1. The Nervous System and Tissue

2. Organization The nervous system has 3 overlapping functions: –Sensory input –Integration –Motor output

3. Copyright © 2010 Pearson Education, Inc. Figure 11.1 The nervous system’s functions. Sensory input Motor output Integration

4. Organization The nervous system is divided into 2 major divisions:  Central Nervous System (CNS) which is made up of the brain and spinal cord

5. Organization The nervous system is divided into 2 major divisions:  Central Nervous System (CNS) which is made up of the brain and spinal cord  Peripheral Nervous System (PNS) which is made up of all nerves out side the CNS

6. Organization The PNS is further divided into the: Afferent division which brings in sensory input Efferent (Motor) division which carries motor signals to muscles and glands

7. Organization The Efferent division is further divided into: Somatic Nervous System which carries out voluntary actions Autonomic Nervous System which carries out involuntary actions

9. Copyright © 2010 Pearson Education, Inc. Figure 11.2 Schematic of levels of organization in the nervous system. Central nervous system (CNS) Brain and spinal cord Integrative and control centers Peripheral nervous system (PNS) Cranial nerves and spinal nerves Communication lines between the CNS and the rest of the body Parasympathetic division Conserves energy Promotes house- keeping functions during rest Motor (efferent) division Motor nerve fibers Conducts impulses from the CNS to effectors (muscles and glands) Sensory (afferent) division Somatic and visceral sensory nerve fibers Conducts impulses from receptors to the CNS Somatic nervous system Somatic motor (voluntary) Conducts impulses from the CNS to skeletal muscles Sympathetic division Mobilizes body systems during activity Autonomic nervous system (ANS) Visceral motor (involuntary) Conducts impulses from the CNS to cardiac muscles, smooth muscles, and glands Structure Function Sensory (afferent) division of PNS Motor (efferent) division of PNS Somatic sensory fiber Visceral sensory fiber Motor fiber of somatic nervous system Skin Stomach Skeletal muscle Heart Bladder Parasympathetic motor fiber of ANS Sympathetic motor fiber of ANS

10. Histology of Nervous Tissue Two cell types make up the nervous system. Those called supporting cells or neuroglia cells and those involved in transmission of nerve impulses, the neurons.

11. Neuroglia There are 6 types of neuroglia cells (glial cells). 4 are associated with the CNS 2 with the PNS.

12. Neuroglia Each has a unique function either producing chemicals to aid in neuron growth, insulating or offering support.

13. Neuroglia of the CNS The four types are: Astrocytes Microglia Ependymal Cells & Oligodendrocytes

14. Astrocytes These are the most abundant and versatile of the glial cells. They have radiating process, hence their name “star cells” that connect to neurons and near by capillaries.

15. Astrocytes They provide support and bracing for the neurons and keep them close to the capillaries, their source of nutrition.

16. Copyright © 2010 Pearson Education, Inc. Figure 11.3a Neuroglia. (a) Astrocytes are the most abundant CNS neuroglia. Capillary Neuron Astrocyte

17. Microglia They monitors the health of the neurons. When injured or invading organisms are present they convert into a special type of macrophage.

18. Copyright © 2010 Pearson Education, Inc. Figure 11.3b Neuroglia. (b) Microglial cells are defensive cells in the CNS. Neuron Microglial cell

19. Ependymal Cells They are found lining the central cavities of the brain and spinal cord. The beating of the cilia helps to circulate the cerebral spinal fluid in the CNS.

20. Copyright © 2010 Pearson Education, Inc. Figure 11.3c Neuroglia. Brain or spinal cord tissue Ependymal cells Fluid-filled cavity (c) Ependymal cells line cerebrospinal fluid-filled cavities.

21. Oligodendrocytes They are responsible for forming the insulating myelin sheaths which aid in nerve conduction.

22. Copyright © 2010 Pearson Education, Inc. Figure 11.3d Neuroglia. (d) Oligodendrocytes have processes that form myelin sheaths around CNS nerve fibers. Nerve fibers Myelin sheath Process of oligodendrocyte

23. Neuroglia cells of the PNS These include Satellite Cells Schwann Cells

24. Satellite & Schwann cells Satellite cells surround the neuron cell bodies and have the same functions as the astrocytes do in the CNS. Schwann cells (neurolemmocytes) surround and form the myelin sheaths

25. Copyright © 2010 Pearson Education, Inc. Figure 11.3e Neuroglia. (e) Satellite cells and Schwann cells (which form myelin) surround neurons in the PNS. Schwann cells (forming myelin sheath) Cell body of neuron Satellite cells Nerve fiber

26. Diseases Demyelinating diseases involving the Schwann cells & Oligodendrocytes include: –Multiple Sclerosis of the CNS –Guillian Barre’ of the PNS

27. Neurons Neurons are more commonly called nerve cells. They are responsible for conducting nerve impulses

28. Neurons They have the following characteristics: Extreme longevity, they can function for a lifetime if maintained. Amitotic, they have lost the ability to divide. High metabolic rate, they require constant supply of oxygen and glucose.

29. Cell Body It is also called the perikaryon or soma. It contains the usual cytoplasmic organelles and is the center for biosynthetic processes.

30. Nissl bodies The rough endoplasmic reticulum is usually well developed and stains darkly with basic dyes. They are also termed Nissl bodies.

31. lipofuscin granules Some neurons contain lipofuscin granules, by products of lysosomal activity. They are sometimes referred to as aging pigment

32. Processes The CNS contains both neuron cell bodies and their processes. The PNS consist primarily of processes. In the CNS bundles of neurons are called tracts. In the PNS they are referred to as nerves.

33. Processes Two types of processes are: Dendrites Axons

34. Dendrites These are short, diffuse branching extensions that are typically found near the cell body. They are designed to provide a huge surface area for receiving signals from other neurons.

35. Copyright © 2010 Pearson Education, Inc. Figure 11.4a Structure of a motor neuron. Dendritic spine Neuron cell body (a)

36. Axons In contrast to the dendrites, each neuron has only one axon. The axon arises from the cell body in an area termed the axon hillock.

37. Axons The axon terminates in a profusion of branches of 10,000 or more axon terminals or synaptic knobs. Think of the neuromuscular junction in muscle.

38. Copyright © 2010 Pearson Education, Inc. Figure 11.4b Structure of a motor neuron. Dendrites (receptive regions) Cell body (biosynthetic center and receptive region) Nucleolus Nucleus Nissl bodies Axon (impulse generating and conducting region) Axon hillock Neurilemma Terminal branches Node of Ranvier Impulse direction Schwann cell (one inter- node) Axon terminals (secretory region) (b)

39. Classification of Neurons Neurons are classified based on structure and function

40. Structural Classification Neurons are grouped depending on the number of processes that extend from the cell body.

41. Structural Classification Multipolar neurons have three or more processes. These consist of one axon and 2 dendrites. They represent the most common type making up 99% of all the neurons.

42. Structural Classification Bipolar neurons have two processes one axon and a dendrite. These are located in the retina of the eye and the olfactory mucosa.

43. Structural Classification Unipolar neurons have a single short process that emerges from the cell body and divides into a T with one called the distal process and the other the proximal process. These are found with sensory neurons.

45. Functional Classification This groups the neurons according to the direction the nerve impulse travels relative to the central nervous system. With this there are three types, motor neurons, sensory neurons and interneurons.

46. Sensory or afferent neurons These transmit impulses from the sensory receptors toward or into the CNS. These are almost always unipolar. The cell bodies are located in the sensory ganglion outside the CNS.

47. Motor or efferent neurons These carry impulses away from the CNS to effector organs such as muscles or glands. Motor neurons are multipolar. Their cell bodies are located in the CNS.

48. Interneurons or association neurons These lie between sensory and motor neurons in the CNS. They make up 99% of the neurons in the body.

50. Membrane Potentials Neurons are excitable cells. When they respond to a stimulus, an electrical impulse is generated. This impulse is always the same regardless of the type of stimulus

51. The Action Potential Neurons send signals over long distances by the generation of and propagation of action potentials (APs).

52. An action potential is a brief reversal of the membrane potential. The total amplitude change is about 100 mV usually ranging from -70 to +30 mV.

53. Copyright © 2010 Pearson Education, Inc. Figure 11.14 Absolute and relative refractory periods in an AP. Stimulus Absolute refractory period Relative refractory period Time (ms) Depolarization (Na + enters) Repolarization (K + leaves) After-hyperpolarization

54. Conduction Velocity Action potentials travel at different velocities depending on the type of neurons. Two factors determine impulse rate: –Axon Diameter –Degree of Myelination

55. Conduction Velocity Axon Diameter: In general, the larger the diameter of the neuron, the faster the impulse.

56. Conduction Velocity Degree of Myelination. Action potentials propagate because they are generated by voltage gated channels

57. Unmyelinated Neurons With unmyelinated axons, the channels are next to each other and conduction is slow. This is called continuous conduction.

58. Myelinated Neurons Depolarization can only occur at the Nodes of Ranvier and this is much faster.  This is termed salutatory conduction.

59. Copyright © 2010 Pearson Education, Inc. Figure 11.15c Action potential propagation in unmyelinated and myelinated axons. Stimulus Myelin sheath Node of Ranvier Myelin sheath (c) In a myelinated axon, myelin keeps current in axons (voltage doesn’t decay much). APs are generated only in the nodes of Ranvier and appear to jump rapidly from node to node. 1 mm

60. Nerve Fiber Classification There are 3 types, based on diameter: Class A, the largest diameter and are the sensory and motor fibers Class B are lightly myelinated Group C smallest and unmyelinated Groups B &C are found in the ANS

61. Types of Synapses A synapse is a junction between one neuron and another neuron or a neuron to an effector cell (muscle or gland).

62. Types of Synapses An axodendritic synapse exists between the axon of one neuron and the dendrites of another.

63. Types of Synapses An axosomatic synapse exists between the axon of one neuron and the cell body (soma) of another neuron.

64. Types of Synapses Less understood are the axoaxonic synapses, these exists between the axon of one neuron and the axon of another

66. The Synapse There are two types of synapses: –Electrical –Chemical

67. Electrical Synapses These are not common Electric synapses are characterized by protein channels called connexons that allow the cytoplasm in adjacent neurons to exchange ions.

69. Chemical Synapses Chemical synapses are designed to release a neurotransmitter. A chemical synapse is made of two parts: 1.An axon terminal in the presynaptic neuron 2.neurotransmitter receptor region 3.Synaptic cleft

70. Postsynaptic Potentials and Integration Excitatory synapse causes depolarization of the postsynaptic membrane. EPSP (Excitatory postsynaptic potentials) work to make a neuron more sensitive to stimulation.

71. Copyright © 2010 Pearson Education, Inc. Figure 11.18a Postsynaptic potentials. An EPSP is a local depolarization of the postsynaptic membrane that brings the neuron closer to AP threshold. Neurotransmitter binding opens chemically gated ion channels, allowing the simultaneous pas- sage of Na + and K +. Time (ms) (a) Excitatory postsynaptic potential (EPSP) Threshold Stimulus Membrane potential (mV)

72. Postsynaptic Potentials and Integration IPSPs (Inhibitory postsynaptic potentials) work to reduce the postsynaptic neurons ability to generate an AP

73. Copyright © 2010 Pearson Education, Inc. Figure 11.18b Postsynaptic potentials. An IPSP is a local hyperpolarization of the postsynaptic membrane and drives the neuron away from AP threshold. Neurotransmitter binding opens K + or Cl – channels. Time (ms) (b) Inhibitory postsynaptic potential (IPSP) Threshold Stimulus Membrane potential (mV)

74. Postsynaptic Potentials and Integration A post synaptic neuron can receive a mixture of EPSPs and IPSPs. The axon hillock serves as a neural integrator, summing all the types of neural information. The one that predominates, wins.The one that predominates, wins.

75. Neurotransmitters and Their Receptors There are over 50 neurotransmitters in the nervous system. Neurotransmitters can be classified functionally and chemically.

76. Chemical Structure Several classes exist based on molecular structure.

77. Copyright © 2010 Pearson Education, Inc. Table 11.3 Neurotransmitters and Neuromodulators (1 of 6)

78. Copyright © 2010 Pearson Education, Inc. Table 11.3 Neurotransmitters and Neuromodulators (2 of 6)

79. Copyright © 2010 Pearson Education, Inc. Table 11.3 Neurotransmitters and Neuromodulators (3 of 6)

80. Copyright © 2010 Pearson Education, Inc. Table 11.3 Neurotransmitters and Neuromodulators (4 of 6)

81. Copyright © 2010 Pearson Education, Inc. Table 11.3 Neurotransmitters and Neuromodulators (5 of 6)

82. Copyright © 2010 Pearson Education, Inc. Table 11.3 Neurotransmitters and Neuromodulators (6 of 6)

83. Neurotransmitter Receptors Channel linked receptors are ligand gated channels that direct transmitter action..

84. Neural Integration To work properly, neurons must be integrated with other components of the nervous system. Neuronal pools are groups of neurons placed in functional groups.

85. Patterns of Neural Processing Serial Processing is when the whole system works in a all or none, predictable fashion. One neuron stimulates the next and so on. This type of processing is seen with reflexes and reflex arc.

86. Copyright © 2010 Pearson Education, Inc. Figure 11.23 A simple reflex arc. 1 2 3 4 5 Receptor Sensory neuron Integration center Motor neuron Effector Stimulus Response Spinal cord (CNS) Interneuron

87. Patterns of Neural Processing Parallel Processing involve many pathways and information is delivered to many areas at once.