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106L09_notes - Introduction to Neuroscience Lecture 9...

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1 Introduction to Neuroscience Lecture 9: Cortical and Descending Motor Systems. Reading Assignment: Bear et al., Ch. 13 & 14 CBNS 106 2 Sensory & Motor Systems Ascending Sensory Pathways Descending Motor Pathways Motor Cortex Somatic Motor System (muscles & their sensory-motor innervations) 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 Excitation-Contraction Coupling CBNS 106 14 The Somatic Motor System
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