Action Potential Analysis

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.

1. Neurons is a basic building block of the nervous system. The sensory nerves carry the message from body tissues to the brain and spinal chord to be processed. The motor neurons are then used to send instructions to the body tissue from the brain and spinal cord. Dendrites, which are connected to the body cell (soma) receive information and pass it through the axon. Myelin sheath covers the axon and helps speed the process. When triggered by a signals from our senses or other neurons, the neuron fires an impulse called the action potential. The resting potential is the neuron’s visual charge of positive

As an action potential travels down the axon of the presynaptic neuron, the action potential reaches the axon terminal synaptic vesicles which migrate toward the synapse. They then release neurotransmitters into the synaptic cleft. The neurotransmitters travel through the synaptic cleft and bind to ligand-gated ion channels on the postsynaptic neuron membrane. The channels open and allow chemicals to enter the cell (i.e. sodium). Then positively charged sodium enters the cell and causes the cell to depolarize. The depolarization spreads down the axon and an action potential is generated. The process then starts over at the axon terminals.

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.

Once a presynaptic neuron is passive, an electrical current is spread along the length of the axon (Schiff, 2012). This is known as action potential (Pinel, 2011). Action potential happens once an abundant amount of depolarisation reaches the limit through the entry of sodium, by means of voltage gated sodium channels

Increasing the extracellular potassium reduces the concentration gradient, and less potassium diffuses out of the neuron and into the cell.

An action potential is a short electrical impulse generated at the axon hillock which travels the length of an axon. Its generation happens in three distinct stages, depolarisation, repolarisation and hyperpolarisation. When the threshold of excitation is reached, depolarisation starts, the threshold is between -55mV and -65mV in most neurons. When the neuron is stimulated voltage-activated Sodium (Na+) channels open, allowing Na+ ions to rush into the neuron. This reverses the polarity in the neuron towards its peak of +40mV. At this peak Na+ channels

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

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.

These layers are made of myelin, produced by Schwann cells that are assigned early in the organism’s development. As these layers develop they become tightly packed around the axons, and the main benefit of this coating is that it prevents the exiting and entering of ions for a distance along the axons. This protection allows the ions to travel further and cause action potentials at a faster rate (Norton and Cammer, 1984). Action potentials are caused by the influx of sodium ions followed by the slow efflux of potassium ions. The process of rapid action potentials jumping from one node to the next is called salutatory conductance (Black et al., 1991).

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

Once in the synapses, the impulses triggers the release of chemical messages called neurotransmitters; which then bind to receptors on the receiving cell as the transmission of the impulse repeated again. The message or impulse continues traveling from one neuron to the next throughout the body until it reaches its destination as it relays a signal. All of this activity happens in less than a split second and without conscious thought. At the end of this process, the brain has the task of interpreting the message and making the decision as to what to do with this new information. (Carlson, 2011.Pg.45-52)

Nerve cells generate electrical signals to transmit information. Neurons are not necessarily intrinsically great electrical conductors, however, they have evolved specialized mechanisms for propagating signals based on the flow of ions across their membranes.

I. Neurons/nerve cells A neuron is a cell specialized to conduct electrochemical impulses called nerve impulses or action potentials. Neuron is the main cellular component of the nervous system, a specialized type of cell that integrates electrochemical activity of the other neurons that are connected to it and that propagates that integrated activity to other neurons. They are the basic information processing structures in the CNS. There are as many as 10,000 specific types of neurons in the human brain, A. Types of Neurons a. Motor neurons >These transmit impulses from the central nervous system to the *

An action potential is an electrical impulse that moves along a neuron axon. They enable signals to travel fast along the neuron fiber. They last less than two milliseconds. When information is passed between two neurons, the first neuron gets stimulated and then an action potential happens and the information is in the other neuron. Action potentials result from the flow of ions across the neuronal cell membrane. Without action potentials information would not get to other