Physiology 3120 Lecture Notes - Pulmonary Stretch Receptors, Peripheral Chemoreceptors, Central Chemoreceptors

14 views2 pages
Published on 26 Nov 2011
School
Western University
Department
Physiology
Course
Physiology 3120
Professor
Human Physiology
Monday, February 8, 2010
“Respiration V”
Regulation of Respiration
Origin
Nerve impulses from brain
Rhythmic discharges from motor neurons that innervate respiratory muscles
Negative feedback loop
Motor neurons supplying inspiratory muscles are inhibited by those supplying the
expiratory muscles
Breathing stops when spinal cord is cut above C3, 4, or 5
Voluntary system (i.e. when swimming, holding your breath, etc.)
Pathway from cerebral cortex through corticospinal tract to the respiratory motor neurons
Limited control
Automatic system
Maintain normal blood-gas values
Very efficient
3 components
1. Receptors; also four types of receptors
Collect info on current blood-gas values; send signals to controller
Central chemoreceptors
oRespond to changes in fluid around it, not the absolute concentration
oLocated in medulla, surrounded by brain ECF
oResponds to change in PCO2; actually an indirect response to pH (H ions
don’t cross the BBB)
Peripheral chemoreceptors
oIn carotid bodies at bifurcation of the common carotid arteries
oRespond to PO2; when arterial PO2 decreases below 60mmHg, get
increased ventilation
oAlso minor response to PCO2 and pH
Lung receptors
oPulmonary stretch receptors; respond to overdistention of the lung, and
slow down ventilation rate
oIrritant receptors (respond to inhaled dust, cigarette smoke, etc.)
Other receptors
oNot clearly defined
oReceptors in nose & airways responding to chemical/mechanical strains
oJoint and muscle receptors that respond during exercise
oPain & temperature receptors
2. Central controller (brain) coordinates responses to information from receptors; actually
has 4 “respiratory centres”
Inspiratory area
oDorsal group of neurons in medulla
oCritical in respiration
oInherent rhythmic excitability (like SA node)
oInitiates inspiratory drive
Pneumotaxic area
oIn the pons
oFine-tuning, but not essential
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