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PowerPoint® Lecture Slides prepared by Vince Austin, University of Kentucky Spinal Cord – Part I Human Anatomy & Physiology, Sixth Edition Elaine N. Marieb Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 12b Spinal Cord CNS tissue is enclosed within the vertebral column from the foramen magnum to L1 Provides two-way communication to and from the brain Protected by bone, meninges, and CSF Epidural space – space between the vertebrae and the dural sheath (dura mater) filled with fat and a network of veins Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Principal Parts Principal Parts 1. 42-45 cm in length; 2.5 cm wide 2. cervical enlargement - C4:T1 supply upper limbs 3. lumbar enlargement - T9:T12 supply lower limbs 4. conus medullaris - tapers off to end at L1-L2 5. filum terminale - pia mater anchors cord to coccyx 6. cauda equina - (horse tail) nerves below L2 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Spinal Cord Figure 12.28a Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Things to NOTE about the Spinal Cord 1. Cord itself ends at L1-L2 vertebrae 2. Lower nerves dangle down in the cauda equina 3. There are 31 pairs of spinal nerves 4. spinal segment - gives rise to one spinal nerve 5. C1-C7 spinal nerves project ABOVE C1-C7 vertebrae 6. C8 spinal nerve projects below C7 vertebra 7. T1-S5 spinal nerves project BELOW T1-S5 vertebrae Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Grey Matter areas vs. White Matter areas 1. grey matter - nerve cell bodies motor & interneurons 2. white matter - myelinated axons of motor & sensory Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Cross-Sectional Anatomy of the Spinal Cord Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.30a Regions in the Grey Matter - H shaped center 1. grey commissure - cross bar of the H 2. central canal - hole in the center 3. anterior (ventral) horns 4. posterior (dorsal) horns 5. lateral (intermediate) horns (T, L, S only) Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Gray Matter and Spinal Roots Figure 12.30b Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Gray Matter: Organization Dorsal half – sensory roots and ganglia Ventral half – motor roots Dorsal and ventral roots fuse laterally to form spinal nerves Four zones are evident within the gray matter – somatic sensory (SS), visceral sensory (VS), visceral motor (VM), and somatic motor (SM) Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Gray Matter: Organization Figure 12.31 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings PowerPoint® Lecture Slides prepared by Vince Austin, University of Kentucky Spinal Nerves Human Anatomy & Physiology, Sixth Edition Elaine N. Marieb Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 13b Spinal Nerves Thirty-one pairs of mixed nerves arise from the spinal cord and supply all parts of the body except the head They are named according to their point of issue 8 cervical (C1-C8) 12 thoracic (T1-T12) 5 lumbar (L1-L5) 5 sacral (S1-S5) 1 coccygeal (C0) Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Spinal Nerves Figure 13.6 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Spinal Nerves: Roots Each spinal nerve connects to the spinal cord via two medial roots Each root forms a series of rootlets that attach to the spinal cord Ventral roots arise from the anterior horn and contain motor (efferent) fibers Dorsal roots arise from sensory neurons in the dorsal root ganglion and contain sensory (afferent) fibers Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Spinal Nerves: Roots Figure 13.7a Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Nerve Plexuses All ventral rami except T2-T12 form interlacing nerve networks called plexuses Plexuses are found in the cervical, brachial, lumbar, and sacral regions Each resulting branch of a plexus contains fibers from several spinal nerves Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Nerve Plexuses Fibers travel to the periphery via several different routes Each muscle receives a nerve supply from more than one spinal nerve Damage to one spinal segment cannot completely paralyze a muscle Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Spinal Nerve Innervation: Back, Anterolateral Thorax, and Abdominal Wall The back is innervated by dorsal rami via several branches The thorax is innervated by ventral rami T1-T12 as intercostal nerves Intercostal nerves supply muscles of the ribs, anterolateral thorax, and abdominal wall Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Spinal Nerve Innervation: Back, Anterolateral Thorax, and Abdominal Wall Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.7b Cervical Plexus The cervical plexus is formed by ventral rami of C1-C4 Most branches are cutaneous nerves of the neck, ear, back of head, and shoulders The most important nerve of this plexus is the phrenic nerve - the major motor and sensory nerve of the diaphragm Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Cervical Plexus Figure 13.8 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Brachial Plexus Formed by C5-C8 and T1 (C4 and T2 may also contribute to this plexus in some people) It gives rise to the nerves that innervate the upper limb Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Brachial Plexus There are four major branches of this plexus Roots – five ventral rami (C5-T1) Trunks – upper, middle, and lower, which form divisions Divisions – anterior and posterior serve the front and back of the limb Cords – lateral, medial, and posterior fiber bundles Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Brachial Plexus Figure 13.9a Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Brachial Plexus: Nerves Axillary – innervates the deltoid and teres minor Musculocutaneous – sends fibers to the biceps brachii and brachialis Median – branches to most of the flexor muscles of arm Ulnar – supplies the flexor carpi ulnaris and part of the flexor digitorum profundus Radial – innervates essentially all extensor muscles Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Brachial Plexus: Distribution of Nerves Figure 13.9c Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Brachial Plexus: Nerves Figure 13.9b Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Lumbar Plexus Arises from L1-L4 and innervates the thigh, abdominal wall, and related muscles The major nerves are the femoral and the obturator Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Lumbar Plexus Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.10 Sacral Plexus Arises from L4-S4 and serves the buttock, lower limb, pelvic structures, and the related sacral areas The major nerve is the sciatic, the longest and thickest nerve of the body The sciatic is actually composed of two nerves: the tibial and the common fibular nerves Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Sacral Plexus Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.11 Dermatomes A dermatome is the area of skin innervated by the cutaneous branches of a single spinal nerve All spinal nerves except C1 participate in dermatomes Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Dermatomes Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.12 PowerPoint® Lecture Slides prepared by Vince Austin, University of Kentucky Spinal Cord – Part II Human Anatomy & Physiology, Sixth Edition Elaine N. Marieb Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 12b White Matter in the Spinal Cord Fibers run in three directions – ascending, descending, and transversely Divided into three funiculi (columns) – posterior, lateral, and anterior Each funiculus contains several fiber tracks Fiber tract names reveal their origin and destination Fiber tracts are composed of axons with similar functions Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings White Matter: Pathway Generalizations Pathways decussate (cross to contralateral side of body) Most consist of two or three neurons in the pathway Most exhibit somatotopy (precise spatial relationships) Pathways are paired (one on each side of the spinal cord or brain) Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Ascending (Sensory) Tracts Figure 12.32 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Ascending Tracts TRACT FUNCTION 1. anterior (ventral) spinothalamic - touch and pressure to thalamus 2. lateral spinothalamic tract - pain & temperature to thalamus 3. fasciculus gracilis & cuneatus - touch, 2-pt. discrimination conscious proprioception, stereognosis, weight discrimination, vibration 4. posterior spinocerebellar - subconscious proprioception 5. anterior spinocerebellar - subconscious proprioception Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Nonspecific Ascending Pathway Nonspecific pathway for pain, temperature, and crude touch within the lateral spinothalamic tract Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.33b Descending (Motor) Pathways Motor pathways involve two neurons (upper motor neuron and lower motor neuron) Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Descending (Motor) Tracts Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Descending (Motor) Pathways TRACTS FUNCTIONS 1. lateral & anterior corticospinal motor output from cortex motor to cells of ant. horn 2. rubrospinal motor from midbrain to anterior horn for precise movement 3. tectospinal motor from midbrain to anterior horn; movements in response to audiovisual/cutaneous stimuli 4. vestibulospinal motor from medulla to anterior horn; coordination/balance 5. lateral reticulospinal motor from medulla to anterior horn; inhibit extensor reflexes 6. medial reticulospinal motor from pons to anterior horn; facilitate extensor reflexes Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings The Direct (Pyramidal) Motor System Direct pathways originate with the pyramidal neurons in the precentral gyri Impulses are sent through the corticospinal tracts and synapse in the anterior horn Stimulation of anterior horn neurons activates skeletal muscles Parts of the direct pathway, called corticobulbar tracts, innervate cranial nerve nuclei The direct pathway regulates fast and fine (skilled) movements Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings The Direct (Pyramidal) System Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.34a Indirect (Extrapyramidal) Motor System Includes the brain stem, motor nuclei, and all motor pathways not part of the pyramidal system This system includes the rubrospinal, vestibulospinal, reticulospinal, and tectospinal tracts These motor pathways are complex and multisynaptic, and regulate: Axial muscles that maintain balance and posture Muscles controlling coarse movements of the proximal portions of limbs Head, neck, and eye movement Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Indirect (Extrapyramidal) System Figure 12.34b Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Extrapyramidal (Multineuronal) Pathways Reticulospinal tracts – maintain balance Rubrospinal tracts – control flexor muscles Superior colliculi and tectospinal tracts mediate head movements Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings White Matter: Pathway Generalizations Figure 12.32 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Spinal Cord Trauma: Paralysis Paralysis – loss of motor function Flaccid paralysis – severe damage to the ventral root or anterior horn cells Lower motor neurons are damaged and impulses do not reach muscles There is no voluntary or involuntary control of muscles Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Spinal Cord Trauma: Paralysis Spastic paralysis – only upper motor neurons of the primary motor cortex are damaged Spinal neurons remain intact and muscles are stimulated irregularly There is no voluntary control of muscles Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Spinal Cord Trauma: Transection Cross sectioning of the spinal cord at any level results in total motor and sensory loss in regions inferior to the cut Paraplegia – transection between T1 and L1 Quadriplegia – transection in the cervical region Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Poliomyelitis Destruction of the anterior horn motor neurons by the poliovirus Early symptoms – fever, headache, muscle pain and weakness, and loss of somatic reflexes Vaccines are available and can prevent infection Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Amyotrophic Lateral Sclerosis (ALS) Lou Gehrig’s disease – neuromuscular condition involving destruction of anterior horn motor neurons and fibers of the pyramidal tract Symptoms – loss of the ability to speak, swallow, and breathe Death occurs within five years Linked to malfunctioning genes for glutamate transporter and/or superoxide dismutase Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings