How does a nerve depolarize

The effects of the neurotransmitter generally lasts few milliseconds before being terminated. The neurotransmitter termination can occur in three ways.

First, reuptake by astrocytes or presynaptic terminal where the neurotransmitter is stored or destroyed by enzymes. Second, degradation by enzymes in the synaptic cleft such as acetylcholinesterase.

Third, diffusion of the neurotransmitter as it moves away from the synapse. Signal summation occurs when impulses add together to reach the threshold of excitation to fire a neuron. Signal summation at the axon hillock : A single neuron can receive both excitatory and inhibitory inputs from multiple neurons. All these inputs are added together at the axon hillock. Each neuron connects with numerous other neurons, often receiving multiple impulses from them. Sometimes, a single excitatory postsynaptic potential EPSP is strong enough to induce an action potential in the postsynaptic neuron, but often multiple presynaptic inputs must create EPSPs around the same time for the postsynaptic neuron to be sufficiently depolarized to fire an action potential.

Summation, either spatial or temporal, is the addition of these impulses at the axon hillock. One neuron often has input from many presynaptic neurons, whether excitatory or inhibitory; therefore, inhibitory postsynaptic potentials IPSPs can cancel out EPSPs and vice versa. The net change in postsynaptic membrane voltage determines whether the postsynaptic cell has reached its threshold of excitation needed to fire an action potential. If the neuron only receives excitatory impulses, it will also generate an action potential.

However, if the neuron receives as many inhibitory as excitatory impulses, the inhibition cancels out the excitation and the nerve impulse will stop there. Spatial summation means that the effects of impulses received at different places on the neuron add up so that the neuron may fire when such impulses are received simultaneously, even if each impulse on its own would not be sufficient to cause firing. Temporal summation means that the effects of impulses received at the same place can add up if the impulses are received in close temporal succession.

Thus, the neuron may fire when multiple impulses are received, even if each impulse on its own would not be sufficient to cause firing.

Synaptic plasticity is the strengthening or weakening of synapses over time in response to increases or decreases in their activity. Plastic change also results from the alteration of the number of receptors located on a synapse. Synaptic plasticity is the basis of learning and memory, enabling a flexible, functioning nervous system. Synaptic plasticity can be either short-term synaptic enhancement or synaptic depression or long-term. Two processes in particular, long-term potentiation LTP and long-term depression LTD , are important forms of synaptic plasticity that occur in synapses in the hippocampus: a brain region involved in storing memories.

Long-term potentiation and depression : Calcium entry through postsynaptic NMDA receptors can initiate two different forms of synaptic plasticity: long-term potentiation LTP and long-term depression LTD.

LTP arises when a single synapse is repeatedly stimulated. The next time glutamate is released from the presynaptic cell, it will bind to both NMDA and the newly-inserted AMPA receptors, thus depolarizing the membrane more efficiently. LTD occurs when few glutamate molecules bind to NMDA receptors at a synapse due to a low firing rate of the presynaptic neuron. The calcium that does flow through NMDA receptors initiates a different calcineurin and protein phosphatase 1-dependent cascade, which results in the endocytosis of AMPA receptors.

This makes the postsynaptic neuron less responsive to glutamate released from the presynaptic neuron. Short-term synaptic plasticity acts on a timescale of tens of milliseconds to a few minutes.

Short-term synaptic enhancement results from more synaptic terminals releasing transmitters in response to presynaptic action potentials. Synapses will strengthen for a short time because of either an increase in size of the readily- releasable pool of packaged transmitter or an increase in the amount of packaged transmitter released in response to each action potential.

Depletion of these readily-releasable vesicles causes synaptic fatigue. Short-term synaptic depression can also arise from post-synaptic processes and from feedback activation of presynaptic receptors. Long-term potentiation LTP is a persistent strengthening of a synaptic connection, which can last for minutes or hours.

These receptors are normally blocked by magnesium ions. Activated AMPA receptors allow positive ions to enter the cell. Therefore, the next time glutamate is released from the presynaptic membrane, it will have a larger excitatory effect EPSP on the postsynaptic cell because the binding of glutamate to these AMPA receptors will allow more positive ions into the cell. The insertion of additional AMPA receptors strengthens the synapse so that the postsynaptic neuron is more likely to fire in response to presynaptic neurotransmitter release.

Some drugs co-opt the LTP pathway; this synaptic strengthening can lead to addiction. In this situation, calcium that enters through NMDA receptors initiates a different signaling cascade, which results in the removal of AMPA receptors from the postsynaptic membrane.

With the decrease in AMPA receptors in the membrane, the postsynaptic neuron is less responsive to the glutamate released from the presynaptic neuron. The weakening and pruning of unused synapses trims unimportant connections, leaving only the salient connections strengthened by long-term potentiation. Privacy Policy. Skip to main content. The Nervous System. Search for:.

How Neurons Communicate. The entire depolarization-to-repolarization event happens in about 2 milliseconds, allowing neurons to fire action potential in fast bursts permitting neuronal communication.

A new action potential cannot take place until the proper electrical charge across the neuron's membrane is restored. This means that the inside of the cell needs to be negative, while the outside needs to be positive. A cell restores this state, or repolarizes itself, by turning on a protein pump in its membrane.

This pump is called the sodium-potassium pump. For every three sodium ions it pumps out of a cell, it pumps in two potassium ones. The pumps do this until the proper charge inside of a cell is reached. David H. Nguyen holds a PhD and is a cancer biologist and science writer. His specialty is tumor biology. He also has a strong interest in the deep intersections between social injustice and cancer health disparities, which particularly affect ethnic minorities and enslaved peoples.

How to Refresh Nimh Batteries. For most of the cells, the resting membrane potential is negative relative to the outside of the cell. The process of generation of resting membrane potential involves passive ion channels, ion pumps, and voltage-gated ion channels. Cells use these machines to keep a high concentration of negative ions inside the cells.

As a result, negative membrane potential is maintained. Usually, cells have more abundant organic anions inside the cells such as oxalate ions etc. The negative charge of these negative anions contributes to the resting membrane potential. In the usual setting, ten times more abundant potassium ions are present inside the cell than in the extracellular space. These potassium ions have diffusion gradient directed towards the extracellular space.

This loss of positively charged ions further contributes to the negative resting membrane potential inside the cell. Sodium potassium pump contributes a lot to the resting membrane potential. The concentration of sodium ions is more outside the cell than on then inside. On the other hand, the concentration of potassium ions is more on the inside of the cell than the outside. Thus, the diffusion gradient of sodium is directed towards the inside of the cell and that of potassium is directed towards the outside of the cell.

Sodium potassium pump is an energy-driven pump that uses ATP to pump the sodium and potassium ions against their concentration gradient. For every two potassium ions pumped inside the cell, three sodium ions are pumped outside. All the above-mentioned factors contribute to the establishment and maintenance of negative membrane potential within the cell.

After understanding the concept of resting membrane potential, we will now discuss the process of depolarization. A cell has the capacity to undergo depolarization after it has established a resting potential. Depolarization causes the rapid change in membrane potential from negative to positive state. The process of depolarization begins with a stimulus. This stimulus can be a simple touch, light, foreign particle, or even electrical stimulus.

This stimulus causes a voltage change in the cell. This initial voltage change causes the opening of voltage-gated sodium and calcium channels inside the cell membrane. The positively charged ions rush through these channels. As a result, the inside of the cell becomes more positive. The membrane potential changes from negative to positive state.

The basic principle of depolarization is the same as described under the heading of physiology. However, different cells in the body respond to different stimuli and use different ion channels to undergo the process of depolarization. All this is in coherence with the function of that cell. We will discuss the process of depolarization in reference to neurons, endothelial cells, and cardiac cells. Neurons can undergo depolarization in response to a number of stimuli such as heat, chemical, light, electrical or physical stimulus.