1 Exam 1 BIO 361T Fall 2014 1 Name Discussion circle one M2 00 M3 00 T2 00 T3 30 Give one proximate and one ultimate explanation for any one of the three reflex arcs we covered 10 points Patella 5 prox neural and molecular pathway or stimulus response 5 ult respond to stimuli quickly prevent tissue damage Aplysia prox neural and molecular pathway or stimulus response ult protect tissue from damage Teleost fish prox neural and molecular pathway or stimulus response ult escape from predators survive 2 Electrochemical Gradients 4 points each a Define the concept of equilibrium potential Keq Voltage at which chemical and electrical gradients are balanced out opposite in direction but equal in magnitude Voltage at which there will be no net flow of the ion Voltage at which flow in equals flow out Reversal potential b Use the concept of Keq to explain why Na will enter the cell when Vm 70 mV Keq of Na is above 70 so Na will enter the cell to bring it up to Keq Chemical gradient and electrical gradient for Na are both pointing into the cell c What will be the net direction of Na flow when Vm 40 mV Still into the cell No explanation necessary but even though electrical gradient is now pointing out it is not stronger than the chemical gradient pointing in as can be deduced from the Keq of 61 mV 3 Explain how the dendrites and soma passively conduct electrical signals Explain why active conduction down the axon is necessary in most neurons 12 points 6 Ion channels in membrane initiate current which spreads via electrotonic conduction charges repel like charges spreading the current down the membrane 6 Necessary because these passive potentials decay over space and time Most neurons are longer than the length over which electrotonic conduction is sufficient 4 Multiple sclerosis is due to progressive demyelination of motor neurons In terms of the length constant explain why multiple sclerosis patients are progressively less able to control voluntary movements 10 points Myelination increases the length constant by increasing Rm so losing this would decrease Rm and decrease the length constant This means signals will be able to travel less distance before they decay so some signals controlling muscles will never make it to the muscle 5 How do axons ensure that an action potential will travel in only one direction 10 points Inactivation of voltage gated Na channels Once they are opened they inactivate and are unable to open again so the action potential cannot go backwards only forwards 2 6 Imagine ACh is applied to two different synapses simultaneously One of the post synaptic neurons depolarizes slightly milliseconds later the other post synaptic neuron hyperpolarizes slightly 6 points each a Explain how the same neurotransmitter can have opposite effects on different cells Different receptors One opens ion channels that depolarize the membrane the other opens ion channels that hyperpolarizes the membrane b Explain how the same neurotransmitter can cause responses with different speeds Ionotropic vs metabotropic receptor Ionotropic receptors are ion channels so the change in membrane potential happens soon after the stimulus Metabotropic receptors are coupled to ion channels through proteins inside the cell so the change in membrane potential takes a little longer after the stimulus 7 What would be the effect of removing the spinal interneuron in the patellar reflex arc 10 points No inhibition of the opposing muscle Could continue to say that the opposing motor neuron won t get activated because there s nothing synapsing on it Or could say that if the sensory afferent is close enough to the motor neuron it would activate both muscles causing the leg to hyperextend instead of kick 8 To demonstrate that the dorsal ramp interneuron DRI is the command neuron of the dorsalventral flexion program in Tritonia experiments had to show that it was both necessary and sufficient to elicit the motor program 3 points each 9 The following actogram shows the nocturnal wheel running of a hamster in complete darkness DD Fill in what you would expect to see due to each of the following events 8 points Label each 10 day section of the actogram as arrhythmic free running or entrained 10 points Day 0 free running Day 10 Begin 12 12 LD cycle entrained Day 20 Surgically remove the animal s retinas free running Day 30 Surgically remove the animal s SCN arrhythmic Day 40 Return to DD cycle arrhythmic
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