise or move elements of the axial body
    • Appendicular: Stabilise or move the appendicular body
  • Attachment concepts (Origin vs Insertion):
    • Origin: attachment to the fixed/stable part; on limbs usually proximal; on torso often inferior attachment
    • Insertion: attachment to the part being moved; on limbs usually distal; on torso often superior attachment
  • These concepts are used to describe how muscles move bones and soft tissues during activity

1. Muscles of Facial Expression

  • General characteristics:
    • Move the highly mobile soft tissue of the face for communication; also functional roles (drinking, sucking, etc.)
    • Attachments: skull at one end and soft tissues at the other
    • Not bound by deep fascia; attach directly to skin/subcutaneous tissue
    • Tend to be thin and delicate; some have strap & orbicular shape
    • Actions mapped by electrical stimulation studies
    • Innervation: facial nerve (Cranial nerve VII, CN VII)
  • 1B – Facial muscles near the mouth
    • Platysma
    • Origin: fascia near scapula and clavicle
    • Insertion: skin near the mandible
    • Innervation: Facial Nerve (CN VII)
    • The modiolus
    • A dense, compact, mobile fibromuscular mass at the angle of the mouth where approx. nine facial expression muscles converge
    • Important for: chewing, biting, drinking, sucking, swallowing, speech, modulation of musical tones, shouting, screaming, crying, facial expression
    • Orbicularis oris
    • SHAPE: Circular (two strap-like structures running between the modioli in this course)
    • ARCHITECTURE: Circular
    • Origin: Skin
    • Insertion: Mucous membrane of lips
    • Function: Compresses and protrudes lips
    • Expression: Kiss
    • Zygomaticus major
    • SHAPE: Strap-like
    • ARCHITECTURE: Parallel fibres
    • Origin: Zygomatic bone
    • Insertion: Modiolus (skin and muscle at the corner of the mouth)
    • Function: Draws corners of mouth laterally and superiorly
    • Expression: Smile
    • Buccinator
    • Orientation: Transverse and anterior; quadrilateral; deepest extrinsic muscle of lips
    • Fibres course anteriorly and medially; central fibres may decussate
    • Origin: Pterygomandibular raphe and lateral surface of the alveolar process of maxilla and mandible in molar region
    • Insertion: Blends with orbicularis oris and submucosa
    • Function: Compresses cheeks against teeth and draws corners of mouth laterally
    • Expression: Disgust (Grey text: not assessed in ANAT1005)
    • Interpreting note: The buccinator is a mesh-like structure that provides strength; it is NOT a muscle of mastication, though it assists mastication by controlling food position during chewing
  • 1B – Facial muscles near the eyes
    • Epicranius (Occipitofrontalis)
    • SHAPE: Sheet
    • ARCHITECTURE: Parallel
    • Components: Frontalis (frontal belly) + Occipitalis (occipital belly) + Epicranial aponeurosis
    • Function: Moves scalp posteriorly; raises eyebrows; wrinkles forehead; antagonist of orbicularis oculi; expression: Surprise
    • Frontalis
    • Origin: Galea aponeurotica (epicranial aponeurosis)
    • Insertion: Supraorbital muscles and skin of the eyebrows and root of the nose
    • Function: Moves scalp, raises eyebrows; contributes to facial expression
    • Orbicularis oculi
    • Structure: Thin, flat, elliptical sphincter muscle in three parts: orbital, palpebral, lacrimal
    • Orbital origin: Medial margin of orbit (frontal bone and maxilla)
    • Palpebral origin: Medial palpebral ligament, contained in eyelids
    • Function: Closes eye (blinking)
    • Expression: Pain, wincing
    • Levator palpebrae superioris
    • FUNCTION: Elevates the superior eyelid (palpebrae)
    • Does not attach to the eyeball
    • Innervation: Oculomotor Nerve (CN III)
    • Note: This is the only muscle of facial expression not innervated by CN VII; has more in common with Extrinsic Eye Muscles than with the facial muscles, but does not move the eye
  • Summary of facial expression muscles significance:
    • They coordinate with the modiolus and orbicularis oris to shape social communication, food handling, and protective reflexes
    • The eyebrow and forehead muscles (frontalis, eyelid closures) contribute to expression and nonverbal cues

2. Extrinsic Eye Muscles

  • Purpose: Control the position of the eye; allow gaze in various directions
  • Composition:
    • 4 rectus (rectus = straight)
    • 2 oblique (oblique = diagonal)
    • For Module 3: Most are innervated by oculomotor nerve (CN III) except:
    • Superior oblique (CN IV – trochlear nerve)
    • Lateral rectus (CN VI – abducens nerve)
  • Muscles and primary actions (simplified):
    • Superior rectus: elevation
    • Inferior rectus: depression
    • Lateral rectus: abduction
    • Medial rectus: adduction
    • Superior oblique: depression
    • Inferior oblique: elevation
  • Anatomical references:
    • Common tendinous ring; optic nerve; trochlea; base of skull references
    • Lateral view, anterior view, and superior views illustrate muscle paths and insertions
  • Movements and axes:
    • Movements are described relative to sagittal and coronal axes; the trochlea acts as a pulley for the superior oblique
  • Clinical testing (visual):
    • Clinician asks patient to perform eye movements such as abduction, adduction, etc. to evaluate function of each muscle
  • Key notes:
    • The eye muscles are arranged to permit coordinated gaze in multiple directions; dysfunction can affect eye movements and vision alignment

3. Muscles of Mastication

  • General group: A cluster of muscles that move the temporomandibular joint (TMJ)
  • Muscles:
    • Superficial: Temporalis; Masseter
    • Deep: Medial pterygoid; Lateral pterygoid
  • Innervation: Trigeminal nerve (CN V)
  • TMJ anatomy and movements:
    • The condylar head of the ramus of the mandible sits in the mandibular (glenoid) fossa of the temporal bone
    • The TMJ is a modified hinge joint that allows both hinge and sliding movements
    • Movements enabled:
    • Elevation
    • Depression
    • Protrusion (protraction)
    • Retrusion (retraction)
    • Lateral deviation (excursion)
  • Individual muscles (origin, insertion, function, innervation, and architecture):
    • Masseter
    • Origin: Zygomatic arch and zygomatic bone
    • Insertion: Lateral surface of mandibular ramus and angle
    • Function: Elevation, protrusion, lateral deviation of the mandible
    • Innervation: Trigeminal nerve (CN V)
    • External shape: Quadrate
    • Internal architecture: Multipennate
    • Grey text: not assessed in ANAT1005
    • Temporalis
    • Origin: Temporal lines/fascia, temporal fossa
    • Insertion: Coronoid process of the mandible
    • Function: Elevation, retraction, lateral deviation
    • Innervation: CN V
    • Architecture: Convergent (external); Bipennate (internal, transverse section)
    • Grey text: not assessed in ANAT1005
    • Medial pterygoid
    • Origin: Medial side of the lateral pterygoid plate (sphenoid bone)
    • Insertion: Medial surface of mandibular angle
    • Function: Elevation, protrusion, lateral deviation of the mandible
    • Architecture: Multipennate
    • Innervation: CN V
    • Lateral pterygoid
    • Origin: Lateral side of the lateral pterygoid plate
    • Insertion: Medial surface of TMJ and neck of the mandible
    • Function: Protrusion, lateral deviation (superior head also elevates)
    • Architecture: NA (not specified here)
    • Innervation: CN V
  • Important concept: The action of the masticatory muscles is to manipulate the mandible to achieve chewing and jaw movements necessary for eating and vocalization

4. Anterolateral Muscles of the Neck

  • Sternocleidomastoid (SCM)
    • Origin: Manubrium and medial portion of the clavicle
    • Insertion: Mastoid process of the temporal bone
    • Function:
    • Unilateral action: Lateral flexion of the neck to the same side and rotation of the face to the opposite side (and upwards)
    • Bilateral action: Flexes the lower neck and extends the upper neck & head
    • Innervation: Accessory nerve (CN XI)
  • Suprahyoid group (attach to the hyoid and either mandible or temporal bone)
    • If mandible fixed: elevate hyoid (swallowing)
    • If hyoid fixed: depress mandible (mastication)
    • Key muscles often listed: Digastric, Mylohyoid, Geniohyoid, Stylohyoid
  • Infrahyoid group (attach to hyoid, thyroid cartilage, and sternum)
    • Key muscles: Sternohyoid, Sternothyroid, Thyrohyoid
  • General notes:
    • These muscles contribute to swallowing, speech, and positioning of the hyoid bone and larynx, facilitating coordinated movements of the jaw and neck
  • Scalenes (anterior, middle, posterior)
    • Origin: Transverse processes of cervical vertebrae
    • Insertion: Ribs 1 and 2
    • Function: Elevates ribs 1 and 2; flexes and rotates the neck
    • Note: Located deep to the SCM; contribute to accessory breathing movements

5. Deep Neck Muscles of the Vertebral Column (Suboccipital Group)

  • Deep posterior neck muscles (postural) – four pairs (suboccipital group)
    • Rectus capitis posterior major
    • Rectus capitis posterior minor
    • Obliquus capitis inferior
    • Obliquus capitis superior
  • Actions of the group:
    • Extend the atlanto-occipital joint (yes, look up)
    • Rotate the atlanto-axial joint (no, look to the side)
  • Note: The suboccipital muscles lie deep to the occipital bone and are arranged to support head posture and fine movements

Additional Context and Notable Points

  • The module emphasizes the relationship between muscle structure and function, including:
    • Attachment patterns (origin vs insertion) as a predictor of action
    • The role of fascia and skin attachments in facial expression muscles
    • The distinction between muscles that move facial soft tissue versus those that move bones/joints
  • Notable anatomical relationships:
    • Modiolus as a central convergence point at the mouth angle enabling complex facial movements
    • The epicranius as a two-bellied muscle with an aponeurosis that moves the scalp and eyebrows
    • Levator palpebrae superioris as a facial-expression-related muscle that nonetheless acts like an eye muscle (CN III innervation)
  • Grey vs blue text on slides indicates assessed vs not assessed content (e.g., Grey text: not assessed in ANAT1005)

Clinical and Exam Preparation Notes

  • Practical focus areas for exams (as reflected in SAQs):
    • Describe the four muscles of mastication with each muscle’s origin, insertion, and primary action
    • Describe the main muscle of the cheek with origin, insertion, and primary action
    • Describe five muscles of facial expression with their attachment/position and primary function
  • Remember the structure-function relationships and the role of the mandible and TMJ movements in daily activities such as chewing and speaking

Next Lecture Preview

  • Next lecture topic: Myology of the Back, Thorax & Abdomen (L12)
  • Reference text: Marieb et al. (2020) 9th ed, Chapter 11 – Muscles of the Body; sections 11.3 and 11.3b (Tables 11.4–11.7)

SAQ Reference (from Slide 49)

  • 1. a) Describe the 4 muscles of mastication (name, origin, insertion, primary action) [4 marks]
  • 1. b) Describe the main muscle of the “cheek” with origin, insertion, and primary action [1 mark]
  • 2. Describe 5 muscles of facial expression with names, attachments/positions, and primary function

Quick Reference Table (Mnemonic Aids)

  • Facial expression regions: mouth (orbicularis oris, zygomaticus major, buccinator) and eyes (orbicularis oculi, levator palpebrae superioris, frontalis)
  • Mastication muscles: Masseter (cheek area, zygomatic arch), Temporalis (temporal fossa), Medial and Lateral Pterygoids (sphenoid region)
  • Eye movements: 4 rectus, 2 obliques with CN III, IV, VI innervation
  • Neck regions: SCM, scalenes, suprahyoid and infrahyoid groups, suboccipital muscles