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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 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. 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 13-3a 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 13-3b The Spinal Cord and Spinal Meninges Meninges ANTERIOR Subarachnoid space Dura mater Arachnoid mater Pia mater Vertebral body 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 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. 13-3 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 • 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 13-5a The Sectional Organization of the Spinal Cord Posterior white column Dorsal root ganglion Lateral white column Posterior gray horn Lateral gray horn Anterior 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 13-5a The Sectional Organization of the Spinal Cord Posterior median sulcus Posterior gray commissure 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. Somatic Visceral Visceral Sensory nuclei Motor nuclei Somatic 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. 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 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 C2C3 NV C2C3 C2 C3 T2 C6 L1 L2 C8 C7 T1 L3 L4 L5 C3 C4 C5 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 L1 L2 L4 L3 L5 C4 C5 T2 C6 T1 C7 SS S2 4 3 L1 S5 C8 S1 L5 L2 S2 L3 S1 L4 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. 13-5 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. 13-6 Reflexes • 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 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 • 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 KEY Sensory neuron (stimulated) Motor neuron (stimulated) Response © 2012 Pearson Education, Inc. 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. 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) 13-8 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 • The Babinski Reflexes • Normal in infants • May indicate CNS damage in adults © 2012 Pearson Education, Inc. Figure 13-21a The Babinski Reflexes The plantar reflex (negative Babinski reflex), a curling of the toes, is seen in healthy adults. © 2012 Pearson Education, Inc. Figure 13-21b 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.