Concept of Neural Conduction in Biopsychology

Concept of Neural Conduction in Biopsychology - This article will explain how neurons transmit and receive signals. Through this article is expected to be able to understand the concepts of neural conduction.

Resting Membrane Potential

Membrane Potential → charge difference between the inside and outside the cell.

To record the membrane potential of a neuron → by positioning the tip of one electrode within the neuron and the other end of the electrode outside the neuron in the extracellular fluid.

When both ends of the electrode are in the extracellular fluid → the voltage difference between the two electrodes is zero.

However, when the tip of the intracellular electrode is inserted into the neuron → steady potential of about -70mV → potential resting neuron is about 70mV smaller than outside the neuron.

Resting potential neurons → neurons in a state of "break" → with a load of -70mV across its membrane → polarized .

Resting potential → the ratio between positive and negative charges inside the neuron is greater than outside the neuron.

Why is unbalanced charge distribution possible? → Relation to the interaction between the four factors → the two factors that act to distribute the ions evenly throughout the intracellular fluid as well as the extracellular nervous system and two features of neural membranes that neutralize the effects of homogenizing .

Homogenizing factors :

Random motion → Ions in neural networks move constantly random → particles in random motion tend to become evenly distributed as they are more likely to decrease the concentration gradient than to increase it → more likely to move from high concentration areas to concentration areas Lower than otherwise
Pressure electrostatic → any accumulated electric charge, positive or negative, in an area is likely to be interrupted by repulsion (repulsive) between electrical charges are the same in an area and attractions (attraction) between charges opposite Will be concentrated elsewhere.

No single group of ions is evenly distributed to either side of the neural membrane.

Four kinds of ions that contribute significantly to the resting potential → sodium ions (Na ⁺ ), potassium ions (K ⁺ ), chloride ions (Cl ^- ) and various negatively charged protein ions.

The concentration of Na ⁺ and Cl ^- outside of resting neurons is greater than inside, while K ⁺ ions are more concentrated inside. Negatively charged protein ions are synthesized inside the neurons and most of them remain there.

Two neural membrane properties are responsible for the distribution of Na ⁺ , K ⁺ , Cl ^- and unequal protein ions in resting neurons. One of the properties is passive → does not involve energy consumption. Other properties are active → involves energy consumption.

In the resting of K ⁺ and Cl ^- neurons can easily pass through the neural membrane, Na ⁺ passes through it with great difficulty, and negatively charged protein ions simply can not pass it → differential permeability .

The ions pass through the neural membrane in the special pores → ion channels → each type is specialized to pass certain ions.

Why are the concentrations of intracellular and extracellular Na ⁺ and K ⁺ ions in neurons constant? → Hodgkin and Huxley found that there are active mechanisms in the cell membrane to reject the influx (inflows) of Na ⁺ ions by pumping out Na ⁺ ions as soon as they enter, and to deny the efflux ( ion outflow) Ion K ⁺ by pumping K ⁺ ions as soon as they break out.

Concept of Neural Conduction in Biopsychology_

Captions: the passive and active factors that affect the distribution of Na ^+, K ^+, Cl ^- ions along the neural membrane. Continuous passive factors push K ⁺ ions out of the resting neurons and Na ⁺ ions enter → K ⁺ ions must be actively pumped out to maintain equilibrium resting .

The transport of ions is carried out by a mechanism that consumes energy in the cell membrane → exchange of 3 Na ⁺ ions in neurons for 2 K ⁺ ions outside the neuron → transported by the transporter → sodium-potassium pumps .

Transporter → the transporter, the mechanism inside the membrane of a cell actively transporting ions or molecules throughout the cell membrane.

Generation and Conducting Potential of the Synaptic Post

When neurons fire ( fire ), neurons release chemicals from the terminal button ( neurotransmitters ), which diffuses across the synaptic cracks and interacts with a specific receptor molecules on the membrane of neurons receptive further along the circuit.

When neurotransmitter molecules are bound to post-synaptic receptors, they usually have two effects, depending on the structure of the neurotransmitter and the receptor in question:

They may depolarize receptive membranes → reduce the resting membrane potential from -70 to -67 mV, for example
They hyperpolarize the receptor membrane → raise the resting membrane potential from -70 mV to -72 mV, for example

Post-synaptic depolarization → excitatory post-synaptic potentials (EPSP) → increases the likelihood that neurons will fire.

Post-synaptic hyperpolarization → inhibitory post-synaptic potentials (IPSP) → reduces the likelihood that neurons will fire.

Both EPSP and IPSP are graded responses → the proportional amplitudes of EPSP and IPSP with the intensity of the signals generating them → weak signals generate small pos- sons of synaptic posi- tions, and strong signals generate large pos- sons of synaptic potential.

EPSP and IPSP passively pass from their generating sites in synapses, usually in dendrites or cell bodies, in a way very similar to electrical signals running through a cable.

Two important characteristics of post-synaptic potential transmission:

Rapid post-synaptic potency
EPSP and IPSP transmissions are decremental → EPSP and IPSP amplitudes decrease as they travel along neurons → most EPSP and IPSP do not go too far along an axon

Synaptic Pos Potential Integration and Potential Action Generation

Whether a neuron fires, depending on the balance between eksitatorik and inhibitorik signals reaching the axon → previously believed that the action potential is raised in axon hillock → they are actually raised in the part adjacent to the axon.

When the amount of depolarization and hyperpolarization reaches the axon portion adjacent to the axon hillock enough to depolarize the membrane to a level called threshold of excitation , which is about -65mV, then an action potential is raised near the axon hillock

Potential action ( action potential ) is a reversal of the membrane potential of about -70mV to about + 50mV that is massive but only briefly (lasts for 1 millisecond). These action potentials are all-or-none response → they appear at full magnitude , or do not appear at all.

The result of the action potential is the addition of all the potential poses of synapses in the multipolar neurons, reaching their axons, and deciding whether to shoot or not to shoot by their numbers.

Addition or merge of individual signals into an overall signal → integration .

There are two kinds of potential sums of pos- synapses:

Spatial summation → the sum of its potential synapses comes from two kinds of synapses
Temporal summation → the summed-synaptic potential of the synapses is derived from the same synapses

Each neuron constantly integrates signals from time to time as well as from space to space as long as it is constantly bombarded with stimuli through thousands of synapses that cover the dendrites and cell bodies.

In some ways, the firing of a neuron is like the firing of a gun → when the weapon trigger is pressed, the trigger will gradually return to its position until it causes the gun to fire the bullet → when a neuron is stimulated, it becomes less polarized until the excitation threshold is reached and Shooting occurred.

Neural shooting is all-or-none events → stimulating a neuron more intensely will not increase the speed or amplitude of the action it produces.

Potential Conduction of Action

Basic Ionic Action Potential

The action potential is produced and is carried along the axon through the action of voltage-activated ion channels → the neuron channel opening or closing in response to the membrane potential rate change .

Membrane potential of a neuron at resting time is relatively constant.But everything suddenly changes when the membrane potential of the axon goes down to the threshold level of excitation → voltage-activated sodium channels in the wide open axon membrane → Na ⁺ ions Rushes into it → suddenly pushing the membrane potential from about -70mV to about + 50mV → triggering the opening of voltage-activated potassium channels → K ⁺ ions near the membrane in the thrust out of the cell through the channels → the action potential Approaching peak → positive internal charge → after about 1 millisecond of sodium channels closing → expiry <aI = 16> rising phase (action phase) action potential and commencement of repolarization-repolarization achieved → potassium channels gradually closing → K ⁺ ions flowing outside the neuron → hyperpolarization for a moment.

The amount of ions flowing through the membrane during the action potential occurs, very little when associated with the total amount in and around the neuron. The action potential involving only ions right next to the membrane → an action potential has only a small effect on the relative concentration of the various ions inside and outside the neuron → resting ion concentration next to the membrane is rapidly re-established by the random movement of ions.

Refractory Period

There is a brief period lasting about 1-2 milliseconds after the initiation of an action potential, which is impossible to generate a second action potential → absolute refractory period → then followed by a relative refractory period (an impossible period to shoot the neuron again, except by applying the rate Stimulation higher than its normal level).

The refractory period is responsible for the important characteristics of neural activity:

The action potential usually runs along the axon in one direction only
The rate of neural shooting is related to the intensity of the stimulation

Potential Conduction of Axial Action

The action potential conduction along an axon differs in two ways by EPSP and IPSP conduction:

The conduction action potentials along the axons are nondecremental → the action potential is not weakened as long as they travel along the axonal membrane
The potential of action is slower than the post-synaptic potential

The reason for these two differences is that the conduction of EPSP and IPSP is passive, while the conduction of axonal action potentials is largely active.

The conduction of the beronelinated axons

In terminated axons can pass through the axonal membranes only in the nodes of Ranvier ( Ranvier nodes ) → the cracks between adjacent myelin segments. In the axons are delineated, the axonal sodium channels are concentrated in the Ranvier node.

When an action potential is generated in a terminated axon the signal is passively (instantaneously and decrementally) along the first myelin segment until the next Ranvier node → the signal is slightly reduced but is strong enough to open the voltage-activated sodium channels at that node and to generate potential Other full actions → the action potential is constructed passively along the axon to the next node → the action potential is raised again → so on.

Myelination increases the speed of axonal conduction.

Transmission of action potential in axonized axons → saltatory conduction → signal "jumps" along the axon, from node to node.

Because of the important role of myelin in neural conduction, it is not surprising that neurodegenarative diseases (nerve-attacking disorders) that attack myelin have detrimental effects on neural and behavioral activity.

Speed of Axonal Conduction

The velocity of the action potential sequenced along the axon depends on the diameter of the axons and the mielinations → conduction in large diameter axons progresses faster and faster in the delineated axons.

Mammalian motor neurons are large and hallucinating - some of which can conduct at a rate of 100 m / sec.

Conversely, unelukelinated axons → conducts action potentials at a speed of about 1 m / s.

Synaptic Transmission

This section examines how the action potentials arriving at the terminal buttons trigger the release of neurotransmitters into synapses and how neurotransmitters carry signals to other cells (see Pinel, 2009, p. 107).

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