Zoo Psych Neuro 523 1 Define briefly Problem Set 1 answers 2016 Astroglial cell A glial cell in the central nervous system Astroglia or astrocytes have end feet that are apposed to neurons and often also to blood vessels They also buffer the external ion concentrations and take up some of the neurotransmitters from extracellular space Other potential functions include establishing the blood brain barrier possible nutritive functions and physical and possibly electrical insulation of subsets of neuronal processes or synapses Kinesin Microtubules are involved in axoplasmic transport Fast transport of synaptic vesicles and new membrane vesicles is mediated by kinesin which carries these components from the end to the end of the tubules In axons the end is always distal from the cell body Intermediate velocity transport of mitochondria is also mediated by kinesin Divergent neuron A neuron that receives few input synapses and makes a relatively large number of output synapses This neuron will have few dendrites and lots of axon terminal synapses Threshold If the membrane potential of a neuron is more positive than threshold an action potential will fire 2 In the circuit drawn below which is meant to represent 2 resistors in series what is the voltage across the 10 9 ohm resistor if a voltage of 50 mV is applied across the terminals marked o o 2X108ohms 109 ohms o The total resistance is 1 2 X 109 ohms so the current through both resistors is 50 X 10 3 1 2 X 109 amps 41 7 X 10 12 amps From Ohm s Law the voltage across the 109 ohm resistor is 109 X 41 7 X 10 12 volts 41 7 X 10 3 volts or 41 7 mV 3 What was the nature of the major disagreement between Cajal and Golgi over the cellular structure of the nervous system Describe the experimental evidence that allowed the dispute to be finally resolved Be brief Golgi believed in the reticular nature of the nervous system i e that each neuron was in cytoplasmic contact with other neurons and that the Golgi stain did not reach the ends of the neurites of each neuron Cajal believed that the Golgi stain was revealing the entire extent of each neuron Two methods showed that Cajal was right electron microscopy showed that neurons had spaces between them and that there was a cell membrane where the staining ended dye injection showed that injected dyes diffused to the extremity of each cell and that the cell morphology was the same as seen by Golgi staining 4 What distinguishes action potentials from sensory potentials and synaptic potentials Action potentials are all or none self limiting arise only if the membrane potential exceeds threshold They propagate over long distances down axons They have a refractory period Both sensory and synaptic potentials are graded have no threshold are generated locally and do not propagate over long distances They have no refractory period They can summate 5 What is the refractory period of a neuron The absolute refractory period is the time after an action potential during which a subsequent action potential cannot be elicited no matter how much the neuron is depolarized We will discuss the mechanism later when we talk about action potentials in more detail