Name - 1 - Biology 125 Midterm #2 (11-15-07) Part 1: (30 pts) Part 2: (40 pts) Part 3: (6 pts) Part 4: (12 pts) Part 5: (12 pts) Total Pages: 9 Total Score: (100 pts) 1
Name - 2 - Part 1: True or False. Circle (T) if the statement is true or (F) when the statement is false. (2 points each, 30 points total) 1. (T) Multiple EPSPs arriving together at different locations on the dendritic tree can summate and help bring a neuron to threshold. 2. (F) The most important factor determining whether a receptor-operated ion channel is inhibitory or excitatory is whether the permeant ion s reversal potential is positive or negative. 3. (F) The two main families of neurotransmitter receptors are cationic and anionic. 4. (F) NMDA receptors allow passage of large amounts of magnesium and calcium when activated. 5. (F) Cocaine acts by blocking GABA A receptors. 6. (T) Peptide neurotransmitters are often released together with nonpeptide transmitters. 7. (T) Protein kinase C is activated by a lipid. 8. (F) The dorsal columns refer to the grey-matter columns on the dorsal side of the spinal cord. 9. (F) In the primary somatosensory cortex, the amount of cortex dedicated to each body part is proportional to its surface area. 10. (T) Regarding the conduction velocity, the axons arising from the peripheral nociceptors include the slowest conducting of the peripheral sensory afferents. 11. (F) Referred pain results when cutaneous sensory neurons send aberrant axonal branches to visceral organs. 12. (T) The placebo effect can be blocked by nalxone, an opioid receptor antagonist. 13. (T) Glycine is commonly used in the spinal cord where it hyperpolarizes the post-synaptic cell. 14. (T) The best stimulus for an on-center ganglion cell is light in its center and darkness in its surround. 15. (T) With respect to mechanosensory receptors, the quality of a stimulus (what it represents and where it is) is determined by both the relevant receptors being activated and the neuron s targets in the brain. 2
Name - 3 - Part2: Choose the best answer for the following multiple-choice questions. (2 points each, 40 points total) 1. Which of the following statements about postsynaptic currents at the neuromuscular end plate is false? A. Depolarizing currents can be recorded from outside-out patches of postsynaptic membrane. B. Individual channels tend to stay open for no more than a few msec. C. Acetylcholine can induce openings of ligand-gated ion channels. D. The end plate potential is due to the opening of thousands or millions of channels. E. The end plate channels show a regenerative opening pattern that propagates an action potential along the length of the muscle fiber. 2 When a muscle is held at a voltage of 0 mv at the neuromuscular end plate, acetylcholine no longer produces a current because A. the acetylcholine receptor channels all close instantly at 0 mv. B. an influx of sodium is balanced by an equal efflux of potassium. C. the membrane conductance for each permeant ion is 0 at 0 mv. D. at 0 mv, the potassium ions lodge in the receptor channel and block the influx of sodium. E. the Nernst potential for both sodium and potassium are 0 mv in muscle fibers. 3. Activating end plate acetylcholine receptor channels produces 0 current at 0 mv, but is still able to elicit action potentials because A. the depolarization occurs so quickly that the membrane potential goes far positive to 0 mv and produces an overshooting action potential. B. there are enough acetylcholine receptors to propagate the action potential along the length of the muscle fiber. C. the receptor is also permeable to calcium, which binds to other channels to elicit action potentials. D. depolarization of the membrane to 0 mv is sufficient to bring nearby membrane regions, which contain voltage-gated sodium channels, to threshold. E. None of the above; acetylcholine does not elicit muscle action potentials 4. Glutamate is A. the most commonly used neurotransmitter in the brain. B. neurotoxic at high concentrations. C. a nonessential amino acid. D. often synthesized from glial-synthesized glutamine. E. All of the above 5. Which of the following is not a catecholamine? A. Dopamine B. Histamine C. Norepinephrine D. Epinephrine E. All of the above are catecholamines. 3
Name - 4-6. In a signal transduction cascade using G-proteins and camp, which of the following is not a signal amplification step? A. Activation of G-proteins by an activated receptor B. Activation of adenylyl cyclase molecules by G-proteins C. Creation of camp molecules by adenylyl cyclase D. Phosphorylation of target proteins by protein kinase A E. All of the above are steps in which amplification occurs. 7. Which of the following is an effector of G-protein initiated signaling mechanisms? A. Adenylyl cyclase B. Guanylyl cyclase C. Phospholipase C D. Membrane-bound ion channels E. All of the above 8. Which of the following is not part of a signaling pathway that directly involves calcium? A. Ryanodine receptor B. IP 3 receptor C. cgmp D. Phospholipase C E. Calmodulin 9. Which of the following is the afferent system with a large receptive field and slow adaptation? A. Pacinian afferent B. Meissner afferent C. Ruffini afferent D. Merkel cell E. Hair follicle receptor 10. Which of the following is not a feature of the muscle-spindle-based proprioceptive system? A. In-series attachment to tendons B. In-parallel alignment with extrafusal muscle fibers C. Mechanically gated ion channels D. Group I and II afferent axons E. Innervation by motor neurons 11. Which of the following structures conveys facial tactile information in much the same way that the dorsal column nuclei transmit lower-body tactile information? A. The principal nucleus of the trigeminal complex B. The spinal nucleus of the trigeminal complex C. The ophthalmic branch of the trigeminal nerve D. The mandibular branch of the trigeminal nerve E. The maxillary branch of the trigeminal nerve 4
Name - 5-12. The major difference between warm thermoceptors and temperature-sensitive nociceptors is that A. the nociceptors require higher temperatures to be activated. B. within the range of painful temperatures the thermoceptors fire at a constant rate. C. over a range of increasingly painful temperatures the nociceptors fire at an increasing rate. D. All of the above E. None of the above 13. Which of the following is not a component of the descending pathways that modulate pain transmission via direct influences on the dorsal horn? A. Periaqueductal gray B. Dorsal raphe C. Locus coeruleus D. Medullary reticular formation E. All of the above 14. In the pupillary light reflex, A. the reflex is elicited only by light stimulation to both eyes. B. light falling on the left eye will cause left pupil constriction. C. light falling on the right eye will cause left pupil constriction. D. light falling on one eye will cause both pupils to constrict. E. None of the above 15. The strictly monocular portion of the visual field is represented exclusively in retina. A. superior B. inferior C. nasal D. temporal E. None of the above 16. In relation to the visual field, the cortical representation/visuotopic map is A. proportionate. B. disproportionate. C. fragmented. D. both a and c. E. both b and c. 17. Which of the following represents the most direct pathway for the transmission of visual information from the eye to the brain? A. Photoreceptor bipolar cell ganglion cell brain B. Horizontal cell bipolar cell ganglion cell brain C. Photoreceptor bipolar cell amacrine cell brain D. Photoreceptor horizontal cell ganglion cell brain E. Photoreceptor bipolar cell amacrine cell ganglion cell brain 5
Name - 6-18. Which of the following statements about color vision processing is false? A. Because there are several different color types of cones, they are sensitive to dimmer illumination levels than is the population of rods. B. Cones (in humans) come in three different colors : blue, green, and red (or short, medium, and long). C. Different wavelengths of light can produce different patterns of activity in the cone population as a whole. D. Information from specific color cones can be selectively relayed to specific regions of a retinal ganglion cell s receptive field. E. All of the above. 19. The center-surround receptive field of the retinal ganglion cell is thought to arise in largest part due to A. the effects of amacrine cells on ganglion cells. B. lateral interactions between ganglion cells. C. the effects of bipolar cells on horizontal cells. D. the effects of horizontal cells on bipolar cells. E. the effects of amacrine cells on bipolar cell terminals. 20. Which of the following areas are not involved in mechanosensory detection? A. Dorsal root ganglia B. Cuneate nucleus C. Ventral posterior lateral nucleus D. Reticular formation E. Principal nucleus of the trigeminal complex. Part 3: Fill in the blank with A, B or A and B based on whether the following statements are referring: A= Ionotropic receptors, B= Metabotropic receptors. (1 pt. each, 6 points total) 1. B Blocked by atropine 2. A, B activation can lead to an EPSP. 3. B Slowest response 4. B Uses a signal transduction signaling mechanism 5. A, B Glutamate receptors 6. B Catecholamine receptors 6
Name - 7 - Part 4: Explain typical defects and/or symptoms of patients with the following lesions. Please limit your answer to 2-3 sentences, draw pictures if you need to. (4 pts each, 12 pts total) 1. A man has a stroke that damages his right Gracile nucleus completely but spares his Cuneate nucleus and spinal cord. This man would lose sub-pain-threshold mechanosensory information from his lower limbs, on the right side of his body. Because the Cuneate nucleus and Trigeminal nuclei are spared, his sensation for the upper limbs, trunk, neck, and face would be normal. 2. A man has an injury that bisected the right optic nerve (Explain what would happen to both the visual field and to his pupillary light reflex of both eyes). Visual Field: The right optic nerve carries all light sensory information from the right eye. Although this eye would be blind, the left eye can compensate for the majority of the visual field, leaving him blind in only his right peripheral visual field. Pupillary light reflex: The pupillary light reflex responding to light shed to the right eye is gone for both eyes. The pupillary light reflex responding to light shed to the left eye is present for both eyes. 3. A man keeps getting hit by cars when crossing the street because he can t judge their speed very well. He knows that cars are there and can tell what color and shape they are. The middle temporal area (MT) is the higher visual region responsible for processing motion information, but not color and shape information. Alternatively, damage to magnocellular RGCs or their associated LGN layers are also acceptable. 7
Name - 8 - Part 5. Answer the following questions within the space provided. (4 pts each, 12 pts total) 1. After a sunburn a normal shower feels painful. What is this called? What is the cause for it? Hyperalgesia. Due to the release of stuff from the damaged cells, such as prostaglandins, bradykinin, histamine, serotonin, ATP can increase the sensitivity of nociceptors by interacting with the channel (directly or indirectly) and making it open easier, or by interacting with other receptors on nociceptive fibers to potentiate activity of TRP channels. 2. Describe Na+ and K+ ion movements during EPC and EPP at the end plate. Why is the end plate potential excitatory? 3. We can see changes in illumination over a wide range of light intensities. What is the molecular mechanism for this light adaptation? At low levels of light more channels close per photon. As light levels increase it takes more photons to close the same number of channels. This is due to the lowering of intracellular Ca2+. Ca2+ can come in through Na+ channels. When they close in response to light stimulation, Ca2+ levels decrease. The decreased Ca2+ concentration activates guanylyl cyclase which makes more cgmp, which opens channels that normally wouldn t be open. 8
Name - 9 - Or: Binding of Ach to the Ach receptor open the channel, which is permeable to both Na+ and K+. At normal resting potentials as the ACh receptor opens, many Na ions rush in and a few K+ rush out. This causes the cell to depolarize. As the potential goes toward Erev, as many K+ go out as Na goes in. Therefore the ACh receptor if open long enough would drive the potential to Erev. If Erev is above threshold- the probability of an action potential happening is increased, an action potential will occur. The EPP is excitatory because the Erev for the nach receptor is more positive than the threshold for generating action potential. 3. We can see changes in illumination over a wide range of light intensities. What is the molecular mechanism for this light adaptation? At low levels of light more channels close per photon. As light levels increase it takes more photons to close the same number of channels. This is due to the lowering of intracellular Ca2+. Ca2+ can come in through Na+ channels. When they close in response to light stimulation, Ca2+ levels decrease. The decreased Ca2+ concentration activates guanylyl cyclase which makes more cgmp, which opens channels that normally wouldn t be open. 9