Muscles Moving the Auditory Ossicles

The Tensor Tympani Muscle

• This muscle is about 2 cm long.

• Origin: superior surface of the cartilaginous part of the auditory tube, the greater wing of the sphenoid bone, and the petrous part of the temporal bone.
• Insertion: handle of the malleus.
• Innervation: mandibular nerve (CN V³) through the nerve to medial pterygoid.

• The tensor tympani muscle pulls the handle of the malleus medially, tensing the tympanic membrane, and reducing the amplitude of its oscillations.
• This tends to prevent damage to the internal ear when one is exposed to load sounds.

The Stapedius Muscle

• This tiny muscle is in the pyramidal eminence or the pyramid.

• Origin: pyramidal eminence on the posterior wall of the tympanic cavity. Its tendon enters the tympanic cavity by traversing a pinpoint foramen in the apex of the pyramid.
• Insertion: neck of the stapes.
• Innervation: nerve to the stapedius muscle, which arises from the facial nerve (CN VII).

• The stapedius muscle pulls the stapes posteriorly and tilts its base in the fenestra vestibuli or oval window, thereby tightening the anular ligament and reducing the oscillatory range.
• It also prevents excessive movement of the stapes.

Muscles of the Pharynx

• This consists of three constrictor muscles and three muscles that descend from the styloid process, the cartilaginous part of the auditory tube and the soft palate.

External Muscles of the Pharynx 

• The paired superior, middle, and inferior constrictor muscles form the external circular part of the muscular layer of the wall.
• These muscles overlap each other and are arranged so that the superior one is innermost and the inferior one is outermost.

• These muscles contract involuntarily in a way that results in contraction taking place sequentially from the superior to inferior end of the pharynx.
• This action propels food into the oesophagus.

• All three constrictors of the pharynx are supplied by the pharyngeal plexus of nerves, which lies on the lateral wall of the pharynx, mainly on the middle constrictor of the pharynx.
• This plexus is formed by pharyngeal branches of the glossopharyngeal (CN IX) and vagus (CN X) nerves.

The Superior Constrictor Muscle

• Origin: pterygoid hamulus, pterygomandibular raphe, posterior end of the mylohyoid line of the mandible, and side of tongue.
• Insertion: median raphe of pharynx and pharyngeal tubercle.
• Innervation: though the pharyngeal plexus of nerves.

• The pterygomandibular raphe is the fibrous line of junction between the buccinator and superior constrictor muscles.

The Middle Constrictor Muscle

• Origin: stylohyoid ligament and greater and lesser horns of hyoid bone.
• Insertion: median raphe of pharynx.
• Innervation: through the pharyngeal plexus of nerves.

The Inferior Constrictor Muscle

• Origin: oblique line of thyroid cartilage and side of cricoid cartilage.
• Insertion: median raphe of pharynx.
• Innervation: through the pharyngeal plexus of nerves.

• The fibres arising from the cricoid cartilage are believed to act as a sphincter, preventing air from entering the oesophagus. 

Gaps in the Pharyngeal Musculature

• The overlapping arrangement of the three constrictor muscles leaves 4 deficiencies or gaps in the pharyngeal musculature.
• Various structures enter and leave the pharynx through these gaps.

• Superior to the superior constrictor muscle, the levator veli palatini muscle, the auditory tube, and the ascending palatine artery pass through a gap between the superior constrictor muscle and the skull.
• Superior to the superior border of the superior constrictor, the pharyngobasilar fascia blends with the buccopharyngeal fascia to form, with the mucous membrane, the thin wall of the pharyngeal recess.

• Between the superior and middle constrictor muscles, the gateway to the mouth, though which pass the stylopharyngeus muscle, the glossopharyngeal nerve (CN IX), and the stylohyoid ligament.

• Between the middle and inferior constrictor muscles, the internal laryngeal nerve and the superior laryngeal artery and vein pass to the larynx.

• Inferior to the inferior constrictor muscles, the recurrent laryngeal nerve and inferior laryngeal artery pass superiorly into the larynx.

3 basic functions
o    protection of respiratory tract during swallowing food/air pathways cross.
    epiglottis provides protection
o    control intra-thoracic pressure (in coughing) -    close off airway to build pressure then rapidly open to release stuff
o    production of sound (in speaking, singing, laughing)

Important structures

o    hyoid bone
o    thyroid cartilage
o    arytenoids cartilage: vocal and muscle process
    sits on slope on posterior side of cricoid - spin and slide
o    cricoid cartilage: signet ring
o    thyroepiglottic ligament

Membranes and ligaments

o    membrane: general; ligament: thickening of membrane
o    folds: free edges of membranes or ligaments
o    names: tell you where located

Important membranes:
    quandrangular/vestibular membrane—from epiglottis to arytenoids
•    inferior edge: false vocal fold
    thyrohyoid membrane
    conus elasticus = cricothyroid = cricovocal
•    superior/medial edge = vocal fold
•    vocal ligaments: true folds, top of cricothyroid membrane

• This is the second cranial nerve (CN II) and is the nerve of sight.

The Walls of the Orbit

• Each orbit has four walls: superior (roof), medial, inferior (floor) and lateral.
• The medial walls of the orbit are almost parallel with each other and with the superior part of the nasal cavities separating them.
• The lateral walls are approximately at right angles to each other