The all-or-none phenomenon as applied to nerve conduction states that the whole nerve cell must be stimulated for conduction to take place. Strong stimuli cause the amplitude of action potentials generated to increase. The action potential is caused by permeability changes in the plasma membrane.
What causes the amplitude of action potentials to increase?
Strong stimuli cause the amplitude of action potentials generated to increase. The action potential is caused by permeability changes in the plasma membrane. An action potential is regarded as an example of a positive feedback. Which of the following examples below best illustrates the positive feedback aspect of an action potential?
How does stimulus strength affect action potentials?
With increasing stimulus strength, subsequent action potentials occur earlier during the relative refractory period of the preceding action potentials. With very strong stimuli, subsequent action potentials occur following the completion of the absolute refractory period of the preceding action potential.
How does summation fire action potentials rapidly?
So you're not firing action potentials rapidly, rather you're using summation to initiate (or inhibit) an action potential. In your example of temporal summation, the frequency of incoming potentials (not action potentials) is high enough that the inward currents sum up to the threshold to produce an action potential.
How does the nervous system use action potentials?
The trick that the nervous system uses is that the strength of the stimulus is coded into the frequency of the action potentials that are generated. Thus, the stronger the stimulus, the higher the frequency at which action potentials are generated (see Figs. 1 and 2 below).
What is the amplitude of action potentials generated to increase?
Strong stimuli cause the amplitude of action potentials generated to increase.
What will most affect the speed of an action potential?
The diameter of the axon also affects speed. The larger the diameter of the axon, the faster the propagation of the action potential down the axon.
What type of stimulus is required for an action potential to be generated?
threshold stimulusThe minimum stimulus needed to achieve an action potential is called the threshold stimulus. The threshold stimulus causes the membrane potential to become less negative (because a stimulus, no matter how small, causes a few sodium channels to open and allows some positively-charged sodium ions to diffuse in).
How an action potential is generated?
Action potentials are caused when different ions cross the neuron membrane. A stimulus first causes sodium channels to open. Because there are many more sodium ions on the outside, and the inside of the neuron is negative relative to the outside, sodium ions rush into the neuron.
What increases action potential conduction velocity?
myelinBy acting as an electrical insulator, myelin greatly speeds up action potential conduction (Figure 3.14). For example, whereas unmyelinated axon conduction velocities range from about 0.5 to 10 m/s, myelinated axons can conduct at velocities up to 150 m/s.
What causes the increase in action potential frequency and what does it imply?
Rather, the frequency or the number of action potentials increases. In general, the greater the intensity of a stimulus, (whether it be a light stimulus to a photoreceptor, a mechanical stimulus to the skin, or a stretch to a muscle receptor) the greater the number of action potentials elicited.
What affects action potential amplitude?
Several factors are associated with increased amplitude, including (1) the proximity of the needle to the motor unit (Figure 15–8), (2) increased number of muscle fibers in a motor unit, (3) increased diameter of muscle fibers (i.e., muscle fiber hypertrophy), and (4) more synchronized firing of the muscle fibers.
Does action potential amplitude change with distance?
Unlike input potentials which spread passively and decrease in amplitude with distance, the action potential does not decay as it travels along the axon to the terminal of the neuron (this distance can be up to 1m).
What effect will the increased stimulus intensity?
4. Predict Question: What effect will the increased stimulus intensity have on the frequency of action potentials? Your answer: The frequency of action potentials will increase.
Which of the following increases when an action potential is initiated?
Diffusion of Na^(+) ions into the neuron.
What causes an action potential quizlet?
An action potential occurs when a neuron sends information down an axon, away from the cell body. The action potential is an explosion of electrical activity that is created by a depolarizing current.
What causes the rapid change in the resting membrane potential to initiate an action potential?
During the resting state, the membrane potential arises because the membrane is predominantly permeable to K+. An action potential begins at the axon hillock as a result of depolarisation. During depolarisation voltage-gated sodium ion channels open due to an electrical stimulus.
What happens when a threshold stimulus is used?
A threshold stimulus will cause the opening of voltage gated sodium ion channels that will cause further depolarizing stimulus. This stimulus will open still more voltage gated sodium ion channels. The depolarization phase of an action potential is punctuated by the closing of inactivation gates in the voltage gated sodium ion channels.
What is a post-synaptic potential?
True. A postsynaptic potential is a graded potential that is the result of a neurotransmitter released into the synapse between two neurons.
What happens to the action potential when the stimulus strength is increased?
If the stimulus strength is increased, the size of the action potential does not get larger (see figure ). If the size (i.e., amplitude) of the action potential is always the same and independent of the size of the stimulus, how then does the nervous system code the intensity of the stimulus? The trick that the nervous system uses is ...
What is threshold stimulus?
Here, a threshold stimulus refers to that which is just strong enough to bring a resting neuron to threshold. Thus, with maintained threshold stimulus, subsequent action potentials occur only at the end of the relative refractory period of the preceding action potential. The top and bottom traces are on the same time scale.
Is the nervous system frequency modulated?
The trick that the nervous system uses is that the strength of the stimulus is coded into the fre quency of the action potentials that are generated. Thus, the stronger the stimulus, the higher the frequency at which action potentials are generated (see Figs. 1 and 2 below). Therefore, we say that our nervous system is frequency-modulated ...