Vision & Hearing Flashcards
Sensation definition
How cells detect stimuli in our environment and transducer them for neurotransmitter release
Perception - definition
Interpretation of external stimuli
Sensory transduction
Process by which sensory stimuli are transducer (concerted) into receptor potentials
Sensory neurons
- Specialized neuron that detects a particular category of physical events (sensory stimuli).
E.g., photoreceptors transduce light into receptor potential - come in all shapes and sizes. Many don’t have axons or action potentials but they all release neurotransmitter and have a resting membrane potential
Sensory neurons without action potentials
Release neurons in a graded fashion, the more depolarize d they are, the more neurotransmitter they release
Photoreceptor cells
The sensory neurons responsible for vision
These cells transduce the electromagnetic energy of visible light into a change in membrane potential, which affects how much neurotransmitter they release. These cells do not have action potential
Opsins
Light sensitive proteins
The opsins in photoreceptors cell are metabotropic receptors.
They’re only sensitive to light because they bind a molecule of retinal, which changes shape in response to light. The change in the shape of retinal is what activates this metabotropic recep
Retinal
- Small molecules (synthesized from vitamin A) that attaches to the opsin proteins I; the photoreceptor cells in our eyes
- The retinal molecule is technically what absorbs the electromagnetic energy of visible light that allows us to see
- when retinal absorbs a wavelength of visible light, it activates the opsin protein
Once the retinal activates the opsin protein
Launches an intracellular G protein signaling cascade that changes the membrane potential of the photoreceptor cell, affecting how much neurotransmitter it releases
4 types of photoreceptor cells that contribute to our conscious perception of vision
- red cone cells: express the red cone opsin
- green cone cells: express the green cone opsin
- blue cone cells: express the blue cone opsin
- rod cells: express the rhodopsin opsin
Visible light - definition
Electromagnetic Energy that has a wavelength between 380 and 760 nm.
We detect light using four kinds of photoreceptor cell (1 rod cell & 3 cone cells)
What is Color perception
A function of the relative rates of activity across the three types of cone cells (I.e. Color’s are discriminated by the ratio of activity across these cells
Blue/Green/Red cone opsins are most sensitive to..
Blue: short wavelengths of light
Green: medium wavelengths of light
Red: long wavelength of light
3 primary Color’s of light vs paint
Light: Green, red, blue
Paint: Yellow, magenta, cyan (reflecting or absorbing light)
3 dimensions of our perception of light
- Brightness: intensity (luminance, amount)
- Saturation: purity (in terms of wavelength mixture)
- Hue: dominant wavelength (Color)
Protanopia
Color vision deficiency
- absence of the red cone opsin (1% of males). People with this condition have trouble distinguishing Color’s in the green-yellow-red spectrum
- visual acuity is normal because red cones cells switch to using the green cone opsin
- simple mutations in of the red cone opsin (1% of males) produce less pronounced deficits in Color vision
Deuteranopia
Color vision deficiency
- absence of the green cone opsin (1% of males). People with this condition have trouble distinguishing Color’s in the green-yellow-red spectrum
- visual acuity is normal because green cone cells switch to using the red
- simple mutation in of the green cone opsin (6% of males) produce less pronounced deficits in Color vision
Tritanopia
Color vision deficiency
- absence of the blue cone opsin (1% of the population)
- blue cone cells do not compensate for this in any, but since the blue cone opsin is not that sensitive to light anyway, visual acuity is not noticeably affected
Achromatopsia
- True Color blindness. Typically caused by mutations in the G protein signaling cascade that is used by all the cone opsins
- No Color at all
- Very rare
Rod cells
- 100x more sensitive to light than any of the cone cells
- there are 3 of them and they’re sensitive to different wavelengths, which is necessary for Color vision
What is the conjunctiva
Mucous membranes that line the eyelid
What is the cornea
The outer, front layer of the eye. It focuses incoming light a fixed amount
What is the Sclera
Opaque and does not permit entry of light
What is the iris
Is a ring of muscle. The contraction and relaxation of this muscle determines the size of the pupil, which determines how much light enters the eye
