OR-instructed axonal projection

However, recent studies demonstrated that OR-instructed axonal projection is established by OR-derived cAMP signals, and not by the direct action of OR molecules. The levels of cAMP establish the anterior-posterior topography of axonal projection via cAMP-dependent PKA at an early stage of development (Imai et al. 2006). The neuronal activity generated by cAMP via CNG channels promotes the fasciculation of OSN axons at a later stage (Serizawa et al. 2006). 

Skeletal muscles are controlled by large nerves in the spinal cord. The nerve cell or neuron is part of the spinal cord, but its projections, the axon and the many dendrites course outward to connect to muscle cells. The nerve axon is a sensory device that senses the muscle cells current condition. The dendrites are motor fibers that deliver the instructions to change its state to the muscle fiber. The area at which the muscle and nerve connect is called the neuromuscular junction. It is here that the end releases a chemical called a neurotransmit-ter that crosses the microscopic space between the nerve and muscle and causes the desired response. Five such neurotransmitters have been described acetylcholine, serotonin, norepinephrine, glycine, and gamma-ammi-nobutyric acid or GABA. Of these, the functions of three are known. Acetylcholine excites muscle activity and glycine and GABA inhibit it. 

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