SENSORY PHYSIOLOGY: THE EAR

MEMBRANOUS LABYRINTH

Vestibular Apparatus: Equilibrium Two parts: 1) semicircular canals -- rotational, or angular, acceleration -- oriented in 3 planes -- help us maintain balance when turning our head, spinning, tumbling 2) otolith organs (utricle and saccule) --provide information about linear acceleration -- utricle: horizontal acceleration --saccule: vertical acceleration

Vestibular Apparatus: Mechanism Bending of hair cells results in the production of action potentials Bending opens up ion channels  depolarization Bent towards kinocilium: depolar- ization bent away from kinocilium: hyperpolarization

Vestibular Apparatus: The otolith organ The hair cells project in an endolymph-filled membrane the membrane contains CaCO3 crystals horizontal acceleration bends utricle hair cells; vertical acceleration bends saccule hair cells

Vestibular Apparatus: Semicircular canals

Neural Pathways

VESTIBULOOCULAR REFLEX Click here for a 30 second you tube video.

Student Activity Meniere’s disease is thought to be due to pressure changes in the inner ear. Why do patients show up at the doctor complaining of dizziness and exhibiting Nystagmus?

Hearing: The Cochlea Sound waves enter the auditory canal and vibrate the tympanic membrane Middle ear: malleus, incus, stapes oval window

Hearing: The Middle Ear This is a close up of the middle ear The stapes is the last bone in the sequence It vibrates the oval window, which mechanically vibrates the endolymph inside the cochlea The eustachian tube (auditory tube) is connected to the nasopharynx. It equalizess the pressure of the middle ear with the changing atmospheric pressure.

Hearing: The Cochlea

Hearing: Cross Section through Cochlea the membrane that the hair cells are stuck into is called the tectorial membrane Fluid makes the basilar membrane bounce and this bends the hair cells and causes depolarization Action potential is sent to cranial nerve VIII

Hearing: PITCH High pitch wiggles the basilar membrane closer to the oval window medium pitch wiggles the basilar membrane further along the path low frequency wiggles the basilar membrane further away In the figure to the left, this is shown as 20,000 Hertz (the lowest frequency).

Neural Pathways for Hearing Sensory neurons from the vc nerve synapse in the medulla oblongata neurons extend from medulla to midbrain neurons extend from midbrain to auditory cortex of temporal lobe

Hearing Impairment Conduction deafness: Sound waves are not conducted from the outer to the inner ear. May be due to a buildup of earwax, too much fluid in the middle ear, damage to the eardrum, or overgrowth of bone in the middle ear Impairs hearing of all sound frequencies Can be helped by hearing aids

Hearing Impairment, cont Sensorineural/perceptive deafness: Nerve impulses are not conducted from the cochlea to the auditory cortex. May be due to damaged hair cells (from loud noises) May only impair hearing of particular sound frequencies and not others May be helped by cochlear implants Presbycusis – age-related hearing impairment