FREE BOOK CHAPTER: Understanding the Brain (From 'A Practical Guide to Subtle Brain Injury Claims' by Pankaj Madan)
21/12/16. As an area of medicine, perhaps less than 5% of all there is to be known is in fact, known about the brain, how it operates and how it controls us and how it can deteriorate.
Without this understanding brain injury is one of the most difficult areas of personal injury law.
It increasingly seems to me however that it is also an injury that creates great sadness. Nothing else quite seems to rob the victim and friends and family of the very essence and core of the personality of the person. The body has returned from the accident seemingly sometimes perhaps relatively physically unscathed at least, but the same person often has not.
Diagnosing subtle brain injury is fraught with difficulty not helped by the adversarial process. Damages can be sizeable but damages in themselves are not enough without rehabilitation and structure to a claimant’s life.
The human brain is a complex structure with around 100 billion neurons. There are more neurons in the human brain than there are stars that have been observed in the sky.
We need to talk about the structure of the brain. Whilst any doctor or biologist may cringe at the over-simplification of what follows, I apologise, but it is often helpful to simplify rather than complicate.
A neuron also sometimes called a neurone or a nerve cell is the basic building block of the brain. It is a cell not too unlike many other cells in the body but it is electrically excitable and is capable of communicating with other cells through chemical and electrical signals. These occur through “synapses” which are specialised connections.
The neuron is similar to other cells in the body in some ways. It has a “nucleus” which is the core of genetic material making up our cells and a cell membrane. They have similar cell bodies which power the cells and regulate them.
The neuron is made up of the “soma” or cell body and the dendrite and the axon. The dendrite is the tree like extension(s) which extend outward from the cell body increasing the surface area of the cell.
The axon is the elongated fibre which that extends from the cell body. It is often covered in a fatty shielding substance called myelin. Axons then connect with other cells in the body, other neurons, muscle tissue, and organs at junctions called “synapses”. The chemicals which cross the synapses are called “neurotransmitters”. Electrical signals as well as chemical ones called “action potentials” also communicate information or signals between cells. There are perhaps around 100 identified neuro-transmitters, consisting of 6 types. One type are acetylcholines. Amino-acids are another type.
Neurons however are also different to other cells in the body. Crucially, shortly after birth, and in contrast to other types of cell, neurons in most parts of the brain stop reproducing so the adult human has a fixed number of them. The neurons within the hippocampus ,a seahorse shaped structure deep within the brain (responsible for memory amongst other things) and the olfactory bulb (dealing with taste and smell) are exceptions.
Neurons are however able to form new connections with other neurons throughout life. These two facts are important to understand brain injury and rehabilitation. We cannot ever re-generate new brain cells but it is possible to find alternative and new pathways using undamaged brain cells. Neurons possess generally around 1000-10,000 connections to other neurons and 1000 trillion synaptic connections.
Estimates of memory capacity of the human brain if one were to compare it to a computer seem to vary from around 1 Terabyte to 1000 Terabytes of data. There are 1000 Gigabytes in a Terabyte. An average computer hard drive may be around 500GB so best estimates mean that the human brain may store 2000 times the information as the average modern computer.
So, the brain, is complex. It consists of lots of neurons but also structural cells called glial cells and astrocytes which support and protect the neurons As you would expect the brain is also very rich in a network of blood vessels to support and nourish the cells.
The brain is surrounded by the “dura” a thick protective membrane which is next to the skull. There are two further membranes, the Arachnoid which is more loosely attached, and then the Pia Mater which is closely attached to the brain.
It is then held and protected within the skull in a cushion of fluid called the Cerebro-spinal fluid.
The skull is of course extremely hard and unyielding. One ton of pressure is needed to deform and reduce the skull diameter by 1 centimetre. This is what protects the brain from external knocks.
It is this hard unyielding cavity however which can ironically contribute to injury to the brain. It means that the brain if injured internally through sub-dural haematoma has no space to expand. This can result in increased intra-cranial pressure which can injure the deep structures of the brain.
The brain itself can be broadly divided into 3 parts. The 4 sections uppermost towards the skull are together called the “Cerebrum”. The Cerebrum controls the “higher” level brain functions.
The 4 parts are called:-
- The frontal lobe – the area occupying the front half of the skull
- The Parietal lobe – the area immediately behind the front half of the skull on top of the head;
- The Occipital lobe – the area at the back of the head above the neck
- The Temporal lobe – the area at the sides of the brain and extending to behind the ears
The frontal lobe
The frontal lobe controls executive function, decision making skills, personality, language, planning and movement. There is a right and left frontal lobe, one in each of the hemispheres. It is the very essence of “who you are”, your personality. The left frontal lobe controls language, verbal skills and positive emotions whilst the right frontal lobe tends to control non-verbal communication and negative emotions. When you are searching for the right word to say, the frontal lobe is responsible. It is also responsible for judgment and attention span regulating mood and emotions. The frontal lobe is also responsible for retaining long term memories which are not task based. Executive based tasks such as planning for the future, organisation and multi-tasking are dealt with by the frontal lobe. The frontal lobe at the point where it rests on the Cribiform plate is particularly vulnerable to diffuse axonal injury. This sort of interference with higher level executive functions and personality changes are a very common complaint following trauma.
If the front part is damaged, any of the following may result:
- Difficulty processing and retaining new information
- Reduced fluency of speech
- Delayed responses to questions
- A lack of inhibition, including socially inappropriate behaviour
If the middle part of the frontal lobe is damaged, people may become apathetic, inattentive and unmotivated. They may describe their thinking as “slowed”.
If the middle back part of the frontal lobe is damaged people may have difficulty in expressing themselves in words (expressive aphasia)
The back part of the frontal lobe controls voluntary movement. Weakness or spasticity or paralysis can result from frontal lobe damage. The left side of the lobe controls the right side of the body and the right side of the lobe controls the left side of the body.
The Parietal lobe
The parietal lobe controls intelligence, reasoning, sensation, and our ability to read. Taste, temperature and touch are co-ordinated here. This lobe processes sensory information. Spatial sense is also co-ordinated and processed here. Knowledge of numbers and numeracy is controlled here. The ability to read, interpret words, letters and other symbols is controlled here too. The right hemisphere is more active in left hand dominant people and the left side of the lobe is more active in right hand dominant people.
Damage to the parietal lobe may cause difficulty in recognising or sensing objects by touch. It can cause numbness or impair sensation on one side of the body. People cannot sometimes tell right from left as easily and may have problems sensing where parts of their body are (proprioception).
If the right side of the parietal lobe is damaged people may be unable to do simple tasks such as brushing their hair or dressing themselves. They may have trouble drawing and may get lost in places which should be familiar to them.
The Occipital lobe
The Occipital lobe is largely responsible for vision. It is the main centre for the processing of visual information. If the occipital lobe is damaged on both sides of the brain people may have severely impaired vision or even go blind even though the eyes are physically working fine. This is called cortical blindness. The front part of the lobe controls recognition of familiar objects and people. In some cases vision may become partial. Blocks of visual deficit, (hemaniopia) can occur. As well as direct injury to the back of the head, dissection of a vessel or interruption of the blood supply to this part of the brain in severe frontal or rearward collisions can result in visual deficits.
The Temporal lobe
The Temporal lobe is responsible for language, behaviour, hearing, vision, emotions and memory. The left side of the lobe in most people tends to control language. Damage to the left side of the lobe can therefore result in loss of memory for words and there is often impairment of the ability to understand language.
Areas of the right temporal lobe tend to control recognition of sound and music. This can result in difficulty in singing.
Damage to the temporal lobe can also result in a lack of a sense of humour, obsessiveness, hallucination of bad smells, and they may have a sense of not being able to control their feelings and a sense of “fuzzy” thinking.
Beneath the Cerebrum is the “Cerebellum” a structure which controls balance, co-ordination and fine muscle control. Damage to this structure may result not so much from direct impact but as a result of raised intra-cranial pressure in response to trauma elsewhere.
Going deeper still, is the “brain stem” which controls the things we do without thinking, such as our heartbeat, breathing and swallowing.
Deeper still at the bottom of the brain, is the spinal cord which extends from the brain all the way to the tail bone. It is about as wide as a small finger.