Hearing and Equilibrium

Auditory sensations and Equilibrium

Hearing and equilibrium rely on mechanoreceptors

The ear is divided into three parts:Outer ear Middle ear Inner ear

Outer ear:

Ceruminous glands – Cerumen - ear wax

in external auditory meatus

Middle ear:

Tympanic antrum – opening into mastoid process

Auditory (Eustachian) Tube

Otitis media – inflammation of the MIDDLE ear

Auditory ossicles or ear bones

Tensor tympani muscle

Stapedius muscle

Tympanic reflex

INNER EAR :

Cochlea – hearing

Vestibule – static equilibrium

Semicircular canals – dynamic equilibrium

Organ of Corti

Vestibulocochlear nerve – cranial nerve VIII

Audible range: 20 -- 20,000 hertz

Ossicles amplify sound 22 X

Some nerve fibers cross over to opposite side of brain; some don’t. Why?

Equilibrium – Balance

Static equilibrium – maintenance of body posture relative to gravity while the body is still.

Dynamic equilibrium – maintenance of the body posture (mainly the head) in response to sudden movements. Tracking a moving object.

Static Equilibrium

Inside the vestibule are two chambers :

utricle and saccule.

Regions of hair cells and supporting cells called maculae.

Otoliths – “ear rocks”

Dynamic Equilibrium

Semicircular canals

In ampulla is the crista ampullaris – contains hair cells and supporting cells covered by a gelatinous mass called the cupula.

Neurological connections between eyes and semicircular canals – for tracking

Nystagmus