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Human Brain—The Controller

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Human Brain

Overview

The human brain is one of the largest, most vital and most intricate organs in the human body. It serves as the centre of intellect, the translator of the senses, the initiator of bodily movement, and the controller of behaviour. All of the characteristics that characterize mankind originate in the brain. It is made up of billions of nerves or nerve cells called neurons, about 86 billions (Herculano-Houzel, 2012), that communicate with each other via trillions of synapses. In other words, the brain governs all bodily functions, including cognition, memory, emotion, touch, motor skills, vision, respiration, temperature, and hunger. The brain is made up of the cerebrum, cerebellum, and brainstem and is protected inside the skull.

An adult human brain weighs approximately 3 pounds (1300 to 1400 grams), while the brain of a newborn human baby weighs between 350 and 400 grams (roughly three-quarters of a pound) (Cherry, 2019). The average male brain is nearly 78 cubic inches or1,274 cubic centimetres in volume, while the average female brain is 69 cubic inches or 1,131 cubic cm (Koch, 2015).

Brain Architecture

The human brain can be divided into three basic units: forebrain, midbrain, and hindbrain.

Forebrain

The forebrain also called the prosencephalon, is the largest and most developed region of the human brain, and controls complex behaviour. It houses the entire cerebrum and several intimately connected structures, including the limbic system, thalamus, hypothalamus, and pineal gland. The outer layer is called the cerebral cortex and consists of the two cerebral hemispheres, which account for two-thirds of the brain’s total mass.

The cerebral cortex sometimes referred to as the "cortex of the brain," is the outer layer of grey matter that fully encircles the two cerebral hemispheres. It has a collection of nerve cell bodies inside and is 2 to 4 mm thick. With ridges called gyri and grooves called sulci, this layer is folded into intricate shapes.

Each cerebral hemisphere is traditionally divided into four lobes—frontal, parietal, temporal, and occipital lobes—each associated with different functions:

(1) The frontal lobe is involved in complex motor control, personality expression, memory, and language.

(2) The parietal lobe, located at the top of the brain, processes sensory information such as touch, body position, and temperature.

(3) The temporal lobe, at the side of the brain, plays a role in processing sound, storing and retrieving memories, and recognising objects.

(4) The occipital lobe is located at the back of the brain and controls vision.

temporal lobes—regions of cerebral hemispheres

temporal lobes—regions of cerebral hemispheres

occipetal lobes in cerebral hemispheres

occipetal lobes in cerebral hemispheres

frontal lobes in both the regions of cerebrum

frontal lobes in both the regions of cerebrum

parietal lobes in cerebral hemisphres

parietal lobes in cerebral hemisphres

Midbrain

The forward-most part of the brainstem, known as the midbrain or mesencephalon, is the central connection between the brain and the spinal cord. The midbrain is the most superior but smallest of the three regions of the brainstem, measuring around 1.5 cm in length (Caminero & Cascella, 2020). It acts as a channel between the forebrain above and the pons and cerebellum below. The primary responsibility of the middle brain is to serve as a highway for nerve impulses travelling up from the spinal cord and down from the forebrain. It is involved in regulating temperature as well as vision, hearing, motor control, sleep and wakefulness, and arousal or consciousness.

The tectum, the tegmentum, and the cerebral peduncles are the three major structural components of the midbrain. The oculomotor and trochlear nerves, which control eye and eyelid movement, are two of the 12 cranial nerves that emerge directly from the midbrain.

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Colliculi are located at the top of the midbrain. It contains two pairs of bulging, layered bundles of neurons called the superior and inferior colliculi. The superior and inferior colliculi compose the posterior section of the midbrain, which is known as the tectum (from the Latin for "roof"). The superior colliculus participates in several visual reflexes, especially the tracking of objects in the visual field, and takes information from the retina and visual cortex. The medial geniculate body, the auditory relay nucleus of the thalamus, receives both crossed and uncrossed auditory fibres from the inferior colliculus.

A cerebral peduncle is a group of nerve cells that connects the forebrain to the hindbrain. The tegmentum, which makes up the midbrain's base, and the crus cerebri, which are nerve lines connecting the cerebrum and the cerebellum, are all part of the cerebral peduncle. Tegmentum (meaning floor) is located in front of the rectum.

The substantia nigra, subthalamus, and thalamus are under the authority of the hindbrain. As a component of the basal ganglia circuitry, the substantia nigra (SN), a midbrain dopaminergic nucleus, plays a crucial part in regulating motor activity and reward functions.

Dopamine is a neurochemical that is produced in large quantities in the substantia nigra and has a wide range of effects on the central nervous system, including movement control, executive processes of thought, and limbic emotional activity. Parkinson's disease is caused by a loss of dopaminergic neurons in the substantia nigra, and its symptoms can be managed via dopamine-supplementation techniques.

Hindbrain—Rhombencephelon

The medulla oblongata, the cerebellum, and the pons make up the hindbrain's three major regions. The hindbrain is home to most of the 12 cranial nerves. The reproductive cycle, muscular activity, sleep, and alertness are only a few of the essential survival processes that the hindbrain orchestrates.

Specific functions and activities are coordinated by the three distinct areas of the hindbrain. The medulla carries electrical impulses from the spinal cord to the cerebral cortex, and it also regulates autonomic processes like respiration and heartbeat. In addition to having cell clusters that transmit information from the cerebrum to the cerebellum, the pons also contains tracts that link the spinal cord with higher regions of the brain. One of those cell groupings, the reticular formation, is a network of neurons that extends across the brainstem and controls attentiveness, sleep, and wakefulness. Additionally, a component of the reticular structure is housed in the medulla.

Purkinje cells and granule cells are more abundant in the cerebellum, the third region of the hindbrain. The coordination of motor activity is greatly aided by Purkinje cells, which are large neurons. However, granule cells, which are incredibly tiny neurons, are assumed to have a significant part in motor learning despite the fact that their exact function is unknown.

Basal Ganglia

A collection of structures located deep inside the cerebral hemispheres is known as the basal ganglia. The caudate nucleus, putamen, and globus pallidus in the cerebrum, the substantia nigra in the midbrain, and the subthalamic nucleus in the diencephalon are the structures that are often included in the basal ganglia.

The caudate nucleus and the putamen are collectively called the striatum.

The basal ganglia are situated close to the base, or bottom, of the brain, thus the term "basal." However, according to current neuroscience jargon, the term "ganglia" is a little misleading. A group of neurons is referred to as a "ganglion," but this word is typically used to refer to neurons in the peripheral nervous system (i.e., outside the brain and spinal cord). In the central nervous system, collections of neurons are referred to as "nuclei" in most cases. Therefore, it could be more correct to refer to the basal ganglia as nuclei.

Lateral View: Human Brain, Basal ganglia highlighted in purple.

Lateral View: Human Brain, Basal ganglia highlighted in purple.

Central Nervous System

The brain and spinal cord make up the central nervous system (CNS), the command centre of the body which regulates how the body moves, thinks, and automatically reacts to its surroundings. Additionally, it manages other bodily functions and systems, including digestion, breathing, and sexual development (puberty). The CNS sends and receives signals from the rest of the body through nerves, which carry chemicals called neurotransmitters that help neurons communicate with each other via a synapse, also called neuronal junction.

"The functions of the central nervous system can be broken down into several areas: receiving and processing information, creating new memories, sending messages to the rest of the body, controlling physical actions, and producing emotions." -Excerpt from Brain-Mind.

CNS is surrounded by meninges, a protective membrane. The system floats in a crystal clear cerebrospinal fluid.

The peripheral nervous system is made up of the spinal nerves that emerge from the spinal cord and the cranial nerves that branch from the brain. The cranial nerves are responsible for controlling and regulating the six pairs of sensory organs. Each of the five senses (vision, hearing, taste, smell, and touch) is assigned to a specific cranial nerve. Nerves carry signals from the body to the brain and from the brain to the body.

In the central nervous system, synapses are specialized connections between two neurons that use chemicals known as neurotransmitters to transmit signals from one cell to another. Based on their positions along with the central nervous system, nerves are classified into three main categories: (1) cranial nerves—those that connect to the brain and the spinal cord; (2) spinal nerves—those that connect to the brain, via the spinal cord, and to the rest of the body; and (3) autonomic nerves—those that connect to the sympathetic nervous system and the parasympathetic nervous system.

Neurons

The fundamental building blocks of the brain and nervous system are neurons, also known as neurones or nerve cells. They are the cells in charge of receiving sensory information from outside the body, sending motor commands to the muscles, and transforming and relaying electrical signals at each stage along the way.

Neurons do not physically touch—there is always a gap between them, called a synapse which can be electrical or chemical i.e, the signal that is carried from the first nerve fibre to the next i.e., from the presynaptic neuron to the postsynaptic, is transmitted by either an electrical or a chemical signal.

Neurons have the ability to change their strength and make up their connections in response to both internal and external stimuli underlies the brain's ability to adapt to ever-changing circumstances, known as brain plasticity. (Mateos-Aparicio & Rodríguez-Moreno, 2019)

Facts About Brain

  • Nearly 60% of the human brain is made up of fat. The proper development of the human brain depends on fats, particularly polyunsaturated and monounsaturated fats. The majority of brain growth is complete before the age of 5 or 6. Essential fatty acids(EFAs), especially omega-3 fatty acids, are crucial for brain development during pregnancy and after birth. The retina and visual cortex require dietary docosahexaenoic acid (DHA) for optimal functional maturation, and additional DHA may even improve mental development and visual acuity (Essential Fatty Acids and Human Brain - PubMed, 2009). DHA is an omega-3 fatty acid, its best sources are cold-water fatty fish such as mackerel, salmon, catfish, trout, and herring.
  • Since water is an essential element in the brain and makes up 75% of the brain mass if the body remains dehydrated for a longer duration, it can affect the brain's cognitive functions (Zhang et al., 2018).
  • Sugar is the main fuel for the brain. Cognitive functions are all tightly correlated with glucose levels and how effectively the brain uses this fuel source. Neurotransmitters are the brain's chemical messengers that are not produced in the brain if there is insufficient glucose present, neural transmission is disrupted. Additionally, hypoglycemia, a common consequence of diabetes brought on by low blood glucose levels, can cause a lack of energy for brain activity and is associated with impaired attention and cognitive performance (Edwards, 2016)
  • The human brain is a highly energy-demanding organ. It consumes, even at rest, a great chunk of energy compared to other organs of the body. The brain makes up about 2% of the body weight of an average adult human. Amazingly, even though it is relatively small, the brain uses 20% of the body's oxygen and, consequently, 20% of its caloric intake (Herculano-Houzel, 2012). If the oxygen supply to the brain is cut off, the activities of the nerve cells stop, and the cells begin to die (Erecińska & Silver, 2001).
An illustration of two aging brains: one is monolingual and another one is bilingual. Bilinguals show more connectivity of frontal lobe with temporal and parietal lobes.

An illustration of two aging brains: one is monolingual and another one is bilingual. Bilinguals show more connectivity of frontal lobe with temporal and parietal lobes.

  • Bilinguals are at a greater advantage than monolinguals. Many studies suggest that it delays cognitive decline during ageing among bilinguals (Gold et al., 2013), (Heim et al., 2019). It may contribute to cognitive reserve, an ability of the brain and mind to withstand damage. Bilingualism makes an individual more efficient in using brain resources (Liu & Wu, 2021). Furthermore, the development of dementia is greatly delayed by bilingualism, which is also crucial in the treatment of Alzheimer's disease, which causes cognitive decline and network dysfunction in the brain (Raji et al., 2017). According to the PASA (Posterior-to-Anterior Shift in Aging) theory, aging in monolinguals is correlated with an increasing dependence on the frontal areas. The aging brain in bilinguals exhibits preservation of the back areas, such as the temporal and parietal cortex, as well as greater connection between the front and back areas, resulting in cognitive reserve (Grant et al., 2014).

References:


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This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

© 2022 Sonal Shrivastava

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