Sensory Pathways | Touch/Proprioception vs Pain/Temperature

hi everybody dr mike here in this video

i want to talk to you about how

sensation

goes from for example our hand or our

feet and travels all the way

up to our brain via the spinal cord so

first thing i want to talk about is

the hand so if someone were to tickle

your hand for example or slightly touch

your finger

it's going to stimulate receptors in

your hand

these receptors pick up this fine touch

and what they're going to do is they're

going to transmit a signal

down that hand down the arm

into the spinal cord now what happens

here

is that as soon as it enters the spinal

cord it

transmits this signal straight up

the same side of the spinal cord that it

entered so remember what type of touch

was this

this was fine touch

or a gentle soft touch going up the

spinal cord up up up up

up up up up until it hits our brain stem

now our brain stem is made up of the

midbrain the top most part pons and the

medulla also known as the medulla

oblongata

and at the medulla it synapses with

another neuron what that means is

this neuron's finished it sends or

passes on that signal to the second

neuron

the second neuron at the medulla or the

brain stem

crosses to the other side now once it

crosses it then continues to travel up

up up up up up until it gets to a deep

part of the brain

called the thalamus now these two things

here this is called the thalamus and

it's the sorting center of the brain

anytime information

from the body wants to get to your brain

for you to be aware of it

it must go through the thalamus so it's

like the post office it's the sorting

center

so there's a third neuron at the

thalamus which then gets the information

and it sends that information about fine

touch of the hand

to the part of our cortex of our brain

that is actually mapped

to the hand we have a map of our entire

body

on our brain where our hand is our arm

is our bodies

and the more sensitive that area of the

body is a larger area of the brain is

dedicated to it

okay so our hand has a large area

dedicated to it

now this is the thing this outer layer

here that i've drawn here that's called

the cortex it's only a couple of

millimeters thick

if information gets to the cortex you

become aware of it

if it doesn't get to the cortex you have

no idea that it happened

so if someone's tickling your hand and

you become aware it's because this has

happened

down the arm up the spinal cord the same

side

synapses where the second neuron at the

brain stem crosses

then goes up to the thalamus synapses

with the third neuron

and then goes to the hand three neuron

chain

now this is for fine touch what if

somebody

right on the same finger were to prick

it with a pin

this is going to be pain for example and

it stimulates

pain receptors i'll just draw it onto

this finger for example

and it sends a signal again down the

hand down the arm into the spinal cord

now here's an important difference pain

will synapse here at the spinal cord

when it enters

and cross over the other side the second

neuron is at the spinal cord

crosses to the other side and then moves

up the spinal cord on the opposing side

up up up up

bypasses the brain stem doesn't care

about that but still must go to the

thalamus

why because you're always aware of pain

right when you get

a painful experience or have a painful

experience

you become aware of it because it must

go to the thalamus that then sorts it

with the third neuron again

and throws it to the area of the brain

that deals with the hand but this time

you don't go oh somebody tickled my hand

you go oh

somebody pricked my hand this is

important

find touch and pain travel up the spinal

cord on opposing

sides and this is important when it

comes to spinal cord injury because

if somebody has a hemisection or a

lesion or damage only to

one side or one half of the spinal cord

there's going to be

different sensory effects i'll talk

about that it's called brown cicad

syndrome