Electrical Signals in Neurons: Graded Potentials and Action Potentials - Prof. Karen Peter, Study notes of Biology

Download Electrical Signals in Neurons: Graded Potentials and Action Potentials - Prof. Karen Peter and more Study notes Biology in PDF only on Docsity! 1 What are the parts of a neuron? What electrical signals occur on them? Graded potentials: dendrites, axon hillock Action potentials Synaptic Potential Generator Potential Dendrite: _______, branched; receptive zone. Axon: __________ branches; high speed electrical transmission. Synaptic terminal (knob/bulb): releases __________ message. How does our nervous system send/receive electrical signals? Biol. 118 Lecture 6, Exam 2 Fall 2008 K+ diffusion through “leakage” channels creates resting membrane potential. __________ fluid: K+ & protein (A-) ions ____________ fluid: mostly Na+ & Cl- ions + + + + + + + + + + - - - - - - - - - - - - - Resting Neural Membrane Resting Neuron Voltage inside charge - outside charge = -70 mV on average http://bcs.whfreeman.com/thelifewire/content/chp44/4401s.swf What is the role of active transport by the sodium- potassium pump in neuron & muscle cell function? Active transport via carrier proteins moves sodium ions (Na+) out of the cells & potassium ions (K+) into the cell. http://student.ccbcmd.edu/courses/bio141/lecguide/unit3/eustruct/sppump__rh_flash.html 2 What is the function of “voltage” gated channels on axons? What signal opens these gates? Diffusion of ions via gated channels causes a rapid voltage change. Voltage changes during an action potential: 1st Depolarization (voltage becomes ___________) 2nd Repolarization (voltage returns to__________) 1st Depolarization 2nd Repolarization http://www.blackwellpublishing.com/matthews/channel.html 1. Na+ voltage-gated channels open allowing Na+ ions to diffuse into neuron. 2. K+ voltage-gated channels open allowing K+ ions to diffuse out of neuron. Time What is the sequence of events that produce action potentials? http://www.portscheller.net/bio/bilder/neuron.swf _____________ feedback: Na+ diffusion “excites” the next part of an axon. Why are action potentials said to be “non-decremental”? 5 What happens when electrical signals are “summed” up both in space & time on a receptor or synapse? http://hsc.uwe.ac.uk/synapses_neuro/Summation.htm Can you explain this summary of graded potentials? Synaptic potential ___will produce more action potentials than potential ___. Why? _______________ Propagation Signal declines with distance because voltage leaks across membrane with distance. How does stimulus strength “translate” into action potentials, if action potentials look alike & travel at same rate on an axon? Stimulus strength (intensity) is converted into ________ of action potentials per unit time. ____ Action Potentials ______ Action Potentials Stronger stimulus Weaker stimulus 6 How do changes in extracellular (plasma) pH affect the electrical activity of neurons? Things to know or review from today’s lecture: 1. Explain why in general, neurons are designed to send signals 1 direction only. Describe the structure & function of these regions of a neuron: dendrites, axons, synaptic terminals. What organelles can be found in the cell body region of a neuron? Where on a neuron might action potentials occur? Where do graded potentials occur? 2. Describe the conditions along a resting neuron’s membrane: distribution of (Na+, K+, Cl- & proteins-) inside & outside of the neuron, charge distribution across the membrane. Why do we say the resting membrane is “polarized”? What is a typical resting membrane potential? 3. What is the role of the Na+-K+ pump in the cell membrane of a neuron or skeletal muscle cell? 4. What type of gated channels are found along axons? What signal opens these channels? Describe the timing of the opening & closing of Na+ & K+ channels in an action potential (what happens in the depolarization vs repolarization phases). Compare an action potential’s speed, travel method & efficiency on a non-myelinated vs myelinated axon. 5. Where can Schwann cells be found? Describe how they myelinate and support axons. Why aren’t all neurons myelinated? What types of neurons are not myelinated? What is the benefit of myelination? More to review from today’s lecture: 1. Why do we say that action potentials are “non-decremental” with distance? Why are synaptic potentials and generator (sensory) potentials called “graded” potentials? 2. Describe the sequence of events at a synaptic junction (ie. from 1 synaptic terminal, across the synaptic cleft & onto the dendritic region of another neuron). How are neurotransmitters broken down or removed from their receptor sites on a dendrite (ie. how does the signal stop?) 3. Explain the terms depolarizing & hyperpolarizing synaptic potentials. Give an example of an ion channel opening that could be depolarizing & one that could be hyperpolarizing. Why are synaptic & generator potentials “decremental”? 4. What stimulus strength on a dendrite will be converted into action potentials? Is stimulus strength converted into bigger action potentials or more action potentials? 5. Explain how acidosis hyperpolarizes neurons & how alkalosis depolarizes neurons. What effects will these pH changes have on overall neuron & muscle activity?