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human phys lec 7 - Peripheral 1 Somatic 2 Autonomic...

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Organization of the nervous system: l d i h l central and peripheral components
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Peripheral motor systems 1. Somatic 2. Autonomic
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Voluntary (somatic) motor systems Includes complex central and peripheral neuronal circuitry Organization in periphery is easy to understand Cannot function properly without sensory feedback Essential for “voluntary” movements but also contributes to Essential for voluntary movements, but also contributes to control of essential activities – such as breathing – that do not require attention. S ti f G k ō Somatic from Greek s ma meaning ‘the body’
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Organization of somatic motor pathways in the periphery i A motor unit An adult muscle fiber is innervated by only one motor neuron. One motor neuron can innervate multiple muscle fibers. A motor unit is comprised of one motor neuron and all of the muscle fibers that it innervates . A motor neuron pool is all the motoneurons that innervate a single muscle .
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Mammalian neuromuscular junction: Each muscle fiber is innervated by only one motor neuron ACh is transmitter Nerve terminal Skeletal muscle fiber These synapses have very high “safety factor”. They are designed to never fail
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Nicotinic receptors: the ionotropic ACh receptor of neuromuscular junctions
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D Tubocurarine: An antagonist of skeletal muscle nicotinic receptors Chondrodendrum tomentosum
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Action potential in muscle fiber e.p.s.p. After D tubocurare, only a portion of the e.p.s.p. is left I hibiti f l j ti ith i i Inhibition of neuromuscular junction e.p.s.p. with increasing concentrations of d tubocurare ECCLES, J. C., KATZ, B. & KUFFLER, S. W. (1941). Nature of the endplate potential in curarized muscle. Journal of Neurophysiology 4, 362 387.
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Action potential in muscle fiber e.p.s.p. After D tubocurare, only a portion of the e.p.s.p. is left I hibiti f l j ti ith i i Inhibition of neuromuscular junction e.p.s.p. with increasing concentrations of d tubocurare ECCLES, J. C., KATZ, B. & KUFFLER, S. W. (1941). Nature of the endplate potential in curarized muscle. Journal of Neurophysiology 4, 362 387.
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Alpha neurotoxins from the venoms of elapid snakes (cobras, kraits) are irreversible nicotinic inhibitors Bungarus (banded krait) Naja (cobra) α Bungarotoxin
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Tagged α‐ bungarotoxin can be used as a biochemical label of nicotinic receptors (and therefore of the endplate region) Endplate M t t i l Motor neuron terminal α bungarotoxin binding Synaptic region of a skeletal neuromuscular junction is often called the “motor endplate”
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Myasthenia gravis: An autoimmune neuromuscular disorder Usually caused by serum antibodies against the nicotinic ACh receptors of muscle. Muscle weakness, starting in head, especially the eyes, often progressing to neck, arms, legs.
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