What is the difference between action potential and graded potential

A sudden change in the membrane potential is referred to as a depolarization. Here, the internal charge changes from negative to positive. The opening of the ion-gated channels causes the membrane depolarization. As the sodium channels are opened, the migration of the positively-charged sodium ions into the nerve cell causes more positive charge inside the cell. The three stages of the action potential are shown in figure 2. Figure 2: Stages of Action Potential.

The restoration of the negative charge inside the nerve cell is known as the repolarization. This is caused by the opening of the potassium channels. The influx of potassium ions into the outside of the nerve cell causes the reduction of the positive charge inside the cell. Refectory period refers to the time period between two action potentials. During the refectory period, sodium-potassium channels are opened to restore the resting potential. In the resting potential, the concentration of the sodium ions is high outside of the nerve cell while the concentration of the potassium ions is high inside the nerve cell.

Graded Potential: Graded potential refers to a membrane potential, which can vary in amplitude. Nodes of Ranvier also save energy for the neuron since the channels only need to be present at the nodes and not along the entire axon. Nodes of Ranvier are gaps in myelin coverage along axons. Action potentials travel down the axon by jumping from one node to the next. This arrangement gives the axon a number of interesting properties. Since myelin is an insulator, it prevents signals from jumping between adjacent nerves crosstalk.

Additionally, the myelinated regions transmit electrical signals at a very high speed, as an ordinary conductor or resistor would. There is no action potential in the myelinated regions so that no cell energy is used in them.

There is an signal loss in the myelin, but the signal is regenerated in the gaps, where the voltage pulse triggers the action potential at full voltage.

So a myelinated axon transmits a nerve impulse faster, with less energy consumption, and is better protected from cross talk than an unmyelinated one. Not all axons are myelinated so that crosstalk and slow signal transmission are a characteristic of the normal operation of these axons, another variable in the nervous system. The degeneration or destruction of the myelin sheaths that surround the nerve fibers impairs signal transmission and can lead to numerous neurological effects. It is more apt to strike younger adults, especially females.

Causes might come from infection, environmental or geographic effects, or genetics. At the moment there is no known cure for MS. Most animal cells can fire or create their own action potential. Muscle cells contract when they fire and are often induced to do so by a nerve impulse. In fact, nerve and muscle cells are physiologically similar, and there are even hybrid cells, such as in the heart, that have characteristics of both nerves and muscles.

Some animals, like the infamous electric eel Figure 7. An electric eel flexes its muscles to create a voltage that stuns prey.

Question 7. Golgi bodies Question 7. Schwann cells b. How are neurons similar to other cells? How are they unique? Compare and contrast resting, graded and action potential?

In your answer, make sure you have included channels and voltage reference as well as relevant structures of the neurons. Once you have come up with an answer, give it to another student to review. Based on the review by your peer, is there something you need to work on in terms of your understanding of the resting, graded and action potential. Multiple sclerosis causes demyelination of axons in the brain and spinal cord.

Why is this problematic? Skip to content 7. Differentiate between resting, graded and action potential with reference to structures of the neuron as well as ion movements and membrane potentials. Parts of a neuron. Types of neurons. Neurogenesis At one time, scientists believed that people were born with all the neurons they would ever have. This site contains more information about neurogenesis, including an interactive laboratory simulation and a video that explains how BrdU labels new cells.

Nerve impulse transmission within a neuron. Neuronal charged membranes. This video discusses the basis of the resting membrane potential. Resting membrane potential. Table 7. The resting membrane potential is a result of different concentrations inside and outside the cell. Action potential. In summary, an action potential is caused by movements of ions across the cell membrane as shown. Depolarization occurs when a stimulus makes the membrane permeable to ions.

Repolarization follows as the membrane again becomes impermeable to and moves from high to low concentration. These changes can lead to the neuron reaching threshold if the changes add together, or summate. The combined effects of different types of graded potentials are illustrated in Figure 2. For receptor potentials, threshold is not a factor because the change in membrane potential for receptor cells directly causes neurotransmitter release.

However, generator potentials can initiate action potentials in the sensory neuron axon, and postsynaptic potentials can initiate an action potential in the axon of other neurons. Graded potentials summate at a specific location at the beginning of the axon to initiate the action potential, namely the initial segment.

For sensory neurons, which do not have a cell body between the dendrites and the axon, the initial segment is directly adjacent to the dendritic endings.

For all other neurons, the axon hillock is essentially the initial segment of the axon, and it is where summation takes place. Summation can be spatial or temporal, meaning it can be the result of multiple graded potentials at different locations on the neuron, or all at the same place but separated in time. Spatial summation is related to associating the activity of multiple inputs to a neuron with each other. Temporal summation is the relationship of multiple action potentials from a single cell resulting in a significant change in the membrane potential.

Spatial and temporal summation can act together, as well. The process of converting electrical signals to chemical signals and back requires subtle changes that can result in transient increases or decreases in membrane voltage. To cause a lasting change in the target cell, multiple signals are usually added together, or summated. Does spatial summation have to happen all at once, or can the separate signals arrive on the postsynaptic neuron at slightly different times?

Explain your answer. There are two types of connections between electrically active cells, chemical synapses and electrical synapses. In a chemical synapse , a chemical signal—namely, a neurotransmitter—is released from one cell and it affects the other cell. In an electrical synapse , there is a direct connection between the two cells so that ions can pass directly from one cell to the next. If one cell is depolarized in an electrical synapse, the joined cell also depolarizes because the ions pass between the cells.

Chemical synapses involve the transmission of chemical information from one cell to the next. This section will concentrate on the chemical type of synapse. An example of a chemical synapse is the neuromuscular junction NMJ described in the chapter on muscle tissue. In the nervous system, there are many more synapses that are essentially the same as the NMJ.

All synapses have common characteristics, which can be summarized in this list:. Other synapses are similar to this, and the specifics are different, but they all contain the same characteristics. Once in the synaptic cleft, the neurotransmitter diffuses the short distance to the postsynaptic membrane and can interact with neurotransmitter receptors. Receptors are specific for the neurotransmitter, and the two fit together like a key and lock. One neurotransmitter binds to its receptor and will not bind to receptors for other neurotransmitters, making the binding a specific chemical event Figure 3.

Figure 3. The Synapse. The synapse is a connection between a neuron and its target cell which is not necessarily a neuron. The neurotransmitter diffuses across the synaptic cleft to bind to its receptor. The neurotransmitter is cleared from the synapse either by enzymatic degradation, neuronal reuptake, or glial reuptake.

There are several systems of neurotransmitters that are found at various synapses in the nervous system. These groups refer to the chemicals that are the neurotransmitters, and within the groups are specific systems.

The first group, which is a neurotransmitter system of its own, is the cholinergic system. It is the system based on acetylcholine. This includes the NMJ as an example of a cholinergic synapse, but cholinergic synapses are found in other parts of the nervous system. JavaScript is not enabled in your browser. Without JavaScript, you will not be able to use some features of this site. Either enable JavaScript in your browser or use another computer in which JavaScript is enabled.

There are important differences between graded potentials and action potentials of neurons see Introduction to this lecture. Table 1 lists the main differences between graded potentials and action potentials. As discussed in this lecture and upcoming lectures, most of these differences are due to the fact that graded potentials result from the passive electrical property of the neuronal membrane, whereas action potentials result from an orchestrated response to depolarizing stimuli, and involve a coordinated activity of voltage-gated ion channels.

Graded potentials must occur to depolarize the neuron to threshold before action potentials can occur. Depending on the cell and type and the nature of stimulus, graded potentials that lead to action potentials are called synaptic potentials i. These graded potentials will be discussed in later lectures.

In the next lecture, we will consider the propagation of neuronal action potentials and we will see that additional neuronal adaptations allow action potentials to travel over long distances without losing any strength i.