When Talking About the Movement of Neurotransmitters, What Can We Accurately Say?

Chapter 4. Brains, Bodies, and Behaviour

4.1 The Neuron Is the Building Block of the Nervous System

Learning Objectives

1. Describe the structure and functions of the neuron.
2. Depict a diagram of the pathways of communication inside and betwixt neurons.
3. List iii of the major neurotransmitters and describe their functions.

The nervous system is composed of more than 100 billion cells known as neurons. A neuron is a cell in the nervous system whose office it is to receive and transmit information. As you tin see in Figure 4.1, "Components of the Neuron," neurons are made up of iii major parts: a jail cell body, or soma, which contains the nucleus of the cell and keeps the cell alive; a branching treelike fibre known as the dendrite, which collects information from other cells and sends the information to the soma; and a long, segmented fibre known as the axon, which transmits information abroad from the cell body toward other neurons or to the muscles and glands. Figure 4.2 shows a photo of neurons taken using confocal microscopy.

Figure 4.1 Components of the Neuron.

Figure 4.two The nervous system, including the brain, is fabricated up of billions of interlinked neurons. This vast interconnected web is responsible for all human thinking, feeling, and behaviour.

Some neurons have hundreds or fifty-fifty thousands of dendrites, and these dendrites may themselves exist branched to allow the cell to receive information from thousands of other cells. The axons are also specialized, and some, such every bit those that send letters from the spinal cord to the muscles in the hands or anxiety, may be very long — fifty-fifty up to several feet in length. To improve the speed of their communication, and to keep their electric charges from shorting out with other neurons, axons are often surrounded past a myelin sheath. The myelin sheath is a layer of fat tissue surrounding the axon of a neuron that both acts equally an insulator and allows faster transmission of the electrical signal. Axons branch out toward their ends, and at the tip of each branch is a terminal button.

Neurons Communicate Using Electricity and Chemicals

The nervous system operates using an electrochemical procedure. An electric accuse moves through the neuron itself, and chemicals are used to transmit information between neurons. Within the neuron, when a signal is received by the dendrites, it is transmitted to the soma in the form of an electrical signal, and, if the signal is potent enough, information technology may so be passed on to the axon and then to the terminal buttons. If the indicate reaches the terminal buttons, they are signalled to emit chemicals known every bit neurotransmitters, which communicate with other neurons across the spaces betwixt the cells, known as synapses.

The following video clip shows a model of the electrochemical action of the neuron and neurotransmitters:

The Electrochemical Activeness of the Neuron [YouTube]: http://www.youtube.com/watch?five=TKG0MtH5crc

The electric signal moves through the neuron every bit a result of changes in the electrical charge of the axon. Normally, the axon remains in the resting potential, a state in which the interior of the neuron contains a greater number of negatively charged ions than does the area outside the cell. When the segment of the axon that is closest to the cell torso is stimulated past an electrical point from the dendrites, and if this electrical point is strong plenty that it passes a certain level or threshold, the prison cell membrane in this first segment opens its gates, allowing positively charged sodium ions that were previously kept out to enter. This change in electric charge that occurs in a neuron when a nerve impulse is transmitted is known as the activeness potential. Once the action potential occurs, the number of positive ions exceeds the number of negative ions in this segment, and the segment temporarily becomes positively charged.

As you can run into in Figure iv.3, "The Myelin Sheath and the Nodes of Ranvier," the axon is segmented past a series of breaks betwixt the sausage-similar segments of the myelin sheath. Each of these gaps is a node of Ranvier.^[1] The electrical charge moves down the axon from segment to segment, in a set up of minor jumps, moving from node to node. When the action potential occurs in the first segment of the axon, information technology quickly creates a similar change in the side by side segment, which so stimulates the next segment, and so forth as the positive electrical impulse continues all the way down to the end of the axon. As each new segment becomes positive, the membrane in the prior segment closes up again, and the segment returns to its negative resting potential. In this fashion the action potential is transmitted along the axon, toward the terminal buttons. The entire response along the length of the axon is very fast — it tin happen up to 1,000 times each second.

Figure 4.3 The Myelin Sheath and the Nodes of Ranvier. The myelin sheath wraps around the axon but too leaves small-scale gaps called the nodes of Ranvier. The action potential jumps from node to node as it travels downward the axon.

An important aspect of the action potential is that it operates in an all or nothing style. What this means is that the neuron either fires completely, such that the action potential moves all the way downwards the axon, or it does not fire at all. Thus neurons tin provide more energy to the neurons down the line by firing faster simply not by firing more strongly. Furthermore, the neuron is prevented from repeated firing by the presence of a refractory period — a brief fourth dimension after the firing of the axon in which the axon cannot fire again because the neuron has non even so returned to its resting potential.

Neurotransmitters: The Body's Chemical Messengers

Not only do the neural signals travel via electric charges within the neuron, but they also travel via chemical transmission between the neurons. Neurons are separated by junction areas known every bit synapses,^[2] areas where the concluding buttons at the end of the axon of one neuron nearly, just don't quite, touch the dendrites of another. The synapses provide a remarkable part because they allow each axon to communicate with many dendrites in neighbouring cells. Considering a neuron may have synaptic connections with thousands of other neurons, the communication links among the neurons in the nervous system allow for a highly sophisticated communication system.

When the electric impulse from the action potential reaches the stop of the axon, it signals the terminal buttons to release neurotransmitters into the synapse. A neurotransmitter is a chemical that relays signals beyond the synapses betwixt neurons. Neurotransmitters travel across the synaptic space between the terminal button of ane neuron and the dendrites of other neurons, where they bind to the dendrites in the neighbouring neurons. Furthermore, different last buttons release different neurotransmitters, and different dendrites are particularly sensitive to different neurotransmitters. The dendrites volition admit the neurotransmitters only if they are the right shape to fit in the receptor sites on the receiving neuron. For this reason, the receptor sites and neurotransmitters are often compared to a lock and key (Figure 4.4, "The Synapse").

Figure 4.four The Synapse. When the nerve impulse reaches the terminal button, information technology triggers the release of neurotransmitters into the synapse. The neurotransmitters fit into receptors on the receiving dendrites in the manner of a lock and fundamental.

When neurotransmitters are accepted past the receptors on the receiving neurons, their effect may be either excitatory (i.e., they make the jail cell more likely to fire) or inhibitory (i.e., they make the jail cell less likely to burn down). Furthermore, if the receiving neuron is able to accept more than one neurotransmitter, it will exist influenced by the excitatory and inhibitory processes of each. If the excitatory effects of the neurotransmitters are greater than the inhibitory influences of the neurotransmitters, the neuron moves closer to its firing threshold; if it reaches the threshold, the action potential and the process of transferring information through the neuron begins.

Neurotransmitters that are not accepted by the receptor sites must be removed from the synapse in order for the adjacent potential stimulation of the neuron to happen. This process occurs in part through the breaking down of the neurotransmitters past enzymes, and in office through reuptake, a process in which neurotransmitters that are in the synapse are reabsorbed into the transmitting terminal buttons, ready to again exist released after the neuron fires.

More than 100 chemical substances produced in the trunk have been identified as neurotransmitters, and these substances take a wide and profound upshot on emotion, cognition, and behaviour. Neurotransmitters regulate our appetite, our memory, our emotions, as well as our musculus action and motility. And as you lot can see in Table iv.1, "The Major Neurotransmitters and Their Functions," some neurotransmitters are also associated with psychological and physical diseases.

Drugs that we might ingest — either for medical reasons or recreationally — can deed like neurotransmitters to influence our thoughts, feelings, and behaviour. An agonist is a drug that has chemic properties like to a particular neurotransmitter and thus mimics the effects of the neurotransmitter. When an agonist is ingested, it binds to the receptor sites in the dendrites to excite the neuron, acting every bit if more of the neurotransmitter had been present. As an example, cocaine is an agonist for the neurotransmitter dopamine. Considering dopamine produces feelings of pleasure when information technology is released by neurons, cocaine creates similar feelings when it is ingested. An adversary is a drug that reduces or stops the normal effects of a neurotransmitter. When an antagonist is ingested, it binds to the receptor sites in the dendrite, thereby blocking the neurotransmitter. As an example, the toxicant curare is an antagonist for the neurotransmitter acetylcholine. When the toxicant enters the brain, it binds to the dendrites, stops communication amongst the neurons, and usually causes death. All the same other drugs work by blocking the reuptake of the neurotransmitter itself — when reuptake is reduced by the drug, more neurotransmitter remains in the synapse, increasing its action.

Table four.one The Major Neurotransmitters and Their Functions

[Skip Table]
Neurotransmitter	Description and function	Notes
Acetylcholine (ACh)	A common neurotransmitter used in the spinal cord and motor neurons to stimulate muscle contractions. It's also used in the brain to regulate memory, sleeping, and dreaming.	Alzheimer's illness is associated with an undersupply of acetylcholine. Nicotine is an agonist that acts like acetylcholine.
Dopamine	Involved in movement, motivation, and emotion, Dopamine produces feelings of pleasance when released by the encephalon's reward organization, and information technology'south too involved in learning.	Schizophrenia is linked to increases in dopamine, whereas Parkinson's disease is linked to reductions in dopamine (and dopamine agonists may be used to treat information technology).
Endorphins	Released in response to behaviours such as vigorous exercise, orgasm, and eating spicy foods.	Endorphins are natural pain relievers. They are related to the compounds found in drugs such as opium, morphine, and heroin. The release of endorphins creates the runner's high that is experienced after intense physical exertion.
GABA (gamma-aminobutyric acrid)	The major inhibitory neurotransmitter in the encephalon.	A lack of GABA tin can lead to involuntary motor actions, including tremors and seizures. Alcohol stimulates the release of GABA, which inhibits the nervous system and makes u.s. feel drunk. Low levels of GABA tin can produce anxiety, and GABA agonists (tranquilizers) are used to reduce anxiety.
Glutamate	The most common neurotransmitter, it's released in more ninety% of the brain's synapses. Glutamate is institute in the food condiment MSG (monosodium glutamate).	Backlog glutamate can cause overstimulation, migraines, and seizures.
Serotonin	Involved in many functions, including mood, appetite, sleep, and aggression.	Low levels of serotonin are associated with depression, and some drugs designed to treat depression (known equally selective serotonin reuptake inhibitors, or SSRIs) serve to prevent their reuptake.

Key Takeaways

• The key nervous system (CNS) is the collection of neurons that make upwards the encephalon and the spinal string.
• The peripheral nervous arrangement (PNS) is the collection of neurons that link the CNS to our skin, muscles, and glands.
• Neurons are specialized cells, plant in the nervous system, which transmit information. Neurons contain a dendrite, a soma, and an axon.
• Some axons are covered with a fatty substance known every bit the myelin sheath, which surrounds the axon, acting as an insulator and assuasive faster manual of the electric signal.
• The dendrite is a treelike extension that receives information from other neurons and transmits electrical stimulation to the soma.
• The axon is an elongated fibre that transfers information from the soma to the terminal buttons.
• Neurotransmitters relay information chemically from the terminal buttons and across the synapses to the receiving dendrites using a lock and key type of system.
• The many different neurotransmitters piece of work together to influence cognition, memory, and behaviour.
• Agonists are drugs that mimic the actions of neurotransmitters, whereas antagonists are drugs that cake the actions of neurotransmitters.

Exercises and Critical Thinking

1. Draw a movie of a neuron and characterization its chief parts.
2. Imagine an action that you lot engage in every 24-hour interval and explain how neurons and neurotransmitters might work together to assistance you lot appoint in that action.

Image Attributions

Figure 4.2: "Confocal microscopy of mouse encephalon, cortex" by ZEISS Microscopy (http://www.flickr.com/photos/zeissmicro/10799674936/in/photostream/) used nether CC By-NC-ND 2.0  (http://creativecommons.org/licenses/by-nc-nd/2.0/deed.en_CA) license.

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Source: https://opentextbc.ca/introductiontopsychology/chapter/3-1-the-neuron-is-the-building-block-of-the-nervous-system/

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