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  • Pictured here is (a) a bipolar neuron, primarily found in sensory systems (for example, vision and audition) and (b) a unipolar neuron, found in the somatosensory system (touch, pain, and the like).

Transcript

  • 1. STRUCTURE ANDFUNCTIONS OF CELLSOF THE NERVOUSSYSTEM
  • 2. Learning Objectives1. Name and describe the parts of a neuron and explain their functions2. Describe the supporting cells of the central and peripheral nervous systems and explain the blood-brain barrier.3. Briefly describe the neural circuitry responsible for a withdrawal reflex and its inhibition by neurons in the brain.4. Describe the measurement of the action potential and explain the how the balance between the forces of diffusion and electrostatic pressure is responsible for the membrane potential.5. Describe the role of ion channels in action potentials and explain the all-or-none law and the rate law.6. Describe the structure of synapses, the release of the neurotransmitter, and the activation of postsynaptic receptors.7. Describe postsynaptic potentials: the ionic movements that cause them, the processes that terminate them, and their integration.8. Describe the role of autoreceptors and axoaxonic synapses in synaptic communication and describe the role of neuromodulators and hormones in nonsynaptic communication
  • 3. Cells of the Nervous Sytem3  Neurons  Receive and transmit information  Glia  Support neurons  Do NOT transmit information  Endothelial Cells  Capillaries
  • 4. Cells of the Nervous System Neurons transmit information Classification  Sensory Neurons  Motor Neurons  Interneurons
  • 5. Neurons: Basic Structure
  • 6. Neurons Multipolar neuron  one axon and many dendrites  most common in CNS Bipolar neuron  one axon and one dendrite  sensory systems Unipolar  one stalk that divides into two branches  Somatosensory system
  • 7. Neurons: Internal Structure
  • 8. Supporting cells Glia (aka neuroglia, glial cells)  “nerve glue”  Functions  Nutrients  Support  Insulation  Housekeeping  Do NOT transmit information
  • 9. Glia: Astrocytes Physical Support Chemical balance Nutrients Clean-up  Phagocytosis
  • 10. Glia: Microglia Smallest glia Phagocytosis Immune function  Microorganisms  Inflammatory reaction
  • 11. Myelinating Glia Oligodendrocytes  CNS Schwann Cells  PNS
  • 12. The Blood-Brain Barrier Selectively permeable Gap junctions Chemical balance Area postrema  Weaker barrier  Vomiting
  • 13. Communication Within aNeuron Electrical  Action potential Remember:  “Brain cells firing in patterns”
  • 14. Neural CommunicationWithdrawal reflex
  • 15. Neural CommunicationVoluntary Control
  • 16. Measuring Electrical Potentials ofAxons Electrode  used to apply electrical stimulation and record electrical potentials. Microelectrode  used to record activity of individual neurons.
  • 17. Measuring Electrical Potentials of Axons Membrane Potential  electrical charge across a cell membrane  difference in electrical potential inside and outside the cell. Outside the cell Resting Potential  membrane potential of a neuron at rest  approximately -70 mV Inside the cell
  • 18. Measuring Electrical Potentials ofAxons Polarization  Depolarization  Hyperpolarization
  • 19. The Membrane Potential: Balanceof Two Forces The force of electrostaticThe force of diffusion pressure Diffusion  Electrolytes  Molecules move  Ions from regions of high  Cations (+) to low  Anions (-) concentrations  Electrostatic pressure  Like charges repel, opposite charges attract
  • 20. The Membrane Potential: Balanceof Two ForcesExtracellular Fluid Intracellular Fluid High Concentration  High Concentration  Sodium (Na+)  Potassium (K+)  Chloride (Cl-)  Low Concentration Low Concentration  Sodium (Na+)  Potassium (K+)  Chloride (Cl-)
  • 21. The Membrane Potential: Balanceof Two Forces
  • 22. The Membrane Ion channel  A specialized protein molecule that permits specific ions to enter or leave the cell. Voltage-dependent ion channel  An ion channel that opens or closes according to the value of the membrane potential.
  • 23. The MembraneSodium-Potassium Transporter  a.k.a. sodium-potassium pump Moves Na+ and K+ across membrane 3 Na+ out  2 K+ in
  • 24. The Action Potential
  • 25. Conduction of the Action Potential All-or-none law Rate Law Speed of signal  Saltatory Conduction
  • 26. Communication BetweenNeurons synaptic transmission  the transmission of messages from one neuron to another through a synapse  these messages are carried by neurotransmitters,  chemicals diffuse across synapses.
  • 27. Communication BetweenNeurons Presynaptic membrane Postsynaptic membrane Postsynaptic potentials
  • 28. Communication BetweenNeurons  Binding site  Ligand A chemical that binds with the binding site of a receptor.
  • 29. Structure of Synapses Types of synapses  Axodendritic  Axosomatic  Axoaxonic
  • 30. Synaptic Structures Presynaptic membrane  Synapticvesicles  Release zone Postsynaptic membrane Synaptic cleft
  • 31. Release of Neurotransmitters Synaptic vesicles A small, hollow, beadlike structure found in the terminal buttons  contains molecules of a neurotransmitter  fuse with the membrane and then break open, spilling their contents into the synaptic cleft.
  • 32. Activation of Receptors Neurotransmitter binds with postsynaptic receptor Opens neurotransmitter dependent ion channels (allows ions to flow in or out)  Ionotropic receptor (fast and direct)  Metabotropic receptor (slow and indirect) G Protein  Second messenger
  • 33. Postsynaptic Potentials Excitatory postsynaptic potential (EPSP)  Depolarizes postsynaptic membrane Inhibitory postsynaptic potential (IPSP)  Hyperpolarizes postsynaptic membrane Effect likelihood a neuron will fire an action potential
  • 34. Termination of Postsynaptic Reuptake of neurotransmitter by transporter molecules Enzymatic deactivation  Acetylcholine  Acetylcholinesterase
  • 35. Neural Integration Involves the effects of EPSP’s and IPSP’s on the likelihood a neuron will fire an action potential
  • 36. Autoreceptors Presynaptic receptors  respond neurotransmitters released by that neuron Metabotropic  regulate internal processes like neurotransmitter synthesis
  • 37. Axoaxonic Synapses Alter amount of neurotransmitter released  Presynaptic inhibition  Presynaptic facilitation
  • 38. Nonsynaptic CommunicationNeuromodulators and hormones Neurotransmitters Neuromodulators Hormones  Released endocrine glands and act on target cells