PowerPoint ® Lecture Slides prepared by Leslie Hendon, University of Alabama, Birmingham HUMAN ANATOMY fifth edition MARIEB | MALLATT | WILHELM 12 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Fundamentals of the Nervous System and Nervous Tissue PART 1

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 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

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Nervous System  Processes and interprets sensory input  Makes decisions – integration  Dictates a response by activating effector organs  Response – motor output

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Basic Divisions of the Nervous System  Central nervous system (CNS)  Brain and spinal cord  Integrating and command center

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 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

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Basic Divisions of the Nervous System Figure 12.2

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 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

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 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

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Types of Sensory and Motor Information Figure 12.3

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 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)

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 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

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 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

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 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

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 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)

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 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

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 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)

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 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

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 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

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings The Cell Body  Neurofibrils – bundles of intermediate filaments  Form a network between chromatophilic bodies

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 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

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Structure of a Typical Large Neuron Figure 12.4

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 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

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 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

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 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

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 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)

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 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

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 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

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Two Neurons Communicating at a Synapse Figure 12.6

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 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

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Some Important Types of Synapses Figure 12.7

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Synapses  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

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Structure of a Synapses Figure 12.8a, b

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 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

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Signals Carried by Neurons Figure 12.9a, b

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 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

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Signals Carried by Neurons Figure 12.9c–d

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 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

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 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