Ears Flashcards
Ears consist of:
- External ear
- Middle ear / Tympanic cavity
- Inner ear/ Labyrinth
External ear consist of:
- Auricle
2. External Auditory Meatus
- paired structure found on either side of the head
- functions to capture and direct sound waves towards the external acoustic meatus
AURICLE
- elastic cartilage
- hairs, sebaceous and
ceruminous glands (barrier)
OUTER 1/3 OF EXTERNAL ACOUSTIC MEATUS
- bone
- measures 1 inch long in the adult
- narrowest 0.2 inch (5mm) from the tympanic membrane
INNER 2/3 OF EXTERNAL ACOUSTIC MEATUS
Nerve supply of the outer ear
- Auricotemporal nerve
2. Auricular branch of vagus nerve
Internal ear consists of:
- Tympanic cavity
- Tympanic membrane
- Auditory ossicles
- Auditory tube
- narrow, oblique, slit like cavity
- communicates with the nasopharynx (via auditory or eustachian tube) and mastoid antrum
TYMPANIC CAVITY
- formed by a thin plate of bone known as tegmen tympani
- separates the tympanic cavity and cranial cavity
ROOF OF TYMPANIC CAVITY
- formed by a thin plate of bone (may be deficient and may be partly replaced by fibrous tissue)
- separates the tympanic cavity from the superior bulb of the internal jugular vein
FLOOR OF TYMPANIC CAVITY
- formed below by a thin plate of bone
- separates the tympanic cavity from the internal carotid artery.
- upper part has two openings into 2 canals:
> lower and larger leads into the auditory tube
> upper and smaller is the entrance into the canal for the tensor tympani muscle
ANTERIOR WALL OF TYMPANIC CAVITY
- upper part has a large, irregular opening, the aditus to the mastoid antrum.
- below this is a small, hollow, conical projection, the pyramid
> from whose apex emerges the tendon of the stapedius muscle.
POSTERIOR WALL OF TYMPANIC CAVITY
- largely formed by the tympanic membrane
LATERAL WALL OF TYMPANIC CAVITY
- pearly gray, thin fibrous membrane
- concaved laterally
- circular, 1 cm in diameter
- separates the outer ear from the middle ear
- vibrates in response to sound pressure waves.
TYMPANIC MEMBRANE
- central depressed portion of the tympanic membrane
- due to the tip of the handle of the malleus
UMBO
Nerve supply of the tympanic membrance
- Auricotemporal nerve
2. Auricular branch of vagus nerve
Auditory ossicles is consists of:
- Malleus (hammer)
- Incus (anvil)
- Stapes (stirrup) smallest bone of the body
- largest ossicle
- rounded head articulates with the incus
- neck
> constricted part below the head - handle/ manubrium
>passes downward and backward and is firmly attached to the medial surface of the TM
MALLEUS
- posseses a large body and two processes
- the body is rounded and articulates anteriorly with the head of the malleus
INCUS
- has a head, a neck, two limbs, and a base.
- head
> is small and articulates with the long process of the incus. - neck
>is narrow and receives the insertion of the stapedius muscle
STAPES
Muscles of the ossicles
- Tensor tympani
2. Stapedius
Origin: from the cartilage of the auditory tube and the bony walls of its own canal.
Insertion: Handle of the malleus
Nerve supply: a branch from the nerve to the medial
pterygoid muscle (a branch of V3)
Action: reflexly damps down the vibrations of the malleus by making the tympanic membrane more tense.
TENSOR TYMPANI MUSCLE
Origin: internal walls of the hollow pyramid
Insertion: the tendon emerges from the apex of the pyramid and is inserted into the neck of the stapes
Nerve supply: Nerve to the stapedius from the facial nerve
Action: reflexly damps down the vibrations of the stapes by pulling on the neck of that bone
STAPEDIUS MUSCLE
- extends from the anterior wall of the tympanic cavity downward, forward, and medially to the nasal pharynx.
- posterior 1/3 is bony and the anterior 2/3 is cartilaginous
- serves to equalize air pressures in the tympanic cavity and the nasal pharynx.
AUDITORY TUBE
