106L09_notes - Introduction to Neuroscience Lecture 9:...

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1 Introduction to Neuroscience Lecture 9: Cortical and Descending Motor Systems. Reading Assignment: CBNS 106 2 Ascending Sensory Pathways Descending Motor Pathways Motor Cortex Somatic Motor System CBNS 106 3 Introduction • Motor Programs – Motor system: Muscles and neurons that control muscles – Role: Generation of coordinated movements – Parts of motor control • Spinal cord coordinated muscle contraction • Brain motor programs in spinal cord CBNS 106 4 The Somatic Motor System • Types of Muscles – Striated: • skeletal (bulk of body muscle mass) • Cardiac (heart) – Smooth: digestive tract, arteries, related structures
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2 CBNS 106 5 The Somatic Motor System • Somatic Musculature – Axial muscles: Trunk movement – Proximal muscles: Shoulder, elbow, pelvis, knee movement – Distal muscles: Hands, feet, digits (fingers and toes) movement CBNS 106 6 The Somatic Motor System • The Lower Motor Neuron – Lower motor neuron: Innervated by ventral horn of spinal cord – Upper motor neuron: Supplies input to the spinal cord CBNS 106 7 The Somatic Motor System • The Motor Unit • Two lower motor neurons • Alpha • Gamma CBNS 106 8 • Graded Control of Muscle Contraction by Alpha Motor Neurons – Varying firing rate of motor neurons – Recruit additional synergistic motor units The Somatic Motor System
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3 CBNS 106 9 • Inputs to Alpha Motor Neurons ALS (Amyotrophic Lateral Sclerosis) = Lou Gehrig’s Desease – Selective degeneration of alpha motor neurons The Somatic Motor System CBNS 106 10 • Neuromuscular Matchmaking • Alternate nerve input – Switch in muscle phenotype (physical characteristics) as a consequence of increased or decreased activity. – Hypertrophy: Exaggerated growth of muscle fibers – Atrophy: Degeneration of muscle fibers The Somatic Motor System CBNS 106 11 • Muscle contraction – Alpha motor neurons release Ach • Innervate muscle fibers – ACh produces large EPSP in muscle fibers (via nicotinic Ach receptors – EPSP evokes action potential – Action potential (excitation) triggers Ca 2+ release, leads to fiber contraction – Relaxation, Ca 2+ levels lowered by organelle reuptake • Myasthenia Gravis (Greek for severe muscle weakness) – NMJ Disease – autoimmune disease; nicotinic ACh Receptors dysfunction – Drugs: AChE blockers Excitation-Contraction Coupling CBNS 106 12 • Muscle Fiber Structure Excitation-Contraction Coupling
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4 CBNS 106 13 • The Molecular Basis of Muscle Contraction – Z lines: Division of myofibril into segments by disks – Sarcomere: Two Z lines and myofibril – Thin filaments: Series of bristles – Thick filaments: Between and among thin filaments – Sliding-filament model: • Binding of Ca 2+ to troponin causes myosin to bind to actin • Myosin heads pivot, cause filaments to slide
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This note was uploaded on 04/15/2008 for the course CBNS 106 taught by Professor Korzus during the Winter '08 term at UC Riverside.

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106L09_notes - Introduction to Neuroscience Lecture 9:...

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