BIOL 455 Hearing
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1. Define sound
2. What does it physically look like?
3. What is it caused by? Examples (2)?
4. What is one cycle?
- 1. Repetive pattern of local increases and decreases in air pressure
- 2. Sine wave
- 3. Vibrating objects (tuning fork, person's larynx)
- 4. single alteration of compression and expansion of air
1. What is a complex sound? has 3 parts
2. Very simply, how does ear analyze sounds? - name and how?
3. What does the above concept deal with? 2
- 1. Sum of pure tones (fundamental frequencies and harmonics and their constructive and deconstructive interferences
- 2. Fast fourier transform - ear deconstructs complex sounds into simple sine waves due to place theory on basilar membrane
- 3. Pitch perception and labeled lines
1. Another word for external ear?
2. Function? (4)
3. What is important about external ears in humans?
4. Who has them?
5. Who does morphology vary between? (2)
6. What are the implications of exchanging pinna?
- 1. Pinna
- 2. Captures, focuses, filters sound & localization
- 3. Filters range of frequency in human speech (2-5 KHz)
- 4. Mammals
- 5. Between species (bats vs. elephants) and among species (luis vs. me)
- 6. Will not be able to hear as well because over lifetime, brain has adapted to perception of sound filtered by pinna.
1. What frequency of sound do pinna in humans filter for? Why?
2. What locations can pinna help discern? What feature of pinnae?
3.Role of plasticity in pinna?
- 1. 2-5 KHz, range perfect for human speech
- 2. In front or behind - asymmetrical pinnae
- 3. Switching pinnae with somebody else will alter your perception of hearing, but due to neuroplasticity, you will be able to adapt.
1. Where is middle ear located?
2. What are the 3 bones?
3. What part of ear is the tympanic membrane part of?
4. What are the functions of the middle ear? (2)
- 1. Between tympanic canal and oval window
- 2. Malleus, incus, and stapes
- 3. None, just separates outer and middle
1. Concentrating mechanical energy from changes in air pressure to fluid-filled chambers of air, allowing recovery of information that would have been lost from going into denser medium.
2. Ear muscles can stiffen
, reducing effectiveness of self-sounds (body movement, swallowing, vocalizations, etc).
Describe mechanism of how middle ear works (3)
What is final result?
How much is recovered? Out of what?
- 1. Changes in air pressure (sound) move tympanic membrane
- 2. --> moves chain of ossicles (malleus, incus, stapes).
- 3. ---> Ossicles concentrate tiny mechanical forces of vibrating particles from LARGE eardrum to small oval window.
Final result: amplification
of sound pressure (increases in intensity and amplitude), so it can recover loss of vibration from going from air to more dense medium
Recovers 20 out of 30 dB that would have been lost.
1. What is the function of the inner ear?
2. Most important structure?
1. Define the cochlea? (2) Where is it located?
2. What does it contain? (3) canals
3. What does the basilar membrane separate? 4. Describe the base of the basilar membrane (2)- what is it closest to? What frequency (musical term) is it best suited for?
5. Same questions for apex.
- 1. Cochlea - auditory portion of the inner ear; coiled, fluid-filled structural in the temporal bone of the skull.
- 2. Scala vestibuli, media, tympani (vestibular, medial, and tympanic canals)
- 3. Vestibular and tympanic canals
- 4. It is narrow and stiff; oval window - high frequencies (treble) cause max displacement at base
- 5. It is wide and bendy; round window - low freqencies (bass) cause max displacement at apex.
1. What enhances maximum displacement of low frequencies at apex?
2. Where would human speech cause max displacement?
3. What is lowest frequency?
4. What happens when the oval window pushes in? What does this connect? Why is this important?
- 1. Curvature of cochlea
- 2. At base (1600 Hz is close to base)
- 3. 25 Hz
- 4. Round window pushes out (connects vestibular and tympanic canals), so ear doesn't burst!
1. Where is organ of corti? (specifically - 2 descriptions)
2. What is its function?
3. Structure? (3)
4. What is tectorial membrane connected to? (2) in what fashion?
- 1. In middle canal on top of basilar membrane
- 2. To transduce mechanical energy into electrical/neural activity
- 3. Hair cells (sensory cells), supporting cells, and terminations of auditory fibers
- 4. To basilar membrane (hingelike fashion) and hair cells (some stereocilia are embedded within it)
1. What is the base of the organ of Corti?
2. What might a picture look like?
3. Which membrane moves in response to changes in fluid pressure in vestibular and tympanic canal? How does their movements relate to each other?
4. What happens when a wave of pressure comes in and hits basilar membrane?
5. What does hinging do to stereocilia? What happens next? (very simply)
- 1. Basilar membrane
- 3. Both basilar and tectorial - independently (kind of)
- 4. Basilar membrane moves --> pushing hair cells up --> tectorial membrane moves
- 5. Deflects stereocilia causing depolarization
1. What do tip links do?
2. Describe mechanism of how hair cells transduce sound into neural activity (6)
1. They connect stereocilia to its adjacent neighbors
- 1. Sounds induce vibrations of
- basilar membrane
- 2. Vibrations bend hair cell
- stereocilia that are inserted into tectorial membrane
- 3. Very small displacements of
- hair bundles (swaying) increases tension on elastic tip links and pop open
- ion channels and immediately snap shut again when hair sways back.
- 4. Opens non-selective ion
- channels allow inrush of K+ and Ca2+ ions and rapid depolarization of
- entire hair cell.
- 5. Initial depolarization leads
- to voltage-gated Ca2+ channels --> rapid influx of Ca2+ at base of hair
- cell, causing synaptic vesicles there to fuse with the presynaptic
- membrane and release their neurotransmitter contents
- 6. Neurotransmitters trigger
- action potentials in afferent fiber axons.
1. What happens if you don't have IHCs? Why?
2. What is purpose of OHCs?
3. What if you don't have these?
- 1. Deafness, because IHCs are connected to 95% of afferent auditory fibers, thus are extremely important for perception of sound.
- 2. OHCs are necessary for cochlear amplifier
- 3. Can still hear, but not as well.
1. What does cochlear amplifier do?
2. What is the smallest difference in frequency we, as humans, can differentiate?
3. How did we know there was the existence of a cochlear amplifier?
- 1. Amplifies movements of basilar membrane in some regions and dampens movements in other regions, sharpening tuning of cochlea.
- 2. 2 Hz
- 3. Because just having the basic physical characteristics of the basilar membrane can't account for such fine differentiation of pitch.
Describe mechanism of cochlear amplifier
2. Mechanism (5)
1. Background: OHCs have voltage-sensitive and voltage-specific proteins - each OHC has a preference for a characteristic oscillatory frequency
- 1. Certain frequency that is perfect for certain OHC enters inner ear
- 2. BM moves in response
- 3. If it moves enough because initial oscillatory frequency was perfect enough, cells will either hyperpolarize or depolarize.
- 4. Prestin - transmembrane protein will mechanically elongate or contract in response to hyperpolarization (lengthening) or depolarization (shortening)
- 5. This lengthening/shortening of hair cell leads to stiffening or relaxing segments of BM to actively sharpen its tuning to different frequencies.
1. Describe, in Burmeister's words, how an OHC that deflects best for 100 Hz will lead to better perception of sound. 6
1. An OHC that deflects best for 100 Hz --> has oscillatory frequency of 100 Hz --> will push tectorial membrane at 100 Hz --> which in turn will deflect IHCs --> IHCs will depolarize --> better perception of sound.
1. Define spontaneous otoacoustic emissions
2. Are these individualized? How can they vary from person to person? (2) Do they stay constant for each person?
3. What is cochlear amplifer development influenced by? Who has more emissions? What does this mean?
4. What would decrease emissions? (2)
5. What is manifested early in life and long-lasting?
- 1. Active, ongoing modulation of basilar membrane (inherent oscillatory frequencies) produces pure tones by pushing back on ear drum.
- 2. Yes. By frequency and number. Yes throughout life.
- 3. Sex - females have more than men (better hearing)
- 4. Being a monozygotic female with a male twin - masculinized by presence of twin --> less emissions
Being a lesbian (gay men don't see a difference
5. Otoacoustic emissions
1. What is place theory?
2. What is it the basis of?
3. What is good evidence of this?
4. What is an example of this in terms of physiology?
5. What does it predict?
6. What happens for complex sounds with components of lots of diff frequencies?
- 1. Pitch is encoded in the physical location of activated receptors along the basilar membrane: activation of receptors near base of cochlea = high frequency; activation of receptors near apex = low frequency signal bass
- 2. Labeled line theory
- 3. The fact that the cochlear nucleus (first place in brain where hair cell afferent fibers terminate) is tonotopically organized based on frequency.
- 4. What I said above about base and treble
- 5. A change in frequency is acompanied by a change in the region of max disturbance of the basilar membrane, as well as activation of auditory receptors found there.
- 6. Fourier transform - different frequencies will activate different areas of membrane
1. What is volley theory? Another name?
3. What is required?
4. What is the max firing rate of neurons w/o any help?
5. What does volley theory allow?
- 1. Frequency theory - frequency of auditory stimuli is directly encoded in firing pattern of auditory neurons. Low frequency is 1:1, while high frequency encodes auditory frequency that is integer multiple - theory of frequency discrimination that emphasizes relationship between sound frequency and firing pattern of nerve cells.
- 2. A 500 Hz sound wave will cause some neurons to fire 500 action potentials per second.
- 3. Population of phase-locked cells that fire at exact same spot on wave (i.e., top or bottom, etc).
- 4. 1200 Hz
- 5. By integrating info from lots of different cells, allows allows us to have larger range of frequencies.
1. What does loudness depend on?
2. Describe how a louder sound will affect transduction?
3. How would you describe how the cells work together? What is this like?
4. How many cells respond if its low intensity? If it's high intensity? why?
- 1. Amplitude
- 2. Greater amplitude --> greater eardrum deflection --> greater BM displacement in the region of peak responsiveness (frequency) --> increased stereocilia deflection --> CNA interprets greater BM oscillation and hair bending as louder sound.
- 3. Range fractionation. Volley theory
- 4. 1. More than one. broader range of frequencies can elicit response from cell, so NS can determine intensity of the stimulus.
1. What does narrow tuning curve mean? What is it better at representing?
2. Where is best excitatory frequency of each fiber? Define best excitatory frequency in relation to intensity
4. What does each color represent?
5. Because these represent threshold measurements....what does htis mean?
6. Why is this important for a louder sound?
7. What does a lower curve indicate?
- 1. More sharply-tuned - better at representing frequency.
- 2. At the trough. The lowest intensity of stimulus needed to get response from cell.
- 4. Different fiber (inner hair cell to cochlear nucleus)
- 5. The lowest point on the curve corresponds with neuron's best characteristic frequency.
- 6. Because at higher amplitudes of sound, the curve is broader, so it's more difficult to determine loudness. By comparing to other activated neurons, you can determine exact amplitude.
1. Are BM and cochlear amplifier required for loudness? What else are they required for?
2. What does cochlear amplifer enable? For what theory?
3. For sound localization, what is auditory system simlar to? What is it different from? (2)
- 1. No, but they are required for pitch perception.
- 2. Labeled lines. CA gives us sharply-tuned auditory fibers, because info is kept separated on precise, tonotopic lines. for place theory
- 3. Olfactory system, because basilar membrane is like olfactory epithelium - stimulus being transduced at a certain location contains no information about the location of the stimulus itself.
This is unlike somatosensory/visual system (retina).
1. What are the interaural cues for localization? (3)
Explain each one.
- What is necessary for the second one? Why? What does it give?
Draw two of the graphs.
1. Latency - onset timing difference and ongoing phase disparity; intensity
- 1. Onset timing difference - difference between two eras in hearing the beginning of the sound.
- 2. Ongoing phase disparity - continuous mismatch between the two ears at the arrival of all the peaks and troughs that make up the sound wave
- - Requires phase-locked cell b/c it has info about frequency due to phase of pressure wave and disparity of wave. Gives amplitude envelope allowing us to receive info throughout sound.
Intensity - difference in loudness arises because head creates sound shadow
blocking off-axis sounds from reaching both ears with equal loudness.
- Most pronounced for higher frequencies, because lower frequencies have longer sound waves that reach around the head.
Describe projections going from ear to brain (6) Also describe where each place is.
1. Where does info start being compared?
2. Where is a map of space created? What else does this thang do?
3. Where does crossing over occur?
4. Where are we first aware of sound?
Ear ---< cochlear nucleus (medulla) ---< superior olive (medulla) ---< inferior colliculus (midbrain) ---< medial geniculate nucleus (thalamus) ----< primary auditory cortex
- 1. Superior olive
- 2. Inferior colliculus -map of space, locating/orienting to sound, descending projections to motor pathways to allow motor response to sound.
- 3. Superior olive nucleus (gets info from ipsilateral and contralateral cochlear nuclei)
- 4. Primary auditory cortex.
1. Where do auditory fibers from hair cells terminate?
2. What do these fibers give info about? (2)
3. What retains this info? What does this info create?
4. What cells are here - slow-adapting? fast-adapting? phasic/tonic? Which cell provides info about onset of stimulus?
- 1. Cochlear nucleus
- 2. Intensity and frequency
- 3. Cochlear nucleus, creating tonotopic map4. Stellate cells (slow-adapting, tonic) one stellate cell fires in response to pure tone, then continues at similar frequency of firing until no more sound.
Bushy cells (super fast-adapting; phasic) - at stimulus, cells fire a single action potential at onset of sound and no more.
1. Draw what happens in lateral superior olive and medial superior olive
2. What does LSO compare?
3. Describe mechanism for Jeffres model of sound localization
- 2. Intensity differences
- 3. can be mapped onto particular timing difference.
- 0. Sound from left of owl's midline is detected by left cochlea slightly earlier than right cochlea.
- 1.Monaural neurons of the left cochlear nucleus of the brainstem become active, sending AP's along axons towards nucleus laminaris.
- 2.Since they were fired earlier, left side AP's have traveled farther on axons.-Shortly after, the monoaural neurons of right cochlear nucleus send their own AP's toward nucleus laminaris.
- 3.So, the AP from left and the AP from right arrive simultaneously at neuron 5, but not at any other binaural neuron.
- 4.Neuron 5 is thus a coincidence detector that signals a particular location to left of midline
1. What processes info from medial superior olive? How?
2. For this to work, what must be detectable?
3. What type of cell is needed?
- 1. Inferior colliculus - determines which cell in array has been most excited, mapping onto particular timing difference
- 2. Real-time diff between stimulus reaching first cell vs. last cell
- 3. Coincidence detectors - Post-synaptic cells that are only going to exceed threshold when they're excited simultaneously
1. What do we need to elicit behavior?
2. What are the two types of motor outputs? Define each.
3. Which doesn't involve brain input? Draw projections
4. Define movements and motor acts
- 1. Motoneurons
- 2. Reflexes - simple, highly stereotyped, and unlearned repsonse to stimulus.
Motor programs - complex set of commands to muscles that is completely established before act occurs (piano playing, escaping)
3. Reflexes (sensory --> spinal cord --> motor)
4. movements - muscle contraction; motor acts - series of movements for certain goal/function
1. Draw hierarchy of motor control (6)
Name what each thing does.
Name two structures in the list not in the map and describe what they do (1: 1 thing; 2 functions. 2: two things, one function)
- 1. Skeletal systems constrain movement
- 2. Spinal cord where motoneurons exist & control muscle movement in response to sensory information (reflex, motor programs), implement motor commands from brain
- integrates motor commands from higher levels of brain and transmits them to spinal cord & relays sensory info about body from spinal cord to forebrain
4. Primary cortex
- command center for initiating movements - has descending outputs to motoneurons in brainstem and spinal cord.
- 1. Non-primary motor cortex - planning and adjustment
- 2. Non-cortical areas - basal ganglia and cerebellum moderate activities.
1. Where do motoneurons exist?
2. Define motoneurons
3. Why are they the final common pathway for motor production?
4. What NT do they release?
- 1. In brainstem and spinal cord.
- 2. Neurons that send their axons to innervate muscle
- 3. Because they are the sole route through which the spinal cord and brain (cranial nerve nuclei) can send APs along their axons to control muscles.
- 4. Ach
1. Define neuromuscular junction
2. What almost always happens when an AP reaches this junction? When doesn't it happen?
3. Define innervation ratio. What does this determine?
4. What happens to muscle fibers when a motoneuron fires?
5. What is the largest cell in spinal cord? What is super large about them?
6. What do you need to increase contraction in muscle?
- 1. Neuromusclar junction: region where motoneuron terminal and adjoining muscle fiber meet.
- 2. Ach is always excitatory, so generally triggers action potential and contraction in innervated muscle fiber. When muscle fiber is fatigued.
- 3. Ratio of muscle fibers:motoneuron. Determines precision. Increased ratio = less precision.
- 4. ALL muscle fibers innervated by that motoneuron contract
- 5. Mooneurons, huge dendrites
- 6. Increase motoneuron activation
1. What does primary motor cortex do? (3)
2. What system descends from M1?
3. Where does this system decussate? What does right cortex control?
4. Does motor cortex have homunculus? If so, what is M1 most devoted to? What does it determine?
5. How is this seen in other animals? Define sparse code.
- 1. responsible for initiating, planning, executing movements, etc.
- 2. Pyramidal
- 3. Pyramid of medulla - right cortex controls left side of body
- 4. Yes. M1 is most devoted to lips, tongue, and hands/fingers. Determines fine motor control.
- 5. Individual neuron action potentials elicit motor programs. Other animals have more precise control in same regions. Birds have sparse code.
1. Describe the experiment that determined whether neurons in M1 represented muscles or movements (Task, what is being measured, independent variables)
4. What was the specific research question?
5. What were the findings?
1. Task: Monkey moves cursor to central target, then peripheral circle shows up as yellow. Monkey must then move cursor to target circle to get treat.
2. Recordings from individual motor cortex neurons
3. Position of forearm - vertical, supination, or pronation to control which muscles are being used.
- 4. Does activity of a cortical motor neuron encode a relatively simple paramater (i.e., contraction of particular muscle) or does it encode more abstract paramter, such as particular movement of hand through space?
- 5. 30% of M1 neurons corresponded to muscle movements, but 50% of M1 neurons corresponded to movements in space, regardless of hand posture.
1. What type of neural plasticity exists in M1?
2. What type of plasticity can change as a result of training?
3. Is this useful during deficit?
4. What two parts are in the non-primary cortex?
- 1. Lifetime
- 2. M1's short-term plasticity can change
- 3. Yes.
- 4. Supplementary motor area (SMA) and premotor cortex
1. What is supplementary motor area importnat for? (2)
2. What happens when there's a lesion for SMA?
3. Where does it receive input from?
4. What does it respond to?
1. What is premotor cortex activated by? Name 3 specific exmaples
2. What important area does it contain? When are these neurons active? (2)
3. What does the above code for?
- 1. External stimuli (walking, gait, coordination)
- 2. Area F5 - mirror neurons (1) when an individual makes a particular movement (2) when an individual watches someone else make a movement
- 3. Codes for GOAL of motor action, not just action
1. How do researchers know that the SMA is important for planning?
2. What are the parts of the extrapyramidal pathways?
- 1. In actually keeping a spring compressed, more blood flow went to contralateral M1, while THINKING about the task increased blood flow to include SMA.
- 2. Basal ganglia, reticular formation, cerebellum.
1. What pathway is it part of?
2. What neurons is it important for?
3. WHat is its role in vocal learning?
4. What does it do in terms of movement?
5. What is special about this?
- 1. Extrapyramidal
- 2. Motoneurons
- 3. Loops enable vocal learning
- 4. Modifies/initiates programs (amplitude of movement/direction)
- 5. Is activated in response to memories.
1. Is it layered?
2. What's important about its size?
3. What does it affect? (3)
4. What types of movements is it especially important for?
5. What is basal ganglia more correlated with? What about cerebellum?
- 1. Yes
- 2. Size is associated with its function/complexity
- 3. Motor programs, coordination, and learning motor tasks (esp sequential).
- 4. Sequential
- 5. BG is more correlated with M1, while cerebellum --> SMA.
1. Is mirror neuron system confined to motor system?
2. When does it fire? (2)
3. Where does it take place?
4. What is its role in language? What area of brain?
- 1. No.
- 2. When an individual does, thinks, or feels something or when it observes someone else doing the asme.
- 3. It takes place in Area F5 in the premotor cortex.
- 4. Broca's area - takes heard phonemes and maps onto motor patterns of phonemes. Even with unfamiliar motoneurons, motoneurons for words are activated upon hearing it.
1. What part is important for emotional responses?
2. What else does this thing code for?
3. What experiment was this proven in?
4. Outside of motor system, where are mirror neurons seen? (2)
- 1. Insula and anterior cingulate cortex2. Codes for intentions of others, understanding the movement of other individuals
- 3. The monkey watching the person grab for an apple/empty space and when it was covered up.
- 4. These same two places.
1. What is evolutionarily great about mirror neuron system?
2. Since mirror system connects anticipation and inferring, what does it have implications for? (2)
3. Describe the experiment testing this in autistic children. What was recorded? Normal children/autistic children:
3a. Watching actor? 3b. Picking up themselvs?
- 1. Saves space instead of having lots of other cells code for other animal's behavior
- 2. Empathy and understanding
- 3. Recorded movement of muscle in jaw of actor putting food in mouth or paper on shoulder.
- 3a. Normal child anticipates chewing when food is picked up, but not paper. Autistic child has no anticipation.
3b.Normal - anticipation for food, not paper. Autism - no anticipation for food or paper.
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