Neurons are excitable cells that are the functional unit of the nervous system. Functionally, each neuron is an integrator, conductor and transmitter of coded information. Neurons are specialized to react to stimuli received on their dendrites or cell body, to transmit the resulting excitation rapidly to other portions of the cell, including their long axon, and then to pass this signal via their axon to other neurons, muscle cells, and glandular cells. The points of contact between cells, through which this information passes, are called synapses. All of the little black dots on the surface of this neuronal cell body and processes are synapses, showing the HUGE number of synapses that are present, and the HUGE amount of information that the neuron integrates and processes.
Neurons communicate with each other and with effector cells by means of synapses.
Synapses are the specialized junctions of neurons through which impulses travel from one neuron to the next. Shown here is a chemical synapse, but electrical synapses also exist. The vesicles that contain the neurotransmitter are easily visible in the axon terminal. The postsynaptic membrane has receptor sites that interact with the neurotransmitter, leading to the development of post-synaptic potentials. Neurons come in a large variety of shapes, sizes and forms.