Lecture 2: Other Special Senses - Hearing, Equilibrium, Smell, and Taste

auricle (pinna)

elastic cartilage covered with skin; funnels sound waves into the external auditory canal

external auditory canal

lined with modified sweat glands that secrete ear wax

ceruminous glands

modified sweat glands that line the external auditory canal and secrete ear wax

repel water and trap outside subtances

functions of ear wax

ear ossicles

malleus, incus, and stapes; transmit sound waves to the inner ear

pharyngotympanic tube

connects the middle ear to the nasopharynx; equalizes air pressure

semicircular canals, vestibule, and cochlea

what are the parts of the inner ear?

semicircular canals

contain swollen region called the ampulla; contains receptors involved in equilibrium

vestibule

contains receptors involved in equilibrium

cochlea

spiral shaped structure that contains receptors involved in hearing

membranous labyrinth

inner edge within the cochlea, filled with endolymph

bony labyrinth

outer edge of the cochlea spiral

perilymph

what fills the space between the bony and membranous labyrinth?

cochlear duct, scala vestibuli, and scala tympani

what are the 3 chambers of the cochlea?

cochlear duct

continuous with the vestibule, contains endolymph

scala vestibuli and scala tympani

cochlear chambers that contain perilymph

vestibular membrane

boundary between scala vestibuli and scala tmypani

sound waves

displacement of air molecules

pitch

frequency; equals the number of cycles in one second, measured in hertz (Hz)

loudness

amplitude; equals the difference between the areas of high and low pressure, measured in decibels (dB)

movement of auditory ossicles causes oval window to vibrate to same frequency

what happens when sound waves strike the tympanic membrane?

produces pressure waves in the perilymph of the scala vestibuli and endolymph of the cochlear duct, causing basilar membrane to vibrate

what happens when the oval window vibrates?

short distance

how long do high-frequency pressure waves travel in the cochlea?

long distance

how long to low-frequency pressure waves travel in the cochlea?

pitch

where the basilar membrane vibrates

loudness

how much the basilar membrane vibrates

hair cells

receptors in the spiral organ

sterocilia

microvilli on the hair cells that project into the cochlear duct

tectorial membrane

membrane on top of the hair cells

they bend

what happens to stereocilia when the basilar membrane vibrates?

open K+ channels that depolarize the hair cell

what do stereocilia do when they bend?

releases NT that triggers action potentials in the axon of cochlear nerve

what do depolarized hair cells do?

auditory pathway

AP propagates through cochlear portion of vestibulocochlear nerve, then to the brainstem, then thalamus, and finally ends at the primary auditory cortex in the temporal lobe

visual, somatosensory, and vestibular

what are the 3 sources of input equilibrium depends on?

vestibular system

vestibule + semicircular canals

static equilibrium

maintaining balance when head and body are not moving; tilting of head and linear acceleration

utricle

the part of the vestibule responsible for horizontal linear movement

saccule

part of the vestibule responsible for vertical linear movement

otolithic membrane

membrane hair cells are embedded in in a maculae

kinocilium

true cilia in the otolithic membrane that either stimulate or inhibit release of NT

dynamic equilibrium

maintaining balance when head and body are moving

hair cells in ampulla

what detects movement for dynamic equilibrium?

cupula

gelatinous material where the ampulla are embedded

vestibular sensation pathway

AP propagate to vestibular branch of vestibulocochlear nerve then to the cerebellum, cranial nerve nuclei, thalamus, and then the inferior parietal lobe

olfaction

involves chemoreceptors call olfactory neurons within the olfactory epithelium

dendrites with cilia

what receives olfactory stimuli?

mitral cells

dendrites with cilia synapse with these cells

primary olfactory cortex in the temporal lobe

where does olfactory information go for processing?

gustation

involves chemoreceptors located in taste buds

papillae

where are taste buds located?

taste buds

gustatory cells that detect different chemicals

glossopharyngeal, facial, and vagus

what cranial nerves are involved in gustation?

primary gustatory cortex in the parietal lobe

where does gustatory information go to in the brain?

microvilli

what structures detect taste in gustatory cells?