Vision and the Retina

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Questions and Answers

What is the primary function of rods in the retina?

To detect light and dark (correct)

To transmit color signals to the brain

To provide color vision

To support the health of cones

In the retinal signal transduction process, what role does transducin play?

It closes sodium channels

It hydrolyzes cGMP

It recycles retinal

It activates phosphodiesterase (PDE) (correct)

Why do cones in the fovea enable better color vision?

They project to multiple bipolar cells

They have a higher density in the fovea (correct)

They provide a larger receptive field

They have more rods associated with them

What occurs in the retina when light hits the photoreceptors?

Photoreceptors hyperpolarize and decrease cGMP levels Signup and view all the answers

What happens at the optic disc in relation to vision?

It has no photoreceptor cells, creating a blind spot Signup and view all the answers

What is the significance of horizontal cells in the retinogeniculate pathway?

They facilitate surround suppression and center response Signup and view all the answers

Which statement best describes the receptive field of rods in relation to bipolar cells?

Multiple rods connect to a single bipolar cell for sensitivity Signup and view all the answers

What effect does a decrease in extracellular cGMP have on photoreceptor cells?

It closes sodium channels Signup and view all the answers

What is the primary role of the organ of Corti in the auditory system?

To translate basal membrane movement to action potentials Signup and view all the answers

What characteristic of sound can humans typically perceive?

Audible sound between ~50 Hz to ~20 kHz Signup and view all the answers

What is the difference in resonance within the cochlea based on frequency?

Low frequencies resonate at the tip, high frequencies at the base Signup and view all the answers

Which component of the olfactory system does NOT require the thalamus?

Pyriform cortex Signup and view all the answers

How do hair cells in the cochlea detect small vibrations?

By being located further from the rotation point of the tectorial membrane Signup and view all the answers

Which type of receptors do olfactory receptor neurons express?

Metabotropic receptors with a unique G protein Signup and view all the answers

What is the role of the auditory cortex in relation to speech?

It is linked to sensory speech and motor speech control areas. Signup and view all the answers

What distinguishes the regeneration ability of olfactory receptor neurons?

They are one of the few neurons replenished in adulthood. Signup and view all the answers

Study Notes

Sight

The retina is formed from the neural tube.
The retina contains 5 cell types, including photoreceptors.
Rod photoreceptors are light-sensitive and responsible for black and white vision.
Cone photoreceptors are less sensitive and are responsible for color vision.
Photoreceptor discs increase surface area.
Light reduces cGMP, decreasing sodium influx (causing hyperpolarisation).
Opsin, activated by light, inactivates the Na+/Ca2+ channel.
Retinal activates Opsin when exposed to light leading to Transducin activation, which in turn activates phosphodiesterase (PDE).
PDE hydrolyses cGMP, reducing its level and causing Ca2+/Na+ channels to close.
Horizontal, bipolar, amacrine, and ganglion cells are other retinal cell types. Ganglion axons form the optic nerve.
Best color vision occurs in the fovea, which contains more cones than rods.
The macula lutea has better light detection, with the fovea at the center.
The optic disc is a blind spot, lacking photoreceptors.
Rods have a large receptive field, as 15-30 rods connect to a single bipolar cell.
Cones project to one bipolar cell, resulting in more precise receptive fields and limited sensitivity.

Optogenetics

Best color vision is in the fovea.
More cones in fovea, fewer rods.
Better light detection in macula lutea.
Rods: 15-30 rods per one bipolar cell, which provides a large receptive field.
Rods in the fovea project to only one bipolar cell, resulting in small, more precise receptive fields.
Cones project to one bipolar cell, providing a small receptive field but also limited sensitivity.

Off and On Cells in Retina

In the dark rods release glutamate to bipolar cells causing On-center cells to fire to the ganglion cells.
In the light the rod cells release less glutamate, the On center cells are depolarized, then fire to the on ganglion cells.
Surrounding suppression happens from horizontal cells.
The hyperpolarization of surrounding cones by light results in the hyperpolarization of connecting horizontal cells.
The horizontal cells reduce suppressive signals to the central cone and depolarize it.
This leads to increased signal focus in the center of the receptive field.
Less glutamate secretion in the center of the receptive feild, results in less stimulation and surrounding cones become more depolarised; causing increased signal focus.

Sound

Sound is created by pressure oscillations.
Humans can hear sounds between 50 Hz and 20 kHz.
Older individuals lose the ability to hear higher frequencies.
The middle ear converts vibrations to mechanical movements, amplifying the amplitude 200x.

The Cochlea

High-frequency sounds cause resonance at the base of the cochlea.
Low-frequency sounds cause resonance at the tip of the cochlea (helicotrema).

Organ of Corti

Translates basal membrane movement into action potentials (APs).
Outer hair cells detect small vibrations, located further from the tectorial membrane.
Hair cells translate vibration to AP's.
The cochlea is tuned, as high frequencies resonate at the base and low frequencies resonate at the tip.

Taste

Taste is projected to the brain via cranial nerves VII, IX, and X.
Microvilli have receptors in taste cells.
Projections to the brain include:
- VPM of the thalamus
- Insular and frontal taste cortices
- Hypothalamus
- Amygdala

Taste Receptors

Salt and acid are ions, causing depolarization via ion channels.
Sweet, bitter, and umami stimulate GPCRs activating TRPM5 calcium channels.

Smell

Humans have relatively few olfactory receptor neurons (ORNs).
Olfactory receptor neurons (ORNs) project to the brain via pyriform cortex (olfactory cortex).
Olfaction is unique from other senses as it doesn't use the thalamus as a relay station.
Aromatic substances respond to concentration.
Olfactory epithelium regenerates in response to damage.
ORNs are replenished by stem cells in the adult.
Receptors are G protein-coupled receptors (GPCRs).
Receptors are at cilia of ORNs.

Pheromones

Detected by the vomeronasal organ.
Play a role in mating, aggression, and rodent behavior.
V1R and V2R receptors are in primates/humans.

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Description

Explore the intricate workings of the retina, including its structure and the functions of different cell types. This quiz delves into the roles of photoreceptors in vision, from black and white sensitivity to color perception, and the mechanisms of signal transduction in visual processing.