Sensory Systems Flashcards
What is ionotropic sensory detection?
the receptor protein itself is part of the ion channel and opens or closes the channel pore by changing its conformation
What is metabotropic sensory detection?
the receptor protein is linked to a G protein that activates a cascade of events that eventually open or close ion channels
Receptor potential
a change in the membrane potential of a sensory cell in response to a stimulus
Stretch receptor pathway
- stretching the muscle = stimulus (that opens ion channels in dendrites)
- depolarization spreads to the cell body > receptor potential
- RP spreads to the hillock (if strong enough to reach threshold > action potential triggered)
Mechanoreceptors
receptors that are sensitive to mechanical forces, involved in many sensory systems
What causes ion channels to open for sensory systems?
physical distortion of mechanoreceptor’s plasma membrane
Surface level mechanoreceptors
Merkel’s disks and Meissner’s corpuscles
Merkel’s disks
surface mechanoreceptors that adapt slowly and provide continuous information
Meissner’s corpuscles
surface mechanoreceptors that adapt rapidly and are very sensitive
Deeper mechanoreceptors
Ruffini corpuscles and Pacinian corpuscles
Ruffini corpuscles
deeper mechanoreceptors that adapt slowly and sense low frequency vibrations
Pacinian corpuscles
deeper mechanoreceptors that adapt quickly and sense high frequency vibrations
What is special about hair cells?
They are a special kind of mechanoreceptor found in the cochlea of the ear that respond to the vibration induced by sound
What are rhodopsins?
a family of photoreceptors that are composed of a pigment (retinal) bound to a protein (opsin)
What are channelrhodopsins and why are they important?
a new “optogenic” tool for stimulating neurons developed by single-called plants
Evolution of eyes
shows progression of complexity
What is an example of de-evolution?
Eastern American mole: vestigial eyes
-they don’t need to create images underground, just differentiate between light and dark
What are ommatidia?
compound eyes consisting of many optical units in arthropods; each ommatidium has a lens that directs light onto photoreceptor cells (retinula cells)
What are retinula cells?
they contain rhodopsin and their axons communicate w/ the nervous system
What kind of view do ommatidia give?
broken-up images
What does insect vision look like?
Mottled impressionist paintings: spots of paint are integrated by our brain into coherent images (Pointillism)
Veretebrae eyes have ___ and ____
rods and cones
What is a rod cell?
A modified neuron that has an outer segment, an inner segment, and a synaptic terminal
What does the inner segment have?
nucleus and many mitochondria
What does the outer segment have?
a stack of membrane-bound discs that are densely packed w/ rhodopsin
What is the role of the discs in the outer segment of vertebrae eyes?
Capture photons
What does light do to a rod cell?
Hyperpolarize
Membrane potential of a rod cell (in the dark/light)
- Rod cell = depolarized resting potential (Na+ channels are partially open)
- cGMP keeps Na+ channels open
- When light is absorbed by rhodopsin, cell becomes photoexcited and activates a G protein called transducin
- Activated transducin activates cGMP phosphodiesterase that converts to cGMP to GMP, causing cGMP levels to fall
- Na+ channels close completely
- Rod cells hyperpolarizes
Organization of the retina
Photoreceptors (rods and cones) synapse onto bipolar cells
Bipolar cells (input from PRs, output to ganglion cells)
Ganglion cells (axons project thru the optic nerve to the brain)
Dark response
depolarized cells release glutamate continuously onto bipolar cells
Light response
hyperpolarized photoreceptor cells stop releasing glutamate
What are Type 2 bipolar cells?
They have metabotropic receptors for Cl- channels.
How do Type 2 bipolar cells function?
When glutamate is released, the Cl- channel in the bipolar cell is open and hyperpolarized (darkness). When glutamate is not released, the metabotropic receptor turns off, closing the Cl- channel. This causes the bipolar cell to depolarize to threshold and fire an action potential
Pathway after depolarization
- Depolarized bipolar cells fire an action potential
- Releases neurotransmitter onto ganglion cells
- Fires an action potential that goes down the optic nerve to the brain
What are the important parts of the eye?
cornea, aqueous humor, iris, pupil, lens, vitreous humor, retina
What is the blind spot on the retina?
An area on the back of the eye where blood vessels and the optic nerve pass through the back of the eye; there are NO photoreceptors
What does the lens do?
Makes fine adjustments in the focus of images on the photosensitive retina at the back of the eye; mammals and birds alter lens shape to focus
What is the most sensitive area of the retina?
the fovea
What causes near-sightedness (myopia) and far-sightedness (hyperopia)?
Changes in the shape of the eyeball that put the focal length outside of the range in which the lens is able to focus
What happens to lenses as we age?
they become less elastic and we lost the ability to focus on objects close at hand (presbyopia)
Rods vs. cones
rods: more sensitive to very low intensities of light (provide high sensitivity B&W vision)
cones: respond to diff wavelengths of light for color vision, provide sharpest vision (fovea only has cone cells)
What kinds of cone cells do humans have?
- one that absorbs violet and blue wavelengths
- one that absorbs green
- one that absorbs yellow and red
What wavelengths can humans not see?
ultraviolet or infrared
Why do squids and octpi might have a more logical eye design?
photoreceptors are the first thing the light hits > less light scattering > NO blind spot
What do sensory systems represent?
What is important for survival and fitness; perception of changes or differences in the environment are emphasized
