1. Copyright 2010, John Wiley & Sons, Inc. Chapter 9 Nervous Tissue https://www.youtube.com/watch?v=qPix_X-9t7E https://www.youtube.com/watch?v=OZG8M_ldA1M

2. Overview of the Nervous System Objectives: List the structures and basic functions of the nervous system Describe the 3 basic functions of the nervous system

3. Copyright 2010, John Wiley & Sons, Inc. Structures of the Nervous System Brain: Neurons enclosed within skull Spinal cord: Connects to brain - Enclosed within spinal cavity Nerves:  Cranial nerves (12 pairs) emerge from brain  Spinal nerves (31 pairs) emerge from spinal cord Ganglia: Groups of neuron cell bodies located outside of brain and spinal cord Enteric plexuses: Networks in digestive tract Sensory receptors: Monitor changes in internal or external environments

4. Copyright 2010, John Wiley & Sons, Inc. Structures of the Nervous System

5. Copyright 2010, John Wiley & Sons, Inc. Organization of the Nervous System Enteric nervous system (ENS): “Brain of the Gut”  Sensory neurons - Monitor chemical changes and stretching of GI wall  Motor neurons - Regulate contractions and endocrine secretions (involuntary)

6. Copyright 2010, John Wiley & Sons, Inc. Organization of the Nervous System

7. Copyright 2010, John Wiley & Sons, Inc. Functions of Nervous System 1. Sensory Function Afferent nerves –Carry information into brain and spinal cord –Sensory receptors and sensory nerves PNS Receptors detect changes in surroundings Neurons 10-6

8. Copyright 2010, John Wiley & Sons, Inc. 2. Integrative Function (Association) CNS (brain and/or spinal cord) Perception = Awareness of sensory input  Sensations  Memory  Thoughts  Decisions Occurs in interneurons Link neurons together  (sensory neuron  interneuron  motor neuron) Functions of Nervous System

9. Copyright 2010, John Wiley & Sons, Inc. 3. Motor Function Efferent nerves PNS Response of a body part/decisions are acted upon Impulses are carried from CNS to effectors Effectors – 2 types  Muscles (that contract)  Glands (secrete a hormone) Neurons Functions of Nervous System

10. Histology of Nervous Tissue Objectives: Contrast the histological characteristics and the functions of neurons and neuroglia Distinguish between gray matter and white matter

11. Copyright 2010, John Wiley & Sons, Inc. Histology of the Nervous System Neurons  Can respond to stimuli and convert stimuli to electrical signals (nerve impulses) that travel along neurons Neuroglia cells:  critical for homeostasis of interstitial fluid around neurons

12. Copyright 2010, John Wiley & Sons, Inc. Neuronal Structure Cell body: nucleus, cytoplasm with typical organelles Dendrites: highly branched structures that carry impulses to the cell body Axon: conducts away from cell body toward another neuron, muscle or gland Axon terminals: contain synaptic vesicles that can release neurotransmitters

13. Copyright 2010, John Wiley & Sons, Inc. Neuronal Structure

14. Copyright 2010, John Wiley & Sons, Inc. Structural Classes of Neurons Multipolar  Have several or many dendrites and one axon  Most common type in brain and spinal cord Bipolar  Have one dendrite and one axon  Example: in retina of eye and inner ear Unipolar  one process from cell body fused dendrite and axon  Only distal ends are dendrites  Sensory neurons of spinal nerves

15. Copyright 2010, John Wiley & Sons, Inc.

16. Neuroglia Cells smaller but much more numerous than neurons Can multiply and divide and fill in brain areas Gliomas: brain tumors derived from neuroglia Do not conduct nerve impulses Do support, nourish and protect neurons

17. Copyright 2010, John Wiley & Sons, Inc. Types of Neuroglial Cells PNS – Schwann Cells produces myelin Satellite Cells Support neurons and regulate exchange of materials between neurons and interstitial fluid CNS – 4 types Provide bulk of brain and spinal cord tissue Oligodendrocyte Microglia Astrocyte Ependyma 10-11

18. Copyright 2010, John Wiley & Sons, Inc. CNS – 4 types 1. Oligodendrocytes Function - produces myelin in CNS Looks like eyeball 2. Microglia Function - phagocytosis  protect CNS cells from disease Looks like spider

19. Copyright 2010, John Wiley & Sons, Inc. 3. Astrocytes Function  Nourishes neurons  Mop up excess ions, etc  Induce synapse formation  Connect neurons to blood vessels Help form blood brain barrier Star-shaped Scar tissue 4. Ependyma Function – lines spaces in CNS  Brain – ventricles  Spinal cord – central canal Epithelial-like layer Ciliated

20. Copyright 2010, John Wiley & Sons, Inc. Myelination Many layers of lipids and proteins:  Insulates neurons Increases speed of nerve conduction Appears white Nodes of Ranvier:  Gaps in the myelin  Important for rapid signal conduction Some diseases destroy myelin:  Multiple sclerosis  Tay-Sachs

21. Copyright 2010, John Wiley & Sons, Inc. Gray and White Matter White matter: primarily myelinated axons Gray matter:  Cell bodies, dendrites, unmyelinated axons, axon terminals, neuroglia Location:  Spinal cord: White matter (tracts) surround centrally located gray matter “H” or “butterfly”  Brain: Gray matter in thin cortex surrounds white matter (tracts)

22. Organization of the Nervous System Objective: Describe the organization of the nervous system

23. Copyright 2010, John Wiley & Sons, Inc. Subdivisions of the Nervous System Central Nervous System (CNS)  Brain and spinal cord Peripheral Nervous System (PNS)  All nervous system structures outside of the CNS

24. Copyright 2010, John Wiley & Sons, Inc. Organization of the Nervous System Somatic (SNS)  Sensory neurons from head, body wall, limbs, special sense organs  Motor neurons to skeletal muscle: voluntary Autonomic (ANS) nervous systems  Sensory neurons from viscera  Motor neurons to viscera (cardiac muscle, smooth muscle, glands): involuntary Sympathetic: “fight-or-flight” Parasympathetic: “rest-and-digest”

25. Copyright 2010, John Wiley & Sons, Inc. Organization of the Nervous System

26. Copyright 2010, John Wiley & Sons, Inc. Organization of the Nervous System Enteric nervous system (ENS): “brain of the gut”  Sensory neurons - monitor chemical changes and stretching of GI wall  Motor neurons - regulate contractions and endocrine secretions (involuntary)

27. Action Potentials Objective: Describe how a nerve impulse is generated and conducted

28. Copyright 2010, John Wiley & Sons, Inc. Cell membrane potential Distribution of Ions Potential Difference (PD) = the difference in electrical charge between 2 points (across cell membrane) Resting Membrane Potential (RMP) = results from the distribution of ions across the cell membrane Resting neuron’s cell membrane – polarized K+ high inside Na+ high outside Cl-high outside Negatively charge proteins or Anions high inside

29. Copyright 2010, John Wiley & Sons, Inc. Resting Membrane Potential

30. Copyright 2010, John Wiley & Sons, Inc. Local Potential Changes Occur on membranes of dendrites and cell bodies caused by various stimuli Chemicals Temperature changes Mechanical forces If membrane potential becomes more negative, hyperpolarized If membrane potential becomes more positive (less negative), depolarized 10-16

31. Copyright 2010, John Wiley & Sons, Inc. Action Potentials When RMP of a neuron is depolarized to -55mV – threshold potential is reached  rapid opening of Na+ channels results in rapid depolarization  Action potential - Start of the nerve impulse - occur on axons  K+ channels open (while Na+ channels close) and repolarization occurs = Recovery Occurs very quickly = 1/1000 sec 10-17

32. Copyright 2010, John Wiley & Sons, Inc. Potential Changes 10-15

33. Copyright 2010, John Wiley & Sons, Inc. Action Potential Recovery  Refractory period (brief): even with adequate stimulus, cell cannot be activated All-or-none principle  If a stimulus is strong enough to cause depolarization to threshold level  Then the impulse will travel the entire length of the neuron at a constant and maximum strength.

34. Copyright 2010, John Wiley & Sons, Inc. Action Potential

35. Copyright 2010, John Wiley & Sons, Inc. Conduction of Nerve Impulses Nerve impulse conduction (propagation)  Each section triggers the next locally as even more Na + channels are opened Row of dominos Types of conduction  Continuous conduction In unmyelinated fibers; slower form of conduction  Saltatory conduction In myelinated fibers; faster as impulses “leap” between nodes of Ranvier Factors that increase rate of conduction  Myelin, large diameter and warm nerve fibers

36. Copyright 2010, John Wiley & Sons, Inc. Conduction of Nerve Impulses

37. Synaptic Transmission Objective: Explain the events of synaptic transmission and the types of neurotransmitters used

38. Copyright 2010, John Wiley & Sons, Inc. Synaptic Transmission Synapse (neuron-neuron) Neuromuscular junction (neuron-muscle fiber) Neuroglandular junction (neuron-gland) Components of synapse:  Sending neuron: presynaptic neuron (releases neurotransmitter)  Space between neurons: synaptic cleft  Receiving neuron: postsynaptic neuron

39. Copyright 2010, John Wiley & Sons, Inc. 10-21 The Synapse

40. Copyright 2010, John Wiley & Sons, Inc. Ca++ channels open Synaptic vesicles release NT (exocytosis) NT depolarizes the post- synaptic neuron’s membrane Action potential  NI begins in the post-synaptic neuron 10-22 Synaptic Transmission

41. Copyright 2010, John Wiley & Sons, Inc. Synaptic Transmission One-way transmission  Presynaptic release NT  Postsynaptic have receptors for NT binding NT must be removed from the cleft  Diffusion out of cleft  Destruction by enzymes (such as ACh-ase) in cleft  Transport back (recycling) into presynaptic cell

42. Copyright 2010, John Wiley & Sons, Inc.Copyright 2009 John Wiley & Sons, Inc. 42 Signal Transmission at the Chemical Synapse

43. Copyright 2010, John Wiley & Sons, Inc. At least 30 different produced by CNS Some neurons release only one while others release many Most typical = acetylcholine All motor neurons  Stimulatory (on skeletal muscles)  Inhibitory (on cardiac muscle) Neurotransmitters

44. Copyright 2010, John Wiley & Sons, Inc. Other NT include Monoamines (modified amino acids) Widely distributed in the brain  Emotional behavior  Circadian rhythm Some motor neurons of the ANS EX: Epinephrine, norepinephrine, dopamine, serotonin, histamine Unmodified amino acids Glutamate, aspartate, GABA, glycine

45. Copyright 2010, John Wiley & Sons, Inc. Neuropeptides Synthesized by CNS neurons Act as NT or neuromodulators  Alter a neuron’s response to a NT  Block the release of a NT Enkephalins Synthesis is increased during painful stress Bind to same receptors in the brain as the narcotic morphine Relieve pain Endorphines Same as above, with more potent and longer lasting effect

46. Copyright 2010, John Wiley & Sons, Inc. Synaptic Potentials EPSP Excitatory postsynaptic potential Graded Depolarizes membrane of postsynaptic neuron Action potential becomes more likely IPSP Inhibitory postsynaptic potential Graded Hyperpolarizes membrane of postsynaptic neuron Action potential becomes less likely 10-23

47. Copyright 2010, John Wiley & Sons, Inc. EPSPs and IPSPs are added together in a process called Summation 10-24 Summation of EPSPs and IPSPs

48. Copyright 2010, John Wiley & Sons, Inc. Impulse Processing Neuronal Pools – neurons that synapse and work together Interneurons work together to perform a common function Working together results in facilitation General excitation that makes stimulation easier to achieve 10-26

49. Copyright 2010, John Wiley & Sons, Inc. 10-27 Convergence Neuron receives input from several neurons Allows nervous system to collect, process, and respond to information Typical motor pathway Many inputs from brain, but usually only one motor response

50. Copyright 2010, John Wiley & Sons, Inc. Divergence 10-28 One neuron sends impulses to several neurons Signal amplifies Typical sensory pathways Reason that a stimulus (odor) can cause many responses

51. Copyright 2010, John Wiley & Sons, Inc. Neuron Regeneration PNS neurons  Axons and dendrite If cell body is intact and Schwann cells functional Form a regeneration tube  grow axons or dendrites if scar tissue does not fill the tube CNS neurons  Very limited even if cell body is intact  Inhibited by neuroglia and by lack of fetal growth- stimulators

52. Copyright 2010, John Wiley & Sons, Inc. Regeneration of A Nerve Axon 10-13

53. Copyright 2010, John Wiley & Sons, Inc. Disorders Associated with NT Imbalances Alzheimers = deficient Ach Clinical Depression = deficient norepinephrine/serotonin Epilepsy = Excess GABA leads to excess norepinephrine & dopamine Hypersomnia = excess serotonin Insomnia = deficient serotonin Mania = excess norepinephrine Schizophrenia = deficient GABA leads to excess dopamine SIDS = excess dopamine

54. Copyright 2010, John Wiley & Sons, Inc. Clinical Application Multiple Sclerosis Symptoms Blurred vision Numb legs or arms Can lead to paralysis Causes Myelin destroyed in various parts of CNS Hard scars (scleroses) form Nerve impulses blocked Muscles do not receive innervation May be related to a virus Treatments No cure Bone marrow transplant Interferon (anti-viral drug) Hormones 10-29

55. Copyright 2010, John Wiley & Sons, Inc. End of Chapter 9 Copyright 2010 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publishers assumes no responsibility for errors, omissions, or damages caused by the use of theses programs or from the use of the information herein.