Muscles of Respiration | Breathing Mechanics | Respiratory Physiology

Summary

This video from Bite Size Med explores the muscles involved in respiration and the mechanics of the chest wall during breathing. It explains how inspiration and expiration are facilitated by the diaphragm, ribs, and accessory muscles. The diaphragm is the primary muscle for inspiration, flattening to increase thoracic volume, while expiration is generally passive due to lung elasticity. The video also highlights the role of external intercostal muscles and the importance of the phrenic nerve in diaphragm function. It concludes with a mnemonic to help remember the respiratory muscles and their actions.

Takeaways

• 🌀 The breathing cycle consists of inspiration (inhaling air into the lungs) and expiration (exhaling air out of the lungs).
• 🏗️ Changes in the volume of the thoracic cavity during respiration are achieved by altering its dimensions vertically, anteroposteriorly, and transversely.
• 📐 The ribs are hinged at the back and angle downwards to attach to the sternum, allowing for changes in the thoracic cavity's diameters.
• 💪 The diaphragm is the primary muscle of respiration, contracting to flatten and increase the vertical dimension of the thoracic cavity during inspiration.
• 🔄 During quiet breathing, expiration is a passive process due to the lungs' elastic properties and does not require muscle contraction.
• 📉 The external intercostal muscles are involved in inspiration, elevating the ribs and moving the sternum forward to increase the thoracic cavity's volume.
• 🔄 Accessory muscles, such as the sternocleidomastoid, serratus anterior, and scalene muscles, assist in respiration when extra effort is needed.
• 📚 The diaphragm is innervated by the phrenic nerve, which originates from C3, C4, and C5, and damage to this nerve can lead to diaphragmatic palsy.
• 📉 The internal intercostal muscles and abdominal wall muscles are involved in expiration, pulling the ribs down and reducing the thoracic cavity's volume.
• 🔄 Quiet expiration is generally a passive process due to the lungs' elastic recoil, but active muscle involvement indicates the need for extra effort.
• 👍 Remembering the muscles of respiration can be aided by associating inspiration with 'E' for external intercostals and expiration with 'I' for internal intercostals.

Q & A

What is the primary function of the diaphragm in the respiratory process?

The diaphragm is the primary muscle of respiration responsible for most of the work during inspiration. When it contracts, it flattens, increasing the vertical dimension of the thoracic cavity, allowing the lungs to expand and draw in air.

What are the two phases of the breathing cycle?

The two phases of the breathing cycle are inspiration, which is the process of taking air into the lungs, and expiration, which is the process of breathing air out.

How do the ribs contribute to the changes in the thoracic cavity's dimensions during respiration?

The ribs, which are hinged at the back and angle downwards, can move to change the diameters of the thoracic cavity from front to back and sideways. The upper ribs move with a pump handle movement, increasing the anteroposterior diameter, while the lower ribs move with a bucket handle movement, increasing the transverse diameter.

What is the difference between active and passive expiration?

Active expiration requires the use of muscles to force air out of the lungs, often during conditions like respiratory distress. Passive expiration, on the other hand, is the result of the lungs' elastic properties causing them to recoil, and it does not require muscle action during quiet breathing.

Which muscles are considered accessory muscles of respiration and when do they come into play?

Accessory muscles of respiration, such as the sternocleidomastoid, serratus anterior, and scalene muscles, come into play during situations that require extra effort, like in respiratory distress, when the primary muscles are not sufficient.

How do the external intercostal muscles assist in inspiration?

The external intercostal muscles are attached to the ribs and are directed forwards and downwards. When they contract, they elevate the ribs, contributing to the increase in the thoracic cavity's volume during inspiration.

What is the role of the internal intercostal muscles during expiration?

The internal intercostal muscles are attached to the ribs with fibers that run downwards and backwards. They contract during expiration to depress the ribs, reducing the thoracic volume and aiding in the passive expulsion of air from the lungs.

What muscles are involved in the abdominal wall that assist in forced expiration?

The muscles of the abdominal wall that assist in forced expiration include the rectus abdominis, external and internal obliques, and the transversus abdominis. These muscles pull the ribs down and increase intra-abdominal pressure, which helps force air out of the lungs.

What nerve supplies the diaphragm and what condition can occur if it is damaged?

The diaphragm is supplied by the phrenic nerve, which originates from the cervical spinal nerves C3, C4, and C5. Damage to this nerve can result in diaphragmatic palsy, a condition that makes breathing difficult.

How does the movement of the ribs and sternum during inspiration and expiration relate to the anteroposterior and transverse diameters of the thoracic cavity?

During inspiration, the ribs move up and the sternum moves forward, increasing the anteroposterior diameter. The lower ribs' bucket handle movement increases the transverse diameter. During expiration, the ribs move down and the sternum falls back, reducing both the anteroposterior and transverse diameters.

What is the mnemonic provided in the script to help remember the muscles involved in inspiration and expiration?

The mnemonic provided in the script is 'E for I and I for E' to help remember that the external intercostal muscles are involved in inspiration and the internal intercostal muscles are involved in expiration.

Outlines

00:00

😀 Muscles of Respiration and Chest Wall Movement

This paragraph introduces the topic of respiratory muscles and the mechanics of the chest wall during breathing. It explains the breathing cycle, which includes inspiration (inhaling air into the lungs) and expiration (exhaling air out). The paragraph details how changes in the volume of the thoracic cavity are achieved through the movement of the ribs, sternum, and diaphragm. The diaphragm, a primary muscle of respiration, contracts during inspiration to increase the vertical dimension of the thoracic cavity, allowing the lungs to expand. During expiration, the diaphragm relaxes, and the lungs recoil due to their elastic properties. The paragraph also describes the role of the external intercostal muscles in elevating the ribs and sternum during inspiration and the involvement of accessory muscles during increased respiratory effort.

05:01

😉 Nerve Supply and Mechanics of Respiration

The second paragraph delves into the nerve supply of the diaphragm, highlighting the importance of the phrenic nerve which originates from cervical vertebrae C3, C4, and C5. Damage to this nerve can result in diaphragmatic palsy, affecting the ability to breathe. The paragraph summarizes the active process of inspiration, where the diaphragm and external intercostal muscles are primarily involved, along with accessory muscles such as the sternocleidomastoid, scalene muscles, and serratus anterior when extra effort is needed. It contrasts this with the passive process of quiet expiration, driven by the elastic recoil of the lungs and relaxed inspiratory muscles. If additional effort is required during expiration, muscles of the abdominal wall and internal intercostal muscles are engaged to depress the ribs and sternum. The paragraph concludes with a mnemonic 'e for i and i for e' to help remember the active and passive phases of respiration.

Keywords

💡Respiration

Respiration refers to the process of inhaling and exhaling, involving the exchange of gases within the lungs. In the context of the video, it is central to understanding how the muscles of the chest wall facilitate this process. The script discusses the active and passive phases of respiration, inspiration and expiration, and how they are achieved through the movement of the diaphragm and ribs.

💡Chest Wall

The chest wall is the bony and muscular structure that encloses the thoracic cavity. It plays a crucial role in the mechanics of breathing, as it changes its dimensions to accommodate the volume of air in the lungs. The script explains how the ribs and sternum move to facilitate inspiration and expiration, contributing to the overall theme of the video.

💡Inspiration

Inspiration is the act of inhaling, where air is taken into the lungs. The script describes it as an active process requiring muscle contraction, primarily of the diaphragm, to increase the volume of the thoracic cavity. It is a key concept in the video, illustrating the dynamic nature of the respiratory cycle.

💡Expiration

Expiration is the act of exhaling, where air is expelled from the lungs. The script explains it as a passive process during quiet breathing, driven by the elastic recoil of the lungs and the relaxation of the muscles involved in inspiration. It is contrasted with inspiration to highlight the different mechanics at play during the respiratory cycle.

💡Diaphragm

The diaphragm is a large, dome-shaped muscle that separates the thoracic cavity from the abdominal cavity. It is the primary muscle of respiration, as its contraction and relaxation directly influence the vertical dimension of the thoracic cavity. The script emphasizes its role in both inspiration, by flattening to increase lung volume, and expiration, by relaxing to decrease it.

💡Ribcage

The ribcage is the framework of the chest wall, consisting of ribs and the sternum. It is pivotal in the movement associated with respiration. The script describes how the ribcage moves up and down, affecting the anteroposterior and transverse diameters, which is essential for understanding the mechanics of breathing.

💡External Intercostal Muscles

The external intercostal muscles are located between the ribs and play a significant role in inspiration. They contract to pull the ribs upward and outward, increasing the thoracic volume. The script mentions these muscles as being integral to the process of inspiration, alongside the diaphragm.

💡Accessory Muscles

Accessory muscles are those that assist in respiration when additional effort is required, such as during respiratory distress. The script identifies several muscles that can serve as accessory muscles, including the sternocleidomastoid, serratus anterior, and scalene muscles, which help in elevating the ribs and sternum during forceful inspiration.

💡Internal Intercostal Muscles

The internal intercostal muscles are the counterparts to the external intercostal muscles, located on the inner side of the ribs. They are involved in expiration, as their contraction helps to depress the ribs and reduce the thoracic volume. The script contrasts these muscles with the external intercostal muscles to illustrate their opposing actions during the respiratory cycle.

💡Abdominal Muscles

Abdominal muscles, such as the rectus abdominis, external and internal obliques, and transversus abdominis, are involved in forced expiration. They contract to pull the ribs downward and increase intra-abdominal pressure, which helps to expel air from the lungs. The script highlights their role in active expiration when extra effort is needed.

💡Phrenic Nerve

The phrenic nerve is a critical nerve that supplies the diaphragm. It originates from the cervical spinal nerves C3, C4, and C5. The script discusses the importance of this nerve for proper diaphragm function, noting that damage to it can result in diaphragmatic palsy, which impairs breathing.

Highlights

The video discusses the muscles of respiration and chest wall movement during the breathing cycle.

Respiration involves inspiration (air intake) and expiration (air outtake), changing thoracic cavity volume.

Chest wall dimensions change vertically, anteroposteriorly, and transversely during respiration.

Rib movement is facilitated by their hinge at the back and angle to the sternum.

The diaphragm is the primary muscle of respiration, responsible for vertical movement.

Inspiration is an active process requiring muscle contraction, unlike passive expiration.

The diaphragm flattens during contraction, increasing the vertical dimension and allowing lung expansion.

Expiration involves the diaphragm relaxing, reducing thoracic volume, and lung contraction.

Ribcage and sternum movement is integral to changing anteroposterior and transverse diameters.

Upper ribs perform a pump-handle movement, increasing anteroposterior diameter.

Lower ribs execute a bucket-handle movement, increasing the transverse diameter.

Muscles of inspiration include the external intercostal muscles, which elevate the ribs.

Accessory muscles assist during increased respiratory effort, such as the sternocleidomastoid.

Accessory muscles include the serratus anterior and scalene muscles, among others.

Quiet expiration is typically passive, relying on lung elasticity and muscle relaxation.

Internal intercostal muscles and abdominal muscles are involved in active expiration.

The phrenic nerve is crucial for diaphragm function, with damage potentially leading to palsy.

A mnemonic 'e for i and i for e' is provided to remember the active and passive phases of respiration.

Transcripts

hi everyone welcome to bite size med

where we talk about quick bite-sized

concepts in basic medical sciences for

study and rapid review

this video is on the muscles of

respiration and how the chest wall moves

during respiration

the breathing cycle involves taking air

into the lungs that's inspiration

and breathing it out expiration this

involves changes in the volume of the

thoracic cavity

and that happens by changing its

dimensions vertically

anteroposteriorly and to some extent

transversely

how does this happen the ribs and the

sternum move

the ribs are hinged at the back and they

angle downwards to attach to the sternum

so they can move to change the diameters

from front to back and sideways

but what about vertically that's the

diaphragm

that is the muscle of respiration it

sort of takes on the entire load itself

inspiration is active muscles actually

actively have to contract for it to

happen

expiration is passive the lungs have

elastic properties

so it results in recoil when it

stretches

so in quiet expiration the muscles used

during inspiration

just relax so let's start with the

diaphragm

most of the work of inspiration is done

by the diaphragm alone

when it contracts it flattens so the

vertical dimension will increase

the lungs expand and air enters the

lungs

during expiration the opposite happens

the diaphragm relaxes

the thoracic volume reduces the lungs

contract

and air gets out the ribcage can move up

or down and since they're attached to

the sternum

when the ribs move up the sternum moves

forward

that increases the diameter from front

to back

when the ribs come down the sternum will

fall back

and the diameter reduces so ribs move up

and sternum moves forward in inspiration

the ribs come down the sternum falls

back in expiration

the upper ribs move with the pump handle

movement

so it moves the sternum up and down and

increases the anteroposterior diameter

the lower ribs have a bucket handle

movement

that increases the transverse diameter

but what moves the ribs muscles

so the muscles that elevate the ribs

will be those of inspiration

and those that depress the ribs will be

those of expiration

so in addition to the diaphragm the

external intercostal muscles are muscles

of inspiration

they are attached to the ribs and

directed forwards

and downwards to attach to the rib below

so sort of like the direction of your

hands when you put them in your jacket

pockets

so because of the direction of these

fibers when they contract

the ribs move up now these two muscles

are good enough during regular

inspiration

but when a little extra effort is needed

more muscles might be required

like in respiratory distress these are

called

accessory muscles they are accessory

and start working when needed

most of the muscles that attach to the

ribs can serve as accessory muscles

solve the muscles of the chest wall

some that are easy to remember start

with the letter s

like the sternocleidomastoid which like

the name suggests

originates from the sternum and the

clavicle so it can lift the sternum

which is helpful during inspiration

the others are the serratus anterior and

the scalene muscles

so like i said any muscle of the chest

wall can contribute

like the pectoral muscles the

transversus thoracic muscles

etc now that was all inspiration

and like i said it's active so there's a

lot of muscles

quiet expiration remember is passive so

quiet exploration doesn't need the

muscles to move

if muscles are being used it's because

extra

effort is needed and these are again

accessory muscles

so these muscles have to depress the

ribs to reduce the volume

now the external intercostals handle

inspiration

here the internal intercostals play a

role

they are also attached to the ribs but

their direction changes

they're downwards and backwards so it

makes sense that the action that they

have on the ribs is the opposite

they depress the ribs the ribs can also

be depressed by contraction of abdominal

muscles

the rectus abdominis the external and

internal

obliques the transversus abdominis they

pull the ribs down and also increase

intra-abdominal pressure

so they can also elevate the diaphragm

and if the lung gets smaller it forces

more air out

the nerve supply to these muscles is

important particularly the diaphragm

the diaphragm is supplied by the phrenic

nerve which originates from c3

c4 and c5 if there's damage to this

nerve

there can be diaphragmatic palsy which

makes it difficult to breathe

so let's put it all together inspiration

is active

most of the job is done by the diaphragm

also the external intercostals

they move the ribs up and the sternum

forwards

accessory muscles are the

sternocleidomastoid

the scalene muscles serratus anterior

and other muscles of the chest wall

expiration quietly is passive it's from

elastic recoil

the muscles of inspiration relax if

extra effort is needed muscles come into

play

the muscles of the abdominal wall and

the internal intercostals

they pull the ribs down and the sternum

falls backwards

so e for i and i for e if you get

confused

and those are the muscles of respiration

and how the chest moves during

respiration

if this video helped you give it a

thumbs up share and subscribe thanks for

watching and i'll see you in the next

one