1. © 2014 Pearson Education, Inc. PowerPoint ® Lecture Presentations prepared by Leslie Hendon University of Alabama, Birmingham 12 Fundamentals of the Nervous System and Nervous Tissue

2. © 2014 Pearson Education, Inc. I. Nervous System Overview A. Master control and communication system 1. Stimulus—changes detected inside or outside the body 2. Sensory receptors - monitor changes inside and outside the body 2. Sensory input—information gathered by receptors 3. Integration—Processes and interprets sensory input 4. Motor output—Dictates response; activates effector organs

3. © 2014 Pearson Education, Inc. Sensory input Motor output Integration Stimulus Sensory receptor Effector Action

4. © 2014 Pearson Education, Inc. II. Basic Organization of the Nervous System A. Central nervous system (CNS) 1. composed of the brain and spinal cord 2. is the integrating and command center B. Peripheral nervous system (PNS) 1. Consists of nerves extending from brain and spinal cord a. cranial nerves (off the brain) b. spinal nerves (off the spinal cord) 2. Peripheral nerves link all regions of the body to the CNS 3. Nucleus – group of nerve cell bodies in the brain/cord 4. Ganglion – group of nerve cell bodies outside brain/cord

5. © 2014 Pearson Education, Inc. Brain Spinal cord Nerves Ganglia CNS PNS

6. © 2014 Pearson Education, Inc. C. Sensory (afferent) division 1. somatic sensory – information from skin, muscle and tendon 2. visceral sensory – information from organs, glands, all else 3. information carried to CNS by spinal and cranial nerves D. Motor (efferent) division 1. somatic motor – (voluntary) information to muscles 2. visceral motor – (involuntary) information to organs, glands, etc. a. also called the autonomic nervous system i. sympathetic division ii. parasympathetic division

7. © 2014 Pearson Education, Inc. Brain and spinal cord Central nervous system (CNS) Cranial nerves and spinal nerves Peripheral nervous system (PNS) Sensory (afferent) divisionMotor (efferent) division Somatic and visceral sensory nerve fibers Motor nerve fibers Somatic motor (voluntary) Conducts impulses from the CNS to skeletal muscles Somatic nervous system Autonomic nervous system (ANS) Visceral motor (involuntary) Conducts impulses from the CNS to cardiac muscles, smooth muscles, and glands Sympathetic division Paraysmpathetic division Mobilizes body systems during activity Conserves energy Promotes house- keeping functions during rest Bladder Heart Parasympathetic motor fiber of ANS Sympathetic motor fiber of ANS Motor fiber of somatic nervous system Skeletal muscle Stomach Skin Visceral sensory fiber Somatic sensory fiber Structure Function Sensory (afferent) division of PNS Motor (efferent) division of PNS

8. © 2014 Pearson Education, Inc. E. Somatic sensory - general (widespread) somatic senses 1. Receptors spread throughout outer tube of body a. Touch, Pain, Vibration, Pressure, Temperature 2. Proprioceptive senses - detect tendon/muscle stretch a. Body sense—position and movement of body in space 3. Special somatic sense - balance

9. © 2014 Pearson Education, Inc. F. Visceral sensory 1. General visceral senses a. stretch, pain, temperature, nausea, and hunger b. felt in digestive and urinary tracts, and reproductive organs 2. Special visceral senses: hearing, vision, taste and smell

10. © 2014 Pearson Education, Inc. III. Somatic vs. Visceral Motor A. Somatic motor 1. general somatic motor—contraction of skeletal muscles a. Under our voluntary control b. Often called “voluntary nervous system” B. Visceral motor 1. regulates the contraction of smooth and cardiac muscle 2. controls function of visceral organs and glands 3. also called the autonomic nervous system (involuntary)

11. © 2014 Pearson Education, Inc. IV. Nervous Tissue A. Neurons - electrical signals to transmit information 1. basic structural unit of the nervous system 2. can send an “action potential” (nerve impulse) down its axon 3. Longevity - can live and function for a lifetime 4. amitotic - fetal neurons lose their ability to undergo mitosis; neural stem cells are an exception 5. High metabolic rate - require abundant oxygen and glucose a. Neurons die after 5 minutes without oxygen

12. © 2014 Pearson Education, Inc. B. Neuroglial cells – “supporting cells” of neurons 1.Most neuroglia have branching processes and a central cell body 2. Outnumber neurons 10 to 1 3. Make up half the mass of the brain 4. Can divide throughout life C. Astrocytes – most abundant type of glial cell 1. Extract blood sugar from capillaries for energy 2. Take up and release ions to control environment around neurons 3. Involved in synapse formation in developing neural tissue 4. Produce molecules necessary for neuronal growth

13. © 2014 Pearson Education, Inc. Capillary Neuron Astrocyte Astrocytes are the most abundant CNS neuroglia.

14. © 2014 Pearson Education, Inc. D. Microglia – smallest and least abundant glial cell 1. phagocytes—the macrophages of the CNS a. engulf invading microorganisms and dead neurons 2. derived from blood cells called monocytes 3. migrate to CNS during embryonic and fetal periods Microglial cells are defensive cells in the CNS. Neuron Microglial cell

15. © 2014 Pearson Education, Inc. E. Ependymal cells – help circulate cerebrospinal fluid (CSF) 1. line the brain ventricles and central canal of spinal cord 2. have cilia to help circulate the CSF Ependymal cells line cerebrospinal fluid-filled cavities. Ependymal cells Brain or spinal cord tissue Fluid-filled cavity

16. © 2014 Pearson Education, Inc. F. Oligodendrocytes – wrap around axons in the CNS 1. this results in the myelin sheath around the axons Oligodendrocytes have processes that form myelin sheaths around long axons in the CNS. Axons Oligodendrocytes Myelin sheath Myelin sheath gap

17. © 2014 Pearson Education, Inc. G. Schwann cells – wrap around axons in the PNS 1. this results in the myelin sheath around the axons Satellite cells and Schwann cells (which form myelin) surround neurons in the PNS. Satellite cells Cell body of neuron Schwann cells (forming myelin sheath) Axon

18. © 2014 Pearson Education, Inc. H. Myelin sheath 1. segmented structures composed of the lipoprotein myelin 2. surround thicker axons 3. forms an insulating layer 4. prevent leakage of electrical current 5. increase the speed of impulse conduction 6. non-myelinated axons are slower 7. nodes of Ranvier – gaps between the surrounding cells

19. © 2014 Pearson Education, Inc. Schwann cell plasma membrane Schwann cell cytoplasm Axon An axon wrapped with a fatty insulating sheath formed from Schwann cells Myelinated axon in PNS Schwann cell nucleus Schwann cell cytoplasm Myelin sheath Schwann cell cytoplasm Axon Cross section of a myelinated axon (TEM 135,000  ) A Schwann cell envelops an axon. 1 2 3 The Schwann cell then rotates around the axon, wrapping its plasma membrane loosely around it in successive layers. The Schwann cell cytplasm is forced from between the membranes. The tight membrane wrappings surrounding the axon form the myelin sheath. Myelin sheath

20. © 2014 Pearson Education, Inc. A. Nerve Cell Body B. Dendrites C. Axon (and axon hillock) ► Myelin Sheath (w/ Nodes of Ranvier) ► Axon Terminals (terminal boutons) D. Synapse V. The Structure of a Neuron (nerve cell)

21. © 2014 Pearson Education, Inc. Nucleus Nucleolus Axon hillock Terminal arborization Schwann cell Myelin sheath gap (node of Ranvier) Terminal boutons (secretory region) Nuclei of neuroglial cells Nucleus with nucleolus Dendrites (receptive regions) Cell body (biosynthetic center and receptive region) Dendrites Neuron cell body Axon (impulse-generating and -conducting region)

22. © 2014 Pearson Education, Inc. A. Nerve cell body 1. site of nucleus, nucleolus and organelles 2. size is from 5 – 150 µm 3. most nerve cell bodies located in the CNS 4. has colorful organelles called Nissl bodies 5. group of cell bodies in the CNS – nucleus 6. group of cell bodies in the PNS – ganglion a. a nucleus or ganglion usually has a common function

23. © 2014 Pearson Education, Inc. Nucleus Nucleolus Axon hillock Terminal arborization Schwann cell Myelin sheath gap (node of Ranvier) Terminal boutons (secretory region) Nuclei of neuroglial cells Nucleus with nucleolus Dendrites (receptive regions) Cell body (biosynthetic center and receptive region) Dendrites Neuron cell body Axon (impulse-generating and -conducting region)

24. © 2014 Pearson Education, Inc. B. Dendrites 1. extend off the nerve cell body 2. can be 10 – 100 in number 3. receive electrical signals from other nerve cells C. Axons 1. one long extension of the plasma membrane 2. send signals from cell body to axon terminals (the synapse) 3. signal is sent in only one direction (cell body >>> synapse) 4. axon hillock – first part of axon attached to cell body 5. may or may not have a myelin sheath wrapped around it 6. end in terminal arboration (tree) with many terminal boutons

25. © 2014 Pearson Education, Inc. Nucleus Nucleolus Axon hillock Terminal arborization Schwann cell Myelin sheath gap (node of Ranvier) Terminal boutons (secretory region) Nuclei of neuroglial cells Nucleus with nucleolus Dendrites (receptive regions) Cell body (biosynthetic center and receptive region) Dendrites Neurofibril Neuron cell body Axon (impulse-generating and -conducting region)

26. © 2014 Pearson Education, Inc. D. The Synapse 1. site where the presynaptic neuron sends signal to postsynaptic neuron 2. almost all synapses are chemical using a neurotransmitter 3. some synapses are electrical using gap junctions between cells 4. most are axondendritic; small number are axosomatic (cell body) 5. space between pre- and postsynaptic cell is the synaptic cleft 6. terminal bouton have vesicles with neurotransmitter

27. © 2014 Pearson Education, Inc. D. The Synapse Two neurons connected by synapses Presynaptic neuron axon Postsynaptic neuron Terminal boutons at synapse Dendrites Postsynaptic neuron axon

28. © 2014 Pearson Education, Inc. Enlarged view of the synapse Synaptic vesicles Synaptic cleft Nerve impulses Presynaptic axon Terminal bouton Vesicle releasing neurotransmitter Mitochondrion Postsynaptic dendrite

29. © 2014 Pearson Education, Inc. VI. Classification of Neurons by Structure A. Multipolar neuron ► cell body surrounded by dendrites; one very long axon e.g. Purkinje cell of cerebellum; pyramidal cell of hippocampus B. Bipolar neuron ► many dendrites > one long dendrite > cell body > axon e.g. olfactory cell; retinal cell C. Unipolar neuron ► long dendrite > (passes by cell body) > long axon e.g. sensory cell of the dorsal root ganglion

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32. VI. Classification of Neurons by Function A. Sensory neurons 1. send nerve impulses toward the CNS 2. almost all are unipolar 3. cell bodies are located in ganglia outside the CNS B. Motor neurons 1. send nerve impulses away from the CNS 2. most motor neurons are multipolar 3. cell bodies located in nuclei within the CNS 4. form synapses with the organs, glands, tissues they innervate

33. © 2014 Pearson Education, Inc. C. Interneurons 1. between sensory and motor; between themselves 2. most numerous of all types 3. only located in the brain and spinal cord (CNS!) 4. mostly multipolar

34. © 2014 Pearson Education, Inc. Sensory input Motor output Integration Stimulus Sensory receptor Effector Action

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36. VII. Structure of a Nerve A. Nerve – bundle of axons wrapped together by connective tissue 1. like a bunch of wires wrapped together in electrical cord 2. most nerves contain myelinated axons 3. Schwann cells form the myelin sheath around single cells B. Layers of Connective Tissue 1. epineurium – around the entire nerve 2. perineurium – around a fascicle of axons 3. endoneurium – around each individual axon

37. © 2014 Pearson Education, Inc. Myelin sheath Axon Fascicle Epineurium Endoneurium Perineurium Blood vessels Myelinated axons Myelin sheath Fascicle Epineurium Schwann cell nucleus Axon Myelin Myelin sheath gap

38. © 2014 Pearson Education, Inc. C. Grey matter – anywhere there are nerve cell bodies located 1. in various regions of the brain 2. in the central “butterfly” region of the spinal cord D. White matter – indicates the presence of myelinated axons 1. in various regions of the brain 2. surrounding the central grey “butterfly” of the spinal cord 3. tracts - bundles of axons carrying common information in the CNS NOTE: bundle of axons in the PNS = nerve; bundle of axons in the CNS = tract

39. © 2014 Pearson Education, Inc. Sensory (afferent) fiber Spinal nerve Motor (efferent) fiber PNS CNS Gray matter White matter - Collection of nerve cell bodies -Bundles of axons carrying common information Dorsal root of the spinal nerve Ventral root of the spinal nerve

40. © 2014 Pearson Education, Inc. White matter Cross section of spinal cord and vertebra, cervical region Grey matter

41. © 2014 Pearson Education, Inc. White matter - ascending and descending “TRACTS” of the spinal cord. Ascending tracts Descending tracts Grey matter

42. © 2014 Pearson Education, Inc. Touch receptor Spinothalamic pathwayDorsal column-medial lemniscal pathwaySpinocerebellar pathway Grey matter White matter Grey matter White matter Grey matter White matter

43. © 2014 Pearson Education, Inc. VIII. Reflex Arcs A. Reflex arcs – simple chain of neurons that allow for reflexes 1. Mechanism for action of simple reflexes e.g. patellar tendon reflex; biceps tendon reflex 2. can be either a somatic reflex or a visceral reflex 3. Consists of five components a. receptor – detects the stimulus b. sensory neuron – transmits the information c. integration center – relay station d. motor neuron – sends message to the effector e. effector – muscle or organ that is activated

44. © 2014 Pearson Education, Inc. Stimulus Skin Receptor Sensory neuron Integration center Motor neuron Effector Interneuron Spinal cord (in cross section) 21345 Synapse Axon Cell body

45. © 2014 Pearson Education, Inc. B. Monosynaptic reflex arc 1. simplest of all reflex pathways 2. one sensory neuron and one motor neuron 3. fastest type of reflex

46. © 2014 Pearson Education, Inc. Sensory (stretch) receptor Sensory (afferent) neuron Motor (efferent) neuron Effector organ 21345 Monosynaptic stretch reflex

47. © 2014 Pearson Education, Inc. B. Polysynaptic reflex arc 1. more common type of reflex pathway 2. one or more interneurons between sensory and motor 3. common in withdrawal reflexes

48. © 2014 Pearson Education, Inc. 21345 Sensory (afferent) neuronSensory receptor Interneuron Motor (efferent) neuron Effector organ Polysynaptic withdrawal reflex

49. © 2014 Pearson Education, Inc. IX. Neuronal Circuits A. Diverging circuit—one presynaptic neuron synapses with several other neurons (divergence) B. Converging circuit—many neurons synapse on a single postsynaptic neuron (convergence) C. Reverberating circuit—circuit that receives feedback via a collateral axon from a neuron in the circuit

50. © 2014 Pearson Education, Inc. Many outputs Input Input 1 Input 2 Input 3 Output Input Output Diverging circuit to multiple pathways Converging circuit Reverberating circuit

51. © 2014 Pearson Education, Inc. X. Types of Processing A. Serial processing - Neurons pass a signal to a specific destination along a single pathway from one to another B. Parallel processing - Input is delivered along many pathways; a single sensory stimulus results in multiple perceptions

52. © 2014 Pearson Education, Inc. XI. Integration Between PNS and CNS A. Neuronal circuits form networks of interneurons Example: painful stimulus ► Immediate response is spinal reflex ► Sensory information passed along to brain ► Pain is felt after reflexive withdrawal

53. © 2014 Pearson Education, Inc. Monosynaptic pathway Sensory pathway up to brain

54. © 2014 Pearson Education, Inc. Sensory pathway through brain Motor response from brain to spinal cord to effector

55. © 2014 Pearson Education, Inc. XII. Neuronal Regeneration A. Neural injuries may cause permanent dysfunction B. If axons alone are destroyed, cell bodies often survive, and the axons may regenerate 1. In PNS macrophages destroy axon distal to the injury a. Axon filaments grow peripherally from injured site b. Partial recovery is sometimes possible 2. In CNS macrophages destroy axon distal to the injury a. neuroglia cannot guide axon back to proper re-growth b. no effective recovery of neurons in natural patient c. stem cell therapy may change this in the future

56. © 2014 Pearson Education, Inc. Regeneration of an axon in a peripheral nerve. EndoneuriumSchwann cells Droplets of myelin Fragmented axon Site of nerve damage 1234 The axon becomes fragmented at the injury site. Macrophages clean out the dead axon distal to the injury. Axon sprouts, or filaments, grow through a regeneration tube formed by Schwann cells. The axon regenerates, and a new myelin sheath forms. Schwann cellMacrophage Aligning Schwann cells form regeneration tube Fine axon sprouts or filaments Schwann cell Single enlarging axon filament Site of new myelin sheath formation