AUDITORY, SOMATOSENSORY, CHEMICAL SENSES Flashcards
Why as we get older we loose the ability to hear high frequency noise?
Because ear hair cells die
What part of the ear captures and directs sound waves?
external ear
What does the eardrum convert?
Air sound waves to pressure waves
How does sound travel in the cochlea?
As pressure waves in incompressible fluid
What does the basilar membrane do in response to pressure waves?
It bends
Where are the auditory receptors located?
On the basilar membrane
What stimulates specific hair cells in the cochlea?
Sounds of different frequencies bending distinct regions of the basilar membrane
What is the function of hair cells in the auditory system?
They are auditory receptors that detect sound.
How do sound waves reach the cochlea?
They travel down the auditory canal to the eardrum.
What happens when the basilar membrane bends?
It stimulates the auditory receptors (hair cells).
Steps of sensory transduction in the auditory system
- Sound wave entry
- Transmission
- Basilar membrane bending
- hair cell activation
- electrical signal generation
- Auditory nerve transmission
Sound wave entry (Steps of sensory transduction in the auditory system)
sound wave enter the external ear -> reach eardrum/tympanic membrane -> causes vibration
Transmission (Steps of sensory transduction in the auditory system)
The vibrations are transmitted through the ossicles to the oval window, creating pressure waves in the cochlea’s incompressible fluid.
Basilar membrane bending (Steps of sensory transduction in the auditory system)
These pressure waves cause the basilar membrane to bend, with different sound frequencies affecting specific regions.
Hair cell activation (Steps of sensory transduction in the auditory system)
The bending stimulates hair cells on the organ of Corti, causing the hair-like stereocilia to bend.
Electrical signal generation (Steps of sensory transduction in the auditory system)
Bending of the stereocilia opens ion channels, leading to depolarization of hair cells and generating electrical signals.
Auditory nerve transmission (Steps of sensory transduction in the auditory system)
These signals are transmitted to the auditory nerve, which sends the information to the brain for processing.
the bending of the basilar membrane in response to sound cause…
the conversion sound into electrical signals that the brain interprets as sound
What structural properties of the basilar membrane create a tonotopic map for sound frequencies?
The basilar membrane is thin and floppy at the end (for low frequencies) and thick and rigid at the base (for high frequencies), causing preferential bending to different sound frequencies.
What role do hair cells play in sensory transduction in the auditory system?
they convert mechanical vibrations from sound waves into electrical signals through bending and depolarization.
What role does the tectorial membrane play in stimulating hair cells in the cochlea?
creates a shearing force that bends hair cell stereocilia
How does bending of hair cells towards the kinocilium contribute to sensory transduction in the auditory system?
opens potassium channels, allowing K+ entry, which causes depolarization and the release of glutamate
Auditory pathways
- Superior Colliculus
-integrates LSO, MSO & cochlear nucleus inputs to
localize & orient sounds in 3D space
- also receives visual info for reflexively orienting to stimuli in 3D space - Inferior Colliculus
- tonotopic map; all ascending pathways converge here
- subcortical projection to Sup. Collic. for fast automatic behaviors
(projection to thalamus-A1 for more complex processing) - Medial Superior Olive
- detects interaural timing differences for localizing sounds - Lateral Superior Olive
- detects interaural amplitude differences for localizing sounds - Cochlear Nucleus
- tonotopic map; integrates acoustic and somatosensory
information to localize sounds and distinguish self from non-self
Where does the MSO receive input from? (MSO circuit mechanism)
The MSO receives input from both ears via the cochlear nuclei.
-eg when the sound is to the right, APs from the right cochlea travel farther than those from the left chochlea
What type of neurons are found in the MSO?
Neurons in the MSO are binaural, meaning they receive input from both the left and right ears.
what does ITD >0 mean?
sound is coming from the right
How do MSO neurons detect interaural time differences (ITD)?
MSO neurons act as coincidence detectors, firing when they receive simultaneous inputs from both ears.
Where does the MSO send output after processing auditory information?
The MSO sends output to higher brain regions, including the lateral lemniscus and inferior colliculus.
Coincidence detectors
- respond specifically when they receive inputs from two different sources simultaneously. In the auditory context, they are primarily used to detect when sound signals arrive at both ears at the same time.
-By comparing the timing of inputs from both ears, coincidence detectors help determine the direction of a sound source. For example, if a sound is coming from the right, it will reach the right ear slightly before the left ear, activating the corresponding MSO neurons.
How are high frequency sound affected?
high frequency sounds are modified by the shape of the ears, head and shoulders
Sound filtering
Occurs based on where the sound is coming from due to anatomical structures of the head and ears
What is the tonotopic organization in the primary auditory cortex (A1)?
In A1, different relevant sounds occupy a greater proportion of the cortex, with specific areas dedicated to different frequencies.
How does the primary auditory cortex exhibit plasticity?
can change based on experience and learning
What is columnar organization in the primary auditory cortex?
Individual columns in A1 respond to specific frequencies; some columns respond to sounds from both ears, while others show ear dominance.
How do higher auditory regions differ from A1?
Higher auditory regions respond to more complex sounds rather than just pure tones.
The vestibular system
- sensory system located in the inner ear
- maintains balance, spatial orientation and coordinates movement
Components of the vestibular system
semicircular canals and otolith organs
Type of otolith organs
Utricle and Saccule
Utricle
- senses horizontal acceleration
- contains different hair cells oriented in various directions to detect movements in multiple horizontal planes (e.g., left/right, forward/backward).
- helps the brain understand movements related to walking, running, or tilting the head sideways.
Saccule
- responsible for sensing
- Its hair cells are oriented to detect up-and-down movements, such as jumping or falling.
- provides information about the position of the head relative to the ground, which is crucial for maintaining balance and posture.
The semicircular canals
consist of three curved tubes oriented at approximately right angles to each other (horizontal, anterior, and posterior)
Detection mechanism of semicircular canals
Head rotates → semicircular canals move → endolymph fluid lags behind (inertia) → pushes on cupula → bends hair cells → bending sends signals to the brain about head rotation direction and speed.
Firing patterns of semicircular canals
When the head moves in the preferred plane of a specific canal, one canal will show increased firing of its neurons, while the opposing canal will exhibit decreased firing.
- orientations (horizontal, anterior and posterior)
- horizontal turning head left or right
- anterior : nodding up and down
- posterior : tilting head toward the sholder
Functionality of semicircular canals
- sensitive to angular acceleration
- they detect changes in motion.
- they are less effective for sensing sustained movement. eg. this is why you might stop feeling dizzy after spinning, the system has adapted to the constant motion (the endolymph fluid moves at the same speed as the canal walls
Purpose of vestibulo-ocular reflex
helps maintain a stable image on the retina by coordinating eye movements with head movements.
Compensatory eye movement
- When the head moves, the VOR causes the eyes to move in the opposite direction
- stabilizes the visual field, allowing activities like reading street signs while walking or keeping focus on a screen during head shifts.
Cerebellum’s role in vestibulo-ocular reflex
It receives signals from the vestibular system, visual inputs, and motor commands.
It can suppress the VOR when necessary (e.g., during specific visual tasks) and adjust or calibrate the reflex, such as when adapting to new glasses.
What happens if one set of canals are damaged?
vertigo and nystagmus
How do vestibular signals reach the vestibular cortex?
via the thalamus
What types of sensory inputs does the vestibular cortex integrate?
Vestibular, visual, and somatosensory inputs.
Why is the integration of sensory inputs in the vestibular cortex important?
It is crucial for the perception of self-motion and orientation.
What is the dorsal stream’s role in relation to the vestibular cortex?
It processes spatial awareness and movement.
What perceptual distortion may occur in patients with parietal lesions?
They may perceive the world as rotated by 90º or 180º.
Two types of mechanoreceptors based on adaptation speed
Rapidly adapting (RA) and slowly adapting (SA)
What do rapidly adapting (RA) mechanoreceptors signal?
Changes in touch
- most common in the hand
-lateral motion
What do slowly adapting (SA) mechanoreceptors signal?
Constant touch
- edges, points, fine details of objects
What are the two types of mechanoreceptors based on size and location?
Type 1 and Type 2.
Describe the characteristics of Type 1 mechanoreceptors.
Small size, small receptive fields (RFs), superficially located, and frequent.
Describe the characteristics of Type 2 mechanoreceptors.
Large size, large receptive fields (RFs), deep, and sparse.
Where do thalamic inputs project in the somatosensory cortex?
to layer IV of S1 (postcentral gyrus of the parietal lobe).
What type of map is found in S1, and what does it represent?
A somatotopic map, where adjacent neurons receive inputs from sensory neurons with adjacent receptive fields.
Is the cortical representation in S1 proportional to body size?
No
What is the columnar organization in S1?
Neurons in the same column respond to similar types of stimuli and have similar receptive fields (e.g., SA1, SA2, RA1, RA2).
How do receptive fields (RFs) in S1 compare to those in sensory neurons?
RFs in S1 are larger than in sensory neurons.
What role does inhibition play in S1 cortical neurons?
Inhibition creates on/excitatory and off/inhibitory fields, sharpening responses and promoting acuity.
What additional factors can influence neuron firing in S2 compared to simple touch location?
Size, orientation, shape of the stimulus, movement, grip force, and hand posture.
In which areas of the brain can receptive fields become bilateral?
In S2 and the posterior parietal cortex.
What is one way that the function of neurons in S2 differs from those in S1?
Neurons in S2 respond to more complex characteristics of stimuli, not just location.
How many types of receptors does each receptor neuron have? (The olfactory system)
Each receptor neuron has only one type of receptor.
How are different types of odorant receptors arranged in the olfactory epithelium?
The different types are randomly scattered.
Where do all receptor neurons of the same class project in the olfactory bulb?
They project to the same few glomeruli.
What type of map exists in the olfactory bulb due to receptor projections?
A chemotopic map.
How do receptor neurons activate in response to specific odorants?
An individual odorant activates multiple receptors/glomeruli.
How does each receptor interact with different odorants?
Each receptor binds multiple different odorants with varying affinity.
What is the significance of the population code in olfactory processing?
The pattern of activity from activated receptors is unique for each odor.
What type of distribution is seen in the sensory neurons for olfactory receptors?
A random and overlapping distribution.
What are the five different taste qualities that can be detected?
Sweet, bitter, sour, salty, and umami.
How does taste differ from flavor?
Taste refers to basic sensations, while flavor is a combination of gustatory, somatosensory, and olfactory signals.
How many taste receptor cells are located in taste buds on the tongue?
Approximately 100 taste receptor cells.
Where else, besides the tongue, can taste receptor cells be found?
In some surrounding tissues.
How are taste cells maintained over time?
They are short-lived and replaced via stem cells.
How are tastants detected by taste cells?
tastants are dissolved in saliva and detected by microvilli in the taste pore.
Do taste cells generate action potentials and release neurotransmitters?
Yes, but they are not neurons; they are derived from epithelial tissue, not neural tissue.
Does each taste cell express multiple types of receptors?
No, mostly a single taste cell expresses a certain receptor.
Which taste qualities interact with G-protein coupled receptors?
Bitter, sweet, and umami.
What compound primarily triggers the umami taste in humans?
Amino acids, especially glutamate.
How many types of bitter receptors exist, and can a single cell express multiple?
There are 30 different bitter receptors, and a single cell can express multiple receptors.
Why do all bitter compounds taste similar?
They integrate into the same receptor cells, intensity may vary.
Which types of tastants interact with ionotropic receptors?
Salty and sour tastants.
How is the salty taste detected?
Through Na+ ions diffusing into the cell or opening Na+ channels.
How is sour taste detected, and why is it innately aversive?
Likely through H+ ions, and it is aversive to help avoid spoiled foods.
Through which structure do gustatory pathways reach the cortex?
The thalamus
Which brain structure projects to the hypothalamus to regulate feeding and autonomic behavior?
The thalamus
What role does the gustatory cortex play in taste perception?
It mediates conscious perception and discrimination of taste.
How do some cells in the gustatory cortex respond to taste types?
Some respond to a single taste type, while others respond to combinations.
What three senses contribute to the perception of flavor?
Taste, olfaction, and somatosensation.
Why might flavors be perceived as coming from the mouth rather than the nose?
Due to somatosensory stimulation of the tongue.
Miraculin
makes bitter things taste sweet
