The Brain & Neurological Conditions
Bitesize
Neurological disorders are medically defined as disorders that affect the brain and also the nerves located throughout our body and the spinal cord. Structural, biochemical or electrical abnormalities in the brain, spinal cord or other nerves can result in a range of symptoms. Examples of symptoms include paralysis, muscle weakness, poor coordination, loss of sensation, seizures, confusion, pain and altered levels of consciousness.
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The exact causes of neurological problems vary, but include genetic disorders, congenital abnormalities or disorders, infections, lifestyle, or environmental health problems including malnutrition, and brain injury, spinal cord injury or nerve injury. There are various recognised neurological disorders, some somewhat frequent, but many are uncommon.
Neurological disabilities include disorders, such as epilepsy, learning disabilities, neuromuscular disorders, autism, attention deficit disorder, brain tumours, and cerebral palsy, to name only a few. Some neurological conditions are genetic, developing before birth. Other conditions may be caused by tumours, degeneration, trauma, infections, or structural deficiencies. Regardless of the cause, all neurological disabilities result from damage to the nervous system. Depending on where the damage takes place, governs to what extent movement, cognition, communication is impacted.
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The Human Brain
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Like various other human organs, understanding the structures and anatomy of the brain has proven to be less complexed compared to understanding its functioning and physiology. This has resulted in different neuroanatomists organising and labelling different parts of the brain in various ways, based on distinctive criteria. The brain can be organised locations and structures, by associated functions, by similar cytological features, etc. However, we should note that the same region of the brain can have various names, depending on what system of organisation you are using at the time.
Traditionally, the brain is largely organised the by its gross anatomy – its large structures that are visible. The human brain can be divided into four major parts, and these bitesize presentations focus on the following:
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The cerebrum, which is the part with the folds and fissures that we typically associate with a mental image of the brain. It comprises of two cerebral hemispheres which are divided by the longitudinal fissure down the centre of the cerebrum.
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The cerebellum, which is also known as the hindbrain. It is in the posterior region of the brain and inferior to the back of the cerebrum. It has an almost-cauliflower appearance, while its exterior consists of thin parallel folds.
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The diencephalon is in the interior of the brain and can only be observed fully when the brain is cut open. In intact brains, only the floor of the diencephalon can be seen directly superior to the brain stem.
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The brain stem (i.e., the midbrain, the pons, and the medulla oblongata)connects directly to the spinal cord but is markedly thicker than the spinal cord below it.
The Circle of Willis
The Circle of Willis circumscribes the stem of the pituitary gland and provides essential communications between the blood supply of the forebrain and hindbrain. Though a complete circle of Willis is present in some people, it is rarely seen radiographically in its entirety; anatomical variations are common and an advanced communication between each of its parts is recognised in less than half of the population.
The circle of Willis begins to form when the right and left internal carotid artery (ICA) enters the cranial cavity and each one splits into two main branches: the anterior cerebral artery and middle cerebral artery. The anterior cerebral arteries are then amalgamated, and blood can cross flow by the anterior communicating artery.
The Structure of Neurones
Our brain contains approximately 100 billion neurones. These neurons are cells within the nervous system that transmit information to other nerve cells, muscle, or gland cells. Neurons have a cell body, an axon, and dendrites. The cell body contains the nucleus and cytoplasm. The axon spreads from the cell body and typically gives rise to several smaller branches before finishing at the nerve terminals. Dendrites extend from the neuron cell body and receive messages from other neurons. Synapses are the contact points where one neuron communicates with another. The dendrites are covered with synapses formed by the ends of axons from other neurons.
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Dendrites extend from the neuron cell body and receive messages from other neurons. Synapses are the main connection, where one neuron communicates with another. The dendrites are covered with synapses formed by the ends of axons from other neurones.
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When neurons receive or send messages, they transmit electrical impulses along their axons, which can range in length from a fraction of a centimetre to about one meter or more. Many axons are covered with a layered myelin sheath, which accelerates the transmission of electrical signals along the axon. This sheath is made by specialized cells called glia. In the brain, the glia that make the sheath are called oligodendrocytes, and in the peripheral nervous system, they are known as Schwann cells.
Strokes are a varied group of disorders involving sudden, focal interruption of cerebral blood flow that causes neurologic deficit. Strokes can be:
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Ischemic (80%), typically resulting from thrombosis or embolism
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Haemorrhagic (20%), resulting from vascular rupture (e.g., subarachnoid haemorrhage, intracerebral haemorrhage)
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Transient stroke symptoms (typically lasting < 1 hour) without evidence of acute cerebral infarction (based on diffusion-weighted MRI) are termed a transient ischemic attack (TIA).
In England, one in six people will have a stroke in their lifetime, and new statistics released show that 57,000 people had their first-time stroke in 2016. It is estimated that around 30% of people who have a stroke will go on to experience another stroke. Strokes involve the arteries of the brain, either the anterior circulation (branches of the internal carotid artery) or the posterior circulation (branches of the vertebral and basilar arteries).
Multiple sclerosis (MS) is characterised by dispersed areas of demyelination in the brain and spinal cord. Common symptoms include visual and oculomotor abnormalities, paraesthesia’s, weakness, spasticity, urinary dysfunction, and mild cognitive symptoms. Usually, there are multiple neurologic deficits, with remissions and exacerbations progressively producing impairment. Diagnosis requires clinical or MRI evidence of ≥ 2 characteristic neurologic lesions that are separated in both time and space (location in the central nervous system). Treatment includes corticosteroids for acute exacerbations, immunomodulatory drugs to prevent exacerbations, and supportive actions.
Parkinson disease is a slowly progressive, degenerative disorder characterised by resting tremor, stiffness, slow and decreased movement, and ultimately gait and/or postural instability. Diagnosis is clinical. Treatment aims to restore dopaminergic function in the brain with levodopa plus carbidopa and/or other drugs (e.g., dopamine agonists, monoamine oxidase type B [MAO-B] inhibitors, amantadine).
Cerebral palsy refers to non-progressive syndromes characterised by impaired voluntary movement or posture resulting from prenatal developmental abnormalities or perinatal or postnatal central nervous system damage. Syndromes are evident before age 2 years. Diagnosis is clinical. Treatment may include physical and occupational therapy, braces, drug therapy or botulinum toxin injections, orthopaedic surgery, intrathecal baclofen, or, in certain cases, dorsal rhizotomy (cutting of some sensory fibres that come from the muscles).