Electrical Synapses Gap Junctions

In order for two cells to be electrically coupled, they must be approximately equal in size and they must be joined by areas of contact with low electrical resistance. In this way, impulses can be regenerated from one cell to the next without interruption. Adjacent cells that are electrically coupled are joined together by gap junctions. In gap junctions, the membranes of the two

168 Chapter Seven

168 Chapter Seven

Structure Gap Junctions

Figure 7.19 The structure of gap junctions. Gap junctions are water-filled channels through which ions can pass from one cell to another. This permits impulses to be conducted directly from one cell to another. Each gap junction is composed of connexin proteins. Six connexin proteins in one plasma membrane line up with six connexin proteins in the other plasma membrane to form each gap junction.

Figure 7.19 The structure of gap junctions. Gap junctions are water-filled channels through which ions can pass from one cell to another. This permits impulses to be conducted directly from one cell to another. Each gap junction is composed of connexin proteins. Six connexin proteins in one plasma membrane line up with six connexin proteins in the other plasma membrane to form each gap junction.

cells are separated by only 2 nanometers (1 nanometer = 10-9 meter). A surface view of gap junctions in the electron microscope reveals hexagonal arrays of particles that function as channels through which ions and molecules may pass from one cell to the next (fig. 7.19). Each gap junction is now known to be composed of twelve proteins known as connexins, which are arranged like staves of a barrel to form a water-filled pore.

Gap junctions are present in cardiac muscle and some smooth muscles, where they allow excitation and rhythmic contraction of large masses of muscle cells. Gap junctions have also been observed in various regions of the brain. Although their functional significance in the brain is unknown, it has been speculated that they may allow a two-way transmission of impulses (in contrast to chemical synapses, which are always oneway). Gap junctions also have been observed between glial cells; these may act as channels for the passage of informational molecules between cells. It is interesting in this regard that gap junctions are present in many embryonic tissues, and that these gap junctions disappear as the tissue becomes more specialized.

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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Responses

  • michelle
    Are electrical synapses one or two way transmission of impulses?
    8 years ago
  • dino
    ARE IMPULSES CONDUCTED FROM ONE MUSCLE CELL TO THE NEXT?
    8 years ago

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