Quiz 34: Sensory Perception
Dopamine is a neurotransmitter that is found in both peripheral and central nervous system (CNS). It acts through the dopaminergic receptors (G-protein coupled receptors). The central effects of dopamine on motor control and behavioural effects (Eg: intake of food) are well established. Dopamine is expected to involve in the drug dependence through the "mesocortical dopaminergic reward pathways." The dopamine releasing drugs such as amphetamine and cocaine were shown to activate these pathways. And drugs inhibiting these pathways affected the food intake behaviour and also are not sensitive to amphetamine and cocaine, which are more prone to addiction. So, the study of drugs affecting dopaminergic pathways can be studied in Aplysia californica (marine mollusk) as it is having only 20,000 neurons. Drugs that are inhibiting the behavioural activities like intake of food, and response to touch may indicate the antagonism at dopaminergic receptors. The receptor type that is involved in drug addiction in humans is thought to be the "D 4 " type receptors. Thus, these marine molluscs help screening the drugs useful to treat drug addiction.
Brain and spinal cord together constitute the central nervous system (CNS). Neurons which run from the effector organ to the CNS are called as afferent (sensory) neurons, and which run from the CNS to the effector organ (glands and muscles) are called as efferent (motor) neurons. Thus, the correct option is (a) motor neurons. Sensory neurons carry information from the muscles and glands to the CNS. Thus, the option (b) is incorrect. Interneurons connect two neurons; they do not directly innervate any muscle or gland. Thus, the option (c) is incorrect. Nervous system is made up of two principle populations namely, neurons and supporting cells. Supporting cells are called as "neuroglia (glia = glue) or glial cells." The nerve cells of the neurons form the gray matter and the nerve fibres from the white matter. Thus, the option (d) is incorrect.
The whole brain tissue is enveloped by a lipid layer called blood-brain barrier (BBB), which restricts the entry of various substances into the brain and thus provides protection against toxins. In newborns, it is not fully matured and so it cannot serve its functions as efficiently as the matured one. Thus, some of the toxic substances may enter into the brain by crossing this undeveloped BBB. So, care must be taken in case of diet that the newborns and premature babies are taking.