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Lecture 6

Lecture 6.docx

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Matthias Niemeier

Lecture 6 SAQ: 1. Tell me about the somatosensory afferent axons a. Aa b. Ab c. Ad d. C 2. Which ones exist 3. How are they different morphologically a. In terms of transmission i. From Aa  C 1. Aa is fastest 2. C is slowest b. In terms of function i. Aa  proprioception ii. Ab  mechanoreception iii. Ad / C  Pain and temperature perception 4. Comment on the transmission speed of pain perception a. What can be experienced subjectively 5. Given that nociception is crucial, what is interesting about the transmission speed? a. Speed of pain is slow  shouldn't it be faster? Chapter 13 Spinal control of movement Motor programs 1. Motor system a. Muscles and neurons that control muscles 2. Role a. Generation of coordinated movements 3. Parts of motor control a. Spinal cord  coordinated muscle contraction b. Brain  motor programs in spinal cord Overview of functional units in the motor system 1. Basal ganglia a. Gating proper initiation of movement b. Projections to motor cortex 2. Cerebellum a. Sensory motor coordination b. Projections to brainstem centers 3. Motor cortex a. Planning, initiating, and directing voluntary movements b. Projections to local circuit neurons and lower motor neurons 4. Brainstem centers a. Basic movements and postural control b. Projections to local circuit neurons and lower motor neurons 5. Local circuit neurons a. Reflex coordination b. Projections to lower motor neurons 6. Lower motor neurons a. Projections to skeletal muscles The somatic motor system 1. Types of muscles a. Smooth i. Digestive tract ii. Arteries b. Striated i. Cardiac ii. Skeltal 2. Somatic musculature a. Axial muscles i. Trunk movement b. Proximal muscles i. Shoulder ii. Elbow iii. Pelvis iv. Knee c. Distal muscles i. Hands ii. Feet iii. Digits 3. Lower motor neuron a. Innervated by ventral horn of spinal cord 4. Upper motor neuron a. Supplies input to spinal cord i. 30 segments to the spinal cord 5. Ventral horn a. Cervical and lumbar swollen areas b. Medial  lateral i. Axial  distal c. Dorsal  ventral i. Flexors  extensors ii. Synergists / antagonists 6. Alpha motor neurons a. Two lower motor neurons i. Alpha ii. Gamma b. One motor unit = alpha neuron + muscle fiber(s) c. Motor neuron pool = populations of lower motor neurons innervating one muscle 7. Graded control of muscle contraction by alpha motor neurons a. Varying firing rate of motor neurons i. Acetylcholine release increases ii. Temporal summation b. Recruit additional synergistic motor units c. Small and large motor neurons d. Renshaw cells 8. Inputs to alpha motor neurons a. Spinal interneurons b. Muscle spindles (sensory input) c. Upper motor neurons 9. Types of motor units a. Red muscle fibers i. Many mitochondria and enzymes ii. Slow to contract iii. Can sustain contraction iv. Slow motor units 1. Slow 2. Slowly fatiguing red fibers b. White muscle fibers i. Few mitochondria ii. Anaerobic metabolism iii. Contract and fatigue rapidly iv. Fast motor units 1. Fast 2. Rapidly fatiguing white fibers Excitation-contraction coupling 1. Muscle contraction a. Alpha motor neurons release ACh i. Innervate muscle fibers b. ACh produces large EPSP in muscle fibers i. Via nicotinic ACh receptors c. EPSP evokes action potential d. Action potential (excitation) triggers Ca2+ release i. Leads to fiber contraction e. Relaxation i. Ca2+ levels lowered by organelle reuptake 2. Muscle fiber structure a. Mitochondria b. Myofibrils c. T-tubules d. Sarcoplasmic reticulum e. Openings of T-tubules f. Sarcolemma 3. The molecular basis of muscle contraction a. Z lines i. Division of myofibril into segments by disks b. Sarcomere i. Two Z lines and myofibril c. Thin filaments i. Series of bristles d. Thick filaments i. Between and among thin filaments e. Sliding filament model i. Ca2+ binds to troponin 1. Myosin binds to actin ii. Myosin heads pivot 1. Causing filaments to slide iii. Disengage with ATP 4. Steps in excitation-contraction coupling a. Excitation i. Action potential ii. ACh release iii. EPSP iv. Action potential in muscle fiber v. Depolarization b. Contraction i. Ca2+ binds to troponin
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