CSB346 Lecture 1 – Inspirational Neuroscience (January 08, 2013)
5 – Why study breathing?
- The respiratory system is critical for life, and it is extremely sensitive to what you are doing.
6 – Central regulation of breathing
- There are a group of cells that generates breathing. It doesn’t need any conscious effort. The
respiratory network makes you have a motor behaviour that you don’t have to think about. The
respiratory system relies on the brain to cause the muscles to contract and relax.
- The brain doesn’t constantly use all the muscles that help you breathe under certain
circumstances. The ultimate goal of the respiratory system is to get you enough O2 to your
working tissue and get rid of the CO2 that your working tissues are producing at a rate that is
not exceeding the metabolic demand.
8 – Functions of the respiratory system
- Acid-base balance
o When you get kidney disease, the acid-base balance is going to be disturbed. This affects
how you breathe. The parts of the brain that listen and recognize are affected, which
has a pathological influences respiration.
- Speaking and vocalization
o The respiratory control in humans is tied to how we can communicate.
- Immune protection
o The lungs are the biggest filters of the air you inhale.
o The lungs are involved in immune protection.
Smokers are constantly sicker than non-smokers.
Smokers have lower immune protection.
- Regulation of body temperature
o Breathing is the way animals warm and cool their bodies. Dogs do not sweat like
humans. Dogs use the respiratory system to regulate the body temperature.
- The respiratory system isn’t just about getting O2 into the tissue and CO2 out of the tissue. It
has to work in unison with so many other systems (e.g., kidneys, immune system, regulatory and
metabolic systems). It does it on the fly, every millisecond. It is a complicated system.
9 – Functions of the respiratory system
- This shows you the functions of the respiratory system in the most four basic ways.
- Pulmonary ventilation
o You have to have it. If you don’t have appropriate lung tissue, then the brain can’t
control you to expand and contract your lungs.
o It delivers O2 to the lung tissue, which diffuses into the vascular system for gas
exchange, so you can transport O2 and CO2 to and from the working tissue.
10 – Respiratory systems across species
- They all have different respiratory systems that have different control mechanisms.
o In a salamander, the lungs are on the outside of the body. There is no muscle
contraction to get gas exchange to occur.
o In a lobster, the movement of water over their respiratory surface (e.g., lungs) is
sufficient to get O2 in and CO2 out of their bodies. Their respiratory control system is
completely different. They don’t have muscles that cause respiration to occur. o In insects and crustaceans, they have passive ventilation. This means that they are not
actively engaging in the contraction of the respiratory muscles for gas exchange to
occur. There is passive movement of O2 across the gas exchanger. It moves O2 and CO3
by passive diffusion.
o All of the above have low metabolic rates, which limit their ability to do things.
- In mammals, we have to actively do something to get O2.
o This course will focus on mammalian breathing.
11 – Anatomy of the respiratory system
- These are the machinery required to ventilate the lung. The mouth and nose are helpful to get
O2 into the lung. The diaphragm is the main respiratory muscle. It causes inflation of the lung by
contracting, lowering down, making the chest cavity bigger, the lung tissue inflates passively,
and O2 and air moves down a pressure gradient to fill the lung.
- The nasal cavity, oral cavity, pharynx, larynx, trachea and bronchus are all part of the respiratory
system, but they have nothing to do with getting O2 into your body. They are highways to get to
the lung tissue.
- The lung tissue (e.g., the alveoli) is the functional part of the respiratory system.
12 – The conducting and respiratory zones
- This is the conducting part of the respiratory system.
- The alveoli are like little balloons. They are made up of epithelial tissue. They are coated in
arteries and veins. The O2 or the air you breathe in gets to these alveoli. The O2 needs to diffuse
from the alveoli into the arterial blood supply. It goes down a concentration gradient.
- Terminology: singular (alveolus), plural (alveoli), cluster (alveolar sac)
13 – Anatomy of the alveoli
- It is made up of lots of epithelial cells. They are coated in capillaries, which allow the O2 to
diffuse in to the working tissue, or CO2 diffuse out of the body.
- The alveolar epithelium is once cell thick. The alveolar epithelium and the capillary are
separated by a small distance, called the respiratory membrane, which allows the O2 to diffuse
across from the alveolus into the capillary, or CO2 to diffuse across from the capillary into the
alveolus. It is one cell thick on both sides. The small distance allows O2 to passively move from
the lung tissue (e.g., alveolus) into the capillary bed.
14 – Blood-gas interface
- O2 diffuses down the concentration gradient into the blood because there is more O2 in the
alveolar space than in the capillary. CO2 diffuses out of the blood. The RBC takes up the O2 and
transport O2 to the working tissue.
- The distance between the alveolus and the capillary is extremely narrow. It is a two-cell thick
structure separated by interstitial fluid. As the O2 gets collected, it goes back to the heart and
then the working tissue.
15 – Smoking and the lungs
- The smoke disrupts the blood-gas exchange.
17 – Smoking and the lungs
- Smoking destroys the structure that allows O2 to get to the blood (e.g., the alveoli).
- Smoking kills the capillaries that take up the O2. o It damages the capillary beds that surround each of the alveoli.
- Smoking pops the alveoli, which damages the capillaries that surround the ones that are left.
o The capillaries can re-generate.
18 – Respiratory muscles
- The diaphragm is the main respiratory muscle. The diaphragm contracts down, opens up the
chest cavity, the lungs are stuck to the chest cavity, the lungs open, and the air flows into the
lungs down a pressure gradient.
19 – Respiratory muscles
- What are the neural inputs that allow the diaphragm to contract and relax?
- The diaphragm contracts, makes the thoracic larger, the pressure gradient goes down, and air
moves down the pressure gradient.
20 – Chest wall and pleural sac
- The pleura surrounds the lungs. The visceral pleura surrounding the lung is attached to the
parietal pleura on the inside of the chest wall. The lungs are physically stuck to the chest wall.
They are stuck together because of the cohesive property of the fluid in between them. There is
suction between the two pleura. This keeps the lungs glued to the chest and the diaphragm.
- This is why the lungs expand when the diaphragm contracts. The lungs move out with the
diaphragm and the chest wall, which creates a pressure gradient.
22 – The pleura
- The one way to disassociate the lung from the chest wall is by being stabbed in the chest. It
disrupts the union between the pleura of the lung and the pleura of the chest cavity. This is a
problem because the cohesive property is now broken. The air gushes in and the lung collapses.
- A spontaneous pneumothorax means you have some kind of tumour or cyst in the lung.
23 – Pneumothorax
- The blood gets in between the parietal pleura and visceral pleura. The lung can’t contract and
expand because the fluid is pushing the lung tissue in.
25 – Secondary pneumothorax
- Another way to get a pneumothorax is if you have emphysema. The texture and the surface
outline of the lung tissue are different. The disease degrades the pleura that cover the lung.
- Another way to get a pneumothorax is when a tumour or a degenerative process physically eats
through the pleura.
26 – Components of the respiratory system
- The pleura that coat the lungs and the inside of the thoracic cage are critical because they form
an organ or structure that allows for the lungs to stick to the rib cage. This process allows the
lungs to expand when the rib cage expands.
- The lungs are not muscles. The lungs are useless tissues by themselves. They are the gas
exchange organ. They are the part of the body that allows O2 to diffuse in and CO2 to diffuse
out. They do not expand and contact by their own properties. The muscles of the rib cage, the
muscles of the diaphragm, and the muscles of the upper airways (e.g., nose, lips, tongue,
pharynx, and larynx) are doing the work to keep the airways open to expand the rib cage. The lungs are effectively stuck to the rib cage. This means that as the rib cage expands, so do the
lungs. The lungs themselves are not muscles. They do not expand and contract.
27 – The major and minor players
- The muscles are doing what the brain tells them to do. They are the action. The brain controls
the muscles of breathing.
- Muscles do not do the same thing all the time. You use some muscles to do various behaviours.
Under some conditions, one muscle can behave as a respiratory muscle. Under another
condition, it can be a muscle that is used to defecate.
28 – The pump
- The main muscle of breathing is the diaphragm. The diaphragm is the main respiratory muscle.
The diaphragm is the dome muscle that sticks along your rib cage.
- The diaphragm that separates the lungs from the guts. It is important in keeping those two
components of your body separated (e.g., the organs in the thorax from the organs in the
- The main job is that it is the muscle that allows the rib cage to expand.
o When the diaphragm contracts, it descends. As it descends, because the diaphragm is
sealing off the thoracic cavity, it effectively makes it a bigger place. When the diaphragm
contracts, the place gets bigger. The place is where the lungs are sitting and stuck to the
diaphragm and the rib cage, and that allows the lungs to expand when the diaphragm
- The diaphragm is the main respiratory muscle because it has most movement. It can move
further than the rib cage. The diaphragm can move a lot. It can move up to 15 cm down. This is a
lot of space to make the rib cage bigger.
- We have to discuss the function of the muscle in the context of breathing. What is the muscle
doing for breathing? Does it contract during inspiration and help you expand your lungs (e.g.,
expire)? Or does it participate in expiration and help you get air out of the lungs (e.g., make the
thoracic cavity or rib cage smaller)?
o We need to think about the MNs (e.g., the nerve cells that tell the muscle what to do).
o Every single muscle in the body is controlled by a set of cells called MNs. They are only
controlled by one set of MNs. The muscle cannot do anything unless the MNs that go to
it tell it do something. One muscle does not have multiple command systems.
o There is a pool of MNs (e.g., motor pool or motor nucleus) that tell the particular muscle
when to be active or when to be inactive.
- The diaphragm is innervated by MNs called phrenic motor neurons.
o The C refers to cervical. The 3 refers to the third cervical vertebrae.
o The phrenic MNs that drive diaphragm activity are located between C3 and C5. This
denotes where the MNs are in the spinal cord.
- Every muscle has its own unique set of MNs. You should be aware what muscle is driven by
what motor pool.
- The blue line shows where the diaphragm normally sits when it is not contracting (e.g., during
expiration). It contracts downward. The contraction moves the diaphragm down and helps to
move the rib cage outward.
29 – The motor nerves
- All of the motor pools (e.g., the nerve cells that communicate with a particular muscle) that we
are going to discuss are located in the spinal cord. o You have the cervical, thoracic and lumbar spinal cord. We are almost going to
exclusively focus on the cervical and thoracic component. Some abdominal muscles can
be innervated by MNs that are located lower down in the spinal cord.
- Each of these is numbered. The phrenic motor neurons that excite the diaphragm are sitting in
the spinal cord around the C3-C5.
- The information coming to the MNs is higher up in the brainstem. If you disrupt the ability of the
MNs to listen to the signals the brain is sending to them, they can’t do their job, which is to send
the information to the diaphragm so the diaphragm knows when to contract and relax. The
diaphragm does what MNs tell them.
o The MNs are the most important part of the nervous system.
o You are a giant object that moves. All the things that your brain d