Special Senses 2 Flashcards
Travelling wave
A vibration on the basilar membrane
Strucure of basilar membrane
Narrow and stiff as the base - 16 Hz
Wide and floppy as the apex - 0.5 Hz (max amplitude)
How are frequencies on certain spot of the basilar membrane?
Each frequency of sounds has maximum movement on a certain spot on the basilar membrane, and the hair cells on that spot will be stimulated
A proof for the traveling wave concept is the fact that exposure to a loud noise of a certain frequency
destroys hair cells at a specific spot of the basilar membrane
Frequencies at the apex vs at the base
Apex: high frequency
Base: low frequency
Bending of stereocilia
- Compression: basilar membrane deflected downwards
- rarefaction: basilar membrane bends upwards
A rarefraction ( bending upwards) causes
Steriocilia being to the left in responce to adequately stimuli = release K+ ions = receptor potential
A bending of the cilia to the left side vs right side evokes a
hyperpolarization of their resting Vm by <1 mV while bending to the right side evokes a depolarization of ~3 mV.
sinusoid wave of a single frequency that the time course of the receptor potential (shown in the lower traces) follows exactly that of the sound pressure changes (shown in the upper trace). The receptor potential can precisely follow back and forward stereocilia movements even when they occur at a rate of >10 kHz. This indicates that the
hair cell mechanoreceptor channels can open and close very rapidly.
Receptor potential and hair cell bending have a
close relation even at >10Hz
Do hair cells have dendrites
No, instead they got mechanosensitve steriocilia which transmit info via neurite from follow neuron form postsynaptic neuron to send AP to auditory cortex
Follow neuron located in
Spiral ganglion
When hair cells bend to the right, influx of K+ =
Depolarization = activation of cytosolic Ca2+ = NT release (glutamate)
Where’s glutamate store in hair cells
In vesicles at the base of the hair cells
What connected the hair cells together
Tip links (Cadherines)
- relaxed (left bend) = channel closed
- no stimulus = partly open
- bending to right = channel activated = depol
Stria vascularis secreted what into the scala media
K+ ions, causing the K+ level in the scala vestibuli and scala tympani to be low
What kind of interstitial fluid found in all three scala in the cochlea
- Perilymph (3 K+, 150 Na+) in scala vestibuli and tympani
- endolymph (150 K+, 15 Na+) in scala media
In the endolymph, the K+ ions follow their
conc gradient, going form high to low conc = into the steriocilia = releasing glutamate
2 pathways for afferent auditory pathway
First
Afferent neuron (spiral ganglion) receive info from HC = excited = glutamate release into axons of vestibulocochlear nerve, AP sent to medulla, excited = neuron activated in superior Oliver’s nucleus (in pons), get excited, AP transmitted via lateral meniscus axon tracts to neuron in inferior follicular (in midbrain), excited = activate neurons in medial geniculate nucleus (in thalamus), excited = activate neurons in auditory cortex.
2 pathways for afferent auditory pathway
Second
second pathway is activated in parallel on the contralateral side. The crossing occurs already (via collaterals) in the nuclei of the medulla oblongata. From there, the action potentials propagate in similar fashion as on the ipsilateral side except, that some axons pass by the superior olivary nucleus in the pons without synapsing onto them.
conjunctiva is a mucous membrane which comprises the
inner surface of the eyelids and covers the forepart of the sclera. The conjunctiva helps to lubricate the eye by producing mucus and tears, although a smaller volume of tears than the lacrimal gland
sclera is the
hard connective tissue that forms the major portion of the almost round eyeball. Located in the middle of the eye is the pupil
pupil is not a structure, but rather a
hole that is covered by a transparent layer through which the light enters the eye
round iris muscle surrounds the pupil and its diameter can be adjusted via the pupil reflex. The pupil reflex makes sure that the
diameter of the pupil is reduced during exposure of the eye to high intensity light signals to protect the photoreceptive structures and the other cells within the retina.
