Dementia terminology decoded

Neuron

Neurons (also spelt neurones) are the cells in the brain that transmit electrical signals through the body. There are three main types of neuron: sensory neurons, motor neurons and interneurons. Sensory neurons detect stimuli in the environment like light, sound and touch, and pass them to the brain for processing. Interneurons send messages to other neurons, while motor neurons transmit signals to a variety of cells like muscle cells, to trigger an output by the body.

Synapse 

Neurons transmit their electrical messages through junctions called synapses. The synapses are located at each end of the neuron. Chemical messengers are released from the end of one neuron and are collected by the receiving cells. The loss and damage of synapses have been associated with the development of Alzheimer's disease and other forms of dementia.

Neurotransmitter

The chemical messengers that travel through the synapses are called neurotransmitters. Dopamine, acetylcholine, adrenaline, glutamate and serotonin are all neurotransmitters. Dopamine is involved in many functions including learning, movement and mood. Parkinson’s disease is caused by decreased dopamine production in the brain, and dopamine has also been shown to be reduced in Alzheimer’s disease. Acetylcholine is the most important neurotransmitter in the automatic part of the nervous system, regulating functions that we don’t consciously control. People with Alzheimer’s disease have fewer neurons that make acetylcholine, so many treatments for Alzheimer’s involve increasing the amount of acetylcholine in the brain.

Glia

Neurons aren’t the only type of cell in the nervous system – another type of brain cell exists called glia. They don’t produce their own electrical signals but support neurons in a variety of ways depending on the specific type, from removing their waste products to providing electrical insulation. Astrocytes (depicted below) are a type of glial cell that have been shown to be activated in Alzheimer’s disease, so research is under way to uncover their involvement in the condition. Meanwhile, microglia are involved in the immune system to defend the neurons – they are also being investigated in dementia research.

Tau

Normally, tau proteins are found inside the stems of neurons – called their axons – to maintain their correct structure. In some forms of dementia, including Alzheimer’s disease and frontotemporal dementia, tau proteins become damaged and detach from their axons. Now moving freely inside the neuron, the abnormal tau proteins clump together, forming what are called neurofibrillary tangles. This dysfunctional tau is toxic to neurons and causes them to die. Find out more about tau in this blog post.

Lewy bodies

Lewy bodies are clumps of different proteins – mainly alpha-synuclein with some others attached – that form inside neurons. They may occur alongside abnormal tau proteins and neurofibrillary tangles and are present in people with Parkinson’s disease and Lewy body dementias – which you can read more about in our blog post. 

Amyloid

Amyloid is a normal protein found in humans that is formed naturally when a larger protein called amyloid precursor protein (APP) is cut into smaller pieces. In Alzheimer’s disease, APP is cut into a type of amyloid called amyloid-beta which is chemically ‘sticky’. This means that, when it accumulates in the brain, the individual amyloid-beta proteins stick together, forming toxic clumps called plaques or aggregates. These plaques stop the neurons communicating and activate immune cells like microglia, causing the neurons to die. Find out more about amyloid in this blog post.

Atrophy

Atrophy is the process of part of the body getting smaller over time – this can happen to individual cells or whole organs. Brain atrophy (also called cerebral atrophy) is the brain shrinking in volume due to the loss of neurons, as shown in the diagram above. Diseases like Alzheimer’s cause brain atrophy. Focal atrophy is where only neurons in certain brain areas die, so just that area shrinks, and only that brain function is affected. Generalised atrophy, meanwhile, involves cells dying all over the brain, resulting in an overall shrinkage.

Vascular 

The vascular system – sometimes called the circulatory system – is the network of blood vessels that carries oxygen through the body. The vascular system is made of blood vessels of different sizes, from the biggest arteries through to medium-sized veins and tiny capillaries. Vascular dementia is a type of dementia that occurs when not enough blood goes to the brain, starving it of oxygen and causing neurons to die.

Cognition

Cognition is a term for the mental processes that take place in the brain, including thinking, attention, language, learning, memory, and perception. Cognitive is the adjective used to describe these mental processes – for example, cognitive tests assess these thinking skills, and cognitive psychology is the study of cognition. Read our blog post on cognition to find out more.

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