Neuron Telephone

Neuron Structure and Function

– How an action potential moves along the Neuron fibre?

 

Information is spread through a neuron by nerve impulses (an electrochemical signal called the Action Potential). The “Action Potential” is caused by the movement of positive ions in and out of the axon. In addition, these signals are caused when the positive ions cross the threshold. If the level of stimulation is too low it will not trigger a neural impulse. Without stimulation, the resting potential is -70 mV. This is because inside the axon there are more positive ions on the outside, thus has a negative net charge. When a stimulus crosses the threshold this causes an action we call depolarization. Where channels within the particular section of the axon open up to allow the inflow of Na+ ions. After depolarization occurs we must get our back to our resting potential, this causes the following action called repolarization. We allow K+ ions within this section of the axon and the charge return to normal and actually goes a little bit lower than the resting potential (estimated -90mV) and this is called the refractory period. And when repolarization occurs this causes the next section of the axon to depolarize.

And how long these messages take to go along the axon depends on the type of neuron. Motor Neuron have very long axons so the message will take ever so longer than say an interneuron which has a very short axon.

  • How is a signal sent from the axon of sending neuron to the dendrite of receiving neuron?

The Action Potential reaches the axon terminal button. The action potential causes synaptic vesicles to release neurotransmitters into the synaptic gap. Neurotransmitters diffuse through synapse and subsequently, the gap then binds the receiving receptors of the dendrite. The synaptic vesicles are then recycled by enzymes and are reabsorbed by the axon terminal so we don’t need to destroy and make new synaptic vesicles every time we send a signal from one axon to the receiving dendrite.

  • How the receiving neuron “determines” whether or not to send its own action potential?

The Neurotransmitter message is received as excitatory or inhibitory. If the message is received as excitatory then stimulation of the Action Potential occurs on the receiving neuron (aka repeating the cycle. But if it is inhibitory the message is repressed and no Action Potential takes place. The same message can be excitatory or inhibitory it all depends on the location in which the signal reacts to within the brain.