Full transcript
0:00This is the first video over chapter 12. We are going over nervous tissue and
0:07introduce you to the basics of the nervous system. So the nervous system is
0:16one of our communication systems. It is the foundation of our personality,
0:21behavior, consciousness, and neurobiology kind of combines behavioral with
0:29psychology, sociology and life sciences. Both the endocrine and the
0:37nervous system are controlling our body in different ways. The endocrine uses
0:44chemical messengers - hormones. They are secreted into the blood and travel to
0:49the target cells. The target cells are going to have the receptors for those
0:56hormones. The nervous system, on the other hand, uses electrical changes the
1:02chemical means that they're talking about, here, are the neurotransmitters and,
1:07again, those neurotransmitters need receptors - and we'll talk about that a
1:13little bit later on. When we look at the nervous system, we've got three basic steps.
1:18First of all you are going to receive that information, any stimuli
1:25to the body, any changes to the body. You are going to process that information
1:31and kind of compare it to your memory, what's going on, figure out what are you
1:37going to do, and then you issue your commands. Now with the nervous system,
1:42mostly where you are going out to, are muscles and glands. If we were to look at
1:50a basic pathway for the nervous system, we start with a receptor - that's what
1:56detects a stimulus. Then that is sent on with a sensory neuron. You can also
2:03call it an afferent neuron (that is just a general word that means going into
2:09something) and you may have three of these in
2:13row. That goes into your central nervous system - that's the integrating
2:19center. This is where you figure out what you are going to do and then you send it
2:25out of the central nervous system on a motor neuron, again you may have more
2:30than one, and this is an efferent neuron (that is a general word meaning coming out of
2:37something) and that goes to an effector. An effector is a structure - in this case
2:45it is, mostly, going to be either a muscle or a gland. Now there are some other
2:51organs that your nervous system may go to but most of it is muscles or glands.
2:59Now let's look at an overview of the nervous system. So we have two major
3:06subdivisions based on anatomy. We have the central nervous system and that is
3:11only the brain and the spinal cord, and those are enclosed by the meninges. The
3:18peripheral nervous system is everything else. So it is all of the nerves coming
3:25out of your brain and out of your spinal cord and the ganglia. So to go over basic
3:34terminology, a nerve is a bundle of axons. These are the nerve fibers wrapped up in
3:41connective tissue. You have nerves or axons coming out of the spinal cord
3:48those are spinal nerves and you have it out of your brain those are the cranial
3:53nerves. A ganglion is where the neuron cell bodies are located. So
4:02we're looking in the peripheral nervous system here. Now let's go and look a
4:08little bit closer - just on the peripheral nervous system - and there's two parts to
4:14it. We have this sensory part - this is the part of the peripheral nervous system
4:20that goes into your central nervous system.
4:23We have somatic fibers that are coming from our skin so it has the sensations from
4:29the skin like touch and pain and tickle and itch; also from our skeletal muscles
4:37and joints. This is going to feed information to our central nervous
4:42system. Visceral fibers are coming from the internal organs like for instance
4:48from your heart, your lungs, your bladder could be talking about "okay, I'm full. I need to
4:55empty", or I might have a stomach ache. That information is going to go go into your
5:01central nervous system on a visceral fiber. Your central nervous system then
5:06figures out what to do and it comes out on motor.
5:13We have two systems with this - we have the somatic nervous system.
5:19Those are somatic fibers; this is strictly nerves going to skeletal
5:25muscles. So you went over that in chapter 11.
5:31You have visceral fibers that are going to smooth muscles, or cardiac muscles of
5:39your heart, or going to a gland either an endocrine or an exocrine gland.
5:45This is part of the autonomic nervous system. So let's look at this motor part
5:53a little bit closer and so you see that
5:59comparing the somatic with the autonomic, the somatic is voluntary.
6:04These are the motor neurons going to skeletal muscles.
6:07You only have one motor neuron that is
6:14used, that is coming out of either your brain or out of your spinal cord, that goes
6:19to a skeletal muscle. Somatic reflexes are involuntary muscle contractions and
6:27the type of muscle we're looking at is skeletal muscle. Now let's look at the
6:34autonomic nervous system. We are looking at motor neurons that are
6:42going to smooth muscle, or it's going to your heart muscle (the cardiac muscle), or
6:46going to endocrine glands or to exocrine glands. In this case, there are two motor
6:53neurons in a row. We will talk more about this in chapter 15 with the autonomic
7:02nervous system. An autonomic or visceral reflexes is an involuntary response that
7:10is using smooth muscle, cardiac muscle, or a gland. So with the autonomic nervous
7:19system - just that motor division here - we have nerves that are going to our organs
7:29that are part of the sympathetic division, so they are there to arouse the
7:35body for action. It's getting ready for that action - so that's your sympathetic
7:42division. You may also have nerves going to the same organ, part of the
7:48parasympathetic division, that does the opposite effect. It has more of a calming effect.
7:55So in the sympathetic division, those neurons are coming from your spinal cord and
8:03specifically from the thoracic and lumbar region of your spinal cord.
8:10Sympathetic is called fight-or-flight responses and your book
8:16also calls it "E" responses - that would be emergency, excitement, exercise and (a
8:25very strange one) embarrassment. Now let's think about this - you're in an
8:30emergency situation. Let's say you almost were in a car wreck - so think about what
8:37your heart is doing. You are going to have motor neurons going to your heart. And so
8:42you already know in an emergency, your heart rate goes up, your breathing rate
8:48goes up, the motor neurons that go to the
8:53pupil of your eye are going to dilate the pupils of your eye. So these are all
8:58things that are getting you ready for an emergency - a stressful situation. Now what
9:05should be in charge is parasympathetic. So it tends to go to almost the same
9:13organs as the sympathetic, but it has the opposite effect. So these neurons are
9:20coming from the brain (cranial) and at the very bottom of your spinal cord, sacrum.
9:26So we call these "resting and digesting" responses and basically this should be
9:36in charge this is where your heart rate goes down into a more calming effect
9:45your breathing rate goes down your pupils of your eyes are more constricted
9:53sludd is an acronym that we use a lot to give you an idea of what would be in
10:02parasympathetic control so sludd stands for salivation so normal salivation is
10:09parasympathetic if you are in a stressful situation like for instance
10:14you have to give a speech that you didn't know you had to give a speech
10:18kind of shuts down salivation your mouth makes more mucus it becomes it feels
10:26more dry lacrimation is tear production normal urination is parasympathetic
10:33normal digestion is parasympathetic defecation is parasympathetic so when we
10:41look at this little diagram here only that center part that is your brain and
10:46spinal cord everything else is the peripheral nervous system so the sensory
10:53somatic and visceral going in the motor coming out and when we look at the
10:58autonomic nervous system you have two divisions
11:02and this kind of shows you on this diagram you have the brain and the
11:06spinal cord that is your central nervous system everything else coming out of it
11:12that is the peripheral this next part is looking at neurons and so when we look
11:25at the histology of Nertz nerve tissue we've got two types of cells the neurons
11:32are the ones that have the electrical signal they transmit that they're the
11:37functional unit of your nervous system the supporting cells are the neuron eula
11:43or glial cells and so we'll talk about those a little bit later now let's just
11:49focus on the neurons what are the properties of neurons first of all they
11:54can respond to the environment okay these changes are called stimuli
11:59and they can produce an electrical signal and we're going to be looking at
12:04these electrical signals probably on the third video just concentrate on these
12:10electrical signals now second property is conductivity you're going to send
12:17that electrical signal down that cell and send it to other cells and then
12:25secretion we are looking at making neurotransmitters and these chemical
12:31neurotransmitters will influence the next cell it can actually cause another
12:37electrical signal or it can prevent an electrical signal when we look at the
12:45functional classes so what they do we divide them up there is sensory or
12:52afferent neurons they're the ones that detect the stimuli they transmit them
12:58information to the CNS inter neurons or Association neurons this is what's in
13:04your brain and your spinal cord and so this is what makes the decision this is
13:09your memory this is what figures out what what you need to do
13:14so that's about 90% of your neurons are inter neurons motor neurons they're
13:21coming out of your central nervous system you're sending a message to your
13:27muscles or glands remember those are your effectors now you cannot change
13:34your functional class if you were a sensory neuron you cannot change and
13:41become an inter neuron or a motor neuron we look at the peripheral nervous system
13:47here on the left hand side sensory you go into the central nervous system
13:53there's your inter neuron you come out on a motor neuron in this case it's
13:58going to skeletal muscle let's look at the structure of a neuron first one is
14:05your soma the soma is the cell body here in the center very very small you're
14:12going to have a nucleus with the nucleolus the cytoplasm has lots of
14:18things it has mitochondria because you have to have lots of ATP
14:23you have lysosomes because you produce waste products that must be broken down
14:29Golgi complex you have a very extensive rough ER
14:36so remember rough ER has ribosomes on the outside of the endoplasmic reticulum
14:42and you're producing proteins the cytoskeleton in here kind of puts the
14:50rough ER in compartments and we call those they're very dark staining column
14:57missile bodies now what is not present are centrioles no centrioles because
15:07this does not do mitosis once you're an adult the neurons you've got are the
15:14neurons you'll have for life you do not get cell division of your neurons so
15:24this is where the extreme longevity comes in
15:28that means they live a very long time now off of this cell body you have
15:37dendrites so this is your plasma membrane being pulled out and held in
15:42that kind of formation with the cytoskeleton these receive signals from
15:52other neurons so the signal the electric signal it will go towards the cell body
15:58the more dendrites you've got the more information you can receive the axon is
16:06the longest part so the soma the cell body and the dendrites are microscopic
16:13but this axon can be up to 3 feet long it looks very much like a tiny little
16:21thread long but very very very narrow and this is why it's called the fiber so
16:30the nerve fiber is talking about the axon and in this case when we look at
16:37the axon you start up at this hillock right here next to the cell body this is
16:43the trigger zone and the signals go away from the cell body you only have one or
16:50you may have none now you may have these little collaterals coming off of it if
16:57we look at your axon the cell membrane the plasma membrane of the axon is
17:03called the EXO lemma and you'll notice that it is wrapped with a myelin sheath
17:10that myelin sheath is an insulation that makes the electrical signal go faster
17:18much faster at the end of the axon you have these terminal axon terminals
17:27sometimes they're called synaptic knobs or terminal buttons
17:32and that is where you stored the neurotransmitter now the
17:36neurotransmitter was made up here in the cell body by that rough ER the Nissel
17:43bodies and it's transported down the axon and stored at the very end of the
17:50axon if we looked at the different types of neurons based on anatomy
18:00we have multipolar what that means is off of your cell body you have one axon
18:09and you have multiple dendrites this is the most common type of neuron in your
18:16central nervous system bipolar you have just one stalk coming off for your
18:25dendrite even though the dendrite could be very very branched only one stock
18:31coming off the cell body and then of course your one axon unipolar this is
18:38where the cell body kind of moves away and then the axon and dendrite kind of
18:45join together that's a unipolar an axon ik means there's no axon so you have a
18:54few neurons that are like this if you look at my drawing of a neuron here this
19:05is very very small microscopic this is going to be your cell body or soma with
19:11the dendrites so I'm showing a multipolar neuron and then starting here
19:18at that trigger zone the hillock that's your axon remember the axon can
19:23be very very long it can be up to 3 feet long this is the part that we call the
19:29fiber at the end of the axon is where we're storing the neurotransmitters
19:35remember the neurotransmitter was made up in the cell body now typically we
19:41don't see just one single neuron we will see a collection of neurons and
19:48so when we see where the cell bodies are all grouped together we can see this in
19:56the central nervous system and in the peripheral nervous system they have
20:00different names in the peripheral nervous system
20:04this collection of cell bodies is called a ganglion in the central nervous system
20:10we call it a nucleus so in this case you can see that the word nucleus is used in
20:16a different way you this is now the third way we've used the word nucleus we
20:22talked about the nucleus of an atom we talked about the nucleus of a cell and
20:26now the nucleus is a collection of cell bodies in your central nervous system
20:33now here on your nerve the fibers here the axons so this collection of axons
20:41here have different names whether you're in the peripheral nervous system or the
20:46central nervous system it is called a nerve in the peripheral nervous system
20:52so each individual axon will be covered with connective tissue and then this can
21:01be grouped as a fascicle and then that is covered with a connective tissue and
21:05then the entire thing can be covered with the connective tissue again you can
21:10see the same sort of thing on a track so in your spinal cord in your brain a
21:19group of these axons are called a track
21:27when we look at neurons you'll see one going to another actually it will go to
21:35many other ones okay so they're all interconnected this is a very simple
21:41diagram where one is going to another you notice that it does not touch each
21:48other that gap there is called a synapse in that synapses where you're going to
21:54put your neurotransmitter it's going to float across to the next neuron or it
22:03could be another structure so this could be a neuron here going to skeletal
22:10muscle or smooth muscle or gland so if we looked at two neurons this is called
22:18the presynaptic neuron because it's before the synapse this is the
22:23postsynaptic neuron the presynaptic neuron is what releases the
22:28neurotransmitter in the synapse the postsynaptic neuron has the receptors
22:33for that neurotransmitter and depending on the neurotransmitter or depending on
22:39the receptor you can either produce an electrical signal that goes down to the
22:46end of your axon or you can prevent an electrical signal from going down now
22:56we've already talked about a little bit about transport you are making your
23:01proteins up into the cell body and so the examples will be the
23:06neurotransmitters you also need to have enzymes you have
23:11to have gates and protein gates that put on the cell membrane and so that's made
23:19into the cell membrane you got to transport it down to the axon into the
23:23terminal and so you have a two-way passage you use microtubules and then
23:31you have these little motor proteins that will carry the proteins you made in
23:37the soma and either carry it down to the end of the axon or carry proteins back
23:45up to the cell body if we're going down the axon to the end
23:51that's anterior gray transport retrograde is where you go from the axon
23:57back up to the cell body
24:02all right so we've talked a little bit about the nervous system the the
24:06fundamental parts of it and we talked about the neurons the next very short
24:16video is going to talk about our support cells