Major Depressive Disorder - Neurobiology and Aetiology

A working knowledge of the normal structure and function of the nervous system is key to understanding psychiatric disorders like Major Depressive Disorder (MDD). This slide deck includes the key components of neurosynaptic transmission, neurotransmitters and hypotheses about the underlying causes of depression. A common genetic basis and environmental factors for MDD are briefly explored.

This slide deck has been developed in collaboration with the former Lundbeck International Neuroscience Foundation.

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Neurobiology and Aetiology

To understand psychiatric disorders, it is important to have a working understanding of the normal structure and function of the nervous system.

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Introduction to neuroanatomy

Major Depressive Disorder – Neurobiology and Aetiology – slide 2

Introduction to neuroanatomy

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Major Depressive Disorder – Neurobiology and Aetiology – slide 3

Organisation of the nervous system

To understand psychiatric disorders, it is important to have a working understanding of the normal structure and function of the nervous system. The central nervous system (CNS; brain, spinal cord) and peripheral nervous system (PNS) are made up of neurones…

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Major Depressive Disorder – Neurobiology and Aetiology – slide 4

Neurones

The neurone constitutes the functional unit of the nervous system; there are over 100 billion neurones in the brain.^{[Purves, Augustine, & Fitzpatrick et al., 2008; Martin 2003]} Each neurone has the ability to interact with and influence many other cells,…

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Major Depressive Disorder – Neurobiology and Aetiology – slide 5

Anatomical regions of the brain

The brain is divided into four anatomical regions: the diencephalon, brainstem, cerebrum, and cerebellum, as described on the slide.^{[Kandel, Schwartz & Jessell, 2000; Tortora & Derrickson, 2009]}

References: Kandel ER, Schwartz JH, Jessell TM (eds). Principles of Neural Science. 4th…

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Major Depressive Disorder – Neurobiology and Aetiology – slide 6

Cerebrum

The cerebral cortex is the main functional unit of the cerebrum. The three main functional areas of the cerebral cortex are:^{[Tortora & Derrickson, 2009; Price & Wilson, 2003]}

motor areas that control voluntary movement (primary, secondary, and association motor…

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Major Depressive Disorder – Neurobiology and Aetiology – slide 7

Lobes of the brain

The brain can be thought of as comprising five ‘lobes’ – the four lobes of the cerebral cortex and a fifth lobe, the insula, deep within the brain, as shown on the slide.^{[Martin 2003; Tortora & Derrickson, 2009; Price &…}

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Neurosynaptic transmission

Major Depressive Disorder – Neurobiology and Aetiology – slide 8

Neurosynaptic transmission

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Neurotransmission

Information moves through the nervous system via two integrated forms of communication – electrical neurotransmission and chemical neurotransmission, as shown on the slide.^{[Kandel, Schwartz & Jessell, 2000]}

An action potential is generated at the origin of the axon following sufficient…

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Major Depressive Disorder – Neurobiology and Aetiology – slide 10

The synapse

Neurones do not physically touch one another; two neurones are separated by a gap, known as a synaptic cleft.^{[Kandel, Schwartz & Jessell, 2000]} Because neurones do not touch, and an action potential cannot ‘jump’ across a synaptic cleft, the signal…

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Major Depressive Disorder – Neurobiology and Aetiology – slide 11

Process of chemical neurotransmission

The idea that neurotransmission occurs at synapses and is mediated by chemicals was, at first, a contentious issue.^{[Purves, Augustine & Fitzpatrick et al., 2008]} It was in the first half of the 1900s that experiments proved chemical neurotransmission occurred.^{[Purves, Augustine…}

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