Muscles of Mastication

Muscles of Mastication

• These muscles facilitate chewing

Digastricus (Biventer)

• Origin: Paracondylar process of the occipital bone.
• Insertion: Body of the mandible, the only muscle that opens the jaw, aided by gravity.
• Innervation:
  • Rostral part: Mandibular nerve (part of cranial nerve 5).
  • Caudal part: Facial nerve (cranial nerve 8).

Masseter Muscle

• Origin: Zygomatic arch.
• Insertion: Masseteric fossa ventrolateral surface of the ramus of the mandible, and the angular process.
• Action: Closes the jaw.
• Innervation: Trigeminal nerve.

Temporalis Muscle

• Located at the temporal fossa and is the largest muscle in the head.
• Origin: Temporal fossa.
• Insertion: Coronoid process of the mandible.
• Action: Closes the jaw.
• Innervation: Trigeminal nerve.

Medial and Lateral Pterygoid Muscles

• Origin: Pterygoid palatine fossa.
• Insertion: Medial surface and caudal margin of the ramus and the angular process.
• Action: Closes the jaw.
• Innervation: Trigeminal nerve.

Muscles of Facial Expression

• Action: Move the skin and appendages of the face and head.
• These muscles are facial expression or mimetic muscles
• These are generally thin cutaneous muscles.
• Innervated by the facial nerve.

Muscles of the Cheek

Platysma

• A cutaneous muscle that passes from the dorsal median raphe of the neck to the angle of the mouth.
• Insertion: Radiates into the orbicularis oris in the lips.
• Action: Draws the angle of the mouth caudally.
• Innervation: Facial nerve.

Buccinator (Trumpeter's Muscle)

• Origin: Attaches to the alveolar margins of the mandible and maxilla and the adjacent buccal mucosa.
• Action: Contraction draws the cheek inwards against the teeth.
• Innervation: Facial nerve.

Muscles of the Lips

Levator Nasolabialis

• Origin: Maxillary bone, courses rostroventrally.
• Insertion: Edge of the superior lip and on the naris.
• Action: Contraction causes dilation of the nostrils and raises the upper lip.
• Innervation: Facial nerve.

Orbicularis Oris

• Origin: Near the free borders of the lips, extending from one lip to the other around the angle of the mouth.
• Insertion: Fibers of each side at the median plane in the incisor region of both jaws.
• Action: Contraction closes the lips by drawing them together into the shape of an "O".
• Innervation: Facial nerve.

Zygomaticus (Smiling Muscle)

• Origin: Zygomatic arch.
• Action: Draws the angle of the mouth caudally, external ear cranially, and ventrally.
• Innervation: Facial nerve.

Mentalis Muscle

• Origin: Pterygoid palatine fossa.
• Action: Contraction stiffens the apical region of the lower lip.
• Innervation: Facial nerve.

Muscles of the Forehead

Frontalis

• A thin sheet of muscle overlying the temporalis muscle.
• Action: Contraction draws the scutular cartilage forward and raises the eyebrow.
• Innervation: Facial nerve.

Muscles of the Eyelid

Orbicularis Oculi

• Origin: Attached medially to the medial palpebral ligament.
• Insertion: The fibers of each side at the median plane in the incisor region of both jaws.
• Action: Closes the palpebral fissure.
• Innervation: Facial nerve.

Retractor Anguli Oculi Lateralis

• Origin: Passes directly caudally from the lateral palpebral angle to blend with the temporal fascia.
• Action: Assists in closing the eye.
• Innervation: Facial nerve.

Levator Anguli Oculi Medialis

• Origin: Passes directly from the medial palpebral angle to attach to the frontal bone.
• Action: Raises the upper lid and erects the eyebrow.
• Innervation: Facial nerve.

Extraocular Muscles

• There are seven extrinsic muscles:
  • Two oblique muscles.
  • Four rectus muscles.
  • One retractor bulbi muscle.
• Insertion: All extrinsic muscles insert on the fibrous coat of the eyeball, sclera, and near the equator of the eyeball.
• Rectus muscle inserts closer to the corneoscleral junction.
• Dorsal rectus elevates the globe.
• Ventral rectus depresses the globe.
• Lateral rectus turns the globe temporally/laterally.
• Retractor bulbi retracts the globe.
• Lateral rectus and retractor bulbi are innervated with the abducent nerve.
• Other three recti are innervated with oculomotor nerve.
• Dorsal oblique inserts globe and rotates 12 o'clock position nasally, innervated by the trochlear nerve.
• Ventral oblique extorts globe, rotates 12 o'clock position temporally, innervated by the oculomotor nerve.

Muscles of the External Ear

Rostral Auricular Muscles

• Muscles that lie on the forehead caudal to the orbit and converge toward the auricular cartilage.
  • Superficial sculutoauricularis
  • Deep sculutoauricularis
  • Frontoscutularis
  • Frontalis
  • Zygomaticoauricularis

Dorsal Auricular Muscles

• Most of these muscles arise from the median raphe of the neck and attach directly to the auricular cartilage.
  • Cervicoscutularis
  • Superficial cervicoauricularis
  • Middle cervicoauricularis
  • Deep cervicoauricularis

Extrinsic Muscles of the Tongue

Styloglossus

• Origin: Stylohyoid bone, passes rostroventrally lateral to the palatine tonsil.
• Insertion: Middle of the tongue.
• Action: Retracts and elevates the tongue.
• Innervation: Hypoglossal nerve.

Genioglossus

• Origin: Intermandibular articulation and adjacent surface of the body of the mandible.
• Action: Caudal fibers protrude the tongue and rostral fibers retract the apex.
• Innervation: Hypoglossal nerve.

Hyoglossus

• Origin: Arises from the thyrohyoid and the basihyoid and passes into the root of the tongue.
• Action: Retracts and depresses the tongue.
• Innervation: Hypoglossal nerve.

Muscles Affecting the Shoulder

• Extensors: Brachiocephalicus
• Flexors: Deltoideus, Teres major, Teres minor
• Fixers: Supraspinatus, Infraspinatus, Subscapularis
• Elevators: Trapezius, Rhomboideus
• Retractors: Latissimus dorsi, Rhomboideus, Superficial pectoral, Deep pectoral
• Abductor: Deltoideus

Muscles Affecting the Elbow

• Flexors: Brachialis, Biceps brachii, Coracobrachialis
• Pronators: Pronator teres, Pronator quadratus
• Extensors: Triceps, Anconeus, Tensor fasciae antebrachii
• Supinator: Supinator

Muscles Affecting the Carpus and Digit

• Extensors: Extensor carpi radialis, Common digital extensor, Extensor digiti quinti, Extensor carpi ulnaris, Ulnaris lateralis, Supinator
• Flexors: Flexor carpi radialis, Flexor carpi ulnaris, Superficial digital flexor (humeral and radial heads), Deep digital flexor (humeral, radial and ulnar heads)

Muscles Affecting the Tarsus and Digit

• Extensors: Long digital extensor, Peroneus longus, Extensor digitalis brevis, Peroneus tertius, Anterior tibial
• Flexors: Superficial flexor (gastrocnemius and plantaris), Deep flexor (long digital flexor, posterior tibial & flexor hallucis longus), Peroneus longus + brevis

Muscles Affecting the Hip

• Abductors: Gracilis, Abductor femoris, Pectineus, External obturator
• Adductors: Superficial gluteal, Middle gluteal, Deep gluteal
• Flexors: Sartorius, Ilio-psoas, Tensor fasciae latae, Quadriceps (vastus medialis, vastus lateralis, vastus intermedius, rectus femoris)
• Extensors: Biceps femoris, Semitendinosus, Semimembranosus, Quadratus femoris, Internal obturator, Gemelli