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Chapter Three

Chapter Three. Cells of the Nervous System. CHAPTER 3 CELLS OF THE NERVOUS SYSTEM. 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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Chapter Three

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  1. Chapter Three Cells of the Nervous System

  2. CHAPTER 3CELLS OF THE NERVOUS SYSTEM

  3. 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

  4. Figure 3.2 The Neural Membrane

  5. Figure 3.3 Three Fiber Types Compose the Cytoskeleton of Neurons

  6. Figure 3.4 Tau Phosphorylation Leads to Cell Death

  7. 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

  8. Figure 3.5 The Neural Cell Body

  9. Figure 3.6 Axons and Dendrites

  10. 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

  11. Figure 3.8 Structural and Functional Classification of Neurons

  12. 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

  13. Glia • Macroglia: Largest of the glial cells • Astrocytes • Oligodendrocytes • Schwann cells • Microglia: Smallest of the glial cells

  14. Table 3.1 Types of Glia

  15. Figure 3.9 Astrocytes

  16. Figure 3.10 Oligodendrocytes and Schwann Cells

  17. 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

  18. Figure 3.12 The Composition of Intracellular and Extracellular Fluids

  19. Figure 3.13 Measuring the Resting Potential of Neurons

  20. 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

  21. Figure 3.14 Diffusion and Electrical Force

  22. 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

  23. 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

  24. Figure 3.15 The Action Potential

  25. The Propagation of the Action Potential • Propagation • Signal reproduces itself down the length of the neuron • Influenced by myelination • Passive conduction = propagation in unmyelinated axon • Saltatory conduction = propagation in myelinated axon

  26. Figure 3.16 Action Potentials Propagate Down the Length of the Axon

  27. Figure 3.17 Propagation in Unmyelinated and Myelinated Axons

  28. The Synapse • Electrical 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

  29. Table 3.2 A Comparison of Electrical and Chemical Synapses

  30. Figure 3.19 The Electrical Synapse

  31. Figure 3.21 Exocytosis Results in the Release of Neurotransmitters

  32. Figure 3.22 Ionotropic and Metabotropic Receptors

  33. Figure 3.23 Methods for Deactivating Neurotransmitters

  34. Figure 3.24 Neural Integration Combines Excitatory and Inhibitory Input

  35. Table 3.3 A Comparison of the Characteristics of Action Potentials, EPSPs and IPSPs

  36. 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

  37. Figure 3.26 Synapses Between Two Axons Modulate the Amount of Neurotransmitter Released

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