Peripheral auditory system
Divided into 3 parts:
- External ear – consisting of auricle and external auditory canal (External acoustic canal) (External auditory meatus)
- Middle Ear – consists of tympanic membrane, tympanic cavity, auditory ossicles, TVP LVP intra-aural muscles and the air cells of the temporal bone (mastoid air cells)
- Inner ear – embedded in the petrous bone and subdivided into vestibule, the semi- circular canal system of the vestibular end organ and the cochlear (the auditory end organ)
NB: The vestibulocochlear nerve (CN VIII) is part of the peripheral auditory system too. It runs in the internal auditory canal and connects the peripheral end organs to the CNS Part of inner ear
Anatomy and physiology of the external ear. Non inflammatory diseases and inflammatory diseases. Otomycosis
The external ear can be functionally and anatomically split into two sections
- Auricle (or pinna)
- External acoustic meatus
The auricle
- External structure or shape is supported by elastic cartilage.
- Function → It captures and transmits sound to the external acoustic meatus.
- On lateral surface, the skin doesn’t have subcutaneous tissue & it is firmly attached to cartilage
- Skin inflammation on the lateral surface affects the perichondrium → Which can lead to permanent damage ex. Auricular hematoma
- The outer curvature of the ear is called the helix.
- Inwards and parallel is the antihelix and it has two crura – the inferoanterior crus, and the superoposterior crus.
- In the middle of the auricle is a hollow depression, called the concha of auricle which acts to direct sound into EAM
- Anterior to the start of the EAM is the tragus.
- Opposite the tragus is the antitragus.
The external acoustic meatus (EAM) Sensitive for temperature & pain (Skin is thin & overlies periosteum)
- S-shaped Is a sigmoid shaped tube from the deep concha to the tympanic membrane. (Medial border)
- Wall structure by elastic cartilage from auricle, and bony support from the temporal bone.
- The ratio of cartilage to bone is 2/3:1/3 Important, for otoscopy » Pulled upwards & back to straighten It out
- The narrowest part is called isthmus
- Santorini fissures
- Natural openings within the anterior cartilage in the lateral aspect of the canal that may allow infectious or neoplastic processes to extend from the parotid gland to the canal
» Contains small hairs & specialised sweat glands, that produce Cerumen (ear wax)
Physiology / function of external ear A A B P
- Antenna → Carries the sound to the sensitive middle ear