Structural elements and mechanisms involved in the transformation of neural activity to muscle contraction and secretion Shokoya Mariam Majida

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

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

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

Thank you for your attention! Sources: https://en.wikipedia.org/wiki/Intrafusal_muscle_fiber https://en.wikipedia.org/wiki/Extrafusal_muscle_fiber https://en.wikipedia.org/wiki/Motor_neuron https://en.wikipedia.org/wiki/Alpha_motor_neuron https://en.wikipedia.org/wiki/Neuromuscular_junction https://en.wikipedia.org/wiki/General_visceral_efferent_fibers https://en.wikipedia.org/wiki/Muscle_spindle