Nerve impulse causes presynaptic membrane to open channels to calcium ions that interact with actin filaments that pull synaptic vesicles to membrane. Neurotransmitter in vesicles is released into synaptic cleft and diffuses across to postsynaptic membrane. If excitatory, the postsynaptic membrane potential is decreased, sodium ion channels open, and likelihood of neuron firing is increased. Neurotransmitters Are Varied a. Twenty-five different types of neurotransmitters include gases CO and NO, and neuropeptides or amino acids and derivatives. Failure to repackage or eliminate neurotransmitters in synapse causes continuous stimulation or inhibition.
Somatic system contains sensory neurons from sense organs and motor neurons to muscles.
Autonomic system contains sensory neurons from viscera and motor neurons to control glands, heart muscle, and smooth muscles of internal organs. Twelve pair of cranial nerves serve the head, neck, and face with a vagus nerve that branches to pharynx, larynx, and internal organs. Spinal nerves have a dorsal root conducting impulses inward from sensory neurons, and a ventral root containing axons of motor neurons. Somatic System Serves Skin and Muscles a. Sensory neuron carries nerve impulse from dendrite to cell body in the dorsal root ganglion to axon.