• Question: what do you know about the brain

    Asked by dean123 to Nina, Rachel on 5 Jun 2019. This question was also asked by emmzyx23x.
    • Photo: Nina Rzechorzek

      Nina Rzechorzek answered on 5 Jun 2019: last edited 5 Jun 2019 2:18 am

      What would you like to know? To me it’s the most beautiful and fascinating organ in the body; it’s the first one to appear during development, and (in the absence of any other major disease) it is generally the last one to fail when we get older. The brain is an incredibly complex organ that is vital for life (it controls key physiological parameters such as breathing, body temperature, and several hormones) and is the basis of how we perceive, interpret, and respond to the world around us, and also how we plan, remember, reason, process, and feel emotions. The brain makes up only about 2% of our body weight but uses about 20% of our oxygen consumption (i.e. it has a very high metabolic demand and consumes a lot of energy). Brain cells cannot store energy as glycogen so they are highly dependent on a continuous supply of glucose; this makes them very vulnerable to injury when blood supply to the brain is compromised. We are really only just beginning to understand how this complex organ works; more recently for example, scientists have found that more than half of the cells in the brain are not actually neurons (the intrinsically excitable brain cells that transmit information in networks connected by ‘synapses’), but that it consists of other supportive cell types – the ‘glia’ which means ‘glue’. The glia were named like this because originally it was thought that these cells were little more than the ‘stuff’ that stuck the neurons together, but now we know they are absolutely essential for proper brain function and can even be the target of certain brain disorders. There are many types of glia (and much less is known about them than neurons), but so far we are aware of 3 main types – (1) the astrocytes (which come in all shapes and sizes and provide metabolic support for neurons but also respond very robustly to injury to form what is known as ‘the glial scar’), (2) the oligodendrocytes (these have a very small cell body with little cytoplasm but lots of complex branching arms that wrap around neuronal axons (axons are like wires that transmit electrical information from one neuron to the next in the network). These wraps are called ‘myelin sheaths’ and are like cable insulation for the neuronal axons, enabling very fast neuronal transmission. Myelin is the major component of the ‘white matter’ of the brain. When we talk about ‘grey matter’ we are referring to the regions of brain comprised mostly of cell bodies, whilst the ‘white matter’ is composed mainly of myelinated neuronal axons. Oligodendrocytes are the key cell type affected in multiple sclerosis which is therefore considered predominantly a ‘white matter disease’. (3) the microglia – these are the immune cells of the brain and again respond very rapidly to injury. It’s important to note that there are many different types of neuron, each with specialised functions, and likely many different types of each of the glial cells too.

      The brain is connected to the spinal cord via the brainstem. Together the brain, brainstem, and spinal cord make up the ‘central nervous system’, where the electrically excitable cells are called neurons, and are insulated with myelin made by oligodendrocytes. Within the brainstem and spinal cord there are some cell bodies of electrically excitable cells that send their axons out into the periphery – these are called nerves, and when they are myelinated, this myelin is made by Schwann cells. Motor nerves carry motor information from the central nervous system to the muscles allowing them to contract (the information is transmitted via ‘neuromuscular junctions’); sensory nerves carry sensory information from the periphery to the central nervous system, allowing us for example to feel pain, heat, cold, touch, pressure etc. There are some special sensory nerves that enable vision, hearing, balance, smell, and taste.

      The ‘oldest’ parts of the brain (in evolutionary terms) are the first to develop and include the brainstem – this region is therefore common to many animal species. The ‘newest’ part of the brain is the cortex (the outer part of the brain) which is very much expanded in humans (and even more in dolphins!) and very highly convoluted which allows the huge surface area to be folded into a smaller space (fitting as many neurons as possible inside the skull!). Within the skull and vertebral column, the brain and spinal cord is also protected by several tissues layers called ‘meninges’ – and these are what become inflamed in ‘meningitis’. The brain and spinal cord is also protected by cerebrospinal fluid which acts like a shock absorber. We sample this fluid when we perform a ‘spinal tap’ or ‘lumbar puncture’ in order to make a diagnosis of meningitis.

      The brain can be affected by many disorders but perhaps the most common ones are recurrent seizures (fits) – this condition is called epilepsy, brain tumours, brain trauma, stroke, neurodegenerative disorders such as Alzheimer’s and Parkinson’s disease. A key diagnostic tool for many brain diseases is magnetic resonance imaging (MRI).

      Let me know if you want any more specific info!