Figure 1: Diagram of a neuron & Schwan cell. The neuron has dendrite branches on one end and the axon terminal at the other. The ‘Schwann’ cell is a separate cell in charge of making a fat coating (called the myelin sheath) around the neuron. This is like the plastic/rubber housing around the wiring in your home. Electric current flows in the direction of the red arrow, from cell body to axon terminal.
Source: Public Domain
The human brain is one part of our nervous system, which is the control system through which all other body systems receive their instructions. Much like the engine of a car, the brain is made up of many different parts. These parts have different functions, but they work closely together, to coordinate complex thoughts, feelings and behaviours.
All organs in the body, including the brain, are made up of cells. Each of the many different cell types in the brain has a specific function. The most recognizable type of brain cell is the neuron (see Figure 1).
The brain is made up of 100 billion neurons. Each of these neurons is connected to at least one other neuron, forming 100 trillion connections in the brain. Electrical signals jump from the axon end of one neuron to the dendrite end of a neighbouring neuron (see Figure 1). To do this it has to cross a tiny gap called a synapse. The electrical signals travel between brain regions at a variety of speeds.
Regions of the brain
Figure 2: Lobes of the human brain (from left to right): Frontal Lobe (blue), Parietal Lobe (yellow), Temporal Lobe (green), Occipital Lobe (pink), Cerebellum (white), Brainstem (white beside cerebellum). Source: Public Domain
Weighing just over 1 300 g and yet using up to 20% of the body’s energy, the brain is the powerhouse of the human body. Contrary to popular belief, humans do not use only 10% of their brain power. The entire brain is involved in coordinating internal and external actions like sneezing, kicking a ball, or texting.
Frontal Lobe: This lobe is located at the front of the brain. It is responsible for actions like critical thinking and planning, feelings of reward and motivation, our knowledge of our self-identity and the long-term storage of memories.
Parietal Lobe: This lobe is located near the back of the brain. It sits behind the frontal lobe and in front of the occipital lobe. The parietal lobe is responsible for sensing proprioception (movement in space in relation to the body), touch, pain and temperature. It is also responsible for language processing (interpreting the rules of language).
Occipital Lobe: This lobe is found at the back of the brain. It contains the visual cortex which is responsible for vision. Damage to this area can lead to blindness, hallucinations and seizures (called occipital lobe epilepsy). The visual system is contralateral, which means that images perceived in your right eye are processed in the visual cortex on the left side of your brain and vice versa.
Figure 3: Diagram of the internal structures of the brain. The highlighted area shows a portion of the cerebrum and the right half of the corpus callosum. These areas are important for the coordination of critical thinking. Source: Patrick J. Lynch, Wikimedia
Temporal Lobe: There are two parts of the temporal lobe - one on each side of the brain – in the part of the head that people call their temples. This lobe is responsible for learning, memory, understanding the meaning behind language and navigating through obstacles in the surrounding space.
Cerebellum: Under the occipital lobe sits the cerebellum. This structure is best known for its role in fine-tuning muscle movement. Disorders of the cerebellum result in disabilities in balance, posture and motor learning.
Brainstem: The brainstem is the part of the brain that connects the base of the brain to the spinal cord. The brainstem acts as the coordinating centre which connects the brain to the internal organs and the rest of the body. It also helps coordinate involuntary actions like breathing and heart rate.
Now we are going to dive deeper into the internal structures of the brain to understand how it functions.
Inside the brain
Numbers correspond to figures on right
1 - Cerebrum and Cerebral Cortex: The cerebrum is the large wrinkly part that spans both hemispheres and sits on top of the brainstem and cerebellum. It is responsible for coordinating complex functions and voluntary actions. The cerebral cortex is the outermost layer of the cerebrum. It is the part known as grey matter (see glossary below).
2 - Corpus Callosum: The corpus callosum is a bridge of nerve fibres that connects both hemispheres of the brain. It allows the two halves of the brain to communicate with one another in order to coordinate and synchronize activity.
Figure 4: Diagram of the internal structures of the brain. The highlighted area shows the regions of the hypothalamus, the thalamus (above the brainstem), and the pituitary gland. Source: Patrick J. Lynch, Wikimedia
3 - Thalamus: This region is located above the brainstem. The thalamus is the part that coordinates all sensory information coming into the brain. It is also involved in regulating sleep and consciousness.
4 - Hypothalamus: The hypothalamus sits just below the thalamus – hence its name. This region links the nervous system to the endocrine (hormones) system. It is responsible for creating brain hormones and controlling the pituitary gland.
5 - Pituitary Gland: This gland is found below the hypothalamus. It is a major part of the endocrine system, and is extremely important during human development. It is the control centre for all other hormone glands in the body.
The Dopamine System: Also known as the reward system, the dopamine system (see Figure 4 and Figure 5) is critical for the control of mood and the reinforcement of behaviours. It consists of the following structures:
- Hippocampus: This structure is found in the temporal lobe (see Figure 2 and Figure 5) and is part of the Hippocampal formation. It is responsible for coordinating a variety of cognitive functions including learning, memory and navigation.
- Ventral Tegmental Area (VTA): This area is the first region involved in the reward system (see Figure 4a and Figure 5). It receives input from the brainstem and sends signals to the striatum and nucleus accumbens (see below).
Figure 5: The reward pathway (black arrows) and the brain regions that make up this system. Source: Public Domain
- Striatum: The striatum plays a major role in the reward system (see Figure 4b and Figure 5). It regulates abilities and feelings such as action-planning, motivation, and decision-making.
- Nucleus Accumbens: This structure is responsible for feelings of pleasure, motivation and learning through reinforcement. It also plays a role in the coordination of movement (see Figure 4c and Figure 5).
White Matter: This makes up the deep tissue of the brain. It consists of axons covered in white myelin (see Figure 1). Myelin is a fatty tissue that insulates the axon and is important for signal transmission.
Grey Matter: This is brain tissue consisting of cells without myelin, including the cell bodies of many neurons (see Figure 1).
Proprioception: Awareness of movement in space in relation to the body.
Contralateral: Coordinated by structure on the opposite side of the body.
Endocrine System: Collection of glands throughout the body that regulate growth, metabolism and mood.
Hippocampal Formation: Region of the brain composed of many structures that are involved in memory, navigation and attention.
Reinforcement Learning: Learning by interacting with the environment and strengthening the associated behaviour. It is like learning by ‘trial and error.’ If the interaction or behaviour creates a feeling of reward, it is more likely to be performed again.