23.5 C Nervous Control of Rhythmic Quiet Breathing

The skeletal muscles of quiet breathing are innervated by what?

motor neurons

Respiratory Center

Group of nuclei within the brainstem that rhythmically coordinate the motor neurons that innervate the skeletal muscles of quiet breathing.

The respiratory center splits into 2 regions

Medullary respiratory center

Pontine respiratory center

Medullary respiratory center

Located within the medulla oblongata and is composed of 2 groups of nuclei:

Ventral respiratory group (VRG) and dorsal respiratory group (DRG)

Ventral respiratory group (VRG)

Located within the anterior region of the medulla(which contains both inspiratory neurons and expiratory neurons)

Dorsal respiratory group (DRG)

located posterior to the VRG.

Pontine Respiratory Center/ pneumotaxic)

Located within the pons

Lower motor neutrons within the ___ innervate the ___

phrenic nerves; diaphragm

Lower motor neurons within the ___nerves innervate the ____muscles

intercostal;intercostal

The phrenic nerves originate within the ___ and continue inferiorly through the __cavity to innervate the diaphragm.

neck; thoracic

Intercostal nerves extend from the ___region and continue laterally to innervate the ____muscles.

thoracic;intercostal

How is quiet inspiration initiated?

Nuclei within the medullary respiratory center initiate signals that are sent through the phrenic nerve and intercostal nerves to the diaphragm and external intercostal muscles.

How long do signals from the nuclei within the medullary respiratory center last for?

2 seconds; intensity of the signals increases over these 2 seconds.

How is quiet expiration initiated?

With the cessation of signals that are relayed through the phrenic nerve and intercostal nerves to the diaphragm and external intercostal muscles.

How long is the cessation of signals?

3 seconds

Respiratory rate

A breathing rhythm that involves 2 seconds of inspiration followed by 3 seconds of expiration. 12 times per minute.

eupnea

Range for the rate of quiet breathing between 12 and 15 times per minutes.

The specific role of the pontine respiratory center(in breathing)

To relay signals to the medullary respiratory center to facilitate a smooth transition between inspiration and expiration.

Chemoreceptors

Dendritic endings of a sensory neuron that serve as sensory receptors for detecting chemicals, either molecules or ions.

Chemoreceptors associated with altering breathing….

are distinguished by their location within the body and the specific chemicals they (O2, CO2, H+).

2 categories: peripheral chemoreceptors and central chemoreceptors.

Peripheral chemoreceptors

located both within the aortic arch (aortic bodies) and at the split of each common carotid artery into the external and internal carotid arteries (carotid bodies). (You may have noticed that these chemoreceptors are in close proximity to the baroreceptors involved in regulating blood pressure, which are described in L section 20.6a.) Peripheral chemoreceptors monitor chemicals within the blood-specifically, arterial blood.

Peripheral chemoreceptors are stimulated by

an increase in Pco2 and an increase in Ht concentration within the blood.

Sensory neurons extend from peripheral chemoreceptors to the —-

medullary respiratory center

From the aortic bodies, the sensory neurons are within the ___ nerves

vagus

From the carotid bodies, the sensory neurons are within the ____nerves

glossopharyngeal nerves

Central chemoreceptors

located within the medulla oblongata in close proximity to the medullary respiratory center, and monitor the contents of the cerebrospinal fluid (CSF). Central chemoreceptors monitor only H+ changes in CSF.

What is the source of H+ that is detected in the CSF by central chemoreceptors?

The source is CO, in the blood and the formation of H*, which occurs as follows: CO, (as a small nonpolar molecule) diffuses from the blood across the BBB into the CSF.

Once in the CSE, CO2is combined with H2O to form HCO3, and Ht through an enzymatic reaction catalyzed by carbonic anhydrase. Central chemoreceptors specifically detect the H+ produced in the CSF from CO, (and H2O) as a result of this chemical reaction.

Central chemoreceptor detection of H+ level in the CSF is an

indirect means of monitoring the CO2 level in the blood

CO2 level in the blood and H+ level in the CSF are

directly related.

Increase in CO2= Increase in H+

H+ levels in the CSF is the only source of H+ that is?

Monitored by the central chemoreceptors

Why is the H+ in the CSF the only monitored CSF?

Because other types cannot cross the BBB (Blood Brain Barrier) to exit the blood and enter the CSF.

CSF lacks ___ to buffer the gain or loss of H+

proteins

Reflexes that alter breathing rate and depth are

homeostatic systems that are regulated by negative feedback

Involves 5 components of a reflex arc.

Steps in chemoreceptors Reflex

Sensory receptors detect stimuli. The peripheral chemoreceptors detect an increase in blood Pco2, an increase in blood Ht concentration, or both, whereas the central chemoreceptors detect an increase in Ht concentration in the CSF (which is produced from CO, that diffused into E the CSF from the blood).

1. Sensory neurons. Peripheral chemoreceptors initiate an increase in signals along sensory neurons within the vagus nerves from the aortic bodies and the glossopharyngeal nerves from the carotid bodies to the medullary respiratory center. In comparison, central chemoreceptors initiate additional signals directly to the closely located medullary respiratory center.

2. Control center. The respiratory center integrates this input.

3. Motor neurons. In response, the respiratory center alters signals relayed along somatic motor neurons to the skeletal muscles of breathing.

4. Effectors. Skeletal muscles are stimulated to contract and then relax to change both the rate and the depth of breathing. Change in the rate of breathing is accomplished by altering the amount of time spent in both inspiration and expiration, whereas altering the depth of breathing is accomplished through stimulation of skeletal muscles of breathing, including accessory muscles of breathing, which results in greater thoracic volume changes (see L section 23.5b). Respiration rate and depth are increased and additional CO_ is expelled, ultimately returning blood Pco2 and CSF Ht levels to their previous set point levels.

Chemoreceptors are very sensitive to change in blood PCO2 levels

increases in Pco, levels as small as 5 mm Hg will double the breathing rate (e.g., from 12 breaths to 24 breaths per minute). The changes in blood Pco, can stimulate respiratory rate changes most powerfully when the carbon dioxide is joined to water, forming Ht in the CSF.