Lesson 34 - Neurons

34: neurons Friday, April 19, 2024 1:01 PM if a molecule of CO2 released into the blood in your left toe is exhaled from your nose, it must pass through all of the following except: a. the pulmonary vein b. the trachea c. the right atrium d. the right ventricle neurons • receive and transmit information within your body • most postsynaptic neurons are presynaptic neurons to other postsynaptic neurons, and vice versa information processing • 3 stages: ○ sensory input: sensory neurons transmit information about stimuli ○ integration: brain integrates information and considers immediate context and experience; mostly interneurons ○ motor output: trigger output such as muscle or gland activity; motor neurons ○ integration: brain integrates information and considers immediate context and experience; mostly interneurons ○ motor output: trigger output such as muscle or gland activity; motor neurons neurons have electrical potential • potential: difference in charge across a structure • resting potential ○ difference in charge across a membrane when cells are not communicating • graded potential ○ shift in membrane potential that varies in magnitude and direction • action potential ○ rapid, massive change in membrane potential, resulting in communication between cells which of the following statements about electrical potential is true? a. graded potential leads to a permanent increase or decrease in resting membrane potential b. action potential requires rapid movement of ions across the neuronal membrane c. resting potential is maintained by unidirectional movement of ions out of the neuron d. all of the above resting potential • typically -60 to -80 mV ○ ions equally distributed inside vs. outside neuron ○ maintained by active and passive transport of K+ and Na+ ions • active transport: sodium-potassium pump ○ uses ATP to move Na+ out and K+ in ○ for every 2 K+ in, 3 Na+ move out + ○ ions equally distributed inside vs. outside neuron ○ maintained by active and passive transport of K+ and Na+ ions • active transport: sodium-potassium pump ○ uses ATP to move Na+ out and K+ in ○ for every 2 K+ in, 3 Na+ move out ○ ensures that K+ concentration is higher inside the neuron ○ re-establishes electrical gradient • passive transport: leak channels ○ K+ leak channels lead to K+ diffusion out of cell ○ buildup of negative charge due to loss of K+ ○ too much negative charge opposes flow of K+ ○ Na+ leak channels exist but in smaller numbers • reflects balance of chemical/electrical gradients ○ alone, K+ moves out along chemical gradient, electrical gradient favors diffusion in ○ alone, Na+ moves in along a chemical gradient, electrical gradient favors diffusion out • equilibrium potential ○ EK= -90mV ○ ENa = +62 mV ○ voltage when chemical and electrical gradients are in equilibrium ○ together, differences in net flow of K+ and Na+ leads resting potential of -60 to -80 mV is it possible for ions to flow through a leak channel from an area of low concentration to an area of high concentration? a. yes, if leak channels use active transport to move against a concentration gradient ○ leak channels are always passive b. yes, if there is an opposing electrical gradient of greater magnitude c. yes, if more leak channels open across the cell membrane a. yes, if leak channels use active transport to move against a concentration gradient ○ leak channels are always passive b. yes, if there is an opposing electrical gradient of greater magnitude c. yes, if more leak channels open across the cell membrane d. no, ions always diffuse from areas of high concentration to areas of low concentration action potential in 3 steps 1. depolarization ○ change in membrane potential from highly negative, to zero, to positive 2. repolarization ○ return to negative membrane potential 3. hyperpolarization ○ undershoot before return to resting potential action potential • stimulus depolarizes membrane, voltage-gated Na+ channels open ○ Na+ ions enter cell • more voltage gated Na+ channels open ○ depolarization reaches threshold ○ Na+ moves toward Ena • voltage-gated Na+ channels inactivate, then close • voltage-gated K+ channels open ○ K+ ions leave cell ○ K+ move towards EK ○ Na+ moves toward Ena • voltage-gated Na+ channels inactivate, then close • voltage-gated K+ channels open ○ K+ ions leave cell ○ K+ move towards EK • voltage-gated K+ channels close ○ undershoot: more K+ than at rest ○ refractory period ○ return to resting potential which of the following best describes the process of moving from resting potential to action potential? a. an increase in charge that depolarizes the membrane above a certain threshold will open Na+ voltage-gated ion channels, initiating an action potential b. an increase in charge that depolarizes the membrane above a certain threshold will open K+ voltage-gated ion channels, initiating an action potential c. an increase in charge that hyperpolarizes the membrane above a certain threshold will open Na+ voltage-gated ion channels, initiating an action potential d. an increase in charge that hyperpolarizes the membrane above a certain threshold will open K+ voltage-gated ion channels, initiating an action potential conducting action potential • the production of an action potential depolarizes the neighboring area of the axon ○ Na+ inflow pushes region past threshold ○ generates another action potential ○ process repeated, signal cascades along the axon ○ insulation from myelin sheaths increase conduction the propagation of action potential along a neuron is like a. the ripples that form after you drop a stone in a lake the propagation of action potential along a neuron is like a. the ripples that form after you drop a stone in a lake b. the mole in the arcade game "whack-a-mole" c. people doing the wave at a sporting event d. like a pendulum swinging in pace a wave of action potential • action potential has unidirectional propagation ○ Na+ inflow influences neighboring regions of axon ○ regions downstream are depolarizes, propagating action potential ○ regions upstream are still in refractory period, preventing propagation action potential is described as an all-or-nothing phenomenon because: I) it is only generated if we hit threshold, II) it leads to all local neurons firing, III) it is only generated if all the K+ leaves the neuron a. I b. I & II c. I & III d. I, II, & III synapses • communication between neurons and other cells • can be electrical or chemical • chemical synapses: ○ action potential depolarizes terminal membrane of pre-synaptic neuron ○ prompts synaptic vessels to release neurotransmitter into synapse ○ neurotransmitter binds to ligand channel • chemical synapses: ○ action potential depolarizes terminal membrane of pre-synaptic neuron ○ prompts synaptic vessels to release neurotransmitter into synapse ○ neurotransmitter binds to ligand channel synapses: graded potential • post-synaptic neuron receives neurotransmitters ○ ligand-gated channels open ○ ions diffuse into post-synaptic neuron ○ creates positive or negative graded potential • summation: adding up post-synaptic potential ○ leads to action potential or prevents action potential