Intercostal Muscles and Breathing Mechanics

Study Notes

The intercostal muscles are a group of muscles located between the ribs.
There are three layers of intercostal muscles: external, internal, and innermost.
The external intercostal muscles run diagonally downward and forward, assisting in inhalation.
The internal intercostal muscles run diagonally downward and backward, helping in exhalation.
The innermost intercostal muscles are the deepest layer, and their function is similar to the internal intercostal muscles.
The sternocleidomastoid and pectoral muscles are associated structures, supporting movement of the ribs and thus aiding breathing.

Breathing is driven by changing pressure in the lungs.
Air moves from areas of higher pressure to lower pressure.
Inhalation involves expanding the rib cage and pulling air into the lungs.
Exhalation involves the rib cage getting smaller, decreasing lung volume and pushing air out.
The diaphragm, a large muscle under the lungs, moves down during inhalation and up during exhalation.

Homeostasis (balance) in breathing is maintained through a three-step process.
Receptors detect changes in CO2 and O2 levels in the blood and cerebrospinal fluid (CSF).
The control center, mainly the medulla oblongata, processes sensory input and regulates breathing rate.
Effectors, like the diaphragm and intercostal muscles, are controlled to carry out the process of breathing.

Inspiratory Reserve Volume (IRV): The extra air that can be inhaled after a normal breath.
Expiratory Reserve Volume (ERV): The extra air that can be exhaled after a normal breath.
Tidal Volume (TV): The amount of air inhaled or exhaled in a normal breath.
Residual Volume (RV): The amount of air remaining in the lungs after a maximum exhalation.
Inspiratory Capacity (IC): The total amount of air that can be inhaled after a normal breathing cycle.
Functional Residual Capacity (FRC): The total amount of air remaining in the lungs after a normal exhalation.
Vital Capacity (VC): The largest amount of air that can be exhaled after a maximum inhalation.
Total Lung Capacity (TLC): The total amount of air the lungs can hold. (TLC = VC + RV)

Resistance to airflow affects breathing.
Narrowed airways or other obstacles can hinder the movement of air in the lungs.
Mucus, blood clots, or other blockage can cause resistance in vessels.
Conditions like smoking can cause resistance.

Emphysema (air sac damage).
Chronic bronchitis (mucus buildup).
Bronchiolitis (small airway inflammation).
Asthma (airway inflammation).
These conditions can reduce the ability of the lungs to effectively exchange gases.

Compliance is how much the lungs can stretch and expand.
This is affected by factors like the elasticity of lung tissue, and the presence of blockages during breathing.