According to the biological model, what can lead to psychological disorders?

Faulty genes and neurotransmitter imbalances

Biological factors influence all aspects of our behaviour. A wide range of biological factors such as faulty genes, endocrine imbalances, malnutrition, injuries and other conditions may interfere with normal development and functioning of the human body. These factors may be potential causes of abnormal behaviour. According to this model, abnormal behaviour has a biochemical or physiological basis. Biological researchers have found that psychological disorders are often related to problems in the transmission of messages from one neuron to another.  A tiny space called synapse separates one neuron from the next, and the message must move across that space. When an electrical impulse reaches a neuron’s ending, the nerve ending is stimulated to release a chemical, called a neuro-transmitter. Studies indicate that abnormal activity by certain neuro-transmitters can lead to specific psychological disorders. Anxiety disorders have been linked to low activity of the neurotransmitter gamma aminobutyric acid (GABA), schizophrenia to excess activity of dopamine, and depression to low activity of serotonin.