University:
Binghamton University
Course:
BIOL 313 | Cellular Neurobiology
Academic year:

2024
Views:

50

Pages:

3
Author:

CrystalMintah

Outer hair cells - move with the basilar membrane tonotopic organization - Not signaling sound to the brain but receiving input from the brain - When the basilar membrane moves up. The outer hair cells depolarize (like the inner hair cells) - Depolarization causes a voltage-sensitive protein in their cell body to shorten - Protein is called prestin - As they shorten they move the basilar membrane up a bit more - At the frequency to which they are tuned When the basilar membrane moves down and past the “resting position” these cells hyperpolarize, prestin is not activated to contract and the outer hair cell body lengthens and the basiler membrane moves down a bit further at that frequency The activity of outer hair cells guarantees a sound that you can record coming out of the ear as they move the basiler membrane Otoacoustic emissions - It can be used diagnostically for hearing loss - Outer hair cells lose function? Hearing is impaired because frequencies are not so well tuned. Can hear sounds but not discriminate especially in conversations Outer hair cells are also used to change the dynamic range of hearing Like vision, you need some channels open / some closed to discriminate sounds Outer hair cells can adjust thus: Feedback from the brain comes to outer hair cells from the (medulla superior ) - Synapses with the outer hair cells and releases Ach - Ach is inhibitory - The Ach receptor on outer hair cells opens a channel for Na+ and Ca++ - Ca++ that enters opens the bK+ channels that are Ca++ activated K+ channels - Hair cell hyperpolarizes This inhibits the basiler membrane motor enhancement of the outer hair cell's import Loud sounds - inner hair cells → brain (medulla ) →Ach released onto outer hair cells → Na and ca channels open → activates Ca-activated potassium channels → outer hair cells have potassium efflux → outer hair cells hyperpolarizes → reduces motion Inner hair cells release neurotransmitters onto the next neurons in line Auditory neurons. There are cell bodies in the ganglion near the ear (spinal ganglion) Send axons → brain Auditory neurons fire action potentials - Action potential frequency depends on how much n.t they receive from the hair cells and stronger stimuli →more n.t → more a.p So can encode intensity based on their firing frequency Auditory neurons receive hair cell inputs by the frequency → they are also tonotopically organized Auditory neurons have tuning curves 1. Record from the cell 2. Play different frequencies 3. Determine what is the lowest intensity to get a response at each frequency 4. Plot threshold vs frequency 5. A low threshold is very sensitive, a high threshold is not so sensitive A is narrowly tuned at about 200 Hz. B is broadly tuned Auditory neurons can encode frequency in two ways Their identity: which auditory neuron is neuronal inputs from which part of the tonotopically organized basiler membrane For inner frequencies , the auditoyr neuron can fire with each cycle of the stimulus These auditory neurons encode sound frequency with their firing pattern Can encode intensity by how many a.ps they fire with each cycle Firing with the sound cycle = phase locking Locking sound - Can localize lower frequency sounds by timing differences which ear receives the sound first, Works for animals with widely spaced ears. In superior olive, have doley line conacnvity