Equilibrium and Hearing

equilibrium

sensation regarding position of the head in space; gravity, linear acceleration, and rotation

hearing

sensations regarding vibrations in the air around the head

Semicircular ducts

contains ampulla and cupula

ampulla

expanded region containing receptors(cristae)

cupula

gelatinous structure extending across ampulla; contains stereocilia and kinocilium

Hair cells of the semicircular ducts:

detects deflection of the cupula, secretes neurotransmitter to sensory neurons; bending of cilia alters rate of neurotransmitter release

Utricle/saccule

each houses a single macula

macula

contains a cluster of hair cells and a otolith embedded with crystals (statoconia)

Hair cells of the maculae:

bending of processes in otolith is cause by gravitational pull when head tilts and inertial drag during acceleration

Pathways for equilibrium:

hair cells monitored by sensory neurons cell bodies in vestibular ganglion fibers form vestibular brand of CN 8

Functions of vestibular nuclei:

1. integrates info from both sides of the head

2. relays info to the cerebrum and cerebellum

3. sends reflex commands to motor nuclei

sound waves

vibrations of air

frequency (pitch)

waves per unit time; highness or lowness of sound

amplitude (volume)

energy of the waves; loudness of softness of sound; indicated by the number of activated receptors

What are the chambers of the cochlea?

1. scala vestibuli; receives vibrations from oval window

2. scala media (cochlear duct)

3. scala tympani; sends vibrations to round window

What are the membranes of the cochlea?

1. vestibular membrane; b/t vestibuli/media

2. basilar membrane; b/t media/tympani

3. tectorial membrane; in scala media

Organ of Corti

hair cells detect relative movement of basilar and tectorial membranes

Reception and transduction of sound:

1. waves are collected and directed to tympanic membrane

2. vibration of tympanic membrane transmitted through auditory ossicles

3. vibration of stapes at oval window
   causes pressure waves in the fluid of the
   scala vestibuli

4. pressure waves are transmitted through scala media to scala tympani

5. a portion of the basilar membrane vibrates relative to tectorial membrane

6. hair cells activate sensory neurons to indicate vibration site / intensity to CNS

Auditory pathways:

cochlear hair cells are monitored by bipolar sensory neurons; synapse in cochlear nuclei

CNS processing of auditory information:

info decussates and ascends to inferior colliculus, info is relayed to medial geniculate nucleus to auditory cortex