Health Tech

Animals Brain

The brain is the central control center of the nervous system in animals. It regulates and controls their behaviours. In mammals, the brain is located in the head and is protected by the skull. It is closely connected to the main sense organs—eyes, nose, tongue, and ears—and is situated nearby. The brain is present in all vertebrate animals, but in amphibians, it exists either as a central brain or as independent ganglia. In some creatures, such as nereids and starfish, it is not centralized but spread throughout the body, while in some animals like sponges, there is no brain at all. In higher animals, such as humans, the brain is extremely complex. The human brain contains approximately 100 million (100,000,000) nerve cells, each forming connections with over ten thousand (10,000) other nerve cells. The brain is the most complex organ.

The brain controls and regulates the functions of various organs of the body. Therefore, it is called the master organ of the body. Its main functions include the regulation and management of knowledge, intelligence, reasoning, memory, thought, decision-making, and personality. The field of neurobiology is rapidly developing worldwide. To deal with major neurological diseases, it has become essential to consider the overall functioning of the brain at molecular, cellular, genetic, and behavioural levels. A new study has concluded that the shape of the brain can provide insights into a person’s personality. In fact, children are born with distinct personalities, and as their brains develop, their personalities also take shape accordingly.

The brain is located within the skull. It is the seat of consciousness and memory. All sensory organs—eyes, ears, nose, tongue, and skin—send impulses here, and understanding or acquiring knowledge is the function of the brain. The main centers that send impulses through nerve fibers to cause muscle contractions and regulate these activities are in the brain, although these actions also occur from different centers in the spinal cord. The work of consolidating, contemplating, and drawing conclusions from knowledge gained through experience also belongs to this organ.

Structure Of The Brain

The upper part of the brain consists of the cerebral hemispheres, located in the skull. Behind them, towards the back of the head, are two small rounded structures called the cerebellum. Ahead of these is the part called the midbrain or mesencephalon. Below it lies the medulla oblongata, also known as the spinal cord.

The cerebrum and cerebellum are covered by membranes called meninges. There are three: dura mater, arachnoid membrane, and pia mater. The outermost membrane, dura mater, contains large veins through which blood returns. Due to injury or damage, blood may escape from these veins and accumulate in the brain, increasing pressure, which can cause the brain cells to become non-functional and lead to paralysis of the limbs. From this membrane, a fold extends between the two hemispheres, forming the corpus callosum, which connects the two halves. The colour of the hemispheres appears gray from the outside.

The outer surface of the hemispheres has many deep grooves, called sulci, where the outer layer of the brain dips inward. It appears as if the surface layer has been peeled back to reveal folds. These grooves create many large and small fissures, which separate specific regions of the brain. The front, lateral, and posterior regions are called lobes based on their position, and these are subdivided into lobules. The frontal lobe is at the front, covered by the frontal bone; the parietal lobe, occipital lobe, and temporal lobe follow. These regions contain various ridges and furrows, with additional specific grooves. Some of the prominent grooves and sulci are described here. The central sulcus, also called Rolando’s fissure, runs from top to bottom, anteriorly, on the parietal lobe. This region controls muscle movements; electrical stimulation here causes muscles to contract. Damage from tumours, inflammation, or pressure can destroy cells in that area, leading to paralysis. Behind this region is the sensory area, where impulses from different parts of the skin are received. The occipital lobe contains the visual area, related to vision, and impulses from the retina are processed here to produce visual impressions. The temporal lobe contains the auditory area, responsible for hearing; impulses from the ear are interpreted here as sound. The hippocampal gyrus within the temporal lobe is responsible for the sense of smell and memory related to odours. The taste region is also associated with this area. The senses of smell and taste are highly developed in some animals compared to humans. The posterior part of the Rolandic fissure contains a large region responsible for tactile sensations.

The frontal lobe is more developed in humans than in other animals, and its anterior part has undergone significant development. This region is connected via association fibers to all motor and sensory centers and is particularly close to centers related to eye movements. It is believed that this part regulates fine motor activities dependent on impulses received by the eyes, involving memory and experience. The precise control of human speaking, writing, and fine hand movements involved in crafting objects arises from here.

The cerebrum is considered the seat of higher emotions. All qualities that distinguish humans from animals reside in the cerebrum.

Lateral Ventricles – If the hemispheres are cut transversely, a hollow space or cavity is found within them. This cavity exists in both hemispheres and is called the ventricle. These ventricles extend from the frontal lobe to the posterior occipital lobe. Inside them, a very fine membrane covers the brain, called the internal membrane. The network of soft tissue surrounds both ventricles. These cavities contain the cerebral medulla, which extends into the third ventricle through a small opening called the foramen of Munro, situated between the optic thalami.

Cerebral Cortex – The thick layer of gray matter covering the surface of the cerebrum is called the cortex. Beneath it is the medulla, a white matter part. Occasionally, gray islands and many small patches called nuclei are present within the medulla.

The cortex primarily consists of nerve cells, although fibers originating from these cells and connective tissues called neuroglia are also present. However, neurons predominate at this level.

There are multiple layers within the cortex. In the layer of fibers, there are two types: one that connects different centers (many of which originate from centers in the medulla or midbrain), and the other that emerges from cells and terminates in the inward input, ultimately reaching the pyramidal tract in the medulla.

In humans and higher animals such as apes and gorillas, the formation of specialized cortical layers indicates advanced development. In lower animals, neither the layered structure of the cortex nor such extensive development of the cerebrum is found.

Inner Matter – This is mainly composed of fibers originating from the cortices and the ascending and descending pathways they produce. Groups of these fibers are located here and there, with grayish color. The inner matter is white.

Diencephalon – Situated beneath the posterior part of the brain, it is linked to the cerebrum by three pillars. Its outer surface is covered with gray matter, giving it a grayish color, while inside it contains white matter similar to the cerebrum. It also has two hemispheres, which, when cut, show a white, branching structure resembling a tree. The deep grooves in the diencephalon divide it into laminae. This structure is called the arbor vitae.

Forebrain – Located below the posterior part of the brain, the forebrain is connected to the brain by three pillars. Its outer surface is gray due to the cortical layers, while the interior contains white matter. It comprises two hemispheres, whose cut surfaces reveal intersecting branches like a tree. These deep grooves divide the forebrain into laminae.

The forebrain is connected mainly to the inner ear and muscles and joints. Sensations from other parts of the body are received here. Its function is to coordinate and regulate all these signals to ensure smooth functioning of the organs. Maintaining the body’s balance is a primary task. The nerves that carry these impulses to the inner matter of the forebrain reach the dentate nucleus within the hemisphere, a large cluster of cells made of gray matter. From there, new fibers project to the red nucleus in the midbrain, and from there, the impulses reach the cerebrum. Structurally, the brain has three main parts: the forebrain, midbrain, and hindbrain. The cerebrum and diencephalon are part of the forebrain; the medulla, pons, and cerebellum are parts of the hindbrain.

Midbrain – The upper part in front of the forebrain is the midbrain, while the lower part is the medulla oblongata. The midbrain connects with the cerebrum through three pillars. Inside the midbrain, fibers pass from the pons to the cerebrum, either toward the same side or crossing the midline to the opposite side.

The central sulcus of the midbrain contains the corpora quadrigemina, which connects the third and fourth ventricles and reaches the brainstem. The upper two colliculi receive fibers from the retina via the optic nerve. These colliculi regulate reflexive eye movements such as constriction and dilation of the pupil, in response to visual stimuli. The lower colliculi receive fibers from the auditory parts of the inner ear, transmitting these impulses to the thalamus and then to the cerebral cortex via new fibers. Other fibers from the brainstem also reach the midbrain. Impulses related to pain, cold, heat, etc., arrive here, gathering into groups, and pass through the medulla and midbrain to reach the thalamus and specific brain centers.

Ahead of the colliculi, other motor and sensory fibers from the lower parts also travel here, and association fibers are also found. The brain exercises control and regulation over various body parts through these fibers. Therefore, the brain is called the master organ of the body. Its main functions include controlling knowledge, intelligence, reasoning, memory, decision-making, and personality. The field of neurobiology is rapidly advancing worldwide.

Pons Varolii – Situated between the medulla and the midbrain, this part connects the cerebral hemispheres. In diagrams, it appears as an elongated protrusion in front. When the brain is protected, fibers passing transversely through it are visible. These fibers originate from the internal input and the midbrain, traveling to the pons and then to the medulla. Not all fibers are superficial; some deeper fibers lie beneath the pyramid fibers that pass through the pons. The pyramid fibers are of particular importance as they run through the pons. Several other fiber groups also pass through the pons, called longitudinal, transverse, and lateral limb fibers. The nuclei of the fifth, sixth, seventh, and eighth cranial nerves are located in this part.

Medulla Oblongata – This appears as part of the medulla when viewed from above and extends into the pons and midbrain; however, its structure differs from that of the spinal cord. Its posterior side is the cerebellum. Here, it doubles in size compared to the spinal cord. The broad, flat surface has a quadrilateral shape, covered by a membrane called the inferior medullary velum, with the fourth ventricle behind it, into which the cerebral aqueduct leads. The posterior side is the cerebellum.

The medulla oblongata is of vital importance. It contains centers that control heartbeat, breathing, and blood circulation, which regulate these functions. It also contains centers for the eighth, ninth, tenth, eleventh, and twelfth cranial nerves. It is connected to the cerebrum, cerebellum, and midbrain via numerous fibers, which pass to and from the medulla. These fibers are grouped into specific clusters, called:

1. Pyramidal tract, 2. Median longitudinal bundles, and 3. Median filler.

The pyramidal tract contains only motor fibers, originating from the motor centers in the cortex, passing through the interna, and descending through the medulla and pons to the spinal cord, where they gather into two bundles situated in front of and behind the median fissure. Some fibers cross to the opposite side at the lower levels, while others continue on the same side before crossing near the muscles and organs, resulting in contralateral muscle control. Damage to one side of the brain or bleeding in that area causes paralysis on the opposite side of the body.

Fibers from the median longitudinal bundles extend from the midbrain and pons into the medulla, linking centers on both sides of the nervous system, helping regulate and coordinate functions.

The median filler contains only sensory fibers. This filler is situated between the above-mentioned bundles. These fibers originate from the spinal cord and, crossing the pyramidal fibers, go to the centers in the opposite hemisphere, with fibers crossing from right to left and vice versa.

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