Somatosensory homunculus | Processing the Environment | MCAT | Khan Academy


If you’ve ever used a
map on your cell phone to get you from
place A to place B, you’re familiar with the
idea that a map is simply a representation of
some sort of area that actually exists
in the real world. So a map on your cell
phone is a digital map of an actual place
somewhere in the world. Similar to this
digital road map, your brain also has
a map of your body. And this map is
something known as the somatosensory homunculus. The somatosensory
homunculus is basically a map of your body
in your brain. And let me go into this because
it is a little bit confusing conceptually at first. So what I’ve drawn over here
is a picture of the brain. Let’s just focus in on
this pink area over here. This pink area is something
known as the cortex. And this region that I
shaded in in orange over here is a specialized
part of your brain that receives sensory input
from your entire body. So whenever you feel
pain or whenever you feel some sort of heat
anywhere in your body, all this information is actually
sent through the spinal cord into the brain. And it all ends up over here
in this one part of the cortex. And this part of the cortex
is known as the sensory strip. So let me just clean
this up a little bit. So if we were to actually
take a cross-sectional look at the sensory strip, so if we
cut the brain just right down the middle and kind of looked at
it this way, what we would see would be this large orange
structure that I drew here. So this orange
structure is basically just the sensory strip. And we’re looking at it
this way if we cut it right down the middle. And so as I mentioned
before, this sensory strip contains a somatosensory
homunculus. And the somatosensory
homunculus is basically a map of the body in the brain. And what I mean by this
is that information that comes from your
hand to the brain will all end up in one
part of the sensory strip. So information from your finger
will actually come over here. Information from these
fingers will come over here. Information from the palm of
your hand will come over here. Information from your
wrist will actually end up over here in
the sensory strip. And similarly, if we
were getting information from your foot, the
information from your foot would all synapse over here
in this part of the cortex. And information from your
toes would synapse over here. So you get the idea. Basically, information from
various parts of the body will come into the brain,
hit the sensory strip, and it will always go to one
part of that sensory strip. So this is your face over here. So this would be the face. And so information from the
lips would come right here, information from the eyes
would go over here, and so on. So basically, the
sensory strip always receives information from
different parts of the body. And that information
will always go to one part of
the sensory strip. So let me again clean
this up a little. If this is still a
little confusing, let me try explaining
it a different way. So let’s imagine that there was
a brain tumor right over here. This brain tumor would
kind of look like this. It would basically be in
this region of the brain. And so in order to figure out
what part of the brain is tumor and what part of
the brain is normal, neurosurgeons can actually
go in with an electrode and touch different
parts of the cortex. So they can actually
come in, and touch this part of the cortex, and
touch this part of the cortex. And this electrode will
actually cause the cells that it touches to stimulate. And so in some
cases, the surgery can actually be conducted
on patients that are awake. And so if a surgeon touches
this part of the cortex, patients can actually
say, oh, I feel as if somebody is
touching my wrist. And if the surgeon touches
this part of the cortex, people might say,
oh, I feel somebody touching my forehead or my eye. So depending on what
part of the cortex the surgeon places
his electrode, the patient will get a
sensation of some part of his or her body
being touched. The reason that
surgeons do this is to make sure that they
aren’t removing parts of the cortex that are
involved in sensation, because if the surgeon were to
remove this part of the cortex, the patient would no longer
have any feeling in the wrist or in the forearm. So they need to make
sure that the part of the cortex that
they’re removing is not involved in sensation. Otherwise, the patient would
actually lose sensation. Similarly, if the
surgeon removed this part of the
cortex, the patient would lose sensation in
the lips because that is part of the cortex actually
receives input from the lips. So let me again clean this up
just to go over everything one last time. So the sensory homunculus
basically maps out the body in the brain. So as information
comes to the brain from different parts of the
body, information from the hand will all synapse in this
region of the cortex. Information from the face
will synapse in this region. Information from the feet
will synapse in this region. And so what this
effectively creates is a topological map
of the entire body in this strip of cortex. And this topological
representation of the body in the
cortex is what’s known as the
somatosensory homunculus.

12 thoughts on “Somatosensory homunculus | Processing the Environment | MCAT | Khan Academy

  1. Thanks for the great video! Just a comment, please practice using non-gendered language when referring to occupations (e.g. surgeons). Referring to surgeons using male pronouns is odd unless you're referring to a specific person and it helps to perpetuate stereotypes that certain occupations are only open to one gender. Language plays an important role in modifying culture and encouraging inclusivity. Thank you 🙂

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