13 The Spinal Cord Spinal Nerves and Spinal

13 The Spinal Cord, Spinal Nerves, and Spinal Reflexes Power. Point® Lecture Presentations prepared by Jason La. Pres Lone Star College—North Harris © 2012 Pearson Education, Inc.

An Introduction to the Spinal Cord, Spinal Nerves, and Spinal Reflexes • Learning Outcomes • 13 -1 Describe the basic structural and organizational characteristics of the nervous system. • 13 -2 Discuss the structure and functions of the spinal cord, and describe three meningeal layers that surround the central nervous system. • 13 -3 Explain the roles of white matter and gray matter in processing and relaying sensory information and motor commands. • 13 -4 Describe the major components of a spinal nerve, and relate the distribution pattern of spinal nerves to the regions they innervate. © 2012 Pearson Education, Inc.

An Introduction to the Spinal Cord, Spinal Nerves, and Spinal Reflexes • Learning Outcomes • 13 -5 Discuss the significance of neuronal pools, and describe the major patterns of interaction among neurons within and among these pools. • 13 -6 Describe the steps in a neural reflex, and classify the types of reflexes. • 13 -7 Distinguish among the types of motor responses produced by various reflexes, and explain how reflexes interact to produce complex behaviors. • 13 -8 Explain how higher centers control and modify reflex responses. © 2012 Pearson Education, Inc.

An Introduction to the Spinal Cord, Spinal Nerves, and Spinal Reflexes • Spinal Reflexes • Rapid, automatic nerve responses triggered by specific stimuli • Controlled by spinal cord alone, not the brain © 2012 Pearson Education, Inc.

Figure 13 -1 An Overview of Chapters 13 and 14 CHAPTER 14: The Brain Sensory receptors Sensory input over cranial nerves Reflex centers in brain Motor output over cranial nerves Effectors Muscles CHAPTER 13: The Spinal Cord Glands Sensory receptors Sensory input over spinal nerves © 2012 Pearson Education, Inc. Reflex centers in spinal cord Motor output over spinal nerves Adipose tissue

13 -2 Spinal Cord • Gross Anatomy of the Spinal Cord • About 18 inches (45 cm) long • 1/2 inch (14 mm) wide • Ends between vertebrae L 1 and L 2 • Bilateral symmetry • Grooves divide the spinal cord into left and right • Posterior median sulcus – on posterior side • Anterior median fissure – deeper groove on anterior side © 2012 Pearson Education, Inc.

13 -2 Spinal Cord • Enlargements of the Spinal Cord • Caused by: • Amount of gray matter in segment • Involvement with sensory and motor nerves of limbs • Cervical enlargement • Nerves of shoulders and upper limbs • Lumbar enlargement • Nerves of pelvis and lower limbs © 2012 Pearson Education, Inc.

13 -2 Spinal Cord • Gross Anatomy of the Spinal Cord • The distal end • Conus medullaris • Thin, conical spinal cord below lumbar enlargement • Filum terminale • Thin thread of fibrous tissue at end of conus medullaris • Attaches to coccygeal ligament • Cauda equina • Nerve roots extending below conus medullaris © 2012 Pearson Education, Inc.

Figure 13 -2 Gross Anatomy of the Adult Spinal Cord Posterior median sulcus Dorsal root ganglion Cervical spinal nerves C 1 C 2 C 3 C 4 C 5 C 6 C 7 C 8 T 1 T 2 T 3 T 4 T 5 T 6 White matter Gray matter Central canal Cervical enlargement Spinal Ventral nerve root Anterior median fissure C 3 T 7 Thoracic spinal nerves T 8 T 9 Posterior median sulcus T 10 T 11 T 3 Lumbar enlargement T 12 L 1 Conus medullaris L 2 Lumbar spinal nerves L 3 L 4 Inferior tip of spinal cord Cauda equina L 5 L 1 Sacral spinal nerves S 1 S 2 S 3 S 4 S 5 Coccygeal nerve (Co 1) © 2012 Pearson Education, Inc. Filum terminale (in coccygeal ligament) S 2

Figure 13 -2 Gross Anatomy of the Adult Spinal Cord Posterior median sulcus Dorsal root ganglion Cervical spinal nerves C 1 C 2 C 3 C 4 C 5 C 6 C 7 C 8 Central canal Cervical enlargement Spinal Ventral nerve root The superficial anatomy and orientation of the adult spinal cord. The numbers to the left identify the spinal nerves and indicate where the nerve roots leave the vertebral canal. The spinal cord extends from the brain only to the level of vertebrae L 1 L 2; the spinal segments found at representative locations are indicated in the cross sections. © 2012 Pearson Education, Inc. White matter Gray matter Anterior median fissure C 3 Inferior views of cross sections through representative segments of the spinal cord, showing the arrangement of gray matter and white matter.

Figure 13 -2 Gross Anatomy of the Adult Spinal Cord T 1 T 2 T 3 T 4 T 5 T 6 T 7 Thoracic spinal nerves T 8 T 9 Posterior median sulcus T 10 T 11 Lumbar enlargement T 12 Conus medullaris © 2012 Pearson Education, Inc. T 3

Figure 13 -2 Gross Anatomy of the Adult Spinal Cord L 1 Conus medullaris L 2 Lumbar spinal nerves L 3 Inferior tip of spinal cord L 4 Cauda equina L 5 L 1 © 2012 Pearson Education, Inc.

Figure 13 -2 Gross Anatomy of the Adult Spinal Cord Inferior tip of spinal cord Cauda equina Sacral spinal nerves S 1 S 2 S 3 S 4 S 5 Coccygeal nerve (Co 1) © 2012 Pearson Education, Inc. Filum terminale (in coccygeal ligament) S 2

13 -2 Spinal Cord • 31 Spinal Cord Segments • Based on vertebrae where spinal nerves originate • Positions of spinal segment and vertebrae change with age • Cervical nerves • Are named for inferior vertebra • All other nerves • Are named for superior vertebra © 2012 Pearson Education, Inc.

13 -2 Spinal Cord • Roots • Two branches of spinal nerves 1. Ventral root • Contains axons of motor neurons 2. Dorsal root • • Contains axons of sensory neurons Dorsal root ganglia • Contain cell bodies of sensory neurons © 2012 Pearson Education, Inc.

13 -2 Spinal Cord • The Spinal Nerve • Each side of spine • Dorsal and ventral roots join • To form a spinal nerve • Mixed Nerves • Carry both afferent (sensory) and efferent (motor) fibers © 2012 Pearson Education, Inc.

Figure 13 -3 a The Spinal Cord and Spinal Meninges White matter Ventral root Gray matter Dorsal root ganglion Spinal nerve Dorsal root Meninges Pia mater Arachnoid mater Dura mater A posterior view of the spinal cord, showing the meningeal layers, superficial landmarks, and distribution of gray matter and white matter © 2012 Pearson Education, Inc.

Figure 13 -3 b The Spinal Cord and Spinal Meninges ANTERIOR Subarachnoid space Vertebral body Dura mater Arachnoid mater Pia mater Rami communicantes Spinal cord Adipose tissue in epidural space A sectional view through the spinal cord and meninges, showing the peripheral distribution of spinal nerves © 2012 Pearson Education, Inc. Autonomic (sympathetic) ganglion Ventral root of spinal nerve Ventral ramus Dorsal ramus Denticulate Dorsal root ligament ganglion POSTERIOR

13 -2 Spinal Cord • The Spinal Meninges • Specialized membranes isolate spinal cord from surroundings • Functions of the spinal meninges include: • Protecting spinal cord • Carrying blood supply • Continuous with cranial meninges • Meningitis • Viral or bacterial infection of meninges © 2012 Pearson Education, Inc.

13 -2 Spinal Cord • The Three Meningeal Layers 1. Dura mater • Outer layer of spinal cord 2. Arachnoid mater • Middle meningeal layer 3. Pia mater • Inner meningeal layer © 2012 Pearson Education, Inc.

13 -2 Spinal Cord • The Dura Mater • Tough and fibrous • Cranially • Fuses with periosteum of occipital bone • Is continuous with cranial dura mater • Caudally • Tapers to dense cord of collagen fibers • Joins filum terminale in coccygeal ligament © 2012 Pearson Education, Inc.

13 -2 Spinal Cord • The Dura Mater • The Epidural Space • Between spinal dura mater and walls of vertebral canal • Contains loose connective and adipose tissue • Anesthetic injection site © 2012 Pearson Education, Inc.

13 -2 Spinal Cord • The Arachnoid Mater • Middle meningeal layer • Arachnoid membrane • Simple squamous epithelia • Covers arachnoid mater © 2012 Pearson Education, Inc.

13 -2 Spinal Cord • The Interlayer Spaces of Arachnoid Mater • Subdural space • Between arachnoid mater and dura mater • Subarachnoid space • Between arachnoid mater and pia mater • Contains collagen/elastin fiber network (arachnoid trabeculae) • Filled with cerebrospinal fluid (CSF) © 2012 Pearson Education, Inc.

13 -2 Spinal Cord • The Interlayer Spaces of Arachnoid Mater • Cerebrospinal Fluid (CSF) • Carries dissolved gases, nutrients, and wastes • Lumbar puncture or spinal tap withdraws CSF © 2012 Pearson Education, Inc.

13 -2 Spinal Cord • The Pia Mater • Is the innermost meningeal layer • Is a mesh of collagen and elastic fibers • Is bound to underlying neural tissue © 2012 Pearson Education, Inc.

13 -2 Spinal Cord • Structures of the Spinal Cord • Paired denticulate ligaments • Extend from pia mater to dura mater • Stabilize side-to-side movement • Blood vessels • Along surface of spinal pia mater • Within subarachnoid space © 2012 Pearson Education, Inc.

Figure 13 -4 The Spinal Cord and Associated Structures Spinal cord Anterior median fissure Pia mater Denticulate ligaments Dorsal root Ventral root, formed by several “rootlets” from one cervical segment Arachnoid mater (reflected) Dura mater (reflected) Spinal blood vessel © 2012 Pearson Education, Inc.

13 -3 Gray Matter and White Matter • Sectional Anatomy of the Spinal Cord • White matter • Is superficial • Contains myelinated and unmyelinated axons • Gray matter • Surrounds central canal of spinal cord • Contains neuron cell bodies, neuroglia, unmyelinated axons • Has projections (gray horns) © 2012 Pearson Education, Inc.

13 -3 Gray Matter and White Matter • Organization of Gray Matter • The gray horns • Posterior gray horns contain somatic and visceral sensory nuclei • Anterior gray horns contain somatic motor nuclei • Lateral gray horns are in thoracic and lumbar segments; contain visceral motor nuclei • Gray commissures • Axons that cross from one side of cord to the other before reaching gray matter © 2012 Pearson Education, Inc.

13 -3 Gray Matter and White Matter • Organization of Gray Matter • The cell bodies of neurons form functional groups called nuclei • Sensory nuclei • Dorsal (posterior) • Connect to peripheral receptors • Motor nuclei • Ventral (anterior) • Connect to peripheral effectors © 2012 Pearson Education, Inc.

13 -3 Gray Matter and White Matter • Control and Location • Sensory or motor nucleus location within the gray matter determines which body part it controls © 2012 Pearson Education, Inc.

13 -3 Gray Matter and White Matter • Organization of White Matter • Posterior white columns lie between posterior gray horns and posterior median sulcus • Anterior white columns lie between anterior gray horns and anterior median fissure • Anterior white commissure area where axons cross from one side of spinal cord to the other • Lateral white columns located on each side of spinal cord between anterior and posterior columns © 2012 Pearson Education, Inc.

13 -3 Gray Matter and White Matter • Organization of White Matter • Tracts or fasciculi • In white columns • Bundles of axons • Relay same information in same direction • Ascending tracts • Carry information to brain • Descending tracts • Carry motor commands to spinal cord © 2012 Pearson Education, Inc.

Figure 13 -5 a The Sectional Organization of the Spinal Cord Posterior white column Dorsal root ganglion Lateral white column Posterior gray horn Lateral gray horn Anterior white column The left half of this sectional view shows important anatomical landmarks, including the three columns of white matter. The right half indicates the functional organization of the nuclei in the anterior, lateral, and posterior gray horns. © 2012 Pearson Education, Inc.

Figure 13 -5 a The Sectional Organization of the Spinal Cord Posterior median sulcus Posterior gray commissure Somatic Visceral Somatic Functional Organization of Gray Matter The cell bodies of neurons in the gray matter of the spinal cord are organized into functional groups called nuclei. Sensory nuclei Motor nuclei Ventral root Anterior gray commissure Anterior white commissure Anterior median fissure The left half of this sectional view shows important anatomical landmarks, including the three columns of white matter. The right half indicates the functional organization of the nuclei in the anterior, lateral, and posterior gray horns. © 2012 Pearson Education, Inc.

Figure 13 -5 b The Sectional Organization of the Spinal Cord POSTERIOR Posterior gray commissure Dura mater Arachnoid mater (broken) Central canal Anterior gray commissure Anterior median fissure Pia mater ANTERIOR A micrograph of a section through the spinal cord, showing major landmarks in and surrounding the cord. © 2012 Pearson Education, Inc.

Figure 13 -5 b The Sectional Organization of the Spinal Cord POSTERIOR Posterior median sulcus Structural Organization of Gray Matter The projections of gray matter toward the outer surface of the spinal cord are called horns. Posterior gray horn Lateral gray horn Dorsal root Anterior gray horn ANTERIOR Dorsal root ganglion Ventral root A micrograph of a section through the spinal cord, showing major landmarks in and surrounding the cord. © 2012 Pearson Education, Inc.

13 -3 Gray Matter and White Matter • Spinal Cord Summary • Spinal cord has a narrow central canal • Surrounded by gray matter • Containing sensory and motor nuclei • Sensory nuclei are dorsal • Motor nuclei are ventral © 2012 Pearson Education, Inc.

13 -3 Gray Matter and White Matter • Spinal Cord Summary • Gray matter • Is covered by a thick layer of white matter • White matter • Consists of ascending and descending axons • Organized in columns • Contains axon bundles with specific functions • Spinal cord is so highly organized • It is possible to predict results of injuries to specific areas © 2012 Pearson Education, Inc.

13 -4 Spinal Nerves and Plexuses • Anatomy of Spinal Nerves • Every spinal cord segment • Is connected to a pair of spinal nerves • Every spinal nerve • Is surrounded by three connective tissue layers • That support structures and contain blood vessels © 2012 Pearson Education, Inc.

13 -4 Spinal Nerves and Plexuses • Three Connective Tissue Layers of Spinal Nerves 1. Epineurium • Outer layer • Dense network of collagen fibers 2. Perineurium • Middle layer • Divides nerve into fascicles (axon bundles) 3. Endoneurium • Inner layer • Surrounds individual axons © 2012 Pearson Education, Inc.

Figure 13 -6 A Peripheral Nerve Blood vessels Connective Tissue Layers Epineurium covering spinal nerve Perineurium (around one fascicle) Endoneurium Myelinated axon Fascicle © 2012 Pearson Education, Inc. Schwann cell

Figure 13 -6 A Peripheral Nerve Blood vessels Perineurium (around one fascicle) © 2012 Pearson Education, Inc. Endoneurium

13 -4 Spinal Nerves and Plexuses • Peripheral Nerves • Interconnecting branches of spinal nerves • Surrounded by connective tissue sheaths © 2012 Pearson Education, Inc.

13 -4 Spinal Nerves and Plexuses • Peripheral Distribution of Spinal Nerves • Spinal nerves • Form lateral to intervertebral foramen • Where dorsal and ventral roots unite • Then branch and form pathways to destination © 2012 Pearson Education, Inc.

13 -4 Spinal Nerves and Plexuses • Peripheral Distribution of Spinal Nerves • Motor nerves • The first branch • White ramus • Carries visceral motor fibers to sympathetic ganglion of autonomic nervous system • Gray ramus • Unmyelinated nerves • Return from sympathetic ganglion to rejoin spinal nerve © 2012 Pearson Education, Inc.

13 -4 Spinal Nerves and Plexuses • Peripheral Distribution of Spinal Nerves • Motor nerves • Dorsal and ventral rami • Dorsal ramus • Contains somatic and visceral motor fibers • Innervates the back • Ventral ramus • Larger branch • Innervates ventrolateral structures and limbs © 2012 Pearson Education, Inc.

Figure 13 -7 Peripheral Distribution of Spinal Nerves To skeletal muscles of back The spinal nerve forms just lateral to the intervertebral foramen, where the dorsal and ventral roots unite. Dorsal root ganglion Postganglionic fibers to smooth muscles, glands, etc. , of back The dorsal ramus contains somatic motor and visceral motor fibers that innervate the skin and skeletal muscles of the back. The axons in the relatively large ventral ramus supply the ventrolateral body surface, structures in the body wall, and the limbs. The ventral root of each spinal nerve contains the axons of somatic motor and visceral motor neurons. To skeletal muscles of body wall, limbs Visceral motor nuclei Somatic motor nuclei Rami communicantes Somatic motor commands Visceral motor commands Postganglionic fibers to smooth muscles, glands, visceral organs in thoracic cavity Preganglionic fibers to sympathetic ganglia innervating abdominopelvic viscera © 2012 Pearson Education, Inc. Sympathetic ganglion Postganglionic fibers to smooth muscles, glands, etc. , of body wall, limbs The white ramus is the first branch from the spinal nerve and carries visceral motor fibers to a nearby sympathetic ganglion. Because these preganglionic axons are myelinated, this branch has a light color and is therefore known as the white ramus. A sympathetic nerve contains preganglionic and postganglionic fibers innervating structures in the thoracic cavity. The gray ramus contains postganglionic fibers that innervate glands and smooth muscles in the body wall or limbs. These fibers are unmyelinated and have a dark gray color.

13 -4 Spinal Nerves and Plexuses • Peripheral Distribution of Spinal Nerves • Sensory nerves • In addition to motor impulses • Dorsal, ventral, and white rami also carry sensory information • Dermatomes • Bilateral region of skin • Monitored by specific pair of spinal nerves © 2012 Pearson Education, Inc.

Figure 13 -7 Peripheral Distribution of Spinal Nerves From interoceptors of back From exteroceptors, proprioceptors of back The dorsal ramus carries sensory information from the skin and skeletal muscles of the back. Somatic sensory nuclei The ventral ramus carries sensory information from the ventrolateral body surface, structures in the body wall, and the limbs. Dorsal root ganglion From exteroceptors, proprioceptors of body wall, limbs From interoceptors of body wall, limbs Rami communicantes Ventral root Somatic sensations Visceral sensations © 2012 Pearson Education, Inc. The dorsal root of each spinal nerve carries sensory information to the spinal cord. The sympathetic nerve carries sensory information from the visceral organs. Visceral sensory nuclei From interoceptors of visceral organs

Figure 13 -8 Dermatomes C 2 C 3 NV C 2 C 3 T 2 C 6 L 1 L 2 C 8 C 7 T 1 L 3 L 4 L 5 C 4 C 5 T 1 T 2 T 3 T 4 T 5 T 6 T 7 T 8 T 9 T 10 T 11 T 12 S 2 C 3 T 2 T 3 T 4 T 5 T 6 T 7 T 8 T 9 T 10 T 11 T 12 L 1 L 2 L 4 L 3 L 5 C 4 C 5 T 2 C 6 T 1 C 7 SS 4 3 L 1 S 1 L 5 S 5 C 8 L 2 S 2 L 3 S 1 L 4 ANTERIOR © 2012 Pearson Education, Inc. POSTERIOR

13 -4 Spinal Nerves and Plexuses • Peripheral Neuropathy • Regional loss of sensory or motor function • Due to trauma or compression © 2012 Pearson Education, Inc.

Figure 13 -9 Shingles © 2012 Pearson Education, Inc.

13 -4 Spinal Nerves and Plexuses • Nerve Plexuses • Complex, interwoven networks of nerve fibers • Formed from blended fibers of ventral rami of adjacent spinal nerves • Control skeletal muscles of the neck and limbs © 2012 Pearson Education, Inc.

13 -4 Spinal Nerves and Plexuses • The Four Major Plexuses of Ventral Rami 1. Cervical plexus 2. Brachial plexus 3. Lumbar plexus 4. Sacral plexus © 2012 Pearson Education, Inc.

Figure 13 -10 Peripheral Nerves and Nerve Plexuses Cervical plexus Brachial plexus C 1 C 2 C 3 C 4 C 5 C 6 C 7 C 8 T 1 T 2 T 3 T 4 T 5 T 6 T 7 T 8 T 9 T 10 T 11 © 2012 Pearson Education, Inc. Lesser occipital nerve Great auricular nerve Transverse cervical nerve Supraclavicular nerve Phrenic nerve Axillary nerve Musculocutaneous nerve Thoracic nerves

Figure 13 -10 Peripheral Nerves and Nerve Plexuses T 12 L 1 Lumbar plexus Sacral plexus Radial nerve L 2 L 3 L 4 L 5 S 1 S 2 S 3 S 4 S 5 Co 1 Ulnar nerve Median nerve Iliohypogastric nerve Ilioinguinal nerve Lateral femoral cutaneous nerve Genitofemoral nerve Femoral nerve Obturator nerve Superior Inferior Gluteal nerves Pudendal nerve Saphenous nerve Sciatic nerve © 2012 Pearson Education, Inc.

13 -4 Spinal Nerves and Plexuses • The Cervical Plexus • Includes ventral rami of spinal nerves C 1–C 5 • Innervates neck, thoracic cavity, diaphragmatic muscles • Major nerve • Phrenic nerve (controls diaphragm) © 2012 Pearson Education, Inc.

Figure 13 -11 The Cervical Plexus Cranial Nerves Accessory nerve (XI) Hypoglossal nerve (XII) Lesser occipital nerve Nerve Roots of Cervical Plexus C 1 C 2 C 3 C 4 C 5 Supraclavicular nerves Clavicle © 2012 Pearson Education, Inc.

Figure 13 -11 The Cervical Plexus Great auricular nerve Geniohyoid muscle Transverse cervical nerve Thyrohyoid muscle Ansa cervicalis Omohyoid muscle Phrenic nerve Sternohyoid muscle Sternothyroid muscle © 2012 Pearson Education, Inc.

Table 13 -1 The Cervical Plexus © 2012 Pearson Education, Inc.

13 -4 Spinal Nerves and Plexuses • The Brachial Plexus • Includes ventral rami of spinal nerves C 5–T 1 • Innervates pectoral girdle and upper limbs • Nerves that form brachial plexus originate from: • Superior, middle, and inferior trunks • Large bundles of axons from several spinal nerves • Lateral, medial, and posterior cords • Smaller branches that originate at trunks © 2012 Pearson Education, Inc.

13 -4 Spinal Nerves and Plexuses • The Brachial Plexus • Major nerves • Musculocutaneous nerve (lateral cord) • Median nerve (lateral and medial cords) • Ulnar nerve (medial cord) • Axillary nerve (posterior cord) • Radial nerve (posterior cord) © 2012 Pearson Education, Inc.

Figure 13 -12 a The Brachial Plexus Trunks of Brachial Plexus Spinal Nerves Forming Brachial Plexus Dorsal scapular nerve Suprascapular nerve C 4 C 5 C 6 C 7 C 8 T 1 Superior Middle Inferior Musculocutaneous nerve Median nerve Ulnar nerve Radial nerve Lateral antebrachial cutaneous nerve Superficial branch of radial nerve Deep radial nerve Ulnar nerve Median nerve Palmar digital nerves Major nerves originating at the right brachial plexus, anterior view © 2012 Pearson Education, Inc.

Figure 13 -12 b The Brachial Plexus Anterior Posterior Radial nerve Ulnar nerve Median nerve Areas of the hands serviced by nerves of the right brachial plexus © 2012 Pearson Education, Inc.

Figure 13 -12 c The Brachial Plexus Dorsal scapular nerve C 5 SUPERIOR TRUNK C 6 Suprascapular nerve MIDDLE TRUNK Lateral cord C 7 Posterior cord C 8 Lateral pectoral nerve Medial pectoral nerve Subscapular nerves T 1 Axillary nerve Medial cord Musculocutaneous nerve First rib Medial antebrachial cutaneous nerve Median nerve Posterior brachial cutaneous nerve INFERIOR TRUNK Long thoracic nerve KEY Ulnar nerve Roots (ventral rami) Radial nerve Right brachial plexus, anterior view © 2012 Pearson Education, Inc. Trunks Divisions Cords Peripheral nerves

Table 13 -2 The Brachial Plexus © 2012 Pearson Education, Inc.

13 -4 Spinal Nerves and Plexuses • The Lumbar Plexus • Includes ventral rami of spinal nerves T 12–L 4 • Major nerves • Genitofemoral nerve • Lateral femoral cutaneous nerve • Femoral nerve © 2012 Pearson Education, Inc.

13 -4 Spinal Nerves and Plexuses • The Sacral Plexus • Includes ventral rami of spinal nerves L 4–S 4 • Major nerves • • Pudendal nerve • Sciatic nerve Two branches of the sciatic nerve 1. Fibular nerve 2. Tibial nerve © 2012 Pearson Education, Inc.

Figure 13 -13 a The Lumbar and Sacral Plexuses T 12 Nerves of the Lumbar Plexus Iliohypogastric Ilioinguinal Genitofemoral Lateral femoral cutaneous Femoral Obturator L 1 L 2 L 3 L 4 L 5 Spinal Nerves Forming the Lumbar Plexus T 12 nerve L 1 nerve L 2 nerve L 3 nerve L 4 nerve Lumbosacral trunk Lumbar plexus, anterior view © 2012 Pearson Education, Inc.

Figure 13 -13 b The Lumbar and Sacral Plexuses Spinal Nerves Forming the Sacral Plexus Lumbosacral trunk L 4 nerve L 5 nerve Nerves of the Sacral Plexus S 1 nerve Superior gluteal S 2 nerve Inferior gluteal S 3 nerve Sciatic Posterior femoral cutaneous S 5 S 4 nerve Co 1 Pudendal Sacral plexus, anterior view © 2012 Pearson Education, Inc.

Figure 13 -13 c The Lumbar and Sacral Plexuses Iliohypogastric nerve Ilioinguinal nerve Genitofemoral nerve Lateral femoral cutaneous nerve Femoral nerve Obturator nerve Superior gluteal nerve Inferior gluteal nerve Pudendal nerve Posterior femoral cutaneous nerve (cut) Sciatic nerve Saphenous nerve Common fibular nerve Superficial fibular nerve Deep fibular nerve © 2012 Pearson Education, Inc. Nerves of the lumbar and sacral plexuses, anterior view

Figure 13 -13 d The Lumbar and Sacral Plexuses Saphenous nerve Sural nerve Tibial nerve Fibular nerve Saphenous nerve Tibial nerve Sural nerve Fibular nerve Cutaneous distribution of the nerves in the foot and ankle © 2012 Pearson Education, Inc.

Figure 13 -13 e The Lumbar and Sacral Plexuses Superior gluteal nerve Inferior gluteal nerve Pudendal nerve Posterior femoral cutaneous nerve Sciatic nerve Tibial nerve Common fibular nerve Sural nerve © 2012 Pearson Education, Inc. Nerves of the sacral plexus, posterior view

Table 13 -3 The Lumbar and Sacral Plexuses © 2012 Pearson Education, Inc.

Table 13 -3 The Lumbar and Sacral Plexuses © 2012 Pearson Education, Inc.

13 -5 Neuronal Pools • Functional Organization of Neurons • Sensory neurons • About 10 million • Deliver information to CNS • Motor neurons • About 1/2 million • Deliver commands to peripheral effectors • Interneurons • About 20 billion • Interpret, plan, and coordinate signals in and out © 2012 Pearson Education, Inc.

13 -5 Neuronal Pools • Functional groups of interconnected neurons (interneurons) • Each with limited input sources and output destinations • May stimulate or depress parts of brain or spinal cord © 2012 Pearson Education, Inc.

13 -5 Neuronal Pools Five Patterns of Neural Circuits in Neuronal Pools 1. Divergence • Spreads stimulation to many neurons or neuronal pools in CNS 2. Convergence • Brings input from many sources to single neuron 3. Serial processing • Moves information in single line © 2012 Pearson Education, Inc.

13 -5 Neuronal Pools • Five Patterns of Neural Circuits in Neuronal Pools 4. Parallel processing • Moves same information along several paths simultaneously 5. Reverberation • Positive feedback mechanism • Functions until inhibited © 2012 Pearson Education, Inc.

Figure 13 -14 a Neural Circuits: The Organization of Neuronal Pools Divergence A mechanism for spreading stimulation to multiple neurons or neuronal pools in the CNS © 2012 Pearson Education, Inc.

Figure 13 -14 b Neural Circuits: The Organization of Neuronal Pools Convergence A mechanism for providing input to a single neuron from multiple sources © 2012 Pearson Education, Inc.

Figure 13 -14 c Neural Circuits: The Organization of Neuronal Pools Serial processing A mechanism in which neurons or pools work sequentially © 2012 Pearson Education, Inc.

Figure 13 -14 d Neural Circuits: The Organization of Neuronal Pools Parallel processing A mechanism in which neurons or pools process the same information simultaneously © 2012 Pearson Education, Inc.

Figure 13 -14 e Neural Circuits: The Organization of Neuronal Pools Reverberation A positive feedback mechanism © 2012 Pearson Education, Inc.

13 -6 Reflexes • Automatic responses coordinated within spinal cord • Through interconnected sensory neurons, motor neurons, and interneurons • Produce simple and complex reflexes © 2012 Pearson Education, Inc.

13 -6 Reflexes • Neural Reflexes • Rapid, automatic responses to specific stimuli • Basic building blocks of neural function • One neural reflex produces one motor response • Reflex arc • The wiring of a single reflex • Beginning at receptor • Ending at peripheral effector • Generally opposes original stimulus (negative feedback) © 2012 Pearson Education, Inc.

13 -6 Reflexes • Five Steps in a Neural Reflex • Step 1: Arrival of stimulus, activation of receptor • Physical or chemical changes • Step 2: Activation of sensory neuron • Graded depolarization • Step 3: Information processing by postsynaptic cell • Triggered by neurotransmitters • Step 4: Activation of motor neuron • Action potential • Step 5: Response of peripheral effector • Triggered by neurotransmitters © 2012 Pearson Education, Inc.

Figure 13 -15 Events in a Neural Reflex Activation of a sensory neuron Arrival of stimulus and activation of receptor Dorsal root Sensation relayed to the brain by axon collaterals Information processing in the CNS REFLEX ARC Receptor Stimulus Response by effector Effector Ventral root Activation of a motor neuron KEY Sensory neuron (stimulated) Excitatory interneuron Motor neuron (stimulated) © 2012 Pearson Education, Inc.

13 -6 Reflexes • Four Classifications of Reflexes 1. By early development 2. By type of motor response 3. By complexity of neural circuit 4. By site of information processing © 2012 Pearson Education, Inc.

13 -6 Reflexes • Development of Reflexes • Innate reflexes • Basic neural reflexes • Formed before birth • Acquired reflexes • Rapid, automatic • Learned motor patterns © 2012 Pearson Education, Inc.

13 -6 Reflexes • Motor Response • Nature of resulting motor response • Somatic reflexes • Involuntary control of nervous system • Superficial reflexes of skin, mucous membranes • Stretch or deep tendon reflexes (e. g. , patellar, or “knee-jerk, ” reflex) • Visceral reflexes (autonomic reflexes) • Control systems other than muscular system © 2012 Pearson Education, Inc.

13 -6 Reflexes • Complexity of Neural Circuit • Monosynaptic reflex • Sensory neuron synapses directly onto motor neuron • Polysynaptic reflex • At least one interneuron between sensory neuron and motor neuron © 2012 Pearson Education, Inc.

13 -6 Reflexes • Site of Information Processing • Spinal reflexes • Occur in spinal cord • Cranial reflexes • Occur in brain © 2012 Pearson Education, Inc.

Figure 13 -16 The Classification of Reflexes can be classified by development response complexity of circuit processing site Innate Reflexes Somatic Reflexes Monosynaptic Spinal Reflexes • Genetically determined • Control skeletal muscle contractions • Include superficial and stretch reflexes Acquired Reflexes Visceral (Autonomic) Reflexes • Learned • Control actions of smooth and cardiac muscles, glands, and adipose tissue © 2012 Pearson Education, Inc. • One synapse Polysynaptic • Multiple synapse (two to several hundred) • Processing in the spinal cord Cranial Reflexes • Processing in the brain

13 -7 Spinal Reflexes • Range in increasing order of complexity • Monosynaptic reflexes • Polysynaptic reflexes • Intersegmental reflex arcs • Many segments interact • Produce highly variable motor response © 2012 Pearson Education, Inc.

13 -7 Spinal Reflexes • Monosynaptic Reflexes • A stretch reflex • Have least delay between sensory input and motor output • For example, stretch reflex (such as patellar reflex) • Completed in 20– 40 msec • Receptor is muscle spindle © 2012 Pearson Education, Inc.

Figure 13 -17 A Stretch Reflex Receptor (muscle spindle) Spinal cord Stretch REFLEX ARC Stimulus Effector Contraction Response © 2012 Pearson Education, Inc. KEY Sensory neuron (stimulated) Motor neuron (stimulated)

13 -7 Spinal Reflexes • Muscle Spindles • The receptors in stretch reflexes • Bundles of small, specialized intrafusal muscle fibers • Innervated by sensory and motor neurons • Surrounded by extrafusal muscle fibers • Which maintain tone and contract muscle © 2012 Pearson Education, Inc.

13 -7 Spinal Reflexes • The Sensory Region • Central region of intrafusal fibers • Wound with dendrites of sensory neurons • Sensory neuron axon enters CNS in dorsal root • Synapses onto motor neurons (gamma motor neurons) • In anterior gray horn of spinal cord © 2012 Pearson Education, Inc.

13 -7 Spinal Reflexes • Gamma Efferents • Axons of the motor neurons • Complete reflex arc • Synapse back onto intrafusal fibers • Important in voluntary muscle contractions • Allow CNS to adjust sensitivity of muscle spindles © 2012 Pearson Education, Inc.

Figure 13 -18 A Muscle Spindle Gamma efferent from CNS Extrafusal fiber To CNS Sensory region Intrafusal fiber Muscle spindle Gamma efferent from CNS © 2012 Pearson Education, Inc.

13 -7 Spinal Reflexes • Postural reflexes • Stretch reflexes • Maintain normal upright posture • Stretched muscle responds by contracting • Automatically maintain balance © 2012 Pearson Education, Inc.

13 -7 Spinal Reflexes • Polysynaptic Reflexes • More complicated than monosynaptic reflexes • Interneurons control more than one muscle group • Produce either EPSPs or IPSPs © 2012 Pearson Education, Inc.

13 -7 Spinal Reflexes • The Tendon Reflex • Prevents skeletal muscles from: • Developing too much tension • Tearing or breaking tendons • Sensory receptors unlike muscle spindles or proprioceptors © 2012 Pearson Education, Inc.

13 -7 Spinal Reflexes • Withdrawal Reflexes • Move body part away from stimulus (pain or pressure) • For example, flexor reflex • Pulls hand away from hot stove • Strength and extent of response • Depend on intensity and location of stimulus © 2012 Pearson Education, Inc.

Figure 13 -19 A Flexor Reflex Distribution within gray horns to other segments of the spinal cord Painful stimulus Flexors stimulated Extensors inhibited KEY Sensory neuron (stimulated) Motor neuron (inhibited) Excitatory interneuron Inhibitory interneuron Motor neuron (stimulated) © 2012 Pearson Education, Inc.

13 -7 Spinal Reflexes • Reciprocal Inhibition • For flexor reflex to work • The stretch reflex of antagonistic (extensor) muscle must be inhibited (reciprocal inhibition) by interneurons in spinal cord © 2012 Pearson Education, Inc.

13 -7 Spinal Reflexes • Reflex Arcs • Ipsilateral reflex arcs • Occur on same side of body as stimulus • Stretch, tendon, and withdrawal reflexes • Crossed extensor reflexes • Involve a contralateral reflex arc • Occur on side opposite stimulus © 2012 Pearson Education, Inc.

13 -7 Spinal Reflexes • Crossed Extensor Reflexes • Occur simultaneously, coordinated with flexor reflex • For example, flexor reflex causes leg to pull up • Crossed extensor reflex straightens other leg • To receive body weight • Maintained by reverberating circuits © 2012 Pearson Education, Inc.

Figure 13 -20 The Crossed Extensor Reflex To motor neurons in other segments of the spinal cord Extensors inhibited Flexors stimulated Extensors stimulated Flexors inhibited KEY Painful stimulus © 2012 Pearson Education, Inc. Sensory neuron (stimulated) Motor neuron (inhibited) Excitatory interneuron Inhibitory interneuron Motor neuron (stimulated)

13 -7 Spinal Reflexes • Five General Characteristics of Polysynaptic Reflexes 1. Involve pools of interneurons 2. Are intersegmental in distribution 3. Involve reciprocal inhibition 4. Have reverberating circuits • Which prolong reflexive motor response 5. Several reflexes cooperate • To produce coordinated, controlled response © 2012 Pearson Education, Inc.

13 -8 The Brain Can Alter Spinal Reflexes • Integration and Control of Spinal Reflexes • Reflex behaviors are automatic • But processing centers in brain can facilitate or inhibit reflex motor patterns based in spinal cord © 2012 Pearson Education, Inc.

13 -8 The Brain Can Alter Spinal Reflexes • Voluntary Movements and Reflex Motor Patterns • Higher centers of brain incorporate lower, reflexive motor patterns • Automatic reflexes • Can be activated by brain as needed • Use few nerve impulses to control complex motor functions • Walking, running, jumping © 2012 Pearson Education, Inc.

13 -8 The Brain Can Alter Spinal Reflexes • Reinforcement of Spinal Reflexes • Higher centers reinforce spinal reflexes • By stimulating excitatory neurons in brain stem or spinal cord • Creating EPSPs at reflex motor neurons • Facilitating postsynaptic neurons © 2012 Pearson Education, Inc.

13 -8 The Brain Can Alter Spinal Reflexes • Inhibition of Spinal Reflexes • Higher centers inhibit spinal reflexes by: • Stimulating inhibitory neurons • Creating IPSPs at reflex motor neurons • Suppressing postsynaptic neurons © 2012 Pearson Education, Inc.

13 -8 The Brain Can Alter Spinal Reflexes • The Babinski Reflexes • Normal in infants • May indicate CNS damage in adults © 2012 Pearson Education, Inc.

Figure 13 -21 a The Babinski Reflexes The plantar reflex (negative Babinski reflex), a curling of the toes, is seen in healthy adults. © 2012 Pearson Education, Inc.

Figure 13 -21 b The Babinski Reflexes The Babinski sign (positive Babinski reflex) occurs in the absence of descending inhibition. It is normal in infants, but pathological in adults. © 2012 Pearson Education, Inc.