Brain Anatomy and How the Brain Works

Being one of the largest and most complex organs of the human body, the brain is made up of over 10 billion nerves which communicate in trillions of connections which are known as synapses. The brain is divided into many different regions which specialise in the different functionalities of the brain. There are many different functional sections which are known as lobes. These include the frontal lobe, the temporal lobe, the parietal lobe, the occipital lobe, the cerebellum and the brain stem. 

The brain is housed inside the skull which provides frontal, lateral and dorsal protection. The skull consists of 22 bones – 14 of which are the facial bones and the remaining 8 constitute the cranial bones. The brain is actually contained within the cranium and is surrounded by Cerebrospinal fluid, a clear colourless body fluid that surrounds the brain and spinal cord. This liquid fills up any of the hollow spaces on the surface of the brain and acts as a buffer, cushioning mechanical shocks and dampening minor jolts. Besides this, it also provides basic immunological protection to the brain.          

The brain and the spinal cord are protected and supported by three meningeal layers known as meninges. The innermost layer is known as the pia mater, the middle layer is known as the arachnoid which is a web-like structure filled with fluid that cushions the brain and finally, the tough outer layer is known as the dura mater.        

The brain can be divided into three main parts:

The Forebrain: The Forebrain is the largest part of the brain: It is subdivided into two subdivisions which are known as the telencephalon and the diencephalon. The diencephalon includes the thalamus, hypothalamus and pineal gland. 

The forebrain is mainly concerned with controlling reproductive functions, emotions, hunger, body temperature and sleep.  

 

a)     Cerebrum: 

     

      This is the largest part of the brain and consists of the cerebral cortex and other subcortical structures. There are two cerebral hemispheres which are joined together by heavy bands of fibre known as the corpus callosum. It accounts for 85% of the brain’s weight. This area of the brain is responsible for all voluntary actions, i.e. motor skills such as communication, emotions, creativity, personality and intelligence.

There are two main layers of the brain – the inner layer and the outer layer. The outer layer is known as the cerebral cortex. It houses the brain’s gray matter and is considered the seat of human consciousness.  This area is in charge of thinking, reasoning, speech, and processing sensory information and emotion. The inner core house of the cerebrum is what is the white matter of the brain. It is known as the corpus callosum, having four parts of nerve tracts which connect to different parts of the hemispheres.      

The cerebrum also has two halves or hemispheres – the left hemisphere and the right hemisphere. It is important to note that the left side of the brain ( left hemisphere) controls the right-hand side of the body and the right-hand side of the brain (right hemisphere) controls the left side of the body. 

Besides this, each area of the brain controls different functions of the body. The left hemisphere is responsible for handling reasoning, language, speech and logic. The right hemisphere is responsible for spatially related tasks and visual understanding.  

 The cerebrum’s left and right hemispheres are divided into four different lobes: the frontal, parietal, occipital and temporal lobes. These lobes are in charge of handling different functions of the body. The lobes are separated from one another by depressions in the cortex known as sulcus and are protected by the skull with bones which are named after their corresponding lobes. 

Thalamus: The thalamus has many functions which include processing and relaying sensory information to different parts of the cerebral cortex, transmitting signals to the cerebral cortex from lower centres such as somatic, auditory, visceral,  gustatory and visual systems and also regulating states of wakefulness and sleep. It also regulates levels of consciousness, regulating arousal and levels of activity. 

Hypothalamus: The hypothalamus is associated with the general regulation of the system and is also closely associated with the pituitary gland. 

Pituitary: The Pituitary gland is mainly related to the production of hormones, as it is also a part of the Endocrine system.      

Cerebral Cortex: This area of the brain is mainly associated with attention, memory storage, awareness, language, thought and consciousness. The outer layers of the cerebrum consist of gray matter. 

The forebrain, the midbrain and the hindbrain structure the three major parts of the brain. The forebrain includes the cerebrum, thalamus, hypothalamus, the pituitary gland, the olfactory bulb and the limbic system. The midbrain consists of the tectum, tegmentum, cranial nerve nuclei, colliculi and crura Celebi. The hindbrain consists of the brainstem and is made up of the medulla, pons, cranial nerves and the back part of the brain known as the cerebellum. 

 The forebrain is in charge of actions such as thirst, hunger, intelligence, memory and body temperature. The midbrain is in charge of reflex responses to auditory, visual and touch input.

  There are four sections of this part of the brain which are also known as lobes that are found here. 

 

1.     The Frontal Lobe: It is located in the front of the brain, running from your forehead to the ears.  This part of the brain is associated with planning, speech, reasoning, behaviour, memory, movements and problem-solving.  The frontal lobe is separated from the parietal lobe by the central sulcus and is protected by a singular frontal skull bone. 

2.     The Parietal Lobe: This area of the brain picks up where the frontal lobe ends and goes until the mid-back part of the brain. This part of the brain is responsible for processing information from the senses – sight, touch, smelling, hearing and sight. It is also in charge of language interpretation, spatial interpretation, the perception of stimuli and orientation and movement. It is separated from all the other four lobes on all four sides – from the frontal lobe by the central sulcus, from the opposite hemisphere by the longitudinal fissure, from the occipital lobe by the parieto-occipital sulcus and from the temporal lobe by a depression known as the lateral sulcus or lateral fissure.   

3.     The Occipital Lobe: This area of the brain is located at the back of the brain and is considered the brain’s visual processing centre. It is separated from the parietal lobe by the parieto-occipital sulcus, from the temporal lobe by the lateral occipital sulcus and from the cerebellum by the cerebellar tentorium (or tentorium cerebelli).    

4.     The Temporal Lobe: This area of the brain is located behind and below the frontal lobe and beneath the parietal lobe, under the lateral fissure. This area is responsible for thinking, intelligence, memory, consciousness, understanding touch, vision and hearing, emotions, memory, speech, language, and auditory and visual processing. It is also in charge of the perception and recognition of auditory stimuli. This area of the brain is responsible for Hypothalamus: This is a very small and important part of the brain that is located right beneath the thalamus. It is the primary region of the brain.

 

The Midbrain: 

Also known as the mesencephalon, the midbrain is the smallest and most central part of the brain. It is the topmost part of the brainstem and has three main parts – the colliculi, the tegmentum and the cerebral peduncles. It is associated with vision, motor control, hearing, sleep and wakefulness, arousal (wakefulness) and temperature regulation. 

This area of the brain connects the pons and the cerebellum with the forebrain. It lies right between the thalamus and the pons. The lateral sides of the midbrain are covered and hidden by the hippocampal gyri of the brain. This area of the brain connects the forebrain and the hindbrain. It acts as a bridge, transmitting signals from the hindbrain and the forebrain.  The midbrain consists of two pairs of bulging, layered bundles of neurons which are known as the superior and the inferior colliculi.   

 

1)    The colliculi: The superior colliculi work on the preliminary processing of visual signals before they are passed on to the occipital lobe at the back of the head. The inferior ones work on auditory signals before they are passed through the thalamus to the main auditory processing centre in the cortex.  

2)    The tegmentum: This area of the brain stretches down the length of the brainstem and a part of it is also part of the midbrain. There are two areas of the brain which are a part of this which are the iron-rich red nucleus which is involved in the coordination of movements and the periaqueductal grey which is involved in suppressing pain. The tegmentum contains connections that play a role in keeping us alert.     

3)    Cerebral Peduncles: This portion of the brain is at the back of the midbrain and contains large nerve fibre bundles which connect the rest of the brainstem to the forebrain. This area of the brain is the main highway for signals which need to be transported from the cortex to other parts of the central nervous system and also for body coordination.   

The Hindbrain is the lower part of the brain and is located near the brainstem and is also known as the rhombencephalon.  

a)     The Cerebellum: Having a convoluted surface, the cerebrum provides more surface to neurons. It is located behind the pons and is rich in Purkinje fibres and granule cells. This area of the brain is very important in motor control and receives sensory signals from the spinal cord and other areas of the brain. This area of the brain is responsible for the coordination, precision and fine-tuning of motor responses. It stores unconscious memories and motor skills such as cycling, swimming, etc.    

      The Medulla: Located at the posterior of the brain which continues to the spinal cord, the medulla is a long stem-like structure.  

It consists of a thick wall having a bundle of nerve tracts, connecting the spinal cord to different parts of the brain. 

This portion of the brain is responsible for regulating different life processes such as 

heartbeat, blood pressure, respiration, gastric secretions, etc. It is also the centre for reflex functions of the body such as vomiting, swallowing, and coughing.

            

  

c)     The Pons:

 

Part of the brainstem, the pons is a structure which links your brain to the spinal cord. Handling unconscious processes and jobs such as the sleep-wake cycle and even breathing the pons also contains junction points for nerves to control muscles and carry information from our senses to our head and face. 

It is the second lowest section of the brainstem and is located right above the medulla. It is the connection between the brain and the medulla and the spinal cord. 

It is a key merging point for many cranial nerves – nerves with direct connections to the brain. 

Some of the main functions of the pons include:

1)    To influence the sleep cycle: It sets the body’s level of alertness when we wake up.

2)    To manage pain signals: It relays and regulates signals which give us the sensation of pain.

3)    To work with other brain structures: It is a key connection point to the cerebellum and works cooperatively with other parts of the brain stem to manage to breathe.