BIO 311D 1st Edition Lecture 24 Outline of Current Lecture I Neurons II Information Processing III Neuron Structure and Function IV Ion Pumps V Resting Potential Current Lecture Neurons 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 brain Neuron 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 signals Introduction 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 the CNS The neurons of the PNS when bundled together form nerves Neuron 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 glia Ion 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 information Formation 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 neurons B Interneurons sensory neurons motor neurons C Sensory neurons interneurons motor neurons D Motor neurons interneurons sensory neurons Modeling 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 balanced Adding 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 outside C The inside of the neuron to become positively charged relative to the outside D Sodium to diffuse out of the cell and potassium to diffuse into the cell Modeling the Resting Potential The equilibrium potential Eion is the membrane voltage for a particular ion at equilibrium and can be calculated using the Nernst equation Eion 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 steady A 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 mV A increase increase B increase decrease C decrease increase D decrease increase
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