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Cells of the Nervous System
Chapter Three Cells of the Nervous System
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CHAPTER 3 CELLS OF THE NERVOUS SYSTEM
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The Structure of neurons
Neurons and Glia The Structure of neurons Neuron membranes separate intracellular fluid from extracellular fluid The neural cytoskeleton provides structural support that maintains the shape of the neuron
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Figure 3.2 The Neural Membrane
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Figure 3.3 Three Fiber Types Compose the Cytoskeleton of Neurons
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Figure 3.4 Tau Phosphorylation Leads to Cell Death
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Structural Features of Neurons
Neurons and Glia Structural Features of Neurons Cell body (soma) contains nucleus and other organelles Dendrites – branches that serve as locations at which information from other neurons is received Axons are responsible for carrying neural messages to other neurons Vary in diameter and length Many covered by myelin
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Figure 3.5 The Neural Cell Body
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Figure 3.6 Axons and Dendrites
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Structural Variations in Neurons
Unipolar Single branch extending from the cell body Bipolar Two branches extending from the neural cell body: one axon and one dendrite Multipolar Many branches extending from the cell body; usually one axon and many dendrites
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Figure 3.8 Structural and Functional Classification of Neurons
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Functional Variations in Neurons
Sensory Neurons Specialized to receive information from the outside world Motor Neurons Transmit commands from the CNS directly to muscles and glands Interneurons Act as bridges between the sensory and motor systems
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Macroglia: Largest of the glial cells
Astrocytes Oligodendrocytes Schwann cells Microglia: Smallest of the glial cells
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Table 3.1 Types of Glia
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Figure 3.9 Astrocytes
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Figure 3.10 Oligodendrocytes and Schwann Cells
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The Generation of the Action Potential
Ionic Composition of the Intracellular and Extracellular Fluids The difference between these fluids provides the neuron with a source of energy for electrical signaling Differ from each other in the relative concentrations of ions they contain
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Figure 3.12 The Composition of Intracellular and Extracellular Fluids
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Figure 3.13 Measuring the Resting Potential of Neurons
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The Generation of the Action Potential
The Movement of Ions Diffusion is the tendency for molecules to distribute themselves equally within a medium Electrical force is an important cause of movement Like electrical charges repel Opposite electrical charges attract
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Figure 3.14 Diffusion and Electrical Force
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The Generation of the Action Potential
The Resting Potential Membrane allows potassium to cross freely Measures about -70mV If potassium levels in extracellular fluid increase, resting potential is wiped out
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Channels open & close during action potential
The Action Potential Threshold When recording reaches about -65mV Channels open & close during action potential Sodium flows into neuron , potassium flows out around the peak of the action potential Refractory period Recording returns to resting potential Absolute versus relative refractory periods The action potential is all-or-none
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Figure 3.15 The Action Potential
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The Propagation of the Action Potential
Signal reproduces itself down the length of the neuron Influenced by myelination Passive conduction = propagation in unmyelinated axon Saltatory conduction = propagation in myelinated axon
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Figure 3.16 Action Potentials Propagate Down the Length of the Axon
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Figure 3.17 Propagation in Unmyelinated and Myelinated Axons
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The Synapse Electrical synapses Chemical synapses
Directly stimulate adjacent cells by sending ions across the gap through channels that actually touch Chemical synapses Stimulate adjacent cells by sending chemical messengers Neurotransmitter release Neurotransmitters bind to postsynaptic receptor sites Termination of the chemical signal Postsynaptic potentials Neural Integration
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Table 3.2 A Comparison of Electrical and Chemical Synapses
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Figure 3.19 The Electrical Synapse
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Figure 3.21 Exocytosis Results in the Release of Neurotransmitters
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Figure 3.22 Ionotropic and Metabotropic Receptors
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Figure 3.23 Methods for Deactivating Neurotransmitters
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Figure 3.24 Neural Integration Combines Excitatory and Inhibitory Input
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Table 3.3 A Comparison of the Characteristics of Action Potentials, EPSPs and IPSPs
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Synapses between an axon terminal and another axon fiber
Neuromodulation Synapses between an axon terminal and another axon fiber Axo-axonic synapses have modulating effect on the release of neurotransmitter by the target axon Presynaptic facilitation Presynaptic inhibition
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Figure 3.26 Synapses Between Two Axons Modulate the Amount of Neurotransmitter Released
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