The Nervous System

3. The Nervous System • The nervous system is unique in the vast complexity of thought processes and control actions it can perform. • It receives each minute literally millions of bits of information from the different sensory nerves and sensory organs and then integrates all these to determine responses to be made by the body.

4. Chapter objectives 1. Principles of neurophysiology The function of neurons Synaptic transmission 2. The functions of nervous system Sensory function Regulation of posture and movement Regulation of visceral function Advanced function

5. Section 1 The Functions of Neuron and Neuroglia

7. (31 pairs)

9. Neuron The basic structural and functional unit of the nervous system is the individual nerve cell, called as neuron. There are about 100 billion neurons in the CNS.

10. Neuron The mostly functionof neurons operates by generating and transmitting electrical signals that move from one part of the cell to another part of the same cell or to neighboring cells.

11. Neuron Theelementary functionsof neuron • Receive the excitations or inhibitions induced by internal or external stimulations. • Analyze and integrate the information from every organs. • Generate or carry the demands regulating the activities of the effectors. • Some neurons have neuroendocrine function.

13. Basic Neuron types • Bipolar----one process projecting from either end of an elongated cell. • Unipolar---nerve cell possessing only a single process. • Multipolar---numerous dendrites projecting from cell body.

15. Structure of neuron Cell body dendrite Receiving part AP Initial segment Conduction of AP Axon collateral axon Transmitter release terminal Fig. Diagrammatic representation of a neuron.

16. Function of Neuron Processing of information. Dendrite: receive the nervous impulse. Soma: intergrate the message Axon: carries the impulse away from the cell body.

18. Action potential propagation in an unmyelinated axon

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21. Propagation of the action potential

22. Conduction Velocity • 1. One way of increasing the speed of conduction is by increasing the size of the axon. This reduces the internal electrical resistance and increases the passive depolarization. • 2. The advantage of myelination is an increase in the speed of conduction, without a large increase in metabolic cost. • 3. Another way of increasing the speed of conduction is by increasing the temperature.

23. Classification of nerve fibers： • 1.The letter system: • Based on electrophysiological properties, mainly the conduction velocity and characteristics of Ap, this electrophysiological classification divides fibers into three groups: A, B and C. 2.The number system: • According to diameters and origins of fibers, they are divided into four groups:Ⅰ, Ⅱ, Ⅲ and Ⅳ.

24. efferent nerves

25. Type Origin Type Ia Muscle spindle, Aα annulospinal ending Ib Golgi tendom organ Aβ II Muscle spindle, flowerspray Aγ ending,touch, pressure III Pain and cold receptor Aδ some touch receptors IV Pain,temperature, and C other receptors. afferent nerves 注：痛觉传入纤维习惯用Aδ类纤维和C类纤维

26. Types of nerve fibers

29. Axoplasmic transport • Anterograde anxoplasmic transport: soma → terminals -Rapid transport : 410mm/d,  organelles with membrane,  neurotransmitters( neuropeptide), mitochondria and enzymes - Slow transport: 1-12(0.5-10)mm/d. microtubuleand microfilament, • Retrograde axoplasmic transport : soma ← terminals 205mm/d. NGF, virus and toxin,etc. by endocytosis.

30. Anterograde axoplasmic transport: • Fast transport: occurs at 400mm/d, such as mitochondria, secretory vesicles. Mechanism :kinesin • Slow transport: occurs at 0.5-10mm/d, such as cytoskeleton proteins. Mechanism :microbule , microfilament Fig. Axopasmic transport

31. Retrograde axoplasmic transport: • nerve growth factor, • viruses. （Rabies） • Mechanism :dynein Fig. The method of horseradish peroxidase

32. Nerve retrograde tract-tracing • HRP is injected to the brain, then take the brain to conduct histochemical reaction after two weeks. HRP can be used to the Nerve retrograde tract-tracing. Fig. The method of horseradish peroxidase

33. HRP • The enzyme horseradish peroxidase, found in horseradish, is used extensively in molecular biology and in antibody amplification and detection, among other things. For example, "In recent years the technique of marking neurons with the enzyme horseradish peroxidase (HRP) has become a major tool. In its brief history, this method has probably been used by more neurobiologists than have used the Golgi stain since its discovery in 1870." Horseradish peroxidase is also highly used in techniques such as Western blotting and ELISAs.  • HRP is widely used as an enzymatic label in immunoassays. Usually, the enzyme is coupled to antibodies, lectins or haptens. Coupling to antibodies etc. may be performed through the carbohydrate side chains of the HRP. 

34. Trophic action between nerve and tissue 1. Neurotrophic action on tissue: muscle atrophy after nerve injury glycogen synthesis ↓ protein decomposition ↑ poliomyelitis

35. poliomyelitis

36. poliomyelitis • An acute infectious disease of humans, particularly children, caused by any of three serotypes of human poliovirus (POLIOVIRUS). Usually the infection is limited to the gastrointestinal tract and nasopharynx, and is often asymptomatic. The central nervous system, primarily the spinal cord, may be affected, leading to rapidly progressive paralysis, coarse FASCICULATION and hyporeflexia. Motor neurons are primarily affected. Encephalitis may also occur. The virus replicates in the nervous system, and may cause significant neuronal loss, most notably in the spinal cord. A rare related condition, nonpoliovirus poliomyelitis, may result from infections with nonpoliovirus enteroviruses. (From Adams et al., Principles of Neurology, 6th ed, pp764-5)

37. Trophic action between nerve and tissue 2. Trophic action on nerve

38. Neurotrophin • Nerve growth factor(NGF) • Brain-derived neurotrophin factor(BDNF) • Neurotrophin 3 • Neurotrophin 4/5 • Neurotrophin 6 • Ciliary neurotrophin factor(CNTF) • Glial cell-derived neurotrophin factor(GDNF) • Leukemia inhibitory factor(LIF) • Insulin-like growth factorⅠ(IGF-Ⅰ) • Transforming growth factor(TGF) • Fibroblast growth factor(TGF) • Platelet-derived growth factor(PDGF)

39. Trophic action between nerve and tissue 3. Receptors for neurotrophic factors

40. Neuroglia • About 1.0×1012~ 5.0×1012 neuroglia cells , 10~50 fold of neurons • Dendrites and axons can not be distinguished clearly • No synapse formed and no AP produced

41. The types of glia • CNS - astrocyte oligodendrocyte microglia ependymal cell Choroidal epithelium • PNS - Schwann cell satellite cell

43. Neuroglial cells Ependymal Cell CNS Microglia Oligodendrocyte Astrocyte

45. Functions of glial cells • Astrocytes (Astroglia) -Support the neurons - Clean up brain "debris"( damaged material) and fill in the damaged area - Transport nutrients to neurons - regulate the external chemical environment of neurons by removing excess ions, and recycling neurotransmitters.

46. Transport nutrients to neurons, • They regulate the external chemical environment of neurons • by removing excess ions, notably potassium, and recycling • neurotransmitters released during synaptic transmission

47. Astrocytes • Regulate extracellular brain fluid composition • Promote tight junctions to form blood-brain barrier

48. Ependymal Cells • Line brain ventricles and spinal cord central canal • Help form choroid plexuses that secrete • cerebrospinal fluid (CSF)

49. Oligodendrocytes and Schwann cells -myelinate axons (1) insulate the axons (2) facilitate the conduction of electrical impulses.

50. Microglia -act as the immune cells of the CNS - remove most of the waste and cellular debris from the CNS - derivation,action in brain injury, action in other diseases.