Week 7. Other Senses Flashcards
What are the 3 properties of audition?
1) Pitch (frequency)
2) Loudness (amplitude)
3) Timbre
What is frequency?
Refers to the number of cycles per second
Higher frequency -> more cycles per second
Related to pitch
high freq -> high pitch
low freq -> low pitch
What is amplitude?
Refers to magnitude of wave as measured from peak to trough.
Related to loudness.
What is timbre?
Tone colour/quality
relates to other secondary frequencies present in the signal. identical air vibrations means same timbre.
What is the pinna and where is it located?
A structure that alters the reflection of sound waves, and helps us locate source of sounds in the vertical axis.
Found in outer ear.
What is the tympanic membrane (eardrum)?
A membrane that connects the outer and middle ear
Vibrates when struck by sound waves
Moves the 3 tiny bones of the middle ear
What are the names of the 3 tiny bones of the middle ear?
Malleus, Incus, Stapes.
What is the middle ear filled with and what is found there?
Air-filled
3 tiny bones found there
What is the oval window?
Connects the middle and inner ear
What is the eustachian tube?
connects middle ear with mouth cavity
What is located in the inner ear?
auditory receptors
Which structure contains auditory receptors and mediates audition?
Cochlea (snail-shaped structure)
What do the 3 semicircular canals do?
Mediate balance
There are 3 chambers in the cochlea. What are they filled with and what are their names?
Fluid-filled chambers. Fluid is called endolymph, which vibrates when the oval window vibrates.
Scala vestibuli, scala media, scala tympani.
Which structure is found in the middle chamber of the cochlea?
Organ of corti
What is the importance of the outer ear?
Reflects sound waves, important for sound localisation
What is the importance of the middle ear?
Amplifies sound waves through 3 tiny bones
What is the importance of the inner ear?
Contains cochlea that mediates audition and semicircular canals that mediate balance.
The organ of corti is composed of 3 structures, what are they?
1) tectorial membrane (top)
2) Hair cells (sensory neurons)
3) Basilar membraine (bottom)
The cilia of haircells in the organ or corti are joined together by molecular chains called ____.
tiplinks
What is mechanotransduction? Where does it occur?
Refers to the conversion of mechanical energy (movement) into electrochemical energy (cell polarisation). Occurs in hair cells.
Describe the general idea of mechanotransduction.
Air vibrations converted into vibrations of tympanic membrane, which in turn moves the 3 tiny bones, which moves the oval window membrane of cochlea. This generates action potentials in auditory nerve.
How do movement of the hair cells generate the auditory nerve?
they excite ganglion cells
What happens to the liquid in the chamber of the cochlea when the oval window membrane vibrates?
Movement of liquid in the chamber moves the membrane up and down at the same frequency as the sound frequency, and with an amplitude proportional to sound amplitude.
The organ of corti moves up when there is a ______ and moves down when there is a _____.
Depolarisation; repolarisation
What happens to the cilia when there is a movement of the organ of corti during a depolarisation?
The upward movement generates a deflection of the cilia towards the left because the tectorial membrane is laying on top of them.
The endolymph in the middle chamber is very ____ in K+ at the apex. The base of the haircell is ___ in K+.
High; low.
What condition results from the damage of delicate hair cells? What treatment can be used?
deafness. cochlea implants can be used to restore audition. array of electrodes is slowly pushed through the chambers to electrically stimulate different sections of the cochlea.
What condition results from the damage of delicate hair cells? What treatment can be used?
deafness. cochlear implants can be used to restore audition. array of electrodes is slowly pushed through the chambers to electrically stimulate different sections of the cochlea. It converts sound waves into patterns of electrical stimulation.
A cochlear implant will be useful to a person that is deaf due to:
haircell damage
middle ear damage
tympanic membrane damage
(all of the above. can mess up anything before that and it will still be useful)
Describe the auditory pathway.
signals from auditory nerve –> ipsilateral cochlear nucleus (brainstem) –> contralateral superior olive (brainstem) –> inferior colliculus (midbrain) –> medial geniculate nucleus (thalamus) –> auditory cortex
Signals from the left ear is processed in the ___ auditory cortex; signals from the right ear is processed in the ____ auditory cortex.
right; left
In the tonotopic map of primary auditory cortex, the low pitch sounds are processed in _____ positions and the high pitch sounds are processed in ____ positions.
anterior; posterior
What happens if there is damage to the primary auditory cortex?
we cannot discriminate different pitches, among other deficits. It does not lead to deafness!
What does the secondary auditory cortex do?
Performs more advanced processing of auditory signals
What are the 2 theories of pitch perception?
1) frequency theory
2) place theory
The frequency theory explains ___ frequency sounds best; the place theory explains ___ frequency sounds best.
low; high
What does the frequency theory propose?
states that the basilar membrane vibrates in synchrony with the sound and causes auditory nerve axons to produce action potentials at the same frequency as the sound.
What does the place theory propose?
states that each area along the basilar membrane has hair cells sensitive to only one specific frequency of wave. So by knowing where in the cochlea the activity came from, we can know the exact pitch.
How is it possible that the auditory nerve activates with frequencies of up to 4000hz, if the refractory period of a neuron only allows it to respond at at most 1000hz?
different neurons respond at different cycles of teh sound wave. so overall considering all neurons, the auditory nerve will become active 4000 times per second even if this exceeds the capacity of individual neurons.
What are the 3 methods of sound localisation in the horizontal axis?
1) Sound shadow
2) Difference in time of arrival of sounds between the ears
3) Phase difference between ears
How does sound shadow help in localising sound in the horizontal axis?
When a sound comes from a specific direction, head creates a shadow. Sound behind the head is lower in amplitude than the front. Brain computes the difference in amplitude to determine the location of sound. useful for high frequency sounds.
How does difference in time of arrival of sounds between the ears help in sound localization in the horizontal axis?
sounds needs to travel a longer distance to reach the further ear location. Depends on speed of sound and size of head. Useful for all frequencies, but only for sounds with sudden clear onset.
What frequency sounds is phase difference between ears useful for?
low
How do we localise sound in the vertical axis?
Interference patterns generated by the pinna
In the cross section of the semicircular canal, what is contained?
Otoliths (calcium carbonate) and endolymph.
The 3 semi-circcular canals convey information of ______.
The 3 axes of head rotation
When you move your head left and right (saying “no”), which semi circular canal’s endolymph moves?
horizontally oriented canal
When you move your head up and down (saying “yes”), which semi circular canal’s endolymph moves?
vertically oriented canal
When you move your head from head to shoulder, which semi circular canal’s endolymph moves?
third canal
What is the proposed role of otoliths in the endolypm of the semi-circular canals?
Thought to help give endolymph more weight, so the hairs are displaced more easily with movement. Hair cells inside the semi-circular canals get activated by specific rotation movements.
What is somatosensation?
Refers to sensations of the body, including touch, pressure, temperature, pain, itch/tickle, and position and movement of joints. Each sensation is mediated by different receptors.
What kind of axons do heat receptors have? What sensation does it mediate?
bare axons. burning pain, burning sensation in chilli (capsaicin)
What sensations do thermoreceptors mediate?
Warm and cold sensations
also have receptors to menthol (hot & cold at same time)
How do sensations reach the CNS?
Sensations reach the CNS through spinal nerves. Each spinal nerve (dermatone) conveys info about specific parts of the body.
What maps have we discussed in sensory areas?
visual - spatiotopic
auditory - tonotopic
senses - somatotopic
Describe the somatotopic map of the body.
Adjacent parts of the cortex process info of adjacent parts of the body.
Which parts of the body are overrepresented in the cortex?
Hands and face
Because we use sensations in our hands and faces for important tasks. Density of touch receptors in these areas is much higher than in other areas.
What is pain receptors called?
Nociceptors. Unmyelinated (slow transmission speed).
What are 2 types of nociceptors?
1) large diameter axon - conduct faster and transmit info about sharp pain
2) small diameter axon - conduct slower and transmit info about dull pain
Mild pain triggers the release of ____ in the spinal cord.
glutamate
Strong pain triggers the release of ____ in the spinal cord.
glutamate + substance P (neuropeptide)
What happens when pain signals reach the spinal cord?
They cross over to the contralateral side immediately. Unlike touch signals which go up the ipsilateral side of the spine and only cross over at the reticular formation of the midbrain.
What are the 2 distinct neural pathways for pain?
1) spinal cord –> thalamus –> primary somatosensory cortex (feeling pain and localising it)
2) spinal cord –> emotional centres (limbic system - amygdala, hippocampus, cingulate cortex) related to negative emotions associated with pain.
What are the 2 brain mechanisms to stop prolonged pain?
1) opioid system (endorphins)
2) cannabinoid system (endocannabinoids)
How do opiate mechanisms work?
Our bodies release a neurotransmitter called endorphin (endogenous morpine). Morphine has pain relief properties. Endorphine-producing neuron synapses onto the axon of the pain afferent, inhibiting it.
Where does opioid pain relief take place?
primarily in spinal cord and pariaqueductal gray area of midbrain.
How do cannabinoid receptors work?
Cannabinoids relief pain. Our bodies produce endocannabinoids which use the cannabinoid receptors.
How does the placebo effect potentially relief pain despite not having any pharmacological effect?
They play a role on blocking emotinoal responses to pain.
What is the neuronal sequence of chemical senses of taste?
Gustatory cells get activated by different chemicals, and then excite ganglion cells that form the gustatory nerve. Taste signals reach the brainstem’s nucleus of tractus solitarius.
What are the 5 types of gustatory cells?
- sweet
- sour
- bitter
- salty
- umami
What does the nucleus of tractus solitarius in the brainstem consist of? (3)
1) thalamus - primary somatosensory cortex (texture of food)
2) hypothalamus - conveyed to areas of limbic system (eg. amygdala, medial prefrontal cortex)
3) insula (primary taste cortex) - process info about taste itself
Describe the sequence of pathways of smell.
smell signals originate in olfactory receptor cells, which contain olfactory cilia which contain olfactory receptor types (hundreds - one for each smell). This information converges on the olfactory bulb, located in the base of the frontal lobe.
