Pathophysiology Of An Electrical Impulse Carrying A Neuronal Message

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.

A. Depolarization; excitatory postsynaptic potential. Sodium would depolarize the membrane and increase the likelihood that the post synaptic neuron would fire an action potential.

f. Depolarized- causes the membrane potential to be decreased. g. Hyperpolarized- the opposite of depolarization where the membrane potential is increased. h. Myelin- provides insulation to axons and speeds up the conduction

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

Partial seizures also referred to as focal seizures, have abnormal excited neuron activity on one part of the brain and in some cases it can increase to other parts of the brain. These specific areas are called the seizure focus. As the activity typically stays around where it started from, there is the potential for it to spread due to the failure of inhibitory mechanisms. Within the seizure focus, neurons experience depolarization, which is then followed by a line of action potentials. The activity involved is defined as proximal depolarizing

While the sodium drives the membrane voltage up the depolarization causes the driving force of potassium, who sits at around -90mV, to become larger. This drives the potassium out and leaves net negative charges within the cell. This continues because potassium wants to reach a voltage of -90mV and the sodium channels are inactive and unable to create an opposing force against it. This causes the cell to dip below resting potential to what is called hyperpolarization. The hyperpolarization phase reactivates the inactivated sodium allowing the cell to depolarize back to resting potential before it deactivates. Calcium also plays a critical role during the action potential, activating the BK channels and contributing to the late repolarization phase. Following the action potentials, after hyperpolarization(AHP) occurs at three different speeds. The fast is caused by the potassium currents through BK channels, the medium AHP is caused by the M-type potassium channels as well as the SK channels, and the slowest AHP is caused by the IsAHP which is a slow-activated calcium-activated potassium channel. (Module 5: Ion channels part

Action potentials act as ‘messengers’ to brain in the form of electrical signals. They are generated by depolarization which is a voltage change in the membrane of a neuron cell. An action potential is produced in each nerve cell and travels along the axon of the nerve cell. The action potential causes a release of a neurotransmitters to

Excitatory post-synaptic potentials (EPSPs) depolarize the membrane and move it closer to the threshold for an action potential.

In our brain we have neurons that communicate every second of the day with one other through their dendrite and axons. Most of the time incoming signals are received in the dendrites and outgoing signals travel down the axon to the nerve terminal. For the neuron to receive the rapid communication due to the long axon, the neuron sends electrical signals, from the cell’s body to the nerve terminal. This process is known as nerve impulses, or action potential. “Brain neurons can transmit signals using a flow of sodium(Na+) and potassium (K+) ions, that produces an electrical spike called an action potential (AP) (Forrest, 2014, P. 1). Action potential is essentially a slight reversal of electric polarity across the membrane. When an action potential takes place, the sodium -potassium pump resets the way sodium and potassium ions were back to their original positions. The sodium-potassium does this to the neuron so when it is then ready to relay another action potential, it will pump when called upon to do so. The Na+/K+ pump has a housekeeping role rather than a direct role in brain signaling (Forrest, 2014, P. 1). For an action potential to be generated the membrane voltage must be strong enough to bring the membrane voltage to a critical value called the threshold.

This is where the Na+ channels are inactivating, this allows the K+ gates to swing open. Due to their being a lot more Na+ ions on the outside and the inside the sodium dashes into the neuron first, sodium is a positive charge, so during depolarization the neurons become a lot more positive. As time passes the Na+ channels inactivates allowing the K+ channels to swing open the K+ channels take more time to open, but once they fully have unfortunately, the internal negativity resting membrane is restored to -70mV (Marieb ; Hoehn;, 2010).

Action potential is an all-or-none response like firing a gun. It begins with a membrane that is outwardly positive and inwardly negative in terms of charge. Sodium is on the outside, and potassium is on the inside. When a stimulus occurs, depolarization takes effect and sodium diffuses into the cell. The reversed polarity initiates an action potential.

The lipid bilayer is impermeable to charged ions, so ions have to pass through ion channels to get in or out of the neuron. When in the resting stage, the sodium channels are almost impermeable to sodium ions. Entry of sodium ions can only be accomplished if the voltage - gated Na+ channel allows it to. This means that there has to be a nerve impulse that results in a change of voltage to open the sodium ion channels allowing Na+ to enter the cell.

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.

Epilepsy is one of the most common neurodegenerative disorder that is occuring in about 1% of the global population (WHO 2016). Epilepsy is defined as a tendency to have more than two recurrent of unprovoked, unpredictable seizures. Epileptic seizures are brief episodes of involuntary movements that involve the entire body (generalized; tonic-clonic) or one part of the body (partial). These seizures are a result of excessive electrical discharges in specific part of the brain (Shneker and Fountain 2003). Different regions of the brain can serve as a site of such unregulated discharges and form different type of seizures. Seizures can range from short lapses of attention and uncontrolled muscle jerks to severe and prolonged convulsions. Nonetheless, one seizure does not signify epilepsy, but more than two in frame time of two years is epilepsy. However, epileptic seizure is manifested with overlapped signs and symptoms with other disorders and disease, which makes it difficult to define specific seizure to epilepsy.

With a basic understanding of neurons and how the nervous system works, it should be known that the brain is a very delicate system; something seemingly minor can cause catastrophic complications. There are two key functions for the neurotransmitters of the brain, one is responsible for communication between cells the other is used to stop or slow it down. Sometimes this complex system becomes out of control and causes a “glitch” in the electrical system of the brain – resulting in what is known as epilepsy.