6: Chemical Control of the Brain and Behaviour

During past week and the lecture six we went through some important topics of chemical control of brain and behavior. The components of the nervous system that operate in expanded space and time are secretory hypothalamus (periventricular area of hypothalamus), autonomic nervous system (sympathetic and parasympathetic nervous systems) and the diffuse modulatory systems of the brain (cell groups that differ with respect to the neurotransmitter they use.)

Hypothalamus maintains the homeostasis of the body by regulating the temperature and blood consumption. The secretory hypothalamus affects their many targets by releasing hormones directly into the bloodstream. It is connected to the pituitary gland by a stalk. It controls the anterior and posterior pituitary gland different ways. Magnocellular cells in the periventricular area of hypothalamus extend axons down the stalk to pituitary and into the posterior lobe. It releases oxytocin and vasopressin. The anterior pituitary is an actual gland which secretes wide range of hormones that regulate secretion from other glands. The anterior lobe is controlled by the parvocellular cells of hypothalamus. There is no axons; they communicate via bloodstream, tiny vessels run down the stalk to anterior lobe where the hormones bind to specific receptors and secrete or stop secreting hormones into the general circulation. Anterior pituitary gland releases hormones such as ACTH, LS, FSH and GH.

In addition, we talked studied the structure and effects of sympathetic and parasympathetic nervous systems. Unlike somatic nervous system, autonomic nervous system is a disynaptic pathway, it contains two neurons from the beginning to the target. It innervates three types of tissues; glands, smooth muscles and cardiac muscles. It also regulates digestive, metabolic functions of the liver, functions of kidney, urinary bladder, large intestine and rectum. It is also essential to the sexual responses of the genitals and interacts with body’s immune system. Sympathetic NS is most active during stress and fight-or-flight situations and parasympathetic during rest.

The diffuse modulatory systems are cores, which each system has a small set of neurons. The neurons arise from the central core of the brain, most from the brain stem. The focus modulatory systems activate specific metabotropic receptors.They use neurotransmitters such as NE, 5-HT, DA and ACh. The neurons of NE arises from Locus Coeruleus and spread vast areas of CNS. Serotonergic nerves arise from Raphe Nuclei and innervates most of the brain. The cholinergic diffuse modulatory systems arise from Pontomesencephalotegmental complex and basal nucleus of Meynert and Medial septal nuclei. Substantia nigra innervates the striatum and Ventral tegmental area the frontal lobe. These use dopaminergic neurons. Many drugs affect on these pathways.

Alexandra & Alisa

 

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