1. Fundamentals of the Nervous System and Nervous Tissue
PART 1
Fundamentals of the Nervous System and Nervous Tissue

2. Master control and communication system
Nervous System
Master control and communication system
Has three overlapping functions
Sensory receptors monitor changes inside and outside the body
Change – a stimulus
Gathered information – sensory input
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3. Processes and interprets sensory input
Nervous System
Processes and interprets sensory input
Makes decisions – integration
Dictates a response by activating effector organs
Response – motor output
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4. Basic Divisions of the Nervous System
Central nervous system (CNS)
Brain and spinal cord
Integrating and command center
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5. Basic Divisions of the Nervous System
Peripheral nervous system (PNS)
Outside the CNS
Consists of nerves extending from brain and spinal cord
Cranial nerves
Spinal nerves
Peripheral nerves link all regions of the body to the CNS
Ganglia are clusters of neuronal cell bodies
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6. Basic Divisions of the Nervous System
Figure 12.2
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7. Sensory Input and Motor Output
Sensory (afferent) signals picked up by sensor receptors
Carried by nerve fibers of PNS to the CNS
Motor (efferent) signals are carried away from the CNS
Innervate muscles and glands
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8. Sensory Input and Motor Output
Divided according to region they serve
Somatic body region
Visceral body region
Results in four main subdivisions
Somatic sensory
Visceral sensory
Somatic motor
Visceral motor
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9. Types of Sensory and Motor Information
Figure 12.3
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10. Basic Divisions of the Nervous System
Somatic sensory
General somatic senses – receptors are widely spread
Touch
Pain
Vibration
Pressure
Temperature
(receptors discussed in Chapter 14)
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11. Basic Divisions of the Nervous System
Somatic sensory (continued)
Proprioceptive senses – detect stretch in tendons and muscle
Body sense – position and movement of body in space
Special somatic senses (Chapter 16)
Hearing
Balance
Vision
Smell
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12. Basic Divisions of the Nervous System
Visceral sensory
General visceral senses – stretch, pain, temperature, nausea, and hunger
Widely felt in digestive and urinary tracts, and reproductive organs
Special visceral senses
Taste
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13. Basic Divisions of the Nervous System
Somatic motor
General somatic motor – signals contraction of skeletal muscles
Under our voluntary control
Often called “voluntary nervous system”
Branchial motor
Typical skeletal muscle derived from somitomeres
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14. Basic Divisions of the Nervous System
Visceral motor
Regulates the contraction of smooth and cardiac muscle
Makes up autonomic nervous system
Controls function of visceral organs
Often called “involuntary nervous system”
Autonomic nervous system (Chapter 15)
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15. Cells are densely packed and intertwined
Nervous Tissue
Cells are densely packed and intertwined
Two main cell types
Neurons – transmit electrical signals
Support cells (neuroglial cells in CNS)
Nonexcitable
Surround and wrap neurons
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16. The human body contains billions of neurons
The Neuron
The human body contains billions of neurons
Basic structural unit of the nervous system
Specialized cells conduct electrical impulses along the plasma membrane
Nerve impulse (action potential)
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17. Other special characteristics
The Neuron
Other special characteristics
Longevity – can live and function for a lifetime
Do not divide – fetal neurons lose their ability to undergo mitosis; neural stem cells are an exception
High metabolic rate – require abundant oxygen and glucose
Neurons die after 5 minutes without oxygen
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18. Clusters of rough ER and free ribosomes
The Cell Body
Cell body (soma)
Perikaryon – around nucleus
Size of cell body varies from 5–140µm
Contains usual organelles plus other structures
Chromatophilic bodies (Nissl bodies)
Clusters of rough ER and free ribosomes
Stain darkly and renew membranes of the cell
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19. Neurofibrils – bundles of intermediate filaments
The Cell Body
Neurofibrils – bundles of intermediate filaments
Form a network between chromatophilic bodies
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20. Most neuronal cell bodies
The Cell Body
Most neuronal cell bodies
Located within the CNS
Protected by bones of the skull and vertebral column
Ganglia – clusters of cell bodies
Lie along nerves in the PNS
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21. Structure of a Typical Large Neuron
Figure 12.4
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22. Neuron Processes Dendrites Extensively branching from the cell body
Transmit electrical signals toward the cell body
Chromatophilic bodies – only extend into the basal part of dendrites and to the base of the axon hillock
Function as receptive sites for receiving signals from other neurons
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23. Neuron Processes Axons Neuron has only one
Impulse generator and conductor
Transmits impulses away from the cell body
Chromatophilic bodies are absent
No protein synthesis in axon
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24. Neuron Processes Axons (continued)
Neurofilaments, actin microfilaments, and microtubules
Provide strength along length of axon
Aid in the transport of substances to and from the cell body
Axonal transport
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25. Neuron Processes Axons Branches along length are infrequent
Axon collaterals
Multiple branches at end of axon
Terminal branches (telodendria)
End in knobs called axon terminals (also called end bulbs or boutons)
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26. Neuron Processes Nerve impulse
Generated at the initial segment of the axon
Conducted along the axon
Releases neurotransmitters at axon terminals
Neurotransmitters – excite or inhibit neurons
Neuron receives and sends signals
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27. Site at which neurons communicate
Synapses
Site at which neurons communicate
Signals pass across synapse in one direction
Presynaptic neuron
Conducts signal toward a synapse
Postsynaptic neuron
Transmits electrical activity away from a synapse
PLAY
Synapse
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28. Two Neurons Communicating at a Synapse
Figure 12.6
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29. Axoaxonic, dendrodendritic, and dendrosomatic
Types of Synapses
Axodendritic
Between axon terminals of one neuron and dendrites of another
Most common type of synapse
Axosomatic
Between axons and neuronal cell bodies
Axoaxonic, dendrodendritic, and dendrosomatic
Uncommon types of synapses
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30. Some Important Types of Synapses
Figure 12.7
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31. Elaborate cell junctions Axodendritic synapses – representative type
Synaptic vesicles on presynaptic side
Membrane-bound sacs containing neurotransmitters
Mitochondria abundant in axon terminals
Synaptic cleft
Separates the plasma membrane of the two neurons
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32. Structure of a Synapses
Figure 12.8a, b
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33. Signals Carried by Neurons
Plasma membranes of neurons conduct electrical signals
Resting neuron – membrane is polarized
Inner, cytoplasmic side is negatively charged
Stimulation of the neuron  depolarization
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34. Signals Carried by Neurons
Figure 12.9a, b
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35. Signals Carried by Neurons
Strong stimulus applied to the axon triggers
Nerve impulse/action potential
Membrane becomes negative externally
Impulse travels the length of the axon
Membrane repolarizes itself
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36. Signals Carried by Neurons
Figure 12.9c–d
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37. Synaptic Potentials Excitatory synapses
Neurotransmitters alter the permeability of the postsynaptic membrane
Leads to an inflow of positive ions
Depolarizes the postsynaptic membrane
Drives the postsynaptic neuron toward impulse generation
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38. Synaptic Potentials Inhibitory synapses
The external surface of the postsynaptic membrane becomes more positive
Reduces the ability of the postsynaptic neuron to generate an action potential
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