Gustation & Vision
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Kayla Coggburn, Grace Davis, Carmen Matthews, and
Charlie Williams
Gustation
• Gustation is taste
• Gustation provides information about the foods and liquids that we put
into our mouths
• We’re able to taste things because of taste buds, which are sensory
structures with specialized epithelial cells
• The tongue contains basal cells, which divide in order to produce other
cells that mature to become gustatory cells
Taste Sensations
• Humans have four primary taste sensations: sweet, salty, sour, and bitter
• There are also two additional, less common taste sensations: Umami and
water
• Umami is a pleasant taste that is associated with parmesan cheese and
soup broth.
Steps to Taste
• 1. Dissolved chemicals bind to the receptor proteins of the gustatory
cells.
• 2. Every taste sensation has a different receptor mechanism
• 2A. Salty & Sour: Chemically gated ions which result in
depolarization
• 2B. Sweet, Bitter, and Umami: G proteins called gustducins
• 3. Neurotransmitters are released by the receptor cell, resulting in taste
receptor stimulation.
• 4. The release of the neurotransmitters generates action potential, which
leads to taste sensations and reception.
Aging and Gustation
• Humans start life with over 10,000 taste buds, but the number drops
around 50.
• As people age they lose sensitivity to foods. Foods that young people find
spicy, older people find bland and with too little flavor.
Vision-Structures of the Eye
• Accessory structures of the eye include: eyelids, superficial epithelium of the
eye, and all the structures that are associated with production, secretion,
and removal of tears.
• Structures that make the exterior of the eye:
 Palpebral fissure - Gap that separates free space of the upper and lower
eyelids
 Medial canthus & lateral canthus – Where the eyelids do connect
 Eyelashes – Hairs that prevent objects from entering eye surface
 Tarsal glands – Secretes a lipid that prevent eyelids from sticking
together
 Conjunctiva – Epithelium that covers inner surfaces of the eyelids &
outer layer of the eye
 Palpebral conjunctiva – Covers inner surface of eyelids
 Ocular conjunctiva – Covers anterior surface of the eye
 Cornea – A transparent part of the outer layer of the eye
The Eye
• The eyes are an irregular spheroid shape, and weigh about 8 oz.
• The eye is cushioned by orbital fat
• The eye contains three layers
1. Outer layer – fibrous tunic
a) Contains the sclera and cornea
2. Middle layer – vascular tunic
b) Contains blood vessels, lymphatic vessels, and
intrinsic
muscles
3. Inner layer – neural tunic (retina)
c) Contains a pigmented part and a neural part
The Retina
• The retina holds photoreceptors, which are responsible for detecting light
• The retina has around 130 million photoreceptors
• There are two types of photoreceptors:
1. Rods – Do NOT determine colors. Allow people to see light
2. Cones – Color vision
• Cones don’t allow you to see color unless there is a strong enough light source to
stimulate them
• Rods and cones synapse with 6 million bipolar cells, which then synapse with
ganglion cells to see color and light
• The lens lets our eye focus by changing its shape
• An astigmatism may occur if the cornea or lens is curved in an odd way, which
causes distortion when looking at something
Photoreceptors, Rods &
Cones
• Photoreceptors detect photons, which are the basic unit of visible light
• The process of detecting and receiving light is called photoreception
• Humans are receptive to wavelengths 700-400nm (visible light spectrum, ROY G
BIV)
(Red photons = greatest wavelength, least energy; Violet photons = shortest
wavelength, most energy)
• Rods are able to give the central nervous system the information needed about
the presence or absence of photons. (Seeing light)
• Cones give the information of the wavelength of photons. (Seeing color)
Photoreception
• Sodium ion channels are chemically regulated in the outer portion of the
photoreceptor.
• In dark: the channels are left open with the presence of cyclic-GMP. Since
the channels are open, the transmembrane potential is lower than normal,
which makes the photoreceptor releasing neurotransmitters continuously
across the inner segment synapses.
• That inner layer is simultaneously pumping sodium ions out of the
cytoplasm. This is called the dark current.
• This is how people are able to vaguely see when the lighting is low
Rhodopsin-based
Photoreception
• Begins when a photon hits a rhodopsin molecule
• 4 Steps in rhodopsin-based photoreception:
 Step 1 – Opsin is activated.
 Step 2 – Opsin activates transducin, which then activates
phosphodiesterase
 Step 3 – Cyclic-GMP levels decline, and the gated sodium channels
close
 Step 4 – The dark current is reduced, and the rate of neurotransmitters
that are released decreases
Recovery
• After a photon is absorbed, the whole rhodopsin molecule has to be broken
down and the put back together
• Bleaching is when a rhodopsin molecule starts to break down into retinene and
opsin
• Retinene must be enzymatically converted by ATP
• Opsin is inactive throughout the process of bleaching
• Cyclic-GMP is produced, and the sodium ion channels are reopened
Color Vision
• There are three types of cones:
1. Blue cones
 16% of all cones
2. Green cones
 10% of all cones
3. Red cones
 74% of all cones
• Every type of cone has its own form of opsin, and different sensitivities
to different wavelength ranges.
• The way that the cones are stimulated is the basis for color vision
• We see color because of the information received from all three cone
types.
 Yellow is a combination of highly stimulated green cones, less
stimulated red cones, and non-stimulated blue cones
 White is a combination of all three cones stimulated equally
Color Blindness
• Color blindness occurs when someone has one or more sets of cones that don’t
function
• The cones could be absent, or just not able to produce the pigment needed
• There is inherited color blindness that involves one to two cones. This is not
uncommon.
• 10% of men have some form of color blindness, but only 0.67% of women do.
• Only 1 person out of 300,000 have total color blindness. Where they have no
cones at all.
Visual Pathway
• The visual pathway starts at the photoreceptors and ends at the visual cortex
• The message must be sent across two synapses before it can be read.
1. Photoreceptor to bipolar cell
2. Bipolar cell to ganglion cell
• M cells give information about the general form and shape of an object, its
motion, and shadows.
• The activation of M cells indicates that light has been detected and has arrived in
a general area.
• P cells give information about edges, detail and color.
Diseases
• Astigmatism – A condition that causes blurred vision from one of three reasons:
1. Irregular shape of the cornea
2. Irregular shape of the cover of the eye
3. Curvature of the lens inside the eye
• Conjunctivitis – An inflammation of the conjunctiva (transparent layer of tissue
that surrounds the inner part of the eye and the white part) Otherwise known
as “pink eye”. It can be caused by:
1. Allergies
2. Bacteria
• Cataract – A cloudy, or yellow, part of the clear and transparent lens of the
eye. Can be caused by:
1. Diabetes
2. Smoking
3. Certain Drugs
4. Nutritional deficiency
Careers
• Ophthalmologist - A medical doctor who specializes in eye and vision care
• Optometrist – A healthcare professional who provides vision care. Things like sight
testing and correction, diagnosis of the problem, treatments, and manages changes
in vision.
• Optician – A technician who designs, verifies and fits glasses lenses, frames and
contact lenses