What is the central nervous system (CNS)?
The central nervous system (CNS) is a division of the nervous system whose function is to analyze and integrate various Intra and extra-personal information, as well as to generate a coordinated response to these stimuli. Simply put, the CNS is the supreme command center of the body.
The central nervous system consists of two organs that are continuous with each other; the brain and spinal cord. They are enveloped and protected by three layers of meninges, and enclosed within two bony structures, the skull, and spinal column, respectively. The brain is made up of the cerebrum, subcortical structures, the brainstem, and the cerebellum.
The spinal cord continues downward from the brainstem and extends through the vertebral canal. By analyzing the information and preparing the appropriate body responses, parts of the brain and spinal cord communicate with each other through many neural pathways. Once the final output is ready, they transmit it to the rest of the body through the nerves of the peripheral nervous system (PNS), which come directly from them.
More specifically, the brain emits 12 cranial nerves supplying the head, neck, and thoracic and abdominal viscera, while the spinal cord emits 31 pairs of spinal nerves. The spinal nerves complement the innervation of the viscera, as well as the rest of the body that is not supplied by the cranial nerves (upper and lower extremities).
Structure of the central nervous system
The CNS has three main components: the brain, spinal cord, and neurons (or nerve cells).
Brain: The brain controls many of the body’s functions, including sensation, thinking, movement, consciousness, and memory. The superficial of the brain is known as the cerebral cortex. The surface of the bark appears irregular thanks to the grooves and folds of the tissue. Each groove is known as a groove, while each stroke is known as a turn.
Most of the brain is known as the cerebrum and is responsible for things like memory, speech, voluntary behaviors, and thinking. The brain is divided into two hemispheres, a right hemisphere, and a left hemisphere. The right hemisphere of the brain controls movements on the left side of the body, while the left hemisphere controls movements on the right side of the body.
Although some functions tend to lateralize, researchers have found that there are no “left brain” or “right-brain” thinkers, as the old myth implies. Both sides of the brain work together to produce various functions. Each hemisphere of the brain is then divided into four interconnected lobes:
- The frontal lobes are related to higher cognition, voluntary movements, and language
- The occipital lobes are associated with visual developments
- The parietal lobes are associated with the processing of sensory information
- The temporal lobes are associated with hearing and interpreting sounds, as well as the formation of memories
Spinal cord: The spinal cord connects to the brain through the brain stem and then down the spinal canal, located inside the vertebra. The spinal cord carries info from various parts of the body to and from the brain. In the case of some reflex movements, responses are controlled by spinal pathways without involving the brain.
Neurons: Neurons are the construction blocks of the central nervous system. Billions of these nerve cells can be found through the body and communicate with each other to crop physical responses and actions. Neurons are the body’s information superhighway. It is estimated that 86 billion neurons can be found in the brain alone.
Protective structures: Since the central nervous system is so important, it is protected by a number of structures. First, the entire CNS is encased in bone. The brain is threatened by the skull, while the spinal cord is protected by the vertebra of the spinal column. The brain and spinal cord are covered with a protective tissue known as the meninges.
The entire central nervous system is also immersed in a substance known as cerebrospinal fluid, which forms a chemical environment that allows nerve fibers to transmit information effectively, as well as offering another layer of protection against possible damage.
All about the central nervous system
White and gray matter
The central nervous system can be unevenly divided into white and gray matter. As a very general rule, the brain consists of an outer cortex of gray matter and an inner area that houses tracts of white matter.
Both types of tissue encompass glial cells, which defend and support neurons. White matter consists mainly of axons (nerve projections) and oligodendrocytes – a type of glial cell – while gray matter consists predominantly of neurons.
Central glial cells
Also called neuroglia, glial cells are often called provision cells for neurons. In the brain, they outnumber nerve cells from 10 to 1. Without glial cells, developing nerves are often lost and struggle to form functional synapses. Glial cells are found in both the CNS and the PNS, but each system has different types. The following are brief descriptions of the glial cell types of the CNS:
- Astrocytes: These cells have frequent projections and anchor neurons to their blood supply. They also control the local environment by eliminating excess ions and recycling neurotransmitters.
- Oligodendrocytes: Responsible for the creation of the myelin sheath – this thin layer lines nerve cells, allowing them to send signals quickly and efficiently.
- Ependymal cells: Which line the brain’s spinal cord and ventricles (fluid-filled spaces), create and secrete cerebrospinal fluid (CSF), and keep it circulating using their whip-like cilia.
- Radial glia: Acts as a scaffold for new nerve cells during the creation of the embryo’s nervous system.
The cranial nerves are 12 pairs of nerves that arise directly from the brain and pass-through holes in the skull instead of traveling along the spinal cord. These nerves gather and send information between the brain and parts of the body, mostly the neck and head. Of these 12 pairs, the olfactory and optic nerves arise from the forebrain and are measured as part of the central nervous system:
- Olfactory nerves (cranial nerve I): Transmit information about odors from the upper section of the nasal cavity to the olfactory bulbs at the base of the brain.
- Optic nerves (cranial nerve II): Carry visual information from the retina to the primary visual nuclei of the brain. Each optic nerve consists of about 1.7 million nerve fibers.
Central nervous system disorders
Nervous system disorders can involve the following:
- Vascular disorders, such as stroke, transient ischemic attack (TIA), subarachnoid hemorrhage, subdural hemorrhage, and extradural hematoma and hemorrhage
- Contagions, such as meningitis, encephalitis, polio, and epidural abscess
- Structural illnesses, such as brain or spinal cord injury, Bell’s palsy, cervical spondylosis, carpal tunnel syndrome, brain or spinal cord tumors, peripheral neuropathy, and Guillain-Barré syndrome
- Useful disorders, such as headache, epilepsy, dizziness, and neuralgia
- Deterioration, such as Parkinson’s disease, multiple sclerosis, amyotrophic lateral sclerosis (ALS), Huntington’s chorea, and Alzheimer’s disease
Central nervous system diseases
The following are the main causes of disorders affecting the CNS:
- Trauma: Depending on the site of injury, symptoms can range widely from paralysis to mood disorders.
- Infections: Some microorganisms and viruses can invade the CNS; these contain fungi, such as cryptococcal meningitis; protozoa, counting malaria; bacteria, as is the case with leprosy, or viruses.
- Degeneration: In some cases, the spinal cord or brain can debase. An example is Parkinson’s disease, which involves the gradual degeneration of dopamine-producing cells in the basal ganglia.
- Structural defects: The most common instances are birth defects; including anencephaly, where parts of the skull, brain, and scalp are missing at birth.
- Tumors: Both cancerous and non-cancerous tumors can move parts of the central nervous system. Both types can cause damage and produce a variety of symptoms depending on where they develop.
- Autoimmune disorders: In some cases, a person’s immune system can base an attack on healthy cells. For example, acute dispersed encephalomyelitis is considered by an immune response against the brain and spinal cord, which attacks myelin (the insulation of nerves) and thus destroys the white matter.
- Stroke: A stroke is an interruption of the blood supply to the brain; the resulting lack of oxygen causes tissue to die in the affected area.