Which of the following is a neurotransmitter used by the sympathetic nervous system?
DefinitionThe autonomic nervous system is made up of 2 subdivisions: sympathetic and parasympathetic systems. The sympathetic system originates from the thoracolumbar regions (T1-L2) of the spinal cord. The parasympathetic system originates from craniosacral regions (brainstem nuclei CN III, VII, IX, and X as well as sacral levels S2-S4). In general, there are 2 neurons that combine to link each effector organ with its respective sympathetic or parasympathetic system. The first neuron is called the preganglionic neuron, and the second is the postganglionic neuron. These neurons synapse together in the autonomic ganglia. The exception to this is the adrenal medulla which is connected directly to the preganglionic neuron. Show
Both sympathetic and parasympathetic preganglionic neurons are cholinergic, meaning they release acetylcholine (Ach) at the synapse in the ganglion. In the parasympathetic system, postganglionic neurons are also cholinergic. However in the sympathetic system, postganglionic are not all the same. Most sympathetic postganglionic neurons are adrenergic (meaning they release norepinephrine (NE)), but a few are cholinergic- such as the ones to sweat glands and to smooth muscles of certain blood vessels. In the cholinergic synapse, released acetylcholine is degraded down by the enzyme acetylcholinesterase, or reabsorbed into the preganglionic neuron. In the adrenergic synapse, released norepinephrine is either reabsorbed into the preganglionic neuron or degraded by catechol-o-methyl transferase (COMT) enzyme. In general, the parasympathetic system is responsible for promoting ‘rest & digest’ functions, and the sympathetic system is responsible for promoting ‘fight or flight’ functions. However, the specific response of the effector organ is dependent on the types of receptors present. For example, the sympathetic system will release NE at both alpha and beta receptors. Some effector organs will have only alpha receptors, some only beta receptors, and some a mixture of both and the response will be based on the relative ratio of these receptors. An example of this is vascular tone. Sympathetic stimulation of an alpha receptor results in vasoconstriction, while stimulation of a beta receptor results in vasodilation. For effector organs that have both sympathetic and parasympathetic innervations, their respective functions are typically opposite each other. It is the balance of the relative sympathetic to parasympathetic tone which dictates the specific action on the effector organ. For example, in the heart the SA node will increase heart rate with sympathetic stimulation but decrease heart rate with parasympathetic stimulation. Thus, the actual heart rate is dependent of the relative balance between these two systems. SubspecialtyRelated MediaKeyword history57%/2012 50%/2009 See Also:SourcesPubMedImage credit: iStockphoto Neurotransmitters are often referred to as the body’s chemical messengers. They are the molecules used by the nervous system to transmit messages between neurons, or from neurons to muscles. Communication between two neurons happens in the synaptic cleft (the small gap between the synapses of neurons). Here, electrical signals that have travelled along the axon are briefly converted into chemical ones through the release of neurotransmitters, causing a specific response in the receiving neuron. A neurotransmitter influences a neuron in one of three ways: excitatory, inhibitory or modulatory. An excitatory transmitter promotes the generation of an electrical signal called an action potential in the receiving neuron, while an inhibitory transmitter prevents it. Whether a neurotransmitter is excitatory or inhibitory depends on the receptor it binds to. Neuromodulators are a bit different, as they are not restricted to the synaptic cleft between two neurons, and so can affect large numbers of neurons at once. Neuromodulators therefore regulate populations of neurons, while also operating over a slower time course than excitatory and inhibitory transmitters. Most neurotransmitters are either small amine molecules, amino acids, or neuropeptides. There are about a dozen known small-molecule neurotransmitters and more than 100 different neuropeptides, and neuroscientists are still discovering more about these chemical messengers. These chemicals and their interactions are involved in countless functions of the nervous system as well as controlling bodily functions. The first neurotransmitter to be discovered was a small molecule called acetylcholine. It plays a major role in the peripheral nervous system, where it is released by motor neurons and neurons of the autonomic nervous system. It also plays an important role in the central nervous system in maintaining cognitive function. Damage to the cholinergic neurons of the CNS is associated with Alzheimer disease. Glutamate is the primary excitatory transmitter in the central nervous system. Conversely, a major inhibitory transmitter is its derivative γ-aminobutyric acid (GABA), while another inhibitory neurotransmitter is the amino acid called glycine, which is mainly found in the spinal cord. Many neuromodulators, such as dopamine, are monoamines. There are several dopamine pathways in the brain, and this neurotransmitter is involved in many functions, including motor control, reward and reinforcement, and motivation. Noradrenaline (or norepinephrine) is another monoamine, and is the primary neurotransmitter in the sympathetic nervous system where it works on the activity of various organs in the body to control blood pressure, heart rate, liver function and many other functions. Neurons that use serotonin (another monoamine) project to various parts of the nervous system. As a result, serotonin is involved in functions such as sleep, memory, appetite, mood and others. It is also produced in the gastrointestinal tract in response to food. Histamine, the last of the major monoamines, plays a role in metabolism, temperature control, regulating various hormones, and controlling the sleep-wake cycle, amongst other functions. Which of the following neurotransmitters is used by the sympathetic nervous system quizlet?Correct answer = C. The neurotransmitter at the sympathetic and parasympathetic ganglia is acetylcholine. Sympathetic neurons release NE and parasympathetic neurons release ACh in the effector cells. Afferent neurons carry signals from the periphery to the CNS.
What is the main neurotransmitter of the sympathetic nervous system quizlet?Norepinephrine is the primary neurotransmitter of the sympathetic nervous system.
What neurotransmitters are mainly used in the sympathetic ganglia?At a first approximation, chemical transmission in the sympathetic system appears simple: preganglionic neurons use acetylcholine as a neurotransmitter, whereas most postganglionic neurons utilize norepinephrine (noradrenaline)—with the major exception that postganglionic neurons innervating sweat glands use ...
What are the main neurotransmitters for the sympathetic and parasympathetic nervous system?Neurotransmitters of the Autonomic Nervous System
The 2 most common neurotransmitters released by neurons of the ANS are acetylcholine and norepinephrine. Neurotransmitters are synthesized in the axon varicosities and stored in vesicles for subsequent release.
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