hearing, balance, taste and olfaction Flashcards
sound
sound is a longitudinal wave
frequency of sound is the number of cycles per second (Hz)
amplitude of sound waves=Db
as air pressure goes up and down it causes movement in the ear drum and that allows us to perceive sound
3 parts of the ear
outer ear (pinna, ear canal and tympanic membrane)
middle ear (ossicles)
inner ear (cochlea and labyrinth)
role of the pinna
capture sound efficiently
sound localisation
ridges and bumps of outer ear reflect sound and focus it into the auditory canal
what is the auditory canal filled with?
air
where does the outer ear stop?
tympanic membrane (ear drum)- vibrates when sound hits
role of the middle ear
transmit mechanical energy captured at the ear drum from sound through the ear to the cochlea
role of the inner ear
mechanical energy - fluid waves - action potential
what are the 3 bones of the ossicles?
malleus, incus and stapes
how do the ossicles and ear drum enable the amplification of sound information?
ossicles are stiff and the ear drum is larger than the oval window where the stapes is means we have an increase in 25 in the energy going from the ear drum to the window
the malleus is attached to the eardrum, and when the eardrum vibrates, it moves the malleus.
the incus is positioned between the malleus and the stapes and acts as a lever, transmitting the vibrations from the malleus to the stapes
the stapes is the last bone in the chain, and it vibrates against the oval window, a membrane-covered opening to the inner ear, transferring the vibrations to the cochlea
direction of the ossicles
tymapnic membrane- malleus- incus- stapes terminates at the oval window
what muscles are by the ossicles?
stapedius and tensor tympani muscles
what is the role of the stapedius and tensor tympani?
stapedius- contracts in response to loud sounds, dampening the vibrations of the stapes, thereby reducing the sound intensity transmitted to the inner ear
tensor tympani- contracts to reduce the movement of the eardrum (tympanic membrane), thereby moderating the sensitivity of the middle ear
what is the middle ear filled with?
air
what is the cochlear composed of (scalae)?
scala vestibululi (starts in the oval window)
scala media
scala tympani (ends in round window)
what is the cochlea filled with?
fluid
what is the organ of corti?
runs the entire length of the cochlea and contains the hair (auditory) receptors along the basilar membrane
pathway of sound
sound causes tympanic membrane to vibrate
these vibrations are passed via the ossicles to the oval window
this causes the stapes to vibrate against the oval window and this generates a fluid wave that travels down the length of the cochlea
oscillatory pressure differences propagate along the scala vestibuli and tympani
what is the hole at the end of the basilar membrane called?
helicotrema
what does the helicotrema allow?
fluid wave to pass through and come down the scala tympani
what happens to left over energy in the ear?
round window bulges out and that absorbs remaining energy so fluid wave can continue
what does a fluid wave do to the basilar membrane?
causes it to move so the hair cells start to move in response to the changing in fluid pressure
what are the two ends of the basilar membrane?
basal (narrow by stapes) and apical (wide)
hair cells on the basal end respond to…
higher frequencies because they are stiff
hair cells on the apical end respons to…
lower frequencies because they are flexible
what is tonotopy?
a map of sound created at the basilar membrane (low and high frequencies)
what partially covers the organ of corti?
the tectorial membrane that causes hair cells to bend
role of inner hair cells
fine perception of sound
role of outer hair cells
fine tuning (more outer than inner)
central auditory pathway
hair cells- cochlear ganglion cells (spiral)- dorsal and ventral cochlear nuclei in medulla- ventral to superior olivary nuleus to inferior colliculus/dorsal straight to IC- medial geniculate nucleus in thalamus- primary auditory cortex
why is it functionally important that the ventral cochlear nuclei is contralateral and ipislateral?
bilateral representation of sound in an early stage of the pathway (means damage to auditory cortex wont necessarily mean being deaf in one ear)
functions of the vestibular system
balance
visual stability
spatial orientation
autonomic functioning
what 2 sets of structures in the vestibular labryrinth help us detect balance?
otolith organs and semicircular canals
what structures does the otolith organs contain?
utricle and saccule
what do otolith organs detect?
detect the force of gravity and head tilits
what do the semicircular canals detect?
3 perpendicular canals that are sensitive to rotational accleration
how do otolith organs cause depolarisation?
if stereocilia hairs bend in direction of the largest hair then there will be an action potential
as head tilits forward, intertia carries otlohtic membrane (gelatinous cap) to move forward and hair bends in the direction of the kinocilium
how do semicircular canals cause depolarisation?
when youre spinning, the endolymph in the canals moves and that causes the hair cells in the cupula to bend causing exictation of the dendrites of neurons in the vestibular ganglion
principle vestibular pathway
hair cells- vestibular ganglion cells- vestibular nuclei via the vestibulocochlear nerve- ventral posterior nucleus- somatosensory cortex
what nuclei does the vestibulocochlear nerve also innervate?
oculomotor
trochlear
abducens
(eye movement)
accessory
how do we detect smell?
chemoreceptors
chemicals in air are breathed in and they become dissolved in the mucus lining the top of the nasal cavity
where are the cilia of the olfactory cells located?
the mucus of the nasal cavity
olfactory epithelium
axons of the olfactory receptor cells constitute the olfactory nerve and penetrate the cribriform plate of the skull
what happens when smell information enters the brain?
olfactory synapses with mitral cells in glomeruli contained within the olfactory bulb (ventral surface)
second-order neurons then form the olfactory tract which pass along the bulb
what is different in the ascedning sensory pathway of olfaction compared to the other special senses?
there is no synapse within the thalamus
what lobe is the olfactory cortex/piriform in?
temporal lobe- conscious perception of smell
what areas of the brain is the olfactory tract assoiated with?
olfactory cortex, hippocampus (olfactory memory), amygdala (emotional responses), reticular formation (visceral responses to smell) and the orbitofrontal cortex
where are taste buds located?
papillae in the tongue and palate
how do we taste?
each taste bud has 50-150 taste receptor cells arranged within the bud
microvilli at the apical end of the taste cells extend into the taste pore, the site where chemicals dissolved in saliva can interact with taste cells
this activates gustatory axons
gustatory pathway
facial and glossopharyngeal nerve (and vagus)
information rises up and synapses in the nucleus of the solitary tract in the medulla oblongata
main ascedning taste information arrives at the ventral posterior medial nucleus of the thalamus
travels to the gustatory cortex in the insula (floor of lateral sulcus)
collateral pathways for gustation
brain regions for control of: respiration, satiety & feeding, muscles of mastication and muscles of swallowing
