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  • in this video I want to talk about nervous system so our nervous system is

  • a complex network that coordinates our body's voluntary and involuntary actions

  • and transmits signals between different parts of the body it is divided into two

  • anatomical divisions the central nervous system CNS which consists of the brain

  • and the spinal cord and the peripheral nervous system PNS which consists of all

  • the nerves and neurons outside of the central nervous system now if we were to

  • look at the cross-section of the spinal cord we would find there three types

  • of neurons that are of importance to us number one afferent neurons which carry

  • signals to the CNS from sensory receptors in peripheral tissues number

  • two efferent neurons that carry signals from the CNS to the effector organs such

  • as muscle and number three interneurons which are located in between afferent

  • and efferent neurons and integrate information that flows between the two

  • so for example if you touch a hot object sensory receptors located in your

  • fingers would immediately initiate a signal that would travel through afferent

  • neurons to the spinal cord and then from there a response signal would be

  • initiated and would travel from the spinal cord through efferent neurons to

  • the muscles in your hand which would result in reflexive withdrawal of the

  • hand and all this would happen in just a fraction of a millisecond now let's take

  • a closer look at the functions of sympathetic and parasympathetic system

  • so I'm going to draw sympathetic division on the left side and

  • parasympathetic division on the right side but first let's quickly talk about

  • the types of neurons that we find in both of these divisions first we have

  • cholinergic neurons which use neurotransmitter acetylcholine

  • to send messages and I'm going to use the red color to draw them and the

  • second we have adrenergic neurons which use neurotransmitters norepinephrine and

  • epinephrine to send messages and I'm going to use color blue to draw them now

  • let's focus on sympathetic division first so sympathetic neurons arise from

  • thoracic and lumbar regions of the spinal cord and first we have

  • preganglionic neurons which originate directly from the spinal cord they are

  • short and they release acetylcholine so they are cholinergic and they synapse

  • with postganglionic neurons which are long and release norepinephrine so they

  • are the adrenergic neurons and for simplicity and to conserve some space

  • I'm going to skip drawing sympathetic ganglion but just keep in mind that

  • there is this chain of synaptic connections of sympathetic neurons that

  • lies alongside the spinal cord so now let's talk about how sympathetic neurons

  • affect each part or organ of our bodies

  • so sympathetic nervous system is responsible for fight-or-flight response

  • and the activation of this system leads to the following dilation of pupils

  • inhibition of salivation relaxation of airways acceleration of the heartbeat

  • inhibition of digestion stimulation of glucose release from the liver

  • inhibition of gall bladder inhibition of intestines activity stimulation of

  • adrenal medulla which results in secretion of epinephrine and

  • norepinephrine relaxation of urinary bladder and stimulation of ejaculation

  • or vaginal contraction and just to clarify the adrenal medulla is the only

  • autonomic neuroeffector organ which is

  • innervated by one long sympathetic cholinergic neuron on the other side we

  • have parasympathetic nervous system which is responsible for rest-and-digest

  • response parasympathetic neurons arise from cranial nerves 3 7 9 and 10 and the

  • sacral region s2 to s4 in contrast to sympathetic division parasympathetic

  • preganglionic neurons are long and postganglionic neurons are short and

  • they actually both release neurotransmitter acetylcholine so the activity of

  • parasympathetic division would have the opposite effect of sympathetic

  • stimulation and would result in the following

  • constriction of pupil stimulation of salivation constriction of airways

  • slowing of the heartbeat stimulation of digestion stimulation of glucose uptake

  • stimulation of intestines activity stimulation of urinary bladder

  • contraction and stimulation of erection now I want to briefly talk about

  • receptors involved in this whole system so let's zoom in on this synapse from

  • sympathetic system and also let's zoom in on this synapse right here from

  • parasympathetic system so the receptors on postganglionic neurons within

  • sympathetic and parasympathetic system are all nicotinic receptors moreover the

  • receptors in skeletal muscle are also nicotinic so nicotinic receptors are

  • also known as ionotropic receptors and this is because they simply work as an

  • ion channel so for example when neurotransmitter such as acetylcholine

  • binds to such channel it causes it to open up allowing passage of ions such as

  • sodium which eventually leads to an action potential

  • on the other hand all the receptors on the effector organs that are receiving

  • signal from sympathetic neurons are called adrenergic receptors and the ones

  • that are receiving signal from parasympathetic neurons are called

  • muscarinic receptors so for example if we zoom in at this area right here where

  • the very ends of these postganglionic neurons meet the smooth muscle cell of

  • the eye the sympathetic adrenergic neuron would stimulate

  • adrenergic receptors leading to pupil dilation and the parasympathetic

  • cholinergic neuron would stimulate muscarinic receptors leading to pupil

  • constriction now adrenergic and muscarinic receptors are of type known

  • as metabotropic receptors and unlike the ionotropic receptors the metabotropic

  • ones are all linked to G protein that acts via intracellular second messengers

  • and this is discussed in more details in pharmacodynamics video so please check

  • it out finally to put all of this in perspective remember that most organs

  • are innervated by both sympathetic and parasympathetic neurons however usually

  • only one system predominates in controlling any given organ overall

  • autonomic nervous system is very dynamic constantly shifting from the dominance

  • of one system to another depending on the situation and with that I wanted to

  • thank you for watching and I hope you enjoyed this video

in this video I want to talk about nervous system so our nervous system is

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B2 中高級 美國腔

藥理學 - 自動神經系統(MADE EASY) (Pharmacology - AUTONOMIC NERVOUS SYSTEM (MADE EASY))

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    turtlelin00 發佈於 2021 年 01 月 14 日
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