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.
transparent cornea protects the
front portion of the eye. It also contributes to a major portion to focusing the light via refraction onto the retina.
extraocular muscles are attached to the middle of the eyeball pointing backwards. Their contraction enables the
movement of the eye towards objects in case the head can not be turned for this purpose.
light passes the outer eye chamber that is filled with
aqueous humor fluid.
Light passes through the transparent lens that is attached via the so- called
zonular fibers comprising connective tissue to the ciliary muscle.
ciliary muscle serves to make the lens
more round when looking at near objects
main inner space of the eyeball that is filled with
vitreous humor
point of sharpest vision, called the
Fovea (centralis), only cones
The optic nerve is also the
Afferent axon
Greatest amount of Refraction occurs where
Refraction def?
At the cornea, minority at the lens.
Light bent opposite direction = mirror image on retina (fixed by CNS)
Myopia
Eyeballs to long = nearsighted (only see close things) = corrected with CONCAVE lense so that light touches the cornea and actually reaches retina
Hyperopia
Eyeballs to short = farsighted (only see far thing) = corrected with CONVEX lense so that light touches cornea correctly and doesn’t pass the retina
Later eyes surgery does what to lense
Reshapes the lense
Accommodation
Increasing lens curvature for near vision
Accommodation how?
Zonular fibres
- stretched = tension when ciliary muscle relaxed = pulls lens = less curved
- relaxed = no tension when ciliary muscle contracted = curved lense = rounded lense = accomodation cuz light now focused on retina
Light pathway through the retina
Goes through ganglion cells (form optic nerve) -> bipolar cells -> horizontal cells -> cones / rods -> pigment epithelium (reflects incoming light so photons detected by photoreceptors) -> choroid
Rods vs cones
Rods:
- dim light = grey light
- longer outer segment = more photopigment
Cones:
- daylight = color vision
- shorter outer segment - less photopigment
Fovea centralis
- Sharpest image represnetion
- ganglion and bipolar cells pushed to the sides, photons more directly on the cones only
Number of photoreceptors
- 30 degrees: little cones, lots of rods
- 60 degrees: little cons, lots but decreasing # of rods
- 0 degree: 0 rods, LOTS of cones
Different extent of convergence
- Temporal retina : many rods, bipolar cells. One cone and follower neuron and optic neuron
- nasal retina: many rods, bipolar cells. One cone and follower neuron and optic neuron
- central retina: one cone, bipolar cell, ganglion/follower, optic nerve
Central retina is what
Center of fovea, this is why it has lowest convergence - best temporal resolution
Phototransduction
In dark: channels kept open by high concentration of the second messenger cGMP. Light strike the retina of the ops in photo pigment, changes conformation, dissociates from opsin = cGMP phosphodiester are in the disc membrane stimulated via action of protein transductin. Activated cGMP phophso. Changes into GMP = decreases the conc. Of cGMP in cytosol and the channels have closed = hyperpolarization cuz influx of Na through open pores = depolarization
Receptive fields in the retina
- Receptive field center: 10-20 photoreceptors
- receptive field surround: peripheral photoreceptors
All connected horizontal cell and one bipolar cell
Direct and indirect pathway of light in receptive field center vs light in reactive field surround
- Light in receptive field center (Direct pathway): photoreceptors hyperpolarized = bipolar depolarizer
- light in receptive field surround (indirect pathway): photoreceptors hyperpolarized = horizontal cells hyperpolarized = bipolar cells hyperpolarized
Stereoscopic vision (depthperception):
only possible in binocular zone: overlapping area of visual field
Visual fields
Left visual field collect info form left eye, projects it onto right side of retina = mirror image
Right visual field collect info form right eye, projects it onto left side of retina = mirror image
Optic chiasm
The crossing of the axons in the brain when the visual fields are crossing pathways between optic nerves (right) and lateral geniculate nucleus (left) , as those two tracts seperate and meet up in the back of the head in the visual cortex of the occipital lobe
