Components of the Central Nervous System

This page summarises basic information about the main parts of the Central Nervous System, sometimes called the CNS.





  • Long Term Memory

  • Co-ordination (e.g. balance)

  • Muscle Tone

  • Movement

  • Posture

Maintenance of muscle tone, balance, and the synchronization of activity in groups of muscles under voluntary control, converting muscular contractions into smooth coordinated movement.

However, it does not initiate movement and plays no part in the perception of conscious sensations or in intelligence.

The cerebellum is the largest part of the hindbrain.

It bulges back behind the pons varolii and the medulla oblongata, and is overhung by the occipital lobes of the cerebrum. Like the cerebrum, it has an outer grey cortex and a core of white matter.

The cerebellum has three broad bands of nerve fibres – the inferior, middle, and superior cerebellar peduncles – which connect it to the medulla, the pons varolii, and the midbrain respectively.

Cerebrospinal Fluid (CSF)

  • Bathes the brain and spinal cord

  • Allows nutrients and waste products to diffuse between the blood and the brain / spinal cord

  • Protects the nerves against mechanical damage

Cerebrospinal fluid is also the subject of cranio-sacral therapy, which is a huge subject in it's own right.

A clear watery fluid whose normal contents include glucose, salts, enzymes, and some white blood cells (but no red blood cells).

This fluid moves within its cavity, typically beating at 6-12 beats per minute, though this can rise to 12-50 beats per minute (such as in the case of a person who has a "pulsating" headache).


The Cerebrum is also known as the Cortex
(Cortex = Cerebrum), and is the largest and most highly developed part of the brain.

This is the ‘learning’ part of the brain, and the seat of all intelligent behaviour. It is responsible for the initiation and coordination of all voluntary activity in the body and for governing the functioning of lower parts of the nervous system.

The cerebrum is composed of two hemispheres separated from each other by the longitudinal fissure in the midline.

Each hemisphere has an outer layer of grey matter, the cerebral cortex, below which lies white matter containing the basal ganglia. Nerves of the cortex are arranged on the outside surfaces as grey matter.

The corpus collosum is a massive bundle of nerve fibers that connect the two hemispheres - at the bottom of the longitudinal fissure.


The hypothalamus is the "Receptor Centre", and "Control Centre" of the body.

It contains several important centers controlling body temperature and eating, and water balance. Examples include osmo-receptors that balance water/salt levels and control the water content of the blood. (See diagram opposite.)

It is also the Saiety Center (that is concerned with 'satisfaction'), for things like hunger, thirst, sex.

It is also closely connected with emotional activity and sleep, and it functions as a center for the integration of hormonal and autonomic nervous activity through its control of the pituitary secretions.

The posterior lobe of the pituitary secrets two hormones:

  • A.D.H. (Anti-diuretic hormone, as known as vasopressin – in U.S.)

    This works on the kidney tubules. Secretion of ADH tells the kidneys to re-absorb more water, resulting in more concentrated urine. Non-secretion of ADH results in more peeing, and weaker urine.

  • Oxytocin

The region of the forebrain in the floor of the third ventricle, linked with the thalamus above and the pituitary gland below.

Medulla Oblongata

The functions of the medulla oblongata concern the body's involuntary processes, such as:

  • Breathing

  • Heart-rate

  • Swallowing

  • Salivation

  • Vomiting

  • Blinking

The cranial nerves VI – XII leave the brain in this region.

The medulla oblongata is the extension within the skull of the upper end of the spinal cord, forming the lowest part of the brainstem.

The Meninges

Mechanical protection of the brain and spinal column.

The meninges consist of three parts, the dura mater, the arachnoid mater, and the pia mater.

The structures of these are mentioned below.

Meninges -
Dura Mater

  • Outermost layer of mechanical protection of the Brain and Spinal column.

The outer-most layer of the meninges is inelastic, tough, and thicker than the other two layers.

Meninges -
Arachnoid Mater

  • Middle layer of mechanical protection of the Brain and Spinal column.

The inner two membranes are together called the leptomeninges; between them circulates the cerebrospinal fluid.

Meninges -
Pia Mater

  • Innermost layer of mechanical protection of the Brain and Spinal column.

Pons Varolii

The pons varolii is the part of the brainstem that links the medulla oblongata with the thalamus.

Contains numerous nerve tracts between the cerebral cortex and the spinal cord, and several nuclei of grey matter.

(The trigeminal nerves emerge from the front surface of the pons varolii.)

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