Neurology | Descending Tracts: Vestibulospinal Tract

Summary

This educational video script delves into the vestibular spinal tract, a crucial component of the nervous system responsible for activating extensor or anti-gravity muscles. It emphasizes the tract's role in maintaining posture and balance during linear and angular acceleration. The script explains the tract's origin in the vestibular nuclear complex, its stimulation from the inner ear and cerebellum, and its pathway to motor neurons. It also highlights the red nucleus's inhibitory function to prevent extensor hypertonus, ensuring a balanced muscle response.

Takeaways

• 🌟 The video series will cover four descending tracks in the nervous system, focusing on the vestibular spinal tract in the first video.
• 🔍 The vestibular spinal tract is primarily responsible for activating extensor muscles, which are crucial for posture and balance.
• 💪 The tract is particularly important for anti-gravity muscles, which help maintain posture and balance during linear and angular acceleration.
• 🏠 The vestibular nuclear complex, located in the upper part of the medulla, is the main structure that receives stimuli for the vestibular spinal tract.
• 🌀 Stimuli to the vestibular nuclear complex come from the inner ear structures, such as the macula and the cristae of the semicircular ducts, and from the cerebellum's vestibular and fastigial nuclei.
• 📢 The lateral and medial vestibular nuclei are the main components of the vestibular spinal tract, with the lateral controlling limb and trunk extension, and the medial controlling head and neck musculature.
• 🚀 The vestibular spinal tract sends fibers down to the spinal cord, where they synapse with alpha and gamma motor neurons to control muscle contractions.
• 👁 The tract also has a role in controlling eye movement through connections with the oculomotor system, although this is not the main focus of the script.
• 🚑 The red nucleus in the midbrain acts as an inhibitory control for the vestibular spinal tract, preventing excessive contraction of extensor muscles.
• 🛑 Without the inhibitory control from the red nucleus, there could be a risk of extensor hypertonus, where the extensor muscles contract excessively.
• 📚 The script emphasizes the importance of understanding the function and control of the vestibular spinal tract for maintaining balance and posture during movement.

Q & A

What is the main function of the vestibulospinal tract?

The main function of the vestibulospinal tract is to activate extensor muscles, specifically anti-gravity muscles that help maintain posture and balance.

What are the primary components of the vestibulospinal tract?

The primary components of the vestibulospinal tract are the lateral vestibular nucleus and the medial vestibular nucleus.

Where is the vestibular nuclear complex located?

The vestibular nuclear complex is located within the upper part of the medulla.

What stimuli do the vestibular nuclei receive?

The vestibular nuclei receive stimuli from the macula in the utricle and saccule (which detect linear acceleration) and from the crista ampullaris in the semicircular ducts (which detect angular acceleration). Additionally, they receive proprioceptive information from the cerebellum.

What role does the cerebellum play in the vestibulospinal tract?

The cerebellum provides proprioceptive information to the vestibular nuclear complex, helping it understand the position of muscles, tendons, joints, and ligaments, which is crucial for coordinating muscle contractions accurately.

What is the difference between the medial and lateral vestibulospinal tracts?

The medial vestibulospinal tract primarily controls head and neck musculature, while the lateral vestibulospinal tract controls limb and trunk extensor muscles, which are important for maintaining posture and balance.

How does the vestibulospinal tract interact with motor neurons?

The vestibulospinal tract sends descending fibers to the spinal cord, where they stimulate alpha and gamma motor neurons in the anterior or ventral gray horn. These motor neurons then innervate extensor muscles to maintain posture and balance.

What is the role of the red nucleus in the vestibulospinal tract system?

The red nucleus provides inhibitory signals to the vestibular nuclear complex, preventing excessive contraction of extensor muscles and ensuring proper muscle tone.

What happens if the inhibitory signals from the red nucleus are absent?

If inhibitory signals from the red nucleus are absent, it could lead to extensor hypertonus, where extensor muscles contract excessively.

What additional function does the vestibular nuclear complex have besides controlling extensor muscles?

The vestibular nuclear complex can also send fibers to control eye movements via the medial longitudinal fasciculus, influencing the third, fourth, and sixth cranial nerves.

Outlines

00:00

🌟 Introduction to the Vestibular Spinal Tract Series

This introductory paragraph sets the stage for a four-part series focusing on various descending tracks, starting with the vestibular spinal tract in this video. The speaker emphasizes the importance of understanding the ultimate function of each tract, especially the vestibular spinal tract's role in activating extensor muscles, also known as anti-gravity muscles, which are crucial for posture and balance. The paragraph also mentions the need to revisit the vestibular pathway for those who have seen previous content on the subject, highlighting the value of repetition in learning.

05:00

🔍 Detailed Exploration of the Vestibular Spinal Tract

The speaker delves into the specifics of the vestibular spinal tract, explaining its origin from the vestibular nuclear complex located in the medulla and the stimuli it receives from the inner ear structures, such as the macula and the cristae of the semicircular ducts, as well as from the cerebellum via the vestibular and fastigial nuclei. The paragraph clarifies the roles of the medial and lateral vestibular nuclei in forming the tract and their respective influences on head, neck, and limb/trunk muscles. The speaker also describes the pathway of the vestibular spinal tract fibers as they descend through the spinal cord and synapse laterally with alpha and gamma motor neurons, which in turn control the contraction of extensor muscles.

10:01

🛑 The Role of the Red Nucleus in Regulating the Vestibular Spinal Tract

In this concluding segment, the speaker introduces the red nucleus as a regulatory component of the vestibular spinal tract system. The red nucleus sends inhibitory signals to the vestibular nuclear complex to prevent excessive contraction of the extensor muscles, thus acting as a 'brake' system. The speaker also touches on the broader implications of the vestibular system, including its influence on eye movement control through the medial longitudinal fasciculus and the importance of the red nucleus's regulatory role in maintaining proper muscle tone and preventing extensor hypertonus.

Keywords

💡Vestibular Spinal Tract

The vestibular spinal tract is a key pathway in the nervous system that primarily activates extensor muscles, which are crucial for maintaining posture and balance. In the video, it is emphasized that this tract is important for anti-gravity muscles, illustrating its role in stabilizing the body during movements involving linear and angular acceleration. The script explains that the tract originates from the vestibular nuclear complex in the medulla and is stimulated by inputs from the inner ear and cerebellum.

💡Extensor Muscles

Extensor muscles are those that extend or straighten the limbs and are vital for posture and balance. The video script highlights the vestibular spinal tract's function in activating these muscles, especially during rapid changes in movement such as when accelerating or decelerating in a vehicle. The activation of extensor muscles helps resist gravity and maintain an upright posture.

💡Anti-Gravity Muscles

Anti-gravity muscles are muscles that work against the force of gravity to maintain an upright posture and balance. The script describes the vestibular spinal tract's role in activating these muscles, which is essential for everyday activities that involve changes in body position or movement, such as walking or running.

💡Vestibular Nuclear Complex

The vestibular nuclear complex, located in the upper part of the medulla, is a group of nuclei that receive and process information about balance and spatial orientation. The script explains that this complex is stimulated by inputs from the inner ear and the cerebellum, which then influence the vestibular spinal tract's activity.

💡Macula

The macula is a sensory structure found in the utricle and saccule of the inner ear, which detects linear acceleration. The script mentions that the macula sends information to the vestibular nuclear complex, which in turn influences the vestibular spinal tract's activation of extensor muscles.

💡Semicircular Ducts

Semicircular ducts are part of the inner ear's vestibular system and are responsible for detecting rotational movements. The script specifies that the cristae within the ampulla of these ducts, known as the semicircular canals, provide input to the vestibular nuclear complex, indicating rotational acceleration.

💡Cerebellum

The cerebellum is a region of the brain that plays a key role in motor control and coordination. In the script, it is mentioned that the cerebellum, through the vestibular nuclear complex, provides proprioceptive information to the vestibular spinal tract, helping to fine-tune muscle contractions for balance and posture.

💡Red Nucleus

The red nucleus is a structure in the midbrain that can inhibit the vestibular nuclear complex, thus controlling the activity of the vestibular spinal tract. The script explains that this inhibition is a 'brake system' to prevent excessive contraction of extensor muscles, which could lead to extensor hypertonus.

💡Alpha and Gamma Motor Neurons

Alpha and gamma motor neurons are types of neurons in the spinal cord that control muscle contraction. The script describes how the vestibular spinal tract stimulates these neurons, with alpha neurons controlling muscle fibers for movement and gamma neurons regulating muscle spindle tension, both contributing to posture and balance.

💡Extensor Hypertonus

Extensor hypertonus refers to an excessive contraction of the extensor muscles, which can lead to stiffness and impaired movement. The script mentions that the red nucleus helps prevent this condition by inhibiting the vestibular nuclear complex and thus controlling the activity of the vestibular spinal tract.

💡Medial and Lateral Vestibular Spinal Tracts

The medial and lateral vestibular spinal tracts are subdivisions of the vestibular spinal tract, each with specific functions. The script explains that the medial tract is associated with head and neck muscles, while the lateral tract controls limb and trunk extension, both playing a role in maintaining balance and posture.

Highlights

The four-part series discusses descending tracks, focusing on the vestibular spinal tract in this video.

The vestibular spinal tract primarily activates extensor muscles, which are crucial for anti-gravity and posture maintenance.

The vestibular nuclear complex, located in the medulla, receives stimuli from the inner ear and cerebellum for balance and posture control.

The macula and cristae ampullares from the inner ear provide information on linear and rotational acceleration to the vestibular nuclear complex.

The lateral and medial vestibular nuclei are the main components of the vestibular spinal tract, with distinct roles in musculature control.

The lateral vestibular nucleus controls limb and trunk extension, while the medial nucleus manages head and neck musculature.

The cerebellum's fastigial and vestibular nuclei send proprioceptive information to the vestibular nuclear complex for coordinated muscle contraction.

Vestibular spinal tract fibers descend into the spinal cord, synapsing laterally with alpha and gamma motor neurons.

Alpha motor neurons are responsible for muscle fiber contraction, while gamma neurons maintain muscle spindle tightness.

The medial vestibular spinal tract targets head and neck muscles, specifically in the cervical region of the spinal cord.

The lateral vestibular spinal tract stimulates axial and appendicular extensors for posture and balance against gravity.

The red nucleus in the midbrain inhibits the vestibular nuclear complex to prevent excessive extensor contraction.

Extensor hypertonus can occur without the red nucleus's inhibitory control, leading to over-contraction of extensor muscles.

The vestibular system also influences eye movement through connections with the medial longitudinal fasciculus and related cranial nerves.

The ultimate goal of the vestibular spinal tract is to control anti-gravity muscles for posture and balance during linear and angular acceleration.

The red nucleus acts as a brake system for the vestibular spinal tract to ensure proper muscle tone and prevent hyperactivity.

Transcripts

iein engineers join us in this four-part

series where we're gonna talk about

descending tracks we're gonna talk about

four individual ones okay so four

separate videos the first video then

we're gonna talk about in this one is

gonna be the vestibular spinal track so

we're gonna talk about that one in this

video the next video we're gonna talk

about the Ponto reticulospinal tract

then we'll talk about the rubra spinal

tract and then finally we'll finish off

with the medullary reticulospinal tract

so let's go ahead and start first on the

vestibular spinal tract alright so let's

go ahead and SART a little bit stupido

spinal tracts so if you guys haven't

already watched the vestibular cochlear

nerve the vestibular pathway we actually

talked about this tract and pretty good

detail in that so if you haven't go

watch that too or anyway we're gonna

cover it again because repetition is

always good alright so the vestibular

spinal tract here's the big thing that I

want to get out of all these videos I

want you guys to remember the ultimate

termination or destination or function

of this track this track this vestibular

spinal tract is mainly going to activate

extensor muscles

extensor muscles but to even be a little

bit more specific

this vestibular spinal tract is also

important for anti-gravity muscles

posture muscles and we'll explain why

but I want you to remember that it's

primarily for extensor muscles but we

can classify this as our anti-gravity

anti-gravity muscles helps to maintain

our posture and and balance right so

anti-gravity muscles okay now why is

this well there's a special set of

nuclear this is your vestibular nuclear

complex your vestibular nuclear complex

is located within the medulla right the

upper part of the medulla so this is our

vestibular nuclear complex and this is

our vestibular nuclear complex you have

our right one and a left one all right

so here's the right side here's the left

side now where do these nuclei get

stimuli from they get it from two

different stimuli so what is the

stimulus well it comes from two

different stimuli one is in the inner

ear you know in the inner ear you have

the macula and the macula if you

remember that was located in the utricle

and the saccule they respond to linear

acceleration but another one was

actually going to be within the

semicircular ducts specifically in the

ampulla of the semicircle a box they

called it the cris day and Belarus if

you remember these two structures gave

what they gave that vestibular branch of

the vestibulocochlear nerve and that

vestibular branch of the

vestibulocochlear nerve came and ended

up on this vestibular nuclear complex

alright now what did it do from that

point remember there's the vestibular

nuclear complex has the superior the

inferior the medial and the lateral

vestibular nucleus why am I telling you

this the reason why is the lateral

vestibular nucleus and the medial

vestibular nucleus are the main

components of this vestibular spinal

tract ire so the medial and the lateral

are the main components of the

vestibular meinl tract

now there's two different stimulations

we said one is coming from the inner ear

right from the macula which is detecting

linear acceleration so pretend you're in

a vehicle and you just hit the hit the

gas or you hit the brakes really fast

either one that they're shifting within

the inner ear which helps to send that

information to the vestibular nuclear

complex another one is if you're lit

you're actually rotational or angular

lis accelerating that activates the

chrisstambo layers and tells the

vestibular nuclear complex of that

there's another situation you know in

the cerebellum here's your cell or

cerebellum right here there's different

types of nuclei in here you know there's

a special nucleus and it's called the

vestigial nucleus and the fastidian

nucleus can actually send information

out to this vestibular nuclear complex

and tell this vestibular nuclear complex

about what the cerebellum knows about

it's proprioception so you know

proprioception is basically the position

of your muscles your tendons your joints

your ligaments our cerebellum has

constant awareness of where our limbs

and our body is in space so the

cerebellum has a way of telling these

vestibular nuclei hey I know where the

arm is I know where the legs are so here

take this information so that whenever

you have these movements these

descending fibers coming down you tell

the muscles exactly how they should

contract in the exact direction the

exact way that they should do it it's a

beautiful system so two different

stimuli one it's coming from the

vestigial nucleus within the cerebellum

and the other one is coming from the

inner ear structure specifically the

macula and the Christian pilaris

now once they get their stimulus like I

told you the lateral and the medial the

ones that are actually primarily forming

the vestibular spinal tract but even

more I want you to remember is most of

the fibers are coming from the lateral

the reason why is the lateral is

controlling specific types of

musculature right so the medial controls

more of your head and neck musculature

all right being able to maintain the

movement of our head and our posture

whenever we're actually Road

accelerating right in the rotational

direction or linearly accelerating we

want to be able to maintain our actual

muscle tone within the head and neck

muscles the lateral vestibular spinal

tract is controlling more of the actual

limb and even trunk extension all right

so that's why it's important so now

let's bring these guys down though okay

so they're gonna come down these fibers

these this actual vestibular spinal

tract when they come down they're going

to go into the actual into the spinal

cord now as they go down through the

spinal cord they're going to give

stimulation it see laterally if see

laterally to the actual cell bodies of

the actual alpha and gamma motor neurons

located within the anterior or ventral

great horn so let's say they here I have

these cell bodies right here right and

let's say I pretend that these are my

alpha motor neurons and then right

adjacent to it all I have maybe I'll

have some gamma motor neurons so over

here I'll have some gamma motor neurons

what would these guys do from here these

alpha motor neurons are going to come

out and go to specific types of muscles

what muscles will they be going to we

said that they're going to extensor

muscles or anti-gravity muscles right or

muscles that help to maintain our

posture and our balance when we're

linearly or rotating accelerating in a

rotational direction now we said if it's

the medial let's pretend that these are

for the medial let's just say these are

for the medial vestibular spinal tract

if this is for the medial vestibular

the Simula spinal tract if this is for

the medial vestibular spinal tract this

will only be going to what type of

muscles you have to remember this this

is for the head

and neck muscles all right this is for

the medial vestibular spinal tract

headed neck muscles so let's pretend

that this is like the cervical section

with spinal cord okay pretend for a

second that this right here is the

cervical section this is the cervical

section of the spinal cord all right so

it's going to be going to the head and

neck muscles now let's say that we keep

following these down so let's say that

we keep following these guys down and

let's presume that now this is going to

be the lateral force stimulus spinal

tract right so now the lateral

vestibular spinal tract is gonna come

over here and go epsy laterally on to

some alpha and gamma motor neurons that

are located within the anterior grey

Horn of the spinal cord and what will

they do they'll come out and stimulate

these actual muscles if you guys haven't

already watched the corticospinal video

you guys will member remember that the

gamma is specifically for the muscle

spindles right to maintain the actual

tightness of the muscle spindles the

Alpha is for the extra fuse of muscle

fibers the muscle fibers that actually

contract and shorten and lengthen the

muscle all right now if it is the

lateral if it is the lateral vestibular

spinal tract the lateral of a stimulus

Pinal tract what type of muscles will

this be going to this will be going to

more of the axial and the appendicular

and appendicular extensors

okay so it's going to be going Sun to

the some of the axial and the athlete

appendicular extensors if you think

about it we want to have these muscles

contracting right to be able to maintain

our posture and our balance and the

right to resist gravity but here's the

important thing there has to be some way

that we could have put a brake on this

system this system has to constantly

whenever it's not necessarily needs to

be stimulated whenever it doesn't need

to be stimulated we need to have some

brake on it way that we can control it

we get my red marker here there's a

special nucleus located within the

midbrain and this nucleus is called the

red nucleus right it's called the red

nucleus the red nucleus can come down

here and inhibit the vestibular nuclear

complex and prevent these actual

vestibular spinal tracts from going down

why to prevent excessive contraction of

the extensors if this this is actually

going to be coming from again.what

nucleus the red nuclei here if these

guys aren't sending these inhibitory

pathways down to the vestibular nuclei

you know what could happen it could

cause what's called extensor hyper tonus

where the extensor muscles are so

crazily contracted more than they need

to be so to prevent that from happening

we have a brake system here and that's

this red nucleus okay they can give

inhibitory descending fibers to inhibit

these vestibular nuclei from

continuously stimulating the actual

vestibular spinal tract via the medial

and the lateral and there's another way

remember I told you that whenever you're

rotating linearly or if you're doing

linear acceleration or angular

acceleration you have to move your head

and neck you have to maintain posture

and balance right but what else did you

do you move your eyes there's another

one we're not going to talk about it but

remember that the vestibular nucleus can

also send fibers upwards to control eye

movement you have the third nerve the

fourth cranial nerve and the sixth

cranial nerve if you remember that was

called the medial longitudinal

fasciculus okay so basic thing that I

want you guys to get out of this is the

vestibular spinal tract it controls your

extensor muscles or you

anti-gravity muscles to maintain posture

and balance during linear and angular

acceleration what are the two stimuli

the inner ear structures macula Kristine

Belarus and it gets some modification

from the vestigial nucleus within the

cerebellum

what's its ultimate goal to send down

via medial and lateral vestibular spinal

tracts into the spinal cord if it's

going to the cervical region it's going

to be the medial supplying the head and

neck muscles and if it's going to more

axial more of the appendicular skeleton

what is it going to be supplying it's

then going to be supplying to be

supplied by the lateral vestibular

spinal tract and then remember we have

to have a brake system on this tract

which is gonna be coming from the red

nucleus ionizer so we covered the

vestibular spinal tract now in the next

video

we're gonna go and talk about the Ponto

reticulospinal tract I'll see you guys

there

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you

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