Neurotransmission. The presynaptic neuron (top) releases neurotransmitter, which activates receptors on the postsynaptic cell (bottom).
In response to a threshold action potential or graded electrical potential, a neurotransmitter is released at the presynaptic terminal. The released neurotransmitter may then move across the synapse to be detected by and bind with receptors in the postsynaptic neuron. Binding of neurotransmitters may influence the postsynaptic neuron in either an inhibitory or excitatory way. The binding of neurotransmitters to receptors in the postsynaptic neuron can trigger either short term changes, such as changes in the membrane potential called postsynaptic potentials, or longer term changes by the activation of signaling cascades. Neurons form elaborate networks through which nerve impulses (action potentials) travel.
File:NeuroPimage1.jpg. Biosynthesis. Biosynthesis (also called biogenesis or "anabolism") is an enzyme-catalyzed process in cells of living organisms by which substrates are converted to more complex products . [ 1 ] The biosynthesis process often consists of several enzymatic steps in which the product of one step is used as substrate in the following step.
Examples for such multi-step biosynthetic pathways are those for the production of amino acids , fatty acids , and natural products . [ 2 ] Biosynthesis plays a major role in all cells, and many dedicated metabolic routes combined constitute general metabolism. Six organelles in the cell are involved in biosynthesis: ribosomes, chloroplasts, smooth endoplasmic reticulum, rough endoplasmic reticulum, plastids, and Golgi bodies. [ 3 ] Neurotransmitter. Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse . [ 1 ] Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane in the axon terminal, on the presynaptic side of a synapse.
They are released into and diffuse across the synaptic cleft , where they bind to specific receptors in the membrane on the postsynaptic side of the synapse. [ 2 ] Release of neurotransmitters usually follows arrival of an action potential at the synapse, but may also follow graded electrical potentials . Low level "baseline" release also occurs without electrical stimulation. Neurotransmitters are synthesized from plentiful and simple precursors, such as amino acids , which are readily available from the diet and which require only a small number of biosynthetic steps to convert. [ 3 ] Discovery [ edit ] Until the early 20th century, scientists assumed that the majority of synaptic communication in the brain was electrical. Synapse. In the nervous system, a synapse is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron.
Some authors generalize this concept to include the communication from a neuron to any other cell type, although such non-neuronal contacts may be referred to as junctions (a historically older term). Santiago Ramón y Cajal proposed that neurons are not continuous throughout the body, yet still communicate with each other, an idea known as the neuron doctrine. Chemical or electrical There are two fundamentally different types of synapses: Vesicle (biology and chemistry) In cell biology, a vesicle is a small structure within a cell, consisting of fluid enclosed by a [lipid bilayer].
Vesicles can form naturally, for example, during the processes of secretion (exocytosis), uptake (phagocytosis and endocytosis) and transport of materials within the cytoplasm. Alternatively, they may be prepared artificially, in which case they are called liposomes. If there is only one phospholipid bilayer, they are called unilamellar liposome vesicles; otherwise they are called multilamellar.
Receptor (biochemistry) Biochemical cascade. A biochemical cascade (or a signaling pathway) is a series of chemical reactions which are initiated by a stimulus (first messenger) acting on a receptor that is transduced to the cell interior through second messengers (which amplify the initial signal) and ultimately to effector molecules, resulting in a cell response to the initial stimulus. At each step of the signaling cascade, various controlling factors are involved to regulate cellular actions, responding effectively to cues about their changing internal and external environments. Introduction Signalling cascades Cells require a full and functional cellular machinery to live.
When they belong to complex multicellular organisms, they need to communicate among themselves and work for symbiosis in order to give life to the organism. These communications between cells triggers intracellular signaling cascades, termed signal transduction pathways, that regulate specific cellular functions. Cellular response Monoamine transporter. Dopamine Transporter (DAT-6) Monoamine transporters (MATs) are protein structures that function as integral plasma-membrane transporters to regulate concentrations of extracellular monoamine neurotransmitters.
Three major classes of MATs (SERT, DAT, NET) are responsible for the reuptake of their associated amine neurotransmitters (serotonin, dopamine, norepinephrine). MATs are located just outside the synaptic cleft (peri-synaptically), transporting monoamine transmitter overflow from the synaptic cleft back to the cytoplasm of the pre-synaptic neuron. MAT regulation generally occurs through phosphorylation and posttranslational modification. Due to their significance in neuronal signaling, MATs are commonly associated with drugs used to treat mental disorders as well as recreational drugs, a line that can become quite blurred in many cases.