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In addition to the lobes of the cerebral cortex, the forebrain includes the thalamus (sensory relay) and limbic system (emotion and memory circuit). Each hemisphere can be subdivided into different lobes: frontal, parietal, temporal, and occipital. The brain consists of two hemispheres, each controlling the opposite side of the body. Sympathetic activation prepares us for fight or flight, while parasympathetic activation is associated with normal functioning under relaxed conditions. The autonomic nervous system controls the function of our organs and glands, and can be divided into the sympathetic and parasympathetic divisions. The somatic nervous system transmits sensory and motor signals to and from the central nervous system. The peripheral nervous system is comprised of the somatic and autonomic nervous systems. The brain and spinal cord make up the central nervous system. Drugs can act either as agonists or as antagonists for a given neurotransmitter system. Therefore, psychotropic drugs are prescribed in an attempt to bring the neurotransmitters back into balance. Often, psychological disorders involve imbalances in a given neurotransmitter system. Action potentials operate on the all-or-none principle and involve the movement of Na + and K + across the neuronal membrane.ĭifferent neurotransmitters are associated with different functions. If the signals received from other neurons are sufficiently strong, an action potential will travel down the length of the axon to the terminal buttons, resulting in the release of neurotransmitters into the synaptic cleft. The dendrites contain receptors for neurotransmitters released by nearby neurons. Neuronal communication is an electrochemical event. At the end of the axon are terminal buttons that contain synaptic vesicles filled with neurotransmitters. The axon is another major extension of the cell body axons are often covered by a myelin sheath, which increases the speed of transmission of neural impulses. The soma contains the cell nucleus, and the dendrites extend from the soma in tree-like branches. Neuronal communication is made possible by the neuron’s specialized structures. While glia generally play supporting roles, the communication between neurons is fundamental to all of the functions associated with the nervous system. Glia and neurons are the two cell types that make up the nervous system. Ultimately, how and when a gene is expressed, and what the outcome will be-in terms of both physical and psychological characteristics-is a function of the interaction between our genes and our environments. Genes affect both physical and psychological characteristics. In order to exhibit a recessive phenotype, an individual must be homozygous for the recessive allele. A dominant allele always results in the dominant phenotype. Different versions of a gene are called alleles-sometimes alleles can be classified as dominant or recessive. Genes are sequences of DNA that code for a particular trait.
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