Autonomic Nervous System

hello friends our topic today is the autonomic nervous system or ans remember that we have one nervous system it can be divided into the peripheral nervous system and the central nervous system the peripheral nervous system can be divided into the somatic nervous system over which we have voluntary control and the autonomic nervous system or ans which we do not control voluntarily the two branches of the ANS include the sympathetic nervous system and the parasympathetic nervous system please also remember that the sympathetic nervous system is very active during a fight-or-flight response and the parasympathetic nervous system is more active during conditions of rest and digest for example the sympathetic nervous system would be very active in your body if you are being chased by a bear in contrast the parasympathetic nervous system is more active in your body when you are sitting on the couch relaxed digesting your food and watching TV like Homer Simpson neurons of the ANS innervate effectors that are not under voluntary control think of organs and glands or effectors in your body which you do not voluntarily control some examples of effectors innervated by the ANS are the heart the smooth muscles of the bronchial tubes and GI tract smooth muscles lining the blood vessels and glands it takes two neurons to get from the CNS to the effectors that are innervated by the ANS the first is called the preganglionic neuron and the second is called the postganglionic neuron notice that the preganglionic neuron for the sympathetic is shorter than the preganglionic for the parasympathetic and notice that the postganglionic for the parasympathetic is shorter than the postganglionic for the sympathetic the action potential will travel down the axon of the preganglionic neuron and reached the axon terminal where neurotransmitters are released all preganglionic neurons of the ANS are cholinergic this means that they make and release acetylcholine abbreviated ACH as their neurotransmitter postganglionic neurons of the parasympathetic nervous system are also cholinergic neurons as our somatic motor neurons that innervate skeletal muscle the postganglionic neuron of the sympathetic nervous system is called an adrenergic neuron this means it makes and releases norepinephrine cholinergic receptors for acetylcholine are located in several places they are found on the dendrites or cell bodies of the postganglionic neurons of the ANS these cholinergic receptors are called nicotinic - or n2 receptors the cholinergic receptors located on effectors innervated by the parasympathetic nervous system are known as muscarinic or M receptors the effectors innervated by somatic motor neurons our skeletal muscles and they also Express cholinergic receptors these receptors are called nicotinic one or n1 receptors the adrenergic receptors located on effectors innervated by the sympathetic nervous system can be either alpha or beta receptors epinephrine also known as adrenaline is released from the adrenal gland and also binds to and activates adrenergic receptors on effectors also remember that the actions of the parasympathetic and sympathetic systems are in opposition to one another for example with the heart the parasympathetic system slows heart rate and the sympathetic system increases heart rate also most organs are innervated by both branches of the ANS this is called dual autonomic innervation lastly remember that one receptor subtype from each system will tend to dominate in a tissue for example on the sympathetic side cardiac myocytes have predominantly beta 1 receptors the smooth muscle of airways have mostly beta 2 receptors and alpha 1 receptors are the predominant receptors on the smooth muscles lining blood vessels there are some exceptions to the dual autonomic innervation rule the vast majority of blood vessels have no parasympathetic innervation just sympathetic another exception is found with sweat glands sweat glands also lack parasympathetic cholinergic innervation and are exclusively innervated by the sympathetic division postganglionic neurons of the sympathetic division that innervate glands responsible for generalized sweating are cholinergic and therefore secrete acetylcholine this is the exception to the rule since postganglionic sympathetic neurons usually secrete norepinephrine after it's released from the postganglionic cell acetylcholine crosses the neural effector Junction and binds to muscarinic receptors expressed on glands for generalized sweating that are important for body temperature regulation localized sweat glands are activated with stress and are those located in the palms soles genitalia and armpits and express alpha-1 receptors which respond to norepinephrine to help keep track of the actions of the receptors please remember that oddly numbers subtypes are usually excitatory and evenly numbered are usually inhibitory is an example beta one is oddly numbered so you would expect it to be excitatory activating beta one on the cardiac myocytes increases heart rate and force of contraction beta 2 is evenly numbered so you would expect it to be inhibitory beta 2 is the predominant adrenergic receptor on the smooth muscle lining the Airways of the respiratory system activating beta 2 causes bronchodilation which means opening the airways for increased ventilation alpha-1 is the predominant receptor on the smooth muscle of vessels activating alpha one causes an excitatory effect and results in contraction of smooth muscles resulting in vasoconstriction and an increase in blood pressure also it's important to know that all adrenergic receptors as well as all muscarinic receptors are g-protein coupled receptors this allows them to be either excitatory or inhibitory in contrast nicotinic receptors are not g-protein coupled receptors but their activation will increase permeability of sodium or calcium in postganglionic neurons or skeletal muscles hence they are always excitatory one more time please remember that evenly numbered adrenergic and muscarinic receptors tend to be inhibitory an oddly number tend to be excitatory nicotinic receptors are always excitatory regardless of the subtype in summary cholinergic neurons release acetylcholine adrenergic neurons release norepinephrine all autonomic nervous system neurons are cholinergic except postganglionic sympathetic neurons which are nearly always adrenergic lastly please take a moment to review the cholinergic and adrenergic receptors and their respective location some questions now for you to assess your understanding please pause the video to make your attempt as always thanks for watching

Channel: PhysioPathoPharmaco

Views: 273,492

Keywords: autonomic nervous system, animation, video, presynaptic, preganglionic, postganglionic, postsynaptic, acetylcholine, norepinephrine, heart, smooth muscle, nicotinic, adrenergic, muscarinic, cholinergic, somatic, parasympathetic, sympathetic

Id: 0J2b2LDjRUI

Length: 11min 17sec (677 seconds)

Published: Fri Nov 10 2017