Neuronal signaling, synaptic junctions

Hgure 4 The cascade for synaptic signal transduction between neuronal cells. Release of the synaptic transmitter gluatamate enhances the intracellular calcium levels and activates the nNOS enzyme. The NO can diffuse to adjacent neurons and activate the guanylate enzyme on both sides of the synaptic junction. 

Skeletal muscles contract when depolarized by neural signals transmitted at the neuromuscular junction. Each muscle fiber has one synaptic connection, but each motor neuron typically branches and controls several muscle fibers. The larger and more powerful muscles are controlled by neurons branched many times. The contractile apparatus composed of motor neuron and all the fibers it controls is called a motor unit. 

The brain consists of cells called neurons there are several hundreds of billions of such cells in our brain. A neuron makes connections to a number (several thousands) of other neurons. The signal travels within a neuron as an electric signal the electric impulse is created by ionic movement through ion channels aaoss the cell membrane such as sodium and potassium channel. When the signal comes to a junction called synapse , it has to be carried by a chemical compound across the narrow gap (which is 5-20 nm wide) between the neurons. Such a chemical compound is called neurotransmitter . A neurotransmitter molecule binds to the receptor site on the surface of a post-synaptic neuron. The receptor is an ion channel, and the binding of a neurotransmitter opens the channel, hence resulting in the creation of a new electric signal on the postsynaptic cell. 

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