1. The Nervous System: Neural Tissue
Chapter 9a

2. Introduction Nervous system = control center & communications network
Functions
Stimulates movements
Maintains homeostasis (with endocrine system)

3. Organization of the Nervous System
Central nervous system (CNS)
Brain & spinal cord
Peripheral Nervous System (PNS)
Afferent (Sensory) System
Efferent (Motor) System
Somatic Nervous System
Autonomic Nervous System
Sympathetic Nervous System
Parasympathetic Nervous System
Human Anatomy, 3rd edition
Prentice Hall, © 2001

4. Organization of the Nervous System
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Title: Functional Overview of the Nervous System
Notes: This diagram shows the relationship between the CNS and PNS and the functions and components of the afferent and efferent divisions.
Keywords: nervous system, central, information processing, sensory, afferent, motor commands, efferent, peripheral, somatic, autonomic, special sensory receptors, somatic sensory receptors, visceral sensory receptors, skeletal muscle, smooth, cardiac, glands
Human Anatomy, 3rd edition
Prentice Hall, © 2001

5. Histology of Nervous Tissue
2 types of cells
Neurons
Structural & functional part of nervous system
Specialized functions
Neuroglia (glial cells)
Gli = glue
Support & protection of nervous system

6. Human Anatomy, 3rd edition
Neurons
Function
Conduct electrical impulses
Structure
Cell body
Nucleus with nucleolus
Cytoplasm
Cytoplasmic processes
Dendrites
Axon
Human Anatomy, 3rd edition
Prentice Hall, © 2001

7. Human Anatomy, 3rd edition
Anatomy of a Neuron
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Title: Anatomy of a Representative Neuron
Notes: A neuron has a cell body (soma), some branching dendrites, and a single axon. (a) Detailed organization of the cell body. (b) A neuron may innervate other (1) neurons, (2) skeletal muscle fibers, or (3) gland cells. Synapses are shown in boxes.
Keywords: neuroanatomy, multipolar neuron, skeletal muscle fibers, gland cells, dendrites, collateral branch, axon, axolemma, synapse, synaptic knobs, telodendria, neuroglandular junction, neuromuscular junction, perikaryon, axon hillock
Human Anatomy, 3rd edition
Prentice Hall, © 2001

8. Nerve Fibers of the PNS An axon and its sheaths Myelinated axon
Axon is surrounded by a myelin sheath
Unmyelinated axon
Axon has no myelin sheath

9. Human Anatomy, 3rd edition
Myelin
White matter of nerves, brain, spinal cord
Composed primarily of phospholipids
Production
Developing Schwann cells wind around axon
Function
Increases speed of impulse conduction
Insulation and maintenance of axon
Human Anatomy, 3rd edition
Prentice Hall, © 2001

10. Human Anatomy, 3rd edition
Myelin
Nodes of Ranvier
Unmyelinated gaps between segments of myelin
Impulses “jump” from node to node
Human Anatomy, 3rd edition
Prentice Hall, © 2001

11. Human Anatomy, 3rd edition
Nerve Fibers of the CNS
Umyelinated
Myelinated
Production of myelin is from oligodendrocytes
Nodes of Ranvier are less numerous
Human Anatomy, 3rd edition
Prentice Hall, © 2001

12. Classification of Neurons
Functional – based on the direction of impulse transmission
Sensory neurons
Motor neurons
Interneurons (association)

13. Functional Classification of Neurons
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Title: A Functional Classification of Neurons
Notes: Neurons are classified functionally into three categories: (1) sensory neurons that detect stimuli in the PNS and transmit information to the CNS, (2) motor neurons carrying information from the CNS to peripheral effectors, and (3) interneurons in the CNS
Keywords: neuron, functional classification, peripheral nervous system, exteroceptors, proprioceptors, interoceptors, afferent, peripheral ganglion, somatic sensory neurons, efferent, central nervous system, ANS, SNS, somatic motor neurons, visceral motor neurons
Human Anatomy, 3rd edition
Prentice Hall, © 2001

14. Nerve Impulse
A change in charge that travels as a wave along the membrane of a neuron
Depends on the movement of K+ and Na+ across the nerve cell membrane.
Called an action potential

15. Resting Neuron
Sodium ions are in large concentration along the outside of the cell membrane
Potassium ions are in large concentration along the inside of the cell membrane
Membrane is polarized

16. Beginning of a Nerve Impulse
Requires a stimulus of adequate strength
Membrane is irritable
Neuron may respond to a stimulus and convert it to an impulse.
When? If above threshold = a critical level
Minimum stimulus required to elicit a response

17. Starting a Nerve Impulse
Depolarization – a stimulus begins the change in charge on the neuron’s membrane
A depolarized membrane allows sodium (Na+) to flow inside the membrane
The exchange of ions initiates an action potential in the neuron
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

18. The Action Potential
If the action potential (nerve impulse) starts, it is propagated over the entire axon
Potassium ions rush out of the neuron after sodium ions rush in
Sodium and potassium are actively transported back to their original positions = repolarization
Membrane is at rest again
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

19. Nerve Impulse Propagation
The impulse continues to move away from the cell body
Impulses travel faster when fibers have a myelin sheath
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

20. Continuation of the Nerve Impulse between Neurons
Impulses are able to cross the synapse to another nerve
Neurotransmitter is released from a nerve’s axon terminal
The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter

21. How Neurons Communicate at Synapses
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

22. Human Anatomy, 3rd edition
Synapses
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Title: Structure of a Synapse
Notes: A synapse is the site of communication between a neuron and another cell. (a) Diagrammatic view of a chemical synapse;color-enhanced TEM of a chemical synapse. (b) There may be thousands of chemical synapses on the surface of a single neuron.
Keywords: synapse, synaptic knobs, telodendria, axon, dendrite, glial cell processes, myelin sheath, synaptic cleft, presynaptic membrane, postsynaptic membrane, synaptic vessicles
Human Anatomy, 3rd edition
Prentice Hall, © 2001

23. Human Anatomy, 3rd edition
Neural Regeneration
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Title: Nerve Regeneration after Injury
Notes: Steps involved in the repair of a peripheral nerve by the process of Wallerian degeneration.
Keywords: nerve regeneration, injury, proximal stump, distal stump, axon, myelin, Schwann cell, macrophage, axon buds
Human Anatomy, 3rd edition
Prentice Hall, © 2001

24. Human Anatomy, 3rd edition
Neural Regeneration
FG13_13B.JPG
Title: Nerve Regeneration after Injury
Notes: Steps involved in the repair of a peripheral nerve by the process of Wallerian degeneration.
Keywords: nerve regeneration, injury, proximal stump, distal stump, axon, myelin, Schwann cell, macrophage, axon buds
Human Anatomy, 3rd edition
Prentice Hall, © 2001

25. Human Anatomy, 3rd edition
Neural Regeneration
FG13_13C.JPG
Title: Nerve Regeneration after Injury
Notes: Steps involved in the repair of a peripheral nerve by the process of Wallerian degeneration.
Keywords: nerve regeneration, injury, proximal stump, distal stump, axon, myelin, Schwann cell, macrophage, axon buds
Human Anatomy, 3rd edition
Prentice Hall, © 2001

26. Human Anatomy, 3rd edition
Neural Regeneration
FG13_13D.JPG
Title: Nerve Regeneration after Injury
Notes: Steps involved in the repair of a peripheral nerve by the process of Wallerian degeneration.
Keywords: nerve regeneration, injury, proximal stump, distal stump, axon, myelin, Schwann cell, macrophage, axon buds
Human Anatomy, 3rd edition
Prentice Hall, © 2001

27. Structure of a Nerve Endoneurium surrounds each fiber
Groups of fibers are bound into fascicles by the perineurium
Fascicles are bound together by epineurium
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

28. Classification of Nerves
Mixed nerves
Both sensory and motor fibers
Afferent (sensory) nerves
Carry impulses toward the CNS
Efferent (motor) nerves
Carry impulses away from the CNS