Name: 藥理學 - 自動神經系統(MADE EASY) (Pharmacology - AUTONOMIC NERVOUS SYSTEM (MADE EASY))
Uploaded: 2021-01-14T07:07:57.000Z
Duration: 8 min 15 s
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in this video I want to talk about
nervous system so our nervous system is

關係子句

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

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

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