Brain: Anatomy and Function

Brain: Have you ever pondered how we think about and react to the opponent’s postures and gestures? What organ is responsible for thinking, reacting, picturing things, and so on? Yes, the brain is a vital organ with the potential to respond to external stimuli. The brain, which governs and organises the body’s many functions, weighs around 3 pounds in a normal adult. Controlling one’s systems is a basic requirement for all living species.

The brain is one of the human body’s biggest and most complicated organs, with billions of neurons (nervous cells) communicating through trillions of synapses. The waves of the brain are recorded using an electroencephalogram (EEG).

What is a Brain?

The brain is the most complex and important organ in the human body. It is a part of the nervous system responsible for many sites like thinking, imagination, intelligence, body movement, senses, behaviour control, etc. The nervous system in humans is divided into the central nervous and peripheral nervous systems, and the brain, along with the spinal cord, constitutes the central nervous system.

Parts of the Human Brain

The brain has the following divisions:

Forebrain

It consists of the cerebrum and diencephalon:

1. Cerebrum: It is the largest part of the brain and is divided into right and left halves called cerebral hemispheres. These are connected together by a sheet of nerve fibres called the corpus callosum. The cerebrum is further subdivided into four sections or parts, and they are as follows:

Frontal Lobe: It is more developed and larger than any other living organism. It is located in the frontal part of the brain, just over the eyes, where the largest section of the brain is located. It helps in the function of movements, reasoning, problem-solving, planning, and various parts of speech.

Parietal Lobe: Parietal lobe lies just behind the frontal lobe and is separated from the frontal lobe by the central sulcus. This part or section mainly helps in movements, taste, orientation, and perceived stimuli.

Occipital Lobe: Occipital lobe is situated at the back of the brain and is primarily engaged in vision. The occipital section mainly helps in visual processing.

Temporal Lobe: The temporal lobe lies in the posterior to the frontal lobe and is separated by a lateral fissure. It helps in speech, auditory stimuli perception, and memory recognition.

Functions of Olfactory Lobes: These are a pair of small club-shaped solid structures lying on the lower surface of cerebral hemispheres. Olfactory lobes are connected with the relay of the sense of smell.

The outer region is called the cortex, contains cell bodies of the neurons, and is thus greyish in colour. So it is also called the grey matter. The grey matter is highly convoluted with ridges and grooves. These convolutions increase the surface area and total grey matter. The number of convolutions is believed to be associated with the degree of intelligence. The inner region of the cerebrum has white matter, which is composed of axons of the neurons.

Functions of Cerebrum: Seat of mental abilities, controls thinking, memory, reasoning, perception, emotions, and speech. Interprets sensations and responds to pain, cold, heat, and pressure.

2. Diencephalon: It lies concealed by the cerebrum. The diencephalon is distinguishable in two parts, the thalamus and the hypothalamus.

(i) Thalamus is concerned with relaying sensory impulses except those of smell and regulation of smooth muscle activity.

(ii) Hypothalamus coordinates various autonomic activities of the body, including water balance, control of the pituitary gland, body temperature, blood pressure, etc. Diencephalon has a cavity called the third ventricle. The roof of the diencephalon possesses an anterior choroid plexus for the formation of cerebrospinal fluid. The inferior surface of the diencephalon bears optic chiasma and the pituitary gland.

Functions of Diencephalon: Relay centre for sensory impulses, such as pain, temperature, and light.

1. Reflex centre for muscular activities.
2. Centre for certain emotions such as anger.
3. Centre for water balance, blood pressure, body temperature, sleep, and hunger.
4. It controls the pituitary gland, which functions as the master gland, body temperature, blood pressure, etc. Hypothalamus strongly influences water preservation and parturition.
5. The fibres from the hypothalamus also control the brainstem autonomic centres, particularly the vasomotor centre (VMC).

Midbrain

The midbrain is significantly small and consists of two heavy fibre tracts, known as cerebral peduncles (crura cerebri), on the ventral side. There are two swellings, superior and inferior colliculi, on each side of the dorsal surface. The midbrain connects the forebrain to the hindbrain and controls muscle toning, modifies some motor activities, and also has reflexes for sight and hearing.

1. The midbrain also contains groups of nerve cells (nuclei) scattered in the white matter. Some of these nuclei control muscle tone and modify certain motor activities initiated by the cortex.
2. Corpora quadrigemina serves as centres for certain visual and auditory reflexes, whereas cerebral peduncles act as coordination centres between the hind and forebrain.

Functions of the Midbrain: It relays motor impulses from the cerebral cortex to the pons and spinal cord and relays sensory impulses from the spinal cord to the thalamus.

Hindbrain

The hindbrain consists of the cerebellum, pons, and medulla oblongata.

1. Cerebellum: It is very well-developed and lies below the cerebrum and above the medulla. It is known as a small brain. It consists of three parts – A middle vermis and two lateral hemispheres. The two hemispheres possess numerous furrows but no convolutions. Pons varoli is a bridge of nerve fibres connecting the two lobes of the cerebellum.

(i) Transmission of impulses across the bridge ensures coordination of muscular movements on both sides of the body. It has an outer cortex of grey matter, while white matter is centrally located. The latter appears like a branching tree. Its fibre tracts are connected with the cerebrum and medulla oblongata.

(ii) This region is a motor area of the brain concerned with coordinating movements of skeletal muscles. It maintains posture, equilibrium, and muscular toning. Alcohol affects the coordination of the head, eyes, and limbs. A drunken driver does not have complete control over the vehicle because, under the influence of alcohol, the cerebellum cannot coordinate muscular movements.

Functions of the Cerebellum: It maintains posture, equilibrium, and muscle tone. Coordinates voluntary movements are initiated by the cerebrum. It mainly controls the balance and posture of the body. Its control is ipsilateral over half of the body on the same side.

2. Pons: On the ventral side of the brain, below the cerebellum, a thick bundle of fibres is present that is known as pons varoli. It transmits impulses from one side of the cerebellum to the other, and together with the medulla, it controls breathing.

Functions of Pons: Transmits impulses from one side of the cerebellum to the other, and together with the medulla, it controls breathing. Pons control the sleep cycles.

3. Medulla Oblongata: It is the lowest part of the brain located at the base of the skull. It is conical in outline and continues below with the spinal cord. It has white matter on the outer side and grey matter on the inner side. Medulla oblongata, pons varoli, midbrain, and hypothalamus are collectively known as the brainstem. They are hidden by the cerebrum and cerebellum.

(i) The roof of the medulla oblongata contains a choroid plexus where cerebrospinal fluid is formed. The posterior medulla controls the activities of the internal organs. It has reflex centres such as cardiac centres, respiratory centres and vasomotor centres.

Functions of the Medulla Oblongata: Contains the centre for cardiac, respiratory, and vasomotor activities. Coordinates reflexes like swallowing, coughing, sneezing, and vomiting.

Ventricles of Brain

There are mainly four ventricles of the brain. Lateral ventricles are the first two ventricles connected to the third ventricle through a central opening called the Foramen of Munro. The communication between the third and the fourth ventricle occurs via the Aqueduct of Silvius, a long tube.

1. Lateral Ventricle: The first and second combined together is called the lateral ventricle; they are enclosed in the cerebral hemispheres.

2. Third Ventricle: It is present in the brain’s centre, and its walls are made up of the hypothalamus and thalamus. The pineal gland is situated behind the third ventricle. It helps to control the body’s inner clock and circadian rhythms through the secretion of melatonin.

3. Fourth Ventricle: The fourth ventricle is located in the posterior or dorsal to the pons and medulla oblongata and is anterior to the cerebellum.

Summary

The nervous system is a very important fortune to the body because it plays a vital role in normal functioning. The brain is the control tower of the human body. It helps control and coordinates the actions and reactions that are received from the surroundings. The brain is divided into three parts: forebrain, midbrain, and hindbrain.

The forebrain is the most significant part of the brain that contains major parts called the cerebrum, hypothalamus, and thalamus. The midbrain is the smallest and central part of the brain that consists of two divisions called the tectum and tegmentum. The last part of the brain is the hindbrain. The lowest part of the brain is composed of the cerebellum, pons, and medulla. The brain can control actions like walking, sleeping, breathing, body temperature, emotions, etc.

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