Explain how neurons communicate. Include electric and chemical components of communication.
Neurons refer to the fundamental units of the brain and the nervous system, responsible for communication. Notably, neurons are made up of specialized parts known as Dendrites, cell bodies, and Axons, specially designed to transmit information into the synapses, thus communicating with the other cells and neurons (Woodruff, 2017). The cell body comprises the nucleus and cell organelles that perform the vital function of the cell, while the dendrites are part of the cell body that receives signals. On the other hand, the axon is a long outcrop of the cell body receives directs signals. Furthermore, neurons can be categorized into afferent and efferent neurons. Afferent neurons are sensory neurons whose function is to transmit and receive stimuli, while efferent neurons are motor neurons that create a reaction in the beset cells. For instance, when the first neuron receives information, an electrical impulse is triggered, releasing the chemical signal (the neurotransmitters). The neurotransmitters then move into the synapse where they bind with receptors, thus relaying the information to the second neuron.
Neurons communicate mainly through electrical and chemical signals. The electrical signals are commonly known as ‘action potentials’ which relays information from one neuron to another. On the other hand, the chemical signals are neurotransmitters transmitting information from one neuron to another (Woodruff, 2017). Upon stimulation by stimuli, a neuron produces an electrical potential that travels through it
There are two types of channels that transmit electrical signals. They include chemical gated and voltage-gated channels. The graded potentials travel over short distances and are stimulated by the opening of chemically gated channels. Action potentials travel over long distances and are motivated by the opening of the voltage-gated channels. The graded potential that results in depolarization is excitatory, while the one that results in hyperpolarization is inhibitory. The membrane threshold voltage is -55Mv in mammals. The graded potentials travel through the neuron to reach the trigger zone. If they depolarize the membrane above the threshold voltage, an action potential is stimulated down the axon.
Spatial summation occurs when the action potentials from simultaneous graded potentials are initiated. The speed of conduction of the action potential depends on the diameter of the axon. The larger the diameter, the lower the resistance, hence, the faster the speed. On the other hand, the myelin sheath acts like an insulator that prevents the leaking out of current from the cells. However, the Nodes of Ranvier constitute the non-insulated regions of the axon. During depolarization, the sodium ions enter through the open channels. The loss of current through the nodes of Ranvier slows down the speed of the action potential.
Nonetheless, a cell may not be able to repeat an action potential. This is referred to as a refractory period. There are two types of refractory periods. An absolute refractory period occurs when a second action potential only occurs after completing the first action potential. A relatively refractory period occurs when a large suprathreshold starts a second action potential. The absolute refractory periods prevent the backpropagation of the Action Potential into the cell body. Generally, refractory periods limit the transmission of signals.
This production comprises the electrical component of neuron communication. As the electrical current approaches the axon terminal, it initiates the release of particular chemical messengers. The release of messenger chemicals, therefore, constitutes the chemical component of neuron communication. The chemical messengers (neurotransmitters) enhance the interaction between one neuron to the other (Dismukes, 1979). A synapse is a gap between the signal transmitting neuron and the signal receiving neuron.
It is important to note that an action potential triggers neurotransmitters- a rapid change in membrane potential that triggers communication impulse, which then triggers a similar ‘action potential’ in the next neuron, thereby relaying communication. When no signal is transmitted, the neurons are at a resting-potential equivalent to -70millivolts. Communication is initiated when an adjacent neuron sends a neurotransmitter. The neurotransmitter binds the neuron. In case it is excitatory, it causing the gated ion channels to open up. Opening up of the gated ion channels allows entry of sodium ions into the cell. Consequently, the cell becomes more positive. If the neurotransmitter is inhibitory, the gated ion channels open to release potassium ions from the cell. As a result, the potential of the cell becomes more negative. An action potential is generated when there are enough excitatory transmitters that can surpass the threshold level. Upon exceeding the threshold level, an electrical potential is transmitted along the axon. This process is referred to as depolarization. Depolarization is followed by the reestablishment of the resting potential by the neuron’s ion pumps. In this process, the neuron gets into a refractory period, characterized by zero action potential. This condition is referred to as hyperpolarization. Restoration of the potential prepares the neuron for a new stimulus (Yuste et al., 2011). In a nutshell, neurotransmitters play a pivotal role as far as communication between neurons is concerned.
References
Dismukes, R. K. (1979). New concepts of molecular communication among neurons. Behavioral and Brain Sciences, 2(3), 409-416.
Peterka, D. S., Takahashi, H., & Yuste, R. (2011). Imaging voltage in neurons. Neuron, 69(1), 9-21.
1.Silverthorn, D.U (1998). Human Physiology: An Integrated Approach. New Jersey: Prentice-Hall. Ch.8, pp.208-224.
Woodruff, A. (2017). Action potentials and synapses. Queensland Brain Institute – University of
Queensland. https://qbi.uq.edu.au/brain-basics/brain/brain-physiology/action-potentials
and-synapses