Neurology / NeurosciencePsychology / Psychiatry

Central nervous system(CNS): What to know

The central nervous system is the cerebrum and the spinal cord. This is called “core” since it incorporates knowledge from the whole body and integrates behaviors around the whole organism.

This article offers a short description of CNS (Central Nervous System). They will look at the types of cells involved, various brain areas, spinal circuitry and how disease and injury can affect the CNS.

Fast facts on the central nervous system

Here are a few key points about the central nervous system. The main article includes more descriptions and supporting material.

  • The CNS consists of the brain and spinal cord.
  • The brain is the most complex organ in the body and uses 20 percent of the total oxygen we breathe in.
  • The brain consists of an estimated 100 billion neurons, with each connected to thousands more.
  • The brain can be divided into four main lobes: temporal, parietal, occipital and frontal.

What is the central nervous system?

What is the central nervous system?
The CNS is the brain and spinal cord.

The CNS consists of the spinal cord and the spine.

The brain is covered by the skull (the cranial cavity), and the spinal cord passes from the back of the brain down through the middle of the spine, ending in the lower back lumbar region.

The brain and spinal cord are all located within a triple-layered protective membrane called the meninges.

Anatomists and physiologists have researched the central nervous system extensively but it still holds many secrets; it regulates our feelings, gestures, emotions, and desires. It also controls our breathing, heart rate, the release of some hormones, body temperature, and much more.

Next to the brain and spinal cord, the retina, optic nerve, olfactory nerves, and olfactory epithelium are also considered a part of CNS. This is because they have no intermediary nerve fibers interacting directly with brain tissue.

Now we will look at some of the parts of the CNS in more detail, starting with the brain.

The brain

The brain is the most complex organ in the human body; it comprises an estimated 15–33 billion neurons in the cerebral cortex (the outermost region of the brain and the largest part by volume), each connected to thousands of other neurons.

The human brain is made up of about 100 billion neurons and 1,000 billion glial (support) cells in total. Our brain uses around 20 percent of the total energy of our body.

The brain is the body’s central control center, which controls operation. From physical motion to hormone production, memory formation and emotional sensation.

The brain is the body’s central control center, which controls operation. From physical motion to hormone production, memory formation and emotional sensation.

Some parts of the brain have dedicated tasks for performing those functions. Nonetheless, other higher functions — reasoning, problem solving, imagination — require various aspects of networking together.

The brain is divided into four lobes, about:

Temporal lobe (green): essential for processing and assigning emotional meaning to the sensory information.

It also deals with creating long-term memories. There are also several references of language understanding here.

Occipital lobe (purple): visual area of brain development, containing the visual cortex.

Parietal lobe (yellow): the parietal lobe combines sensory information including touch, spatial perception and navigation knowledge.

Ultimately, touch pressure from the skin is sent to the parietal lobe. This also plays an significant part in language acquisition.

Frontal lobe (pink): located at the front of the brain, the frontal lobe comprises most dopamine-sensitive neurons and is involved in focus, reward, short-term memory, motivation and planning.

Brain regions

First, we’ll look in a little more depth at some different brain regions:

Basal ganglia: participation in the regulation of voluntary motor movements, procedural thinking, and decisions about what motor tasks to carry out. Diseases affecting this area include Parkinson’s illness and Huntington’s illness.

Cerebellum: often involved in specific operation of the motor but also in language and treatment. The primary symptom when the cerebellum is impaired is decreased motor coordination, known as ataxia.

Broca’s area: this small region on the left side of the brain (in left-handed individuals often on the right) is essential to language processing. An person finds it difficult to talk when he’s impaired, but still can understand speech. Often, Stuttering is associated with an underactive region of Broca.

Corpus callosum: a large band of nerve fibers that cross the hemispheres of the left and right. It is the largest layer of white matter in the brain, which enables contact between the two hemispheres. Dyslexic children have smaller callosums in the corpus; left-handed men, ambidextrous men, and usually larger musicians.

Medulla oblongata: it stretches under the skull and includes involvement in involuntary processes such as vomiting, coughing, sneezing and maintaining the required blood pressure.

Hypothalamus: the hypothalamus secludes a variety of neurohormones and regulates body temperature regulation, thirst, and appetite just above the brain stem and about the size of an almond.

Thalamus: located in the middle of the brain, the thalamus receives feedback from the sensory and motor and relays it to the rest of the cerebral cortex. It includes the control of consciousness, sleep, cognition and alertness.

Amygdala: two nuclei in the form of an almond, deep within the temporal lobe. They’re involved in decision taking, memory, and emotional responses; particularly negative emotions.

Spinal cord

The spinal cord carries information from the brain to the rest of the body.
The spinal cord carries information from the brain to the rest of the body.

The spinal cord, which stretches almost the entire length of the back, carries information between the brain and body but also performs other tasks.

Thirty-one spinal nerves come in from the brain stem, where the spinal cord enters the spine.

It connects along its length with the peripheral nervous system (PNS) nerves which run in from the skin, muscles, and joints.

Engine signals from the brain pass from the spine to the muscles and sensory input passes from the sensory tissues — like the skin — to the spinal cord and eventually to the brain.

The spinal cord includes circuits that regulate such reflexive responses, such as your arm’s involuntary movement whenever your finger hits a flamme.

Also, the circuits within the spine can produce more complex movements like walking. Even without brain input, all of the muscles required to walk can be controlled by the spinal nerves. Of example, if a cat’s brain is removed from its spine in such a way that its brain has no connection with its body, it will start walking instinctively when put on a treadmill. The brain would just need to stop and start the cycle, or make adjustments if an obstacle appears in your path, for example.

White and gray matter

The CNS can be separated approximately into white and grey matter. The brain consists of an outer cortex of gray matter and an inner layer that contains tracts of white matter, as a very general rule.

Both tissue types contain glial cells which protect neurons and support them. White matter consists mostly of axons (nerve projections) and oligodendrocytes — a type of glial cell — while gray matter primarily consists of neurons.

Central glial cells

Glial cells are often called neuroglia, and are also called neuron support cells. We outnumber nerve cells in the brain by 10 to 1.

Developing nerves frequently lose their way without glial cells, and fail to shape functional synapses.

Glial cells are present in both the CNS and the PNS but there are different forms of growing form. Brief definitions of the CNS glial cell types are as follows:

Astrocytes: these cells have multiple projections to their blood supply and anchor neurons. By removing excess ions and recycling neurotransmitters they also control the local environment.

Oligodendrocytes: responsible for forming the myelin sheath — this thin layer protects nerve cells, allowing them to send out signals rapidly and efficiently.

Ependymal cells: lining the spinal cord and the ventricles of the brain (fluid-filled spaces), these produce and secrete cerebrospinal fluid (CSF) and keep it flowing with their whip-like cilia.

Radial glia: serve as scaffolding in the development of the embryo’s nervous system for new nerve cells.

Cranial nerves

The cranial nerves are 12 pairs of nerves that come directly from the brain and pass through skull openings, rather than passing down the spinal cord. Such nerves collect and transmit information between the brain and body parts-mainly the neck and head.

The olfactory and optic nerves of these 12 pairs derive from the forebrain and are considered a part of the central nervous system:

Olfactory nerves (cranial nerve I): transmit odor information from the upper part of the nasal cavity to olfactory bulbs at the base of the brain.

Optic nerves (Cranial Nerve II): carry visual information from the retina to the brain’s main visual nuclei. Each optic nerve consists of approximately 1.7 million fibres.

Central nervous system diseases

Tumors can affect the CNS.
Tumors can affect the CNS.

These are the main causes of CNS-affected disorders:

Trauma: depending on the site of the injury, symptoms can differ greatly from paralysis to mood disorder.

Infections: some micro-organisms and viruses that invade the CNS; these include fungi, such as cryptococcal meningitis; protozoa, including malaria; bacteria, such as leprosy, or viruses.

Degeneration: The spinal cord or brain can degenerate in some cases. One example is Parkinson’s disease involving the progressive degeneration in the basal ganglia of dopamine-producing cells.

Structural abnormalities: birth defects are the most common examples; including anencephaly, in which parts of the skull, brain, and scalp are missing at birth.

Tumors: Tumors may affect parts of the central nervous system, both cancerous and noncancerous. All forms can cause harm and produce a variety of symptoms depending on where they originate.

Autoimmune disorders: an assault on healthy cells may be launched in certain cases by an individual’s immune system. For example, acute disseminated encephalomyelitis is characterized by an immune response to the brain and spinal cord, targeting myelin (isolation of the nerves), and thereby killing white matter.

Stroke: a stroke is blood flow disruption to the brain; the resulting loss of oxygen causes tissue to die in the affected area.

Difference between the CNS and peripheral nervous system

The term PNS refers to any part of the nervous system that is outside the brain and spinal cord. The CNS is distinct from the peripheral nervous system but there is interconnection between the two systems.

CNS and PNS have a variety of differences; one difference is the size of the cells. The CNS nerve axons — the slender nerve cell projections which carry impulses — are much shorter. The PNS nerve axons can be up to 1 meter long (for example, the nerve that stimulates the big toe) while they are rarely longer than a few millimeters inside the CNS.

Another important difference between the CNS and the PNS includes regeneration (cell regrowth). Most of the PNS has the potential to regenerate; if a nerve is cut in your finger it may regenerate again. But the CNS does not have the capability.

Further separate the elements of the central nervous system into a multitude of sections. Below, we’ll explain in a little more detail some of those pieces.

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