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Nervous System and Neurons: A Guide to Communication and Response

This chapter explains the stimulus-response process in the nervous system, discussing the structure and function of neurons, action potentials, synaptic transmission, and the integration of signals. It also covers common neurotransmitters and the condition multiple sclerosis.

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Nervous System and Neurons: A Guide to Communication and Response

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  1. Chapter 34: Nervous System

  2. stimulus Line of Communication receptors sensory neurons integrators interneurons motor neurons effectors muscles, glands response Fig. 34-2, p.574

  3. Vertebrate Nervous Systems • Earliest fishlike vertebrates had a hollow, tubular nerve cord • Modification and expansion of nerve cord produced spinal cord and brain • Nerve cord persists in vertebrate embryos as a neural tube • Cephalization-formation of head and brain

  4. Fig. 34-4, p.575

  5. HumanNervous Systems

  6. Communication Lines Stimulus (input) Receptors (sensory neurons) Integrators (interneurons) motor neurons Effectors (muscles, glands) Response (output) Figure 34.5Page 575

  7. Neurons • Basic units of communication in nearly all nervous systems • Monitor information in and around the body and issue commands for responsive actions

  8. Neurons Fig. 34-6d2, p.576

  9. Motor Neuron dendrites Input Zone cell body axon axon endings Trigger Zone Conducting Zone Output Zone Stepped Art Fig. 34-6d1, p.576

  10. Three Classes of Neurons • Sensory neurons • Interneurons • Motor neurons

  11. dendrites axon cell body Fig. 34-6a, p.576

  12. dendrites dendrites cell body axon Fig. 34-6b,c, p.576

  13. Structure of a Neuron dendrites input zone cell body trigger zone conducting zone axon endings axon output zone Fig. 34-6d1, p.576

  14. Resting Potential • Charge difference across the plasma membrane of a neuron • Fluid just outside cell is more negatively charged than fluid inside • Potential is measured in millivolts • Resting potential is usually about -70mv

  15. How Ions Move across Membrane Interstitial fluid Cytoplasm Na+/K+ pump Passive transporters with open channels Passive transporters with voltage-sensitive gated channels Active transporters Lipid bilayer of neuron membrane Figure 34.7Page 577

  16. Ion Concentrations at Resting Potential • Potassium (K+) • Higher inside than outside • Sodium (Na+) • Higher outside than inside

  17. Na+ K+ outside plasma membrane inside Na+ K+ p.577

  18. Action Potential • A transitory reversal in membrane potential • Voltage change causes voltage-gated channels in the membrane to open • Inside of neuron briefly becomes more positive than outside

  19. Action Potential 1 Na+ 2 Na+ Na+ K+ K+ K+ K+ K+ K+ K+ Na+ Na+ Na+ Na+ 3 4 Na+ Na+ Figure 34.8a-dPage 578-79

  20. Positive Feedback more Na+ ions flow into the neuron more gated channels for Na+ open neuron becomes more positive inside

  21. All or Nothing • All action potentials are the same size • If stimulation is below threshold level, no action potential occurs • If it is above threshold level, cell is always depolarized to the same level

  22. Repolarization • Once peak depolarization is reached, Na+ gates close and K+ gates open • Movement of K+ out of cell repolarizes the cell • The inside of the cell once again becomes more negative than the outside

  23. electrode outside electrode inside unstimulated axon Fig. 34-9b, p.579

  24. stimulated axon Fig. 34-9e1, p.579

  25. action potential threshold level resting level Fig. 34-9e2, p.579

  26. Propagation of Action Potentials • An action potential in one part of an axon brings a neighboring region to threshold • Action potential occurs in one patch of membrane after another

  27. Chemical Synapse • Gap between the terminal ending of an axon and the input zone of another cell plasma membrane of axon ending of presynapic cell plasma membrane of postsynapic cell synaptic vesicle synaptic cleft membrane receptor Figure 34.10aPage 580

  28. Synaptic Transmission • Action potential in axon ending of presynaptic cell causes voltage-gated calcium channels to open • Flow of calcium into presynaptic cell causes release of neurotransmitter into synaptic cleft

  29. Synaptic Transmission • Neurotransmitter diffuses across cleft and binds to receptors on membrane of postsynaptic cell • Binding of neurotransmitter to receptors opens ion channels in the membrane of postsynaptic cell

  30. Ion Gates Open neurotransmitter ions receptor for neurotransmitter gated channel protein Figure 34.10cPage 580

  31. Synaptic Integration what action potential spiking would look like threshold -65 Membrane potential (milliseconds) EPSP integrated potential resting membrane potential -70 IPSP Figure 34.12Page 581 -75

  32. neuromuscular junction motor neuron axons from spinal cord to skeletal muscle cells transverse slice of spinal cord part of a skeletal muscle Fig. 34-11a, p.581

  33. axon ending muscle fiber Fig. 34-11b, p.581

  34. Neurotransmitters • ACh • Norepinephrine • Epinephrine • Dopamine • Serotonin • GABA • Derived from amino acids

  35. Multiple Sclerosis • A condition in which nerve fibers lose their myelin • Slows conduction • Symptoms include visual problems, numbness, muscle weakness, and fatigue

  36. Fig. 34-13a, p.582

  37. Fig. 34-13b,c, p.582

  38. Fig. 34-14, p.583

  39. axon myelin sheath nerve fascicle Nerve • A bundle of axons enclosed within a connective tissue sheath Figure 34.15Page 584

  40. Myelin Sheath • A series of Schwann cells • Sheath blocks ion movements • Action potential must “jump” from node to node Figure 34.15bPage 584

  41. Reflexes • Automatic movements made in response to stimuli • In the simplest reflex arcs, sensory neurons synapse directly on motor neurons • Most reflexes involve an interneuron

  42. Stretch Reflex STIMULUS Biceps stretches. sensoryneuron motorneuron Response Biceps contracts. Figure 34.16Page 585

  43. Central and Peripheral Nervous Systems • Central nervous system (CNS) • Brain • Spinal cord • Peripheral nervous system • Nerves that thread through the body

  44. Peripheral Nervous System • Somatic nerves • Motor functions • (Shown in green) • Autonomic nerves • Visceral functions • (Shown in red)

  45. Function of the Spinal Cord • Expressway for signals between brain and peripheral nerves • Sensory and motor neurons make direct reflex connections in the spinal cord • Spinal reflexes do not involve the brain

  46. Brain Development midbrain hindbrain forebrain Brain at 7 weeks Fig. 34-19b, p.588

  47. Brain Development Brain at 9 weeks Fig. 34-19c, p.588

  48. Brain Development Brain at birth Fig. 34-19d, p.588

  49. right ventricle left ventricle third ventricle fourth ventricle spinal canal Fig. 34-20, p.588

  50. Vertebrate Brains olfactory lobe olfactory lobe (part of forebrain) forebrain forebrain midbrain hindbrain midbrain hindbrain fish (shark) reptile (alligator) mammal (horse) Figure 34.21Page 589

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