We explain the anatomy of the human nervous system.
Whether consciously or unconsciously, our body tells us what to do. Actions as simple as blinking and other more complex ones such as speaking or feeling emotions .
Of course, the nervous system, in which the brain and other very important structures are located, are fundamental to our survival and relationship with the world.
It is fascinating to study it and try to understand it more thoroughly, and that is why we are going to see what the nervous system is, how it is subdivided and what its main structures are .
- Recommended article: “Human brain: its parts and main functions”
What is the nervous system?
The nervous system is a set of structures that are responsible for organizing, coordinating and regulating the functions that all parts of the body must perform. As with the circulatory system, the nervous system is made up of an extensive network through which information is collected and sent in the form of nerve impulses.
This information can come from outside, being captured by the organs in the form of different sensory signals and sent to the brain, which is the center of operations. It can also come from the brain itself, being sent to different parts of the body, such as joints or organs, so that a specific movement is carried out or a certain function is fulfilled, such as the beating of the heart or digestion.
The main functional unit of this system are neurons , cells specialized in communication through chemical and electrical signals, which travel throughout the body, being processed in the brain. Attempts have been made to estimate the number of neurons that each human individual possesses, varying markedly between studies, pointing to between 10 and 26 billion of these cells.
Given how important this system is for the human species, especially because it is what allows us to continue living and be aware that we exist, there are many who have studied it extensively. The nervous system is very complex, and it is impossible to describe all its particularities in a single article, for this reason we are going to describe it based on its anatomy, having the central nervous system and the peripheral nervous system.
central nervous system
The central nervous system is usually the best known part of the nervous system in general, being made up of the brain and the spinal cord . This subsystem has its own peculiarities that allow it to be differentiated from the peripheral nervous system:
- Structures protected by three meninges: pia mater, arachnoid mater, and dura mater.
- The cells that compose it form two types of matter: gray and white.
- It has a substance that nourishes it and offers protection: the cerebrospinal fluid.
1. Brain
The brain is a nervous structure that is strongly protected by the skull . It can be considered as the most important part of the central nervous system, since it is the center of operations of this system: it dominates over all organic functions, whether voluntary or involuntary.
Anatomically speaking, it is not a uniform structure. It has three main subdivisions: cerebrum, cerebellum , and brainstem.
1.1. Brain
The brain is the best known and largest organ , although there are many who use it as if it were synonymous with any nervous structure that is inside the skull. It is divided into two parts, called hemispheres, with one right and one left.
The line that divides the hemispheres is the interhemispheric or Silvio fissure, but they are not isolated from each other, since they are connected by a structure of nerve fibers called the corpus callosum.
The outer area of the brain is called the cortex or cerebral cortex, formed from gray matter and wrinkled into convolutions. Beneath the gray matter is the white matter and structures that make it up, such as the thalamus, caudate nucleus, and hypothalamus.
The brain processes sensory information and is also responsible for motor control, as well as being essential in cognition, emotions, learning and memory.
1.2. Cerebellum
It is situated in the lower posterior part of the brain, that is, pulling back on the head . This structure is responsible for integrating the sensory and motor processes of the body.
It is connected to other structures in the brain and spinal cord by various nerves. It participates in all the signals that are sent from the cerebral cortex to the locomotor system.
Multiple functions and capacities have been associated with it, including the processing of musical stimulation, balance and coordination.
1.3. Tallo cerebral
Also called the brain stem, the brain stem is the main pathway of communication between the brain, spinal cord, and the nerves that make up the peripheral nervous system.
It has the ability to control several tasks, among which breathing or heart rate can be highlighted.
It is subdivided into: mesencephalon, pons and medulla oblongata.
2. Spinal cord
The spinal cord is responsible for sending information from the brain to 31 pairs of nerves that are part of the peripheral nervous system. This information passes, mainly, in two ways:
- Afferent pathway: the information goes from the trunk, neck and extremities to the brain.
- Efferent pathway: the nerve impulse travels from the brain to the parts of the body.
In addition to this, the spinal cord carries out functions that are more of a vegetative type, such as maintaining walking or reflexes.
The peripheral nervous system
The peripheral nervous system is responsible for transmitting nerve signals through two types of nerves: cranial and spinal . These nerves are part of the nervous system, but they are not within the central nervous system, so they are not as well protected compared to other nervous structures, such as the brain or spinal cord.
Despite this, they are of vital importance, since they connect the organs and systems of the body with the brain and the spinal cord, mutually informing each other of the organic state and what functions each part of our body must fulfill.
There are two criteria for describing the peripheral nervous system. One, which is what we detail below, is the anatomical criterion, that is, based on the nerves that compose it. The other is based on the functions performed by its parts, distinguishing the somatic part from the autonomous part, which will be seen in more detail towards the end of this section.
3. Cranial nerves
The cranial nerves are a total of 12 pairs, which originate in the brain and at the level of the brain stem . These nerves are distributed throughout the body through holes located at the base of the skull, in the neck, torso and abdomen. Each of these nerves fulfill a specific mission, which gives each one its name:
- I. Olfactory: olfactory impulses.
- II. Optical: visual information to the brain.
- III. Oculomotor: movements of the eyes and related parts.
- IV. Trochlear: rotation of the eye.
- V. Trigeminal: sensory information from the face and chewing.
- 6. Abducens: abduce the eyeball.
- VII. Facial: muscles of the face.
- VIII. Vestibulocochlear: perception of sounds, rotation and gravity.
- IX. Glossopharyngeal: sense of taste and salivation.
- X. Vagus: movements in the pharynx and larynx.
- XI. Spinal: control of the sternocleidomastoid muscle and trapezius.
- XII. Hypoglossal: movements of the tongue.
The nerves that are responsible for transmitting motor information travel through the efferent pathway, having their origin in the brainstem, while those that are responsible for receiving sensory signals travel through the afferent pathway and originate outside the brainstem.
It should be noted that the existence of a thirteenth cranial nerve, called the zero cranial nerve, has been proposed, which could have an important role in the detection of pheromones and that, during embryonic development in humans, ends up joining the olfactory cranial nerve.
4. Spinal nerves
The spinal nerves, also called spinal nerves, are a total of 31 pairs of nerves whose mission is to transmit sensory signals, such as touch, pain or temperature, from the chest and extremities of the body to the nervous system. central.
Their existence is fundamental thanks to the fact that it is through them that information passes that is relevant when making a specific body posture, tensing the muscles for a specific purpose or other action ordered from the brain.
Somatic nervous system and autonomic nervous system
As we have already mentioned, the peripheral nervous system can be subdivided into two other systems.
The somatic nervous system is responsible for mediating between the internal body and the external environment , taking charge of the voluntary control of the skeletal muscles. On the other hand, the vegetative or autonomic nervous system is responsible for more involuntary functions, such as the control of the muscles responsible for keeping the heart beating, the dilation and contraction of the pupils or making the skin goosebumps.
Bibliographic references
- Fuller G. N., Burger P. C. (1990). Nervus terminalis (cranial nerve zero) in the adult human. Clin. Neuropathol. 9 (6): 279-83.
- Kandel, ER; Schwartz, JH and Jessell, TM (2001). Neuroscience principles. Fourth edition. McGraw-Hill Interamericana. Madrid.
- Richard S. Snell (2003). Clinical Neuroanatomy (5th edition). Pan American Medical.
- Stein PSG (1999). Neurons, Networks, and Motor Behavior. MIT Press. pp. 38 – 44.
- Tortora, G.J., Derrickson, B. (2016). Principles of Anatomy and Physiology (15th edition). Hoboken: Wiley.
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.