Sensory Pathways MADE EASY!!
Summary
TLDRThis 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
🧠 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.
🔍 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.
🤕 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.
Mindmap
Keywords
💡Dorsal Column Medial Lemniscus Pathway
💡Somatosensory Cortex
💡Three-Neuron Chain
💡Decussation
💡Proprioception
💡Spinal Cord
💡Medulla
💡Thalamus
💡Pain Pathway
💡Spinothalamic Pathway
💡Lesion
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
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