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82 Cards in this Set
- Front
- Back
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What is the difference between pain and other somatic sensory submodalities?
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Pain has an urgent and primitive quality based in sensory and emotional experience. Pain is also affected by surrounding conditions. For example, the same stimulus in similar conditions can produce different responses in different people.
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What is the difference between nociception and the perception of pain?
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Nociception is the recognition of stimuli by nociceptors. However, stimulation of nociceptors does not necessarily result in the perception of pain. Perception is based on the brain's abstraction and elaboration of sensory input.
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What is the difference between nociceptive pain and neuropathic pain?
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Nociceptive pain results from direct activation of nociceptors in the skin or soft tissues in response to injury or damage.
Neuropathic pain results from direct injury to nerves. |
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What are some examples of nociceptive pain and neuropathic pain?
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Nociceptive: sprain, strain, arthritis
Neuropathic: postherpetic neuralgia, phantom limb pain, anesthesia dolorosa |
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What is known about the mechanism by which noxious stimuli depolarize free sensory endings and generate action potentials in pain fibers?
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Not much. It is believed to involve a protein in the membrane that converts the energy of the noxious stimuli into depolarizing potential.
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What is capsaicin?
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the active ingredient in hot peppers
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Where are capsaicin receptors found and what stimuli activate them?
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Also called vanilloid receptors. They are found exclusively in primary afferent nociceptors and they mediate the pain-producing actions of capsaicin. They also respond to noxious heat stimuli.
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To where do Adelta fibers project?
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Neurons in Lamina I, which projects up the spinal cord, and neurons in Lamina V.
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To where do C fibers project?
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Interneurons in Lamina II, which can be inhibitory or excitatory. Lamina II neurons contact Lamina I neurons, projecting up the spinal cord, and to Lamina V neurons.
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To where do Abeta fibers project?
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To Lamina V neurons, which ascend the spinal cord.
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How does the circuitry in the spinal cord give rise to the experience of "referred pain" in situations such as myocardial infarction?
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There is convergence of somatic and visceral nociceptive input to Lamina V. The signal sent to the brain from Lamina V is the same and cannot be distinguished, so the brain perceives the pain as being from the more commonly stimulated somatic nociceptors.
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What is the major excitatory neurotransmitter released by Adelta and C fibers? What neuropeptide is also often released from the same terminals?
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NT: Glutamate
NP: Substance P |
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What is the effect of neuropeptides released from pain fibers on the action of glutamate released from the same fibers?
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Neuropeptides enhance and prolong the actions of glutamate
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What is sensitization?
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Repeated application of noxious mechanical stimuli causes nearby nociceptors that were previously unresponsive to become responsive or to lower their threshold.
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What is allodynia? What is hyperalgesia?
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Allodynia is pain that results from stimuli that are normally innocuous (like lightly touching a sunburn); this pain is not constant and occurs only in the presence of a stimulus.
Hyperalgesia is an excessive response to stimuli and often pain is perceived spontaneously. |
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What are some substances that cause sensitization or activation of nociceptors after injury? What is the cellular source of each?
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K+: from damaged cells
Serotonin: from platelets Bradykinin: from plasma kininogen Histamine: from mast cells Substance P: from primary afferents Prostaglandins and Leukotrienes: from arachidonic acid or damaged cells |
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What are the 3 signs of inflammation?
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Heat (calor)
Redness (rubor) Swelling (tumor) |
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How could substance P and CGRP release from damaged nerve endings lead to the production of other compounds?
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Substance P acts on local mast cells, causing them to release histamine, which directly excites nociceptors; it also produces plasma extravasation.
CGRP produces dilation of peripheral blood vessels. The resultant edema causes additional liberation of bradykinin. |
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How does aspirin alleviate pain?
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It blocks the enzyme cyclooxygenase, preventing the synthesis of prostaglandins. Prostaglandins activate/sensitize nociceptors.
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What is neurogenic inflammation?
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Inflammation mediated by neural activity
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What is the relationship between repeated activation of NMDA receptors on dorsal horn neurons and central sensitization?
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Under conditions of severe and persistent injury, C fibers fire repetitively and the response of dorsal horn neurons increases progressively. This is called "wind up" and is dependent on the release of glutamate from C fibers and consequent opening of postsynaptic ion channels gated by the NMDA-type glutamate receptor. NMDA-type glutamate receptors can therefore produce long-term changes in the dorsal horn neurons and produce the hyperexcitability phenomenon known as central sensitization.
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How can the phenomenon of "phantom limb pain" that typically occurs following limb amputation under general surgery be prevented?
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By supplementing general surgery with direct spinal administration of an analgesic agent during surgery to prevent central sensitization.
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How many ascending pain pathways are there?
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5 (3 major)
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What is the most prominent ascending pain pathway in the spinal cord?
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Spinothalamic tract
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What pain pathway is believed to contribute to the affective component of pain?
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Spinomesencephalic tract
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What is the contribution of the cingulate gyrus and the insular cortex to pain?
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The cingulate gyrus is thought to be involved with processing the emotional component of pain.
The insular cortex processes information on the internal state of the body, contributing to the autonomic component of the overall pain response. |
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What is the cause of central pain?
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injury of the spinothalamic tract and its targets.
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What is dysesthesia?
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Spontaneous burning pain and other abnormal sensations.
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What is asymbolia for pain?
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It is caused by a lesion of the insular cortex. Patients can correctly perceive noxious stimuli and distinguish sharp pain from dull pain, but do not display appropriate emotional responses to pain.
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What is the gate control theory of pain?
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Nociceptive afferents open, and non-nociceptive afferents close, a gate to the central transmission of noxious input. Lamina V neurons receive convergent excitatory input from Abeta, Adelta, and C fibers. Non-nociceptive Abeta fibers inhibit Lamina V neurons through inhibitory interneurons in Lamina II. Nociceptive Adelta and C fibers inhibit the firing of the inhibitory interneurons of Lamina II. Rubbing and vibratory stimulation selectively stimulate Abeta fibers and relieve pain.
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What is transcutaneous electrical stimulation (TENS)?
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It involves placing electrodes on the skin in the area of the pain and stimulating the Abeta fibers to relieve the pain condition being treated.
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What are the 3 classes of opiate receptors?
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mu, delta, and kappa
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Which type of opiate receptor has the highest affinity for morphine?
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mu
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What are the 3 regions of the endogenous analgesia system that have a high concentration of mu receptors?
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PAG
Ventral medulla Superficial dorsal horn of the spinal cord |
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What are the 3 major classes of endogenous opioid peptides? What is the affinity of each for opiate receptors?
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Enkephalins (mu, delta)
Beta-endorphin (?) Dynorphin (kappa) |
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Where are enkephalin- and dynorphin-containing neurons found?
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PAG
Rostral ventral medulla Lamina I and II in dorsal horn of spinal cord |
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Where are Beta-endorphin-containing neurons found?
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Hypothalamus neurons that project to the PAG
Noradrenergic nuclei in the brainstem |
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What is the effect of electrical stimulation or application of morphine on pain?
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Both stimulate the PAG, which projects to the serotonergic neurons in the nucleus raphe magnus. These neurons project to the spinal cord via the dorsal part of the lateral funiculus and make the inhibitory connections with neurons in Laminae I, II, and V of the dorsal horn.
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Describe the descending pathway that reduces the amount of information about a painful stimulus that travels up the pain pathways.
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PAG --> nucleus raphe magnus --> dorsal horn through dorsal funiculus
Locus ceruleus --> dorsal horn |
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What is the effect of naloxone on morphine-induced analgesia?
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It binds to the mu receptor and is an antagonist (blocker) of morphine.
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What are some undesirable effects of opiate administration?
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Constipation: it blocks receptors in bowel muscles and the anal sphincter
Respiratory depression, cardiovascular changes: it blocks receptors in the solitary nucleus of the brainstem |
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How can the use of morphine for the treatment of pain during surgery or in disease be changed in order to minimize side effects?
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It can be administered locally into the spinal cord rather than intravenously, because the drug does not diffuse far from the site of injection.
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Describe the passage of light through the eye to the retina.
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The cornea and the lens focus light, which passes through the vitreous humor, travels through the layers of retinal neurons, and either reaches the photoreceptors in the retina or falls on the pigment epithelium. In the fovea, the cell bodies of the proximal retinal neurons are shifted aside, especially in the foveola. This area has the least obstructed pathway for light to reach photoreceptors and the greatest photoreceptor density.
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What is the function of the pigment epithelial layer of the retina?
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To absorb light that's not absorbed by the retinal photoreceptors in order to prevent reflection - and subsequent degradation - of the visual image.
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Why is there a lack of myelination of axons of the proximal retina?
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It makes the layers of proximal retinal neurons more transparent.
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Compare and contrast the morphologies of rods and cones.
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1) Both have inner and outer segments connected by a cilium. The inner segment contains the cell's nucleus and most of its biosynthetic machinery. The outer segment contains the light-transducing apparatus.
2) In both, the outer segment consists of a stack of membranous discs, which contain the light-absorbing photopigment. 3) In both types of cells, the discs are formed by infolding of the plasma membrane. In rods however, the folds pinch off from the membrane so that the discs are free-floating within the outer segment, whereas in cones the discs remain a part of the plasma membrane. |
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How are the photoreceptors oriented relative to the trajectory of in-coming light?
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The outer segments, containing the photoreceptor proteins, are pointed away from the direction of the source of light.
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Rods vs. Cones:
Photopigment |
R: Rhodopsin
C: 3 unique cone opsin isoforms |
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Rods v. Cones:
Amount of pigment |
R: more
C: less |
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Rods vs. Cones:
Amplification |
R: More
C: Less |
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Rods vs. Cones:
Sensitivity |
R: 1 photon required
C: 10s-100s of photons required |
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Rods vs. Cones:
Presence in fovea |
R: Not present
C: Very dense |
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Rods vs. Cones:
Acuity due |
R: Low acuity
C: High acuity |
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Rods vs. Cones:
Conditions |
R: Dim/night
C: Daytime/color |
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What is the structure of rhodopsin?
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It is a transmembrane protein, consisting of a covalent complex of a large protein (opsin) that is embedded in the disc membrane, and a small light-absorbing compound called retinal.
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What conformational change occurs in retinal when rhodopsin absorbs a photon of light?
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The retinal changes from the 11-cis form to the all-trans form. As a result, retinal no longer fits in the binding site of opsin. Opsin subsequently changes to the semi-stable conformation called metarhodopsin II, which triggers the second step of phototransduction.
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What is the fate of all-trans-retinal when it is released from a photopigment?
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It is transported to the epithelial pigment cells where it is reduced to the all-trans retinol (Vit A), the precursor of 11-cis retinal.
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How is Vitamin A related to blindness?
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All-trans retinol (Vit A) cannot be synthesized by humans and is a dietary necessity. A deficiency affects the functioning of rods, which are responsible for night vision.
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Describe the dark current that flows into photoreceptors when they are unstimulated. What is the effect on resting potential?
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The dark current involves a net influx of Na+ into the outer segment, and a net efflux of K+ out of the inner segment. The steady state is maintained by numerous Na+/K+ pumps in the inner segment plasma membrane. This keeps the resting membrane potential at about -40 mV.
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How does the resting membrane potential of unstimulated photoreceptors compare to the resting potential of most neuronal types?
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The resting potential of photoreceptors is depolarized compared to most neurons.
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What is the effect of cGMP on the ion channels that control the inward current in photoreceptors?
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The cGMP gates the inward ion channels. High concentrations of cGMP keep the channels open. Light reduces the concentration of cGMP.
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What two ions form the inward (dark) current?
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Na+ and Ca2+
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What are the steps of phototransduction?
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1) Light is absorbed by and activates pigment molecules in the disc membrane
2) The activated pigment stimulates a G protein, which in turn activates cGMP phosphodiesterase 3) cGMP phosphodiesterase breaks down cGMP into 5'-GMP 4) cGMP concentration decreases and cGMP-gated channels close, reducing the inward current and causing the photoreceptor to hyperpolarize |
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What is the effect on membrane potential of photoreceptors as a consequence of phototransduction?
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hyperpolarization
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What types of potentials are generated in photoreceptors?
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graded
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Compare the release of neurotransmitter from an unstimulated and an activated photoreceptor.
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In the dark, photoreceptor cells are depolarized and release glutamate. In the light, the cells are hyperpolarized and stop releasing glutamate.
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Briefly describe the Ca2+-linked process by which they eyes adapt to an increase in light intensity.
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When the cell is hyperpolarized, cGMP-gated channels close, halting the influx of Ca2+. Ca2+ is still being extruded by a carrier, so its intracellular concentration slowly decreases. This slow decrease allows the membrane potential to recover from hyperpolarization because Ca2+ inhibits guanylyl cyclase (which synthesizes cGMP). Therefore, the intracellular concentration of cGMP increases and reopens the cGMP-gated channels, which depolarize the cell.
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What output neurons of the retina provide the axons that form the optic nerve?
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Ganglion cells
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How does the electrical potential generated by ganglion cells differ from those of other neurons in the retina?
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They are action potentials (rather than graded potentials)
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What are the two parts of a ganglion neuron's receptive field?
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The receptive field center is a circular zone in the middle of the receptive field. The surround is the doughnut shaped remaining portion of the receptive field.
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What is the activity of ganglion neurons in the dark?
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They're never silent, not even in the dark.
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How do on-center ganglion neurons respond to light?
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Light spots in the center excite
Light covering the whole center maximizes excitement Light spots in the surround inhibit, but firing momentarily increases when the light spots in the surround are removed. |
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How do off-center ganglion neurons respond to light stimuli?
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Light on the surround excites
Light to the center inhibits Light to the entire surround maximally excites When both center and surround are illuminated, there is minimal effect |
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What are the two types of bipolar neurons? What type of ganglion neuron does each contact?
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On-center bipolar cells contact on-center ganglion cells
Off-center bipolar cells contact off-center ganglion cells |
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What is the effect of glutamate release from photoreceptors on bipolar cells and their membrane potentials?
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Glutamate is released by photoreceptors in the dark. In light, glutamate release is stopped. This hyperpolarizes off-center bipolar cells and therefore inhibits off-center ganglion cells. Also, it depolarizes on-center bipolar cells and therefore excites on-center ganglion cells.
Thus, glutamate release depolarizes off-center bipolar cells and hyperpolarizes on-center bipolar cells. |
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What do ganglion neurons best respond to?
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Contrasts of light in parts of their receptive fields
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Compare the size of the receptive fields of P and M ganglion neurons.
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M cells have large receptive fields.
P cells have smaller receptive fields. |
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What do M and P cells optimally respond to?
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M: large objects and rapid changes
P: specific wavelengths; they determine color, form, and fine detail |
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What are the 3 main neuronal types that make up the direct pathway through the retina?
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Photoreceptors
Bipolar cells Ganglion cells |
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Are photoreceptors in the direct pathway in the center or surround region of the ganglion cells they influence?
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Center
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What are the 4 main neuronal types that make up the indirect pathway through the retina?
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Photoreceptors
Bipolar cells Horizontal and amacrine cells Ganglion cells |
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Are photoreceptors in the indirect pathway in the center or surround region of the ganglion cells they influence?
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Surround
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