1- Ears (Anatomy and physiology) Flashcards
The ear is subdivided into 3 main parts:
1) the external ear 2) the middle ear 3) the inner ear
External
- Pinna- outer curve of the ear
- External auditory meatus lined with skin-> air filled canal leading to the middle ear
- Supplied by the greater auricular nerve, lesser occipital and facial nerve
The pinna
x
The pinna consists of elastic cartilage, thrown into folds (see Figure 23), and a fibrofatty lobule.
- It is supplied by the greater auricular nerve, lesser occipital and facial nerve.
External auditory canal
- Oblique tube 2.5-3cm in length- sigmoid in shape
- Outer 1/3 is cartilage (wax), inner 2/3 is bony (petroud bone
- Ceruminous glands only exist in the outer 1/3 -> wax
- Tympanic membrane from the medial boundary of the canal
- Nerve supply- auriculotemporal nerve and auricular branch of the vagus nerve
- Self cleaning function
self cleaning function of the external auditory meatus
- Epithelial migration
- Surface of the skin moves laterally from the tympanic membrane towards the ear canal
middle ear
- Air filled cavity
- Pharyngotympanic tube (PT) intermittently opens-> allows air filled cavity of the PT equilibrate with air pressure in the Nasopharynx (NP)
- Ossicles-> amplify and transmit sound energy
- Tympanic membrane
ossciles
malleus
incus
stapes
malleus
largest and lateral process is attached to tympanic membranic membrane
Incus
head of malleus articulates with incus
Stapes
two limbs (anterior crus and posterior crus) attached to oval window footplate
tympanic membrane
- Forms the lateral boundary of the middle ear cavity. It is a circular shape and roughly 1cm in greatest diameter.
- Nerve supply- outer surface by the auriculotemporal nerve and the auricular branch of the vagus.
- The membrane is normally greyish/ pinkish in colour.
- When the membrane is examined with an otoscope, the concavity of the structure produces a cone reflex in the anteroinferior quadrant.
- The tip of the handle of malleus forms the deepest concavity of the membrane called the umbo, which is where the cone of light radiates from.
pars flaccida vs pars tensa
- The pars flaccida is the weakest and most flaccid area of the tympanic membrane.
-> It plays a vital role in the pathophysiology of cholesteatoma.
- The pars tensa forms the remainder of the tympanic membrane.
inner ear
- Fluid filled structures
- Located in the petrous part of the temporal bone
- Cochlear canal
- Semi-circular canal
Cochlear canal
Hearing
- Where action potentials are generated for sending signals to the brain to be perceived as sound
- Fluid filled
Vestibular apparatus (Semi-circular canals)
balance
- 3
- Orientated at 90 degrees to one another
- Fluid filled
- APs carried to the brain to be perceived as position and balance
Inner ear
Consists of 2 important structures
Vestibular apparatus
Cochlea
MOA of cochlea
- Fluid movement (generated by footplate of stapes)
- Converted into AP (in the CN VIII- vestibulocochlear nerve) -> perceived as sound in the temporal lobe for perception of sound
Vestibular apparatus MOA
- Fluid movement (generated by position and rotation of head)
- Converted into APs (CNVIII) -> perceived as position sense and balance
Inner ear pathology presents with a combination of
- Hearing loss
- Tinnitus
- Disturbances in balance and vertigo (specific to inner ear)
Mechanism of hearing
- Auricle and external auditory canal focuses and funnels sound waves towards the tympanic membrane which vibrates
- Vibration of TM causes vibration across chain of ossicles (amplifies) and ends in vibration of the foot of the stapes on the oval window
- Fluid filled cochlea duct
- Within the duct is the organ of corti – where we found the stereocilia
- Vibration created by ossicles leads to waves in the channels of fluid which lead to movement of stereocilia (nerve cells) AND TRIGGERS AP IN COCHLEAR PART OF CN VIII
- Generates sound
- PRIMARY AUTITORY CORTEX= TEMPORAL LOBE
Physiology of the Eustachian Tube
- Connects middle ear (ossicles) into the post nasal space
- Lining = mucosal
- Usually closed in healthy individual, but opens regularly when you swallow or chew
- Opening the tube allows:
1. Mucus to drain out of the ear
2. Allows air to move from the post-nasal space (atmospheric pressure) and middle ear-> this equilibrates the pressure
when the ET is blocked
- Ear pressure cannot equilibrate with atmospheric pressure
- Mucus cannot drain out of the middle ear
- If the pressure in the middle ear decreases
- retraction of the TM
- otitis media with effusion (not getting pressure equilibrated- air in middle ear space gets reabsorbed -> leaving mucosal fluid- negative middle ear pressure)
If pressure in the middle ear increases
bulging – acute otitis media (inflammatory exudate produced by mucosa increased air pressure)
why is ET dysfunction more common in children
o Small diameter of eustachian tube
o More horizontal
o More coughs and cold
o Large adenoids
Mechanism of hearing
- Auricle and external auditory canal focuses and funnels sound waves towards the tympanic membrane which vibrates
- Vibration of TM causes vibration across chain of ossicles (amplifies) and ends in vibration of the foot of the stapes on the oval window
- Fluid filled cochlea duct
- Within the duct is the organ of corti – where we found the stereocilia
- Vibration created by ossicles leads to waves in the channels of fluid which lead to movement of stereocilia (nerve cells) AND TRIGGERS AP IN COCHLEAR PART OF CN VIII
- Generates sound
- PRIMARY AUTITORY CORTEX= TEMPORAL LOBE
