Sensory Pathways | Touch/Proprioception vs Pain/Temperature

Summary

In this educational video, Dr. Mike explains the process by which sensations from the hand or feet are transmitted to the brain. He details how fine touch receptors send signals up the spinal cord, synapsing at the medulla before crossing to the opposite side and reaching the thalamus, the brain's sorting center. Here, a third neuron relays the touch information to the hand's cortical representation. Pain signals, however, cross immediately upon entering the spinal cord, bypassing the brain stem but still reaching the thalamus, indicating the brain's prioritization of pain awareness. The explanation highlights the complexity of sensory pathways and their implications in spinal cord injuries, such as Brown-Séquard syndrome.

Takeaways

• 👋 Sensation from the hand is initiated by receptors that detect touch and transmit signals to the spinal cord.
• 🔁 The signal for fine touch travels up the same side of the spinal cord from which it originated.
• 🌟 The brain stem, consisting of the midbrain, pons, and medulla, is where the first signal synapses and the second neuron crosses to the opposite side.
• 🔄 The second neuron's crossing over is crucial for the transmission of sensory information to the opposite side of the brain.
• 📮 The thalamus acts as the brain's sorting center, directing sensory information to the appropriate areas of the cortex.
• 🧠 The cortex is responsible for awareness; without signals reaching it, we remain unaware of sensations.
• 🤲 The hand has a large area dedicated in the cortex due to its sensitivity, indicating the brain's detailed mapping of the body.
• 💉 Pain signals from the hand, such as from a pinprick, also travel to the spinal cord but synapse and cross over immediately upon entry.
• 🚫 Pain signals bypass the brain stem but are still routed through the thalamus to the brain's pain processing area.
• 🔄 The distinction between fine touch and pain signals is evident in how they travel up the spinal cord—fine touch on the same side and pain on the opposite.
• 🩺 Understanding these pathways is important for diagnosing conditions like Brown-Séquard syndrome, which involves spinal cord injuries affecting sensory perception differently on each side of the body.

Q & A

What is the purpose of the video by Dr. Mike?

The purpose of the video is to explain how sensations, such as touch and pain, are transmitted from the hand or feet to the brain via the spinal cord.

What receptors are stimulated when someone tickles your hand?

Fine touch receptors in the hand are stimulated, which pick up the gentle soft touch and transmit a signal to the brain.

How does the signal from the hand travel to the brain?

The signal travels down the arm, enters the spinal cord, and goes up the same side of the spinal cord until it reaches the brain stem.

What part of the brain does the signal first synapse with after reaching the brain stem?

The signal first synapses at the medulla, which is part of the brain stem, with another neuron.

What is the role of the thalamus in the process of sensation transmission?

The thalamus acts as the sorting center of the brain, where all information from the body that wants to reach the conscious brain must pass through.

How is the area of the brain dedicated to the hand represented?

The hand is represented by a large area on the cortex of the brain, which is mapped according to the sensitivity of different body parts.

What happens if the signal does not reach the cortex?

If the signal does not reach the cortex, the person will not be aware of the sensation, as the cortex is responsible for conscious awareness.

How does the transmission of pain differ from the transmission of fine touch?

Pain signals synapse at the spinal cord and cross over to the other side immediately upon entering, while fine touch signals go up to the brain stem before crossing over.

Why is it significant that fine touch and pain travel on opposing sides of the spinal cord?

This is significant for understanding the effects of spinal cord injuries, such as hemisection or lesions, which can result in different sensory effects due to damage to one side of the spinal cord.

What is Brown-Séquard syndrome, and how is it related to the script's content?

Brown-Séquard syndrome is a condition resulting from damage to one side of the spinal cord, leading to different sensory and motor effects on the opposite side of the body, which is discussed in the context of the script.

Why does the video mention that pain is always processed by the thalamus?

The video mentions this because pain signals must always reach the thalamus to be sorted and then sent to the appropriate area of the brain, ensuring the person is aware of the painful experience.

Outlines

00:00

🤲 Sensation Transmission from Hand to Brain

Dr. Mike explains the process of how the sensation from a light touch on the hand is transmitted to the brain. When the hand is tickled or touched, receptors in the hand detect this and send a signal up the arm to the spinal cord. The signal travels up the same side of the spinal cord and synapses at the medulla, where it crosses to the opposite side. It then continues to the thalamus, the brain's sorting center, and finally reaches the cortex, which is the brain's map of the body. The cortex's awareness of the touch indicates that the signal has successfully reached its destination.

🔪 Pain Sensation and Its Unique Pathway

The script discusses the difference in the neural pathway for pain sensation compared to fine touch. When the same finger is pricked with a pin, pain receptors are stimulated, and the signal travels down the arm and into the spinal cord. Unlike the fine touch, the pain signal crosses to the opposite side immediately upon entering the spinal cord. It bypasses the brain stem but still travels to the thalamus, which is essential for awareness of pain. The signal is then sent to the brain area responsible for the hand, but instead of a tickle, the sensation is recognized as a prick, highlighting the distinct pathways and awareness for different types of sensations.

Keywords

💡Sensation

Sensation refers to the physical or emotional experience that results from stimulation of the nervous system. In the video, it is the process by which sensory information from the hand or feet is transmitted to the brain. The script describes how a light touch or tickle on the hand stimulates receptors, initiating a sensory signal that travels to the brain via the spinal cord.

💡Receptors

Receptors are specialized cells or nerve endings that detect stimuli such as touch, pressure, or pain. In the context of the video, receptors in the hand pick up on fine touch and transmit signals to the spinal cord. They are crucial for the initial step in the process of sensation transmission.

💡Spinal Cord

The spinal cord is a part of the central nervous system that connects the brain to the rest of the body. It serves as a pathway for sensory signals and motor commands. The script explains how the signal from the hand travels down the arm and enters the spinal cord, which then transmits the signal upwards to the brain.

💡Brain Stem

The brain stem is the lower part of the brain that connects to the spinal cord and is involved in many vital functions, including processing sensory information. The video describes how the signal from the hand synapses at the medulla, part of the brain stem, before crossing to the opposite side and continuing to the thalamus.

💡Medulla Oblongata

The medulla oblongata is a part of the brain stem that plays a critical role in controlling autonomic functions and processing sensory information. In the script, it is the location where the sensory signal from the hand synapses and is passed to another neuron that crosses to the other side of the brain.

💡Thalamus

The thalamus is a deep part of the brain that acts as a relay station for sensory and motor signals. It is referred to in the video as the 'sorting center' of the brain, where all sensory information must pass through before reaching the cortex. The thalamus is essential for the awareness of sensations like touch and pain.

💡Cortex

The cortex is the outer layer of the brain involved in higher cognitive functions and the awareness of sensory information. The script explains that if sensory information reaches the cortex, such as the area mapped for the hand, it results in awareness of the sensation, like being tickled or pricked by a pin.

💡Fine Touch

Fine touch refers to the sensation experienced from gentle or soft contact, such as a light tickle or touch. In the video, the script illustrates how fine touch is transmitted through specific neurons to the brain, resulting in the awareness of the sensation.

💡Pain Receptors

Pain receptors are specialized nerve endings that detect potentially damaging stimuli and send signals to the brain. The script describes how pricking a finger with a pin stimulates pain receptors, which then send a signal to the brain, indicating a potentially harmful event.

💡Synapse

A synapse is the junction between two neurons where information is passed from one to another through the release of neurotransmitters. In the video, the script explains that the sensory signal synapses at various points, such as the medulla and the thalamus, as it travels to the brain.

💡Brown-Séquard Syndrome

Brown-Séquard Syndrome is a condition resulting from damage to one side of the spinal cord, leading to different sensory and motor effects on the opposite side of the body. The script mentions this syndrome to illustrate the importance of the spinal cord's role in transmitting sensory information and the consequences of injury.

Highlights

Sensation from the hand or feet travels to the brain via the spinal cord.

Stimulation of receptors in the hand by fine touch triggers a signal transmission to the brain.

The signal from the hand ascends the same side of the spinal cord it entered.

The brain stem, composed of the midbrain, pons, and medulla, is where the signal first synapses.

The second neuron crosses to the opposite side of the brain at the medulla.

The thalamus acts as the brain's sorting center for sensory information.

All body information must pass through the thalamus to reach consciousness.

The cortex's map of the body allocates more brain area to more sensitive body parts.

The cortex's awareness of sensation is contingent upon signal arrival.

Pain receptors, unlike fine touch, synapse and cross at the spinal cord immediately upon signal entry.

Pain signals bypass the brain stem but must still reach the thalamus for awareness.

Brown-Séquard syndrome results from hemisection or damage to one half of the spinal cord, affecting sensory effects differently.

Fine touch and pain travel on opposing sides of the spinal cord, crucial for understanding spinal cord injuries.

The hand has a large dedicated area in the cortex due to its sensitivity.

Conscious awareness of sensation is directly linked to the cortex's reception of signals.

The three-neuron chain is essential for both fine touch and pain sensation to reach consciousness.

Transcripts

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