Lecture 11 : Sight and Sound Flashcards
(9 cards)
How is light turned into sight
Retina Structure I need to know
Photoreceptors (rods and cones) - detect light
Horizontal cells - modulate signals between photoreceptors and bipolar cells
Bipolar cells - Relay signals from photoreceptors to ganglion cells (laterally)
Amacrine cells - Modulate signals between bipolar and ganglion cells
Ganglion cells - generate action potentials
Optic disc - Where optic nerve exists eye, no photo receptors, blind spot
Optic nerve - Carries visual signals from retina to brain
Structure of photoreceptors
Outer Segment - Membranous disks contain light sensitive photopigments (rods and cones) that absorb light
Inner segment - Changes membrane potential
Synaptic Terminals - Releases glutamate
Phototransduction in the DARK
- cGMP gated cation channel is open
- Inward Na+ current
- Photoreceptor membrane depolarised
- Releaes of glutamate
Phototransduction in the LIGHT
- cGMP gated cation channel closed
- Na+ inward current stops
- Photoreceptor membrane hyperpolarised
- Reduced release of glutamate
Lateral Inhibition
Where active neurons inhibit neighboring neurons in retina.
Horizontal and amacrine cells mediate this effect.
It sharpens visual signals by reducing activity in adjacent less stimulated photoreceptors or ganglion cells.
Results in improved edge detection and contrast in visual image.
How is sound
Stereocilia detect mechanical movement from sound vibrations, bending them.
Mechanosensitive K+ channels at their tips open, causing a K+ influx, causing depolarisation.
Voltage gated calcium channels open.
Ca2+ influx causes neurotransmitter glutamate to be released at synapse.
Activates sensory neurone and an action potential is created.
Hair cells in ear
Cochlear Amplifier
