Nervous System Chapter 9 Copyright 2016 by Elsevier

Learning Objectives Lesson 9. 1: Nervous System 1. 2. 3. 4. 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 functions of each. Identify the anatomical components of a reflex arc and explain its function. Explain the mechanisms of transmission of a nerve impulse along a nerve fiber and across a synapse. Copyright © 2016 by Elsevier Inc. All rights reserved. 2

Learning Objectives Lesson 9. 1: Nervous System (Cont. ) 5. 6. 7. Identify the major anatomical components of the brain and spinal cord and briefly comment on the functions of each. Compare and contrast cranial and spinal nerves. Discuss the anatomical and functional characteristics of the two divisions of the autonomic nervous system. Copyright © 2016 by Elsevier Inc. All rights reserved. 3

Organization of the Nervous System Central nervous system (CNS) Ø Ø Brain Spinal cord Peripheral nervous system (PNS) Ø Ø All nerves Autonomic nervous system (ANS) Copyright © 2016 by Elsevier Inc. All rights reserved. 4

Divisions of the Nervous System Copyright © 2016 by Elsevier Inc. All rights reserved.

Cells of the Nervous System Neurons Ø Neuron structure: Each neuron consists of three main parts (Figure 9 -2): • • • Ø Cell body of neuron Dendrites: Branching projections that conduct impulses to cell body of neuron Axon: Elongated projection that conducts impulses away from cell body of neuron Types of neurons: Classified according to function • • • Sensory (afferent) neurons: Conduct impulses to the spinal cord and brain Motor (efferent) neurons: Conduct impulses away from brain and spinal cord to muscles and glands Interneurons: Conduct impulses from sensory neurons to motor neurons or among a network of interneurons; also known as central or connecting neurons Copyright © 2016 by Elsevier Inc. All rights reserved. 6

Neuron Courtesy Dennis Streete. Copyright © 2016 by Elsevier Inc. All rights reserved. 7

Nerves and Tracts Nerve: Bundle of peripheral axons Ø Ø Ø Tract: Bundle 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 Nerve coverings: Fibrous connective tissue Ø Ø Ø Endoneurium: Surrounds individual fibers within a nerve Perineurium: Surrounds a group (fascicle) of nerve fibers Epineurium: Surrounds the entire nerve Copyright © 2016 by Elsevier Inc. All rights reserved. 8

The Nerve Courtesy Dr. Richard Kessel, Professor of Biological Sciences, University of Iowa, Iowa

Knee-Jerk Reflex Copyright © 2016 by Elsevier Inc. All rights reserved. 10

Central Nervous System Divisions of the brain: Brainstem Ø Consists of three parts of brain, named in ascending order • • • Ø Structure • Ø Medulla oblongata Pons Midbrain White matter with bits of gray matter scattered through it Functions • All three parts of brainstem conduct impulses to the higher parts of the brain 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 Copyright © 2016 by Elsevier Inc. All rights reserved. 11

Major Regions of the Central Nervous System From Vidic B, Suarez FR: Photographic atlas

Functions of Major Division of the Brain Copyright © 2016 by Elsevier Inc. All

Central Nervous System (Cont. ) Divisions of the brain: Cerebellum Ø Structure • • • Ø Second largest part of the human brain Gray matter outer layer is thin but highly folded, forming a large surface area for processing information Arbor vitae: Internal, treelike network of white matter tracts Functions • • Helps control muscle contractions to produce coordinated movements for maintaining balance, moving smoothly, and sustaining normal postures Variety of additional coordinating effects, assisting the cerebrum and other regions of the brain Copyright © 2016 by Elsevier Inc. All rights reserved. 14

Central Nervous System (Cont. ) Divisions of the brain: Diencephalon (hypothalamus, and pineal gland) Ø Hypothalamus • • Consists mainly of the posterior pituitary gland, pituitary stalk, and gray matter Acts as the major center for controlling the ANS; therefore, it 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 body temperature, appetite, wakefulness, and pleasure Copyright © 2016 by Elsevier Inc. All rights reserved. 15

Central Nervous System (Cont. ) Divisions of the brain: Diencephalon (hypothalamus, and pineal gland) Ø Thalamus • • • Ø Dumbbell-shaped mass of gray matter extending toward each cerebral hemisphere Relays sensory impulses to cerebral cortex sensory areas In some way produces the emotions of pleasantness or unpleasantness associated with sensations Pineal gland (pineal body) • • Small body resembling a pine nut behind the thalamus Adjusts output of “time-keeping hormone” melatonin in response to changing levels of external light (sunlight and moonlight) Copyright © 2016 by Elsevier Inc. All rights reserved. 16

Central Nervous System (Cont. ) Divisions of the brain: Cerebrum (Figure 9 -11) Ø Ø Ø Largest part of the human brain Outer layers of gray matter are the cerebral cortex; made up of lobes; composed mainly of dendrites and cell bodies of neurons Interior of the cerebrum composed mainly of white matter • • Ø Tracts: Nerve fibers arranged in bundles Basal nuclei: Islands of gray matter regulate automatic movements and posture Functions of the cerebrum • Mental processes of all types, including sensations, consciousness, memory, and voluntary control of movements Copyright © 2016 by Elsevier Inc. All rights reserved. 17

The Cerebrum From Vidic B, Suarez FR: Photographic atlas of the human body, St

The Cerebrum (Cont. ) From Vidic B, Suarez FR: Photographic atlas of the human

Central Nervous System (Cont. ) Spinal cord (Figure 9 -12) Ø Ø Columns of white matter, composed of bundles of myelinated nerve fibers, form the outer portion of the H-shaped core of the spinal cord; bundles of axons called tracts Interior composed of gray matter made up mainly of neuron dendrites and cell bodies Spinal cord tracts provide two-way conduction paths: Ascending and descending 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 Copyright © 2016 by Elsevier Inc. All rights reserved. 20

Spinal Cord and Spinal Nerves From Vidic B, Suarez FR: Photographic atlas of the

Central Nervous System (Cont. ) Coverings (Figure 9 -14) Ø Ø Cranial bones and vertebrae Cerebral and spinal meninges • • • Dura mater Pia mater Arachnoid mater Fluid spaces Ø Ø Ø Subarachnoid spaces of meninges Central canal inside cord Ventricles in brain Copyright © 2016 by Elsevier Inc. All rights reserved. 22

Spinal Cord and Its Coverings Copyright © 2016 by Elsevier Inc. All rights reserved.

Peripheral Nervous System Cranial nerves (Figure 9 -17 and Table 9 -2) Ø Ø Twelve pairs: Attached to undersurface of the brain Connect brain with the neck and structures in the thorax and abdomen Spinal nerves Ø Ø Ø Thirty-one pairs: Contain dendrites of sensory neurons and axons of motor neurons Conduct impulses necessary for sensations and voluntary movements Dermatome: Skin surface area supplied by a single cranial or spinal nerve Copyright © 2016 by Elsevier Inc. All rights reserved. 24

Cranial Nerves Copyright © 2016 by Elsevier Inc. All rights reserved. 25

Cranial Nerves (Cont. ) Copyright © 2016 by Elsevier Inc. All rights reserved. 26

Autonomic Nervous System ANS consists of motor neurons that conduct impulses from the CNS to cardiac muscle, smooth muscle, and glandular epithelial tissue; regulates the body’s automatic or involuntary functions (Figure 9 -19) Functional anatomy: Ø Ø Preganglionic autonomic neurons conduct impulses from spinal cord or brainstem to an autonomic ganglion Postganglionic neurons conduct from autonomic ganglia to cardiac muscle, smooth muscle, and glandular epithelial tissue Copyright © 2016 by Elsevier Inc. All rights reserved. 27

Autonomic Nervous System (Cont. ) Functional anatomy: Autonomic or visceral effectors are the tissues to which autonomic neurons conduct impulses (i. e. , cardiac and smooth muscle and glandular epithelial tissue) Composed of two divisions Ø Ø Sympathetic system Parasympathetic system Copyright © 2016 by Elsevier Inc. All rights reserved. 28

Innervation of Major Target Organs by the Autonomic Nervous System Copyright © 2016 by

Autonomic Nervous System (Cont. ) Autonomic conduction paths Ø Ø Consist of two-neuron relays (that is, preganglionic neurons from the CNS to autonomic ganglia, synapses, postganglionic neurons from ganglia to visceral effectors) In contrast, somatic motor neurons conduct all the way from the CNS to somatic effectors with no intervening synapses Copyright © 2016 by Elsevier Inc. All rights reserved. 30

Autonomic Nervous System (Cont. ) Sympathetic division: Structure Ø Ø Ø Dendrites and cell bodies of sympathetic preganglionic neurons are located in the gray matter of the thoracic and upper lumbar segments of the spinal cord Axons leave the spinal cord in the anterior roots of spinal nerves, extend to sympathetic or collateral ganglia, and synapse with several postganglionic neurons whose axons extend to spinal or autonomic nerves to terminate in visceral effectors A chain of sympathetic ganglia is in front of and at each side of the spinal column Copyright © 2016 by Elsevier Inc. All rights reserved. 31

Autonomic Nervous System (Cont. ) Sympathetic division: Functions Ø Ø Serves as the emergency or stress system, controlling visceral effectors during strenuous exercise and when strong emotions (anger, fear, hate, or anxiety) are triggered Group of changes induced by sympathetic control is called the fight-or-flight response Copyright © 2016 by Elsevier Inc. All rights reserved. 32

Autonomic Nervous System (Cont. ) Parasympathetic division: Structure Ø Parasympathetic preganglionic neurons • • • Have dendrites and cell bodies in the gray matter of the brainstem and the sacral segments of the spinal cord Terminate in parasympathetic ganglia located in the head and the thoracic and abdominal cavities close to visceral effectors Each parasympathetic preganglionic neuron synapses with postganglionic neurons to only one effector Parasympathetic Ø Ø division: Functions Dominates control of many visceral effectors under normal, everyday conditions Counterbalances sympathetic function Copyright © 2016 by Elsevier Inc. All rights reserved. 33

Autonomic Nervous System (Cont. ) Autonomic neurotransmitters Ø Cholinergic fibers • Ø Preganglionic axons of parasympathetic and sympathetic systems and parasympathetic postganglionic axons release acetylcholine Adrenergic fibers • Axons of sympathetic postganglionic neurons release norepinephrine (noradrenaline) Copyright © 2016 by Elsevier Inc. All rights reserved. 34

Autonomic Nervous System (Cont. ) Autonomic nervous system as a whole Ø Ø Regulates the body’s automatic functions in ways that maintain or quickly restore homeostasis Many visceral effectors are doubly innervated (that is, they receive fibers from parasympathetic and sympathetic divisions and are influenced in opposite ways by the two divisions) Copyright © 2016 by Elsevier Inc. All rights reserved. 35