Neural Control of Respiration Flashcards
What are the main muscles involved in respiration and what are the nerves innervating them ?
Diaphragm and Intercostals
Phrenic and Intercostal nerves
Explain the process of expiration, focusing on the action of the nerves innervating the muscles responsible for respiration.
Neurons cease the discharge of action potentials and the chest recoils back to FRC (basic pattern).
Draw a graph demonstrating a) change in number of active inspiratory nerves and b) tidal volume, over the cycle of respiration.
Refer to slide 4 of lecture on “Neural Control of Respiration”.
During inspiration, activity of inspiratory neurons increases steadily, apparently through a positive feedback mechanism. At the end of inspiration, activity shuts off abruptly (but still some inspiratory neurons active) and expiration takes place through recoil of elastic tissue.
Describe the experimental evidence which helps us better understand where the rhythmic pattern of respiration originate, and explain the implications of this evidence on the origin of the rhythmic pattern of respiration.
- If the brainstem is cut above the level of the pons, the basic rhythm continues
- If all the afferent nerves to the brainstem are cut, the basic rhythm continues
- If you section the spinal cord below C3-C5, the intercostal muscles are paralysed
- If you section below the medulla, all respiration ceases
Hence,
a) the respiratory muscles themselves do not have an intrinsic rhythmicity (unlike the heart).
b) the brainstem contains all the components to generate a rhythmic pattern of respiration (i.e. if stimulate various areas of the brainstem, you can alter the pattern of breathing)
Where is respiratory rhythm generated ?
Medulla Oblongata and Pons, both in the brainstem (specifically in respiratory centers), controls diaphragm, intercostals, central chemoreceptors, peripheral chemoreceptors, and other receptors.
Cortex and other brain areas can influence the medulla.
However, cortex and other areas can by-pass the medulla and affect the lower motor neurones directly (i.e. affect diaphragm and intercostals, to consciously decide to hold your breath or alter ventilation rates).
Identify the main mechanisms of regulation of respiration.
- Nervous or neural
* Chemical
Define respiratory centers.
A series of nerve centers (contain both afferent and efferent nerves) -the apneustic, pneumotaxic, and medullary respiratory centers- in the medulla and pons that coordinate respiratory movements.
Why is the term “respiratory center” a misnomer ?
Because “respiratory center” describes diffuse networks, possibly at higher density which are active together to bring about the respiratory effect, rather than discrete anatomical regions or bodies that can be identified macro- or microscopically.
Identify the main ways to control blood pH. Which one is more useful ? Why ?
Urination
Breathing (more useful, because more frequent)
Where are the respiratory centers located ?
In the medulla and pons
What is the function of the respiratory centers?
Collect sensory information about the levels of oxygen and carbon dioxide in blood that determines the signal sent to respiratory muscles (stimulation of these muscles provides respiratory movements which produce alveolar ventilation).
Does the process of breathing normally take a lot, or a little energy ? Why ?
Pattern of breathing is aimed to minimise the amount of work done (economy of energy, evolutionary beneficial). For instance lungs are kept partially inflated even at the end of expiration, which allows for its inflation with less energy than would be required if it had been full deflated.
List the respiratory centers. State and show their location on an image of the brainstem.
Pontine Centres:
- Pneumotaxic (located in upper Pons)
- Apneustic (located in lower Pons)
Medullary Centres:
1. Inspiratory (located in upper part of medulla oblongata)
2. Expiratory (located in medulla oblongata, anterior and lateral to the inspiratory
centre)
For location, refer to slide 9 of lecture on “Neural Control of Breathing”.
Identify the function of the medullary respiratory centers.
Identify the muscles and nerves involved with each center.
Inspiratory = Driving inspiration. Diaphragm and external intercostals involved. Exclusively inspiratory neurons inside it.
Expiratory = Centre is inactive during quiet breathing and when inspiratory centre is active, but during forced breathing or when inspiratory centre is inhibited it becomes active. Drives internal intercostals.
Mixture of inspiratory and expiratory neurons inside it.
Identify the other names of inspiratory and expiratory respiratory centers.
Inspiratory centre (= Dorsal Respiratory Group (DRG))
Expiratory centre (=Ventral Respiratory Group (VRG))
Identify the function of the pontine respiratory centers.
Pneumotaxic centre: Controls medullary respiratory centres, especially the inspiratory centre through the apnuestic centre. It influences inspiratory centre so that duration of inspiration is under control.
Apnuestic centre: Increases depth of inspiration by acting on inspiratory centre.
Describe the path of the afferent and efferent nervous pathways for respiration.
Afferent pathway: deliver impulses via vagus
(movement of thoracic region and lungs) and glossopharyngeal nerves (impulses from chemoreceptors), to respiratory centers.
Efferent pathway: nerves from respiratory centre leave brain in anterior part of lateral column in spinal cord, terminate in motor neurons in cervical and thoracic segments of spinal cord, and supply phrenic (controls diaphragm) and intercostal (controls intercostals), thereby driving inspiration and expiration.
Identify the factors which affect the respiratory centers.
- Impulses from higher centres
- stretch receptors of lung slowly adapting pulmonary receptors
- ‘J’ receptors, or pulmonary C-fibres
- Irritant receptors of lungs
- Proprioreceptors
- Thermoreceptors
- Pain receptors
- Cough reflex
- Sneezing reflex
- Deglution reflex
Describe the impulses from higher centers , in affecting the respiratory centers.
Impulses from cerebral cortex, limbic system, hypothalamus, can stimulate or inhibit respiratory centres directly.
Describe the role of stretch receptors of lung (slowly adapting pulmonary receptors), in affecting the respiratory centers.
= Hering-Breur Reflex
Smooth muscle of upper airways has slowly adapting stretch receptors. When lung is inflated these neurons send impulses to DRG (i.e. inspiratory center) via the vagus nerve. This input is inhibitory, limiting inspiration, prevents overinflation of lungs. Active more in first year of life and during strenuous exercise when tidal volume over 1 liter.
Describe the role of ‘J’ receptors, or pulmonary C-fibres, in affecting the respiratory centers.
- Juxtacapillary receptors present in wall of alveoli, in close contact with pulmonary capillaries.
- Stimulated during conditions like pulmonary oedema, congestion, pneumonia, Also from endogenous chemicals such as histamine (i.e. inflammatory process in lungs).
- Stimulation of J receptors induces apnea – temporary suspension of breathing- followed by rapid shallow breathing + induces mucus secretion + induces bronchoconstriction.
Describe the role of irritant receptors of the lungs, in affecting the respiratory centers.
- Situated on walls of bronchi and bronchioles
- Rapidly adapting receptors –powerfully stimulated by inhalation of irritants (e.g. harmful chemicals like ammonia, or cigarette smoke)
- Induces rapid shallow breathing, mainly from shortening of expiration + also, and possibly confusingly, long deep augmented breaths, which are taken by mammals every 5-20 mins on average to reverse slow collapse of lungs that occurs during quiet breathing + induces coughing + induces bronchoconstriction
Describe the role of proprioreceptors of the lungs, in affecting the respiratory centers.
- Situated in chest wall (in joints, muscles, tendons)
- Aim is for reflexes from muscles and joints to stabilise ventilation (i.e. normal breathing) in the face of changing mechanical conditions
1) In joints, e.g. measure the velocity of rib movement
2) In tendons –found within muscles of respiration (diaphragm and intercostals), detect strength of muscle contraction
3) In muscle spindles – monitors length of fibers both statically and dynamically – length and velocity.
Identify some of the external receptors which affect the respiratory centers.
Thermoreceptors, pain receptors.
