Examining different properties of compound action potentials (CAPs) by studying the effects of stimulus voltage and stimulus interval in the sciatic nerve of Rana pipiens
Abstract
To gain a better understanding of compound action potentials (CAPs), we observed extracellular recordings from an isolated sciatic nerve of the leopard frog, Rana pipiens. We analyzed properties of CAPs in regards to membrane potential threshold, temporal summation, refractory period, and conduction velocity through various experiments. First we applied increasing stimulus voltage to determine the threshold and maximal CAP amplitude. Our threshold was recorded at 70 mV, which was observed by the first recordable CAP elicited. In order to determine what stimulus would cause all individual neurons to be fired, we continued to increase the voltage by 10 mV until there was no
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The temporal summation is defined as two or more excitatory potentials occurring in succession. When this occurs, an action potential can be observed. The initial time interval used was 1000 µs, but the first elicited compound action potential occurred at a time interval of 400 µs (Figure 2). As the interval was decreased by 100 µs, the amplitude increased along an upward trend.
Following, two successive supra-maximum stimuli and varying the inter-stimulus-interval (ISI) we used to observe the effect of a refractory period on the second compound action potential. At a stimulus voltage of 170 mV, two CAPs were observed to determine the refractory period (Figure 3). As ISI decreased, the first CAP stayed constant but the second CAP decreased as time gap decreased. The refractory period prevented the second CAP from propagating as the ISI decreased to limit the frequency of action potentials and to ensure action potentials propagate in a unidirectional
In the beginning phases of muscle contraction, a “cocked” motor neuron in the spinal cord is activated to form a neuromuscular junction with each muscle fiber when it begins branching out to each cell. An action potential is passed down the nerve, releasing calcium, which simultaneously stimulates the release of acetylcholine onto the sarcolemma. As long as calcium and ATP are present, the contraction will continue. Acetylcholine then initiates the resting potential’s change under the motor end plate, stimulates the action potential, and passes along both directions on the surface of the muscle fiber. Sodium ions rush into the cell through the open channels to depolarize the sarcolemma. The depolarization spreads. The potassium channels open while the sodium channels close off, which repolarizes the entire cell. The action potential is dispersed throughout the cell through the transverse tubule, causing the sarcoplasmic reticulum to release
As the time interval was changed between the shocks, the amplitude of the second CAP began to increase. This was seen when the time interval increased from 1.0 to 1.5. The compound action potential went from 0 to 0.1. The height (or maximum threshold) of the amplitude was seen at about 2.6. Once the time interval was increased past that point the compound action potential fell back down to zero. This was seen in the intervals of 8.0 to 9.0, where the amplitude is 0. To understand why these results were seen in relation to absolute, and relative refractory periods one should understand there definitions. The absolute refractory period, “is a time during which another stimulus given to the neuron (no matter how strong) will not lead to a second action potential” (PhysiologyWeb,2012). This period takes about 1 to 2 milliseconds, and it is a time when the sodium ion channels are inactive. The relative refractory period, “is a period during which a stronger than normal stimulus is needed in order to elicit an action potential”
The merging of certain senses points to a crossing of signals in the brain. Although the theory is an old one, it has come to the forefront of the scientific researcher's minds, with increased focus on the topic.
Action potentials in neurons are facilitated by neurotransmitters released from the terminal button of the presynaptic neuron into the synaptic gap where the neurotransmitter binds with receptor sites on the postsynaptic neuron. Dopamine (DA) is released into the synaptic gap exciting the neighboring neuron, and is then reabsorbed into the neuron of origin through dopamine transporter...
...tory interference model; based on the difference and interference of theta phase between the soma and dendritic processes which results in periodic spatial activity derived from the temporal signal (Burgess N, Barry C, O'Keefe 2007 and Giacomo, Zilli 2007) and the attractor model; based on network dynamics, with the reciprocal firing of grid cells as the basis of periodicity. As the importance of theta cannot yet be effectively determined in humans elucidating the mechanism of grid periodicity will have long lasting implications on the direction of research and may require a critical rethinking of many of the currently accepted models. The chosen papers explore this in two ways: the first paper by examines the effects of the removal of theta on grid cell periodicity and the second seeks to determine if the presence of theta is necessary for normal grid cell activity.
Palka, J. and Olberg, R. (1977). The cercus-to-giant interneuron system of crickets. III. Receptive field organization. J. comp. Physiol. 119, 301–317
The brain is part of the central nervous system, which consists of neurons and glia. Neurons which are the excitable nerve cells of the nervous system that conduct electrical impulses, or signals, that serve as communication between the brain, sensory receptors, muscles, and spinal cord. In order to achieve rapid communication over a long distance, neurons have developed a special ability for sending electrical signals, called action potentials, along axons. The way in which the cell body of a neuron communicates with its own terminals via the axon is called conduction. In order for conduction to occur, an action potential which is an electrical signal that occurs in a neuron due to ions moving across the neuronal membrane which results in depolarization of a neuron, is to be generated near the cell body area of the axon. Wh...
The occurrence of action potential is a very short process. When action potential occurs in the neuron the sodium channels open along the axon and sodium comes in. Because the sodium is positive it make the inside of the axon positive. When both the inside and outside are comparative in charge the sodium storms rushing in and starts the depolarization of the action potential. After this happens the sodium channels begin to close and the potassium channels begin to ...
Kandel, E. R., J. H. Schwarz, and T. M. Jessel. Principles of Neural Science. 3rd ed. Elsevier. New York: 1991.
Schurger, A., Sitt, J. D., & Dehaene, S. (2012). An accumulator model for spontaneous neural activity prior to self-initiated movement. Proceedings of the National Academy of Sciences, 109(42), E2904-E2913. Retrieved March 21, 2014, from http://dx.doi.org/10.1073/pnas.1210467109
These nerve cells are neurons that connected through synapses in a web-like fashion forming neural networks (Coon & Mitterer, 2001). Neural networks make generation and transmission of action potentials (known as electrical impulses) possible along neurons. An action potential is generated across an axon hillock of a nerve cell and is propagated along the axon by the opening of voltage-gated ion channels one after the other causing positive ions to flow in and out the axon (Johnson, 2013). Transmission of action potentials from one neuron to the next involves the release of neurotransmitters from a presynaptic neuron to postsynaptic neurons across a synaptic g... ... middle of paper ... ...
The neuron has two important structures called the dendrite and axon, also called nerve fibers. The dendrites are like tentacles that sprout from the cell and the axon is one long extension of the cell. The dendrites receive signals from other neurons, while the axon sends impulses to other neurons. Axons can extend to more than a meter long. Average sized neurons have hundreds of dendrites; therefore it can receive thousands of signals simultaneously from other neurons. The neuron sends impulses by connection the axon to the dendrites of another nerve cell. The synapse is a gap between the axon and the adjacent neuron, which is where data is transmitted from one neuron to another. The neuron is negatively charged and it bathes in fluids that contain positively charged potassium and sodium ions. The membrane of the neuron holds negatively charged protein molecules. The neuron has pores called ion channels to allow sodium ions to pass into the membrane, but prevent the protein molecules from escaping (potassium ions can freely pass through the membrane since the ion channels mostly restrict sodium ions). When a neuron is stimulated (not at rest), the pores open and the sodium ions rush in because of its attraction to the negatively charged protein molecules, which makes the cell positively charged. As a result, potential energy is released and the neurons send electrical impulses through the axon until the impulse reaches the synapse of any neurons near it.
Action potentials are started at one end of the node, flow passively through the myelinated axon, and pop out the other side to jump to the next node. This jumping of action potentials is called saltatory.
Miller, Kenneth R., and Joseph S. Levine. "The Nervous System." Miller & Levine Biology. Boston, MA: Pearson, 2012. 894-917. Print.