An action potential is an electrical discharge that propagates along the length of a cell to transmit a signal. It is initiated by depolarizing the cell via an ion influx until the cell becomes positive in comparison to its external environment, and then rapidly repolarizes to its negative resting state again. The action potential is the means by which electrical signals are sent along the central nervous system to cause muscular contraction and stimulate some glands. What we know about the means by which the action potential is initiated can be attributed to two experimental techniques. Initially the voltage clamp gave us the basic understanding of the action potential and many hypotheses were inferred from it, then the patch clamp refined and corrected these ideas into the view we have today. Thus in considering whether or not the patch clamp has given us more information we must consider the level of understanding we have gained from the voltage clamp experiments.
The voltage clamp is used to measure the ion current across a neural membrane whilst holding the membrane voltage at a set level. The voltage clamp allows manipulation of the membrane voltage independently of the ionic currents and therefore allows the current-voltage relationship of the membrane channels to be studied.
[...] Thus the arrival of an action potential at the pre synaptic neurone causes a rapid quantal release of these packets of acetylcholine. By lowering the concentration of free calcium ions surrounding a synapse we find less acetylcholine is released when an action potential arrives at the pre synaptic neurone. Thus calcium ions were deemed to enter the pre synaptic neurone and cause the packets to fuse with the membrane to cause the release of acetylcholine. The electron microscope has helped to prove and refine these ideas. [...]
[...] It can also be deduced from the patch clamp experiments that the effects of changes in the membranes electrical field affects charged groups within ion gates and polarises binds between various atoms, which therefore exerts forces on their molecular structure, causing them to open or close. Synapses are specialised junctions between cells of the nervous system that allow signalling between neural cells, and to non neural cells such as muscles or glands. Synapses allow neurones in the central nervous system to form interconnected neural circuits and are therefore crucial to the biological principles behind perception and thought, thus providing a means by which the nervous system can connect to and influence the other systems of the body. [...]
[...] The post synaptic membrane contains receptor proteins that the neurotransmitter will being to causing near by ion channels to open, causing an influx of ion to change the trans-membrane potential, this can result in the initiation of an action potential. Despite chemical synapses occupying the majority of synapses in the nervous system, their method of quantal release to transmit signals is not uniform among other synapses, such as electrical synapses. An electrical synapse is an electrically conductive link between two neural cells in close proximity that is formed at a narrow gap between the pre and postsynaptic components, known as the gap junction. [...]
[...] The aggregate current is recorded using the voltage clamp, but the patch clamp allows us to record the current flowing through individual channels, thereby proving their existence and the part they play in the initiation of the action potential. In doing this experiment on a single sodium ion channel we begin by depolarising the membrane by an abrupt shift in potential. A number of current records are then taken from a number of experiments from the same patch of membrane, which result in the following traces. [...]
[...] Again, these were all presumptions based on what they inferred from the voltage clamp results, these ideas could not proven to be true or false until the advent of the patch clamp. The patch clamp is a refined version of the voltage clamp that allows the study of individual ion channels in cells. It is used to study excitable cells such as neurones, muscle fibres and beta cells in the pancreas. It uses a micropipette that is attached to the cell membrane via suction. [...]
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