Copyright © 2005, Elsevier, Inc. All rights reserved. Slide 0 0 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

1 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. List the organs and divisions of the nervous system and describe the generalized functions of the system as a whole Identify the major types of cells in the nervous system and discuss the function of each Identify the anatomical and functional components of a three-neuron reflex arc. Compare and contrast the propagation of a nerve impulse along a nerve fiber and across a synaptic cleft Learning Objectives

2 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Identify the major anatomical components of the brain and spinal cord and briefly comment on the function of each Compare and contrast spinal and cranial nerves. Discuss the anatomical and functional characteristics of the two divisions of the autonomic nervous system Learning Objectives (cont’d.)

5 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Organs and Divisions of the Nervous System Central nervous system (CNS): Brain and spinal cord Peripheral nervous system (PNS): All nerves  Autonomic nervous system (ANS)

7 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Cells of the Nervous System Neurons  Consist of three main parts  Dendrites  Cell body  Axon  Classified according to function  Sensory  Motor  Interneurons

9 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Cells of the Nervous System (cont’d.)  Schwann cells form myelin sheaths of axons in the peripheral nervous system (PNS).  What is the purpose of a myelin sheath?

10 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Glia (neuroglia)  Support cells, bringing the cells of nervous tissue together structurally and functionally  Three main types of glial cells of the CNS  What are they? Cells of the Nervous System (cont'd.)

13 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Nerves Nerve: Bundle of peripheral axons  Tract of central axons  White matter: Tissue composed primarily of myelinated axons (nerves or tracts)  Gray matter: Tissue composed primarily of cell bodies and unmyelinated fibers

14 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Nerves (cont'd.) Nerve coverings: Fibrous connective tissue  Endoneurium: Surrounds individual fibers within a nerve  Perineurium: Surrounds a group (fascicle) of nerve fibers  Epineurium: Surrounds the entire nerve

16 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Reflex Arcs Nerve impulses are conducted from receptors to effectors over neuron pathways or reflex arcs Conduction by a reflex arc results in a reflex, either contraction by a muscle or secretion by a gland

17 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Reflex Arcs (cont'd.) Simplest reflex arcs are two-neuron arcs; they consist of sensory neurons synapsing in the spinal cord with motor neurons Three-neuron arcs consist of sensory neurons synapsing in the spinal cord with interneurons that synapse with motor neurons

19 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Nerve Impulses Self-propagating waves of electrical disturbances that travel along the surface of a neuron membrane

20 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Nerve Impulses (cont'd.) Mechanism  Stimulus triggers the opening of Na + channels in the plasma membrane of the neuron  Inward movement of positive sodium ions leaves a slight excess of negative ions outside at a stimulated point  Marks beginning of a nerve impulse

22 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. The Synapse Chemical compounds are released from axon terminals (of a presynaptic neuron) into a synaptic cleft Neurotransmitters bind to specific receptor molecules in the membrane of a postsynaptic neuron  Open ion channels, stimulate impulse conduction by the membrane

24 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. The Synapse (cont'd.) Types of neurotransmitters  Acetylcholine  Catecholamines (norepinephrine, dopamine, and serotonin)  Other compounds

27 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Central Nervous System Divisions of the brain (What do they each do?)  Brainstem  Medulla oblongata  Pons  Midbrain

29 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Central Nervous System (cont'd.)  Cerebellum  Second largest part of the human brain  Helps control muscle contractions to produce coordinated movements so that we can maintain balance, move smoothly, and sustain posture

30 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Central Nervous System (cont'd.)  Cerebrum  Largest part of the human brain  Outer layer of gray matter is the cerebral cortex, composed mainly of dendrites and cell bodies of neurons  Interior of the cerebrum composed mainly of white matter (nerve fibers arranged in bundles called tracts)

34 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Central Nervous System (cont'd.) Spinal cord  Outer part composed of white matter made up of many bundles of axons called tracts  Interior is composed of gray matter made up mainly of neuron dendrites and cell bodies  Functions as the center for all spinal cord reflexes  Sensory tracts conduct impulses to the brain  Motor tracts conduct impulses from the brain

36 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Coverings and fluid spaces of the brain and spinal cord  Coverings  Cranial bones and vertebrae  Cerebral and spinal meninges—dura mater, arachnoid mater, and pia mater  Fluid spaces—subarachnoid spaces of meninges, central canal inside cord, and ventricles in the brain Central Nervous System (cont'd.)

38 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Peripheral Nervous System Cranial nerves  Structure—12 pairs are attached to the undersurface of the brain  Function—conducts impulses between the brain and structures in the head and neck and in the thoracic and abdominal cavities

39 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Peripheral Nervous System (cont’d.) Spinal nerves  Structure—contains dendrites of sensory neurons and axons of motor neurons  Functions—conducts impulses necessary for sensations and voluntary movements

42 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Autonomic Nervous System Motor neurons that conduct impulses from the central nervous system to cardiac muscle, smooth muscle, and glandular epithelial tissue Regulates the body’s autonomic or involuntary functions

44 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Autonomic neurons  Preganglionic autonomic neurons conduct from spinal cord or brainstem to autonomic ganglia  Postganglionic neurons conduct from autonomic ganglia to cardiac muscle, smooth muscle, and glandular epithelial tissue Autonomic Nervous System (cont'd.)

45 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Autonomic or visceral effectors  Tissues to which autonomic neurons conduct impulses Autonomic conduction paths  Consist of two-neuron relays Autonomic Nervous System (cont'd.)

46 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Sympathetic nervous system  Structure  Sympathetic preganglionic neurons have dendrites and cell bodies in gray matter of thoracic and upper lumbar segments of the spinal cord  Sympathetic postganglionic neurons have dendrites and cell bodies in sympathetic ganglia Autonomic Nervous System (cont'd.)

47 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Sympathetic nervous system:  Functions  Serves as the emergency or stress system  Group of changes induced by sympathetic control is called the fight-or-flight response Autonomic Nervous System (cont'd.)

48 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Parasympathetic nervous system:  Structure  Parasympathetic preganglionic neurons have dendrites and cell bodies in the gray matter of brainstem and sacral segments of the spinal cord  Parasympathetic preganglionic neurons terminate in parasympathetic ganglia located in the head and the thoracic and abdominal cavities close to visceral effectors Autonomic Nervous System (cont'd.)

49 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Parasympathetic nervous system  Function  Dominates control of many visceral effectors under normal, everyday conditions What are examples of parasympathetic responses? Autonomic Nervous System (cont'd.)

51 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Autonomic neurotransmitters:  Cholinergic fibers  Preganglionic axons of parasympathetic and sympathetic systems and parasympathetic postganglionic axons  Release acetylcholine Autonomic Nervous System (cont'd.)

52 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Autonomic Nervous System (cont'd.) Autonomic neurotransmitters  Adrenergic fibers  Axons of sympathetic postganglionic neurons  Release norepinephrine (noradrenaline)

53 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Autonomic Nervous System (cont'd.) Autonomic nervous system as a whole  Regulates the body’s autonomic functions in ways that maintain or quickly restore homeostasis

55 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Question Some individuals who are depressed have an abnormally small amount of the neurotransmitter serotonin at certain synapses in the brain. One category of antidepressant drugs is called selective serotonin reuptake inhibitors. Can you deduce what action this drug has at a synapse to increase the amount of serotonin present in the synaptic cleft?

56 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Answer The name of the drug category tells you that the drug decreases the amount of serotonin that is taken back into the presynaptic knob after a nerve impulse has caused its release into the synaptic cleft. Because the amount of serotonin being taken from the synaptic cleft decreases, the amount remaining in the synaptic cleft increases. This restores the chemical imbalance associated with depression and hopefully relieves the symptoms. (Hint: The name of the drug is a clue, as is the discussion in the section about the synapse on pp. 193-195 in the text.)

57 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Question Another type of antidepressant inhibits the enzymes that naturally break down serotonin at the synaptic cleft. Can you explain how this might reduce the symptoms of depression?

58 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Answer As explained in the text, some neurotransmitter molecules are taken back into the presynaptic knob, whereas others are broken down by specific enzymes. This particular category of antidepressants inhibits the breakdown of serotonin after it is released. Such inhibition of serotonin destruction increases the amount of serotonin present in the synaptic cleft, restoring the original balance and removing the chemical basis for depression.

60 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Answer The medulla oblongata is an enlarged upward extension of the spinal cord that lies inside the cranial cavity above the hole in the occipital bone. It is the lowest part of the brainstem. It has a two-way conduction pathway between the spinal cord and higher brain centers, such as the cardiac, respiratory, and vasomotor centers.

62 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Answer The cerebellum is the second- largest part of the brain. It plays an essential part in smooth coordinated movement, maintaining equilibrium, and sustaining normal posture.

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Copyright © 2005, Elsevier, Inc. All rights reserved. Slide 0 0 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

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