Central sulcus

Overview:

All the functions performed by the body are a result of many coordinated actions that take place and lead to the execution of single or multiple tasks. There are numerous kinds of data that is received by the body’s sensory organs and tissues which is sent to the relevant centres of the brain for it to process and interpret that information. Furthermore, appropriate responses are generated once this information is received and the body reacts accordingly, whether the target sites of reception of these brain messages are glands or muscles.

All this systematic working of the brain suggests that it is indeed responsible for carrying out many complex and delicate functions, without which the body would not be able to function properly, or at all. To understand these functions and these pathways, the brain is divided into many sections based on its appearance and structural components.

On the surface of the brain, there are grooves and bumps, known as sulci and gyri. Brain gyri and sulci perform two critical functions: they help to increase the surface area of the cerebral cortex and shape brain divisions. Expanding the brain’s surface area enables more nerve cells to be loaded into the cortex, allowing it to handle more relevant data.

In this article, one of the most prominent sulci in the brain, the central sulcus, will be explained and its structural formation and developmental stages will be described. The concept of gyri and sulci will be explained along with a special focus on the clinical importance of the central sulcus.

Summary:

  • The cerebral cortex’s numerous creases and ridges have an added benefit in that they provide a larger surface area for an increased number of nerve cells to survive, allowing for the processing of large amounts of data
  • A gyrus (plural gyri) is a term used to describe the ridges and grooves on the cerebral cortex, which is the layer that forms the brain’s outer boundary
  • A sulcus (plural: sulci) is another term for a furrow on the cerebral cortex
  • Every gyrus is surrounded by sulci, which collaborate to increase the surface area of the cortex and establish distinctions in the brain surface to understand its divisions
  • The lateral sulcus is a furrow or groove that is very deep and connects the temporal lobe to the parietal lobe of the brain
  • The parieto-occipital sulcus is also a very deep furrow in the cerebral cortex  that connects the occipital lobe and the parietal lobe
  • The longitudinal fissure like every other fissure is very deep and is present in the brain’s centre that separates the right hemisphere and the left hemispheres
  • The central sulcus connects the frontal lobe and the parietal lobe. It is also recognized as the Rolando sulcus.  It separates the primary motor cortex from the primary somatosensory cortex, and also the frontal and parietal lobes
  • Cerebral amyloid angiopathy and William’s syndrome are related to damage to the central sulcus

The Brain’s structural components:

The cerebral cortex is the human brain’s outer covering, and it is correlated with the body’s greatest possible cognitive capacities. This cortex is mainly comprised of grey matter (which is nerve cell groups made up of relevant neurons), with not just one hundred thousand or one million cells, but a total of around fourteen to sixteen billion neurons are detected in this region. The cerebral cortex’s many creases and ridges have an added advantage, which is the availability of a larger surface area for an enhanced number of nerve cells to survive, allowing for large volumes of data to be handled.

Even though the cerebral cortex is only just a few millimetres in thickness, it accounts for roughly fifty per cent of the total brain tissue. The cortex appears to be wrinkled, with protrusions called gyri and deep grooves called sulci.

The cortex can be categorized into two hemispheres (the right hemisphere and the left hemisphere), by a huge sulcus known as the medial longitudinal fissure.

These two hemispheres of the cerebral cortex are linked by a group of nerve fibres known as the corpus callosum, which functionally allows the right and left hemispheres of the cerebral cortex to interact with one another and for more linkages to be created. The cerebral cortex controls a wide range of operations via the lobes, which are partitioned depending on the position of sulci and gyri.  There are a total of four lobes are known as the occipital, temporal, frontal, and parietal lobes.

The cerebral cortex’s surface, as mentioned before, is very irregular, with a specific design of creases or bumps known as gyri and furrows known as sulci (singular: gyrus and sulcus). These gyri and sulci act as significant locations, allowing scientists to divide the brain into operational centres.

Given below are details about the gyri and sulci of the brain (Figure 1).

Gyrus:

The cerebral cortex has a somewhat creased appearance with numerous grooves and perforations. A gyrus (plural called gyri) is the word used to describe the ridges and grooves on the cerebral cortex, which is the layer that is present in the outer boundary of the brain. 

Gyri are made up of grey matter structures located on the surface of the cerebral cortex that is comprised of neurons cell bodies and their extensions called dendrites.

Gyri are distinct frameworks that are crucial because they enhance the brain’s surface and region.  A greater surface area allows so many more nerve cells to be crammed into the cortex, allowing it to handle more relevant data. Finally, gyri will improve cognitive abilities without increasing the true brain dimensions which would not be accommodated into a skull.

One other major aspect is the superior temporal gyrus, which contains Wernicke’s area, which is essential for language learning and speech understanding and interpretation. 

Gyri are clinically significant because they are essential to the structural development and framework of the brain. Some gyri anomalies, for instance, can contribute to disorders like epilepsy.

Figure 1: The cerebral folds, gyri and sulci. The upward folds are known as gyri (plural: gyrus), while the downward ridges are known as sulci (singular: sulcus)

Sulcus:

A sulcus (plural called sulci) is also another word for a furrow present on the cerebral cortex. Every gyrus is encircled by sulci, which work with each other to contribute to increasing the surface area of the cortex and establish distinctions in the brain surface to understand its divisions. 

They create brain segments by drawing lines in between lobes, making them easily recognizable and dividing the cerebral cortex into two hemispheres. A sulcus is a superficial furrow that envelops a gyrus, and fissures are bigger or comparatively more deep sulci.

The longitudinal fissure is a big groove that separates the two hemispheres into right and left halves. Because a seamless cortex can only develop to a particular limit and range, sulci in the surfaces enable sustained growth, consequently boosting brain activity and operations. Sulci are categorized into two kinds that form at various times. The primary sulci (for example, the central sulcus) develop independently before the birth of a child.   Secondary sulci, on the other hand, are those developed by variables other than development in adjacent regions of the brain (for instance the parieto-occipital sulci).

Sulci can also be classified according to how deep they are.  A proper sulcus is one with a very deep furrow (for example, the collateral sulcus), while an imperfect sulcus does not have a very deep furrow (for instance the paracentral sulcus).

Sulci present in the brain:

A few sulci that are located on the brain’s surface are briefly described below (Figure 2).

The lateral sulcus: The lateral sulcus is a furrow or groove that is very deep and connects the temporal lobe to the parietal lobe of the brain. The Sylvian sulcus starts to emerge close to the forebrain and extends to the side brain surface with the insular cortex positioned immediately deep inside this sulcus.

The parieto-occipital sulcus: The parieto-occipital sulcus is also a very deep furrow in the cerebral cortex that connects the occipital lobe and the parietal lobe. This sulcus established a mark on the cortex’s outer layer, indicating the location of the occipital and parietal lobes. Because it establishes after a person is born, this sulcus is indeed secondary.

The longitudinal fissure: The longitudinal fissure like every other fissure is very deep and is present in the brain’s centre that separates the right hemisphere and the left hemispheres.  A bundle of nerve fibres is present in the brain that attaches to the right hemisphere and the left hemisphere and is called the corpus callosum. This helps in sending visual, hearing-related and somatosensory data back and forth between these hemispheres. 

An operculated sulcus: When a sulcus is existing between two fundamentally separate regions, and another sulcus is present within its wall but not be visible on the surface, it is referred to as an operculated sulcus. An example is a lunate sulcus. Grafton Elliot Smith was a biologist who discovered the lunate sulcus, also known as the “ape sulcus,” on the posterolateral part of the head. It was discovered to be a characteristic of the brain of an ape, but it is not only found in apes; it is found in human brains.

Central sulcus:

The central sulcus connects the frontal lobe and the parietal lobe. It is also recognized as the Rolando sulcus.  This is an important sulcus because it separates the primary motor cortex from the primary somatosensory cortex, and also the frontal and parietal lobes. Some scientists believe and have put forward the concept that the surface area of the central sulcus can influence a person’s handedness. This implies that a right-handed person will have a bigger central sulcus on the left side of the left hemisphere, and a left-handed person will have a bigger sulcus in the right hemisphere. Because of its responsibilities in segregating the sensory and motor cortices, the structure of the central sulcus is thought to modify as motor operations establish further. 

Figure 2: The sulci of the brain. When analyzing cranial anatomy, it is evident that the central sulcus is a specific structure that can aid in orientation.

Development of Central Sulcus:

The central sulcus starts to develop roughly around thirteen weeks of gestational age and grows at its quickest between thirteen and fifteen weeks of gestational age. Nevertheless, the most energetic developmental stage occurs between eighteen and nineteen weeks of gestation. This is ascertained since there is the biggest number of nerve cells and fibre relocation.

It starts as a spot or furrow in the parasagittal area of the brain. At around twenty-two to twenty-three weeks of gestational age, it transforms into a distinguishable protrusion that enlarges more towards the lateral sulcus and the longitudinal fissure. Between the ages of two and three years, the location ‘Pli de Passage Frontoparietal Moyen’ (PPFM), a sunken surface buried at the centre of the central sulcus, appears. The average depth curve of the central sulcus at three years of age is equivalent to that of older people.

The form of the central sulcus is bound to evolve as motor features establish. This is attributable to the central sulcus’s duties in dividing the primary motor cortex from the primary somatosensory cortex. Distinctions across the central sulcus, for instance, have been noted in artists, specifically concerning an omega emergence along the centre part of the central sulcus, colloquially known as the “hand knob.”   This omega configuration is unique to the right central sulcus in performers who specialize in string containing musical instruments. Nevertheless, in the case of pianists, this omega formation takes place on both sides but more notably on the left side. 

Both genetic and non-genetic aspects play a role in affecting the form of the central sulcus. The deep framework of the central sulcus has been noticed to be more coherent across brains than the surface level structure, implying that the superficial formation is more vulnerable to non-genetic influences.

Complications involving central sulcus:

An unusual sequence of gyri and sulci in the initial phases of development can lead to serious problems. Cell growth and migration abnormalities in the evolving cortex can at times lead to aberrations. Destruction or maturational abnormalities in particular gyri or sulci can have an impact on specific operations and capabilities. 

Cerebral amyloid angiopathy (CAA):  

Cerebral amyloid angiopathy (CAA) is a situation wherein amyloid proteins accumulate on the borders of the arteries that are present in the brain. Cerebral amyloid angiopathy raises the danger of stroke and dementia triggered by bleeding.

In a study conducted (Chamarthy et al., 2012), the association of damage to the central sulcus was associated with cerebral amyloid angiopathy (CAA). Central sulcus haemorrhage is an uncommon imaging discovery in a normotensive non-traumatic older patient that could be connected to cerebral amyloidosis and can be displayed as a separated discovery or in conjunction with other regions of engagement.

A separated central sulcus haemorrhage is uncommon and is most closely aligned with cerebral amyloidosis. Even though histopathological assessment is rarely investigated, a secluded central sulcus haemorrhage may imply a prospective assessment of cerebral amyloid angiopathy, particularly if further image analysis and clinical demonstration rule out other diagnostic tests.

Williams syndrome (WMS): 

Williams syndrome (WMS) is a genetic disorder caused by a chromosome 7 hemideletion that tends to cause cognitive problems as well as a wide range of development and physical deformities. Some symptoms of this syndrome include:

  1. Facial characteristics such as wide mouth, a tiny upward nose, spaced teeth, and plump lips
  2. Learning disabilities
  3. Colic or feeding issues
  4. The pinky finger is bent towards the inner side
  5.  ADHD stands for attention deficit hyperactivity disorder (ADHD) and is a common symptom
  6. Very particular phobias 

The morphological characteristics of the central sulcus have been proposed to be involved in people who suffer from Williams syndrome. The central sulcus foreshortening has also been identified as an irregularity connected with this disorder. People with Williams syndrome have an unusual dorsal end of the central sulcus.

The unusual dorsal end of the central sulcus, on the other hand, has not been associated with impairment of intellectual ability.  However, the precise role of this unusual segment of the central sulcus is still unknown. 

Conclusion:

The numerous creases and ridges of the cerebral cortex have the added benefit of providing a larger surface area for an increased number of nerve cells to survive, allowing for the processing of large amounts of data. A gyrus (plural gyri) is a term used to describe the ridges and grooves on the cerebral cortex, which is the outermost layer of the brain. A sulcus (plural: sulci) is another term for a furrow on the cerebral cortex. The frontal and parietal lobes are linked by the central sulcus. It’s also known as the Rolando sulcus. This sulcus is significant because it separates the primary motor cortex from the primary somatosensory cortex, as well as the frontal and parietal lobes. Cerebral amyloid angiopathy and William’s syndrome are related to damage to the central sulcus.                                                            

Reference list

  • Chamarthy, M.R. et al. (2012) ‘Isolated central sulcus hemorrhage: a rare presentation most frequently associated with cerebral amyloid angiopathy’, Case Reports in Radiology, 2012, p. 574849. doi: 10.1155/2012/574849
  • Deshmukh, V.R. and Kumar, D. (2019) ‘Lunate Sulcus’, in Encyclopedia of Animal Cognition and Behavior: Springer, Cham, pp. 1–3. Available at: https://link.springer.com/referenceworkentry/10.1007%2F978-3-319-47829-6_1478-1.
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  • Jackowski, A.P. and Schultz, R.T. (2005) ‘Foreshortened Dorsal Extension of the Central Sulcus in Williams Syndrome’, Cortex, 41(3), pp. 282–290. doi: 10.1016/S0010-9452(08)70266-1
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  • Stepwards (2021) Radiological Anatomy: Central Sulcus – Stepwards, 11 July. Available at: https://www.stepwards.com/?page_id=22705 (Accessed: 11 July 2021).
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  • Zhang, H. et al. (2016) ‘Early development of the fetal central sulcus on 7.0T magnetic resonance imaging’, International Journal of Developmental Neuroscience : the Official Journal of the International Society for Developmental Neuroscience, 48(1), pp. 18–23. doi: 10.1016/j.ijdevneu.2015.10.006