THE NERVOUS SYSTEM PART C Copyright 2010 Pearson

THE NERVOUS SYSTEM: PART C Copyright © 2010 Pearson Education, Inc.

Central nervous system (CNS) Peripheral nervous system (PNS) Sensory (afferent) division Copyright © 2010 Pearson Education, Inc. Motor (efferent) division Somatic nervous system Autonomic nervous system (ANS) Sympathetic division Parasympathetic division

Spinal Cord • Location • Begins at the foramen magnum • Ends at L 1 vertebra • Functions • Provides two-way communication to and from the brain • Contains spinal reflex centers Copyright © 2010 Pearson Education, Inc.

Spinal Cord • Spinal nerves • 31 pairs • Cauda equina • The collection of nerve roots at the inferior end of the vertebral canal Copyright © 2010 Pearson Education, Inc.

Spinal Cord Protection • Bone • Meninges • CSF Copyright © 2010 Pearson Education, Inc.

Cervical spinal nerves Dura and arachnoid mater Cauda equina Thoracic spinal nerves Lumbar spinal nerves Sacral spinal nerves Copyright © 2010 Pearson Education, Inc. Figure 7. 18

Gray Matter • Dorsal horns—interneurons that receive sensory input • Ventral horns—somatic motor neurons whose axons exit the cord via ventral roots • Dorsal root (spinal) ganglia—contain cell bodies of sensory neurons Copyright © 2010 Pearson Education, Inc.

Dorsal root (sensory) Dorsal root ganglion Dorsal horn (interneurons) Somatic sensory neuron Visceral motor neuron Somatic motor neuron Spinal nerve Ventral root (motor) Ventral horn (motor neurons) Interneurons receiving input from somatic sensory neurons Interneurons receiving input from visceral sensory neurons Visceral motor (autonomic) neurons Somatic motor neurons Copyright © 2010 Pearson Education, Inc. Figure 12. 32

Dorsal root ganglion White matter Dorsal horn Gray Ventral horn matter Lateral horn Spinal nerve Central canal Dorsal root Ventral root Pia mater Arachnoid mater Spinal dura mater (b) The spinal cord and its meningeal coverings Copyright © 2010 Pearson Education, Inc. Figure 7. 19

White Matter • Mainly ascending (sensory) and descending (motor) tracts • Tracts are located in three white columns on each side—posterior, lateral, and anterior columns Copyright © 2010 Pearson Education, Inc.

Spinal Cord Trauma • Flaccid paralysis—severe damage to the ventral root or ventral horn cells • Impulses do not reach muscles; there is no voluntary or involuntary control of muscles • Muscles atrophy Copyright © 2010 Pearson Education, Inc.

Structure of a Nerve • Cordlike organ of the PNS • Bundle of myelinated and unmyelinated peripheral axons enclosed by CT Copyright © 2010 Pearson Education, Inc.

Structure of a Nerve • Connective tissue coverings include: • Endoneurium—loose CT; encloses axons and their myelin sheaths • Perineurium—coarse CT ; bundles fibers into fascicles • Epineurium—tough fibrous sheath around a nerve Copyright © 2010 Pearson Education, Inc.

Endoneurium Axon Myelin sheath Perineurium Epineurium Fascicle Blood vessels Copyright © 2010 Pearson Education, Inc. Figure 7. 20

Classifying Nerves • Mixed nerves carry both sensory and motor fibers • Afferent (sensory) nerves carry impulses toward CNS • Efferent (motor) nerves carry impulses away from CNS 20 Copyright © 2010 Pearson Education, Inc.

Spinal Nerves • A spinal nerve is formed where ventral and dorsal roots fuse • After spinal nerve is formed it divides into dorsal and ventral rami • Ventral Rami form intercostal nerves (T 1 -T 12) and networks of nerves called plexuses • Plexuses serve limbs: • Brachial plexus • Lumbar plexus • Sacral plexus 23 Copyright © 2010 Pearson Education, Inc.

Cranial Nerves • 12 pairs • Extend from base of brain • Primarily innervate head and neck (except Vagus N. ) 21 Copyright © 2010 Pearson Education, Inc.

22 Copyright © 2010 Pearson Education, Inc.

Cranial Nerves • Sensory only • CN I (Olfactory) -smell • CN II (Optic) -vision • CN VIII (Vestibulocochlear) -Hearing and balance • Remaining cranial nerves are motor or mixed 11 Copyright © 2010 Pearson Education, Inc.

Somatic & Autonomic Nervous System Compared Somatic Nervous System The axon of ONE motor neuron extends all the way to skeletal muscle Copyright © 2010 Pearson Education, Inc. Autonomic Nervous System A chain of TWO motor neurons

Somatic & Autonomic Nervous System Compared • Somatic nervous system • All somatic motor neurons release acetylcholine (ACh) • ANS • Preganglionic fibers release acetylcholine (Ach) • Postganglionic fibers release norepinephrine or ACh at effectors Copyright © 2010 Pearson Education, Inc.

Cell bodies in central nervous system Peripheral nervous system SOMATIC NERVOUS SYSTEM Single neuron from CNS to effector organs Neurotransmitter at effector Effector organs Effect ACh Skeletal muscle NE SYMPATHETIC ACh Ganglion ACh Epinephrine and norepinephrine Adrenal medulla PARASYMPATHETIC AUTONOMIC NERVOUS SYSTEM Two-neuron chain from CNS to effector organs Acetylcholine (ACh) ACh Ganglion Blood vessel ACh Smooth muscle (e. g. , in gut), glands, cardiac muscle Norepinephrine (NE) Copyright © 2010 Pearson Education, Inc. Figure 7. 24

Divisions of the ANS 1. Sympathetic division 2. Parasympathetic division • Dual innervation • Most visceral organs are served by both divisions, but they cause opposite effects Copyright © 2010 Pearson Education, Inc.

Role of the Sympathetic Division • Mobilizes the body during activity; “fight-orflight” system • Promotes adjustments during exercise, or when threatened • Blood flow directed to skeletal muscles & heart • Bronchioles dilate • Liver releases glucose Copyright © 2010 Pearson Education, Inc.

Role of the Parasympathetic Division • Promotes maintenance activities, conserves body energy • Its activity is illustrated in a person who relaxes, reading, after a meal • Blood pressure, heart rate, and respiratory rates are low • GI tract activity is high Copyright © 2010 Pearson Education, Inc.

Parasympathetic Sympathetic Eye Brain stem Salivary glands Heart Cervical Sympathetic ganglia Liver and gallbladder Salivary glands Lungs T 1 Pancreas Skin* Cranial Lungs Stomach Eye Heart Stomach Thoracic Pancreas Liver and gallbladder L 1 Adrenal gland Lumbar Bladder Genitals Copyright © 2010 Pearson Education, Inc. Sacral Figure 7. 25

Sympathetic Division • Preganglionic fibers pass through white rami communicantes and enter sympathetic trunk Copyright © 2010 Pearson Education, Inc.

Spinal cord Dorsal root Ventral root Sympathetic trunk ganglion Sympathetic trunk Ventral ramus of spinal nerve Gray ramus communicans White ramus communicans (a) Location of the sympathetic trunk Copyright © 2010 Pearson Education, Inc.

Sympathetic Trunks and Pathways • Upon entering a sympathetic trunk ganglion a preganglionic fiber may do one of the following: 1. Synapse with a ganglionic neuron at the same level 2. Ascend or descend the sympathetic trunk to synapse at another level 3. Pass through trunk ganglion and emerge without synapsing Copyright © 2010 Pearson Education, Inc.

Lateral horn (visceral motor zone) Skin (arrector pili muscles and sweat glands) Dorsal root ganglion Dorsal ramus of spinal nerve Ventral ramus of spinal nerve Gray ramus communicans White ramus communicans To effector Ventral root Sympathetic trunk ganglion Sympathetic trunk 1 Synapse at the same level Blood vessels (b) Three pathways of sympathetic innervation Copyright © 2010 Pearson Education, Inc. Figure 7. 26

Skin (arrector pili muscles and sweat glands) To effector Blood vessels 2 Synapse at a higher or lower level (b) Three pathways of sympathetic innervation Copyright © 2010 Pearson Education, Inc. Figure 7. 26

Splanchnic nerve Collateral ganglion Target organ in abdomen 3 Synapse in a distant collateral ganglion anterior to the vertebral column (b) Three pathways of sympathetic innervation Copyright © 2010 Pearson Education, Inc. Figure 7. 26

Dorsal root ganglion White matter Dorsal horn Gray Ventral horn matter Lateral horn Spinal nerve Central canal Dorsal root (fans out into dorsal rootlets) Ventral root (derived from several ventral rootlets) Pia mater Arachnoid mater Spinal dura mater (b) The spinal cord and its meningeal coverings Copyright © 2010 Pearson Education, Inc. Figure 7. 19