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Published byEunice Wheeler Modified over 7 years ago
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Structural elements and mechanisms involved in the transformation of neural activity to muscle contraction and secretion Shokoya Mariam Majida
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MOTOR NEURON: Cell body located in the spinal cord Axon is efferent, it carries information from the spinal cord to the effectors in the PNS (muscles and glands) Two main categories : Somatic / Visceral motor neurons Somatic motor neurons: Originate from CNS direct axons to skeletal muscles control locomotion Types of efferent motor neurons: Alpha / Beta / Gamma motor neurons Types of muscle fibers they innervate: Intrafusal / Extrafusal muscle fibers
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Extrafusal muscle fibers:
generate tension allow skeletal movement mostly striated fibers attached to the bone by tendons innervated by ALPHA motor neurons : cell body in ventral horn of the spinal cord contribute to maintain muscle tone resist further stretches Intrafusal muscle fibers: serve as sensory organs detect the amount of change in the muscle innervated by both sensory afferent and motor efferent neurons Motor neurons are BETA and GAMMA beta: axon collateral to extrafusal muscle gamma: regulate sensitivity of the fiber to stretching
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Visceral motor neurons:
indirectly innervate cardiac muscle, smooth muscle and glands disynaptic command: visceral motor neuron (CNS) ganglionic neuron (PNS) visceral muscles (PNS) sypmpathetic (noradrenalin release) or parasympathetic (acetylcholin release) nerve fibers Basicly all motor neurons release acetylcholin. Neuromuscular junction: action potencial Calcium ion inflow in axon terminal fusion of synaptic vesicles release Acetylcholin postsynaptic membrane: binding to nicotinic acetylcholin receptors depolarization of muscle fiber contraction
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