Comprehensive Bullet-Point Notes – Head & Neck Muscles

Muscle Types

  • Skeletal (striated) muscle
    • Voluntary, somatic
    • Forms almost all muscles that move or stabilize the skeleton
    • Cells: striated, tubular, multinucleated
    • Usually attached to bones
  • Cardiac (striated) muscle
    • Involuntary, visceral
    • Walls of heart + origins of great vessels
    • Cells: striated, tubular, branched, uninucleated
  • Smooth (un-striated) muscle
    • Involuntary, visceral
    • Walls of most vessels & hollow organs
    • Cells: narrow, tapered (rod-shaped), non-striated, uninucleated

Basic Muscle Anatomy & Connective Tissues

  • Tendon
    • Tough band of fibrous C.T.; connects muscle → bone
    • Serves as attachment site
  • Origin
    • Attachment that remains relatively fixed during contraction
    • Generally proximal
  • Insertion
    • Attachment that moves during contraction
    • Generally distal
  • Belly
    • Fleshy, contractile portion between the attachments
  • Ligament: fibrous tissue connecting bone → bone
  • Aponeurosis: flat, broad, sheet-like tendon

Lever Example – Biceps Brachii (Page 6)

  • Effort (E): contraction of biceps brachii
  • Fulcrum (F): elbow joint
  • Resistance (R): weight of forearm + external load
  • Insertion: radial tuberosity via tendon
  • Demonstrates a third-class lever (E placed between F & R) producing forearm flexion

Fascial System

  • Fascia = fibrous tissue investing & separating muscles, vessels, nerves
    • Provides friction-free gliding during movement

Arrangement of Fascicles (Fiber Orientation)

  • Parallel
    • Fibers parallel to long axis; terminate in flat tendons
  • Fusiform
    • Nearly parallel; belly wider than tendons → spindle shape (e.g., Stylohyoid)
  • Circular
    • Concentric rings forming sphincters (e.g., Orbicularis oculi)
  • Triangular (Convergent)
    • Broad origin, converge to thick tendon (e.g., Pectoralis major)
  • Pennate (short fibers, long tendon)
    • Unipennate – fibers on one side (e.g., Extensor digitorum longus)
    • Bipennate – fibers on both sides (e.g., Rectus femoris)
    • Multipennate – many tendons with oblique fibers (e.g., Deltoid)

Functional Coordination of Muscles

  • Agonist (Prime Mover) – produces desired motion
  • Antagonist – opposes or controls movement; relaxes while agonist contracts
  • Synergist – assists agonist, fine-tunes direction or force
  • Fixator – stabilizes origin, permitting efficient action

Mimetic (Facial Expression) Muscles

Around the Eye

  • Orbicularis oculi
    • Parts: pars palpebralis, pars orbitalis, pars lacrimalis
    • Origin / Insertion: circular around orbit; medial palpebral ligament; lacrimal crest
    • Action: closes eyelids; pars lacrimalis enlarges lacrimal sac
    • Nerve: Facial (CN VII)
  • Corrugator supercilii – draws eyebrows medially/inferiorly → vertical glabellar lines
  • Procerus – pulls medial brow inferiorly → transverse wrinkles over root of nose

Around the Mouth (All innervated by Facial n.)

  • Orbicularis oris – closes & protrudes lips (puckering)
  • Levator labii superioris – elevates upper lip
  • Levator labii superioris alaeque nasi – elevates upper lip & dilates nostril
  • Levator anguli oris – elevates oral angle
  • Zygomaticus major & minor – draw angle of mouth superolaterally (smile)
  • Risorius – retracts angle of mouth laterally
  • Buccinator – compresses cheek (sucking, blowing), keeps food between molars
  • Depressor anguli oris – depresses mouth angle
  • Depressor labii inferioris – depresses lower lip
  • Mentalis – elevates skin of chin, protrudes lower lip

Nasal Muscle

  • Nasalis – compresses nostrils (alar part can dilate)

Epicranial Group

  • Occipitofrontalis
    • Occipital belly: tenses scalp posteriorly, smooths forehead wrinkles
    • Frontal belly: raises eyebrows, creates transverse forehead wrinkles
  • Temporoparietalis – elevates auricle (ear) cranially

Muscles of Mastication (CN V₃ – Mandibular division of Trigeminal)

  • Temporalis
    • Origin: temporal fossa to inferior temporal line & deep temporal fascia
    • Insertion: coronoid process of mandible
    • Action: elevation & retrusion of mandible
  • Masseter
    • Superficial head: zygomatic bone/arch (ant ⅔) → masseteric tuberosity; elevates & protrudes
    • Deep head: posterior ⅓ of arch → mandibular ramus; elevates & retrudes
  • Medial pterygoid
    • Medial head: pterygoid fossa → pterygoid tuberosity; elevation
    • Lateral head: maxillary tuber → same insertion; assists elevation
  • Lateral pterygoid
    • Superior head: infratemporal surface of sphenoid → articular disc & pterygoid fovea
    • Inferior head: lateral pterygoid plate → disc & fovea
    • Action: protrusion & depression (opens mouth); unilateral action → contralateral deviation

Cervical Muscles

Superficial Layer

  • Platysma (CN VII)
    • Origin: pectoral & deltoid fascia → skin over mandible base
    • Action: tenses cervical skin
  • Sternocleidomastoid (SCM) (Spinal Accessory n. + C2-3)
    • Origin: manubrium & medial ⅓ clavicle
    • Insertion: mastoid process, superior nuchal line
    • Bilateral: head/neck extension (dorsiflexion) & flexion; Unilateral: ipsilateral lateral flexion & contralateral rotation; accessory inspiration

Scalene Group (Cervical Plexus)

  • Anterior & Medius: C-transverse processes → 1st rib
  • Posterior: C-transverse processes → 2nd rib
  • Actions: lateral flexion, slight rotation; bilaterally flex neck; accessory inspiration

Suprahyoid Group

  • Mylohyoid (n. to Mylohyoid)
  • Digastric
    • Posterior belly – CN VII; elevates hyoid
    • Anterior belly – n. to Mylohyoid; depresses mandible when hyoid fixed
  • Stylohyoid (CN VII) – elevates & retracts hyoid
  • Geniohyoid (C1-C2 via hypoglossal) – depresses mandible / elevates hyoid

Infrahyoid Group (Ansa cervicalis)

  • Sternohyoid – depresses hyoid & larynx
  • Sternothyroid – depresses larynx
  • Thyrohyoid – depresses hyoid, elevates larynx when hyoid fixed
  • Omohyoid
    • Inferior belly: scapular margin → intermediate tendon
    • Superior belly: tendon → hyoid
    • Depresses hyoid & larynx

Prevertebral Muscles (Cervical Plexus)

  • Longus colli – bodies & TPs of C-vertebrae → anterior arch; flexes/laterally flexes neck
  • Longus capitis – C-TPs → basilar occipital bone
  • Rectus capitis anterior & lateralis – atlas TP → occipital bone
  • Actions: bilateral flexion; unilateral lateral flexion

Suboccipital Group (brief)

  • Rectus capitis posterior major/minor, Obliquus capitis superior/inferior – fine posture & rotation control of atlanto-occipital & atlanto-axial joints; innervated by dorsal ramus of C1 (suboccipital n.)

Cervical Fasciae

  • Superficial fascia – directly deep to skin
  • Deep cervical fascia subdivided into:
    • Deep (Investing) layer
    • Encircles entire neck; splits to envelop SCM & trapezius
    • Superior attachments: inferior mandible, hyoid body (inf. border), mandible angle, zygomatic arch’s inferior border, mastoid & styloid processes
    • Inferior attachments: manubrium, clavicles, scapular spine
    • Visceral (Pretracheal) fascia
    • Surrounds visceral compartment (trachea, esophagus, thyroid)
    • Superior: hyoid bone → base of skull
    • Inferior: descends into superior mediastinum → blends with pericardium
    • Prevertebral fascia
    • Encloses cervical vertebrae & associated muscles
    • Superior: base of skull
    • Inferior: fuses with investing fascia of back muscles & anterior longitudinal ligament of thoracic spine
    • Anterior division splits → Alar fascia
      • Extends laterally to transverse processes, forming retropharyngeal space boundary

Key Functional & Clinical Correlations

  • Facial muscles insert into skin → produce expressions; paralysis (e.g., Bell’s palsy) impairs non-verbal communication & oral competence
  • Mastication muscles generate large forces; disorders (TMJ dysfunction) often involve lateral pterygoid overactivity
  • Infrahyoid & suprahyoid synergy critical for swallowing & phonation
  • Scalene hypertrophy or cervical rib may compress brachial plexus → thoracic outlet syndrome
  • Fascial planes create potential spaces (e.g., retropharyngeal) for infection spread from neck to mediastinum

Summary Check-List for Exam

  • Identify three muscle tissue types & their microscopic traits
  • Define origin, insertion, belly, tendon, ligament, aponeurosis
  • Recognize fascicle arrangements & give one example of each
  • Explain lever mechanics of elbow flexion (class III lever)
  • List roles of agonist, antagonist, synergist, fixator
  • For each facial expression muscle: origin, insertion, action, CN VII innervation
  • Mastication muscles: origin, insertion, action, CN V₃
  • Neck layers: superficial, suprahyoid, infrahyoid, prevertebral, SCM, scalene – actions & nerves
  • Map deep cervical fascia layers & clinical spaces
  • Apply clinical examples (Bell’s palsy, TMJ, thoracic outlet, deep-neck infections).

Muscle Types

  • Skeletal (striated) muscle
    • Voluntary, somatic
    • Forms almost all muscles that move or stabilize the skeleton
    • Cells: striated, tubular, multinucleated
    • Usually attached to bones
  • Cardiac (striated) muscle
    • Involuntary, visceral
    • Walls of heart + origins of great vessels
    • Cells: striated, tubular, branched, uninucleated
  • Smooth (un-striated) muscle
    • Involuntary, visceral
    • Walls of most vessels & hollow organs
    • Cells: narrow, tapered (rod-shaped), non-striated, uninucleated

Basic Muscle Anatomy & Connective Tissues

  • Tendon
    • Tough band of fibrous C.T.; connects muscle → bone
    • Serves as attachment site
  • Origin
    • Attachment that remains relatively fixed during contraction
    • Generally proximal
  • Insertion
    • Attachment that moves during contraction
    • Generally distal
  • Belly
    • Fleshy, contractile portion between the attachments
  • Ligament: fibrous tissue connecting bone → bone
  • Aponeurosis: flat, broad, sheet-like tendon

Lever Example – Biceps Brachii (Page 6)

  • Effort (E): contraction of biceps brachii
  • Fulcrum (F): elbow joint
  • Resistance (R): weight of forearm + external load
  • Insertion: radial tuberosity via tendon
  • Demonstrates a third-class lever (E placed between F & R) producing forearm flexion

Fascial System

  • Fascia = fibrous tissue investing & separating muscles, vessels, nerves
    • Provides friction-free gliding during movement

Arrangement of Fascicles (Fiber Orientation)

  • Parallel
    • Fibers parallel to long axis; terminate in flat tendons
  • Fusiform
    • Nearly parallel; belly wider than tendons → spindle shape (e.g., Stylohyoid)
  • Circular
    • Concentric rings forming sphincters (e.g., Orbicularis oculi)
  • Triangular (Convergent)
    • Broad origin, converge to thick tendon (e.g., Pectoralis major)
  • Pennate (short fibers, long tendon)
    • Unipennate – fibers on one side (e.g., Extensor digitorum longus)
    • Bipennate – fibers on both sides (e.g., Rectus femoris)
    • Multipennate – many tendons with oblique fibers (e.g., Deltoid)

Functional Coordination of Muscles

  • Agonist (Prime Mover) – produces desired motion
  • Antagonist – opposes or controls movement; relaxes while agonist contracts
  • Synergist – assists agonist, fine-tunes direction or force
  • Fixator – stabilizes origin, permitting efficient action

Mimetic (Facial Expression) Muscles

Around the Eye
  • Orbicularis oculi
    • Parts: pars palpebralis, pars orbitalis, pars lacrimalis
    • Origin / Insertion: circular around orbit; medial palpebral ligament; lacrimal crest
    • Action: closes eyelids; pars lacrimalis enlarges lacrimal sac
    • Nerve: Facial (CN VII)
  • Corrugator supercilii – draws eyebrows medially/inferiorly → vertical glabellar lines
  • Procerus – pulls medial brow inferiorly → transverse wrinkles over root of nose
Around the Mouth (All innervated by Facial n.)
  • Orbicularis oris – closes & protrudes lips (puckering)
  • Levator labii superioris – elevates upper lip
  • Levator labii superioris alaeque nasi – elevates upper lip & dilates nostril
  • Levator anguli oris – elevates oral angle
  • Zygomaticus major & minor – draw angle of mouth superolaterally (smile)
  • Risorius – retracts angle of mouth laterally
  • Buccinator – compresses cheek (sucking, blowing), keeps food between molars
  • Depressor anguli oris – depresses mouth angle
  • Depressor labii inferioris – depresses lower lip
  • Mentalis – elevates skin of chin, protrudes lower lip
Nasal Muscle
  • Nasalis – compresses nostrils (alar part can dilate)
Epicranial Group
  • Occipitofrontalis
    • Occipital belly: tenses scalp posteriorly, smooths forehead wrinkles
    • Frontal belly: raises eyebrows, creates transverse forehead wrinkles
  • Temporoparietalis – elevates auricle (ear) cranially

Muscles of Mastication (CN V₃ – Mandibular division of Trigeminal)

  • Temporalis
    • Origin: temporal fossa to inferior temporal line & deep temporal fascia
    • Insertion: coronoid process of mandible
    • Action: elevation & retrusion of mandible
  • Masseter
    • Superficial head: zygomatic bone/arch (ant ⅔) → masseteric tuberosity; elevates & protrudes
    • Deep head: posterior ⅓ of arch → mandibular ramus; elevates & retrudes
  • Medial pterygoid
    • Medial head: pterygoid fossa → pterygoid tuberosity; elevation
    • Lateral head: maxillary tuber → same insertion; assists elevation
  • Lateral pterygoid
    • Superior head: infratemporal surface of sphenoid → articular disc & pterygoid fovea
    • Inferior head: lateral pterygoid plate → disc & fovea
    • Action: protrusion & depression (opens mouth); unilateral action → contralateral deviation

Cervical Muscles

Superficial Layer
  • Platysma (CN VII)
    • Origin: pectoral & deltoid fascia → skin over mandible base
    • Action: tenses cervical skin
  • Sternocleidomastoid (SCM) (Spinal Accessory n. + C2-3)
    • Origin: manubrium & medial ⅓ clavicle
    • Insertion: mastoid process, superior nuchal line
    • Bilateral: head/neck extension (dorsiflexion) & flexion; Unilateral: ipsilateral lateral flexion & contralateral rotation; accessory inspiration
Scalene Group (Cervical Plexus)
  • Anterior & Medius: C-transverse processes → 1st rib
  • Posterior: C-transverse processes → 2nd rib
  • Actions: lateral flexion, slight rotation; bilaterally flex neck; accessory inspiration
Suprahyoid Group
  • Mylohyoid (n. to Mylohyoid)
  • Digastric
    • Posterior belly – CN VII; elevates hyoid
    • Anterior belly – n. to Mylohyoid; depresses mandible when hyoid fixed
  • Stylohyoid (CN VII) – elevates & retracts hyoid
  • Geniohyoid (C1-C2 via hypoglossal) – depresses mandible / elevates hyoid
Infrahyoid Group (Ansa cervicalis)
  • Sternohyoid – depresses hyoid & larynx
  • Sternothyroid – depresses larynx
  • Thyrohyoid – depresses hyoid, elevates larynx when hyoid fixed
  • Omohyoid
    • Inferior belly: scapular margin → intermediate tendon
    • Superior belly: tendon → hyoid
    • Depresses hyoid & larynx
Prevertebral Muscles (Cervical Plexus)
  • Longus colli – bodies & TPs of C-vertebrae → anterior arch; flexes/laterally flex neck
  • Longus capitis – C-TPs → basilar occipital bone
  • Rectus capitis anterior & lateralis – atlas TP → occipital bone
  • Actions: bilateral flexion; unilateral lateral flexion
Suboccipital Group (brief)
  • Rectus capitis posterior major/minor, Obliquus capitis superior/inferior – fine posture & rotation control of atlanto-occipital & atlanto-axial joints; innervated by dorsal ramus of C1 (suboccipital n.)

Cervical Fasciae

  • Superficial fascia – directly deep to skin
  • Deep cervical fascia subdivided into:
    • Deep (Investing) layer
    • Encircles entire neck; splits to envelop SCM & trapezius
    • Superior attachments: inferior mandible, hyoid body (inf. border), mandible angle, zygomatic arch’s inferior border, mastoid & styloid processes
    • Inferior attachments: manubrium, clavicles, scapular spine
    • Visceral (Pretracheal) fascia
    • Surrounds visceral compartment (trachea, esophagus, thyroid)
    • Superior: hyoid bone → base of skull
    • Inferior: descends into superior mediastinum → blends with pericardium
    • Prevertebral fascia
    • Encloses cervical vertebrae & associated muscles
    • Superior: base of skull
    • Inferior: fuses with investing fascia of back muscles & anterior longitudinal ligament of thoracic spine
    • Anterior division splits → Alar fascia
    • Extends laterally to transverse processes, forming retropharyngeal space boundary

Key Functional & Clinical Correlations

  • Facial muscles insert into skin → produce expressions; paralysis (e.g., Bell’s palsy) impairs