CH 50 Sensory Systems
Photosensitivity
- sensitivity to light - ranges from the ability to orient to the sun to the ability to see (which way is up & down)
What are the three types of taste receptors?
-The sensations of sweet, unami, and bitter require specific G-protein-coupled receptors (GPCRs). Meaning they activate a enzyme which will cause a transduction pathway in which ions open/close -The receptors for sour belong to the TRP family and is similar to capsaicin and other thermoreceptor proteins -The taste receptor for salt is a sodium channel
What does each olfactory receptor neuron in the nose express?
ONLY ONE type of olfactory receptor
Gustation
Sense of taste is dependent on the chemicals called tastants
What is sensory transmission?
Sensory info travels through the nervous system as action potentials. -Sensory receptors may be neurons or non-neuronal receptors -The size of a receptor potential increases with the intensity of the stimulus -In sensory neurons that spontaneously generate AP's at a low rate, a stimulus changes how often AP is produced.
Iris
changes diamter of the pupil to control how much light eneters. (The pupil is the hole light enters and light falls on the retina)
What does the decrease in glutamate result in
changes the membrane potential of bipolar cells
How does distance vision work
ciliary muscles relax, and border of choroid moves away from lens. Suspensory ligaments pull against lens. The lens becomes flatter focusing on distant objects.
In the dark rods and cones
continually release the neurotransmitter glutamate into synapses with neurons called bipolar cells.
In the presence of light
cyclic GMP breaks down and the Na+ channels close, this hyperpolarizes the cell. The signal transduction pathway usually shuts off again as enzymes convert retinal back to the cis form
Fovea
responsible for vision w detail EX: read, drive. The center of the visual field and contains no rods but high density conesss If damaged ability to see in detail decreases
What does trans-retinal activate
rhodopsin, which activates a G protein, eventually leading to hydrolysis of cyclic GMP
Olfaction
sense of smell is dependent on the detection of odorant molecules. Depends on chemoreceptors
Mechanoreceptors
sense physical deformation caused by forms of mechanical energy such as pressure, stretch, motion,touch, and sound
What are the two type of sensory receptors?
1. Iontropic sensory detection(DIRECT); the receptor protein itself is part of an ion channel and by changing its conformation opens or closes the channel pore EX: Mechanoreceptor 2. metabotropic sensory detection (INDIRECT); the receptor protein is linked to a G protein that activates (usually an enzyme) a cascade of intracellular events that eventually open or close ion channels. EX: Chemoreceptor and photoreceptor
What are the four basic functions that sesnory pathways have in common?
1. sensory reception 2. transduction 3. transmision\ 4. perception
What 2 cavities does the lens divide into
1. the front of the lens is the clear and watery aqueous humor 2. Behind it is a the jellylike vitreous humor
How many olfactory receptors do humans have?
20 million, humans have about a thousand genes for olfactory receptors. Of these genes only ~380 produce functional olfactory receptors; the other genes have mutations and are pseudo-genes
In humans preception of color is based on
3 types of cones, each with different visual pigment: red, green or blue.
How many taste buds do we have?
5000-10000 taste buds embedded in the epithelium of the tongue
Age-related macular degeneration (AMD)
A eye disease in which the photoreceptors in the macula malfunction and over time degenerate. It is the leading cause of central vision blindness in the US. Causes are unknown however the peripheral vision still functions
What does a higher frequency of odorant molecules produce?
A higher frequency of APs and is percieved as a stronger smell
How does near vision work?
Ciliary muscles contract, pulling border of choroid towards lens. Suspensory ligaments relax and lens become thicker and rounder focusing on nearby objects
What do we do since the number of odorant molecules greatly exceeds the number of diff receptor proteins?
Each odorant may bind to one or more specific receptor proteins, a specific odorant is distinguished according to the different and unique combination of cells it activates. -Odorants come in combinations which allows most odorants to activate more than one type of receptor. This provides for the identification of almost limitless number of diff molecules.
How does vision occur in vertebrates
Eyes detect colors and light, but the brain assembles the info and perceives the image (makes sense of it)
How does taste occur?
Food molecules bind to a taste pore on the tongue, the sesnsory receptor cells (taste buds) detect the taste and release neurotransmitters to the sensory neuron to be taken to the brain
What does the density of tactile mechanoreceptors influence?
How finely stimulation can be resolved EX: on fingertips the finer spatial discrimination is possible bc mechanoreceptors are much more dense
ganglion cells
In the retina, the specialized neurons that connect to the bipolar cells; the bundled axons of the ganglion cells form the optic nerve. A single ganglion recieves info from an array of rods and cones.
Retina
Light entering strikes the retina, reaching the rods and cones, two types of photo receptors. The neurons of the retina then relay visual info via the optic nerve to the brain
What are the five categories of sensory receptors and what they detect
Mechanoreceptors; pressure, touch Chemoreceptors; chemical, taste, smell Electromagnetic receptors: electromagnetic energy, light, magnetic fields Thermoreceptors; temp Pain receptors; pain
How are receptor cells for taste in mammals?
Modified epithelial cells organized into taste buds, located in several areas of the tongue and mouth -Most taste buds are associated with projections called papillae -Any region with taste buds can detect any of the 5 types of taste
What are abnormal color vision a result from?
Mutations in the genes for one or more photopsin proteins. EX Red/Green color blindness which is more common in males bc its on the X-chromosome
When light strikes
Na+ channels close, rods hyperpolarize, inhibiting glutamate release. No action potential occuring of the bipolar cells
Difference between neuronal receptors and non-neuronal receptors.
Neuronal receptors have receptors that is afferent neuron. The stimulus is detected by the sensory neuron and can go straight to the CNS. Non-neuronal receptors: occur when receptors regulates afferent neuron. The stimulus leads to neurotransmitters being released from the sensory receptor to bind to a receptor protein and then travel to the CNS.
What are olfactory sensors?
Neurons embedded in a layer of epithelial cells at the top of the nasal cavity
What is perception?
Perceptions are the brains construction of stimuli. Stimuli from different sensory receptors travel as AP's along dedicated nueral pathways -The brain distinguishes stimuli from different receptors based on the path by which action potentials arrive.
What are the color pigments called?
Photopspins which absorb light at diff wavelengths and are formed when retinal binds to three distinct opsin proteins
What are odorants
Smell chemicals that bind to olfacotry receptor proteins. -Molecules from the enviroment diffuse through nasal mucus to reach the surface of the olfactory cillia
What two senses are similar
Taste and smell are both chemoreceptors which are metabotrophic sensory receptors
How is light focused by the eye?
The Lens. The lens is composed of transparent disk of protein used to focus light onto the retina
What causes a sensory cell to fire action potential? What occurs if the receptor cell doesnt fire APs?
The change in membrane potential -If the receptor doesnt fire APs it will induce the secretion of a neurotransmitter onto an associated neuron that fires action potentials. -The intensity of the stimulus influences how much neurotransmitters is released. -The intensity of the stimulus is encoded in the frequency of the action potentials produced.
What is sensory transduction?
The conversion of stimulus energy into a change in the membrane potential of a sensory receptor, this change in membrane potential is called receptor potential.
How does smell occur?
The dendrites of the cilia bind to the odorant molecules and traveldown the olfactory receptor cell to the olfactory bulb of the brain. Action potentials then go to the brain
Retinal is derived from
Vitamin A, which is why we need a constant supply of RETINOL (type of vitamin A) to make the all-trans-retinal
What is lateral inhibition?
When a rod or cones stimulates a horizontal cell and the horizontal cell then inhibits more distant photoreceptors and bipolar cells. This causes regions recieving light appear lighter an dark surroundings even darker. This enhances contrast in an image.
How does a sensory pathway begin?
With sensory reception detection of stimuli by sensory receptors. Sensory receptors are sensory cells or organs which interact with stimuli both inside and outside the body.
Can information be sensed without our being conscious of it?
Yes for example the brain receives continuous info about body temp, levels of CO2, blood sugar, and O2. Such info is important for the maintenance of homeostasis but does not necessary result in conscious sensation.
What can rhodopsins consisit of
a protein called opsin and a light absorbing group 11-cis-retinal
Optic disk
blind spot bc there are no photoreceptors
Primary sensory cells
generate action potentials directly ex . crayfish stretch receptor
Secondary sensory cells
generate action potentials indirectly by inducing the release of neurotransmitter EX: photoreceptor
What do olfactory receptors do?
give sense of smell when olfactory receptor protein binds to particular odorant molecules, which activates a G protein. The G protein then activates enzymes that increase the level of the 2nd messenger cAMP. cAMP opens a cation channel. This leads to depolarization of the membrane and an action potential is fired
Carrots
good source of beta-carotene
What can skin sensory cells detect
heat, pressure, movement, and tissue damagae (pain)
suspensory ligaments
hold the lens in place; very elastic/strechy
Cyclic GMP
in the dark binds to sodium ion channels and keeps them open
What is sensory adaptation?
is a decrease in responsiveness to continued stimulation
11-cis-retinal
is covalently bound in the center of the opsin molecule, when 11-cis-retinal absorbs a photon, it changes to all-trans-retinal, which changes the conformation of the opsin. This change signals detection of light
What is the eye surrounded by?
layers of tissue the outermost layer: Sclera: strength holds eye together 2nd layer: choroid ( a thin, pigmented layer which contains a lot of blood vessels) are the neurons and photoreceptors of the retina
What are mechanoreceptors involved in
many sensory systems inclduing skin sensations (their stretch receptors in our blood vessels that adjust) and sensing blood pressure -they typically consist of ion channels linked to structures that extend outside the cell such as hairs in the ear (cilia)
Rods
more sensitive to light but do not distinguish colors (black/gray)
Vitamin A deficiency
night blindness, more common in developing countries
How many taste perceptions can a taste cell detect?
one; BUT within the taste cell, the taste bud receptor can detect all 5 tastes
Cones
provide color vision (useless at night)
The mammalian sense of touch
relies on mechanoreceptors that are dendrites of sensory neurons
Photoreceptors
specialized cells are modfied neurons that can detect light. Modified neurons dont fire AP they release neurotransmitters
What are modified neurons?
specialized cells for detecting different kinds of stimuli such as pressure, heat, light , etc
What are the five taste perceptions
sweet, sour, salty, bitter, umami (flavor enhancer, savory meats)
What is papillae?
taste buds
night blindness
the inability to see well in dim light; occurs without adequate amounts of retinal, regeneration of rhodopsin is incomplete.
What are rhodopsins?
the light receptor molecule. Rhodopsin molecules can absorb photons of light and undergo conformational changes.
In the absence of light
the photoreceptor is depolarized (we have inactive rhodopsin & phosophodiesterase) Na+ channels are open
Where does processing of visual info begin
the retina
What is amplification
the strengthening of a sensory signal during transduction
What are receptor potentials?
they are graded potentials; their magnitude varies with the strength of the stimulus
What do sensory receptors do? What occurs when a stimulus is recieved
transduce stimulus energy and trasnmit signals to the central nervous system -all stimuli represent forms of energy -a sensory receptor converts stimulus energy into a change in the membrane potential -when a stimullus is received and processed by the nervous system a motor response may be generated -this may involve a simple ref;ec or more elaborate process
sensory transduction in the eye
transduction of visual info to the nervous system begins when light induces the conversion of cis-retinal to trans-retinal
Chemoreceptors
transmit information about the total solute concentration of a solution -other chemoreceptors repsond to individual kinds of molecules -when a stimulus molecule binds to a chemoreceptor the chemoreceptor becomes more or less permeable to ions
What is glouscoma
vision loss due to ducts not being able to be drained
Receptive field
when rods and cones that are feeding info to one ganglion cell define this. A smaller receptive field typical results in a sharper image.