Synapses are the key functional elements of the brain.  The essential function of the brain is cell-to-cell communication, and synapses are the points at which communication occurs. The human brain has been estimated to contain approximately 100 trillion synapses; even the brain of a fruit fly contains several million. The functions of these synapses are very diverse: some are excitatory (excite the target cell); others are inhibitory; others work by activating second messenger systems that change the internal chemistry of their target cells in complex ways.  A large fraction of synapses are dynamically modifiable; that is, they are capable of changing strength in a way that is controlled by the patterns of signals that pass through them. It is widely believed that activity-dependent modification of synapses is the brain’s primary mechanism for learning and memory.

      In short, synapses occur constantly and jump from cell to cell in our brains.  You might find the following interesting:    

      The human brain is the center of the human nervous system. It has the same general structure as the brains of other mammals, but is larger than expected on the basis of body size among other primates.  Estimates for the number of neurons (nerve cells) in the human brain range from 80 to 120 billion.  Most of the expansion comes from the cerebral cortex, especially the frontal lobes, which are associated with executive functions such as self-control, planning, reasoning, and abstract thought. The portion of the cerebral cortex devoted to vision is also greatly enlarged in human beings, and several cortical areas play specific roles in language, a skill that is unique to humans.

      Despite being protected by the thick bones of the skull, suspended in cerebrospinal fluid, and isolated from the bloodstream by the blood–brain barrier, the human brain is susceptible to many types of damage and disease. The most common forms of physical damage are closed head injuries such as a blow to the head, a stroke, or poisoning by a variety of chemicals that can act as neurotoxins. Infection of the brain, though serious, is rare due to the biological barriers which protect it. The human brain is also susceptible to degenerative disorders, such as Parkinson’s disease, multiple sclerosis, and Alzheimer’s disease. A number of psychiatric conditions, such as schizophrenia and depression, are thought to be associated with brain dysfunctions, although the nature of such brain anomalies is not well understood.

      Researchers who study the functions of the cortex divide it into three functional categories of regions, or areas. One consists of the primary sensory areas, which receive signals from the sensory nerves and tracts by way of relay nuclei in the thalamus. Primary sensory areas include the visual area of the occipital lobe, the auditory area in parts of the temporal lobe and insular cortex, and the somatosensory area in the parietal lobe. A second category is the primary motor area, which sends axons down to motor neurons in the brainstem and spinal cord. This area occupies the rear portion of the frontal lobe, directly in front of the somatosensory area. The third category consists of the remaining parts of the cortex, which are called the association areas. These areas receive input from the sensory areas and lower parts of the brain and are involved in the complex process that we call perception, thought, and decision making.

     There is a whole lot online and other places about this very complex organ. 

Source:  Wikipedia