Hearing and Balance Flashcards
Describe the components of the anatomy of the external ear
The external ear includes the AURICLE and the EXTERNAL ACOUSTIC MEATUS.
Sound waves are collected and channelled by the auricle into the external acoustic meatus where they cause the tympanic membrane (eardrum) to vibrate. The outer (lateral) third of the external acoustic meatus is comprised of elastic cartilage, while the inner (medial) two- thirds is walled by part of the temporal bone. Identify the external acoustic meatus on a skull, and note its proximity to the mastoid process and temporomandibular joint.
What are the parts of the AURICLE
The auricle has several named parts, including the
helix, antihelix, tragus, antitragus, lobule, and concha.
Most of the auricle contains a core of elastic cartilage.
Dscribe the components of anatomy of the middle ear:
The middle ear is contained within the petrous part of the temporal bone.
The middle ear includes the
epitympanic recess and tympanic cavity,
Auditory ossicles: (malleus, incus, and stapes;
Stapedius muscle (attached to the stapes),
tensor tympani muscle (attached to the handle of the malleus, which is attached to the tympanic membrane),
Chorda tympani nerve.
Describe the Tympanic cavity
The tympanic cavity is described as having four walls, a roof, and a floor, most of which are formed by the petrous part of the temporal bone
The lateral part of the tympanic cavity is formed mostly by the tympanic membrane
Describe the medial wall of the tympanic cavity
Separates the tympanic cavity from the inner ear and has two sealed openings - the oval (vestibular) window (closed by the stapes) and the round (cochlear) window , closed by the secondary tympanic membrane
Describe the eardrum
The eardrum is concave laterally, with the central depression called the umbo. The eardrum is attached to the manubrium (handle) of the malleus, one of the auditory ossicles, in the anterosuperior quadrant. At the superior end of the handle of the malleus (at its lateral process), anterior and posterior mallear folds of the eardrum are seen. A “cone of light” is reflected in the anteroinferior quadrant. Sketch and label the appearance of the right and left tympanic membranes as viewed by the otoscope.
Describe the roof of the typmanic cavity
The roof of the tympanic cavity corresponds to part of the posterior part of the middle cranial fossa, where the temporal lobe of the brain is located.
Describe the floor of the typmanic cavity
The floor separates the tympanic cavity from the internal jugular vein – on a skull, identify the groove for the sigmoid sinus which leads to the jugular foramen.
Describe the anterior wall of the tympanic cavity
The anterior wall separates the tympanic cavity from the internal carotid artery in the carotid canal (identify this on the base of a skull); and there are two openings: the opening of auditory tube, and for the tensor tympani muscle.
Describe the posterior wall of the tympanic cavity
The posterior wall is open superiorly into the mastoid antrum, which leads to mastoid air cells in the mastoid process of the temporal bone. Identify as many of these features as you can on the ear models and the dissected temporal bone.
What muscle attaches to the handle of the malleus (attached to tympanic membrane)
Tensor tympani
What is the msall muscle on the posterior wall of he middle ear?
The Stapedius
What are the functions of the tensor tympani and stapedius and by what nerves are they innervated?
The TT: damben the noise produced in chewing- reduces percieved amplitudes of soulds by pulling the malleos medially and hence tensing the tympanic membrane and dampening the vibratio in the ear ossicles - innervated by CNV3 (medial pterygoid nerve)
The Stapedius: dampens the vibrations of the stapes by pulling on the neck of the bone - innervated by CNVII
Explain the course of the facial nerve from the brainstem - where does it exit?
& its course to get to the ear.
What nerve leaves the facial nerve before it exits the skull? what hole do each nerve exit through
The facial nerve (CN VII) is closely related to the middle and inner ears as it travels through the petrous part of the temporal bone.
It exits the cerebellopontine angle of the brainstem and enters the internal acoustic meatus (with CN VIII).
Its course through the temporal bone is complicated. It runs first along the medial wall and then the posterior wall of the tympanic cavity.
It finally exits at the stylomastoid foramen.
The chorda tympani nerve leaves the facial nerve superior to the stylomastoid foramen, and travels through the middle ear cavity, between the malleus and incus.
What kinds of fibres are contained within the chorda tympani nerve?
Taste fibres: anterior 2/3 of tongue (joins with lingual)
Parasympathetic fibres for sublingual and submandibular salivary glands)
