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Nervous System Organization
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hi welcome to our lecture on the nervous
system so how do we get information from
the outside world receive it and pass it
along to the entire body by the nervous
system so we talked about how the neuron
is this tiny information processing
system well the nervous system is a much
bigger information processing system so
we can break it down into two main parts
the first is the central nervous system
that's going to be made up of the brain
the spinal cord and the brain stem we
can call this our command center this is
the main part of our nervous system
we're going to study the brain in the
brainstem in more detail in the next
class but right now let's look a little
bit more at the spinal cord the spinal
cord controls truck trunk and limb muscles
muscles
it carries vital information from the
rest of the body into and out of the
brain but it doesn't simply relay
messages it can also initiate some
automatic behaviors on its own we call
these involuntary automatic behaviors
reflexes so with a reflex a signal
that's received it's only the
information is only going to travel as
far as a spinal cord and then action is
going to be initiated the spinal cord is
going to initiate that action and then
later on the brain will be notified so a
popular reflex is the nature you ever
it's a knee-jerk reflex hyperreflexia
can be demonstrated in the patellar
reflex in this case the patient has
suffered a stroke affecting the left
side of the brain the patellar tendon
extends from below the patella which is
right here it's a broad band of tissue
it's easily palpable if you're not sure
where it is have the patient
extend their leg which will cause the
tendon to shorten and you can start
directly on the tendon unless reflexes
are very brisk in fact there are a few
extra beats of movement which referred
to as clovis again classic for an upper
motor neuron syndrome in cases like this
the reflux can be elicited by simply
tapping on the tendon often we see the
same reflex requires very little
stimulus prepared again with the normal
side patellar tendon again extending
from below the patella strike on the
tendon so that would be a normal reflex
and certainly image compared with the
sizes hyperreflexia
another popular reflex is the one with
know it feels like they really want to
hold our hand or thumb or finger like
because they love us but really it's
just automatic it's a reflex their brain
isn't even notified now okay they're
older maybe they're doing on purpose you
really want to believe that maybe
they've decided okay I really want to
hold your finger you're special it's
called the grasp reflex stroking the
palm of a baby's hand causes a baby to
close his or her finger fingers in a
grasp this reflex lasts until about five
or six months of age okay so if they're
older than five or six months you can
say that they're holding your fingers
these are born with a set of reflexes
critical for survival in the outside
world some of these reflexes are so
obvious you might not think to look for
them such as the breathing reflex or the
eye blink reflex routing is one of the
most critical reflexes by touching four
week old Lily's cheek she'll turn her
head and open her mouth and preparation
for nursing once the baby is in contact
with a breast a bottle or even a finger
the sucking reflex takes over
involuntary at first the neonate will
gradually gained control over sucking
during the first year placing liquid in
the mouth will induce the swallowing
reflex in the first few weeks of life it
takes all the babies concentration just
to control these various uncoordinated
reflexes at this age feeding julia can
take over an hour after about six weeks
though julia will be a pro there are
other reflexes babies are born with that
we don't completely understand in the
first two months babies exhibit the
stepping reflex this is probably a
precursor to walking watch Lily's toes
fan out and curl this is the Babinski reflex
reflex
which occurs when the bottom of a baby's
foot is stroked [Music]
when pressure is placed on the baby's
hand you can see the grasping reflex at
work Lily's grasp is strong enough to
support almost her entire body weight
for a few seconds at least when startled
or dropped a baby may respond with the
Moro reflex the arms fling outward and
in look as if the baby were groping for
support two month old Julia doesn't even
need to be awake to demonstrate this
reflex so there's all these reflexes and
some of them go away as we develop but
others stick around like the nature so
let's look at an example of a reflex
action well if you touch a hot pot on a
stove you're automatically gonna pull
your hand back the information is only
gonna go as far as the spinal cord and
then you're gonna pull your hand back
and then later on the brain's gonna be
notified oh I was burned so this is
necessary it helps with our survival
back in the day they used to study
reflexes back when people were
decapitated and all of a sudden the
person's head was separated from their
body their brain was separated from the
body but their body would be jerking
around these were reflexes so we could
see that some movement was possible
without the brain okay so the spinal
cord the brain and the brainstem form
the central nervous system again this is
our command center and because of this
we can process information and adapt to
our environment in ways that no other
animal can ok the second major part of
the nervous system is going to be all
the nerves outside of the brain and the
spinal cord this is called the
peripheral nervous system the peripheral
nervous system links brains but the
brain in the spinal cord to the body
sense receptors muscles and glands it's
made up of the Scout like sensory motor
neurons that carry messages to and from
the central nervous system to the
periphery of the body so as kept connect
the central nervous system to the rest
of the body in carrying information back
and forth it's all the nerves outside of
remember nerds are groups of neurons
okay so now let's separate the
peripheral nervous system into two
subsystems we're gonna have the somatic
nervous system and the autonomic nervous
system let's start with the autonomic
nervous system this functions like
autopilot meaning it operates on its own
it mediates an organism's response
responses to stress and also various
kinds of vegetative functions so these
functions that happen on their own that
we do not consciously control so it's
responsible for things like involuntary
tasks like heart rate digestion pupil
dilation and breathing and of course we
said that it mediates the organisms
responses to stress and the stress
response can impact these involuntary
tasks like heart rate digestion pupil
dilation and breathing so on the other
side you know we just separated the
peripheral nervous system into the
autonomic nervous system and then the
somatic nervous system look at the
somatic nervous system in opposition to
the autonomic nervous system the
autonomic is like automatic functions on
autopilot operates on its own the
somatic nervous system on the other hand
is also known as the voluntary nervous
system it's like a two-way street
first carrying sensory information to
the brain and spinal cord and then
carries messages from the central
nervous system to the skeletal muscles
it's going to be the things it controls
all the things that we are aware of and
can consciously influence such as moving
our arms and legs and other parts of our
body it's also associated with reflexes
something interesting to point out is
soma we mentioned this once before so
means body so how I remember this is it
has to do with us moving our body moving
our arms and legs and other parts of the
body and is connecting the central
nervous system to the rest of the body
okay back to the autonomic nervous
system we're going to separate that one
into two systems so we've gone central
nervous system peripheral nervous system
peripheral nervous system gets separated
to the somatic and autonomic now we're
looking at the autonomic and we're gonna
separate that into two the autonomic
said multiple times has to do with
mediating on organisms responses to
stress so let's look at these two next
two subsystems one's called the
sympathetic nervous system and the
others the parasympathetic nervous
system these two I like these systems
because they function like children on a
teeter totter when one is up the other
is down when one is up the other is down
they function in opposition to each
other but they're essentially
complementary in nature you see they're
linked even though they're in opposition
and they complement each other now must
have each other's backs
so the sympathetic nervous system that's
the nervous system that winds you up
this system when you're stressed this
system kicks in to mobilize bodily
resources to respond to the stressor it
when you're stressed it kicks in to
mobilize bodily resources to respond to
the stressor it's going to organize the
body to meet emergencies this emergency
response is normally called the most you
all have heard this flight-or-fight
we're going to talk a lot more about
fight-or-flight when we talk about
stress we're going to talk about how
there's tender befriend or fight or
flight or freeze the sympathetic nervous
system is concerned with getting more
oxygenated blood and energy to the
skeletal muscles it's going to shut down
trivial functions is going to stop
digestive and eliminative processes
these trivial functions that we don't
need in the moment for survival and it's
going to take all the energy and blast
it at the things that matter so send all
the energy to the heart to the brain to
it's an increased heart rate is going to
increase respiration it's going to
increase blood pressure it's going to
release hormones interestingly the
nervous system directs your endocrine
system but you're entered kisum
endocrine system directs the nervous
system it's this weird little circle and
we'll talk about that more later as well
all of this this bodily response is
supposed to allow us to cope with the
stress to face the stressor to either
fight or flee it's our body empowering
itself now something interesting is
nowadays the sympathetic nervous system
is activated by all kinds of things
things that are not really putting us in
mortal danger less life less threatening
events such as traffic jams or
activating the system so the question is
well what's happening when the system is
becoming activated all the time and
we'll talk about that more later the
other child on the child on the teeter-totter
teeter-totter
is going to be the parasympathetic
nervous system this winds you down
so one the sympathetic nervous systems
kicked in it winds you up after the
stressor goes away the parasympathetic
nervous system is supposed to go active
and the sympathetic nervous system is
supposed to deactivate so the
sympathetic nervous system activates
winds you up you meet the stressor it
shuts down and the parasympathetic
nervous system activates and this whines
you down it's responsible for calm in
our bodies and conserving energy it
restores our bodily resources when the
sympathetic nervous system winds you up
it depletes all your bodily resources it
uses all your energy it takes everything
in your energy tank and it just uses it
all it burns all your gas the
parasympathetic system refills you
refills your energy refills your gas
restore is your bodily resources now the
sympathetic nervous system is very quick
in its onset very rapid onset and offset
turns on turns off and it acts like a
unit when you're stressed the
parasympathetic on the other hand is
relatively slow when it comes to its
onset it doesn't just turn on it slowly
turns on and it acts discriminately only
where needed so maybe you've been
exposed to some kind of acute stressor
and maybe when the stressor goes away
you feel like you've crashed a little
bit well this makes sense you use all
your resources all your energy and it's
taking some time for that
parasympathetic system to engage and
it's taking time to restore those bodily
resources so you're going to feel like
you've crashed okay so that's a
breakdown of the nervous system next
class we'll be looking at the central
nervous system focusing on the brain and
the brain stem but this class we looked
at the peripheral nervous system so
remember that's all the nerves outside
of the
brain in the spinal cord it's connecting
the central nervous system to the rest
of the body and the rest of the body to
the central nervous system we we divided
the peripheral nervous system into two
categories the somatic nervous system
and the autonomic nervous system the
autonomic says vegetative functions it's
functioning on its own autopilot we
don't have to think all the time
I gotta breathe I gotta breathe oh my
heart's got a pump I gotta breathe my
heart's got a pump I gotta breathe my
heart's got a pump people will see you
dilate oh I need to digest my food we
him can't handle thinking about all that
wouldn't be able to function all that's
controlled by the autonomic nervous
system the somatic nervous system it is
a voluntary nervous system it's all the
controls all the things that we are
aware of and are consciously influencing
such as moving our arms and legs and
other parts of the body
we divided the autonomic nervous system
into two systems the sympathetic and the
parasympathetic like two children on
teeter-totter when one's up the other
ones down when one's activated the other
ones deactivated the sympathetic nervous
systems gonna wind you up and use all
your resources empower you to meet a
stressor once a stressor is gone and
sympathetic system is turned off the
parasympathetic in is gonna restore all
your resources they work together to
keep us functioning okay so that's it
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