membrane biology Membrane biology is the study of the biological and physiochemical characteristics of membranes, with applications in the study of cellular physiology. Membrane bioelectrical impulses are described by the Hodgkin cycle. Biophysics Membrane bio ...

, the Hodgkin cycle is a key component of membrane physiology that describes bioelectrical impulses, especially prevalent in

neural In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes ...

and

muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscle ...

tissues. It was identified by British

physiologist Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemica ...

and biophysicist Sir

Alan Lloyd Hodgkin Sir Alan Lloyd Hodgkin (5 February 1914 – 20 December 1998) was an English physiologist and biophysicist who shared the 1963 Nobel Prize in Physiology or Medicine with Andrew Huxley and John Eccles. Early life and education Hodgkin was bo ...

. The Hodgkin cycle represents a

positive feedback Positive feedback (exacerbating feedback, self-reinforcing feedback) is a process that occurs in a feedback loop which exacerbates the effects of a small disturbance. That is, the effects of a perturbation on a system include an increase in the ...

loop in which an initial membrane

depolarization In biology, depolarization or hypopolarization is a change within a cell, during which the cell undergoes a shift in electric charge distribution, resulting in less negative charge inside the cell compared to the outside. Depolarization is e ...

leads to uncontrolled deflection of the

membrane potential Membrane potential (also transmembrane potential or membrane voltage) is the difference in electric potential between the interior and the exterior of a biological cell. That is, there is a difference in the energy required for electric charges ...

to near V_Na. The initial depolarization must reach or surpass a certain threshold in order to activate voltage-gated Na⁺ channels. The opening of Na⁺ channels allows Na⁺ inflow, which, in turn, further depolarizes the membrane. Additional depolarization activates additional Na⁺ channels. This cycle leads to a very rapid rise in Na⁺ conductance (g_Na), which moves the membrane potential close to V_Na. The cycle is broken when the membrane potential reaches to the sodium equilibrium potential and

potassium channel Potassium channels are the most widely distributed type of ion channel found in virtually all organisms. They form potassium-selective pores that span cell membranes. Potassium channels are found in most cell types and control a wide variety of c ...

s open to re-polarize the membrane potential. This positive feedback loop means that the closer these voltage-gated Na⁺ channels are to each other, the lower the threshold of

activation Activation, in chemistry and biology, is the process whereby something is prepared or excited for a subsequent reaction. Chemistry In chemistry, "activation" refers to the reversible transition of a molecule into a nearly identical chemical or ...

Importance in cell physiology

An understanding of membrane physiology is needed in order to understand how cells communicate with one another. Signalling between cells, such as

neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. ...

s for example, revolves around changes in the electrical potentials across their membranes. In a healthy cell at rest, the

intracellular This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions ...

area is usually negatively charged relative to the

extracellular This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions ...

region. Depolarization refers to when the intracellular region is neutralized to be at the same

voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to mo ...

relative to the extracellular region. The concentration of sodium ions is intimately related to the electrical potential across a membrane. Depolarization often occurs via the influx of sodium ions to the intracellular region. Given that sodium ions have a positive charge, the intracellular region becomes less negatively charged relative to the extracellular region.

References

{{reflist Membrane biology