Sensory physiology 2 Flashcards
What does sound cause? What does the loudness of sound affect?
Vibration of surrounding air molecules: starts to compress the air molecules and create areas of compression and rarefaction
- So will see patterns of high density air and low density air
Loudness of sound affects the pattern of compression and rarefaction (the difference in absolute pressure between the compression and rarefaction)
How is the loudness of sound measured?
In dB
Frequency (Hz)
How often compression/rarefaction happen per unit time
What do wavelength/frequency (Hz) of sound affect?
Affects the pitch of a sound
The ear is separated into what 3 general components?
- Outer ear
- Middle ear
- Inner ear
Pinna functions (2)
- Funnels sound towards inner ear (some animals can change pinna positioning to help with sound functioning)
- Aids in sound localization
What 2 things allow for sound localization?
- Timing of sound
- Amplitude of sound
Describe how the timing of the sound aids in sound localization
Sound arrives at one ear slightly before it reaches the other ear
- Difference in the timing helps determine where sound is coming from when sound is coming from one side (not in front or back of individual)
Describe how amplitude of sound aids in sound localization
Head can attenuate sound that passes through the head
- Sound shadow: what reaches the other ear is going to be reduced in amplitude
- Doesn’t work great if the sound is directly in front of us vs. directly behind us (good for detecting sounds coming from different sides)
What 4 components make up the middle ear?
- Malleus ossicle (hammer)
- Touches back of tympanic membrane - Incus (anvil)
- Touches malleus and stapes - Stapes (stirrup)
- Stapes is making contact with the oval window - Tympanic membrane
- Structure that represents the beginning of the middle ear
What are the 3 main purposes of auditory ossicles?
- To transmit sound waves to inner ear
- To amplify incoming signal (VERY important)
- To protect sensitive inner ear from loud sounds (through the activity of muscles connected to the ossicles)
Why is amplification of sound by ossicles important?
The outer + middle ears are filled with air, while the inner ear is fluid-filled (more dense than air)
- When you go from low density to high density, sound waves lose energy (sound gets muffled - attenuated)
- Ossicles ensure sound doesn’t get attenuated.
What 2 muscles are connected to the auditory ossicles? What do both of these muscles help with?
- Tensor tympani muscle
- Stapedius muscle
Both help with the acoustic reflex: the muscles prevent overstimulation of the ear from chewing + talking, but also automatically contract and clamp down on the ossicles to decrease the sound energy when a very loud sound is encountered
Tensor tympani muscle functions (2)
- Pulls malleus medially (reduces the amount that the malleus can vibrate, which protects the ear from loud sounds
- Reduces the amount of the chewing sound that reaches the inner ear
Stapedius muscle functions (2)
- Pulls on the stapes
- As you speak, this muscle contracts and reduces the energy from your vocal cords vibrating that reaches your inner ear.
True or false: the acoustic reflex always works
False
- The acoustic reflex is very quick but not quick enough for a very quick sound like a gunshot (so this can still cause hearing damage)
What does the oval window serve as?
The barrier between the middle ear and the inner ear
What is the main structure that makes up the inner ear?
The cochlea
What parts make up the cochlea? Draw the cochlea out and label all its parts (5)
- Scala vestibuli/vestibular canal (connected to oval window)
- Extends the entire length of the cochlea - Helicotrema (end of scala vestibuli, start of scala tympani)
- Scala tympani/tympanic canal
- Scala media (between scala vestibuli and scala tympani)
- Basal membrane
- border between the bottom of the scala vestibuli and the top of the scala tympani
What pathway of sound waves through the cochlea causes tranduction of sound energy?
Sound waves moving through scala media (not through scala vestibuli and around cochlea)
- Disruption of fluid in scala media and basilar membrane starts to vibrate -> so organ of corti sitting on the basilar membrane starts vibration -> transduction
True or false: the basilar membrane is a uniform thickness throughout the entire cochlea
False
- Basilar membrane is narrow and still near oval window, and gradually gets thicker (wider + fluid) towards helicotrema
Low frequencies allow for the ____ basilar membrane near the ____ to vibrate and transduce sound energy into action potentials
Thicker, helicotrema
High frequencies allow for the ___ basilar membrane near the ____ to vibrate and transduce sound energy into action potentials
Thinner, oval window
True or false: as we age, we lose our ability to hear higher pitched sounds (higher frequencies), resulting from changes to our oval window
True
Describe how the frequency distribution of the basilar membrane vibrations related to the labelled lines principle
Sensory neurons in the basilar membrane synapse with different regions in the cortex
- So primary auditory is organized by frequency
Draw and label the organ of Corti. What is contained within the organ of Corti?
- Tectorial membrane (stereocilia from hair cells attach here)
- Support cells (organ of Corti does not include the basilar membrane)
- Inner hair cells
- responsible for the vast majority of auditory transduction - Outer hair cells
What specifically causes the transduction of sound?
The bending of the stereocilia extending from the hair cells
- As the basilar membrane starts to vibrate, the stereocilia of the hair cells gets pushed and pulled only in the area where the basilar membrane is moving
What is the kinocilium?
A large, rigid stereocilium on hair cells (on tallest stereocilium)
- Not present in the auditory system but present in other hair cells
What links stereocilia together?
Tip links (protein)
Describe how stereocilia movement leads to signal transduction
As stereocilia bend toward tall stereocilium, the tip links connected to stretch-activated channels open these channels and allow for depolarization of the hair cells
- As stereocilia bend towards short stereocilium, hyperpolarization occurs due to channels closing
What ions cause depolarization of hair cells?
K+ mainly, and some Ca2+
- Not Na+ like in the somatosensory system
The ____lymph is found in the scala vestibuli and the scala tympani, while ___lymph is found in the scala media
Perilymph, endolymph
Perilymph is similar to…
Extracellular fluid (high Na+, low K+ and high Cl-)
Endolymph is similar to…
- Explain the result of this
Intracellular fluid (high K+)
- Why K+ flows into hair cells to depolarize them
True or false: Hair cells generate action potentials
False
- Their membrane potential changes as hair cells move, which allows for neurotransmitter exocytosis.
- The neurotransmitters then bind to neurons that connect to the brain
Why do hair cells cause a resting discharge of action potentials?
When the hair cell is sitting at rest, some channels are open -> still some neurotransmitter released so neuron fires action potentials
Increased action potential frequency occurs when…
There’s a change in sound of a given frequency
What 3 organs make up the vestibular system?
- Semicircular canals
- Utricle
- Saccule
Otolith organs
Utricle and saccule
Describe how semicircular canals help with balance? What ions cause depolarization?
When the head rotates, the endolymph in the semicircular canals delays a bit and flows in the opposite direction. This bends the cupula/ampulla, and organ filled with hair cells which is at the bottom of each of the semicircular canals and causes stretch-activated channels to open.
- K+ and Ca2+ flow into these hair cells as well.
The direction of the endolymph and cupula bending in semicircular canals is (the same/opposite) when the head rotates, which helps with…
Opposite
- Causes hyperpolarization in one group of hair cells and depolarization in the other, which helps with fidelity of signal reaching brain.
The semicircular canals identify…
Rotation of the head
What are the three types of rotational movement of the head?
- Shaking head
- Nodding
- Tilting head to the side
What structure in semicircular canals houses all the hair cells?
The cupula (in the apex)
How are semicircular canals oriented relative to each other?
~90 degrees
True or false: hair cells in the cupula have a kinocilium
True
- but not present in auditory system
- kinocilium helps support stereocilia as they stand upright
Vestibular and auditory nerves?
Nerves that merge all the sensory neurons from the vestibular/auditory system.
What do otolith organs detect?
Linear movement (no head rotation, either motion in a straight line or slow tilting of the head relative to gravity)
How do otolith organs detect linear movement?
A gelatinous layer covered with otoliths (calcium carbonate) is present above the hair cells
- The otoliths are heavier which causes them to lag behind the gelatinous layer
- Causes stereocilia to bend
What type of linear movement is best identified by the utricle and why?
Horizontal movement (e.g. moving forward or back) because it’s oriented horizontally
What type of linear movement is best identified by the saccule and why?
Vertical movement (e.g. head while squatting) because it’s oriented vertically
True or false: The saccule stereocilia is a little bit bent in its resting position so the saccule hair cells are always active
False
- They are bent, but that doesn’t mean they’re always active
- Any vertical movement will cause lagging of the otoliths
We have 3 semicircular canals which allows for detection of movement in all 3 orientations. However, we only have 2 otolith organs. So how is the third orientation of linear movement (e.g. lunges) detected?
We are able to detect the third dimension because of the way in which the stereocilia are positioned within the saccule and urticle.
