0:07 hi welcome to our lecture on the nervous
0:11 system so how do we get information from
0:14 the outside world receive it and pass it
0:16 along to the entire body by the nervous
0:19 system so we talked about how the neuron
0:21 is this tiny information processing
0:24 system well the nervous system is a much
0:28 bigger information processing system so
0:30 we can break it down into two main parts
0:34 the first is the central nervous system
0:36 that's going to be made up of the brain
0:39 the spinal cord and the brain stem we
0:42 can call this our command center this is
0:44 the main part of our nervous system
0:47 we're going to study the brain in the
0:50 brainstem in more detail in the next
0:53 class but right now let's look a little
0:56 bit more at the spinal cord the spinal
0:58 cord controls truck trunk and limb muscles
0:59 muscles
1:02 it carries vital information from the
1:04 rest of the body into and out of the
1:07 brain but it doesn't simply relay
1:10 messages it can also initiate some
1:13 automatic behaviors on its own we call
1:16 these involuntary automatic behaviors
1:22 reflexes so with a reflex a signal
1:24 that's received it's only the
1:26 information is only going to travel as
1:28 far as a spinal cord and then action is
1:30 going to be initiated the spinal cord is
1:33 going to initiate that action and then
1:37 later on the brain will be notified so a
1:39 popular reflex is the nature you ever
1:48 it's a knee-jerk reflex hyperreflexia
1:50 can be demonstrated in the patellar
1:52 reflex in this case the patient has
1:54 suffered a stroke affecting the left
1:57 side of the brain the patellar tendon
2:00 extends from below the patella which is
2:02 right here it's a broad band of tissue
2:05 it's easily palpable if you're not sure
2:07 where it is have the patient
2:09 extend their leg which will cause the
2:12 tendon to shorten and you can start
2:16 directly on the tendon unless reflexes
2:18 are very brisk in fact there are a few
2:20 extra beats of movement which referred
2:23 to as clovis again classic for an upper
2:25 motor neuron syndrome in cases like this
2:27 the reflux can be elicited by simply
2:31 tapping on the tendon often we see the
2:32 same reflex requires very little
2:38 stimulus prepared again with the normal
2:41 side patellar tendon again extending
2:46 from below the patella strike on the
2:52 tendon so that would be a normal reflex
2:55 and certainly image compared with the
2:57 sizes hyperreflexia
3:01 another popular reflex is the one with
3:08 know it feels like they really want to
3:11 hold our hand or thumb or finger like
3:13 because they love us but really it's
3:15 just automatic it's a reflex their brain
3:18 isn't even notified now okay they're
3:20 older maybe they're doing on purpose you
3:21 really want to believe that maybe
3:23 they've decided okay I really want to
3:25 hold your finger you're special it's
3:28 called the grasp reflex stroking the
3:30 palm of a baby's hand causes a baby to
3:33 close his or her finger fingers in a
3:38 grasp this reflex lasts until about five
3:40 or six months of age okay so if they're
3:42 older than five or six months you can
3:43 say that they're holding your fingers
3:48 these are born with a set of reflexes
3:50 critical for survival in the outside
3:52 world some of these reflexes are so
3:55 obvious you might not think to look for
3:57 them such as the breathing reflex or the
4:03 eye blink reflex routing is one of the
4:07 most critical reflexes by touching four
4:09 week old Lily's cheek she'll turn her
4:11 head and open her mouth and preparation
4:17 for nursing once the baby is in contact
4:19 with a breast a bottle or even a finger
4:21 the sucking reflex takes over
4:24 involuntary at first the neonate will
4:26 gradually gained control over sucking
4:31 during the first year placing liquid in
4:33 the mouth will induce the swallowing
4:39 reflex in the first few weeks of life it
4:42 takes all the babies concentration just
4:44 to control these various uncoordinated
4:48 reflexes at this age feeding julia can
4:51 take over an hour after about six weeks
4:55 though julia will be a pro there are
4:57 other reflexes babies are born with that
5:00 we don't completely understand in the
5:03 first two months babies exhibit the
5:05 stepping reflex this is probably a
5:09 precursor to walking watch Lily's toes
5:12 fan out and curl this is the Babinski reflex
5:14 reflex
5:16 which occurs when the bottom of a baby's
5:17 foot is stroked [Music]
5:26 when pressure is placed on the baby's
5:29 hand you can see the grasping reflex at
5:33 work Lily's grasp is strong enough to
5:36 support almost her entire body weight
5:40 for a few seconds at least when startled
5:43 or dropped a baby may respond with the
5:46 Moro reflex the arms fling outward and
5:49 in look as if the baby were groping for
5:52 support two month old Julia doesn't even
5:55 need to be awake to demonstrate this
5:59 reflex so there's all these reflexes and
6:00 some of them go away as we develop but
6:03 others stick around like the nature so
6:06 let's look at an example of a reflex
6:10 action well if you touch a hot pot on a
6:13 stove you're automatically gonna pull
6:15 your hand back the information is only
6:17 gonna go as far as the spinal cord and
6:18 then you're gonna pull your hand back
6:20 and then later on the brain's gonna be
6:24 notified oh I was burned so this is
6:27 necessary it helps with our survival
6:29 back in the day they used to study
6:32 reflexes back when people were
6:35 decapitated and all of a sudden the
6:36 person's head was separated from their
6:38 body their brain was separated from the
6:40 body but their body would be jerking
6:45 around these were reflexes so we could
6:47 see that some movement was possible
6:51 without the brain okay so the spinal
6:53 cord the brain and the brainstem form
6:55 the central nervous system again this is
6:58 our command center and because of this
7:01 we can process information and adapt to
7:02 our environment in ways that no other
7:07 animal can ok the second major part of
7:09 the nervous system is going to be all
7:11 the nerves outside of the brain and the
7:12 spinal cord this is called the
7:16 peripheral nervous system the peripheral
7:19 nervous system links brains but the
7:21 brain in the spinal cord to the body
7:24 sense receptors muscles and glands it's
7:26 made up of the Scout like sensory motor
7:28 neurons that carry messages to and from
7:30 the central nervous system to the
7:33 periphery of the body so as kept connect
7:34 the central nervous system to the rest
7:37 of the body in carrying information back
7:41 and forth it's all the nerves outside of
7:48 remember nerds are groups of neurons
7:51 okay so now let's separate the
7:52 peripheral nervous system into two
7:55 subsystems we're gonna have the somatic
7:57 nervous system and the autonomic nervous
8:00 system let's start with the autonomic
8:03 nervous system this functions like
8:05 autopilot meaning it operates on its own
8:09 it mediates an organism's response
8:12 responses to stress and also various
8:17 kinds of vegetative functions so these
8:19 functions that happen on their own that
8:22 we do not consciously control so it's
8:24 responsible for things like involuntary
8:28 tasks like heart rate digestion pupil
8:35 dilation and breathing and of course we
8:37 said that it mediates the organisms
8:40 responses to stress and the stress
8:42 response can impact these involuntary
8:44 tasks like heart rate digestion pupil
8:50 dilation and breathing so on the other
8:52 side you know we just separated the
8:53 peripheral nervous system into the
8:56 autonomic nervous system and then the
8:58 somatic nervous system look at the
9:00 somatic nervous system in opposition to
9:03 the autonomic nervous system the
9:05 autonomic is like automatic functions on
9:08 autopilot operates on its own the
9:10 somatic nervous system on the other hand
9:12 is also known as the voluntary nervous
9:17 system it's like a two-way street
9:19 first carrying sensory information to
9:21 the brain and spinal cord and then
9:23 carries messages from the central
9:25 nervous system to the skeletal muscles
9:28 it's going to be the things it controls
9:31 all the things that we are aware of and
9:34 can consciously influence such as moving
9:37 our arms and legs and other parts of our
9:41 body it's also associated with reflexes
9:43 something interesting to point out is
9:46 soma we mentioned this once before so
9:50 means body so how I remember this is it
9:55 has to do with us moving our body moving
9:56 our arms and legs and other parts of the
9:59 body and is connecting the central
10:02 nervous system to the rest of the body
10:05 okay back to the autonomic nervous
10:08 system we're going to separate that one
10:12 into two systems so we've gone central
10:14 nervous system peripheral nervous system
10:16 peripheral nervous system gets separated
10:20 to the somatic and autonomic now we're
10:22 looking at the autonomic and we're gonna
10:24 separate that into two the autonomic
10:27 said multiple times has to do with
10:29 mediating on organisms responses to
10:32 stress so let's look at these two next
10:34 two subsystems one's called the
10:36 sympathetic nervous system and the
10:38 others the parasympathetic nervous
10:41 system these two I like these systems
10:43 because they function like children on a
10:46 teeter totter when one is up the other
10:51 is down when one is up the other is down
10:54 they function in opposition to each
10:55 other but they're essentially
10:59 complementary in nature you see they're
11:01 linked even though they're in opposition
11:04 and they complement each other now must
11:05 have each other's backs
11:09 so the sympathetic nervous system that's
11:12 the nervous system that winds you up
11:15 this system when you're stressed this
11:17 system kicks in to mobilize bodily
11:21 resources to respond to the stressor it
11:39 when you're stressed it kicks in to
11:41 mobilize bodily resources to respond to
11:44 the stressor it's going to organize the
11:49 body to meet emergencies this emergency
11:51 response is normally called the most you
11:52 all have heard this flight-or-fight
11:54 we're going to talk a lot more about
11:56 fight-or-flight when we talk about
11:58 stress we're going to talk about how
12:01 there's tender befriend or fight or
12:04 flight or freeze the sympathetic nervous
12:06 system is concerned with getting more
12:08 oxygenated blood and energy to the
12:12 skeletal muscles it's going to shut down
12:15 trivial functions is going to stop
12:19 digestive and eliminative processes
12:21 these trivial functions that we don't
12:24 need in the moment for survival and it's
12:27 going to take all the energy and blast
12:30 it at the things that matter so send all
12:32 the energy to the heart to the brain to
12:37 it's an increased heart rate is going to
12:40 increase respiration it's going to
12:43 increase blood pressure it's going to
12:49 release hormones interestingly the
12:51 nervous system directs your endocrine
12:52 system but you're entered kisum
12:54 endocrine system directs the nervous
12:57 system it's this weird little circle and
12:59 we'll talk about that more later as well
13:02 all of this this bodily response is
13:04 supposed to allow us to cope with the
13:08 stress to face the stressor to either
13:12 fight or flee it's our body empowering
13:14 itself now something interesting is
13:16 nowadays the sympathetic nervous system
13:19 is activated by all kinds of things
13:22 things that are not really putting us in
13:27 mortal danger less life less threatening
13:29 events such as traffic jams or
13:33 activating the system so the question is
13:34 well what's happening when the system is
13:37 becoming activated all the time and
13:40 we'll talk about that more later the
13:42 other child on the child on the teeter-totter
13:43 teeter-totter
13:46 is going to be the parasympathetic
13:49 nervous system this winds you down
13:52 so one the sympathetic nervous systems
13:56 kicked in it winds you up after the
13:58 stressor goes away the parasympathetic
14:00 nervous system is supposed to go active
14:01 and the sympathetic nervous system is
14:06 supposed to deactivate so the
14:08 sympathetic nervous system activates
14:10 winds you up you meet the stressor it
14:12 shuts down and the parasympathetic
14:15 nervous system activates and this whines
14:18 you down it's responsible for calm in
14:22 our bodies and conserving energy it
14:26 restores our bodily resources when the
14:28 sympathetic nervous system winds you up
14:31 it depletes all your bodily resources it
14:33 uses all your energy it takes everything
14:36 in your energy tank and it just uses it
14:39 all it burns all your gas the
14:43 parasympathetic system refills you
14:47 refills your energy refills your gas
14:51 restore is your bodily resources now the
14:55 sympathetic nervous system is very quick
14:59 in its onset very rapid onset and offset
15:03 turns on turns off and it acts like a
15:06 unit when you're stressed the
15:08 parasympathetic on the other hand is
15:10 relatively slow when it comes to its
15:14 onset it doesn't just turn on it slowly
15:18 turns on and it acts discriminately only
15:20 where needed so maybe you've been
15:22 exposed to some kind of acute stressor
15:25 and maybe when the stressor goes away
15:28 you feel like you've crashed a little
15:31 bit well this makes sense you use all
15:34 your resources all your energy and it's
15:35 taking some time for that
15:38 parasympathetic system to engage and
15:41 it's taking time to restore those bodily
15:44 resources so you're going to feel like
15:47 you've crashed okay so that's a
15:50 breakdown of the nervous system next
15:52 class we'll be looking at the central
15:54 nervous system focusing on the brain and
15:57 the brain stem but this class we looked
16:01 at the peripheral nervous system so
16:03 remember that's all the nerves outside
16:03 of the
16:05 brain in the spinal cord it's connecting
16:07 the central nervous system to the rest
16:09 of the body and the rest of the body to
16:12 the central nervous system we we divided
16:13 the peripheral nervous system into two
16:15 categories the somatic nervous system
16:17 and the autonomic nervous system the
16:21 autonomic says vegetative functions it's
16:23 functioning on its own autopilot we
16:25 don't have to think all the time
16:27 I gotta breathe I gotta breathe oh my
16:29 heart's got a pump I gotta breathe my
16:30 heart's got a pump I gotta breathe my
16:31 heart's got a pump people will see you
16:35 dilate oh I need to digest my food we
16:37 him can't handle thinking about all that
16:40 wouldn't be able to function all that's
16:41 controlled by the autonomic nervous
16:44 system the somatic nervous system it is
16:46 a voluntary nervous system it's all the
16:48 controls all the things that we are
16:50 aware of and are consciously influencing
16:52 such as moving our arms and legs and
16:53 other parts of the body
16:55 we divided the autonomic nervous system
16:56 into two systems the sympathetic and the
16:58 parasympathetic like two children on
17:01 teeter-totter when one's up the other
17:03 ones down when one's activated the other
17:05 ones deactivated the sympathetic nervous
17:07 systems gonna wind you up and use all
17:08 your resources empower you to meet a
17:11 stressor once a stressor is gone and
17:12 sympathetic system is turned off the
17:15 parasympathetic in is gonna restore all
17:17 your resources they work together to
17:20 keep us functioning okay so that's it
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