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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 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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YouTube Transcript:
Nervous System Organization