Ch 13-14 Spinal Nerves & Brain Structure - Mulhern PDF

Figure 13-1 An Overview of Chapters 13 and 14. CHAPTER 14: The Brain Sensory input Motor output over cranial over cranial nerves Reflex nerves Effectors...

Figure 13-1 An Overview of Chapters 13 and 14. CHAPTER 14: The Brain Sensory input Motor output over cranial over cranial nerves Reflex nerves Effectors Sensory centers in Muscles receptors brain CHAPTER 13: The Spinal Cord Glands Sensory input Motor output over Reflex over spinal nerves spinal nerves Sensory centers in receptors spinal cord Adipose tissue  13-2 The Spinal Cord ▪ Spinal cord – Housed within: Protective membranes (meninges) Vertebral column – Carries sensory and motor information between brain and most other parts of body – Gives rise to spinal nerves 2 © 2018 Pearson Education, Inc.  13-2 The Spinal Cord ▪ Gross anatomy of the spinal cord – From brain only to vertebrae L1 and L2 Stops lengthening around age 4 vertebral column still grows – 4 regions: Cervical, thoracic, lumbar, sacral – Bilateral symmetry – 31 segments Give rise to spinal nerves – Grooves divide spinal cord into left and right Posterior median sulcus Anterior median fissure (deeper groove) ▪ Central canal contains cerebrospinal fluid (CSF) 3 © 2018 Pearson Education, Inc. Figure 13-2 Gross Anatomy of the Adult Spinal Cord. Posterior median sulcus C3 Dorsal root Cervical enlargement - Nerves Dorsal root ganglion White matter of shoulders and upper limbs Gray C1 matter Central canal C2 Cervical spinal C3 Lumbar enlargement - Nerves nerves C4 C5 Spinal Ventral C6 of pelvis and lower limbs C7 Cervical enlargement nerve root Anterior median fissure C8 T1 CSF fills the central T2 T3 T4 canal; acts as shock T5 T6 absorber and T7 exchange of material Thoracic T8 Posterior spinal T9 median sulcus nerves KEY Spinal cord regions = Cervical T10 T3 = Thoracic T11 Lumbar enlargement = Lumbar T12 = Sacral L1 Conus medullaris L2 Conus medullaris Lumbar L3 Inferior tip of spinal cord Thin, conical spinal cord spinal L4 Cauda equina nerves below lumbar enlargement L5 L1 More Gray matter Cauda equina Sacral spinal nerves S1 S2 (“enlargements”) = Nerve roots extending S3 S4 dedication to sensory below conus medullaris S5 Coccygeal Filum terminale S2 and motor control nerve (Co1) (in coccygeal ligament) b Inferior views of cross sections through representative segments of the spinal cord, showing the arrangement of gray matter and white matter. a 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 L1–L2; the spinal segments found at representative locations are indicated in the cross sections. Figure 13-2 Gross Anatomy of the Adult Spinal Cord (Part 4 of 4). Cauda equina Nerve roots extending below conus medullaris Inferior Filum terminale tip of spinal Thin thread of fibrous tissue at cord end of conus medullaris Cauda equina Attaches to coccygeal ligament S1 Sacral spinal nerves S2 S3 S4 S5 Filum terminale S2 Coccygeal nerve (Co1) (in coccygeal ligament) b Inferior views of cross sections through representative segments of the spinal cord, showing the arrangement of gray matter and white matter. a 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 L1– L2; the spinal segments found at representative locations are indicated in the cross sections. Naming of Segments Cervical nerves named based on the cervical vertebrae immediately inferior to it. Thoracic, lumbar ad sacral nerves named based on the vertebrae immediately superior to it. © 2013 Pearson Education, Inc. https://radiopaedia.org/articles/spinal-cord?lang=us  13-2 The Spinal Cord ▪ Spinal nerves – Formed by union of posterior and anterior roots – Pairs—one from each side at each vertebral level – Each has a white ramus communicans and a gray ramus communicans that innervate glands and smooth muscle – Mixed nerves—contain both afferent and efferent fibers – Each spinal nerve quickly divides into rami: Posterior ramus supplies skin/muscles of back Anterior ramus supplies most of body wall, skin, limbs 7 © 2018 Pearson Education, Inc. Figure 13–2c Gross Anatomy of the Adult Spinal Cord. 8 © 2018 Pearson Education, Inc. Figure 13-3a The Spinal Cord and Spinal Meninges. White matter Gray matter Ventral rootlets of spinal nerve Dorsal root ganglion Ventral root Spinal nerve Dorsal root Dorsal rootlets of Meninges Dorsal spinal nerve Pia mater - sensory Arachnoid mater Ventral Dura mater - control somatic and visceral effectors intervertebral foramen a A posterior view of the Pedicle spinal cord, showing the meningeal layers, superficial landmarks, and distribution Every segment has pair of spinal of gray matter and white matter ganglia, that contain cell bodies of sensory neurons. Figure 13-3b The Spinal Cord and Spinal Meninges. White Rami- myelinated axons Meninges Gray Rami- unmyelinated; nerves for glands and smooth muscles Dura mater Arachnoid mater ANTERIOR Pia mater Subarachnoid space Vertebral body Autonomic (sympathetic) ganglion Rami communicantes Ventral root of spinal nerve Ventral ramus Dorsal Spinal cord ramus Adipose tissue Denticulate Dorsal root in epidural space ligament ganglion POSTERIOR b A sectional view through the spinal cord and meninges, showing the relationship of the meninges, spinal cord, and spinal nerves 13-2 Spinal Cord Spinal Meninges – Specialized membranes isolate spinal cord from surroundings Including bony walls of vertebral column – Functions of the spinal meninges include: Protecting spinal cord – Physical stability and shock absorption Provide blood supply Continuous with cranial meninges – Meningitis Viral or bacterial infection of meninges 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  13-2 Spinal Cord Dura Mater – Tough and fibrous collagen – 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 Longitudinal stability 13-2 Spinal Cord Arachnoid Mater – Middle meningeal layer – Arachnoid membrane Simple squamous epithelia Pia Mater – Innermost meningeal layer – Mesh of collagen and elastic fibers – Bound to underlying neural tissue Note: Subarachnoid space contains CSF. 13-2 Spinal Cord – The epidural space Between spinal dura mater and walls of vertebral canal Contains loose connective and adipose tissue Anesthetic injection site 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) Site for lumbar punctures 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 – Why lumbar region? 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 Provide nutrients/oxygen and waste exchange 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 Figure 13-3b The Spinal Cord and Spinal Meninges. Meninges Dura mater Arachnoid mater ANTERIOR Pia mater Subarachnoid space Vertebral body Autonomic (sympathetic) ganglion Rami communicantes Ventral root of spinal nerve Ventral ramus Dorsal Spinal cord ramus Adipose tissue Denticulate Dorsal root in epidural space ligament ganglion POSTERIOR b A sectional view through the spinal cord and meninges, showing the relationship of the meninges, spinal cord, and spinal nerves © 2013 Pearson Education, Inc.  13-3 Gray Matter and White Matter ▪ Functional organization of gray matter – Masses of gray matter within CNS are called nuclei and are organized into regions called horns Posterior horns – Somatic and visceral sensory nuclei Incoming information from receptors Anterior horns – Somatic motor nuclei Outgoing information to effectors Lateral horns – Thoracic and lumbar segments Visceral motor nuclei 22 © 2018 Pearson Education, Inc.  13-3 Gray Matter and White Matter ▪ Structural organization of white matter – Three columns Posterior white columns – between posterior horns and posterior median sulcus Anterior white columns – between anterior horns and anterior median fissure – Anterior white commissure—where axons cross from one side of spinal cord to the other Lateral white columns – on each side of spinal cord, between anterior and posterior columns 23 © 2018 Pearson Education, Inc.  13-3 Gray Matter and White Matter ▪ Functional organization of white matter – Tract—bundle of axons in CNS Relay same type of information in same direction Ascending tracts—sensory information up toward the brain Descending tracts—motor commands down to the spinal cord 24 © 2018 Pearson Education, Inc. 13.3 Gray and White Matter Organization “commissures”- bridge posterior and anterior sides to central canal. “Tracts” - bundles of axons in white matter in CNS; ascending and descending Posterior Posterior Posterior gray white column median sulcus commissure Functional Organization of Gray Matter From posterior root The cell bodies of neurons in the gray matter of the spinal cord are organized into functional groups called nuclei. Posterior Somatic horn Sensory nuclei (Up to brain) Lateral Visceral Spinal Lateral horn white Visceral ganglion column Anterior Motor nuclei (Down spinal cord) horn Somatic To anterior root Anterior root Anterior gray commissure Anterior white commissure Anterior white column 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 horns. The red arrows represent sensory input from the posterior root and motor output to the anterior root. Lateral horn only in thoracic/lumbar sections of spinal cord; controls visceral motor nuclei 25 13-4 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 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 Figure 13-6a A Peripheral Nerve. Blood vessels Connective Tissue Layers Epineurium covering peripheral nerve Perineurium (around one fascicle) Endoneurium Schwann cell Myelinated axon Fascicle a A typical peripheral nerve and its connective tissue wrappings  13-4 Spinal Nerves and Plexuses ▪ Spinal nerves – Pair of spinal nerves emerges laterally from each spinal cord segment – Form by junction of anterior and posterior roots – All are mixed nerves ▪ Peripheral nerves – Form from branching and re-sorting of spinal nerves. – All are mixed nerves (sensory and motor) – Same connective tissue layers as spinal nerves (continuous with each other) 29 © 2018 Pearson Education, Inc. 13-4 Spinal Nerves and Plexuses Peripheral Distribution of Spinal Nerves Motor nerves – Distribute motor commands from motor nuclei to thoracic/ lumbar segments of spinal cord. – Rami Communicantes: White ramus – Carries visceral motor fibers – To sympathetic ganglion of autonomic nervous system Gray ramus – Unmyelinated nerves – From sympathetic ganglion 13-4 Spinal Nerves and Plexuses Motor nerves cont. – Dorsal ramus Contains somatic and visceral motor fibers Innervates the back – Ventral ramus Larger branch Innervates ventrolateral structures and limbs Figure 13-8 Peripheral Distribution of Spinal Nerves (Part 1 of 2). From interoceptors of From exteroceptors, 4 Sensory Info back proprioceptors of back The dorsal root of each spinal nerve carriers 3 sensory information to the The dorsal ramus carries sensory spinal cord. information from the skin and skeletal muscles of the back. Somatic sensory nuclei 2 The ventral ramus carries sensory information from the ventrolateral body surface, structures in the body, wall, and the limbs. Dorsal root From exteroceptors, ganglion proprioceptors of body wall, limbs From interoceptors of body wall, limbs Rami communicantes Visceral sensory Ventral root nuclei KEY = Somatic sensations (eyes, ears, tongue, skin) 1 = Visceral The sympathetic nerve carriers sensations sensory information from the From interceptors of (internal organs) visceral organs. visceral organs Figure 13-8 Peripheral Distribution of Spinal Nerves (Part 2 of 2). Postganglionic fibers to Motor Commands To skeletal muscles of back smooth muscles, glands, etc., of back 2 The spinal nerve forms just lateral to the intervertebral 3 foramen, where the dorsal and The dorsal ramus contains somatic ventral roots unite. motor and visceral motor fibers that innervate the skin and skeletal muscles Dorsal root of the back. Dorsal root ganglion 4 The axons in the relatively large 1 ventral ramus supply the The ventral root of each spinal nerve ventrolateral body surface, contains the axons of somatic motor structures in the body wall, and and visceral motor neurons. the limbs. Visceral motor nuclei To skeletal muscles of body wall, limbs Somatic motor nuclei Rami communicantes Postganglionic fibers to KEY smooth muscles, and = Somatic motor commands glands of body wall, limbs Sympathetic ganglion = Visceral motor commands 5 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 Postganglionic fibers to branch has a light color and is therefore known as the white ramus. smooth muscles, White rami are only found between T1 and L2. glands, visceral organs in thoracic cavity 7 A sympathetic nerve 6 contains preganglionic and The gray ramus communicans contains preganglionic fibers that Preganglionic fibers to postganglionic fibers innervate glands and smooth muscles in the sympathetic ganglia innervating structures in the body wall or limbs. These fibers are unmyelinated and have innervating thoracic cavity. abdominopelvic viscera 1 a dark gray color. Gray rami are associated with each spinal nerve. 13-4 Spinal Nerves and Plexuses Peripheral Distribution of Spinal Nerves – Sensory nerves Sensory information from periphery sensors and delivers them to the sensory nuclei in spinal cord (lumbar and thoracic) In addition to motor impulses: – Dorsal, ventral, and white rami also carry sensory information – Dermatomes Specific bilateral region of skin Monitored by specific pair of spinal nerves Figure 13-7 Dermatomes. NV Peripheral neuropathies —regional losses of neural Dermatomes C2–C3 C2 function that affect C3 C3 dermatomes, often from C4 C5 T2 C4 nerve trauma, T3 T1 T2 T4 compression, various T5 C5 T3 T4 T6 illnesses T7 T5 T8 T6 T9 T2 T2 T7 T10 T11 T8 T9 T12 C6 Shingles—rash/symptoms L1 T10 L2 T1 occur along dermatomes T11 L4 L3 C7 C6 T12 L5 L1 S4 S 3 L2 S2 C8 L3 C8 T1 L1 S5 C7 S1 L5 L4 L2 S2 KEY L5 L3 Spinal cord regions = Cervical = Thoracic S1 = Lumbar = Sacral L4 ANTERIOR POSTERIOR 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 Note: ONLY anterior rami form plexus – Control skeletal muscles of the neck and limbs 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 Figure 13-9 Peripheral Nerves and Nerve Plexuses (Part 1 of 2). C1 Lesser occipital nerve C2 Great auricular nerve Cervical C3 Transverse cervical nerve plexus C4 C5 Supraclavicular nerve C6 C7 Phrenic nerve Brachial C8 plexus T1 T2 T3 Axillary nerve T4 T5 T6 T7 Musculocutaneous T8 nerve T9 Thoracic nerves T10 T11 Figure 13-9 Peripheral Nerves and Nerve Plexuses (Part 2 of 2). T12 L1 Radial nerve Lumbar L2 plexus Ulnar nerve L3 L4 Median nerve L5 S1 Iliohypogastric Sacral nerve S2 plexus S3 S4 Ilioinguinal nerve S5 Co1 Lateral femoral cutaneous nerve Genitofemoral nerve Femoral nerve Obturator nerve Superior Gluteal nerves Inferior Pudendal nerve Saphenous nerve Sciatic nerve 13-4 Spinal Nerves and Plexuses The Cervical Plexus – Includes ventral rami of spinal nerves C1–C5 – Innervates neck, thoracic cavity, diaphragmatic muscles – Major nerve Phrenic nerve – controls diaphragm – “C3, C4, C5 keeps the diaphragm alive” 13-4 Spinal Nerves and Plexuses The Brachial Plexus – Includes ventral rami of spinal nerves C5–T1 – Innervates pectoral girdle and upper limbs – Nerves that form brachial plexus originate from: Superior, middle, and inferior trunks* Lateral, medial, and posterior cords Smaller branches (few) that originate at trunks – Naming based on position to axillary artery Figure 13-11b The Brachial Plexus. Randy Travis Drinks Cold Beer 13-4 Spinal Nerves and Plexuses The Brachial Plexus Carpal tunnel syndrome: compression of Median nerve. – Major nerves Musculocutaneous nerve – Biceps area Median nerve – Flexor muscles, thumb movement; carpel tunnel syndrome Ulnar nerve – opening/closing fingers; “funny bone” Axillary nerve – deltoids, raising arms Radial nerve – triceps, hand/forearm movement Mnemonic 13-4 Spinal Nerves and Plexuses The Lumbar Plexus – Includes ventral rami of spinal nerves T12–L4 – Major nerves Genitofemoral nerve Lateral femoral cutaneous nerve Femoral nerve Figure 13–12a The Lumbar and Sacral Plexuses Nerve Roots of Lumbar Plexus T12 subcostal nerve Lumbar Plexus Spinal The lumbar Segments Nerve and Distribution T12 plexus is formed by the anterior Iliohypogastric rami of T12 – L4. T12–L1 External and internal oblique and transverse abdominis; L1 T12 skin over the inferior abdomen and buttocks L1 Ilio-inguinal L2 L2 L1 Abdominal muscles (with iliohypogastric nerve); skin over superior, medial thigh and portions of external genitalia L3 Genitofemoral L3 L1–L2 Skin over anteromedial thigh and portions of external genitalia Lateral Femoral Cutaneous L4 L4 L2–L3 Skin over anterior, lateral, and posterior thigh Femoral L2–L4 Quadriceps femoris, sartorius, pectineus, and iliopsoas; skin of L5 the anteromedial thigh, and medial surface of the leg and foot Lumbosacral trunk Obturator L2–L4 Gracilis, and adductor magnus, brevis and longus; skin from the medial surface of the thigh a Lumbar plexus, anterior view 45 See notes for mnemonic 13-4 Spinal Nerves and Plexuses The Sacral Plexus – Includes ventral rami of spinal nerves L4–S4 – Major nerves Pudendal nerve – muscles in pelvic region; genitals and waste excretion Sciatic nerve – muscles and sensations in legs – Largest in body – Two branches of the sciatic nerve 1. Fibular nerve – anterior/lateral muscles of lower legs 2. Tibial nerve – motor and sensory for posterior leg and foot Figure 13-12b The Lumbar and Sacral Plexuses. Lumbosacral trunk Nerve Roots of Sacral Plexus Sacral Plexus L4 The sacral plexus is formed by a branch Spinal from L4 and ventral Segments Nerve and Distribution rami of L5–S4. Superior Gluteal L5 L4–S2 Gluteus minimus, gluteus medius, and tensor fasciae latae L5 muscles Inferior Gluteal S1 L4–S2 Gluteus maximus muscle S2 Posterior Femoral Cutaneous Sacrum S3 S1–S3 Skin over perineum and posterior thigh and leg S4 Sciatic L4–S3 Semimembranosus, semitendinosus, and adductor magnus muscles; branches into tibial and fibular nerves S5 Pudendal Co1 S2–S4 Muscles of the perineum; skin over external genitalia, bulbospongiosus and ischiocavernosus muscles b Sacral plexus, anterior view Figure 13-12c 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 c Nerves of the lumbar and sacral plexuses, anterior view Figure 13-12d 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 d Nerves of the sacral plexus, posterior view  Saphenous Sural Nerve nerve – Mapping touch/pain Sural nerve perception and checking Fibular nerve muscle function – can determine damage to specific peripheral nerves Tibial nerve Saphenous Sural nerve nerve Saphenous Sural nerve nerve Fibular Tibial Sural nerve used in nerve grafts. nerve nerve 50  Basic Concepts of Neural Integration Neurons function in groups – Sensory, motor, or interneurons Groups contribute to broader neural functions Billions of nerves must be integrated Functional groups of neurons = neuronal pools – Integrate incoming information received from receptors or other neuronal pools – Forward processed info to other destinations – Each has limited input sources output destinations © 2013 Pearson Education, Inc. 13-5 Neuronal Pools 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 4. Parallel processing Moves same information along several paths simultaneously 5. Reverberation Positive feedback mechanism Functions until inhibited Figure 13-13a Neural Circuits: The Organization of Neuronal Pools. Diverging Circuit One input, many outputs An amplifying circuit Examples: A single neuron in the brain can activate 100+ motor neurons in the spinal cord and 1,000s of skeletal muscle fibers Visual information to adjust posture and balance Figure 13-13b Neural Circuits: The Organization of Neuronal Pools. Convergence Circuit Many inputs, one output Concentrating circuit to illicit the same response Examples: Different sensory stimuli can all elicit the same memory Diaphragm can be subconsciously or consciously controlled Figure 13-13c Neural Circuits: The Organization of Neuronal Pools. Serial Processing Sequential, one-to-one processing Stimulus always causes same response Occurs over pathways called reflex arches Examples Spinal reflexes Rapid, automatic responses to stimuli Pain sensation Figure 13-13d Neural Circuits: The Organization of Neuronal Pools. Parallel Processing 2+ neurons detect a stimuli at the same time Multiple (divergent) responses occur at the same time Examples: A sensed smell may remind one of an odor and any associated experiences Stepping on a Lego Figure 13-13e Neural Circuits: The Organization of Neuronal Pools. Reverberation Signal travels through a chain of neurons, each feeding back to previous neurons Positive feedback loop An oscillating circuit Controls rhythmic activity Examples: Breathing Sleep-wake cycle (consciousness) Repetitive motor activities such as walking Patterns of Neural Processing: Serial Processing Input travels along one pathway to a specific destination Produces specific, anticipated response Works all-or-none manner Occurs over pathways called reflex arcs: Five components – Receptor – sensory neuron – CNS integration center – Motor neuron – Effector  Figure 11.24 A simple reflex arc. Stimulus 1 Receptor Interneuron 2 Sensory neuron 3 Integration center 4 Motor neuron 5 Effector Spinal cord (CNS) Response © 2013 Pearson Education, Inc. 13-6 Reflexes Reflex Arc – “Wiring” of a single reflex – Generally, opposes original stimulus (negative feedback) Neuronal Reflexes – Basic building blocks of neural function* – One neural reflex produces one set of motor response – Goal to maintain homeostasis 13-6 Reflexes Reflexes – Automatic responses coordinated within spinal cord Through interconnected sensory, motor, and inter-neurons – Produce simple and complex reflexes Sites of Information Processing – Spinal reflexes Occur in spinal cord – Cranial reflexes Occur in brain  Events of a Reflex Arch 1 2 Dorsal root Arrival of Activation of a Sensation stimulus and sensory neuron relayed to the activation of brain by axon receptor collaterals Spinal cord 3 Information REFLEX processing in Receptor ARC the CNS Stimulus 5 Response by a peripheral effector Effector Ventral root KEY 4 Sensory neuron Activation of a motor (stimulated) neuron Excitatory interneuron Motor neuron (stimulated) Figure 13-14 Spinal Reflexes (Part 1 of 4). SmartArt Video: The Reflex Arc 63 Four Classifications of Reflexes By: 1. Early development - Innate or acquired 2. Type of motor response - Visceral or somatic 3. Complexity of neural circuit - Monosynaptic or polysynaptic 4. Site of information processing - Brain or spinal cord Figure 13–15 The Classification of Reflexes Reflexes can be classified by Development Response Complexity of Circuit Processing Site Innate Reflexes Somatic Reflexes Monosynaptic Spinal Reflexes Genetically Control skeletal muscle contractions One synapse Processing in determined Include superficial and stretch reflexes the spinal cord Acquired Reflexes Visceral (Autonomic) Reflexes Polysynaptic Cranial Reflexes Learned Control actions of smooth and Multiple synapses Processing in cardiac muscles, and glands (two to several hundred) the brain Examples: Babies sucking/rooting vs. driving (Development) Walking along a cliff vs. digestion (Response) 65 Note: we can control some reflexes 13-7 Spinal Reflexes In increasing order of complexity: Monosynaptic reflexes – Most rapid motor responses – Sensory neuron directly activates motor neuron Polysynaptic reflexes – More complicated than monosynaptic reflexes – Interneurons control more than one muscle group – Produce either EPSPs or IPSPs Intersegmental reflex arcs – Many segments interact – Produce highly variable motor response  Monosynaptic Reflexes Ex. Stretch reflex (Such as patellar reflex) Receptor Stretch (muscle Spinal cord spindle*) Stimulus REFLEX ARC Contraction Effector Response - Automatic regulation of muscle lengths - Have least delay between sensory input and motor output - Completed in 20–40 msec - Receptor is muscle spindle Figure 13-14 Spinal Reflexes (Part 2 of 4). 13-7 Spinal Reflexes Postural Reflexes – Stretch reflexes and polysynaptic reflexes – Maintain normal upright posture Back and abdomen muscles, etc. – Stretched muscle responds by contracting Automatically maintains balance 13-7 Spinal Reflexes The Tendon Reflex Polysynaptic reflex Produces muscle relaxation (lengthening) in response to tension Sensory receptor – Tendon Organ Prevents skeletal muscles from: – Developing too much tension – Tearing or breaking tendons  Withdrawal Reflexes Example: Move body part away from stimulus due Flexor reflex to pain or pressure Pulls hand away from hot stove Polysynaptic reflex Strength and extent of response depend on intensity and location of stimulus Distribution within gray horns to other segments of the spinal cord Painful stimulus Flexors stimulated Extensors inhibited Reciprocal Inhibition For flexor reflex to work, the stretch reflex of antagonistic (extensor) muscle must be inhibited (reciprocal inhibition) by interneurons in spinal cord. 13-7 Spinal Reflexes Reflex Arcs Ipsilateral reflex arcs – Occur on same side of body as stimulus Ex: Stretch, tendon, and withdrawal reflexes Contralateral reflex arc – Occur on side opposite stimulus Ex: Crossed extensor reflexes Crossed Extensor Reflexes Polysynaptic reflex Occur simultaneously and coordinated with flexor reflex Ex: stepping on a lego To motor neurons in other segments of the spinal cord Flexor reflex causes leg to pull up Crossed extensor reflex straightens other leg to receive body weight Maintained by reverberating circuits Extensors inhibited Flexors stimulated Extensors stimulated Flexors inhibited KEY Sensory neuron Motor neuron (stimulated) (inhibited) Excitatory Inhibitory interneuron interneuron Motor neuron (stimulated) Painful stimulus  Figure 13.20 The crossed-extensor reflex. Interneurons + + Afferent Efferent fiber fibers Efferent fibers Extensor Flexor inhibited inhibited xes Flexor Fle Arm movements Extensor stimulated stimulated s end Ext Site of stimulus: Site of reciprocal A noxious stimulus activation: At the causes a flexor same time, the reflex on the same extensor muscles side, withdrawing on the opposite that limb. side are activated. + Excitatory synapse – Inhibitory synapse © 2013 Pearson Education, Inc. 13-7 Spinal Reflexes ▪ Five general characteristics of polysynaptic reflexes 1. Involve pools of interneurons May cause excitation or inhibition 2. Involve more than one spinal segment Can activate muscles in multiple areas 3. Involve reciprocal inhibition Coordinates contractions and reduces resistance 4. Have reverberating circuits Prolongs reflexive motor response 5. Several reflexes may cooperate To produce coordinated, controlled response 74 13-8 The Brain Can Alter Spinal Reflexes Voluntary Movements use Reflex Motor Patterns – Higher centers of brain incorporate lower, reflexive motor patterns* – Automatic spinal reflexes: Can be activated by brain, as needed Use fewer nerve impulses to control complex motor functions – Ex: Walking, running, jumping Integration and Control of Spinal Reflexes – Spinal reflexes are automatic but processing centers in brain can facilitate or inhibit them 13-8 The Brain Can Alter Spinal Reflexes Reinforcement of Spinal Reflexes – Higher centers reinforce by: Stimulating excitatory neurons in brain stem or spinal cord Creating EPSPs at reflex motor neurons Facilitating postsynaptic neurons – Note: reflex stimuli are more sensitive and cannot be consciously controlled. 13-8 The Brain Can Alter Spinal Reflexes Inhibition of Spinal Reflexes – Higher centers inhibit by: Stimulating inhibitory neurons Creating IPSPs at reflex motor neurons Suppressing postsynaptic neurons – Increases amount of stimulus needed to initiate a reflex response  The Plantar and Babinski Reflexes Normal in infants May indicate CNS damage in adults Example of inhibition of a reflex a The plantar reflex (negative Babinski reflex), a curling of the toes, is seen in healthy adults. Figure 13-17a The Babinski Reflexes. Ch 14: The Brain Regions and Organization Adult brain regions: 1. Cerebral hemispheres (cerebrum) 2. Diencephalon 3. Brain stem Midbrain Pons Medulla 4. Cerebellum © 2013 Pearson Education, Inc. Ventricles of the Brain Paired, C-shaped lateral ventricles in cerebral hemispheres – Separated anteriorly by septum pellucidum Third ventricle in diencephalon Fourth ventricle in brainstem © 2013 Pearson Education, Inc.  Figure 12.3 Ventricles of the brain. Lateral ventricle Anterior horn Posterior Septum horn pellucidum Interventricular foramen Inferior horn Third ventricle Inferior horn Lateral Cerebral aqueduct Median aperture aperture Fourth ventricle Lateral aperture Central canal Anterior view Left lateral view © 2013 Pearson Education, Inc. Cerebral Hemispheres Five lobes – Frontal – Parietal – Temporal – Occipital – Insula © 2013 Pearson Education, Inc.  Figure 12.4d Lobes, sulci, and fissures of the cerebral hemispheres. Central Frontal lobe sulcus Gyri of insula Temporal lobe (pulled down) © 2013 Pearson Education, Inc. Location of the insula lobe Cerebral Hemispheres Surface markings – Ridges (gyri) – Shallow grooves (sulci) – Deep grooves (fissures) – Longitudinal fissure Separates two hemispheres – Transverse cerebral fissure Separates cerebrum and cerebellum © 2013 Pearson Education, Inc.  Gyrus Sulcus © 2013 Pearson Education, Inc. Cerebral Hemispheres Central sulcus – Separates precentral gyrus of frontal lobe and postcentral gyrus of parietal lobe Parieto-occipital sulcus – Separates occipital and parietal lobes Lateral sulcus – Outlines temporal lobes © 2013 Pearson Education, Inc.  Figure 12.4c Lobes, sulci, and fissures of the cerebral hemispheres. Central Precentral sulcus Postcentral gyrus gyrus Frontal lobe Parietal lobe Parieto-occipital sulcus (on medial surface of hemisphere) Lateral sulcus Occipital lobe Temporal lobe Transverse cerebral fissure Cerebellum Pons Medulla oblongata Fissure Spinal cord (a deep sulcus) Gyrus Cortex (gray matter) Sulcus White matter Lobes and sulci of the cerebrum © 2013 Pearson Education, Inc. Cerebral Hemispheres Three basic regions – White matter - internal – Cerebral cortex - superficial gray matter – Basal nuclei - deep within white matter © 2013 Pearson Education, Inc. 14-9 The Cerebrum White Matter of the Cerebrum Communication/transfer of info between and within hemispheres Three types: – Association fibers Connections within one hemisphere – Commissural fibers Bands of fibers connecting two hemispheres – Projection fibers Connect cerebrum with lower areas 14-9 The Cerebrum Association Fibers – Arcuate fibers Are short fibers Connect one gyrus to another – Longitudinal fasciculi Are longer bundles Connect frontal lobe to other lobes in same hemisphere 14-9 The Cerebrum ▪ White matter of the cerebrum – Commissural fibers Corpus callosum – 200 millions axons, 4 billion impulses/sec – Plays a role in problem solving, verbal processing, and executive performance Anterior commissure – Connects hemispheres to fornix – Olfactory and non-olfactory fibers – Mostly relays info to corpus callosum or hippocampus Decline with age 91 14-9 The Cerebrum ▪ White matter of the cerebrum – Projection fibers Link cerebral cortex to: – diencephalon, brainstem, cerebellum, and spinal cord Internal capsule – Collection of all ascending and descending projection fibers 92 Figure 14-14a Fibers of the White Matter of the Cerebrum. Fibers of the White Matter of the Cerebrum Fibers/Tracts Function Association fibers Interconnect cortical areas within the same hemisphere Arcuate fibers Interconnect gyri within a lobe a Lateral view Longitudinal fasciculi Interconnect the frontal lobe with other cerebral lobes  Figure 12.8a White fiber tracts of the cerebral hemispheres. Association fibers Longitudinal fissure (within hemisphere) Superior Commissural fibers Lateral (between hemispheres) ventricle Corpus callosum Basal nuclei Projection fibers Caudate (cerebral cortex Putamen to lower area) Globus Corona pallidus radiata Internal Thalamus capsule Gray matter Third White matter ventricle Pons Decussation Medulla oblongata (cross-over) Frontal section of pyramids © 2013 Pearson Education, Inc.  Cerebral Cortex Thin (2–4 mm) superficial layer of gray matter 40% mass of brain Site of conscious mind: – awareness, sensory perception, voluntary motor initiation, communication, memory storage, understanding © 2013 Pearson Education, Inc. 4 General Considerations of Cerebral Cortex 1. Lateralization of cortical function in hemispheres 2. Each hemisphere concerned with contralateral side of body – Each cerebral hemisphere receives sensory information from, and sends motor commands to, the opposite side of the body 3. Conscious behavior involves entire cortex in some way 4. Three types of functional areas I. Motor areas—control voluntary movement II. Sensory areas—conscious awareness of sensation III. Association areas—integrate diverse information © 2013 Pearson Education, Inc. 14-9 The Cerebrum Conscious thought, intellectual functions, awareness, memory, communication, sensory perception, etc. Left Hemisphere – Reading, writing, and math – Decision making – Speech and language – Premotor cortex for right-handed people – Dominant hemisphere for most people Right Hemisphere – Senses (touch, smell, sight, taste, feel) – Recognition (faces, voice inflections. i.e. tone) – Premotor cortex for left-handed people Figure 14-17 Hemispheric Lateralization (Part 1 of 2). Left Cerebral Hemisphere LEFT HAND Prefrontal cortex Speech center C O R P Writing U S C Auditory cortex A (right ear) L L O S General interpretive center U (language and mathematical M calculation) Visual cortex (right visual field) Figure 14-17 Hemispheric Lateralization (Part 2 of 2). Right Cerebral Hemisphere RIGHT HAND Prefrontal cortex Anterior commissure C O R P U S Analysis by touch C A Auditory cortex L (left ear) L O S U Spatial visualization M and analysis Visual cortex (left visual field) Table 14-3 The Cerebral Cortex. 14-9 The Cerebrum ▪ Motor areas – Primary motor cortex Surface of precentral gyrus Voluntary movements controlled by neurons (Pyramidal cells) in brain stem and spinal cord - Central Sulcus separates these areas - ▪ Sensory areas – Primary somatosensory cortex Surface of postcentral gyrus of parietal lobe General senses from skin and proprioceptors Spatial discrimination/ texture discrimination ID of body region receiving stimulus Sensations only perceived if nuclei in thalamus relayed here 101 Homunculi - upside-down Posterior caricatures represent contralateral motor innervation of body regions Motor Sensory Anterior Motor map in Sensory map in Shoul precentral gyrus postcentral gyrus Head Ha arm Trunk Neck Trunk Elb m Knee Hip Leg Fo w Elb t Arm Wri Hip re Ha Ar der o nd s Fi er ow nd s ng ng er Fi Knee s Th um b um Foot b e Th Nec k