Voiceover: In this video, we are going to talk
about somatosensation. If we have someone
walking down the street, he is receiving all kinds of information from the world around him. He's receiving different
types of sensations, so different types of sensations. He's also receiving information about different intensities of these sensations, so is it really hot outside,
is it kind of hot outside? He's receiving information about the intensity of the different sensations. He's also receiving
information about the timing. When does he set his
foot down on the ground? When does he lift the foot off the ground? If somebody drives by him and throws a hamburger at him, when
does the hamburger hit him, when does the hamburger stop hitting him? There's also information about timing that he's receiving from
the world around him. Finally, he's also receiving
information about where in his body the sense is originating. If a bird comes by and pecks his arm, the brain needs to realize,
there's something going on on my arm, so there's also location. Information about location
needs to be addressed. What are the different
types of senses that he can have, as he's walking down the street? Of course, we need to
get information about the temperature, so is
it really cold outside, is it really hot outside? The sensation of temperature, is something known as thermoception. Thermoception He also needs to get
information about pressure. When does he set his
foot down on the ground? If somebody came by, like we said, and threw a hamburger at him, how hard did the hamburger hit him? We need to get information about pressure. This is also known as mechanoception. Mechanoception What else does he need to know? He also needs to get
information about pain. If the bird did come
down and peck his arm, it would be a little painful, so he needs to get information about pain. Pain is known as nociception. Finally, he needs to get information about where his body is in space,
so as he's walking along, is he really close to
the sidewalk, is he close to someone else? He needs to get information
about his body's location in space. This is
known as proprioception. These are the different
types of information that he needs to acquire
from the world around him, through his body surface. He also needs to know
something about the intensity of the various stimuli. If it's really, really hot
outside, it would be really nice to know that, versus if
it's kind of cold outside. The way intensity is encoded in the body, is by how quickly the neurons fire. There are different neurons that are sensitive to temperature,
there are different neurons that are sensitive to pressure, so if it's really cold
outside, then the neurons might not fire that much.
They might fire a few times. If it's kind of cold
outside, it's not that hot, they'll just fire a few times
over the course of a minute. If it's really hot outside, they might fire a whole bunch of times. So how quickly they fire,
is how intensity is coded. Another thing that we need to acquire from our environment is the
timing, so if a bird were to come down, so
we've got a little bird coming down, he's going to peck this man. He's coming down, he's flying,
he's got a straight shot for the arm, and he pecks him right there. The guy actually needs to know, okay, when does the pecking start? When does the pecking stop? In order for a neuron to encode timing, there are three different
ways he can do that. There's a neuron that, the
entire time the bird is pecking him, it will consistently
fire action potentials. This type of neuron is non-adapting. It's non-adapting because
you can look at the action potentials and
there is an equal amount of space between each
successive action potential. Basically, the entire
time some sort of stimulus is being applied, there is
no change in the firing rate. Another type of neuron, will start
firing really, really quickly, so there's a whole bunch
of action potentials, and then over time, it will slow down. The space between the
action potentials increases. As you can see here, it
starts firing really fast at the beginning of the
stimulus, and then it slows down, so the spacing actually increases. This is known as a slow adapting neuron. It's slow adapting
because it's really slow to adapt to the change in the stimulus. Another type of neuron
is going to fire really quickly, as soon as the stimulus starts, and then it's going to stop
firing and then it will fire again when the stimulus stops. This is known as a fast adapting
neuron, so fast adapting. Okay, What's the final
piece of information that we need to get from the world around us? If this bird is coming in to peck him, he needs to know that
it is pecking his arm. There needs to be some
sort of way that the brain is able to register that, okay it's my arm that's being pecked, not my leg. In order for the brain to do that, it relies on things called dermatomes. If we were to draw a person here, there is the torso, he's got his arm, he's got his other arm,
and he's got his legs. Each little part of the
body is innervated by a particular nerve, and that
nerve goes up to the brain. If a bird is pecking his arm, we know okay, this arm is being pecked, so this arm will send
a nerve to the brain, and the brain is able to figure out, okay it's this arm that's being pecked. All right, so I cleaned that up a bit. Let's imagine that we've
got somebody flying in from the sky, and
he's headed right at our innocent bystander
walking down the street. This man just happens
to have a red cape and people call him a super hero, but he's headed right for this guy. As this guy is coming in,
he's going to crash into this poor fellow walking down the street. What types of receptors would
be activated in this case? Temperature? No, not really. There's no change in temperature. Pressure? Definitely. This
guy is just bombarding right into this innocent
bystander, so he's going to feel a lot of pressure
from the super hero's body. Pain? You betcha. He's going
to be in a lot of pain. This guys is coming 100 miles per hour, headed straight for this guy. He's probably going to feel a little pain. He's probably also going to
get knocked off his feet, so he's going to feel
a change in position. These three different senses will go off. Let's look at intensity. How
intense is this interaction? It looks pretty intense. You've got a super hero
coming in right at you. His neurons, all these
three different types of neurons, are going to
fire really, really quickly. Let's look at timing.
We're going to definitely have some non-adapting neurons firing, because the entire time
this guy, this super hero, is in contact with the innocent bystander, there's going to be different
neurons firing steadily just so that it lets his brain know, hey, there's something going on here. There are also going to
be fast-adapting neurons that will fire as soon
as the super hero hits the innocent bystander, and then as soon as he gets off of him, so there's going to be
fast-adapting neurons firing. There will also be
slow-adapting neurons firing the entire time the super
hero and the innocent bystander are making contact. What about location? The superhero is headed
straight for this guy's torso. The entire torso is going to be lit up, maybe some of his arms
are going to be lit up. Basically, there are going to
be nerves that innervate these three different parts of the
body, and they're all going to be sending information to the brain saying, hey we've got a little bit
of pain, some pressure, and there's a change in position here.