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UT BIO 311D - Neurons, Synapses, and Signaling (Part I)
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BIO 311D 1st Edition Lecture 24 Outline of Current Lecture I. NeuronsII. Information ProcessingIII. Neuron Structure and FunctionIV. Ion PumpsV. Resting PotentialCurrent LectureNeurons, synapses, and signaling• Interpreting signals in the nervous system involves sorting a complex set of paths and connections• Processing of information takes place in simple clusters of neurons called ganglia or a more complex organization of neurons called a brainNeuron organization and structure reflect function in information transfer• The squid possesses extremely large nerve cells and has played a crucial role in the discovery of how neurons transmit signalsIntroduction to Information Processing• Nervous systems process information in three stages: sensory input, integration, and motor output• Sensors detect external stimuli and internal conditions and transmit information along sensory neurons• Sensory information is sent to the brain or ganglia, where interneurons integrate the information• Motor output leaves the brain or ganglia via motor neurons, which trigger muscle or gland activity• Many animals have a complex nervous system that consists of• A central nervous system (CNS) where integration takes place; this includes the brain and a nerve cord• A peripheral nervous system (PNS), which carries information into and out of theCNS • The neurons of the PNS, when bundled together, form nervesNeuron Structure and Function• Most of a neuron’s organelles are in the cell body• Most neurons have dendrites, highly branched extensions that receive signals from other neurons• The axon is typically a much longer extension that transmits signals to other cells at synapses• The cone-shaped base of an axon is called the axon hillock• The synaptic terminal of one axon passes information across the synapse in the form of chemical messengers called neurotransmitters• A synapse is a junction between an axon and another cell• Information is transmitted from a presynaptic cell (a neuron) to a postsynaptic cell (a neuron, muscle, or gland cell)• Most neurons are nourished or insulated by cells called gliaIon pumps and ion channels establish the resting potential of a neuron• Every cell has a voltage (difference in electrical charge) across its plasma membrane called a membrane potential• The resting potential is the membrane potential of a neuron not sending signals• Changes in membrane potential act as signals, transmitting and processing informationFormation of the Resting Potential• In a mammalian neuron at resting potential, the concentration of K+ is highest inside the cell, while the concentration of Na+ is highest outside the cell • Sodium-potassium pumps use the energy of ATP to maintain these K+ and Na+ gradients across the plasma membrane• These concentration gradients represent chemical potential energy• The opening of ion channels in the plasma membrane converts chemical potential to electrical potential• A neuron at resting potential contains many open K+ channels and fewer open Na+ channels; K+ diffuses out of the cell• The resulting buildup of negative charge within the neuron is the major source of membrane potential Choose the correct pathway of the information flow through neurons while taking a test, starting with reading a question and ending with marking an answer.A. Interneurons  motor neurons  sensory neuronsB. Interneurons  sensory neurons  motor neuronsC. Sensory neurons interneurons  motor neuronsD. Motor neurons  interneurons  sensory neuronsModeling the Resting Potential• Resting potential can be modeled by an artificial membrane that separates two chambers– The concentration of KCl is higher in the inner chamber and lower in the outer chamber– K+ diffuses down its gradient to the outer chamber– Negative charge (Cl–) builds up in the inner chamber• At equilibri um, both the electrical and chemical gradients are balancedAdding a poison that specifically disables the Na+ and aK + to a culture of neurons will cause:A. The resting membrane potential to drop to 0 mV B. The inside of the neuron to become more negative relative to the outsideC. The inside of the neuron to become positively charged relative to the outsideD. Sodium to diffuse out of the cell and potassium to diffuse into the cellModeling the Resting Potential• The equilibrium potential (Eion) is the membrane voltage for a particular ion at equilibrium and can be calculated using the Nernst equationEion = 62 mV (log[ion]outside/[ion]inside)• The equilibrium potential of K+ (EK) is negative, while the equilibrium potential of Na+ (ENa) is positive• In a resting neuron, the currents of K+ and Na+ are equal and opposite, and the resting potential across the membrane remains steadyA(n) ____ in Na+ permeability and or an ___ in K+ permeability across a neuron’s plasma membrane could shift membrane potential from -70 mV to -80 mVA. increase; increaseB. increase; decreaseC. decrease; increaseD. decrease;


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UT BIO 311D - Neurons, Synapses, and Signaling (Part I)

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