2. Section 9 The Nervous System

3. 2 LIU Chuan Yong 刘传勇 Institute of Physiology Medical School of SDU Tel 88381175 (lab) 88382098 (office) Email: liucy@sdu.edu.cnliucy@sdu.edu.cn Website: www.physiology.sdu.edu.cn

4. Reference – Website and Textbook

5. Chapter 29. Cells in Nervous System and Their Function Neurocyte Neuroglia (Glia cell)

6. 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)

7. Central Nervous System Consists of –Brain –Spinal cord Brain and spinal cord –Continuous with each other

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

9. Nervous System Organization

10. 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

11. Part 1 Neuron

12. 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 1.Structure and Function

13. 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

14. 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

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

16. By function (connections) Interneuron SensoryMotor

17. Neuron Classification

18. Neuron Anatomy  Extensions outside the cell body  Dendrites – conduct impulses toward the cell body  Axons – conduct impulses away from the cell body

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

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

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

22. Myelin Sheath 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

23. Myelin CNS: oligodendroglia or oligodendrocytes PNS: Schwann cells ~

24. Nodes of Ranvier Gaps in the myelin sheath between adjacent Schwann cells The sites where collaterals can emerge Saltatory conduction

25. Myelin Sheath and Neurilemma: Formation Formed by Schwann cells in the PNS A Schwann cell: –Encloses the axon with its plasma membrane –Concentric layers of membrane make up the myelin sheath Neurilemma （神经鞘） – remaining nucleus and cytoplasm of a Schwann cell

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

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

30. 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

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

32. . Conducting Action Potential Conducting Action Potential 2). velocities of AP propagation: – 0.5~120m/s – The factors that influence the AP propagation Diameter Myelin sheath Temperature

33. 3). Classification of NF Efferent nerve – A , A , A , A  ; B, C. Afferent nerve – I, II, III, IV.

34. 4) Axoplasmic transport The concept: Various organelles and materials is moved from the cell body 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.

35.  Axoplasmic transport 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 ： – 205mm/d, – NGF, tetanic toxin, horseradish peroxidase (HRP).

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

37. 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 denervation atrophy follows. – Fibrous tissue replaces the muscle

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

39. 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)

40. Neuroglia of CNS Microglia –Specialized macrophages Oligodendrocytes –Form myelin sheaths if surround axon

41. 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