The brain is an intricate and complex structure. Together with the spinal cord, it makes up the central nervous system, which coordinates all functions of the body and acts as its control centre. The brain is made from grey matter filled with billions of neurons which are connected to each other by synapses and axions.
The largest structure of the brain is the cerebrum, also called the cerebral cortex. This is located in the forebrain, and is divided into four sections: the frontal, parietal, occipital and temporal lobes. Each lobe is associated with higher brain functions relating to thought and action.
The frontal lobe is associated with the greatest range of functions, including problem solving, emotions, speech, movement, reasoning and planning. The parietal lobe is also associated with movement, and with recognition, orientation, language and the perception of stimuli. The occipital lobe is dedicated to visual processing such as distance, shape and colour, and the temporal lobe deals with memory, speech and auditory stimuli.
The entire surface of the cerebrum is wrinkled and folded. This cortical folding, or gyrencephalisation, increases the efficiency of the brain by providing a large surface area with room for a greater number of neurons. The cerebrum is divided into two halves by a deep furrow. The halves are termed the left and right hemispheres, and are connected by a bundle of axons; the corpus callosum.
Each hemisphere functions differently, with the left associated with logic and the right with creativity. Each hemisphere controls and processes information from the opposite side of the body, i.e. the right hemisphere controls the left side of the body, and vice versa.
The cerebellum is very similar in design to the cerebrum, with two hemispheres and a folded surface. The word cerebellum means ‘little brain’, and it makes up around one-tenth of the human brain. It is the lower part of the brain, located below the cerebrum, and is associated with movement. It regulates and coordinates many functions that are carried out automatically or subconsciously, such as posture, balance and movement. Scientists believe the cerebellum developed in animals before the evolution of humans.
The limbic system, located deep within the cerebrum, can be described as the ‘emotional brain’. It is made up of the thalamus, hypothalamus, amygdala and hippocampus.
The thalamus controls sleep and consciousness, receives and relays many types of sensory signals and regulates motor control. The tiny hypothalamus, which is no larger than a pearl, also plays a role in sleeping and waking, regulates thirst and hunger, and controls many important functions such as hormone secretions, homeostasis and emotional response.
The amygdala comprises two small, almond-shaped groups of cells that are associated with strong emotional sensory input such as fear, excitement, sexual desire and anger. The hippocampus is responsible for short-term conscious memory, and is unusual in having white matter on its outside surface, rather than grey matter. The hippocampus is named after the Latin for sea-horse, whose shape it resembles.
The brain stem lies at the base of the brain, at the top of the spinal cord. While considered the simplest part of the brain, it plays a vital role in controlling basic functions such as heartbeat, blood pressure, breathing, swallowing and eye movements.
Neurons travel through the brainstem to the upper parts of the brain and relay signals to and from the spinal cord. In reptiles, and other creatures, the entire brain consists only of the brain stem. The brain stem is made up of the midbrain, pons and medulla oblongata.