Study Notes on Muscles of the Face, Teeth, Tongue, and Sensory Innervation

MUSCLES OF THE FACE

Introduction

• Facial muscles are situated within the subcutaneous tissues and are responsible for the movement of skin folds, creating different facial expressions.
• They originate from the bones of facial expression and insert into the skin.

Major Muscles of the Face

• Orbicularis oculi
• Zygomaticus major
• Zygomaticus minor
• Risorius
• Buccinator
• Mentalis
• Depressor anguli oris
• Depressor labii inferioris
• Levator anguli oris
• Levator labii superioris
• Corrugator supercilii
• Procerus
• Transverse part of nasalis
• Ala part of nasalis
• Depressor septi nasi

Detailed Descriptions of Selected Muscles

Orbicularis Oculi

• Definition: The sphincter of the eye, comprising three parts:
  • Orbital part:
  • Actions: Forcibly closes the eyes.
  • Palpebral part:
  • Origin: Medial palpebral ligament.
  • Insertion: Lateral palpebral ligament.
  • Actions: Gently closes the eyelids.
  • Lacrimal part:
  • Origin: Posterior lacrimal crest.
  • Actions: Closes and dilates the lacrimal sac for drainage.
• Clinical Anatomy:
  • Injury to the facial nerve affects the orbicularis oculi, leading to:
  1. Exposure Keratitis: Inability of the eye to shut, resulting in drying of the cornea.
  2. Ectropion: Drooping of the lower eyelid, causing tears pooling and inability to spread them across the eye's surface.

Orbicularis Oris

• Definition: A sphincter formed by fibers surrounding the mouth, playing a crucial role in lip movements.
• Actions:
  1. Closes the mouth.
  2. Compresses the lips against the teeth.
  3. Aids in speech, whistling, and kissing.
• Nerve Supply: Branches of the facial nerve.

Buccinator

• Definition: A quadrilateral muscle acting on the cheeks.
• Origin: Alveolar margin of maxilla and mandible opposite the third molar teeth.
• Insertion: Angle of the mouth; it occupies the space between the mandibular and maxillary bones, forming a critical part of the cheek.
• Actions:
  1. Facilitates mastication by keeping food in place.
  2. Prevents food accumulation in the vestibule of the mouth.
  3. Expels air distending the cheeks.
  4. Used in whistling and suckling.
• Nerve Supply: Buccal branch of the facial nerve.

TEETH AND MASTICATION

Introduction to Teeth

• Teeth are an integral part of the masticatory apparatus, fixed to the jaws.

Sets of Teeth

Temporal (Deciduous) Teeth

• Total of 20 teeth comprises:
  • 4 Incisors
  • 2 Canines
  • 4 Molars
• Eruption Timeline:
  • First incisor eruption: 6-8 months
  • First molar: 1 year
  • Shedding begins around 6-7 years

Permanent Teeth

• Total of 32 teeth comprises:
  • 4 Incisors
  • 2 Canines
  • 4 Premolars
  • 6 Molars
• Eruption Timeline:
  • First molar: 6-7 years
  • Medial incisor: 7-8 years
  • Lateral incisor: 8-10 years
  • Second premolar: 10-11 years
  • Canine: 12-13 years
  • Second molar: 13-14 years
  • Third molar: 17-25 years

Blood Supply, Lymphatic Drainage, and Nerve Supply

• Blood Supply:

  • Branches of the maxillary artery supply both upper and lower teeth.

• Lymphatic Drainage:

  • Lymph vessels from the teeth and gingiva pass to the submandibular lymph nodes.

• Nerve Supply:

  • Upper teeth: Supplied by branches of the maxillary nerve.
  • Lower teeth: Supplied by the inferior alveolar nerve, a branch of the mandibular nerve.

TONGUE

Structure and Function

• The tongue is a muscular organ covered by a mucous membrane, functioning in taste, speech, chewing, swallowing, and cleansing the mouth.
• Parts of the Tongue:
  1. Root: Attached to the mandible and hyoid bone.
  2. Apex: Tip of the tongue.
  3. Dorsum: Contains various papillae.
  4. Ventral Surface: Attached to the floor of the mouth by the frenulum.

Papillae Types

• Fungiform Papillae: Round shape with taste buds, scattered across the tongue's surface.
• Circumvallate Papillae: Large, blunt-ended structures located at the posterior part of the tongue, surrounded by a trench filled with taste buds.
• Foliate Papillae: Leaf-shaped projections found on the lateral borders of the tongue.
• Filiform Papillae: The most numerous, providing texture and aiding in the mechanical aspect of food manipulation without taste buds.

Muscles of the Tongue

Extrinsic Muscles

1. Genioglossus: Protrudes the tongue.
2. Hyoglossus: Depresses the tongue.
3. Styloglossus: Retracts and elevates the tongue.
4. Palatoglossus: Draws the tip back and down.

Intrinsic Muscles

• Superior Longitudinal Muscle: Elevates the tip of the tongue.
• Inferior Longitudinal Muscle: Depresses the tip of the tongue.
• Transverse Muscle: Narrows and elongates the tongue.
• Vertical Muscle: Flattens and widens the tongue.

Clinical Anatomy

1. Oral Cancer: Growths appear on the tongue and can be caused by smoking and heavy alcohol use.
2. Macroglossia: Enlarged tongue can stem from various causes, including congenital disorders or acquired conditions.
3. Frenectomy: Surgical removal of the frenulum if it restricts tongue movement.

SENSORY INNERVATION OF THE FACE

Introduction

• The skin of the face is supplied by branches of the trigeminal nerve, categorized into three divisions:
  • Ophthalmic
  • Maxillary
  • Mandibular

Branches of Trigeminal Nerve

1. Ophthalmic Nerve:

   • Supraorbital Nerve: Supplies forehead and scalp region.
   • Supratrochlear Nerve: Supplies the medial part of the upper eyelid.
   • Infratrochlear Nerve: Supplies skin over the nose.

2. Maxillary Nerve:

   • Infraorbital Nerve: Supplies the lower eyelid, cheek, and upper lip.
   • Zygomaticofacial Nerve: Supplies the skin over the zygomatic bone.
   • Zygomaticotemporal Nerve: Supplies the temple region.

3. Mandibular Nerve:

   • Auriculotemporal Nerve: Supplies parts of the ear and temporal region.
   • Buccal Nerve: Supplies the cheeks.
   • Mental Nerve: Supplies the skin and mucous membrane of the lower lip and chin.

Applied Anatomy

1. Facial Nerve Dysfunction: Loss of sensation or movement in the affected areas may arise from conditions affecting the facial nerve.