Chapter 44: Neurons and Nervous Systems CHAPTER 44 Neurons and Nervous Systems
Chapter 44: Neurons and Nervous Systems Nervous Systems: Cells and Functions Nervous Systems: Cells and Functions Neurons: Generating and Conducting Nerve Impulses Neurons: Generating and Conducting Nerve Impulses Neurons, Synapses, and Communication Neurons, Synapses, and Communication Neurons in Networks Neurons in Networks
Chapter 44: Neurons and Nervous Systems Nervous Systems: Cells and Functions Nervous systems consist of cells that process and transmit information.Nervous systems consist of cells that process and transmit information.3
Chapter 44: Neurons and Nervous Systems Nervous Systems: Cells and Functions Sensory cells transduce information from the environment and body.Sensory cells transduce information from the environment and body. This communicates commands to effectors such as muscles or glands.This communicates commands to effectors such as muscles or glands.4
Chapter 44: Neurons and Nervous Systems Nervous Systems: Cells and Functions The nervous systems of different species vary, but all are composed of cells called neurons.The nervous systems of different species vary, but all are composed of cells called neurons. Review Figures 44.1,
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Chapter 44: Neurons and Nervous Systems Nervous Systems: Cells and Functions In vertebrates, brain and spinal cord form the central nervous system.In vertebrates, brain and spinal cord form the central nervous system. They communicate with other body tissues via the peripheral nervous system.They communicate with other body tissues via the peripheral nervous system.8
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Chapter 44: Neurons and Nervous Systems Nervous Systems: Cells and Functions Neurons receive information mostly via their dendrites and transmit information over their axons.Neurons receive information mostly via their dendrites and transmit information over their axons. They function in networks.They function in networks. Review Figure
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Chapter 44: Neurons and Nervous Systems Nervous Systems: Cells and Functions Information that neurons process is in the form of electrical events in their plasma membranes.Information that neurons process is in the form of electrical events in their plasma membranes. Where neurons and other cells meet, information is transmitted mostly by release of chemical signals called neurotransmitters.Where neurons and other cells meet, information is transmitted mostly by release of chemical signals called neurotransmitters.12
Chapter 44: Neurons and Nervous Systems Nervous Systems: Cells and Functions Glial cells physically support neurons and perform many housekeeping functions.Glial cells physically support neurons and perform many housekeeping functions. Schwann cells and oligodendrocytes produce myelin, which insulates neurons.Schwann cells and oligodendrocytes produce myelin, which insulates neurons. Astrocytes create the blood–brain barrier.Astrocytes create the blood–brain barrier. Review Figure
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Chapter 44: Neurons and Nervous Systems Neurons: Generating and Conducting Nerve Impulses Neurons have an electric charge difference across their plasma membranes.Neurons have an electric charge difference across their plasma membranes. This resting potential is created by ion pumps and channels.This resting potential is created by ion pumps and channels. Review Figure
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Chapter 44: Neurons and Nervous Systems Neurons: Generating and Conducting Nerve Impulses The sodium–potassium pump concentrates K + ions on the insides and Na + ions on the outsides of neurons.The sodium–potassium pump concentrates K + ions on the insides and Na + ions on the outsides of neurons. Ion channels allow K + ions to leak out, leaving behind unbalanced negative charges, leading to the resting potential.Ion channels allow K + ions to leak out, leaving behind unbalanced negative charges, leading to the resting potential. Review Figures 44.6,
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Chapter 44: Neurons and Nervous Systems Neurons: Generating and Conducting Nerve Impulses A potassium equilibrium potential exists when an electric charge that develops across the membrane is sufficient to prevent net diffusion of potassium ions down their concentration gradient.A potassium equilibrium potential exists when an electric charge that develops across the membrane is sufficient to prevent net diffusion of potassium ions down their concentration gradient. This potential can be calculated with the Nernst equation.This potential can be calculated with the Nernst equation. Review Figure
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Chapter 44: Neurons and Nervous Systems Neurons: Generating and Conducting Nerve Impulses The resting potential is perturbed when ion channels open or close, thus changing plasma membrane permeability to charged ions.The resting potential is perturbed when ion channels open or close, thus changing plasma membrane permeability to charged ions. Thus, neurons become depolarized or hyperpolarized in response to stimuli.Thus, neurons become depolarized or hyperpolarized in response to stimuli. Review Figure
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Chapter 44: Neurons and Nervous Systems Neurons: Generating and Conducting Nerve Impulses Rapid reversals in charge across portions of the plasma membrane, resulting from opening and closing of voltage-gated sodium and potassium channels, produce action potentials.Rapid reversals in charge across portions of the plasma membrane, resulting from opening and closing of voltage-gated sodium and potassium channels, produce action potentials. These changes occur when the plasma membrane depolarizes to a threshold level.These changes occur when the plasma membrane depolarizes to a threshold level. Review Figure
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Chapter 44: Neurons and Nervous Systems Neurons: Generating and Conducting Nerve Impulses Action potentials are conducted down axons because of local current flowAction potentials are conducted down axons because of local current flow This depolarizes adjacent regions of membrane and brings them to threshold for the opening of voltage-gated sodium channels.This depolarizes adjacent regions of membrane and brings them to threshold for the opening of voltage-gated sodium channels. Review Figure
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Chapter 44: Neurons and Nervous Systems Neurons: Generating and Conducting Nerve Impulses Patch clamping allows us to study single ion channels.Patch clamping allows us to study single ion channels. Review Figure
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Chapter 44: Neurons and Nervous Systems Neurons: Generating and Conducting Nerve Impulses In myelinated axons, the action potentials appear to jump between nodes of Ranvier, patches of plasma membrane not covered by myelin.In myelinated axons, the action potentials appear to jump between nodes of Ranvier, patches of plasma membrane not covered by myelin. Review Figure
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Chapter 44: Neurons and Nervous Systems Neurons, Synapses, and Communication Neurons communicate with each other and other cells at specialized junctions called synapses, where plasma membranes of two cells come close together.Neurons communicate with each other and other cells at specialized junctions called synapses, where plasma membranes of two cells come close together.36
Chapter 44: Neurons and Nervous Systems Neurons, Synapses, and Communication The classic chemical synapse is the neuromuscular junction, a synapse between a motor neuron and muscle cell.The classic chemical synapse is the neuromuscular junction, a synapse between a motor neuron and muscle cell. Its neurotransmitter is acetylcholine, which causes a depolarization of the postsynaptic membrane when it binds to its receptor.Its neurotransmitter is acetylcholine, which causes a depolarization of the postsynaptic membrane when it binds to its receptor. Review Figure
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Chapter 44: Neurons and Nervous Systems Neurons, Synapses, and Communication When an action potential reaches an axon terminal of the presynaptic cell, it causes the release of neurotransmitters.When an action potential reaches an axon terminal of the presynaptic cell, it causes the release of neurotransmitters. These chemical signals diffuse across the synaptic cleft and bind to receptors on the postsynaptic membrane.These chemical signals diffuse across the synaptic cleft and bind to receptors on the postsynaptic membrane. Review Figures 44.15,
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Chapter 44: Neurons and Nervous Systems Neurons, Synapses, and Communication Synapses between neurons are either excitatory or inhibitory.Synapses between neurons are either excitatory or inhibitory. Excitatory responses are caused by membrane depolarization.Excitatory responses are caused by membrane depolarization. Inhibitory responses are caused by hyperpolarization of membranes.Inhibitory responses are caused by hyperpolarization of membranes.42
Chapter 44: Neurons and Nervous Systems Neurons, Synapses, and Communication A postsynaptic neuron integrates information by summing its synaptic inputs in space and time.A postsynaptic neuron integrates information by summing its synaptic inputs in space and time. Review Figure
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Chapter 44: Neurons and Nervous Systems Neurons, Synapses, and Communication Ionotropic neurotransmitter receptors are ion channels.Ionotropic neurotransmitter receptors are ion channels. Metabotropic receptors influence the postsynaptic cell through various signal transduction pathways that involve G proteins.Metabotropic receptors influence the postsynaptic cell through various signal transduction pathways that involve G proteins. These pathways can result in changes in ion channels, alterations of enzyme activity, and gene expression.These pathways can result in changes in ion channels, alterations of enzyme activity, and gene expression. Actions of ionotropic synapses are generally faster than those of metabotropic synapses.Actions of ionotropic synapses are generally faster than those of metabotropic synapses. Review Figures 44.18,
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Chapter 44: Neurons and Nervous Systems Neurons, Synapses, and Communication Electrical synapses pass electric signals between cells without the use of neurotransmitters.Electrical synapses pass electric signals between cells without the use of neurotransmitters. Connexons make physical contact between the cells.Connexons make physical contact between the cells.48
Chapter 44: Neurons and Nervous Systems Neurons, Synapses, and Communication There are many different neurotransmitters and even more receptors.There are many different neurotransmitters and even more receptors. The action of a neurotransmitter depends on the receptor to which it binds.The action of a neurotransmitter depends on the receptor to which it binds. Review Table
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Chapter 44: Neurons and Nervous Systems Neurons, Synapses, and Communication Glutamate binds to ionotropic and metabotropic receptors, and may be involved in learning and memory.Glutamate binds to ionotropic and metabotropic receptors, and may be involved in learning and memory. Review Figure
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Chapter 44: Neurons and Nervous Systems Neurons, Synapses, and Communication With repeated stimulation, a neuron can become more sensitive to its inputs.With repeated stimulation, a neuron can become more sensitive to its inputs. Since this increased sensitivity can last a long time, it is called long-term potentiation, or LTP.Since this increased sensitivity can last a long time, it is called long-term potentiation, or LTP. Properties of the NMDA glutamate receptor appear to explain LTP. Properties of the NMDA glutamate receptor appear to explain LTP. Review Figure
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Chapter 44: Neurons and Nervous Systems Neurons, Synapses, and Communication In chemical synapses, the transmitter must be cleared rapidly from the synapse.In chemical synapses, the transmitter must be cleared rapidly from the synapse. Some poisons and drugs block or slow the clearance of transmitter from the synapse.Some poisons and drugs block or slow the clearance of transmitter from the synapse.56
Chapter 44: Neurons and Nervous Systems Neurons in Networks Neurons work together in networks to accomplish specific tasks.Neurons work together in networks to accomplish specific tasks. The networks use all of the mechanisms we have discussed in this chapter.The networks use all of the mechanisms we have discussed in this chapter.57