Sensory Pathways MADE EASY!!

Summary

This educational video script delves into the complex but crucial dorsal column medial lemniscus pathway, responsible for conveying fine touch, two-point discrimination, and proprioception to our sensory cortex. It explains the three-neuron chain of this ascending sensory pathway, contrasting it with the spinothalamic pain and temperature pathway. The script highlights the importance of understanding these pathways for diagnosing spinal cord injuries, emphasizing the differences in neural transmission and the implications for sensation below the level of injury.

Takeaways

• 🧠 The dorsal column medial lemniscus pathway is crucial for our ability to sense fine touch, two-point discrimination, and proprioception at the sensory cortex.
• 🌐 This pathway is an ascending sensory pathway, meaning it carries sensory information up the spinal cord towards the brain.
• 🔁 All ascending sensory pathways to the brain involve a three-neuron chain, starting with a sensory neuron that detects the stimulus.
• 📍 The somatosensory cortex, located in the postcentral gyrus behind the central sulcus, is where sensory information is processed.
• 🔄 The first neuron in the pathway synapses with the second neuron in the spinal cord, and the second neuron decussates, or crosses over, to the opposite side of the body.
• 🚀 The second neuron then ascends to the thalamus, where it synapses with the third neuron, which carries the information to the somatosensory cortex.
• 🌡️ The pain pathway is different from the dorsal column medial lemniscus pathway; it involves the spinothalamic tract and synapses at the level of the spinal cord before decussating.
• ⏫ The pain and temperature pathway bypasses the brainstem and goes directly to the thalamus, unlike the fine touch pathway which synapses in the medulla before reaching the thalamus.
• 🤕 In cases of spinal cord injury, the type of sensation affected can help determine the location and extent of the injury, as different pathways are affected differently.
• 🧩 The somatosensory cortex has a topographical map of the body, which is important for localized sensory perception.
• 🔍 Testing for spinal injury often involves stimulating different sensory pathways to assess which sensations are affected and to identify the side and level of injury.

Q & A

What is the dorsal column medial lemniscus pathway responsible for?

The dorsal column medial lemniscus pathway is responsible for the sensation of fine touch, two-point discrimination, and proprioception, which is the awareness of one's body position in space.

How many neurons are involved in ascending sensory pathways to the brain?

All ascending sensory pathways to the brain involve a three-neuron chain.

Where is the somatosensory cortex located in the brain?

The somatosensory cortex is located in the postcentral gyrus, just behind the central sulcus in the brain.

What is the difference between the dorsal column medial lemniscus pathway and the pain pathway in terms of how they ascend the spinal cord?

The dorsal column medial lemniscus pathway ascends on the same side of the spinal cord where it enters, synapses at the medulla, and then crosses to the opposite side. The pain pathway, however, crosses over to the opposite side immediately upon entering the spinal cord and ascends contralaterally without synapsing at the medulla.

What is the term used for the crossing of neurons in the spinal cord?

The term used for the crossing of neurons in the spinal cord is decussation.

What is the role of the thalamus in sensory pathways?

The thalamus acts as a relay station for all sensory information before it reaches the cortex. It is often referred to as the gateway to the cortex.

How does the body's topographical map on the somatosensory cortex relate to the sensations we feel?

The topographical map on the somatosensory cortex represents different parts of the body, indicating which areas of the body are associated with specific sensory inputs.

What is the name of the pathway responsible for pain and temperature sensations?

The pathway responsible for pain and temperature sensations is called the spinothalamic pathway.

Why is it important to understand the difference between the dorsal column medial lemniscus pathway and the pain pathway in terms of spinal cord injuries?

Understanding the difference is important because it helps in diagnosing spinal cord injuries, as damage to one side of the spinal cord can affect different sensations on the contralateral side below the level of injury.

How can medical professionals test for spinal cord injuries in the context of the different sensory pathways?

Medical professionals can test for spinal cord injuries by stimulating different sensory pathways, such as using fine touch or temperature stimuli, to determine if the patient can feel sensations on both sides of the body below the level of injury.

What is the significance of the ipsilateral and contralateral sides in relation to spinal cord injuries?

The significance lies in the fact that damage to one side of the spinal cord can result in the loss of pain and temperature sensation on the contralateral side below the level of injury, while fine touch may still be felt on that side but not on the ipsilateral side below the injury.

Outlines

00:00

🧠 Sensory Pathway for Fine Touch and Proprioception

This paragraph introduces the dorsal column medial lemniscus pathway, which is crucial for the perception of fine touch, two-point discrimination, and proprioception. It explains that this sensory pathway is an ascending pathway involving a three-neuron chain that carries sensory information from the body to the brain. The first neuron synapses in the spinal cord, the second neuron crosses to the opposite side at the medulla and synapses again, and the third neuron travels to the somatosensory cortex in the postcentral gyrus. The paragraph also contrasts this pathway with the pain pathway and emphasizes the importance of understanding these pathways for diagnosing spinal cord injuries.

05:04

🔍 Comparing Sensory Pathways: Fine Touch vs. Pain

The second paragraph delves into the differences between the fine touch/proprioception pathway and the pain pathway. It describes the spinothalamic pathway, which is responsible for pain and temperature sensations, and highlights its distinct route through the spinal cord. Unlike the fine touch pathway, the pain pathway crosses to the opposite side immediately upon entering the spinal cord and bypasses the brainstem, going directly to the thalamus. The explanation includes the implications of spinal cord injuries on sensory perception, such as the ability to feel touch on one side of the body while losing pain and temperature sensation on the other, depending on the location and extent of the injury. This understanding is critical for medical professionals assessing spinal cord damage.

10:05

🤕 Implications of Spinal Cord Injury on Sensory Perception

The final paragraph, although incomplete, begins to discuss the practical implications of spinal cord injuries on sensory perception. It suggests that the knowledge of these pathways is essential for medical diagnosis and treatment, particularly in distinguishing between injuries on different sides of the body. The paragraph likely would have continued to explain how testing for different sensory responses can indicate the presence and severity of spinal cord damage.

Keywords

💡Dorsal Column Medial Lemniscus Pathway

The Dorsal Column Medial Lemniscus Pathway is a crucial neurological pathway responsible for transmitting fine touch, two-point discrimination, and proprioceptive sensations from the body to the brain. In the script, it is described as a complex term but essential for understanding how the body senses its position and movement in space. The pathway is highlighted as an ascending sensory pathway that involves a three-neuron chain.

💡Somatosensory Cortex

The somatosensory cortex is the area of the brain where sensory information from the body is processed. It is located in the postcentral gyrus, just behind the central sulcus. The script emphasizes its importance as the destination for the sensory information traveling through the dorsal column medial lemniscus pathway, creating a topographical map of the body's sensations.

💡Three-Neuron Chain

A three-neuron chain refers to the series of three neurons involved in transmitting sensory information from the periphery to the brain. The script explains that this chain is a fundamental aspect of all ascending sensory pathways, including the dorsal column medial lemniscus pathway, where the first neuron synapses with the second in the spinal cord, and the second neuron crosses to the opposite side and synapses with the third neuron in the thalamus.

💡Decussation

Decussation is the process where the second-order neuron in the sensory pathway crosses to the opposite side of the body after synapsing in the spinal cord. In the script, decussation is a key point that differentiates the dorsal column medial lemniscus pathway from the pain pathway, as it highlights the crossover of sensory information to the contralateral side of the brain.

💡Proprioception

Proprioception is the sense of the relative position of one's body parts and the strength of effort being employed in movement. The script discusses it as one of the essential functions of the dorsal column medial lemniscus pathway, allowing individuals to be aware of their body's position in space without relying on visual input.

💡Spinal Cord

The spinal cord is a central component of the nervous system that carries sensory and motor information between the brain and the rest of the body. In the script, it is the initial site where sensory neurons from the body enter and begin the process of transmitting information through the dorsal column medial lemniscus pathway.

💡Medulla

The medulla is a part of the brainstem where many vital functions, including the control of heart rate and blood pressure, are regulated. In the script, it is the location where the second-order neuron in the dorsal column medial lemniscus pathway synapses and decussates before ascending to the thalamus.

💡Thalamus

The thalamus acts as a relay station for sensory and motor information on its way to the cerebral cortex. The script describes it as the 'gateway to the cortex' for all sensory information, including that from the dorsal column medial lemniscus pathway, which must pass through the thalamus before reaching the somatosensory cortex.

💡Pain Pathway

The pain pathway, also known as the spinothalamic pathway in the script, is a different sensory pathway that transmits pain and temperature sensations. It is contrasted with the dorsal column medial lemniscus pathway to illustrate the differences in how the body processes and transmits different types of sensory information to the brain.

💡Spinothalamic Pathway

The spinothalamic pathway is the specific term for the pain and temperature sensory pathway that travels directly from the spinal cord to the thalamus, bypassing the brainstem. The script uses this term to highlight the distinct route and function of this pathway compared to the dorsal column medial lemniscus pathway.

💡Lesion

A lesion refers to a damaged area of the body, often resulting from injury or disease. In the context of the script, a spinal cord lesion can disrupt the transmission of sensory information, affecting the ability to feel pain, temperature, or touch on one side of the body below the level of the lesion. This concept is used to explain the clinical implications of spinal cord injuries on sensory perception.

Highlights

The dorsal column medial lemniscus pathway is essential for sensing fine touch, two-point discrimination, and proprioception at the sensory cortex.

All afferent sensory pathways to the brain are a three-neuron chain, including the dorsal column medial lemniscus pathway.

The somatosensory cortex is located behind the central sulcus, specifically in the postcentral gyrus.

A simplistic schematic of the pathway is presented to understand the process of sensory information reaching the brain.

The pathway for fine touch involves a synapse in the spinal cord and a decussation at the medulla before reaching the thalamus.

The thalamus acts as a gateway to the cortex, sorting sensory information before it reaches the somatosensory cortex.

A topographical map of the body exists on the somatosensory cortex, indicating the body part associated with each region.

The pain pathway differs from the dorsal column medial lemniscus pathway in its neural route and synapse locations.

The spinothalamic pathway, responsible for pain and temperature, ascends contralaterally after decussation in the spinal cord.

A lesion on one side of the spinal cord can affect the sensation of pain and temperature on the opposite side below the level of injury.

Despite a lesion, fine touch sensation on the contralateral side below the injury can still be felt due to the different neural pathways.

Testing for spinal injury involves stimulating different sensory pathways to determine the extent of damage to the spinal cord.

The distinction between the pathways for fine touch and pain is crucial for diagnosing and understanding sensory deficits post-injury.

The dorsal column medial lemniscus pathway's complexity is highlighted by comparing it with the more direct spinothalamic pain pathway.

Understanding the neural pathways of sensation is fundamental for neurological assessments and treatments.

The video provides a comprehensive overview of the sensory pathways, emphasizing the importance of the dorsal column medial lemniscus pathway.

Transcripts

so in this video we're going to discuss

the dorsal column medial lemniscus

pathway which is a bit of a mouthful but

basically what it is is the pathway in

order for us to be able to sense at our

cortex our sensory cortex fine touch

two-point discrimination and also

proprioception and proprioception has to

do with where you are in your own space

okay so this is a sensory pathway

obviously which means it's an a sending

pathway so it's going up the spinal cord

towards the brain now this may be a

sensation that's coming from my toe or

my leg or my hand or my joints for

example and what one really important

piece of information that you need to be

aware of is that all a sending sensory

pathways to the brain are a three neuron

chain that means there's only three

neurons associated with for example if

someone were to touch my finger in order

for me to be aware of it in my

somatosensory cortex remember where is

the somatosensory cortex you have that

central gyrus oh sorry the central

sulcus and behind the central sulcus is

a bump called the post central gyrus

that's the somatosensory cortex so if I

need to understand or feel somebody

touching my finger it's a three neuron

chain going from my finger into my

spinal cord up to my medulla to my

thalmus to my cortex three neurons so

the very first thing I want to do is

show you the most simplistic schematic

of this pathway and compare it to

another a sending sensory pathway which

is the pain pathway so let's have a look

so the first thing you need to draw up

here is the brain

now what type of section have I

performed here performed a coronal

section also known as a frontal section

so I've got the brain or the cerebrum

we've got the midbrain we have the pons

and we have the medulla I'm not going to

draw the cerebellum today because we're

not talking about it and then the spinal

cord going down okay so I want to tell

you that if somebody again were to touch

my finger so fine touch remember this is

the part that we were talking about fine

touch so maybe it's the sensation of me

holding a pen for example how does this

pathway get to my brain so very simply

you need to stimulate a sensory neuron

let's say in my finger it will go into

the spinal cord and on the same side of

the spinal cord that it enters it jumps

into the white matter now remember

you've got gray matter and white matter

grey matter or where are the bodies of

the neuron set that's where the

information comes into play that's where

we make sense of information it's

interpreted and the white matter it's

simply the highways okay so that's the

axons so something that's stimulated my

finger will go into my spinal cord on

the same side of the spinal cord it will

go up the white matter tracks so it goes

up now it's going to go remember you got

the midbrain the pons and the medulla

when it gets to the medulla that's where

it's going to sign apps with the second

neuron remember there's three neurons

that's the first neuron it sign-ups us

with the second and here at the medulla

the second neuron will cross to the

other side this crossing is called

decussation so the second order neuron

is the neuron that dekha sites then it's

on the other side of the body now and it

continues to ace in now it's going to

keep going up there's two structures I

haven't drawn they have a film I or the

thalamus you're going to have here and

here

remember the thalamus is the gateway to

the cortex so any sensory information

that's coming up if you want to be aware

of it it has to go through the cortex

first it's like the postal service if

you need to send a parcel somewhere must

go to the postal

service first so they can sort it they

can have a look and see where it's

supposed to go

so this signals coming up it goes to the

thalamus sign APS's with the third water

neuron and then this third order neuron

goes to where it finally needs to get to

which is the somatosensory cortex at the

post central gyrus remember there's a

topographical map of the body on the

somatosensory cortex which tells you you

know it's going to have for example over

here it's going to have the pharynx and

larynx and then the head and then it's

going to have the hand and then the arm

and then the trunk and then the knee and

leg and genitals now this is coming from

the hand so it shouldn't be going there

if I want to be a bit more accurate

should be going around about yeah and

this is the three neuron chain for fine

touch two-point discrimination of

proprioception into the spinal cord a

sends up the same side of the spinal

cord synapse is with the second order

neuron at the medulla

so it's labeled medulla it then a sends

up on the opposing side of the body

until hits the thalamus let's label the

thalamus and then the Thelma's will sort

it and send it to the somatosensory

cortex

now that's a very simplistic view of how

this pathway goes up now I want to

compare it to that of the pain pathway

now the pain pathway is also an a

sending sensory pathway but it actually

travels to the brain through a different

set of tracks let's have a look again

let's say that I prick my finger so

before I touched it now I'm pricking the

exact same part of my finger so let's

use the pain pathway in red now this

green pup I'm just going to write up

remember it's called the dorsal column

medial lemniscus pathway I'll tell you

about what all those terms mean shortly

but let's write D C dorsal column and

medial lemniscus pathway to represent

that now let's look at the pain pathway

so I've pricked my finger and this

signal will go into the spinal cord now

here's one of the differences as soon as

the pain neuron gets into the spinal

cord that's where it synapse is with its

second order neuron more importantly

it's also where it deca sites or crosses

over to the other side of the body and

then it begins to a sound so it goes up

all the way up the spinal cord it

bypasses the brain stem so bypasses the

medulla the pons and the midbrain and

then goes to the thalamus remember every

sensory input that we need to be aware

of we need to be aware of pain has to go

to the thalamus first and then it's sign

APS's with its third order neuron and

then it goes to where it needs to get to

now the reason why I'm showing you this

again this is the pain pathway now it's

not just pain it's actually the pain and

temperature pathway and of course it's

not good the pain and temperature purple

I just like this green one isn't called

the fine touch or proprioceptive or

two-point discrimination pathway it's

got a complex name the complex known for

pain and temperature is spinothalamic

and that's simply because it goes from

the spine to the thalamus easy alright

why am i showing you this it's really

important for a couple of reasons one is

what's the most apparent thing that you

can see that's different between the

where you can see that touch goes up

once eyeless barnacles actually the same

side of enters that's called epsilon or

L if it goes if it's the same side pain

goes up the contralateral this is the

opposing side of the spinal cord this is

important because if an individual gets

some sort of injury or maybe a lesion so

some sort of damage to one side of the

spinal cord let's just say here what

does that mean in regards to what type

of sensations they can or cannot feel

we'll have a look an individual who has

a lesion for example let's just say this

is the left side and this is the right

side an individual who has a lesion on

the left hand side of the spinal cord

they will not feel pain or temperature

on the contralateral side below the

level of injury you can see that because

it's stopping the paint pathway from

going up but they will be able to feel

touch on the contralateral side below

the injury now remember all these

signals aren't just coming in from one

side they're coming in from this side as

well which means it could have very

simply draw it up again coming in this

side here's touch goes up that same side

which it did over there sign-ups is at

the medulla crosses over goes to the

other thalamus and then goes to the

cortex and then pain pain is going to

come in sign-ups then cross then go up

to the thalamus synapse and go over

there so again here's that lesion on one

side and what I said before was that a

lesion on one side of a spinal cord may

mean that the individual will not feel

pain on the contralateral side below the

level of injury but they will feel fine

touch on the contralateral side below

the injury but they will not feel fine

touch on the ipsilateral the same side

blood level of injury but they will feel

pain and temperature on the ipsilateral

side below the level of injury now

obviously that takes a bit of time to

sort of work through your head but

hopefully

makes sense this is one of the reasons

why if somebody's in a spot in a car

crash to test the spinal injury they'll

sometimes touch the patient or rub down

their legs so touch them that's fine

touch or they'll get an ice cube for

example or an ice pack and rub it down

the leg enough ask them if they feel

that because they're feeling to

different pathways to different pathways

coming up and it helps to distinguish

whether there's an injury on one side of

the body when injuring the other side of

the body

that's the first thing I want to talk