Action Potential in the Neuron Flashcards
4 Main parts of a neuron and their function:
- Dendrites = receive information
- Cell body = processes and integrates that information
- Axon = carries the information along long distances from 1 part of the neuron to another
- Axon terminal = transmits the information to the next cell in the chain
A bundle of axons travelling together is called a ___________
Nerve
Part of the neuron that receives incoming signal
Dendrites
Based on the strength of the incoming simulation, the neuron must decide whether to pass that signal along or not. If the stimulation is strong enough, the signal is transmitted along the entire length of the axon in a phenomenon called an __________. When this happens, we say the neuron fires.
Action potential
Transmission of the neuronal signal is entirely dependent on the movement of ions or charged particles. Various ions including Na+, K+, and Cl+ are unequally distributed between the inside and the outside of the cell. The presence and movement of these ions is not only important when a neuron fires but also at rest.
Let’s think about the positively-charged Na and K ions. When a neuron is not sending a signal, it is considered to be at rest. In a typical neuron in its resting state, the concentration of Na ions is higher (inside, outside) the cell than (inside, outside).
outside; inside
The relative concentration of K ions is the opposite, with more ions (inside, outside) the cell than (inside, outside)
inside; outside
The ionic separation occurs right at the cell membrane and creates a _________ across the membrane.
chemical gradient
Because ions are charged particles, we also need to consider their charge when thinking about their distribution across the membrane. At rest, there are more (positively, negatively) charged ions outside the cell relative to the inside. This creates a difference in charge across the membrane which is called an _________. Together with the chemical gradient we already mentioned, we refer to this ionic imbalance as the ____________.
Outside; electrical gradient; electrochemical gradient
The difference in total charge inside and outside of the cell is called a __________.
membrane potential
At rest, when no signals are being transmitted, neuronal membrane has a resting potential of approximately _______. This means that the inside of the cell is approximately —– mV less positive than the outside.
-70 mV
Both the chemical and the electrical gradient contribute to establishing the membrane potential. While the inside of the cell has a net negative charge and the outside of the cell has a net positive charge, the charges line up at the membrane and the bulk solution on either side is actually electrically neutral. The resting membrane potential is the point where the cell has achieved __________. This means that the concentration gradient and the electrochemical gradient for each ion is equal and opposite.
electrochemical equilibrium
Ions cannot simply move across the membrane at will. Instead, they need a protein embedded in the membrane to facilitate their movement. Most ions cross the membrane through a structure called an _______.
ion channel
Ions move through channels by ___________ along their concentration gradient.
passive diffusion
Some ion channels are always open but many require signal to tell them to open or close. For example, voltage -gated channels only open when the membrane potential reaches a certain value. On the other hand, ligand-gated ion channels are triggered to open when they are bound by a specific molecule. Mechanically-gated ion channels open in response to physical force such as changes in length or changes in pressure.
Most ion channels are selectively permeable, meaning that they only allow 1, or a small subset of ions, to pass through. Voltage-gated ion channels typically only allow a single ion to cross the membrane when they open. This means that we need separate ion channels for each ion i.e. voltage-gated sodium ion channels, as well as voltage-gated potassium channels.
As ions move through a channel and cross from 1 side of the cell membrane too the other, they cause the membrane potential to move away from its resting potential. If the resulting change in membrane potential is small, we call this a _________. ——— can vary in size, can be either positive or negative, are transient, and typically do not result from the opening of voltage-gated ion channels.
Graded potential;
When ion channels open and a graded potential occurs, the neuron moves quickly to reset its membrane potential to resting values. This is accomplished primarily by the use of the sodium-potassium pump which uses the energy generated by ATP hydrolysis, to actively transport ions across the membrane against their concentration gradient. In other words, sodium is transported to the outside of the cell, where its concentration is higher, and potassium is transported back into the cell, where its concentration is higher.
1 cycle of this pump transports 3 sodium ions outside the cell and brings 2 potassium ions inside the cell. This unbalanced charge transfer contributes to the separation of charge across the membrane and also to the ionic concentrations we see at rest, thus resting the chemical and electrical gradients to their resting levels.
Maintaining these ionic balance in neurons is so important that this process can account for 20% to 40% of the brain’s total energy use.
Only when the resting membrane potential and ion distributions are maintained at precise levels will the neuron be poised and ready to fire an action potential.
When the outside stimulation is large enough to bring the membrane potential in the neuron body up from -70 mV to the threshold voltage of -55 mV are higher, this triggers an action potential at the ________, which then travels down the axon.
Axon hillock
Voltage-gated ion channels have 3 states:
Open
Close - at rest
Inactive
Once the cell membrane reaches the threshold voltage, the channel changes to an open position and sodium rushes into the cell because of the electrochemical gradient. As positive sodium ions enter the cell, the membrane potential becomes less negative and more positive as it approaches 0 mV. This is called _________. Eventually, the voltage gradient goes to 0 and beyond 0, up to a positive 30 mV. This is called an ___________. As the membrane potential becomes positive, the sodium channel inactivation gate shuts, making the channel inactivated. This stops the flow of sodium ions into the cell. The change in membrane potential also opens the voltage-gated potassium channels, though they open and close more slowly. Because of the potassium electrochemical gradient, potassium ions flow out of the cell, making it less positive and eventually negative. This process is called ____________. Because the potassium channels are a little slow to close for a brief peroid, the membrane potential is __________. It’s more negative than the resting potential
Depolarization; Overshoot; Repolarization; Hyperpolarized
During hyperpolarization, the potassium channels close. Throughout all these, the sodium-potassium pump is still working. The pump restores the chemical gradients by putting the sodium and potassium back in place. And the pump reestablishes the potential gradient by moving more sodium ions out than potassium ions in. This returns the membrane potential back to its resting potential.
During repolarization, the inactivated sodium channels won’t respond to any stimulus at all. During this time, the neuron is in its _______________, the period of time when a nerve cannot fire another action potential, no matter how strongly it’s stimulated. The ——— prevents action potentials from happening again too quickly and prevents action potential from travelling backwards along the axon.
Absolute refractory period
