–       A chemoreceptor, also known as chemosensor, is a specialized sensory receptor cell which transduces (converts) a chemical substance (endogenous or induced) and generates a biological signal.


–       The pons is the other respiratory center and is located underneath the medulla. Its main function is to control the rate or speed of involuntary respiration.

Respiratory Muscles

–       The muscles of respiration are those muscles that contribute to inhalation and exhalation, by aiding in the expansion and contraction of the thoracic cavity. The diaphragm and, to a lesser extent, the intercostal muscles drive respiration during quiet breathing.

Medulla Oblongata

–       The medulla oblongata is a portion of the hindbrain that controls autonomic functions such as breathing, digestion, heart and blood vessel function, swallowing, and sneezing. Motor and sensory neurons from the midbrain and forebrain travel through the medulla.

Rhythm Controllers in the Brainstem

1.    Medulla

Dorsal respiratory group – associated with inspiration

Ventral respiratory group – associated with expiration

Pre-Botzinger complex – pattern generator, also ventral

2.    Pons

Apneusic center – has an excitatory function

Pneumotaxic center – can inhibit inspiration

Other Regions of the Brain That Can Affect Respiration

1.    Cortex

–       Can exercise voluntary control

2.    Limbic System and Hypothalamus

–       Emotional states


1.    Diaphragm- The diaphragm is a thin skeletal muscle that sits at the base of the chest and separates the abdomen from the chest. It contracts and flattens when you inhale. This creates a vacuum effect that pulls air into the lungs. When you exhale, the diaphragm relaxes and the air is pushed out of lungs.

2.    Intercostal Muscles– Intercostal muscles are several groups of muscles that run between the ribs, and help form and move the chest wall. The intercostal muscles are mainly involved in the mechanical aspect of breathing. These muscles help expand and shrink the size of the chest cavity to facilitate breathing.

3.    Abdominal Muscles– The abdominal muscles form the anterior and lateral abdominal wall and consist of the external abdominal obliques, the internal abdominal obliques, the rectus abdominis and the transversus abdominis . Acting together these muscles form a firm wall that protects the viscera and they help to maintain erect posture.

4.    Accesory Muscles– An accessory muscle is a relatively rare anatomic duplication of a muscle that may appear anywhere in the muscular system. Treatment is not indicated unless the accessory muscle interferes with normal function.


1.    Central Chemoreceptor – Central chemoreceptors of the central nervous system, located on the ventrolateral medullary surface in the vicinity of the exit of the 9th and 10th cranial nerves, are sensitive to the pH of their environment.

2.    Peripheral Chemoreceptors – Peripheral chemoreceptors are so named because they are sensory extensions of the peripheral nervous system into blood vessels where they detect changes in chemical concentrations.

3.    Lung Receptors – Pulmonary stretch receptors are mechanoreceptors found in the lungs. When the lung expands, the receptors initiate the Hering-Breuer reflex, which reduces the respiratory rate. Increased firing from the stretch receptors also increases production of pulmonary surfactant.

4.    Other receptors


–       Specialized tissues that responds to a change in the chemical composition of the blood or other fluid


–       Baroreceptors are mechanoreceptors located in the carotid sinus and in the aortic arch. Their function is to sense pressure changes by responding to change in the tension of the arterial wall. The baroreflex mechanism is a fast response to changes in blood pressure

Carotid Bodies

–       Carotid bodies are sensory organs that detect changes in arterial blood oxygen, and the ensuing reflexes are critical for maintaining homeostasis during hypoxemia. During the past decade, tremendous progress has been made toward understanding the cellular mechanisms underlying oxygen sensing at the carotid body.

Lung Receptors

1.    Pulmonary Stretch Receptors – (also called slowly-adapting pulmonary stretch receptors)

–       Responsible for the Hering- Breuer Reflex

2.    Irritant Receptors – (also called rapidly-adapting pulmonary stretch receptors)

3.    J Receptors – juxta capillary receptors

4.    Bronchial C Fibers

Other Receptors

1.    Nose and Upper Airways

2.    Joint and muscle

3.    Gamma system

4.    Arterial baroreceptors

5.    Pain and temperature

Response to Reduced PO2

·         No role under normoxic conditions

·         Measured by rebreathing from a bag

·         Increased response if the PCO2is raised

·         Important in high altitude

·         Important in some patients with chronic lung disease

Sleep Apnea

–       Sleep apnea is a potentially serious sleep disorder in which breathing repeatedly stops and starts. If you snore loudly and feel tired even after a full night’s sleep, you might have sleep apnea. The main types of sleep apnea are: Obstructive sleep apnea, the more common form that occurs when throat muscles relax.