Cellular Molecules: A Compound Action Potential

Summation of Excitatory postsynaptic potential and Inhibitory postsynaptic potential must take place. More specifically spatial summation, which means that all the types of potential must add up to be greater (less negative) than the threshold potential of -55mv for an action potential to occur in the postsynaptic neuron.

1. Exceeding the threshold depolarization at the trigger zone DECREASES the likelihood of generation of action potential.

If the nerve impulse is not released than it will not cause an action potential.

As well as these there are also the axon of the cell which is covered in myelin sheaths which carried information away from the cell body and hands the action potentials, these are small short bursts of change in the electrical charge of the axon membrane through openings of ion channels, off to the following neurons dendrites through terminal buttons at the end of the axons. Whenever an action potential is passed through these terminal buttons it releases a chemicals that pass on the action potential on to the next neuron through the terminal button and dendrite connection. The chemicals that are

To send a message, a neuron will send a ripple of electrical energy down its axon. This ripple is called "action potential." The way it works is by changing the chemical makeup of the axon's negatively charged interior. Positively charged sodium ions move into the cell and negatively charged potassium ions move out, then the ions move to their original positions. This produces a wave of positively charged

This stage is called repolarisation. The K+ channels then close, the sodium-potassium pump restarts, restoring the normal distribution of ions either side of the cell surface membrane and thus restoring the resting potential. In response to this the Na+ channels in that area would open up, allowing Na+ ions to flood into the cell and thus reducing the resting potential of the cells. If the resting potential of the cell drops to the threshold level, then an action potential has been generated and an impulse will be fired.

CAP or compound action potential is a measure of the sum of the "all or none" single action potential of a group of fibers in a single nerve. The single action potentials are events that occur when sodium channels are activated causing the depolarization of a neuron. Single Action potentials are considered to be all or none responses, they travel down the length of the axon and then release a neurotransmitter into the synapse.

3. A nerve is a bundle of axons, and some nerves are less sensitive to lidocaine. If a nerve, rather than an axon, had been used in the lidocaine experiment, the responses recorded at R1 and R2 would be the sum of all the action potentials (called a compound action potential). Would the response at R2 after lidocaine application necessarily be zero? Why or why not?

When a membrane is excited depolarization begins. When the membrane depolarizes the resting membrane potential of -70 mV becomes less negative. When the membrane potential reaches 0 mV, indicating there is no charge difference across the membrane. the sodium ion channels start to close and potassium ion channels open. By the time the sodium ion channels finally close. The membrane potential has reached +35 mV. The opening of the potassium channels allows K+ to flow out of the cell down its electrochemical gradient ( ion of like charge are repelled from each other). The flow of K+ out of the cell causes the membrane potential to move in a negative direction. This is referred to as repolarization. ( Marieb & Mitchell, 2009). As the transmembrane potential comes back down towards its resting potential level and the potassium channels begins to close, the trasmembrane potential level goes just below -90mV, causing a brief period of hyperpolarization (Martini, Nath & Bartholomew, 2012). Finally, as the potassium channels close, the membrane turns back to its resting potential until it is excited or inhibited again.

Depolarization in membrane potential triggers an action potential because nearby axonal membranes will be depolarized to values near or above threshold voltage.

Every organism has thousands of these junctions that control the movements of the body and cause the heart to beat. The neuromuscular junction is a chemical synapse consisting of the point of contact, between the axe on terminals of a motor neuron and the motor endplate other skeletal muscle fiber. The events at the neuromuscular occur in seven coordinated steps. 1. The action potential arrives at the axon terminal. 2. Voltage-regulated calcium channels open allowing calcium ions to enter the axon terminal. 3. Presence of calcium ions in the axon terminal cause synaptic vesicles to fuse with the membrane. 4. Acetylcholine is released into the synaptic cleft and calcium ions are pumped out of the axon terminal. 5. Acetylcholine binds to receptor sites on the motor end plate, causing an influx of sodium ions and a small efflux of potassium ions, which results in a local depolarization of the motor end plate. 6. An action potential is generated which propagates along the sarcolemma in all directions and down the T tubules. 7. The action potential causes the release of calcium ions from the terminal cisternae into the

It is a neurological process which involves passing of nerve impulses from one neuron to another. This process is triggered through chemical and electrical means. This process has following stages; stage 1, where nerve cells are at rest with many components. Stage 2, nerve cells are stimulated. Stage 3, the sodium channels open. Stage 4, their diffusion takes place. Stage 5, the channels of Potassium open. Stage 6, the diffusion of K ions happens. Stage 7, action potential triggers current. Stage 8, action potential takes place in sequence with axon length in the form of impulse.

Excitatory Postsynaptic Potentials (EPSPs): EPSPs increase the postsynaptic neuron’s likelihood to generate an action potential by generating a local depolarization. EPSPs result from excitatory stimuli, such as an excitatory neurotransmitter (Glutamate) released by the presynaptic neuron. Excitatory stimuli will bind and open ligand-gated Na+ channels, allowing Na+ ions to move inside a cell down their concentration gradient. The influx of Na+ ions will cause a local depolarization at the postsynaptic membrane, which if summated can reach threshold and fire an action potential.

Whenever the balance is altered, the process of transmitting electrical signals, which is called action potential initiates by carrying information across a neuron’s axon; which is called resting membrane potential. This process occurs as uneven ions distribution flow across cell membrane, creating electrical potential. As a result, the duration of active potential can be as fast as 1 ms. Similarly, the average resting membrane is between -40 mV and -80 mV. Since the membrane from inside is more negatively charged than the outside, it reflected on the negative average voltage readings of the resting membrane.

The compound action potential adds up all the action potentials that each individual neuron experiences in the sciatic nerve. Different stimulus amplitudes cause different neurons to fire an action potential; this is due to the fact that each neuron has a different threshold potential, or the minimum voltage the neuron needs to fire an action potential. The individual neuron action potential is an ‘all-or-nothing’ event, but the CAP, as a summation of different individual neurons, is not. The CAP amplitude will increase with larger stimulus potentials because more neurons with higher individual thresholds will be recruited. For this frog sciatic nerve, there are three fiber types, A, B, and C. A fibers are further divided, in the order of decreasing diameter, into α, β, γ, and δ fibers. There is an inverse relationship between the diameter of the nerve fiber and the threshold potential: the larger the diameter, the lower the threshold. Thus, as the largest fibers, the Aα neurons will be the first to be stimulated at a low stimulus potential, and the Aδ neuron fibers will be the last to be recruited. Because the sciatic nerve is mostly composed of A fibers, the recruitment of A-subtype nerve fibers are more readily distinguishable from the data. The minimum potential required to stimulate the Aα fibers was between 75 mV and 80 mV. Once the stimulus potential reached 90 mV, Aβ neurons were recruited and contributed to the increase in amplitude of the CAP. At a stimulus