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The Spinal Cord & Peripheral Nervous System Lesson 7
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Dorsal Ventral Horns
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Spinal Cord n Dorsal root ganglion (DRG) l Sensory input n Ventral root l Motor output n Caudal spinal cord l Cauda equina ~
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Spinal Cord Tracts n Major descending & ascending tracts n Motor n 1. corticospinal tract l distal muscles l only descending tract with overt effects n 1a. Rubrospinal tract l Red nucleus to spinal cord ~
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Spinal Cord Tracts n Sensory n 2. Dorsal column-medial lemniscal tract l touch, vibration, & proprioception l axons ascend ipsilaterally l synapse then decussate at medulla n 3. Spinothalamic tract (anterolateral) l pain & temperature l decussate at SC entry level l ascends contralaterally ~
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Medulla Dorsal column-medial lemniscal path Spinothalamic path Corticospinal tract
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Dorsal Ventral Spinal Cord
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Peripheral N. S. n Cranial Nerves - 12 pair n Spinal Nerves - 31 pair n Somatic Division l Sensory info l Body Movement n Autonomic division - Homeostasis l regulation ~
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Cranial Nerves n From ventral surface l numbered anterior posterior n Sensory, motor, or mixed n Mnemonic ~
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Oh To Touch And Feel Very Green Vegetables A H Olfactory Optic Oculomotor Trochlear Trigeminal Abducens Facial Vestibulococlear Glossopharangeal Vagus Accessory (Spinal) Hypoglossal I II III IV V VI VII VIII IX X XI XII On Old Olympus’s Towering Top A Famous Vocal German Viewed Some Hops
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Spinal Nerves n 1 pair for each vertebral segment n 8 pr. cervical (C1-C8) n 12 pr. thoracic (T1-T12) n 5 pr. lumbar (L1-L5) n 5 pr. sacral (S1-S5) n 1 pr coccygeal ~
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Spinal Nerves n Thoracic nerves relatively small back & ribs n Cervical, lumbar, & sacral: large nerves rest of the body n All Interconnect l after leaving vertebral canal l form 4 major plexuses cervical, brachial, lumbar, sacral~
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Somatic Nervous System n Sensory input l receptors DRG dorsal SC l Dorsal column-medial lemniscal pathway l Spinolthalamic tract n Motor output l Lateral SC ventral horns muscles l Corticospinal tract l Rubrospinal tract ~
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Dermatomes n Sensory innervation l each spinal nerve has receptive field n Overlap at distal branches l redundancy l retain some sensation even if a complete spinal nerve destroyed ~
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The Lateral Pathway n Voluntary movement l distal limbs l 2 tracts n Corticospinal tract about 1 million axons n Rubrospinal tract small part of pathway ~ Somatic N.S.: Motor Output
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Motor N.S. n Striate muscle l uninterrupted neuron a motor neuron l nerve-dependent n Excitatory only at neuroeffector synapse l NT is acetylcholine (ACh) cholinergic l Nicotine = direct agonist (AG) l Curare = direct antagonist (ANT) ~
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Somatic Motor N. S. Spinal Cord Motor Neuron Effector ACh
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Autonomic N. S. n Homeostasis n Effectors l Smooth Muscle l Cardiac Muscle l Glands ~
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Autonomic Subdivisions n Not nerve-dependent n Sympathetic l Emergency, flight/fight n Parasympathetic l Conservation / vegetative ~
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Effector Ganglion Preganglionic neuron Postganglionic neuron Autonomic N. S.: General Features
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Effector Autonomic N. S.: General Features ACh n Ganglionic synapse: Nicotinic (nACh) l different than neuromuscular l Neuroeffector junction l Sympathetic: Norepinephrine l Parasympathetic: nACh & mACh ~
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Sympathetic vs. Parasympathetic n Sympathetic l ganglia near spinal cord l interconnected active together l long-lasting effects n Parasympathetic l ganglia near effector l discrete active independently l transient effects n Antagonistic regulation ~
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Effector Responses Effector Sympathetic Parasympathetic Heart Respiration GI Immune system Iris (radial) (sphincter) Sweat glands no input Adrenal glands no input ~
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Parasympathetic Post- Pre- Sympathetic Adrenal Glands ACh Glands Smooth muscle NE
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Sympathetic Arousal Syndrome n Fight or flight situations l Diffuse sympathetic activation n Adrenal glands l releases NE into blood l maintains sympathetic arousal n Parasympathetic rebound l antagonistic regulation ~
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