Occular and Vestibulocochlear systems Flashcards
What is the function of the hair cell?
Transduction of the stimuli
If a hair cell is moved what occurs?
K+ enter via mechanically gated ion channels
Glutamate is released.
What dictates whether TMC-1 channels are open or closed?
Tilt of the cilia
What triggers the movement of the cilia?
Vibration of the tectorial membrane
What is the tectorial membrane?
One of two membranes within the cochlear.
What happens upon entry of K+ ?
Membrane depolarisation as endolymph has v.high K+ concentration.
What is tonotropy?
Ability to detect pitch
What membrane enables the detection of pitch?
Basal Membrane
Flexible so vibrates in sync with fluid motion.
How is the Basal Membrane able to detect pitch?
Width decreases the further along the basal membrane you go as width decreases flexibility increases.
This determines the distance a frequency will travel and in turn activate the afferent neurones specific to that area.
Higher frequency sounds are detected where?
Within the thinner regions of the basal ganglia.
Thinner the basal membrane the higher the frequency.
Inner hair cell
Main source of afferent signal in auditory VIII nerve
Outer hair cell
Efferent input
Controls stiffness to amplify membrane vibration
What is the function of Prestin?
Alters the length of the cell, when depolarised it contracts bringing the basal membrane closer to the tectoral membrane.
Contraction of Prestin does what?
Amplifies membrane vibration.
Which regions of the brain help locate the source of sound in space
Lateral and Medial superior olive
What is the basic understanding of what the lateral and medial superior olive does?
Works out from the fact that the ipsilateral side (to the sound) receives sound sooner than the contralateral from this time difference it generates an orientation and distance.
What is the main function of the vestibular system?
Where am I going and which way is up?
What do the Semicircular Canals do?
Head rotation
Head angle
Acceleration
What do the Saccule Uctricle do?
Linear acceleration
Gravity
What are the semicircular canals?
3x fluid filled chambers at right angles to each other.
Crista
Sheet of cells where hairs are clustered
Ampulla
Bulge along the canal where crista are located.
Cilia
All orientated in the same direction
Project into the gelatinous cupola
Movement of the fluid shifts the cilia
Vestibular canals - Left Horizontal Turn
Excite left horizontal
Inhibit right horizontal
Vestibular canals - Right Horizontal Turn
Excite right horizontal
Inhibit left horizontal
Vestibular canals - Left Forward tilt
Left anterior excited
Right Posterior Inhibted
Vestibular Canals - Left Backwards tilt
Left Posterior Excited
Right anterior inhibited
Vestibular Canals - Right forward tilt
Left Posterior Inhibit
Right anterior excited
Vestibular Canals - Right backwards tilt
Excite right posterior
Inhibit left anterior
Otolith organs
Utricle - Horizontal
Saccule - Vertical
What is the function of otolith organs
Linear Acceleration
Gravity
Where can hair cells be found within the otoliths?
Within the macula
How are hair cells orientated in otolith organs?
Multidirectional each otoliths divided by strida with each separate patch having hair cells orientated in a certain and different direction.
Otoconia Otoliths
Crystals of calcium carbonate on the otolithic membrane.
What is the function of the otolithic membrane?
Movement of the membrane stimulates the cilia
What is the Vestibulo Ocular Reflex?
Eyes stay still in space when head moves
What is the vestibule colic reflex?
Head still in space in space or level when walking
What is the vestibulo spinal reflex?
Adjusts posture for rapid changes in position
Why does alcohol affect your balance?
Alters the consistency of the cupola so that in floats more in the endolymph so is far more sensitive to movement.
List the cells of the retina from deepest to the shallowest.
Photoreceptor cells
Bipolar cells
Ganglion cells
In what direction does light pass the cells of the retina.
Passes through the ganglion and bipolar cells to reach the photoreceptors.
What do photoreceptor cells do?
Produce an electrical signal that if the summation is enough will trigger an AP in the ganglion cells.
Current is generated by the presence of light? T/F explain.
False it is generated in the absence of light
Na+ are open producing a depolarising current -40mV
What chemical reaction does the presence of light drive?
Converts 11-Cis-Retina to all Trans retinal
What does All-Trans-Retinal do?
G protein (Transducin) is activated
Increased PDE
PDE hydrolysis cGMP reducing its conc
Na+ Channels close
What is the affect of the closure of Na+ channels?
Hyperpolarisation which leads to a glutamate release
What cells aid in the lateral connection within the retina?
Amacrine cells
What do Amacrine cells do?
Receive input from bipolar cells and project to ganglion bipolar and other Amacrine cells.
Why are rod cells more sensitive?
As there is a greater convergence as many photoreceptor relay to a single ganglion cell.
Why do rod cells have little acuity?
As the greater the convergence and the sensitivity the lesser the acuity.
What light conditions are the rod cells useful for?
Dim light
Describe Cone cells.
Higher acuity as 1 or 2 photoreceptors converge on 1 ganglion cell, as a result not as sensitive.
Where would you find cone cell?
Highest concentration around the fovea
What are activated by different wavelengths?
Opsins
What do different wavelength result in?
Colour
Rods
Achromatic - no colour
High Convergence and Sensitivity
Low Acuity
Cones
Chromatic - colour
Low Convergence and sensitivity
High Acuity
M Cells
Provide information on movement
P Cells
Information on colour and shape
What is the purpose of Centre Surround Organisation / Lateral Inhibition
Emphasises areas of difference and enhance contrast
Ours eyes perceive the difference in light levels not the actual amount of light .
Helps localise the source of the light.
How do Bipolar cells react to Glutamate?
Either hyper polarise or depolarise depending on the cell.
Two pathways On or OFF pathways
In the OFF pathway how do Bipolar cells react to an increase in glutamate due to the dark?
Depolarise
In the OFF pathway how do Bipolar cells react to a decrease in glutamate due to the light?
Hyperpolarising
In the On pathway how do bipolar cells react to a decrease in glutamate due to the light?
Depolarise
In the On pathway how do bipolar cells react to an increase in glutamate due to the dark?
Hyperpolarise
If the bipolar cells hyperpolarise regardless of whether there is light or not what happens to the ganglion?
It is inhibited and hyperpolarised
If the bipolar cells depolarise regardless of whether there is light or not what happens to the ganglion cell?
It is excited and depolarised.
How many layers if the lateral geniculate nucleus divided into?
6
What layers do M cells relay information into?
Bottom 2 layers - 1,2
What layers do P Cells relay information into?
3,4,5,6
The lateral geniculate nucleus sends axons into which layer of the primary visual cortex?
4c
What area of the eye takes up the largest proportion of the primary visual cortex?
Fovea - sight of the highest acuity due to concentration of cone cells.
