Posted in Psychology & Medicine

Viscera: Brain

(Learn more about the organs of the human bodies in other posts in the Viscera series here:

(NB: I have written MANY ARK posts about the brain and all the delightful ways it screws up. Some of them are probably the most interesting posts on my blog. Please click the hyperlinks to check out the various related articles! 😀 Alternatively, here’s a convenient list:

Among the many organs of the human body, no organ comes close to the magnificent complexity that is the brain. The brain acts as the command centre of the body. It receives massive amounts of information through the various senses, processes it and sends out electrical signals to control how the body operates. Not only does it control “basic” functions such as movement of muscles, controlling organ functions and regulating homeostasis, it is also responsible for the so-called “higher functions” such as consciousness, emotions and cognition. It is the true seat of the mind and soul.


The brain is the only major visceral organ not located in the trunk (body). It is enclosed in the cranium of the skull, which acts as a protective casing. Because it is a closed box, even a small increase in volume (such as due to a bleed or a tumour) can cause extreme pressures to build, causing severe problems. The entire brain and spinal cord are bathed in a fluid called cerebrospinal fluid (CSF), all enclosed by a sheath made of three layers (dura, arachnoid and pia maters). The brain sends out nerves to the rest of the body, which act as electrical wiring transmitting signals. These include the cranial nerves and the spinal cord, which leaves the bottom of the skull down the spine. The spinal cord branches off into many nerves that supply every nook and cranny of the body. The brain itself is made up of two large hemispheres, which are connected by a bridge called the corpus callosum. Despite popular belief, the actions of the two hemispheres are much more complicated than “analytical vs. creative”. The brain also encompasses the cerebellum (the small stripey structure at the back), which controls coordination and speech articulation, and the brainstem, which is involved in autonomic control of life-sustaining functions such as breathing, and also the source of the cranial nerves.

In the last century, scientists have learned that specific parts of the brain play a specific role. This thought started with the field of phrenology, where small areas of the brain were mapped to a certain mental faculty, such as love, wit or destructiveness. Although this turned out to be complete hokum, the idea stayed and we now know the actual functions of each part of the brain. The brain is broadly divided into four lobes: frontal, parietal, temporal and occipital. The frontal lobe is the domain of thought, personality, motor function and other higher functions. The parietal lobe is related to spatial awareness and sensory functions (such as touch). The temporal lobe is linked to hearing, comprehension of language and storing new memories. The occipital lobe is primarily associated with vision. The brain can then be subdivided into more focussed areas, such as Broca’s area that governs speech and Wernicke’s area that governs listening. It should be noted that the four lobes only describe areas on the surface of the brain (cerebral cortex) where the higher functions belong. The inside of the brain is just as complicated and has many different parts, such as the hypothalamus that is involved in homeostasis, and the hippocampus that converts short-term memories into long-term memories.

How does a lump of cells weighing around 1.5kg produce such wondrous abilities such as philosophical thought, deduction, emotions and calculation? The truth is that we still do not know how the brain functions exactly. However, we know that the brain is composed of a large number of neurons (nerve cells) – about 100 billion of them. These neurons connect to one another via a synapse, which is a gap between two nerve cells where neurotransmitters travel to and fro (allowing electrical impulses to jump from one neuron to another). Using these connections, neurons form an unbelievably intricate and complex network of electrical activity. Because one neuron can connect to many more others, the number of synapses is estimated to be around 100~1000 trillion – significantly more powerful compared to any computer in the world. The number of synapses directly correlates to intelligence and it seems intellectual activities such as reading a book increases the number of synapses in the brain. We have yet to understand exactly how the brain uses this incredible computational power to produce cognition and self-awareness.


(Video of neuronal activities in a zebrafish brain)

Because the brain uses electrical impulses for most of its functions, a common abnormality that is seen with the brain is when the electrical activity becomes disorganised and out of control – a seizure. This abnormal electrical activity may be due to a focal problem such as a tumour, or a generalised misfiring of neurons or altered regulation of electrical activity. When a seizure happens, the disorganised activity results in the brain not being able to function normally. For example, the most common consequence is a fit (tonic-clonic seizure) where every muscle spasms out of control, because the muscles are overloaded with chaotic signals. Focal seizures can cause fascinating symptoms depending on the location, such as temporal lobe seizures causing religious visions (hallucination). This also disrupts consciousness, which is why most epilepsy patients do not remember the event.

Posted in Psychology & Medicine

Time Perception

What exactly is the present? The present is the middle point between the past and future, the world that we experience and perceive on a real-time basis. But would you believe it if the world you perceive is not the true “present”? To experience the world, we use our five senses. The brain collates all these sensory information and processes it to construct “the present”. This process takes about 80 milliseconds. Ergo, the world we experience is actually the world as it was 80 milliseconds ago. For a similar phenomenon, consider the stars. The stars we observe are not what they look like now, but what the stars looked liked when they emitted the light that we see. Thus, the star you are looking at may not even exist anymore.

But 80 milliseconds is a very short time; surely it has no impact on our everyday life? To prove that this delay has a critical impact on our understanding of cause and effect, neuroscientists designed the following experiment. The researchers would ask the participant to press a button that caused a light to blink after a short delay. After about ten tries, the participants reported that the delay had disappeared and the light flashed immediately after they pressed the button. This was due to their brain editing out the time delay and directly connecting the cause (button) and the effect (flash). But a much more peculiar phenomenon was seen when the researches removed the delay between the button press and the flash. Participants reported that they saw the light flash before they even pressed the button. The participant’s brain had become so used to the editing process that it was confusing the order of the cause and the effect.

The brain’s time-editing ability can be seen in the following simple experiment. If you touch your nose and toe at the same time, logic dictates that as the toe is further from your brain, the signal will have to travel further and it will be felt later. But in reality, you feel both at the exact same time. This is because your brain uses a map of the body to edit the relative time the signal takes to reach the brain to better construct a “real-time present”.

Posted in Psychology & Medicine

Cranial Nerves

Nerves can be divided broadly as spinal nerves and cranial nerves: the latter which is directly from the brain. There are 12 pairs of cranial nerves:

  1. CN IOlfactory nerve (smell)
  2. CN IIOptic nerve (sight)
  3. CN IIIOculomotor nerve (eye movements, control of pupil and lens)
  4. CN IVTrochlear nerve (eye movements)
  5. CN VTrigeminal nerve (sensory information from face and mouth, chewing)
  6. CN VIAbducens nerve (eye movements)
  7. CN VIIFacial nerve (taste, tear and salivary glands secretion, facial expressions)
  8. CN VIIIVestibulocochlear nerve (hearing and sense of balance)
  9. CN IXGlossopharyngeal nerve (taste, swallowing, parotid gland secretion, sensory information from oral cavity, information about blood)
  10. CN XVagus nerve (sensory and motor signals to and from many internal organs, glands and muscles)
  11. CN XIAccessory nerve (movement of SCM and trapezius, which are neck/shoulder muscles)
  12. CN XIIHypoglossal nerve (tongue movements)

As there are so many nerves and the names are all varied, there is a simple (yet very obscene) mnemonic to help medical students remember the names and order of nerves:

Oh, Oh, Oh, To Touch And Feel Virgin Girls’ Vaginas And Hymens
Oh, Oh, Oh, To Touch And Feel A Girl’s Very Soft Hands
(where vestibulocochlear -> auditory)

It is also worth noting the mnemonic for the types of nerves is:

Some Say Marry Money, But My Brother Says Big Boobs Matter More

Perhaps the only way to survive medical school is through humour.