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Chapter 10

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  • 1. The Nervous System Chapter 10
  • 2. 10.1: Introduction
    • Cell types in neural tissue:
      • Neurons
      • Neuroglial cells - also known as neuroglia, glia, and glial
  • 3. Divisions of the Nervous System
    • Central Nervous System (CNS)
      • Brain
      • Spinal cord
    • Peripheral Nervous System (PNS)
      • Cranial nerves
      • Spinal nerves
  • 4. Divisions of Peripheral Nervous System
    • Motor Division
      • Carries information to muscles and glands
    • Divisions of the Motor Division:
      • Somatic – carries information to skeletal muscle
      • Autonomic – carries information to smooth muscle, cardiac muscle, and glands
    • Sensory Division
      • Picks up sensory information and delivers it to the CNS
  • 5. Divisions Nervous System Sensory division Sensory receptors Motor division Skeletal muscle Brain (a) (b) Spinal cord Spinal nerves Cranial nerves Central Nervous System (brain and spinal cord) Peripheral Nervous System (cranial and spinal nerves) Smooth muscle Cardiac muscle Glands Autonomic Nervous System Somatic Nervous System
  • 6. 10.1 Clinical Application
    • Migraine
  • 7. 10.2: General Functions of the Nervous System
    • The three general functions of the nervous system:
      • Receiving stimuli = sensory function
      • Deciding about stimuli = integrative function
      • Reacting to stimuli = motor function
  • 8. Functions of Nervous System
    • Motor Function
      • Decisions are acted upon
      • Impulses are carried to effectors
    • Sensory Function
      • Sensory receptors gather information
      • Information is carried to the CNS
    • Integrative Function
      • Sensory information used to create:
        • Sensations
        • Memory
        • Thoughts
        • Decisions
  • 9. 10.3: Description of Cells of the Nervous System
    • Neurons vary in size and shape
    • They may differ in length and size of their axons and dendrites
    • Neurons share certain features:
      • Dendrites
      • A cell body
      • An axon
  • 10. Neuron Structure
  • 11. Myelination of Axons
    • White Matter
      • Contains myelinated axons
      • Considered fiber tracts
    • Gray Matter
      • Contains unmyelinated structures
      • Cell bodies, dendrites
  • 12. 10.2 Clinical Application
    • Multiple Sclerosis
  • 13. 10.4: Classification of Neurons and Neuroglia
    • Neurons vary in function
      • They can be sensory, motor, or integrative neurons
    • Neurons vary in size and shape, and in the number of axons and dendrites that they may have
    • Due to structural differences, neurons can be classified into three (3) major groups:
      • Bipolar neurons
      • Unipolar neurons
      • Multipolar neurons
  • 14. Classification of Neurons: Structural Differences
    • Bipolar neurons
      • Two processes
      • Eyes, ears, nose
    • Unipolar neurons
      • One process
      • Ganglia of PNS
      • Sensory
    • Multipolar neurons
      • 99% of neurons
      • Many processes
      • Most neurons of CNS
    Dendrites Axon Axon Axon Direction of impulse (a) Multipolar Central process Peripheral process (c) Unipolar (b) Bipolar
  • 15. Classification of Neurons: Functional Differences
    • Sensory Neurons
      • Afferent
      • Carry impulse to CNS
      • Most are unipolar
      • Some are bipolar
    • Interneurons
      • Link neurons
      • Aka association neurons or internuncial neurons
      • Multipolar
      • Located in CNS
    • Motor Neurons
      • Multipolar
      • Carry impulses away from CNS
      • Carry impulses to effectors
    Central nervous system Peripheral nervous system Cell body Interneurons Dendrites Axon Axon Sensory (afferent) neuron Motor (efferent) neuron Cell body Axon (central process) Axon (peripheral process) Sensory receptor Effector (muscle or gland) Axon terminal
  • 16. Types of Neuroglial Cells in the PNS
    • 1) Schwann Cells
      • Produce myelin found on peripheral myelinated neurons
      • Speed up neurotransmission
    • 2) Satellite Cells
      • Support clusters of neuron cell bodies (ganglia)
  • 17. Types of Neuroglial Cells in the CNS
    • 1) Microglia
      • CNS
      • Phagocytic cell
    • 2) Astrocytes
      • CNS
      • Scar tissue
      • Mop up excess ions, etc.
      • Induce synapse formation
      • Connect neurons to blood vessels
    • 3) Oligodendrocytes
      • CNS
      • Myelinating cell
    • 4) Ependyma or ependymal
      • CNS
      • Ciliated
      • Line central canal of spinal cord
      • Line ventricles of brain
  • 18. Types of Neuroglial Cells Microglial cell Axon Oligodendrocyte Astrocyte Capillary Neuron Myelin sheath (cut) Node of Ranvier Ependymal cell Fluid-filled cavity of the brain or spinal cord
  • 19. Regeneration of A Nerve Axon Axon Site of injury Schwann cells (a) (b) (c) (d) (e) Changes over time Motor neuron cell body Former connection reestablished Schwann cells proliferate Schwann cells degenerate Proximal end of injured axon regenerates into tube of sheath cells Distal portion of axon degenerates Skeletal muscle fiber 21
  • 20. 10.5: The Synapse
    • Nerve impulses pass from neuron to neuron at synapses , moving from a pre-synaptic neuron to a post-synaptic neuron .
  • 21. Synaptic Transmission
    • Neurotransmitters are released when impulse reaches synaptic knob
    Mitochondrion Synaptic knob (a) Synaptic cleft Neurotransmitter Axon Ca +2 Presynaptic neuron Direction of nerve impulse Synaptic vesicles Cell body or dendrite of postsynaptic neuron Synaptic vesicle Vesicle releasing neurotransmitter Axon membrane Polarized membrane Depolarized membrane Ca +2 Ca +2
  • 22. 10.6: Cell Membrane Potential
    • A cell membrane is usually electrically charged, or polarized, so that the inside of the membrane is negatively charged with respect to the outside of the membrane (which is then positively charged).
    • This is as a result of unequal distribution of ions on the inside and the outside of the membrane.
  • 23. Distribution of Ions
    • Potassium (K+) ions are the major intracellular positive ions (cations).
    • Sodium (Na+) ions are the major extracellular positive ions (cations).
    • This distribution is largely created by the Sodium/Potassium Pump (Na+/K+ pump).
      • This pump actively transports sodium ions out of the cell and potassium ions into the cell .
  • 24. Resting Potential
    • Resting Membrane Potential (RMP) :
      • 70 mV difference from inside to outside of cell
      • It is a polarized membrane
      • Inside of cell is negative relative to the outside of the cell
      • RMP = -70 mV
      • Due to distribution of ions inside vs. outside
      • Na + /K + pump restores
    Axon Cell body Low Na + Axon terminal Low K + High K + High Na + (a) + + – – + + – – + + – + – – + – + – + – + – + – + – + – + – + – + – + – – 70 mV (b) + + – – + + – – + + – + – – + – + – + – + – + – + – + – + – + – – 70 mV Low Na + Low K + High K + High Na + Na + K + (c) Pump Impermeant anions 26
  • 25. Local Potential Changes
    • Caused by various stimuli:
      • Temperature changes
      • Light
      • Pressure
    • Environmental changes affect the membrane potential by opening a gated ion channel
    • Channels are 1 ) chemically gated, 2) voltage gated, or 3) mechanically gated
    Animation
  • 26. Local Potential Changes
    • If membrane potential becomes more negative , it has hyperpolarized
    • If membrane potential becomes less negative , it has depolarized
    • Graded (or proportional) to intensity of stimulation reaching threshold potential
    • Reaching threshold potential results in a nerve impulse, starting an action potential
  • 27. Local Potential Changes – 62 mV Na + Na + Neurotransmitter (a) – 55 mV Na + Na + Na + Na + Na + Trigger zone (b) Chemically-gated Na + channel Presynaptic neuron Voltage-gated Na + channel
  • 28. Action Potentials
    • At rest, the membrane is polarized (RMP = -70)
    • Sodium channels open and membrane depolarizes (toward 0)
    • Potassium leaves cytoplasm and membrane repolarizes (+30)
    • Threshold stimulus reached (-55)
    • Brief period of hyperpolarization (-90)
    (a) Region of depolarization (b) Region of repolarization (c) – 70 – 0 – 70 – 0 – 70 – 0 K + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + K + K + K + K + K + K + K + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + K + K + K + K + K + K + K + K + Na + Na + Na + Na + Na + Na + Na + Na + K + K + K + K + K + Na + Na + Na + Na + Na + Na + Na + Na + K + K + K + K + K + K + K + K + K + K + K + Na + Na + Na + Na + Na + Na + Threshold stimulus Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + K + K + K + K + K + K + K + K + K + K + Na + Na + Na + Na + Na + Na + K + K + K + K + K + K + K + K + Na + channels open K + channels closed K + channels open Na + channels closed Animation
  • 29. Action Potentials Milliseconds 1 0 0 +20 +40 2 3 4 5 6 7 8 Membrane potential (millivolts) Action potential Hyperpolarization – 40 – 20 – 60 – 80 Resting potential Resting potential reestablished
  • 30. Action Potentials (a) Direction of nerve impulse + + + + + – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – + + + + + + + + + + + + + + + + + (b) + + + + + + + + + + + + + + + + + + + + + + (c) + + + + + + + + + + + + + + + + + + + + + + Region of action potential
  • 31. All-or-None Response
    • If a neuron responds at all, it responds completely
    • A nerve impulse is conducted whenever a stimulus of threshold intensity or above is applied to an axon
    • All impulses carried on an axon are the same strength
  • 32. Refractory Period
    • Absolute Refractory Period
      • Time when threshold stimulus does not start another action potential
    • Relative Refractory Period
      • Time when stronger threshold stimulus can start another action potential
    Animation
  • 33. Impulse Conduction
  • 34. 10.3 Clinical Application
    • Factors Affecting Impulse Conduction
  • 35. 10.7: Synaptic Transmission
    • This is where released neurotransmitters cross the synaptic cleft and react with specific molecules called receptors in the postsynaptic neuron membrane.
    • Effects of neurotransmitters vary.
    • Some neurotransmitters may open ion channels and others may close ion channels.
  • 36. Synaptic Potentials
    • EPSP
      • Excitatory postsynaptic potential
      • Graded
      • Depolarizes membrane of postsynaptic neuron
      • Action potential of postsynaptic neuron becomes more likely
    • IPSP
      • Inhibitory postsynaptic potential
      • Graded
      • Hyperpolarizes membrane of postsynaptic neuron
      • Action potential of postsynaptic neuron becomes less likely
  • 37. Summation of EPSPs and IPSPs
    • EPSPs and IPSPs are added together in a process called summation
    • More EPSPs lead to greater probability of an action potential
    Nucleus Neuron cell body Presynaptic knob Presynaptic axon 39
  • 38. Neurotransmitters
  • 39. Neurotransmitters
  • 40. Neuropeptides
    • Neurons in the brain or spinal cord synthesize neuropeptides.
    • These neuropeptides act as neurotransmitters.
    • Examples include:
      • Enkephalins
      • Beta endorphin
      • Substance P
  • 41. 10.4 Clinical Application
    • Opiates in the Human Body
  • 42. 10.8: Impulse Processing
    • Way the nervous system processes nerve impulses and acts upon them
      • Neuronal Pools
        • Interneurons
        • Work together to perform a common function
        • May excite or inhibit
      • Convergence
        • Various sensory receptors
        • Can allow for summation of impulses
      • Divergence
        • Branching axon
        • Stimulation of many neurons ultimately
  • 43. Neuronal Pools
    • Groups of interneurons that make synaptic connections with each other
    • Interneurons work together to perform a common function
    • Each pool receives input from other neurons
    • Each pool generates output to other neurons
  • 44. Convergence
    • Neuron receives input from several neurons
    • Incoming impulses represent information from different types of sensory receptors
    • Allows nervous system to collect, process, and respond to information
    • Makes it possible for a neuron to sum impulses from different sources
    1 2 3 (a) 46
  • 45. Divergence
    • One neuron sends impulses to several neurons
    • Can amplify an impulse
    • Impulse from a single neuron in CNS may be amplified to activate enough motor units needed for muscle contraction
    (b) 4 5 6 47
  • 46. Important Points in Chapter 10:
    • 10.1: Introduction
    • Describe the general functions of the nervous system.
    • Identify the two types of cells that comprise nervous tissue.
    • Identify the two major groups of nervous system organs.
    • 10.2: General Functions of the Nervous System
    • List the functions of sensory receptors.
    • Describe how the nervous system responds to stimuli.
    • 10.3: Description of Cells of the Nervous System
    • Describe the three major parts of a neuron.
    • Define neurofibrils and chromatophilic substance.
  • 47. Important Points in Chapter 10:
    • Describe the relationship among myelin, the neurilemma, and the nodes of Ranvier.
    • Distinguish between the sources of white matter and gray matter.
    • 10.4: Classification of Neurons and Neuroglia
    • Identify structural and functional differences among neurons.
    • Identify the types of neuroglia in the central nervous system and their functions.
    • Describe the Schwann cells of the peripheral nervous system.
    • 10.5: The Synapse
    • Define presynaptic and postsynaptic.
    • Explain how information passes from a presynaptic to a postsynaptic neuron.
  • 48. Important Points in Chapter 10:
    • 10.6: Cell Membrane Potential
    • Explain how a cell membrane becomes polarized.
    • Define resting potential, local potential, and action potential.
    • Describe the events leading to the conduction of a nerve impulse.
    • Compare nerve impulse conduction in myelinated and unmyelinated neurons.
    • 10.7: Synaptic Transmission
    • Identify the changes in membrane potential associated with excitatory and inhibitory neurotransmitters.
    • 10.8: Impulse Processing
    • Describe the basic ways in which the nervous system processes information.
  • 49. The End