Ear Flashcards
Describe site, attachment & parts of tympanic membrane
S: make 55deg with the floor of meatus so its outer surface is facinf downwards & forwards
Attached to tympanic sulcus of tympanic plate except superiorly where it is a attached to groove in suprameatal part of temporal bone.
Parts; Pars flaccida, upper small triangular part
Pars tensa, the larger part that is kept tense by its attachment to tympanic sulcus
Describe structure of tympanic membrane & important relations
Outer cuticular skin
Middle fibrous layer (superficial radiating fibers & deep circular fibers)
Inner mucous layer lined by ciliated columnar cells
*the chorda tympani which is a branch of CN VII passes between fibrous & the mucosal layers in upper part.
Inner surface of tympanic membrane provides attachment to……point of most convexity is called…..
Handle of malleus
Umbo
BS & LD of tympanic membrane
Art: outer by deep auricular branch of maxillary, inner by ant & post tympanic arts
Vein: outer veins drain into IJV, inner veins drain into transverse sinus
LD: preauricular & retripharyngeal LNs
Nerve supply of tympanic membrane
Outer surface: antero-inferiorly by auriculotemporal, postero-inferiorly by auricular branch of vagus
Inner surface: by tympanic branch of CN IX
Describe roof & floor middle ear cavity
R, formed by thin plate of bone called tegmen tympani which separates tympanic cavity from temporal lobe
F, formed of thin plate of bone separates tympanic cavity from IJV
Mention features of anterior and posterior walls of middle ear
Ant: has 2 openings one for passage of tensor tympani muscle the other for auditory tube
Post: has bony projection called pyramid for stapedius muscle, opening for mastoid antrum, fossa incudis for short process of incus
Describe features of medial wall of middle ear
- Promontry formed by basal turn of choclea
- Fenestra vestibuli (oval window) closed by stapes
- Fenestra cochlea (round window) closed by 2ry tympanic membrane
- Sinus tympani between 2&3
- Horizontal part of facial canal above promontry & oval window
……. Of malleus articulates with…..of incus. While,……of stapes articulates with…..of incus.
Head, body
Head, long process
Joints between ossicles are…..
Synovial
Describe attachment, supply & action of tensor tympani
-It arises from cartilage of auditory tube attached to malleus & thus to tympainc membrane
-Supplied by branch of mandibular (n to medial pterygoid)
-It tenses tympanic membrane restricting its movements, it prevents wide excrusions of ossicles
Describe attachment, supply & action of stapedius
-It arises from wall of pyramid; it is attached to the neck of stapes
-it is supplied by facial n
-prevents excessive movements of stapes
Enumerate nerves of middle ear
- Chorda tympani
- Tympanic plexus: found on medial wall (promontry), contibuting nerves are tympanic branch of CN IX(sensory) and from carotid plexus around ICA (vasomotor). Distributed to mucosa of the tympanic cavity, auditory tube & mastoid antrum.
Describe extension of pharyngotympanic tube & its function
-Bony part begins at ant wall of tympanic cavity ends at junction between squamous & tympanic parts of temporal bone
-Cartilagenous part begins in the groove between petrous part & greater wing of sphenoid it ends in lateral wall of nasopharynx
It equalizes pressure on both sides of tympanic membrane
Mention muscles attached to Eustachian tube
Tensor tympani, tenosor palati, levator palati, salpingopharyngeus
Mastoid antrum is connected to middle ear by…..
Aditus ad antrum
Describe bounds of mastoid antrum
Ant: aditus ad antrum
Post: sigmoid sinus & cerebellum
Med: petrous part of temporal bone
Lat: suprameatal triangle
Roof: continuation of tegmen tympani
Floor: communication with mastoid air cells
Define mastoid air cells
A series of interconnected air cells within mastoid process which look like honeycomb. Lined with mucous membrane continuous with that ofthe mastoid antrum & tympanic cavity.
The first order neuron of auditory pathway is….
Central processes of Bipolar neurons of spiral ganglion of inner ear
Describe 2nd order neuron of auditory pathway
Dorsal and ventral cochlear nuclei axons form trapezoid body that synapse with superior olivary nucleus OF THE SAME & OPPOSITE SIDES
Describe 3rd order neuron of auditory pathway
Axons of superior olivary n or trapezoid n of same or opposite side ascend in lateral leminiscus. Some fibers end in nucleus of lateral leminiscus, some fibers end in inferior colliculus, some fibers pass in brachium of inferior colliculus to synapse in MGB
Describe 4th order neuron of auditory pathway
Axons of cells in MGB form the auditory radiation that pass in sublentiform part of internal capsule, to the 1ry auditory area, (area 41&42), upper lip of posterior limb of lateral sulcus.
Unilateral auditory cortex lesion causes…..
Impaired hearing not hearing loss
The 1ry auditory area projects to……….
Auditory association area. AII (area 22) which is located in superior temporal gyrus around the 1ry auditory area.
They ear ascend to eye level by…..
Development of the mandible
External auditory meatus develops from……, and the meatal plug dissolves at….
1st pharyngeal cleft
7th month
Describe embryological origin of tympanic membrane
- Ectodermal epithelial lining
- Mesenchymal intermediate layer
- Endodermal lining from 1st pharyngeal pouch
Describe embryology of the middle ear
- Lining epithelium of tympanic cavity and auditory tube is derived from the endodermal tubitympanic recess of the 1st pharyngeal pouch
- Ossicles are derived from cartilage of 1st (malleus & incus) & 2nd (stapes) pharyngeal arches
- Muscles arise from 1st (tensor tympani, CN V3) and 2nd (stapedius, CN VII) pharyngeal arches
Mastoid antrum is formed by…..
Dorsal expansion of tympanic cavity by vacuolation of surrounding tissue
An infectious cause of congenital deafness
Rubella during 7th-8th week
Variations of auricle may point to……or be a part of……
Kidney malformations
1st arch syndrome
The sensory ganglion of facial n is….located at…..
Geniculate ganglion
Trunk of intrapetrous part of facial n
Describe how the lacrimatory nucleus & the uncertain nucleus fibers reach their target
Bith are nuclei of facial nerve their fibers pass in greater petrosal branch of facial n then relay in pterygopalatine ganglion which gives postganglionic parasymp fibers to lacrimal gland (lacrimatory nucleus) OR glands of palate, pharynx & nose (uncertain nucleus)
…….contains autonomic & sensory fibers of facial n
Nervus intermedius
Describe intrapetrous course of facial n
Both its roots enter through internal acoustic meatus and at the fundus of meatus unite and enter bony facial canal, where it runs in 3 directions:
1st, laterally, above the vestibule of inner ear, this part ends at the geniculate ganglion
2nd, backwards, in medial wall of tympanic cavity above promontry
3rd, downwards vertically behind tympanic cavity to exit through stylomastoid foramen.
Mention branches of facial n:
1. Within petrous temporal bone
2. Below stylomastoid foramen
- Greater petrosal n, chorda tympani, n to stapedius
- Posterior auricular n, nerve to stylohyoid and posterior belly of digastric
Greater petrosal n carries taste fibers from…..
Describe its course
Originate from geniculate ganglion passes in hiatus in petrous part of temporal bone to reach middle cranial cavity passing below tigeminal ganglion to foramen lacerum where it unites with deep petrosal n to form nerve of oterygoid canal that relays in pterygopalatine ganglion.
The most common cause of supranuclear facial n lesion is…..
Hemorrhage in internal capsule
Describe results of infranuclear facial n lesion proximal to geniculate ganglion
In addition to ipsilateral facial muscles paralysis:
1. Loss of taste from ant 2/3 of tongue & oral surface of soft palate on affected side
2. Hyperacusis
3. Impaired secretion of submandibular, sublingual & lacrimal glands
What is Bell’s palsy
Idiopathic facial nerve palsy may be caused by sudden exposure to cold
