4. External auditory canal
The external acoustic meatus is a sigmoid shaped tube that
extends from the deep part of the concha to the tympanic
membrane. The walls of the external 1/3 are formed by cartilage,
whereas the inner 2/3 are formed by the temporal bone.
The external acoustic meatus does not have a straight path, its
outer part is directed upward,backward,medially while its inner
move downward,forward, medially .
5. External Auditory canal
1.cartilaginous part
skin lining this part of canal is thick containing ceruminous and
pilosebaceceous glands .
8mm length
fissure of santorini: two defects in this part of canal through which
infection from parotid and mastoid can appear in the canal and vice versa .
2.Bony part
16mm length
isthmus
anterior recess
Its skin is thin and does not contain glands
foramen huschke
7. • The tympanic membrane lies at the distal end of the external acoustic meatus. It
is a connective tissue structure, covered with skin on the outside and a mucous
membrane on the inside. The membrane is connected to the surrounding
temporal bone by a fibrocartilaginous ring.it is trilaminar ,oval,semitransparent
• it is 9-10mm tall,8-9mmwide,0.1mm thick
•Pars tensa: it forms most of the part of membrane its periphery is
thickened to form a fibrocartilagious ring called annulus tympanicus
which fits in tympanic sulcus
the cental part is tented inward at the level of tip of melleus to form umbo a
bright cone of light can be seen radiating from the tip
• The handle of malleus continues superiorly, and at its highest point, a small
projection called the lateral process of the malleus can be seen. The parts of the
tympanic membrane moving away from the lateral process are called the
anterior and posterior malleolar folds.
• Par flaccida (shrapnell’s membrane):
• It is not so taut and may appear slightly pink
9. Arterial supply of external ear
• Vasculature
• The external ear is supplied by branches of the external
carotid artery:
• Posterior auricular artery
• Superficial temporal artery
• Occipital artery
• Maxillary artery (deep auricular branch) – supplies the deep
aspect of the external acoustic meatus and tympanic
membrane only
11. Nerve supply of ear
• The sensory innervation to the skin of the auricle comes from
numerous nerves:
• Greater auricular nerve (branch of the cervical plexus) – innervates
the skin of the auricle
• Lesser occipital nerve (branch of the cervical plexus) – innervates
the skin of the auricle
• Auriculotemporal nerve (branch of the mandibular nerve) –
innervates the skin of the auricle and external auditory meatus.
• Branches of the facial and vagus nerves – innervates the deeper
aspect of the auricle and external auditory meatus
• Some individuals can complain of an involuntary cough when
cleaning their ears – this is due to stimulation of the auricular
branch of the vagus nerve (the vagus nerve is also responsible for
the cough reflex
12.
13. Nerve supply of TM
• Lateral surface is supplied by auriculotemporal nerve and
auricular branches of vagus
• Medial surface is supplied by tympanic branches of
glossopharyngeal nerve
The lymphatic drainage of the external ear is to the
superficial parotid, mastoid, upper deep cervical and
superficial cervical nodes.
14. Middle ear
Middle ear extend beyound the limit tympanic membrane which
forms it lateral boundary and divide.
1. Mesotympanum line opposite the pars tensa.
2. Epitympanum(lying above the pars tensa but medial to
sharapnell’s membrane).
3. Hypotympanum the portion of middle ear around the
tympanic orifice of the eustachian tube.
Middle ear together with eustachian tube aditus, antrum and
mastoid ear cells is called middle ear cleft. It is lined by mucous
membrane and filled with air.
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32. Ossicles of the middle ear
It consists of three ossicles.
1. Malleus
2. Incus
3. Stapes
38. Intratyampanic muscles
1. Tensortympani
the tensor tympani is attached to the malleus; it is
innervated by a branch of the Vth cranial nerve. The action of
both muscles is to decrease sound transmission through the
middle ear.
2.Stapedius: Attach to neck of stapes
supplied by facial nerve
39.
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41. Blood supply of the middle ear
1. Interior tympanic branch of maxillary artery which supply
tympanic membrane.
2. Stylomastoid branch of posterior oriculler artery which
supply middle ear and mastoid air cells.
3. Petrosal branch of middle meningeal artery.
4. Superiour tympanic branch of middle meningeal artery.
5. Branches of pterygoid canal.
6. Tympanic branch of internal carotid.
