Brain stem

Summary

In this educational video, Dr. Mikey explores the brainstem's three main components: the midbrain, pons, and medulla oblongata. He explains their critical roles in autonomic functions and reflexes, such as the accommodation reflex and the pupillary light reflex. The script delves into the cranial nerves associated with these parts, emphasizing their sensory and motor functions. The midbrain's role in the dopaminergic system for movement and behavior is highlighted, while the pons and medulla's involvement in respiratory and cardiovascular functions is underscored, illustrating the brainstem's vital role in sustaining life.

Takeaways

• 🧠 The brainstem is composed of the midbrain, pons, and medulla oblongata, and is crucial for subconscious autonomic functions and reflexes.
• 📐 Above the brainstem lies the cerebrum, and the diencephalon, which includes the thalamus, hypothalamus, and pineal gland.
• 👀 The optic nerve (cranial nerve II) is associated with the thalamus and is responsible for vision, connecting sensory input to the brain.
• 👁️ The midbrain is involved in visual reflexes like accommodation and the pupillary light reflex, and contains the substantia nigra which is part of the dopaminergic system.
• 💊 The substantia nigra's dopaminergic neurons are essential for movement initiation and behavior, with Parkinson's disease linked to their degeneration.
• 🦴 The pons contains the trigeminal nerve (cranial nerve V) and is associated with the jaw jerk reflex and the corneal blink reflex.
• 👅 The medulla oblongata is involved in swallowing, gag, cough, and sneeze reflexes, and is the site of decussation for many sensory and motor neurons.
• 🔄 The medulla is also the pathway for the dorsal column medial lemniscus pathway, which carries sensory information for fine touch, vibration, and proprioception.
• 💔 Damage to the reticular formation in the brainstem can affect respiratory and cardiovascular functions, as well as consciousness and wakefulness.
• 🔁 The reticular formation plays a key role in regulating sleep-wake cycles, circadian rhythms, and is involved in respiratory and cardiovascular control.
• 🧬 The brainstem's cranial nerves are integral for both sensory input and motor output, with 12 pairs serving various functions throughout the body.

Q & A

What are the three main components of the brainstem?

The three main components of the brainstem are the midbrain, the pons, and the medulla oblongata.

What is the function of the optic nerve (cranial nerve II) in relation to the brainstem?

The optic nerve is a sensory nerve associated with the thalamus, responsible for transmitting visual information from the eyes to the brain.

Which cranial nerves are associated with the midbrain and what are their roles?

The oculomotor nerve (cranial nerve III) and the trochlear nerve (cranial nerve IV) are associated with the midbrain. They are motor nerves that control eye movement.

What is the role of the trigeminal nerve (cranial nerve V) in the pons?

The trigeminal nerve is both sensory and motor, playing a role in facial sensation and the movement of the jaw and other facial muscles.

What are the two reflexes associated with the midbrain and vision?

The two reflexes associated with the midbrain and vision are the accommodation reflex and the pupillary light reflex.

What is the substantia nigra and why is it important?

The substantia nigra is a part of the midbrain that contains a pigment called melanin and is responsible for producing the neurotransmitter dopamine, which is crucial for movement and behavior.

What are the reflexes associated with the pons and how do they function?

The jaw jerk reflex and the corneal blink reflex are associated with the pons. They involve the trigeminal nerve for sensory input and motor output to control jaw movement and blinking, respectively.

What is the role of the glossopharyngeal nerve (cranial nerve IX) in the medulla?

The glossopharyngeal nerve is both sensory and motor, involved in the swallowing and gag reflexes, as well as the sensation of taste from the back of the tongue.

What is the reticular formation and where is it located?

The reticular formation is a system of neurons located deep within the brainstem, with nuclei in the midbrain, pons, and medulla. It plays a crucial role in regulating functions such as wakefulness, consciousness, respiratory, and cardiovascular control.

What is the significance of decussation in the medulla and what pathways are involved?

Decussation in the medulla is the crossing of neurons from one side of the body to the other. It is significant for the transmission of sensory and motor signals. The dorsal column medial lemniscus pathway for fine touch, vibration, and proprioception, and motor neurons controlling movement are examples of pathways that decussate in the medulla.

Outlines

00:00

🧠 Introduction to the Brainstem Components and Functions

This paragraph introduces the brainstem, highlighting its three main parts: the midbrain, pons, and medulla, also known as the medulla oblongata. It explains the brainstem's position relative to the cerebrum and the diencephalon, and its connection to the spinal cord. The importance of the brainstem in subconscious autonomic functions and reflexes is emphasized. The paragraph also outlines the role of the 12 pairs of cranial nerves associated with the brainstem, which are crucial for sensory input and motor responses, and introduces the concept of the brainstem as a 'lizard brain' involved in basic survival reflexes.

05:01

👀 Midbrain's Role in Vision and Dopaminergic System

The midbrain's function in the visual system is explored, focusing on its involvement in the accommodation reflex and the pupillary light reflex, both of which are essential for adjusting to visual stimuli. The paragraph delves into the midbrain's role in the production of dopamine, a neurotransmitter critical for movement and behavior. It explains the substantia nigra's part in the dopaminergic system and its implications for conditions like Parkinson's disease, which affects motor movement initiation and smoothness. The summary also touches on the role of dopamine in motivation and reward.

10:01

🦴 Reflexes and Neuronal Pathways in the Pons and Medulla

This paragraph discusses the pons and medulla's involvement in various reflexes, including the jaw jerk reflex, the corneal blink reflex, and the tensor tympani and stapedius reflex, which protect the ear from loud sounds. It also covers the medulla's role in swallowing, gag, cough, and sneeze reflexes, emphasizing the decussation of sensory and motor neurons that cross from one side to the other within the medulla. The importance of the reticular formation, a system of neurons deep to the brainstem involved in wakefulness, consciousness, respiratory, and cardiovascular functions, is highlighted. The paragraph concludes by noting the critical functions of the pons and medulla in maintaining basic life processes.

Keywords

💡Brainstem

The brainstem is a crucial part of the brain that connects the cerebrum with the spinal cord and is responsible for many autonomic functions. It is composed of three main parts: the midbrain, pons, and medulla oblongata. In the video, the brainstem is discussed as the 'lizard brain' or 'old brain,' highlighting its role in subconscious autonomic functions and reflexes that are vital for survival.

💡Cranial Nerves

Cranial nerves are the nerves that enter and exit the brain or brainstem, with 12 pairs identified in total. They are responsible for transmitting sensory information to the brain and motor commands from the brain. The video script mentions several cranial nerves associated with the brainstem, such as the oculomotor (CN III) and the trigeminal (CN V), emphasizing their roles in various reflexes and functions.

💡Midbrain

The midbrain is the uppermost part of the brainstem and plays a significant role in the visual system and certain reflexes. It is associated with the oculomotor nerve (CN III) and the trochlear nerve (CN IV). The video describes the midbrain's involvement in the accommodation reflex and the pupillary light reflex, both of which are essential for vision.

💡Pons

The pons is a part of the brainstem located between the midbrain and the medulla oblongata. It is associated with the trigeminal nerve (CN V), which is both sensory and motor. The script discusses the pons' role in reflexes such as the jaw jerk reflex and the corneal blink reflex, illustrating its importance in facial movements and responses.

💡Medulla Oblongata

The medulla oblongata is the lower part of the brainstem, connected to the spinal cord. It is involved in many vital functions, including the control of heart rate, respiration, and several reflexes. The script mentions the medulla's role in the swallowing and gag reflex, cough and sneeze reflex, and the decussation of sensory and motor neurons.

💡Substantia Nigra

The substantia nigra is a region within the midbrain that contains a pigment called melanin, giving it a dark appearance. It is a key component of the dopaminergic system, which is crucial for movement and behavior. The video explains that the substantia nigra's role in the production of dopamine is linked to motor movement initiation and Parkinson's disease.

💡Dopaminergic System

The dopaminergic system refers to the network of neurons that produce the neurotransmitter dopamine. It plays a critical role in movement, motivation, and reward. The video script connects the substantia nigra's part in this system to the initiation and smoothness of motor movements, as well as to behaviors related to motivation and reward.

💡Reflexes

Reflexes are automatic, involuntary responses to stimuli that occur without conscious thought. The video script describes various reflexes mediated by the brainstem, such as the accommodation reflex, pupillary light reflex, jaw jerk reflex, and corneal blink reflex, emphasizing the brainstem's role in immediate responses for survival.

💡Reticular Formation

The reticular formation is a network of neurons located deep within the brainstem that plays a significant role in regulating arousal, sleep-wake cycles, and consciousness. The video script highlights the importance of the reticular formation in maintaining wakefulness and consciousness, as well as its involvement in respiratory and cardiovascular functions.

💡Decussation

Decussation refers to the crossing of nerve fibers from one side of the body to the other. In the context of the brainstem, the script mentions that many sensory and motor neurons cross at the medulla, which is crucial for the integration of information from both sides of the body and the coordination of responses.

💡Autonomic Functions

Autonomic functions are the body's unconscious processes that regulate activities such as heart rate, digestion, respiratory rate, and more. The video script describes the brainstem as being involved in subconscious autonomic functions, emphasizing its role in maintaining life-sustaining processes without the need for conscious control.

Highlights

The brainstem consists of three parts: the midbrain, pons, and medulla, each with distinct functions.

The diencephalon, including the thalamus, hypothalamus, and pineal gland, sits above the brainstem.

The brainstem is associated with 12 pairs of cranial nerves, critical for sensory and motor functions.

The brainstem is sometimes referred to as the 'lizard brain' due to its role in subconscious autonomic functions.

Reflexes, such as the accommodation reflex and the pupillary light reflex, are mediated by the midbrain.

The substantia nigra in the midbrain is part of the dopaminergic system, crucial for movement and behavior.

Parkinson's disease is linked to the degeneration of dopaminergic neurons in the substantia nigra.

The pons is involved in reflexes like the jaw jerk reflex and the corneal blink reflex.

The tensor tympani and stapedius reflexes in the pons protect the ear from loud sounds.

The medulla oblongata is responsible for reflexes like swallowing, gag, cough, and sneeze.

The medulla is a site of decussation for sensory and motor neurons, essential for coordination.

The reticular formation in the brainstem plays a vital role in wakefulness, consciousness, respiratory, and cardiovascular functions.

Damage to the reticular formation can result in unconsciousness and affect respiratory and cardiovascular rhythms.

The optic nerve (cranial nerve II) is sensory and associated with the thalamus.

The oculomotor (cranial nerve III) and trochlear (cranial nerve IV) nerves are motor and linked to eye movement.

The trigeminal nerve (cranial nerve V) has both sensory and motor functions, significant for facial sensations and movements.

Cranial nerves VI, VII, and VIII are associated with the pons and medulla, controlling abduction of the eye, facial expressions, and hearing.

Glossopharyngeal (cranial nerve IX), vagus (cranial nerve X), and hypoglossal (cranial nerve XII) nerves have roles in both sensory and motor functions.

The olfactory nerve (cranial nerve I) and accessory nerve (cranial nerve XI) have higher brain functions and are associated with spinal cord survival mechanisms.

Transcripts

I've run dr. Mikey in this video we're

going to take a look at the three

components of the brainstem and go

through their function all right so to

begin when we look at the brainstem it's

made up of three parts the midbrain the

pons and the medulla now above the

brainstem sits the brain or the cerebrum

itself if I were to take off the two

cerebral hemispheres we're left with

something called the diencephalon which

is basically the thalamus and

hypothalamus and pineal gland underneath

that is where we've got the brainstem

now underneath the brainstem or at least

underneath the medulla or medulla

oblongata

we've got the first part of the spinal

cord the cervical aspect so the three

parts are midbrain pons and medulla also

known as the medulla oblongata we're

going to go through the cranial nerves

associated with the brainstem because a

lot of their function is attributed to

the cranial nerves they remember there's

12 pairs of cranial nerves these are

nerves that enter the brain or brain

stem and leave the brain and brain stem

the ones that enter a sensory telling

the brain and brainstem information

about the surroundings of the body and

the information going out is motor so

telling it to do something or respond

the brainstem you may have heard been

referred to as a lizard brain or an old

brain but in actual fact it's more so

involved when it comes to very basic

subconscious autonomic function and

that's what we're going to talk about

today a lot of reflexes things that we

don't consciously control reflexes are

when a sensory signal goes in and a

motor signal immediately comes back out

to respond to keep us alive in that

moment so we first need to look at the

cranial nerves associated with the

brainstem so we can look at the function

all right 12 pairs but not all 12 enter

and leave the brainstem so we need to

start first with the thalamus itself and

I'll tell you why very shortly but the

first cranial nerve associated with the

thalamus is that of the optic nerve and

the optic nerve is the second cranial

nerve and it's sensory so if I draw an

arrow

going towards this central component is

going to be sensory if an arrow going

away it's going to be motor yeah so

optic nerves so cell with the thalamus

let's look at the midbrain so the

midbrain has two cranial nerves that you

need to really be aware of these cranial

nodes are both motor nerves the first

one is going to be oculomotor and the

oculomotor nerve is cranial nerve three

and then the second one is going to be

trochlea and trochlea is cranial nerve

four all right now let's move to the

pons the pons has one really important

cranial nerve you need to be aware of

and that's going to be the trigeminal

nerve and the trigeminal nerve is both

sensory and motor and that's cranial

nerve five now as we move to the bottom

of the pot so at the pons and then go

into the Ponto medullary junction so

that's the the region between the pons

and medulla and then the start of the

medulla we've got three cranial nerves

we need to put in here we've got the

abducens which is going to be motor

which is cranial nerve six facial which

is both sensory and motor which is

cranial nerve seven and vestibular

cochlea which is sensory

which is cranial nerve eight now once we

get to the medulla itself three really

important cranial nerves you need to be

around we're off okay

first is glossopharyngeal now

glossopharyngeal is both sensory and

motor and glosso pharyngeal is cream

nerve nine then we've got the vagus

nerve both sensory and motor and this is

cranial nerve 10 and then the last one

need to be aware of is the hypoglossal

which is a motor nerve and that's

cranial nerve 12 alright we've missed

out on two cranial nerves here right

first of which is the olfactory

olfactory sense of smell it actually

comes in higher more at the brain nah we

haven't looked at cranial nerve 11 which

is going to be the accessory nerve you

know plays a role in shrugging this is

more so associated with the survival

portion of the spinal cord all right now

that we've drawn this up we can now look

at the functions of the brainstem

so let's start with the midbrain

midbrain plays a really important role

in a couple of reflexes associated with

vision so have a look ocular motor motor

movement of the eye chalkeley are motor

movement of the eye so midbrain really

important role for the visual system all

right two reflexes you need to know here

first is what we call the accommodation

reflex

now the accommodation reflex so remember

it's a reflex so since we in moaña out

the accommodation reflex is basically

when you see an object and you focus on

the object right sensory in motor out

the sensory no that's coming in is the

optic nerve and the motor nerve coming

out is the oculomotor nerve optic in

ocular motor out that's the reflex for

accomodation the other one you need to

be aware of here is the pea

hillarie light reflex now the pupillary

light reflex is where you shine a light

at the pupil and both just one but both

pupils constrict sensory in motor out

the sensory in is optic again and the

motor out is oculomotor again so these

are two really important reflexes

associated with the midbrain but another

important point you need to be aware of

with the midbrain is it contains the

substantia now substantia

means black substance because it

contains a pigment called melanin and it

produces an important neurotransmitter

called dopamine

so the substantia contains part of

what we call the dopaminergic system

dopa min urge ik system now the

dopaminergic system is really important

when it comes to movement and behavior

let's write that down movement and

behavior

now when it comes to movement with the

dopaminergic system this has branches

that go to the basal ganglia okay and it

helps with initiating motor movement and

smoothing out motor movement some

individuals these dopaminergic neurons

die if they die it's hard to initiate

motor movement and it's hard to smooth

it out and the resulting issue here is

Parkinson's disease these individuals

can't start a movement very well and

what happens is they have a resting

tremor all right so this is the

dopaminergic system part of the

substantial agar and the behavior plays

a role in motivation and reward dopamine

is really important in motivation and

reward so this is the midbrain now let's

have a look at the pons when we look at

the pons we've got two important

reflexes you need to know first is the

jaw jerk reflex the jaw jerk reflex okay

Giorgio's free flex this is where if you

open your jaw you stretch certain

muscles such as the masseter temporalis

medial pterygoid and this sends a

sensory signal in to tell the motor

neuron coming out to close the jaw so

the sensory in is going to be the

trigeminal nerve and the motor out is

the trigeminal nerve and this is the

georgia reflex another reflex you need

to know that's mediated here at the pons

is going to be called the corneil blink

reflex corneil blink reflex and what

happens here is if you were to rub the

cornea both eyes blink reflexively this

is because the sensory component is

going to be trigeminal and the motor

component to blink is facial sensory

trigeminal motor facial coming out

that's the georgia o'queef looked reflex

and the corneal reflex now let's move

down and have a look at oh one more that

we should be aware of at the pons which

is called the tensor tympani and

stapedius reflex

tensor tympani and stapedius reflux this

is where you hear a really loud sound

what happens is the tensor tympani and

stapedius reflexively contract and it

means that any other incoming sound is

dampened because you don't want to

damage the cochlear you don't want to

damage the eardrum itself so what's

happening here is this the sensory in is

going to be vestibular cochlea coming in

tells tensor tympani it's the P Deus to

contract that's motor the motor that's

coming out to do this is going to be the

trigeminal your stimuli cochlea coming

in try and general going out all right

now let's look at the medulla when we

look at the medulla there's a couple of

important reflexes here first thing we

need to look at for the medulla is

swallowing and gag reflex the swallowing

and gag reflex now the sensory coming in

is both glossopharyngeal and Vegas and

the motor going out is both Glossner

pharyngeal and Vegas and this is the

same when it comes to the cough and

sneeze reflex cough and sneeze reflex

now another important point for the

medulla is this is the site of

decussation for many neurons so

decussation is wearing neuron crosses

from one side to another it may be this

side to that side or that side to this

side they may be sensory neurons coming

up they may be mode in Euron's coming

down in actual fact there is a group of

sensory neurons that come up the same

side synapse at the medulla and go to

the other side to go up to the thalamus

these neurons that take this pathway and

neurons for fine touch vibration and

proprioception so fine touch vibration

and proprioception

all right this is called the dorsal

column medial lemniscus pathway going up

so sensory now sometimes as motor

neurons that come down and they cross at

the medulla they decussate here at the

medulla and these are motor neurons

coming down so that's another important

point for the medulla but last point I

want to finish with is that deep to the

brainstem there are some nuclei of some

neurons that play really important

functional roles and we don't know all

of their roles but we know some now this

deep system of neurons is called the

reticular formation and you're going to

have some nuclei sitting in the midbrain

you have some sitting in the pons you

have some sitting in the medulla and

like I said it's called the reticular

formation reticular formation now the

nuclei associated at the mid midbrain

play a really important role for

wakefulness wakefulness and

consciousness so sleep-wake cycles for

example circadian rhythm and

consciousness so damage to this

particular era can result in individuals

being unconscious those are both the

pons and the medulla are associated with

so both the pons and medulla are

associated with respiratory and

cardiovascular basic function this

includes the rhythmicity of these

systems the tone of these systems and

how they basically work pons and medulla

again damage to these areas damaged

basic respiratory function and basic

cardiovascular function so what we've

got here is a general overview of the

functions of the brainstem