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Neurotransmitter Actions

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Neurotransmitter Actions Central University of South Bihar Panchanpur, Gaya, India E-Learning Resources Department of Biotechnology NB: These materials are taken/borrowed/modified/compiled from various resources like research articles and freely available internet websites, and are meant to be used solely for the teaching purpose in a public university, and for serving the needs of specified educational programmes. Dr. Jawaid Ahsan Assistant Professor Department of Biotechnology Central University of South Bihar (CUSB) Course Code: MSBTN2003E04 Course Name: Neuroscience Neurotransmitter Actions • Excitatory Action: – A neurotransmitter that puts a neuron closer to an action potential (facilitation) or causes an action potential • Inhibitory Action: – A neurotransmitter that moves a neuron further away from an action potential • Response of neuron: – Responds according to the sum of all the neurotransmitters received at one time Neurotransmitters • Acetylcholine • Monoamines – modified amino acids • Amino acids • Neuropeptides- short chains of amino acids • Depression: – Caused by the imbalances of neurotransmitters • Many drugs imitate neurotransmitters – Ex: Prozac, zoloft, alcohol, drugs, tobacco Release of Neurotransmitters • When an action potential reaches the end of an axon, Ca+ channels in the neuron open • Causes Ca+ to rush in – Cause the synaptic vesicles to fuse with the cell membrane – Release the neurotransmitters into the synaptic cleft • After binding, neurotransmitters will either: – Be destroyed in the synaptic cleft OR – Taken back in to surrounding neurons (reuptake) Excitable cells: Definition: Refers to the ability of some cells to be electrically excited resulting in the generation of action potentials. Neurons, muscle cells (skeletal, cardiac, and smooth), and some endocrine cells (e.g., insulin- releasing pancreatic β cells) are excitable cells. With the exception of neurons, muscle cells, and some endocrine cells, all cells in the body are non-excitable. In muscle cells, changes in the membrane potential bring about contraction. In endocrine cells, changes in the membrane potential bring about hormone secretion. Membrane as Capacitor charge (Q) The membrane potential is similar to a voltage difference across the plates of a capacitor. - hydrophobic membrane core (∼3 nm) - conductive extracellular and intracellular electrolyte solutions. - electrical potential difference across the bilayer (referred to as the membrane potential, Vm) - resting membrane potential (Vrest) refers to a situation in which the cell is at rest and no perturbations have been done to change the potential. Resting Membrane Potential In most cells examined, the resting membrane potential is inside negative (i.e., inside of the cell is negative with respect to the outside, which serves as the reference). In most mammalian cells, the resting membrane potential is around −50 mV (−0.05 V). The value of the resting membrane potential varies from cell to cell, and ranges from about −20 mV to −100 mV. For example, in a typical neuron, its value is −70 mV, in a typical skeletal muscle cell, its value is −90 mV, and in a typical epithelial cell, its value is closer to −50 mV. The symbol V is normally used to refer to the membrane potential (because the Volt is the SI unit for voltage). In non-excitable cells, such as epithelial cells and adipose cells (and others), the resting membrane potential does not change appreciably over time. Therefore, Vm = Vrest at all times. In excitable cells (such as neurons, muscle cells, and some endocrine cells), however, upon stimulation of the cell, the membrane potential can change dramatically for short periods of time (milliseconds to hundreds of milliseconds). Therefore, in excitable cells the membrane potential is not always at the resting membrane potential. Depolarization, repolarization, and hyperpolarization. Using the resting membrane potential as the reference point, a change in the membrane potential in the positive direction (i.e., more positive than the resting potential) is called depolarization. After a depolarization, return to the resting membrane potential is called repolarization. Using the resting membrane potential as the reference point, a change in the membrane potential in the negative direction (i.e., more negative than the resting potential) is called hyperpolarization. Ca2+ concentration is much higher outside cell. Serotonin (5-HT) Neurotransmitters Neurotransmitters are molecules that inhibit or stimulate a postsynaptic cell, which is released in the body by the presynaptic nerve cell to produce a response to a certain stimuli. Neurotransmitters, also known as chemical messengers, are endogenous chemicals that enable neurotransmission. NEUROTRANSMITTERS are the brain chemicals that communicate information throughout our brain and body. They relay signals between nerve cells, called “neurons.” They transmit signals across a chemical synapse, such as a neuromuscular junction, from one neuron (nerve cell) to another "target" neuron, muscle cell, or gland cell. The brain uses neurotransmitters to tell your heart to beat, your lungs to breathe, and your stomach to digest. They can also affect mood, sleep, concentration, weight, and can cause adverse symptoms when they are out of balance. Some examples of neurotransmitter substances are serotonin, glycine, endorphins, gamma amino butyric acid (GABA), acetylcholine, norepinephrine, and dopamine. There are two kinds of neurotransmitters – EXCITATORY and INHIBITORY. Excitatory neurotransmitters are not necessarily exciting – they are what stimulate the brain. Those that calm the brain and help create balance are called inhibitory. Inhibitory neurotransmitters balance mood and are easily depleted when the excitatory neurotransmitters are overactive. Serotonin This substance, which is found in the brainstem, the gastrointestinal tract and the platelets, is responsible for sleep induction and good mood. When the concentrations are elevated, it is often associated with delusions and schizophrenia. Glycine Glycine is found in the spinal cord and the brain. This acts in an inhibitory manner in the spinal cord and enters the neuron, resulting to Inhibitory Postsynaptic Potential or IPSP (opposite is Excitatory Postsynaptic Potential or EPSP). Endorphins You can find these neurotransmitters in both the central nervous system and the peripheral nervous system. It is also known as the endogenous morphine because it has almost the same effect as morphine. Morphine acts as an anesthetic agent and induces euphoria and a false sense of well-being. Gamma Amino Butyric Acid or GABA GABA inhibits almost 90 percent of non-glutamate receptors. Most neurons in the central nervous system contain GABA receptors, which makes it the most common. Acetylcholine Acetylcholine is one of the more popular neurotransmitters and is found mostly in neuromuscular junctions. The enzyme acetylcholinesterase catalyzes the conversion of acetylcholine to other products, which the body could use again. Norepinephrine Norepinephrine is found in the brain and spinal cord and is rapidly metabolized and recycled. This catecholamine has an excitatory or inhibitory effect in the body. Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical in the catecholamine family that functions in the brain and body as a hormone (adrenal gland) and neurotransmitter. Dopamine This substance has an excitatory effect and is found in the Autonomic Nervous System or ANS. Oversecretion of this substance results to schizophrenia. .
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