Overview
This lecture covers the identification, function, and innervation of the major muscles of the head and neck, with emphasis on orientation, muscle groupings, and key anatomical relationships.
Orientation & Muscle Groupings
- The head muscle model has anterior (front), posterior (back), and lateral (side) views, with superficial and deep muscle layers.
- Muscles are named using Latin/Greek roots indicating position, attachment, and function.
Muscles of the Scalp & Face
- The epicranius (occipitofrontalis) spans from the forehead to the back of the skull, with frontal and occipital bellies joined by the galea aponeurotica.
- Orbicularis oculi surrounds each eye; corrugator supercilii (deep) pulls brows together; procerus draws the brows medially (frown).
- Nasalis lies on the side of the nose.
- Major mouth muscles: levator labii superioris (lifts upper lip), zygomaticus minor/major (smile), risorius (smile/laugh), masseter (chewing), depressor anguli oris (lowers mouth corners), levator anguli oris (raises mouth corners), depressor labii inferioris (lowers bottom lip).
- Orbicularis oris encircles the mouth; mentalis covers the chin.
- Buccinator draws cheeks inward; parotid (Stenson’s) duct passes through it to deliver saliva at upper second molar.
Muscles of Mastication
- The four muscles: masseter, temporalis, medial pterygoid, and lateral pterygoid.
- Temporalis is on the temporal bone; pterygoids are deep (lateral = above medial).
Muscle Innervation
- Facial expression (mimetic) muscles: innervated by cranial nerve VII (facial nerve).
- Muscles of mastication: innervated by the mandibular branch of cranial nerve V (trigeminal nerve).
Suprahyoid and Infrahyoid Muscles
- Suprahyoid muscles (above hyoid): mylohyoid, anterior/posterior digastric, stylohyoid, geniohyoid, hyoglossus; no lab-based innervation questions.
- Infrahyoid muscles (below hyoid, "TOSS" group): thyrohyoid, omohyoid (superior/inferior bellies), sternohyoid, sternothyroid; innervated by the cervical ansa (C1–C3).
Scalene Muscles & Scalene Gap
- Three scalene muscles: anterior, middle, posterior.
- The scalene gap is bordered by anterior and middle scalenes and transmits the subclavian artery and brachial plexus.
Key Terms & Definitions
- Epicranius (Occipitofrontalis) — scalp muscle with frontal and occipital bellies.
- Galea aponeurotica — connective tissue joining scalp bellies.
- Mimetic Muscles — facial expression muscles.
- Muscles of Mastication — muscles for chewing (masseter, temporalis, medial/lateral pterygoid).
- Suprahyoid Muscles — muscles above the hyoid bone.
- Infrahyoid Muscles ("TOSS") — muscles below the hyoid: thyrohyoid, omohyoid, sternohyoid, sternothyroid.
- Cervical ansa — nerve loop from C1–C3 innervating infrahyoid muscles.
- Scalene Gap — space between anterior and middle scalene muscles.
- Brachial plexus — nerve network to the upper limb.
Action Items / Next Steps
- Study muscle names, locations, functions, and innervations, especially facial, mastication, and neck muscles.
- Memorize the TOSS muscles and their innervation (cervical ansa).
- Learn the borders and contents of the scalene gap.
- Review the difference between mimetic and mastication muscles and their cranial nerve innervations.