© 2015 Pearson Education, Inc. Lecture Presentation by Lee Ann Frederick University of Texas at Arlington Chapter 13 The Spinal Cord, Spinal Nerves, and Spinal Reflexes

© 2015 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 Discuss the structure and functions of the spinal cord, and describe the three meningeal layers that surround the central nervous system Explain the roles of white matter and gray matter in processing and relaying sensory information and motor commands Describe the major components of a spinal nerve, and relate the distribution pattern of spinal nerves to the regions they innervate.

© 2015 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 Describe the steps in a neural reflex, and classify the types of reflexes Distinguish among the types of motor responses produced by various reflexes, and explain how reflexes interact to produce complex behaviors Explain how higher centers control and modify reflex responses.

© 2015 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

© 2015 Pearson Education, Inc. Figure 13-1 An Overview of Chapters 13 and 14. CHAPTER 14: The Brain CHAPTER 13: The Spinal Cord Sensory receptors Sensory input over cranial nerves Reflex centers in brain Motor output over cranial nerves Muscles Effectors Glands Adipose tissue Sensory receptors Sensory input over spinal nerves Motor output over spinal nerves Reflex centers in spinal cord

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc. Figure 13-2 Gross Anatomy of the Adult Spinal Cord. = Cervical = Thoracic = Lumbar = Sacral KEY Spinal cord regions Coccygeal nerve (Co 1 ) Sacral spinal nerves Lumbar spinal nerves Thoracic spinal nerves Cervical spinal nerves Cervical enlargement Posterior median sulcus Lumbar enlargement Conus medullaris Inferior tip of spinal cord Cauda equina Filum terminale (in coccygeal ligament) 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 adult 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. Inferior views of cross sections through representative segments of the spinal cord, showing the arrangement of gray matter and white matter. Spinal nerve Ventral root Dorsal root Dorsal root ganglion Central canal Gray matter White matter Posterior median sulcus Anterior median fissure C3C3 T3T3 L1L1 S2S2 b a S5S5 S4S4 S3S3 S2S2 S1S1 L1L1 L2L2 L3L3 L4L4 L5L5 T 12 T 11 T 10 T9T9 T8T8 T7T7 T6T6 T5T5 T4T4 T3T3 T2T2 T1T1 C1C1 C2C2 C3C3 C4C4 C5C5 C6C6 C7C7 C8C8

© 2015 Pearson Education, Inc. Figure 13-2 Gross Anatomy of the Adult Spinal Cord (Part 1 of 4). Cervical spinal nerves Cervical enlargement Central canal Spinal nerve Ventral root Dorsal root ganglion Dorsal root White matter Gray matter Anterior median fissure Posterior median sulcus C3C3 C3C3 C8C8 C4C4 C6C6 C7C7 C2C2 C1C1 C5C5 a b 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 adult 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. Inferior views of cross sections through representative segments of the spinal cord, showing the arrangement of gray matter and white matter.

© 2015 Pearson Education, Inc. Figure 13-2 Gross Anatomy of the Adult Spinal Cord (Part 2 of 4). Thoracic spinal nerves T 10 T 12 T9T9 T1T1 T 11 a b 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 adult 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. Inferior views of cross sections through representative segments of the spinal cord, showing the arrangement of gray matter and white matter. T2T2 T3T3 T4T4 T5T5 T6T6 T7T7 T8T8 Posterior median sulcus Lumbar enlargement Conus medullaris T3T3

© 2015 Pearson Education, Inc. Figure 13-2 Gross Anatomy of the Adult Spinal Cord (Part 3 of 4). L3L3 L5L5 L2L2 L1L1 L4L4 a b 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 adult 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. Inferior views of cross sections through representative segments of the spinal cord, showing the arrangement of gray matter and white matter. L1L1 Lumbar spinal nerves Inferior tip of spinal cord Conus medullaris Cauda equina

© 2015 Pearson Education, Inc. Figure 13-2 Gross Anatomy of the Adult Spinal Cord (Part 4 of 4). Sacral spinal nerves S3S3 S5S5 S2S2 S1S1 S4S4 a b 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 adult 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. Inferior views of cross sections through representative segments of the spinal cord, showing the arrangement of gray matter and white matter. Cauda equina Inferior tip of spinal cord S2S2 Coccygeal nerve (Co 1 ) Filum terminale (in coccygeal ligament)

© 2015 Pearson Education, Inc Spinal Cord 31 Spinal Cord Segments Based on vertebrae where spinal nerves originate Positions of spinal segment and vertebrae change with age Cervical nerves Named for inferior vertebra All other nerves Named for superior vertebra

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc. Figure 13-3a The Spinal Cord and Spinal Meninges. a A posterior view of the spinal cord, showing the meningeal layers, superficial landmarks, and distribution of gray matter and white matter White matter Ventral rootlets of spinal nerve Ventral root Dorsal root Dorsal root ganglion Dorsal rootlets of spinal nerve Gray matter Spinal nerve Meninges Pia mater Arachnoid mater Dura mater

© 2015 Pearson Education, Inc. Figure 13-3b The Spinal Cord and Spinal Meninges. b A sectional view through the spinal cord and meninges, showing the relationship of the meninges, spinal cord, and spinal nerves Dura mater Meninges Pia mater Arachnoid mater Vertebral body Subarachnoid space Rami communicantes Autonomic (sympathetic) ganglion Ventral root of spinal nerve Ventral ramus Dorsal ramus Dorsal root ganglion Denticulate ligament Adipose tissue in epidural space Spinal cord POSTERIOR ANTERIOR

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc Spinal Cord The Arachnoid Mater Middle meningeal layer Arachnoid membrane Simple squamous epithelia Covers arachnoid mater

© 2015 Pearson Education, Inc 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)

© 2015 Pearson Education, Inc Spinal Cord The Interlayer Spaces of Arachnoid Mater Cerebrospinal Fluid (CSF) Carries dissolved gases, nutrients, and wastes Lumbar puncture or spinal tap withdraws CSF

© 2015 Pearson Education, Inc Spinal Cord The Pia Mater Is the innermost meningeal layer Is a mesh of collagen and elastic fibers Is bound to underlying neural tissue

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc. Figure 13-4 The Spinal Cord and Associated Structures. Anterior median fissure Pia mater Denticulate ligaments Spinal cord Dorsal root Ventral root, formed by several “rootlets” from one cervical segment Arachnoid mater (reflected) Dura mater (reflected) Spinal blood vessel

© 2015 Pearson Education, Inc Gray Matter and White Matter Sectional Anatomy of the Spinal Cord White matter Is superficial Contains myelinated and unmyelinated axons Gray matter Surrounds the central canal of spinal cord Contains neuron cell bodies, neuroglia, unmyelinated axons Has projections (gray horns)

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc Gray Matter and White Matter Control and Location Sensory or motor nucleus location within the gray matter determines which body part it controls

© 2015 Pearson Education, Inc 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 is 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

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc. Figure 13-5a The Sectional Organization of the Spinal Cord (Part 1 of 2). Dorsal root ganglion Lateral white column Posterior gray horn Lateral gray horn Anterio r gray horn Anterior white column Posterior white column a 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.

© 2015 Pearson Education, Inc. Figure 13-5a The Sectional Organization of the Spinal Cord (Part 2 of 2). Posterior median sulcus Posterior gray commissure Somatic Visceral Somatic Visceral Ventral root Sensory nuclei Motor nuclei The cell bodies of neurons in the gray matter of the spinal cord are organized into functional groups called nuclei. Functional Organization of Gray Matter Anterior gray commissure Anterior white commissure Anterior median fissure a 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.

© 2015 Pearson Education, Inc. Figure 13-5b The Sectional Organization of the Spinal Cord (Part 1 of 2). b Posterior gray commissure Dura mater Arachnoid mater (broken) Central canal Anterior gray commissure Anterior median fissure Pia mater ANTERIOR POSTERIOR A micrograph of a transverse section through the spinal cord, showing major landmarks in and surrounding the cord.

© 2015 Pearson Education, Inc. Figure 13-5b The Sectional Organization of the Spinal Cord (Part 2 of 2). Posterior median sulcus b ANTERIOR POSTERIOR 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 Dorsal root ganglion Ventral root A micrograph of a transverse section through the spinal cord, showing major landmarks in and surrounding the cord.

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc Spinal Nerves and Plexuses Anatomy of Spinal Nerves Each spinal cord segment: Is connected to a pair of spinal nerves Each spinal nerve: Is surrounded by three connective tissue layers That support structures and contain blood vessels

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc. Figure 13-6a A Peripheral Nerve. a A typical peripheral nerve and its connective tissue wrappings Fascicle Myelinated axon Schwann cell Endoneurium Perineurium (around one fascicle) Epineurium covering peripheral nerve Connective Tissue Layers Blood vessels

© 2015 Pearson Education, Inc. Figure 13-6b A Peripheral Nerve. b Endoneurium Perineurium (around one fascicle) Connective Tissue Layers Blood vessels

© 2015 Pearson Education, Inc Spinal Nerves and Plexuses Peripheral Nerves Interconnecting branches of spinal nerves Surrounded by connective tissue sheaths

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc. Figure 13-8 Peripheral Distribution of Spinal Nerves (Part 2 of 2). The spinal nerve forms just lateral to the intervertebral foramen, where the dorsal and ventral roots unite The ventral root of each spinal nerve contains the axons of somatic motor and visceral motor neurons. Visceral motor nuclei Somatic motor nuclei = Visceral motor commands = Somatic motor commands KEY Postganglionic fibers to smooth muscles, glands, visceral organs in thoracic cavity Sympathetic ganglion Preganglionic fibers to sympathetic ganglia innervating abdominopelvic viscera A sympathetic nerve contains preganglionic and postganglionic fibers innervating structures in the thoracic cavity. The gray ramus communicans contains preganglionic fibers that innervate glands and smooth muscles in the body wall or limbs. These fibers are unmyelinated and have a dark gray color. Gray rami are associated with each spinal nerve. The white ramus communicans 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. White rami are only found between T 1 and L 2. Rami communicantes Postganglionic fibers to smooth muscles, and glands of body wall, limbs To skeletal muscles of body wall, limbs The axons in the relatively large ventral ramus supply the ventrolateral body surface, structures in the body wall, and the limbs. The dorsal ramus contains somatic motor and visceral motor fibers that innervate the skin and skeletal muscles of the back. Dorsal root ganglion Dorsal root To skeletal muscles of back Postganglionic fibers to smooth muscles, glands, etc., of back

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc. Figure 13-8 Peripheral Distribution of Spinal Nerves (Part 1 of 2). From interoceptors of back From exteroceptors, proprioceptors of back The dorsal ramus carries sensory information from the skin and skeletal muscles of the back. 3 2 The ventral ramus carries sensory information from the ventrolateral body surface, structures in the body, wall, and the limbs. From exteroceptors, proprioceptors of body wall, limbs From interoceptors of body wall, limbs Rami communicantes KEY 1 The sympathetic nerve carriers sensory information from the visceral organs. From interceptors of visceral organs Ventral root Visceral sensory nuclei Dorsal root ganglion Somatic sensory nuclei The dorsal root of each spinal nerve carriers sensory information to the spinal cord. 4 = Visceral sensations = Somatic sensations

© 2015 Pearson Education, Inc. Figure 13-7 Dermatomes. N V C 2 –C 3 C2C2 C3C3 C4C4 C3C3 C4C4 C5C5 C5C5 T1T1 T2T2 T2T2 T2T2 T7T7 T3T3 T4T4 T5T5 T6T6 T8T8 T9T9 T 10 T 11 T 12 T2T2 T1T1 T2T2 T7T7 T3T3 T4T4 T5T5 T6T6 T8T8 T9T9 T 10 T 11 T 12 C6C6 C7C7 C6C6 C7C7 C8C8 T1T1 C8C8 L1L1 L2L2 L3L3 L4L4 L5L5 L1L1 L2L2 L3L3 L4L4 L1L1 S2S2 S1S1 S2S2 S3S3 S4S4 S5S5 L5L5 L1L1 L2L2 L3L3 L5L5 L4L4 S1S1 ANTERIORPOSTERIOR KEY Spinal cord regions = Cervical = Thoracic = Lumbar = Sacral

© 2015 Pearson Education, Inc Spinal Nerves and Plexuses Peripheral Neuropathy Regional loss of sensory or motor function Due to trauma or compression

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc Spinal Nerves and Plexuses The Four Major Plexuses of Ventral Rami 1. Cervical plexus 2. Brachial plexus 3. Lumbar plexus 4. Sacral plexus

© 2015 Pearson Education, Inc. Figure 13-9 Peripheral Nerves and Nerve Plexuses (Part 1 of 2). Cervical plexus Brachial plexus C2C2 C3C3 C5C5 T1T1 T2T2 T7T7 T3T3 T4T4 T5T5 T6T6 C1C1 C4C4 C6C6 C7C7 C8C8 T8T8 T9T9 T 10 T 11 Lesser occipital nerve Great auricular nerve Transverse cervical nerve Supraclavicular nerve Phrenic nerve Axillary nerve Musculocutaneous nerve Thoracic nerves

© 2015 Pearson Education, Inc. Figure 13-9 Peripheral Nerves and Nerve Plexuses (Part 2 of 2). T 12 Lumbar plexus Sacral plexus L1L1 L2L2 L2L2 L3L3 L4L4 L5L5 S1S1 S2S2 S3S3 S4S4 S5S5 Co 1 Radial nerve Ulnar nerve Median nerve Iliohypogastric nerve Ilioinguinal nerve Lateral femoral cutaneous nerve Genitofemoral nerve Femoral nerve Obturator nerve Gluteal nerves Superior Inferior Pudendal nerve Saphenous nerve Sciatic nerve

© 2015 Pearson Education, Inc 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)

© 2015 Pearson Education, Inc. Figure The Cervical Plexus (Part 1 of 2). Cranial Nerves Nerve Roots of Cervical Plexus Accessory nerve (N XII) Hypoglossal nerve (N XII) C2C2 C1C1 C3C3 C4C4 C5C5 Clavicle

© 2015 Pearson Education, Inc. Figure The Cervical Plexus (Part 2 of 2).

© 2015 Pearson Education, Inc. Figure The Cervical Plexus (Part 2 of 2).

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc 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)

© 2015 Pearson Education, Inc. Figure 13-11a The Brachial Plexus.

© 2015 Pearson Education, Inc. Figure 13-11a The Brachial Plexus.

© 2015 Pearson Education, Inc. Figure 13-11b The Brachial Plexus.

© 2015 Pearson Education, Inc. Figure 13-11b The Brachial Plexus.

© 2015 Pearson Education, Inc. Figure 13-11b The Brachial Plexus.

© 2015 Pearson Education, Inc. Figure 13-11b The Brachial Plexus.

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc. Figure 13-12a The Lumbar and Sacral Plexuses.

© 2015 Pearson Education, Inc. Figure 13-12a The Lumbar and Sacral Plexuses.

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc. Figure 13-12b The Lumbar and Sacral Plexuses. Superior Gluteal Sacral Plexus Spinal Segments Nerve and Distribution L 4 –S 2 Gluteus minimus, gluteus medius, and tensor fasciae latae muscles Sacral plexus, anterior view b Nerve Roots of Sacral Plexus The sacral plexus is formed by a branch from L 4 and ventral rami of L 5 –S 4. L4L4 Inferior Gluteal Posterior Femoral Cutaneous Sciatic Pudendal L 4 –S 2 L 4 –S 3 S 1 –S 3 S 2 –S 4 Gluteus maximus muscle Skin over perineum and posterior thigh and leg Semimembranosus, semitendinosus, and adductor magnus muscles; branches into tibial and fibular nerves Muscles of the perineum; skin over external genitalia, bulbospongiosus and ischiocavernosus muscles L5L5 Sacrum Lumbosacral trunk L5L5 S1S1 S2S2 S3S3 S4S4 S5S5 Co 1

© 2015 Pearson Education, Inc. Figure 13-12c The Lumbar and Sacral Plexuses. Nerves of the lumbar and sacral plexuses, anterior view c 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

© 2015 Pearson Education, Inc. Figure 13-12d The Lumbar and Sacral Plexuses. Nerves of the sacral plexus, posterior view d Inferior gluteal nerve Common fibular nerve Sural nerve Tibial nerve Pudendal nerve Posterior femoral cutaneous nerve Sciatic nerve Superior gluteal nerve

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc Neuronal Pools 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

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc. Figure 13-13a Neural Circuits: The Organization of Neuronal Pools. a Divergence A mechanism for spreading stimulation to multiple neurons or neuronal pools in the CNS

© 2015 Pearson Education, Inc. Figure 13-13b Neural Circuits: The Organization of Neuronal Pools. b Convergence A mechanism for providing input to a single neuron from multiple sources

© 2015 Pearson Education, Inc. Figure 13-13c Neural Circuits: The Organization of Neuronal Pools. c Serial processing A mechanism in which neurons or pools work sequentially

© 2015 Pearson Education, Inc. Figure 13-13d Neural Circuits: The Organization of Neuronal Pools. Parallel processing d A mechanism in which neurons or pools process the same information simultaneously

© 2015 Pearson Education, Inc. Figure 13-13e Neural Circuits: The Organization of Neuronal Pools. e Reverberation A positive feedback mechanism

© 2015 Pearson Education, Inc Reflexes Reflexes Automatic responses coordinated within spinal cord Through interconnected sensory neurons, motor neurons, and interneurons Produce simple and complex reflexes

© 2015 Pearson Education, Inc 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)

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc. Figure Spinal Reflexes (Part 1 of 4). Arrival of stimulus and activation of receptor Activation of a sensory neuron Dorsal root Sensation relayed to the brain by axon collaterals Spinal cord Receptor Stimulus Effector Response by a peripheral effector Activation of a motor neuron Ventral root REFLEX ARC KEY Sensory neuron (stimulated ) Excitatory interneuron Motor neuron (stimulated) Information processing in the CNS

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc Reflexes Development of Reflexes Innate reflexes Basic neural reflexes Formed before birth Acquired reflexes Rapid, automatic Learned motor patterns

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc Reflexes Sites of Information Processing Spinal reflexes Occur in spinal cord Cranial reflexes Occur in brain

© 2015 Pearson Education, Inc. Figure The Classification of Reflexes. Learned Control skeletal muscle contractions Include superficial and stretch reflexes One synapse Spinal Reflexes Cranial Reflexes Monosynaptic Polysynaptic Somatic Reflexes Visceral (Autonomic) Reflexes Innate Reflexes Acquired Reflexes Reflexes can be classified by developmentresponsecomplexity of circuitprocessing site Control actions of smooth and cardiac muscles, glands, and adipose tissue Multiple synapses (two to several hundred) Processing in the brain Genetically determined Processing in the spinal cord

© 2015 Pearson Education, Inc Spinal Reflexes Spinal Reflexes Range in increasing order of complexity Monosynaptic reflexes Polysynaptic reflexes Intersegmental reflex arcs Many segments interact Produce highly variable motor response

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc. Figure Spinal Reflexes (Part 2 of 4). Response REFLEX ARC Stimulus Stretch Receptor (muscle spindle) Contraction Effector Spinal cord Sensory neuron (stimulated) Motor neuron (stimulated) KEY

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc. Figure A Muscle Spindle. Extrafusal fiber Sensory region Intrafusal fiber Muscle spindle Gamma efferent from CNS To CNS

© 2015 Pearson Education, Inc Spinal Reflexes Postural Reflexes Stretch reflexes Maintain normal upright posture Stretched muscle responds by contracting Automatically maintains balance

© 2015 Pearson Education, Inc Spinal Reflexes Polysynaptic Reflexes More complicated than monosynaptic reflexes Interneurons control more than one muscle group Produce either EPSPs or IPSPs

© 2015 Pearson Education, Inc Spinal Reflexes The Tendon Reflex Prevents skeletal muscles from: Developing too much tension Tearing or breaking tendons Sensory receptors unlike muscle spindles or proprioceptors

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc. Figure Spinal Reflexes (Part 3 of 4). Painful stimulus Flexors stimulated Extensors inhibited Distribution within gray horns to other segments of the spinal cord

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc. Figure Spinal Reflexes (Part 4 of 4). Flexors stimulated Extensors inhibited Flexors inhibited Extensors stimulated Painful stimulus Sensory neuron (stimulated) Excitatory interneuron Motor neuron (stimulated) Motor neuron (inhibited) Inhibitory interneuron KEY To motor neurons in other segments of the spinal cord

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc 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

© 2015 Pearson Education, Inc The Brain Can Alter Spinal Reflexes The Babinski Reflexes Normal in infants May indicate CNS damage in adults

© 2015 Pearson Education, Inc. Figure 13-17a The Babinski Reflexes. a The plantar reflex (negative Babinski reflex), a curling of the toes, is seen in healthy adults.

© 2015 Pearson Education, Inc. Figure 13-17b The Babinski Reflexes. b The Babinski sign (positive Babinski reflex) occurs in the absence of descending inhibition. It is normal in infants, but pathological in adults.