Download File

Describe the anatomy of the ears, Eustachian tubes and pharynx
Week 30
1. Understand the terminology used to describe the gross anatomy of the ear and upper
air passages viz. nose pharynx & larynx
2. Identify the constituent parts and major internal features of the upper respiratory
tract including the nose, nasopharynx, oropharynx, laryngopharynx, and larynx.
Ear
see LO 3
Nose
 the part of the respiratory tract superior to the hard palate and contains the peripheral
organ of smell
 external nose
o consists of bone (paired nasal and maxillae), hyaline cartilage and fibro-fatty tissue
 external nares (nostrils)
 the skin extends into the vestibules of the nose (entrance) where it has a variable number of
stiff hairs (vibrissae)
Nasal Cavity
 paired cavities separated by midline nasal septum
 inter nares = choanae – open posteriorly into
nasopharynx
 nasal choncae dividethe nasal cavity into 4
passages:
o spehnoethmoidal recess (receives opening
of sphenoidal sinus)
o superior meatus
o middle meatus
o inferior meatus
 choncae produce turbulence which:
 warms
 humidifies
 filters air
Paranasal air sinuses
 air filled extensions of respiratory part of
nasal cavity
 frontal, ethmoid, sphenoid, maxilla
(Pneumatic bones)
 lighten skull and contribute to vocal
resonance
Pharynx:
About 15cm long, the pharynx extends from base of skull to the inferior border of the cricoid
cartilage anteriorly and the inferior border of C6 posteriorly.
 The superior pharynx receives the posterior openings of the choanae.
 located posterior to the nasal and oral cavities and the larynx.
 conducts food to the oesophagus, and air to the larynx and lungs.
Divided into three parts:
 Nasopharynx:
 Posterior to the nose and superior to soft palate
 pharyngeal tonsil in mucous membrane of roof and posterior wall
 Pharyngeal openings of the auditory tubes (eustachian tube).
 Oropharynx:
 Posterior to mouth
 soft palate – superior border of epiglottis
 palatine tonsils in the interval between palatoglossal and palatopharyngeal arches
 Opens into the oral cavity anteriorly via the fauces (the area at the back of the oral
cavity bounded by the palatine tonsils and their enclosing palatoglossal &
palatopharyngeal mucosal folds).
 Contains the lingual tonsil located on the posterior surface of the base of the tongue.
 Laryngopharynx:
 Posterior to the larynx
 superior border of epiglottis to inferior border of cricoid cartilage (C6)
Larynx:
 anterior to laryngopharynx
 extends from C4-C6 and in adult males
is around 5cm in length. In females and
children it is shorter. The hyoid is at the
level of C3.
 The framework of the larynx is made up
of cartilages and associated ligaments
and membranes.
 The larynx is the organ of voice
production. It consists of a framework
of cartilages and elastic membranes
housing the vocal folds and the muscles
which control the position and tension
of these elements.
 The larynx consists of 9 cartilages that
are joined by various ligaments and
membranes. Three of the cartilages are
single (thyroid, cricoid and epiglottis)
and three are paired (arytenoids,
corniculate and cuneiform).
 The position of the larynx is seen
anteriorly by the ‘Adam's apple’ which
is formed by the thyroid cartilage of the larynx. It serves as an external indication of the
level of the fifth cervical vertebra.
3. Describe the anatomical subdivisions of the ear.
The External Ear:
 The external ear is composed of a fleshy cartilaginous (elastic) flap called the auricle,
which surrounds the external acoustic meautus (EAM)
 The auricle provides protection for the opening of the ear and funnels sound into the
external auditory canal. It is made up of cartilage covered with skin
The external acoustic meautus:
 S-shaped passageway that passes through the tympanic part of the temporal bone and
ends at the tympanic membrane (ear drum).
 tympanic membrane is a thin semi-transparent sheet that also signifies the limit of the
external ear. The external ear’s nerve supply is by the auriculo-temporal nerve (CN V)
and great auricular nerve from C2.
 Lymph from the external ear is drained to the parotid, mastoid and jugular lymph
nodes.
 The lateral portion is cartilagenous with thick skin that is continuous with skin of
auricle. The skin contains ceruminous and sebaceous glands which produce cerumen
(ear wax).
 The medial portion is bony and very thin skin lies directly over the bone and is
continuous with external layer of the tympanic membrane.
Tympanic membrane:
 thin oval, semitransparent membrane at the medial end of the external auditory canal.
 It is roughly 1cm in diameter and conical in shape, with the concave aspect facing the
auditory canal. The apex is supported medially by the malleus.
 The shallow, cone-like central depression’s peak = umbo (remember umbrella)
 When viewed with otoscope, bright reflection (= Cone of light) radiates anteroinferiorly
from umbo
Divided into two parts:
 Flaccid part = Thin part of tympanic membrane superior to the lateral process of the malleus
 lacks the radial and circular fibres of the rest of the membrane.
 Tense part = Rest of tympanic membrane.
The Middle Ear:
 The middle ear is in the petrous part of the temporal bone.
 air filled cavity separated from the external auditory canal by the tympanic membrane.
 includes:
o tympanic cavity, which is the space directly internal to the tympanic membrane
o epitympanic recess, which is the space superior to the tympanic membrane.
 Posterosuperiorly, the tympanic cavity connects with the mastoid air cells via the
mastoid antrum.
 middle ear is separated from the brain only by a thin piece of bone in the roof of the
tympanic cavity called the tegmen tympani (infection in the middle ear can spread
through this bone and penetrate into the brain).
 The middle ear communicates with the nasopharynx via the auditory tube or
Eustachian tube.
 The auditory tube is about 4cm long and has two different sections:
o section near the middle ear is supported by cartilage,
o section near the nasopharynx is funnel shaped and broader.
 Auditory tube functions to equalize pressure on either side of the tympanic membrane.
 middle ear also communicates with the mastoid air cells via numerous tiny connections.
The middle ear is connected to the inner ear via the oval and round window.
 The middle ear contains the auditory ossicles (malleus, incus and stapes). The ossicles
increase the force x10 but decrease the amplitude of sound vibrations transmitted from
the tympanic membrane.
 Two muscles, the stapedius and tensor tympani, attach to the stapes and malleus
respectively and contract to dampen vibrations.
 The middle ear’s nervous supply comes from the facial (CNVII), glossopharyngeal (CN IX)
and vagus (CN X).
Walls of the tympanic cavity:
Tegmental roof
Floor (jugular wall)
Lateral (membranous) wall
Medial (labyrinthine) wall
Anterior (carotid) wall
Posterior (mastoid) wall
Thin plate of bone, tegmen tympani.
Seperates the tympanic cavity from the
cranial cavity.
Layer of bone separating tympanic
cavity from the internal jugular vein.
Mostly by tympanic membrane;
superiorly it is formed by bony wall of
epitympanic recess
Separates tympanic cavity from the
inner ear.
Separates tympanic cavity from the
carotid canal and the internal carotid
artery.
Has opening in superior part – the
aditus to the mastoid antrum –
connecting tympanic cavity to mastoid
cells.
The Inner Ear:
 The vestibulcochlear apparatis is responsible for the sense of equilibrium
 made up of a system of spaces in the petrous temporal bone – bony labyrinth containg
perilymph
 filling these spaces is a closed system of membrane bound sacs and tubules –
membranous labyrinth containing endolymph
 both fluids carry sounds waves to end organs for hearing and balancing
 Bony labyrinth composed of 3 parts: cochlea, vestibule and semicircular canals
4. Identify and describe the arrangement and function of the ear ossicles within the middle
ear.
The Auditory Ossicles:
 The auditory ossicles are three tiny bones in the middle ear. They connect the tympanic
membrane to the oval window of the inner ear. The three bones articulate via synovial
joints.
 transmit and amplify sound-induced vin=brations of TM to inner ear
Malleus (hammer):
 The most lateral of the three bones.
 Head (rounded superior part) lies in epitympanic recess (upper portion of the tympanic
cavity above the tympanic membrane and articulates with the incus.
 Neck lies against the flaccid part of the tympanic membraneTM .
 The Handle is embedded in the tympanic membrane and it functions as a lever.
 Tendon of tensor tympani muscle inserts into the handle near the neck. It responds to  or
 sound by tensing or relaxing respectively to change the transmittance of sound.
Incus (anvil):
 The middle ossicle bone.
 Body lies in the epitympanic recess  Articulates with the head of the stapes.
 Long limb articulates with stapes.
 Short limb connected by ligament to posterior wall of the tympanic cavity.
attaches the malleus to the stapes (stirrup). The base of the stapes is bound to a ligamentous
sheet that spans the oval window, an opening in the bone that surrounds the inner ear.
Stapes (stirrup):
 Has head and base united by two limbs.
 Head articulates with the incus.
 Base is bound to the ligamentous sheet that spans the oval window on the medial wall of
the tympanic cavity. The oval membrane is considerably smaller than the tympanic
membrane so the vibratory force of the stapes is increased by ~10x over that of the
tympanic membrane.
 The stapedius muscle restrains the stapes.
Muscles associated with the ossicles:
Two muscles dampen (resist movement) of ossicles; one also dampens the vibration of the
tympanic membrane.
Tensor tympani:
 Inserts into the handle of the malleus.
 Pulls handle medially, tensing the tympanic membrane and decreases the amplitude of
oscillations.
 It therefore prevents inner ear damage when exposed to loud sounds.
 Supplied by the mandibular branch of the trigeminal nerve.
Stapedius:
 Inserts into the neck of the stapes.
 Pulls stapes posteriorly, tilting its base in the oval window.
 Tightens the annular ligament and reduces the oscillatory range.
 Supplied by a branch of the facial nerve.
5. Describe the inter-connections and relationships of the middle ear to the mastoid air cells,
and the anatomical basis of infections spreading from the pharynx to the middle ear and
mastoid sinuses.


the middle ear (tympanic cavity) has a roof, floor and 4 walls as described above
A section of the mastoid process of the temporal bone of the cranium shows it to be
hollowed out into a number of spaces, the mastoid cells
Mastoid Antrum
 Cavity in mastoid process
 Separated from middle cranial fossa by tegmen tympani
 Floor of antrum has several apertures that communicate with mastoid cells
 Middle ear is connected to mastoid air cells via mastoid antrum
 Antrum + mastoid cells are lined by mucus membrane continuous with lining of middle
ear
 Related to canal for facial nerve
ANATOMICAL BASIS OF INFECTIONS SPREADING FROM PHARYNX TO MIDDLE EAR + MASTOID
SINUSES
 Infection of pharynx may spread to middle ear via pharyngotympanic (Eustachian) tube
 Infection of middle ear may spread to mastoid sinuses via mastoid antrum = Mastoiditis
 Main risk = Spread of infection to brain via facial nerve