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Chapter 10 Nervous System

Chapter 10 Nervous System. The Nervous System. Components Brain, spinal cord, nerves, sensory receptors Responsible for Sensory perceptions, mental activities, stimulating muscle movements, secretions of many glands Subdivisions Central nervous system (CNS) Peripheral nervous system (PNS).

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Chapter 10 Nervous System

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  1. Chapter 10 Nervous System

  2. The Nervous System • Components • Brain, spinal cord, nerves, sensory receptors • Responsible for • Sensory perceptions, mental activities, stimulating muscle movements, secretions of many glands • Subdivisions • Central nervous system (CNS) • Peripheral nervous system (PNS)

  3. Central Nervous System • Consists of • Brain • Spinal cord • Brain and spinal cord • Continuous with each other

  4. Peripheral Nervous System • Two subcategories • Sensory or afferent • Motor or efferent • Divisions • Somatic nervous system • Autonomic nervous system (ANS) • Sympathetic • Parasympathetic • Enteric

  5. Nervous System Organization

  6. Cells of Nervous System • Neurons or nerve cells • Receive stimuli and transmit action potentials • Organization • Cell body or soma • Dendrites: Input • Axons: Output • Neuroglia or glial cells • Support and protect neurons

  7. Section 1 General Function of Neuron and Neuroglia I Neuron

  8. Structure and Function Typical Neuron has 4 Regions • Cell Body • Dendrites • Axon • Presynaptic Terminals • Each region is specialized for its particular function • Information flows in a single direction

  9. Neuron Cell Body Location • Most are found in the central nervous system • Gray matter – cell bodies and unmylenated fibers • Nuclei – clusters of cell bodies within the white matter of the central nervous system • Ganglia – collections of cell bodies outside the central nervous system

  10. Functional Classification of Neurons • Sensory (afferent) neurons • Carry impulses from the sensory receptors • Cutaneous sense organs • Proprioceptors – detect stretch or tension • Motor (efferent) neurons • Carry impulses from the central nervous system

  11. Functional Classification of Neurons • Interneurons (association neurons) • Found in neural pathways in the central nervous system • Connect sensory and motor neurons

  12. Sensory Motor Interneuron By function (connections)

  13. Neuron Classification

  14. Neuron Anatomy • Extensions outside the cell body • Dendrites – conduct impulses toward the cell body • Axons – conduct impulses away from the cell body (only 1!)

  15. Dendrites of Motor Neurons • Short, tapering, and diffusely branched processes • They are the receptive, or input, regions of the neuron • Electrical signals are conveyed as graded potentials (not action potentials)

  16. Axons: Structure • Slender processes of uniform diameter arising from the hillock • Long axons are called nerve fibers • Usually there is only one unbranched axon per neuron • Rare branches, if present, are called axon collaterals • Axonal terminal – branched terminus of an axon

  17. Axons: Function • Generate and transmit action potentials • Secrete neurotransmitters from the axonal terminals

  18. Whitish, fatty (protein-lipid), segmented sheath around most long axons • It functions in: • Protection of the axon • Electrically insulating fibers from one another • Increasing the speed of nerve impulse transmission Myelin Sheath

  19. Myelin • CNS: oligodendroglia • or oligodendrocytes • PNS: Schwann cells ~

  20. Nodes of Ranvier • Gaps in the myelin sheath between adjacent Schwann cells • They are the sites where collaterals can emerge • Saltatory conduction

  21. Myelin Sheath and Neurilemma: Formation • Formed by Schwann cells in the PNS • A Schwann cell: • Envelopes an axon in a trough • Encloses the axon with its plasma membrane • Concentric layers of membrane make up the myelin sheath • Neurilemma – remaining nucleus and cytoplasm of a Schwann cell

  22. Myelin Sheath and Neurilemma: Formation Figure 11.5a-d

  23. Unmyelinated Axons • A Schwann cell surrounds nerve fibers but coiling does not take place • Schwann cells partially enclose 15 or more axons

  24. Axons of the CNS • Both myelinated and unmyelinated fibers are present • Myelin sheaths are formed by oligodendrocytes • Nodes of Ranvier are widely spaced • There is no neurilemma

  25. 2. Classification and Function of Nerve Fibers • Function: conducting action potential • 1)Characteristic •  physiological integration (anesthetic and tetrodotoxin, TTX) •  insulation, •  two direction •  no fatigue

  26. 2).Conducting velocities of AP propagation: 0.5~120m/s. The factors that influence the AP propagation: ~The diameter of NF: 0.2 -20 mm, The larger the diameter is , The faster A.P. propagates. ~ Myelin sheath: ~Temperature:

  27. 3). The general classification of NF  Electrical physiological classification (efferent nerve): A, A, A, A; B, C.  Morphological classification (afferent nerve): I, II, III, IV.

  28. 4) Axoplasmic transport The concept: Various organelles and materials must be moved from the cell body, where they are made, to the axon and its terminals in order to maintain the structure and function of the cell axon. The mechanisms: Cytoskeletal filaments in the axon and cell body, which serve as the rails along which the transport occurs, are linked by proteins to the substances and organelles being moved.

  29. Anterograde axoplasmic transport ~ fast axoplasmic transport: 410mm/day, mitochondria, vesicles, secretory granule. ~ slow axoplasmic transport:1-12 mm/d, cytoskeletal elements & soluble proteins  Retrograde axoplasmic transport：Axon transport of certain materials are from the axon terminals to the cell body. 205mm/d, NGF, tetanic toxin, horseradish peroxidase (HRP).

  30. Fig. Axopasmic transport Fig. The method of horseraidish peroxidase

  31. 5) Trophic action of the nerve to the target The motor nerve release some substance that has trophic action on the skeletal muscle The denervated muscle does not receive nerve signals and due to this, muscle atrophy begins. After two months, the muscle fibers degenerate and denervationatrophy follows. Fibrous tissue replaces the muscle

  32. II Supporting Cells: Neuroglia Ependymal Cell Microglia Oligodendrocyte Astrocyte Martini, F. Fundamentals of Anatomy and Physiology, Fig 12-6.

  33. Neuroglia of CNS • Astrocytes • Regulate extracellular brain fluid composition • Promote tight junctions to form blood-brain barrier • Ependymal Cells • Line brain ventricles and spinal cord central canal • Help form choroid plexuses that secrete cerebrospinal fluid (CSF)

  34. Neuroglia of CNS • Microglia • Specialized macrophages • Oligodendrocytes • Form myelin sheaths if surround axon

  35. Neuroglia of PNS • Schwann cells or neurolemmocytes • Wrap around portion of only one axon to form myelin sheath • Satellite cells • Surround neuron cell bodies in ganglia, provide support and nutrients

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