The central nervous system is essential for the maintenance of the organism and the formation of responses to external stimuli. A review of its parts and functions.
From a physiological point of view, the nervous system can be defined as a set of cells specialized in the conduction of electrical signals whose basic unit are neurons and glial cells. Beyond the terminological field, this set of nervous structures allows living beings to control and create survival alternatives and adaptations in the face of environmental challenges.
To give you an idea of the importance and magnitude of this system, we will tell you thatan adult human being contains about 100,000 million neuronsand that the speed at which each nerve transmission occurs varies from 24 to 400 kilometers / hour. During the day, our brains generate so much electricity that they could turn on a 25-watt light fixture.
All these data show, even with a few brushstrokes, how important the nervous system is in the development and permanence of all anatomically complex living beings in the environment. Today we will describe the central nervous system (CNS) and its characteristics, as it is an essential part for the understanding of the transmission of information in the human body. Don’t miss it.
- We recommend you read: “Sympathetic and parasympathetic nervous system: what they are, differences and functions”
What is the central nervous system?
Before launching ourselves fully into the characteristics of this exciting system, we must note that what we know as the nervous system is divided into two large structural groups. These are as follows:
- Central nervous system (CNS): consisting of the brain and spinal cord.
- Peripheral nervous system (PNS): composed of all nerves that branch off from the spinal cord and extend to all parts of the body.
Thus, we can conclude that the CNS encompasses the following elements: brain + cerebellum (brain) + spinal cord. On the other hand, the PNS would be as follows: cranial and spinal nerves + ganglia + nerve endings. The central nervous system, beyond the structures that compose it, could be defined asresponsible for perceiving external stimuli, processing the information received and transmitting impulsesto nerves and muscles so that they act accordingly in different living beings.
Basic structures of the central nervous system
We have said that theCNS is composed of the brain and spinal cordbut, before describing each of these sections at length, we must briefly review the functional units that make up this very complex system. Let’s get to it.
The neuron is the basic structure of the nervous system, as we have said in previous lines. It has a complex body, formed by a cell body or soma (with the nucleus) and a series of extensions called axons and dendrites. Sets of axons (nerves proper) are found throughout the body, which is why they allow neuronal communication despite the physical separation of both cells.
When a dendrite of a neuron is excited, it sends an electrical signal along its entire structure to the tip of its axon, where a neurotransmitter is released. The tip of the dendrite of another neuron is excited by this neurotransmitter, thus producing the phenomenon called synapses. Broadly speaking, the transmission of nerve impulses presents events of a chemical and electrical nature.
On the other hand, we must note that, if we make a cross section in any section of the central nervous system, we will find two types of tissues especially representative. These are as follows:
- Gray matter: contains the bodies of neurons and glial cells. It forms the cerebral cortex and the anterior, lateral, and posterior horns of the spinal cord, among many other things.
- White matter: contains axons, which are accompanied by other types of glial cells.
In addition to all this, we can not leave aside the glial cells that we have just named, which are not neurons but are present in the CNS, with functions of support, protection, metabolism and immune response. We show you the most basic types in a cursory way:
- Perocytes: act in the filtration and exchange of blood between the circulatory system and the CNS.
- Astrocytes: they fulfill a very important metabolic function essential for the proper functioning of the central nervous system.
- Oligodendrocytes: are mainly characterized by forming the myelin sheaths that line axons in the white matter of the CNS.
In turn, the gray matter and white matter are covered by 3 membranes essential in the exchange of fluids and with various immune and physiological functions: pia mater, arachnoid and dura mater (generally known as meninges) in turn protected by bony envelopes: the skull and the spine, respectively.
What are the parts of the CNS?
All this information is most relevant, because the microstructure of this system is just as important to understand it as the organs that make it up. Now, we tell you each of the parts of the central nervous system at a much more macroscopic level. Remember the following:
CNS: Brain (Brain + cerebellum) + Spinal cord
1. Brain
The brain is the nervous organ par excellence, because, with a weight of just 1,500 grams (0.8%-2% of the total mass of an adult human), it centralizes all the physiological functions of our species, which is said soon. Anatomically this fascinating structure is divided into two hemispheres, the right and the left, separated by a central groove called the longitudinal fissure. Each hemisphere is divided, in turn, into 4 different lobes:
- Occipital lobe: located at the back of the brain. It is responsible for the reception and analysis of information of a visual nature.
- Temporal lobe: in this the area responsible for auditory reception is located. It has great importance in the linguistic function and comprehension of words.
- Frontal lobe: the bulkiest of the 4. It intervenes in functions of personality, intelligence, language and control of voluntary movements.
- Parietal lobe: intervenes in the identification of objects, spatial relationships and sensory processes that encompass pain and touch, for example.
- Read more: “The 6 lobes of the human brain (anatomy, functions and images)”
2. Cerebellum
The cerebellum, on the other hand, can be defined as the back of the brain constituted by a mass of nervous tissue, responsible for muscle coordination and other movements not controlled by the will. Being one of the centers of integration between sensory pathways and motor pathways, it has a large number of nerve bundles connected to other structures and the spinal cord.
In the cerebellum two main areas are distinguished: the cortical and the medullary. The first one is the most superficial and is rich in nerve cells, while the medullary is lined by the anterior and is formed exclusively by myelinated nerve fibers. This last layer sends multiple projections and folds that, as a whole, are known as the cerebellar cortex.
- Read more: “Human Cerebellum: Anatomy, Parts and Functions”
3. Spinal cord
At last we abandoned the brain. The spinal cord is a long cylindrical structure located in the spinal canal with a very clear but essential function: to transmit nerve impulses to the 31 pairs of spinal nerves, communicating the brain with the body, through two basic functions, the afferent (receive) and the efferent (send).
We are facing a really large structure, as it is estimated that it reaches 45 centimeters in length on average in men and 42 in women, with a slightly flattened diameter of about 2 centimeters. It is interesting to know that, in addition, in 80% of cases the spinal cord is asymmetrical, with the right side being larger as a general rule.
If we make a cross section in the spinal cord, we can observe a dark nucleus with a “butterfly” shape covered by a peripheral white matter: that’s right, the inner part corresponds to gray matter and the outer part to white matter. This butterfly shape is catalogued in anterior, posterior and lateral antlers, all of them formed by gray matter.
Summary
Explaining the characteristics of the central nervous system in a few lines is a real challenge, because each of the microscopic and macroscopic structures that make it up contain enough particularities to fill a book by themselves. If we want to make clear an idea behind all this terminological conglomerate, this is the following: the CNS is composed of two main materials, the gray matter and the white matter, formed in turn by neurons and glial cells. At the macroscopic level, the CNS is composed of the brain, cerebellum, and spinal cord.
On the other hand, this system is responsible for coordinating, integrating and controlling the body. It is also their job to receive stimuli, process them and make the appropriate responses according to the environmental context. Without a doubt, without the CNS we would be nothing.
To the classic question “what do you do?” I always answer “basically I am a psychologist”. In fact, my academic training has revolved around the psychology of development, education and community, a field of study influenced my volunteer activities, as well as my first work experiences in personal services.