BIOLOGICAL BASES OF BEHAVIOR: NERVOUS SYSTEM, BRAIN - NEUROPSYCHOLOGY - 2024

The study of the biological bases of behavior is the union between two disciplines in charge of understanding human behavior: psychology and biology. Although an important part of our behavior is determined by our social environment, our biology has a great weight on who we are and how we act.

Although the exact relationship between our biology and our behavior is still not entirely clear, in recent decades much progress has been made in the study of this discipline. Among other topics, researchers have focused on better understanding the functioning of our nervous system and its relationship to our mental processes.

Of special importance is the study of our brain, a discipline known as neuroscience. On the other hand, thanks to theoretical models such as biopsychosocial, more and more emphasis is placed on the relationship between biology, environment and mental processes to explain human behavior.

Nervous system

The nervous system is the part of an organism in charge of detecting signals from both the external and internal world, and of creating and transmitting the appropriate responses to the motor organs. It is one of the fundamental components of animal organisms.

In the case of humans, the nervous system is especially complex. It is usually considered that the bodies in charge of transmitting information and preparing responses are organized into two large groups:

- The central nervous system, made up of the spinal cord and the brain.

- The peripheral nervous system, made up of several types of nerves that transmit information from the organs to the brain and vice versa.

Both subgroups of the nervous system are made up mainly of neurons, a special type of cell responsible for transmitting and processing information.

Central Nervous System

The vast majority of multicellular animals have a central nervous system, with the exception of some simple organisms such as sponges.

However, the complexity of the central nervous system differs enormously between species, but in almost all it consists of a brain, a central nervous cord, and a large number of peripheral nerves leading from it.

In the case of humans, our brain is the most complex in the entire animal kingdom. This organ is in charge of processing all the information provided by the senses, which it receives through the spinal cord thanks to the action of the peripheral nerves.

Once the information is processed, our brain is able to elaborate an appropriate response to the situation and transmit it back to the challenge of the body, specifically to the effector organs. These responses can be made consciously or unconsciously, depending on where in the brain they are formed.

For its part, the spinal cord is made up of a set of nerves protected by the spinal column.

Through this, all the information provided by the sensory organs and peripheral nerves is collected, to be later transmitted to the brain. Later, the medulla is responsible for carrying the response to the effector organs.

Peripheral nervous system

The second subset of the nervous system is made up of all the peripheral nerves, which collect information from the sensory organs and transmit it to the spinal cord. Later, they also carry the responses from the marrow to the organs in charge of carrying them out.

The nerves responsible for transmitting information from the brain to the effector organs are called "motor" or "efferent." On the other hand, those that transmit sensory information to the central nervous system are known as "sensory" or "afferent."

In turn, we can distinguish three subgroups within the peripheral nervous system:

- Somatic nervous system, in charge of voluntary movements.

- Autonomic nervous system, related to the involuntary responses of our body. It is usually divided into the sympathetic and parasympathetic nervous systems.

- Enteric nervous system, located entirely within the digestive system and responsible for properly digesting food.

Brain

The brain is the most important organ in the entire nervous system. It is responsible for receiving and processing all the information from the senses, as well as preparing the appropriate responses for each situation. It is also the most complex organ of vertebrate organisms.

The human brain is especially powerful, thanks to its approximately 33 trillion neurons and the trillions of synapses (connections between neurons) that it houses.

This large number of neurons and synapses allows us to analyze information incredibly quickly: some experts believe that we can process about 14 million bits per second.

In addition to information processing, the main function of the brain is to control the rest of the body's organs. This is done mainly in two ways: by controlling the muscles (voluntary and involuntary), and by secreting hormones.

Most of our body's responses need to be processed by the brain before they are carried out.

The brain is divided into several distinct parts, but they are all interconnected with each other. The oldest parts of the brain carry more weight in our behavior than the more recent ones.

The three main systems of the brain are:

- Reptilian brain, in charge of our instincts and automatic responses.

- Limbic brain, a system that processes and generates our emotions.

- Cerebral cortex, responsible for logical and rational thought and the appearance of consciousness.

Reptilian brain

The reptilian brain receives this name because evolutionarily it first appeared in reptiles. In our brain, this system is made up of the brain stem and the cerebellum.

The reptilian brain takes care of all those instinctive behaviors that we need to survive. Its functions include controlling autonomous functions such as breathing or heartbeat, balance, and involuntary movements of the muscles.

In this part of the brain are also located the basic needs of humans, such as water, food or sex. That is why these instincts are the strongest we can feel, and they completely dominate our rational mind on many occasions.

Limbic brain

The limbic brain is made up of the amygdala, hippocampus, and hypothalamus. This brain subsystem first appeared in mammals and is responsible for regulating emotions.

The main function of the limbic system is to classify our experiences as pleasant or unpleasant, in such a way that we can learn what hurts us and what helps us. Therefore, it is also responsible for memory, in such a way that our experiences are stored in the hippocampus.

In the case of humans, although we have a series of basic emotions, our interpretation of them is mediated by the cerebral cortex. In this way, our rationality influences our emotions, and vice versa.

Cerebral cortex

The last subsystem of the brain is also known as the neocortex. It is responsible for the higher functions of the brain, such as rationality, cognition or especially complex movements. In turn, it is the part that gives us the ability to think and be aware of ourselves.

This part of the brain is the most recent one, being present only in some species of higher mammals such as dolphins or chimpanzees. However, in no species is it as developed as in humans.

It is worth saying that the neocortex has less influence on our behavior than the other two subsystems. Some experiments indicate that its main function is to rationalize the decisions that we make unconsciously using the reptilian and limbic brains.

Neurons and information transmission

Neurons are the cells that make up the vast majority of the nervous system. It is a highly specialized type of cell that receives, processes, and transmits information using electrical impulses and chemical signals. Neurons are connected to each other through synapses.

Neurons differ from other cells in many ways, one of the most important being the fact that they cannot reproduce.

Until very recently it was believed that the adult human brain was not capable of producing new neurons, although recent studies seem to indicate that this is not true.

There are several types of neurons based on the function they perform:

-Sensory neurons, capable of detecting a type of stimulus.

–Motor neurons, which receive information from the brain and spinal cord, causing muscle contractions and hormonal responses.

-Interneurons, responsible for connecting brain or spinal cord neurons forming neural networks.

Structure of neurons

Neurons are mainly made up of three components: soma, dendrites, and axon.

- The soma is the body of the neuron, occupying the largest percentage of the cell's space. Inside are the organelles that allow the neuron to perform its function.

- The dendrites are small extensions that arise from the soma, and that connect with the axon of another neuron. Through these connections, the cell is able to receive information.

- The axon is a larger extension of the neuron, through which it is capable of transmitting information through a synapse. In humans, the axon of a neuron can be up to a meter in length.

Information transmission

Through synapses, neurons are able to transmit information to each other extremely quickly. This process of transmitting information is produced by electrical impulses, which travel between the different neurons through the alteration of the neuronal chemical balance.

The electrical potentials of neurons are controlled by the amount of sodium and potassium present both inside and outside; the alteration of these potentials is what causes the transmission of information in the synapses.

Exocrine and endocrine glands

The last component of the human nervous system is the glands. These are sets of cells whose function is to synthesize substances such as hormones, which are later released into the bloodstream (endocrine glands) or in specific parts of the body (exocrine glands).

Endocrine glands

These glands are responsible for producing hormonal responses in our body. Hormones transmit chemical signals that help control various bodily functions, working in conjunction with the central and peripheral nervous systems.

The most important endocrine glands are the pineal gland, the pituitary gland, the pancreas, the ovaries and testes, the thyroid and parathyroid glands, the hypothalamus, and the adrenal glands.

The substances they generate are directly released into the bloodstream, altering the functioning of the organs and producing all kinds of responses.

Exocrine glands

The other type of glands present in the human body, the exocrine glands, differ from the former in that they release the substances they produce in different ducts of the human body or on the outside. For example, the salivary or sweat glands are part of this group.

There are different classifications for exocrine glands, although the most used is the one that divides them into apocrine, holocrine and merocrine.

- Apocrine glands are those that lose a part of their cells when they produce their secretion. Some glands such as sweat or mammary glands are part of this type.

- The holocrine glands are those whose cells completely disintegrate when their secretion occurs. An example of this type of gland is the sebaceous.

- The merocrine glands generate their secretions through a process known as exocytosis. The salivary and lacrimal glands are part of this group.

Classification according to the type of discharge

Another of the most common classifications for exocrine glands is the one that differentiates them based on the type of substance they release. According to this classification, there are three main types of exocrine glands:

- Serous glands, which produce a watery secretion, normally rich in proteins. An example of this type is the sweat glands.

- Mucous glands, responsible for producing a viscous secretion rich in carbohydrates. The main example of this type of gland are goblet cells, which are responsible for lining the digestive and respiratory systems with a mucous layer to avoid damage due to contact with the outside.

- Sebaceous glands, which secrete a fatty liquid rich in lipid substances. One of the types of sebaceous glands are the Meibomian glands, which are found on the inside of the eyelids and are responsible for protecting the eye from the outside.

References

1. "Nervous system" in: Wikipedia. Retrieved on: April 7, 2018 from Wikipedia: en.wikipedia.org.
2. "Brain" in: Wikipedia. Retrieved on: April 7, 2018 from Wikipedia: en.wikipedia.org.
3. "Neuron" in: Wikipedia. Retrieved on: April 7, 2018 from Wikipedia: en.wikipedia.org.
4. "Triune Brain" in: Wikipedia. Retrieved on: April 7, 2018 from Wikipedia: en.wikipedia.org.
5. "Gland" in: Wikipedia. Retrieved on: April 7, 2018 from Wikipedia: en.wikipedia.org.