Endocrine System

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The Neurotransmitters

2.6     Neurons are separated from each other and from other body cells by a tiny gap called a synapse. When a nerve impulse reaches a synapse, the axon releases a chemical called a neurotransmitter. The neurotransmitter transfers the impulse across the synapse to the target cell. Then, the synapse is cleared so that another impulse can cross. Over 60 different chemicals have been identified either as neurotransmitters or as substances that modify the activity of neurotransmitters.

2.7     Neurotransmitters and Drugs – The use of psychoactive drugs alters the transmission of nerve impulses. For example, caffeine stimulates the nervous system by facilitating synaptic transmission. Cocaine, amphetamines, and some antidepressant drugs cause substances to remain in the synapse longer. The result is prolonged stimulation of the nervous system. Some psychoactive drugs are addictive. The body adjusts to the changes these drugs cause. If the drug is withdrawn, the body will be unable to function as it had previously. The addicted drug user will then experience withdrawal symptoms.

 The Brain

2.8     The brain weighing about 1.4 kg contains about 1 trillion cells, and it consists of three basic parts: the cerebrum, the cerebellum and the brain stem. The cerebrum, which is the largest part of the brain, initiates all the body’s voluntary actions. The cerebellum controls balance of the muscle movement. The brain stem, which connects the cerebrum to the spinal cord, has nerve centres that regulate swallowing, the digestive process, circulation and respiration.

2.9     Cerebral Hemispheres – The cerebrum is made up of a right hemisphere and a left hemisphere, each divided into four lobes. Each hemisphere controls the actions of the opposite side of the body. In most people, the left hemisphere is dominant. In general, the left hemisphere is responsible for speech, writing, and reading. It also plays a major role in verbal, analytical, and computational skills. The right hemisphere is more involved with nonverbal functions, such as emotion, intuition, awareness and interpretation of space and connected by a structure called the corpus callosum, and there is constant communication between the two sides.