NROS 418 Exam 1 Already SCORED A+

Which 2 groups originally classified neurons by morphology? - ANSWER 1. Golgi 2. Ramon y Cajal What was the first technique used to visualize the neuron? - ANSWER Golgi staining technique How does golgi staining technique work? - ANSWER If you put brain tissue into solution with silver nitrate for a few days the solution goes into neuron and makes it visible What debate occurred between Golgi and Ramon/Cajal - ANSWER - Golgi thought that the nervous system was one connected network, which is wrong - Ramon and Cajal said they are cell bodies and neurons connect through synapses, which is correct What proved Ramon and Cajal to be correct over Golgi? - ANSWER electron microscopy showed us that they are separate neurons, not a single corrected network What modern techniques are now used to visualize neurons? - ANSWER Modern technology allows us to use fluorescent proteins (GFP) to label neurons What modern imaging tecnique is used? - ANSWER Brainbow technique What is the brainbow technique? - ANSWER label neurons with different colors to visualize morphology What are 4 different kinds of neurons: - ANSWER 1. unipolar 2. bipolar 3. pseudo-unipolar 4. multipolar What are unipolar cells? - ANSWER dendrites and axon on one side What are bipolar cells? - ANSWER Dendrites on one side, axon on the other What are pseudo-unipolar cells? - ANSWER A pseudounipolar neuron is a type of neuron which has one extension from its cell body. This type of neuron contains an axon that has split into two branches; one branch travels to the peripheral nervous system and the other to the central nervous system. What are multipolar neurons? - ANSWER A multipolar neuron is a type of neuron that possesses a single axon and many dendrites (and dendritic branches), allowing for the integration of a great deal of information from other neurons. These processes are projections from the neuron cell body. What are different classifcations of neurons by electrophysiological properties? - ANSWER 1. tonic firing (cell fires consistently without tiring or stopping) 2. burst firing (hits threshold, fires a ton of action potentials of high frequency, and then stops), or bursts in response to stimulus 3. regular firing (fires action potential in response to stimulus) What determines firing of a neuron - ANSWER ion channels (type and number) What do we use to classify neurons by electrophysiological properties? - ANSWER Patch clamp recordings What does classifying neurons using genetic markers ultimately allow us to do? - ANSWER - separate genes that have different functions even if they are in the same location How can neurons connections be tools for classification? - ANSWER - they can have different functional connections with downstream targets - aka you can classify one connection as excitatory whereas another is inhibitory What determines a connection to be excitatory or inhibitory? - ANSWER - presynaptic neurotransmitter and postynaptic receptor together What is the simplest excitatory neural circuit system? - ANSWER Stretch reflex circuit for knee jerk How does the knee jerk stretch reflex circuit work? - ANSWER - 2 neurons - input of hammer causes muscle spindle neuron to reach threshold and fire action potential and send to sensory neuron - sensory neuron sends information to motor neuron - motor neuron sends information to muscle - muscle is excited and it contracts, causing knee jerk - also has an inhibitory pathway What are the three basic components of the knee jerk reflex - ANSWER - inputs (hammer) - integration (information processing) - output (knee jerk) Describe how convergent excitation circuit motifs work. - ANSWER - Neuron receives excitatory input from several different neurons and has to converge the inputs together. - if many fire together, you get action potential Describe how feedforward excitation circuit motifs work. - ANSWER Neuron A activates B, activates C Describe how feedback excitation circuit motifs work. - ANSWER Feedback from B to excite A Amplification system Describe how feedforward inhibition circuit motifs work. - ANSWER A excites B and C, B inhibits C. What is the saying for disinhibition? - ANSWER - Disinhibition mimics excitation - because B inhibits C but if B is inhibited, then C is disinhibited (excited) Describe how lateral inhibition circuit motifs work. - ANSWER - 3 feedforward exciation pathways - When 1 neuron activates, it activates inhibitory interneuron that inhibits the neighboring neurons - If 1 activates and other 2 don't then the other 2 are suppressed. Describe how disinhibition circuit motifs work. - ANSWER A is inhibitory, inhibits B, and B inhibits neuron C. Thus C excites. A inhibiting B removes inhibition from B on C , so C excites Describe how feedback inhibition circuit motifs work. - ANSWER A excites B. B inhibits itself. negative feedback What can circuit connections be shaped by? - ANSWER Neuromodulators What are factors that modulate neural circuits? - ANSWER 1. neuromodulators 2. neurotransmitters 3. behavioral experiences 4. internal states (happy,sad,hungry) 5. disease/pathology What are some neural circuits that can be modulated by neuromodulators, transmitters, behavioral expereinces, external states? - ANSWER strength duration/timing loss/formation of connections (grow new synapses or get rid of unecessary connections) What is the horizontal plane - ANSWER parallel to the ground What is the coronal plane - ANSWER divides body into front and back What is the saggital plane - ANSWER divides body into left and right What is the brain atlas for human brain/animal? - ANSWER - dorsal (superior) is up - ventral (inferior) is down) - rostral is front - caudal is back What is the brain atlas for human spine (below brain) - ANSWER - dorsal (posterior) is back - ventral (anterior) is front - caudal is down - rostral is up Describe the major types of cells in the retina - ANSWER There are five types of neurons in the retina: photoreceptors, bipolar cells, ganglion cells, horizontal cells, and amacrine cells. How are the major types of cells organized in the retina (Draw them) - ANSWER - photoreceptors at top, bipolar cells middle, retinal ganglion cells bottom that go to optic nerve - amacrine and bipolar cells doing lateral inhbition (touching many other cells) - amacrine postsynaptic to bipolar cell and presynaptic to ganglion cells What is the direct flow of information in the retina - ANSWER A direct three-neuron chain—photoreceptor cell to bipolar cell to ganglion cell—is the major route of information flow from photoreceptors to the optic nerve. What do horizontal and amacrine cells do? Where do they do this? - ANSWER Horizontal cells and amacrine cells mediate lateral interactions in the outer and inner plexiform layers, respectively. Where do amacrine cells work? - ANSWER The processes of amacrine cells are postsynaptic to bipolar cell terminals and presynaptic to the dendrites of ganglion cells Describe the organization of the LGN. Consider its layers, the distribution of parvocellular and magnocellular neurons - ANSWER LGN has 6 layers that looks roughly like a thumbprint. Layers 1-2 consist of magnocellular neurons and layers 3-6 consist of parvocellular neurons What is the difference between parvocellular and magnocellular neurons? - ANSWER parvocellular: small receptive field, input primarily from cones, responsive to color, fine detail, magnocellular: large receptive fields, input primarily from rods (light/dark information, no color), very sensitive to movement How is the visual field represented in each LGN? - ANSWER - topographic organization: Cells in the six layers that align have receptive fields in the same area of the retina. - In addition, the optic nerve fibers from the two eyes project to distinct layers of LGN. Fibers from the eye on the same side project to layers 2, 3, and 5 of LGN, whereas fibers from the opposite eye project to layers 1, 4, and 6 Describe the receptive field of LGN neurons - ANSWER The receptive field of LGN cells is center surround (same as retinal ganglion cells). They can either be on center off surround (excitation if light hits center) or off center on surround (excitation if light hits surround). Delinate the pathways from the sensory receptors in retina to their primary V1 cortex - ANSWER Light hits photoreceptors (rods and cones) in the back of the eye. Information travels to the bipolar cells and then to the retinal ganglion cells. The retinal ganglion cells carry the information to the optic nerve. The vast majority of optic tracts from the optic nerve terminate in LGN neurons within the thalamus (parvocellular from rods to layers 3-6 and magnocellular from cones to layers 1-2. The LGN neurons carry information to different layers or sublayers of the primary visual cortex (V1) in the occipital lobe. How does light pass through the eye in order? - ANSWER - cornea, pupil, lens, retina (retinal ganglion cells -- bipolar cells -- photoreceptors) What is special about the pupil? - ANSWER It is controlled by muscles and can change size dramatically to adjust to light What is located in the back of the eye? - ANSWER the retina Since the eye is made up of a lot of tissue, what does the eye contain a lot of? - ANSWER major blood vessels that connect to the rest of the body What is the optic nerve made up of? - ANSWER axons of the retinal ganglion cells that are bundled with blood vessels. the vessels and axons converge into a bundle before going to the brain Is the retina part of CNS or PNS? - ANSWER CNS Why is retina considered part of the CNS? - ANSWER - Neurodevelopment: CNS and PNS have different origins. Retina derives from the same structure as the CNS - also retina very similar to brain structure (has many different layers like cortex cells) What pathology happens in the eye? - ANSWER diabetic blindness What are the two types of retinal blindness? - ANSWER non proliferative diabetic retinopathy and proliferative diabetic retinopathy What does the retinal image look like for an individual with proliferative diabetic retinopathy? - ANSWER abnormal blood vessels What does the retinal image look like for an individual with nonproliferative diabetic retinopathy? - ANSWER aneurysm, hemorrhages (blood vessels are leaky and blood go elsewhere), hard exudates What percentage of people in US are overweight and obese? - ANSWER overweight - 50% obese - 1/3 What is at the center of the retina? - ANSWER the fovea What is light sensitivity and resolution like in the fovea? - ANSWER low sensitivity but high resolution What is at the very back of the eye behind the layer of photoreceptors? - ANSWER pigment epithelium What is some advantages of having photoreceptors behind the bipolar and ganglion cells? - ANSWER 1. photoreceptors are protected in the back since light must go through ganglion and bipolar cells that do not respond to light. perhaps photoreceptors would be damaged if they were at the front 2. pigment epithelium layer is in the back and has lots of nutrients and important molecule. So photoreceptors might be in the back so it can interact with the pigment epithelium What is the disadvantage of the retina being inverted? (photoreceptors in the back?) - ANSWER - There is blind spot because optic nerve has to be in the back as well - and it requires a lot of transduction to bring light to electrical signal What is the mechanism of the blind spot? - ANSWER that big axon bundle of retinal ganglion cells and blood vessels in back of retina has no photoreceptors. Spot that is missing. If light hits that area, the image will be lost What are all of the different layers in the retina starting at the back? - ANSWER 1. Outsegment (OS) layer 2. outer nuclear level (ONL) 3. Outer plexiform layer 4. Inner nuclear layer (INL) 5. Inner plexiform layer 6. Ganglion Cell layer (GCL) What is in the outsegment layer? - ANSWER rods and cones (the tips) What is in the ONL? - ANSWER cell bodies of the rods and cones What is in the outer plexiform layer - ANSWER terminal end rod and cone axons and dendrties of cells from inner nuclear layer What is in the inner nuclear layer - ANSWER cell bodies of bipolar cells What is in the inner plexiform layer? - ANSWER axons from bipolar cells and dendrites from retinal ganglion cells What is in the ganglion cell layer - ANSWER cell bodies of ganglion cells What is below the ganglion cell layer? - ANSWER Bundles of axons/blood vessels that go to the optic nerve What are the other 2 cells in the retina? What do they do? - ANSWER horizontal and amacrine cells are interneurons that mediate information What do horizontal cells specifically do? - ANSWER mediate information between photoreceptor and bipolar cells What do amacrine cells specifically do? - ANSWER mediate information between bipolar cells and retinal ganglion cells Why is the retina a good model to study? - ANSWER locaton is PNS but function is CNS Why type of things do rods detect? - ANSWER black and white in high sensitvity What type of things do cones detect? - ANSWER colors with high resolution Where are majority of cones and rods distributed in the retina? - ANSWER cones - fovea rods - peripheries Where is resolution highest - ANSWER Fovea Which is faster in response to light - rods or cones? How do we know? - ANSWER - Cones respond to light faster than rods - cones reach peak hyperpolarization much faster time scale than rods Which is more sensitive to light - rods or cones? How do we know? - ANSWER Rods are more sensitive to light - Rods hyperpolarize much more for the same flash of light than cones do What does voltage do in response to light hitting photoreceptors? - ANSWER hyerpolarization In what direction is current flow in photoreceptors during hyperpolarization? - ANSWER Outwards - current goes out of the membrane What molecule in rods/cones detects light? - ANSWER opsins, particularly rhodopsin What is rhodopsin made of? What is it exactly? - ANSWER 7 transmembrane domains - it is a GPCR What is the ligand for rhodopsin to activate rhodopsin when light hits it? WHere is the ligand - ANSWER retinal sits inside the rhodopsin How does retinal activate the opsin? - ANSWER light hits - retinal changes conformation, goes from 11-cis retinal to all trans retinal, thus activating the GPCR What is occurring in the dark condition inside the photoreceptor? - ANSWER - Guanylyl cyclase converts GTP into cGMP - cGMP keeps CNGC open, allowing constant current into the cell of calcium and sodium in (pumps pumping them out to maintain resting membrane potential) What is occurring in the light condition inside the photoreceptor? - ANSWER - light turns 11-cis retinal into all trans retinal and activates GPCR - G protein activates and splits into beta-gamma units and alpha unit with GTP (from GDP) - alpha GTP unit activates PDE - PDE breaks down cGMP into GMP - less cGMP makes the CNGC close - no more sodium/calcium flowing in through CNGC along with pumps still pumping them out results in hyperpolarization and an outwards current What is the G protein of the visual system called - ANSWER Transducin How does 1 photon have so much of an effect on the retina? - ANSWER Because of amplification Describe how amplification results in 1 photon having a large effect on the retina? - ANSWER 1 R* (photon) activates 20 transducin (G protein) which hydrolysizes 10^4 cGMP per second What are two important concepts of the visual system? - ANSWER Recovery and adaptation Define recovery in the visual system - ANSWER Light-activated photoreceptor cells return to the dark state so you can detect light again. How does recovery of the visual system occur? - ANSWER - arrestin inhibits the GPCR, which inhibits light from activating rhodopsin - GPCR turns off and and CNGCs reopen. Allows dark condition to return Define adaptation in the visual system - ANSWER - Photoreceptors become less sensitive to the same intensity of stimulation when the background illumination is higher - e.g. your eyes adjust to dark or bright areas What happens if there is a mutation in arrestin? - ANSWER visual problems because you cannot return to dark condition and recovery will not happen How does adaptation occur? - ANSWER - as light intensity changes, calcium level changes through homeostatic regulation - level of calcium modulates function to help eyes adapt to dark or light Describe the spectral sensitivity of human photoreceptors (aka how can humans tell different colors?) - ANSWER - 3 different cones detect different wavelengths of light - Combining input from different cones (different opsins) allows us to see a spectrum of colors What are the opsins of rods and cones? - ANSWER rods- rhodopsin cones -photopsins (cone pigments) What are the 3 different cones and the colors they detect? - ANSWER short cones = blue medium cones = green large cones = red What is the system of cones in the human eye called? And why? - ANSWER Trichromats because humans have three types of cones Which cones are we most/least sensitive to? - ANSWER we are very sensitive to red and green cones but very insensitive to blue cones why are we insensitive to blue cones in comparison to green and red? - ANSWER because only 5% of our cones are s cones (blue) in the fovea Why do dogs have such good vision (even at night)? - ANSWER Because, unlike us, they have lots of rods in the fovea so they have sensitivity even at night What is it called if humans only have 2 working cones? - ANSWER dichromat instead of trichromat Which cone is often missing in trichromat? - ANSWER M cone - missing the green cone What is optogenetics? - ANSWER a biological technique which involves the use of light to control neurons, that have been genetically modified to express light-sensitive ion channels. What is the most important part of visual system in recognizing objects? - ANSWER contrast Define receptive field - ANSWER physical thing in environment that best affects firing rate How does the receptive field change as you move from PR to bipolar to retinal ganglion cells? What principle does this follow? - ANSWER Principle: convergence 20 to 100 cones synapse onto 3-15 bipolar cells which synapse onto 1 RGC What type of receptive field do RGCs have? - ANSWER Center surround - on center off surround - off center on surround How is contrast analyzed in the visual system? - ANSWER - retinal ganglion cells use center surround receptive fields to analyze contrast - action potentials fire only if light hits the "on" portion and inhibiton occurs if light hits the "off" - this allows for contrast What NT is constantly being released by PR onto bipolar cells at rest (dark current)? - ANSWER glutamate Is glutamate released by PR onto bipolar cells excitatory or inhibitory? - ANSWER both - depe