Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Chapter 9 The Nervous System

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 2 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)

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4 Cells of the Nervous System Neurons –Consist of three parts Cell body of neuron—main part Dendrites—branching projections that conduct impulses to cell body of neuron Axon—elongated projection that conducts impulses away from cell body of neuron

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6 Cells of the Nervous System Neurons –Neurons classified according to function or direction of impulse Sensory neurons: conduct impulses to the spinal cord and brain; also called afferent neurons Motor neurons: conduct impulses away from brain and spinal cord to muscles and glands; also called efferent neurons Interneurons: conduct impulses from sensory neurons to motor neurons; also called central or connecting neurons

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 7 Cells of the Nervous System Glia (neuroglia) –Support cells, bringing the cells of nervous tissue together structurally and functionally –Three main types of connective tissue cells of the CNS Astrocytes—star-shaped cells that anchor small blood vessels to neurons Microglia—small cells that move in inflamed brain tissue carrying on phagocytosis Oligodendrocytes—form myelin sheaths on axons in the CNS (Schwann cells form myelin sheaths in PNS only)

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9 Nerves Nerve—bundle of peripheral axons –Tract—bundle of central axons –White matter—brain or cord tissue composed primarily of myelinated axons (tracts) –Gray matter—brain or cord tissue composed primarily of cell bodies and unmyelinated fibers

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Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 11 Nerves 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

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 12 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 (i.e., contraction by a muscle or secretion by a gland) The simplest reflex arcs are two-neuron arcs— consisting 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

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Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 14 Nerve Impulses Definition—self-propagating wave of electrical disturbance that travels along the surface of a neuron membrane; sometimes called action potentials

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Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 16 The Synapse Definition—the place where impulses are transmitted from one neuron to another (the postsynaptic neuron)

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Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 19 Central Nervous System Divisions of the brain –Brainstem Consists of three parts, named in ascending order: medulla oblongata, pons, and midbrain Structure—white matter with bits of gray matter scattered through it

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Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 21 Central Nervous System Divisions of the brain –Brainstem Functions –Sensory tracts in the brainstem conduct impulses to the higher parts of the brain –Motor tracts conduct from the higher parts of the brain to the spinal cord –Many important reflex centers lie in the brainstem

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 22 Central Nervous System –Diencephalon Hypothalamus Controls the ANS; therefore, helps control the functioning of most internal organs –Controls hormone secretion by anterior and posterior pituitary glands; therefore, it indirectly helps control hormone secretion by most other endocrine glands –Contains centers for controlling appetite, wakefulness, pleasure, etc Thalamus- sensations, emotions, awareness sensation

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 23 Central Nervous System –Cerebellum Second largest part of the human brain Equilibrium, balance and posture

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 24 Central Nervous System –Cerebrum Largest part of the human brain Functions of the cerebrum—mental processes of all types, including sensations, consciousness, memory, and voluntary control of movements

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 25 Central Nervous System Spinal cord- Occipital bone to the bottom of the first lumbar vertebra –Spinal cord tracts provide two-way conduction paths— ascending -to brain and descending-from brain –Spinal cord functions as the primary center for all spinal cord reflexes; sensory tracts conduct impulses to the brain, and motor tracts conduct impulses from the brain –Spinal nerves named for what part of the vetebrae

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Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 27 Central Nervous System Coverings and fluid spaces of the brain and spinal cord –Coverings Cranial bones and vertebrae Cerebral and spinal meninges—the dura mater, arachnoid mater, and the pia mater –Fluid spaces Subarachnoid spaces of meninges Central canal inside cord Ventricles in brain

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Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 29 Peripheral Nervous System Cranial nerves –12 pairs—attached to undersurface of the brain –Connect brain with the neck and structures in the thorax and abdomen

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Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 31 Autonomic Nervous System Autonomic nervous system—motor neurons that conduct impulses from the central nervous system to cardiac muscle smooth muscle glandular epithelial tissue regulates body’s automatic or involuntary functions

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Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 33 Autonomic Nervous System Composed of two divisions: sympathetic system (SNS) parasympathetic system (PSNS) Visceral effectors-cardiac, smooth, glandular Somatic effectors-skeletal

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 34 Autonomic Nervous System –Functions of the sympathetic nervous system Serves as the emergency or stress system, controlling visceral effectors during strenuous exercise and when strong emotions (anger, fear, hate, or anxiety) are elicited Group of changes induced by sympathetic control is called the fight-or-flight response

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 35 Autonomic Nervous System Parasympathetic nervous system- Normal everyday conditions- Slow heartbeat, increase peristalsis, increase secretion of digestive juices and insulin

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 36 Autonomic Nervous System Neurotransmitters-chemicals by which neurons communicate-examples: Endorphins, serotonin, dopamine, nitric oxide --Cholinergic fibers—acetylcholine –Adrenergic fibers—epinephrine/adrenalin

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 37 Autonomic Nervous System Autonomic nervous system as a whole –Regulates the body’s automatic functions in ways that maintain or quickly restore homeostasis –Many visceral effectors are doubly innervated (i.e., they receive fibers from parasympathetic and sympathetic divisions and are influenced in opposite ways by the two divisions)