Lecture 46 - Hearing, Olfaction and Gustation Flashcards
Sound is measured in (2)
decibels or hurtz
Decibel
Smallest difference in loudness intensity that can be perceived
Frequency is measured in
Hertz
Frequency is equal to
Pitch
What are the 3 structures of the outer ear
What are the structures and muscles of the middle ear
Stapedius is connected to
The stapes and uses the facial nerve to dampen low tones
The tensor tympani is connected to
The malleus and uses the trigeminal nerve to dampen low tones
Bone conduction
Sound waves can be conducted through bones of skull
Hyperacusis
Hypersensitivity to sound because of damage to facial or trigeminal nerve
Eustachian Tube
Is a pressure equalizer and drain
2 structures of the internal ear
Cochlea
Sound waves are transduced into electrical signals that are then perceived by the brain
Membranous labyrinth is filled with
Endolymph
Bony labyrinth is filled with
Perilymph
What are the 3 fluid-filled spaces of the cochlea
What structure occupies the entire oval window to vibrate
Stapes
Pathway of sound in the cochlea
Scala tympani and Scala vestibuli contain the perilymph and are continuous with one another to the helicotrema
stapes vibrates -> oval window vibrates -> causes pressure waves in perilymph of scala vestibuli that go to helicotrema -> waves go to scala tympani -> round window -> also waves go to cochlear duct to transduce electrical signals that are sent to brain
Round window
Flexible membrane that releases pressure
T or F: If stapes and oval window move outwards, the round window moves inwards
T
What are the 2 key membranes of the cochlear duct and their function
- Reissner Membrane (Vestibular): Separates scala vestibuli and cochlear duct
- Basilar Membrane: Separates scala tympani and cochlear duct (contains hair cells = sensory receptors)
The cochlea has what type of localization
Tonotopic localization
Describe the frequencies found in tonotopic organization of cochlea
Apex = low frequency (wider and more flexible)
Base = High frequency (more narrow and less flexible)
The spiral organ of corti is made of
Receptor and supportive cells in the cochlear duct
The receptor hair cells of the organ of corti can be classified into what 2 groups
1) Inner hair cells
2) Outer hair cells
The hair cells are imbedded in the (auditory)
Tectorial membrane from the basilar membrane
How are signals activated through the basilar and tectorial membrane
When basilar membrane moves in response to sound or pressure waves in cochlea it creates a sheering force which activates hair cells by pushing them against the tectorial membrane that causes an activation signal
Compare inner hair cells and outer hair cells
Inner: Single row
Outer: 3-5 rows depending on location
Similarities: Both arrange stereocilia from shortest to longest and the stereocilia is embedded in the tectorial membrane
Bending towards stereocilia (longest hair cell)
causes depolarization
Bending away from stereocilia (longest hair cell)
causes hyperpolarization
What is the innervation of inner and outer hair cells
Hair cells are innervated by primary auditory neurons in spiral ganglion
Inner: 1:1 synaptic relationship with many ganglion cells (up to 20) which allows for greater tonotopic discrimination (discriminate between tones)
Outer: Each ganglion cell synapses on many hair cells and is innervated also by efferent olivocochlear fibers (superior olivary nucleus in pons) which increases height of outer hair cells and stiffness of stereocilia which influence basilar membrane to regulate selective attention to certain sounds (can alter response of inner hair cells and amplify sounds of particular regions of basilar membranes)
Do medications affect outer or inner hair cells
Outer hair cells
Frequency (tone) is coded by
the location of the basilar membrane activated
Intensity (measured in db) is coded by
Firing frequency of afferents and number of activated afferents (recruitment)
Describe the auditory pathway starting with the hair cell
- Hair cells receive sound and innervated by ganglion cells
- Axons of ganglion cells form cochlear nerve
- Cochlear nerve projects to cochlear nuclei
- Cochlear nuclei span medulla and pons
- Cochlear nuclei decussates and projects ipsilaterally and contralaterally to each side (auditory pathway = bilateral)
- Superior olivary nucleus localizes sound because it receives input from cochlear nuclei on both sides of head
- Superior olivary nucleus in pons projects using olivocochlear fibers to the cochlea to regulate selective attention to certain sounds. They also play a role in acoustic reflex (attenuation) by dampening sound (trigeminal and facial nerve) and innervates muscle in middle ear. Superior olivary nucleus also projects to inferior colliculus (midbrain) via lateral lemniscus.
- Inferior colliculus communicates with contralateral inferior colliculus via commissure pathway. It also projects to thalamus (medial geniculate nucleus).
- Medial geniculate nucleus of thalamus projects auditory radiations to the primary auditory cortex
Inferior Colliculus
All auditory pathways converge here and is responsible for signal integration and frequency recognition and discrimination
T or F: In the auditory cortex we see tonotopy and neurons respond to increasingly complex stimuli differently
True
T or F: Other cortical areas respond to auditory info
T (Wernicke’s Area)
what happens with Lesions to auditory cortex
1. Whole cortex
2. Partial lesions
All cortex destroyed = deafness
Partial Lesions = can still show normal auditory perception due to redundancy of bilateral pathways
T or F: tonotopy is observed in all parts of the auditory pathway
T
How to determine hearing impairment
Use screening test of few key tones and compare to average threshold
How to classify different types of hearing
Deaf compared to profound/hard of hearing
Deaf is profound hearing loss and do NOT benefit from hearing amplification (eg. hearing aid)
Conductive Hearing loss
1) Occurs in outer/middle ear
2) Affects intensity but not clarity
3) Responsive to surgical or medical intervention
4) Does not exceed 65dB
5) Benefit from hearing aid
Sensorineural Hearing Loss
1) Occurs in inner hear
2) Affects conversion to neural impulses (hair cells damage)
3) Referred to nerve deafness and results in changes in perceived intensity and distortion of sound
T or F: We are more sensitive to bad than good smells
T
Pheromones
Chemical signals for reproductive behavior’s that trigger a social response
Olfactory dysfunction results in
Negative interpersonal functioning
What are the 3 different receptors/cells that make up the olfactory epithelium
1) Olfactory cells/receptors (blue) are neurons that penetrate the cribriform plate in the ethmoid bone and have cilia that project from surface (replaced every 4-8 weeks)
2) Supportive Cells: Produce mucous (replaced every 10 mins) = protective function containing enzymes and antibodies
3) Basal cells: Produce our olfactory receptor cells
Rabies Virus
Transmitted through eyes, nose, mouth or through bite and virus targets CNS to cause brain dysfunction and death
Who has better olfactory acuity, humans or dogs? Mouse?
Humans have the worst acuity
Mitral cells
Send axons as olfactory tract that projects to olfactory cortex WITHOUT passing through thalamus
Anosmia
Loss of sense of smell due to blow to the head because of cribiform plate being sensitive to breaking
Pathway of olfactory signalling
Describe the signaling in the olfactory bulb
Different receptor cells synapse onto glomerulus (map out odor information) and glomerulus is attached to dendrites of mitral cells
T or F: Glomerulus can be modified
T
Olfactory cortex is found in
Primary - temporal lobe
Secondary - frontal lobe
What other structures does the olfactory tract project to
1) temporal lobe (amygdala) -emotions with smells
2) Hippocampus - learning and memory of smells
3) Orbitofrontal cortex - linking smell to taste and discriminating smells
Temporal lobe epilepsy - Aura
Someone is about to have a seizure so they will have an aura (smell a certain smell right before their seizure eg. burnt toast) due to location in temporal lobe
How does the brain discern smells (3)
1) Olfactory population coding: Combination of responses from many smells, not just one receptor cell (eg. smelling onions involves many cells)
2) Olfactory Map: Sensory map and their is spatial representation of particular odours in the bulb (depends also on concentration of odourant)
3) Temporal Coding: Oudor cells fire together in synch (not firing rate) producing intensity and quality of a smell
T or F: There is evidence for aromatherapy in rehab
F, not yet still trying to learn if smells can affect treatments for cancer and reduce anxiety or stress
Chemical senses
Taste and smell arise from specific chemical receptors and perception of these senses occurs in cerebral cortex
Flavor is perceived by using both
taste and smell
Gustation and olfaction are strongly linked to our most basic needs. What are these needs.
thirst, hunger, emotion, sex, and memory
Flavor aversion learning
Where we learn to dislike certain foods results and it is stored in associative memory (amygdala)
Flavour aversion learning can be used to stop
Alcohol or drug addiction or nail biting by making it taste bad
What are the 5 basic tastes and where is it sensitive
Flavour is a combination of
taste and smell (eg. onion might taste like apple when nose is plugged)
T or F: We also consider what our food feels like
T (taste, temperature, and pain)
What cranial nerves innervate the tongue
1) Facial Nerve: Anterior 2/3 of tongue
2) Glossopharyngeal Nerve: Posterior 1/3 of tongue
What nerve innervates the throat (glottis, epiglottis, and pharynx)
Vagus nerve
Papillae
Taste sensitive structures of tongue (contain taste buds)
What are the 4 papillae of tongue
Threshold concentration
Each papillae requires a certain stimulus to acquire a specific perception of taste
Higher concentration = papillae become less specific and respond to more types of taste
Lower concentration = papillae become more specialized
T or F: Taste receptor cells undergo regeneration every 2 weeks because they undergo regeneration and death constanly
T
What is a taste receptor cell made of
- Taste pore
- Taste cell
- Microvilli
Basal Stem cells replace
the taste cells
Gustatory afferent
Synapse at base of taste cells and form gustatory afferent nerve that send info via glossopharyngeal, facial or vagus nerve depending on location of tongue
What is the taste signaling pathway
The taste signaling pathway runs
Ipsilaterally
The primary gustatory cortex is located in the
parietal lobe
Lesions to thalamus or gustatory cortex (3rd order neurons) can cause ageusia which is
Loss of tase perception
Taste pathways are linked to (what other areas of the brain)
1) Brainstem regions involved in swallowing, salivation, gagging, vomiting, digestion and respiration
2) Hypothalamus: Involved in hunger and digestion, hormones, and feeding behavior’s
3) Limbic System (Amygdala): Link emotions with eating or how we feel
