Cerebrum- Intelligence, Thought Process

The  cer ebrum  is  divided  into  two symmetrical halves, called the Cerebral Hemispheres. Although the two hemispheres appear identical, functionally one hemisphere usually dominates the other. For example, the left hemisphere usually controls language behaviour. The right hemisphere is usually specialised to deal with images, spatial relationships, and pattern recognition. These two hemispheres are connected by a white bundle of myelinated fibers, called Corpus Callosum that carries messages back and forth between the hemispheres.

Lobes of Cerebral Cortex:

The Frontal lobe is mainly concerned with cognitive functions, such as attention, thinking, memory, learning, and reasoning, but it also exerts inhibitory effects on autonomic and emotional responses. The Parietal  lobe is mainly concerned with cutaneous sensations and their coordination with visual and auditory sensations. The Temporal  lobe is primarily concerned with the processing of auditory information. Memory for symbolic sounds and words resides here. Understanding of speech and written language depends on this lobe. The Occipital lobe is mainly concerned with visual information. It is believed that interpretation of visual impulses, memory for visual stimuli and colour visual orientation is performed by this lobe. Physiologists and psychologists have tried to identify specific functions associated with specific brain structures. They have found that no activity of the brain is performed only by a single part of the cortex. Normally, other parts are involved, but it is also correct that there is some localisation of functions, i.e. for a particular function, a particular part of the cortex plays a more important role than the other parts. For example, if you are driving a car, you see the road and other vehicles by the function of your occipital lobe, hear the horns by the function of your temporal lobe, do many motor activities controlled by parietal lobe, and make decisions by the help of frontal lobe. The whole brain acts as a well coordinated unit in which different parts contribute their functions separately.

 

Forebrain- Associated Structures

It is considered to be the most important part of the brain because it performs all cognitive, emotional, and motor activities. We will discuss four major parts of the forebrain: hypothalamus, thalamus, limbic system, and cerebrum.

Hypothalamus : The hypothalamus is one of the smallest structures in the brain, but plays a vital role in our behaviour. It regulates physiological processes involved in emotional and motivational behaviour, such as eating, drinking, sleeping, temperature regulation, and sexual arousal. It also regulates and controls the internal environment of the body (e.g., heart rate, blood pressure, temperature) and regulates the secretion of hormones from various endocrine glands.

Thalamus : It consists of an egg-shaped cluster of neurons situated on the ventral (upper) side of the hypothalamus. It is like a relay station that receives all incoming sensory signals from sense organs and sends them to appropriate parts  of  the cortex for processing. It also receives  all outgoing motor signals coming from the cortex and sends them to appropriate parts of the body.

The Limbic System : This system is composed of a group of structures that form part of the old mammalian brain. It helps in maintaining internal homeostasis by regulating body temperature, blood pressure, and blood sugar level. It has close links with the hypothalamus. Besides hypothalamus, the limbic system comprises the Hippocampus and Amygdala. The hippocampus plays an important role in long-term memory. The amygdala plays an important role in emotional behaviour.

The Cerebrum : Also known as Cerebral Cortex, this part regulates all higher levels of cognitive functions, such as attention, perception, learning, memory, language behaviour, reasoning, and problem solving. The cerebrum makes two-third of the total mass of the human brain. Its thickness varies from 1.5 mm to 4 mm, which covers the entire surface of the brain and contains neurons, neural nets, and bundles of axons. All these make it possible for us to perform organised actions  and  cr eate  images,  symbols, associations, and memories.

Midbrain

The midbrain is relatively small in size and it connects the hindbrain with the forebrain. A few neural centres related to some special reflexes and visual and auditory sensations are found here. An important part of midbrain, known as Reticular Activating System (RAS), is responsible for our arousal. It makes us alert and active by regulating sensory inputs. It also helps us in selecting information from the environment.

 

The Central Nervous System- Hind Brain, Fore Brain, Mid Brain

The central nervous system (CNS) is the centre of all neural activity. It integrates all incoming sensory information, performs all kinds of cognitive  activities,  and  issues  motor Brain scanning reveals that while some mental functions are distributed among different areas of the brain, many activities are localised also. For example, the occipital lobe of the brain is a specialised area for vision.

The CNS comprises (a) brain and (b) spinal cord.  It is believed that the human brain has evolved over millions of years from the brains of lower animals, and this evolutionary process still continues. We can examine the levels of structures in the brain, from its earliest to the most recent form in the process of evolution. The limbic system, brain stem and cerebellum are the oldest structures, while Cerebral Cortex is the latest development in the course of evolution. An adult brain weighs about

1.36 kg and contains around 100 billion neurons. However, the most amazing thing about the brain is not its number of neurons but its ability to guide human behaviour and thought. The brain is organised into structures and regions that perform specific functions.

Hindbrain- Main Structures

Medulla Oblongata : It is the lowest part of the brain that exists in continuation of the spinal cord. It contains neural centres, which regulate basic life supporting activities like breathing, heart rate, and blood pressure. This is why medulla is known as the vital centre of the brain. It has some centres of autonomic activities also.

Pons : It is connected with medulla on one side and with the midbrain on the other. A nucleus (neural centre) of pons receives auditory signals relayed by our ears. It is believed that pons is involved in sleep mechanism, particularly the sleep characterised by dreaming. It contains nuclei affecting respiratory movement and facial expressions also.

Cerebellum : This highly developed part of the hindbrain can be easily recognised by its wrinkled surface. It maintains and controls posture and equilibrium of the body. Its main function is coordination of muscular movements. Though the motor commands originate in the forebrain, the cerebellum receives and coordinates them to relay to the muscles. It also stores the memory of movement patterns so that we do not have to concentrate on how to walk, dance, or ride a bicycle.