Movement, the fundamental component of behavior and the principal extrinsic action of the brain, is produced when skeletal muscles contract and relax in response to patterns of action potentials ge...

/pdf/synaptic-control-of-motoneuronal-excitability-104bymieik.pdf

Synaptic Control of Motoneuronal Excitability

Contraction of the diaphragm is controlled by phrenic motoneurons that receive input from sources that are not fully established. Bulbospinal (second-order) neurons projecting to phrenic motoneurons and propriobulbar (third-order) neurons projecting to these bulbspinal neurons were investigated in rat by transsynaptic transport of the neuroinvasive pseudorabies virus. Bulbospinal neurons were located predominantly in the medullary lateral tegmental field in two functionally described regions, the ventral respiratory group and Botzinger complex. An intervening region, the pre-Botzinger complex, contained essentially no phrenic premotoneurons. Bulbospinal neurons were also located in ventral, interstitial, and ventrolateral subnuclei of the solitary tract, and gigantocellular, Kolliker-Fuse, parabrachial, and medullary raphe nuclei. A monosynaptic pathway to phrenic motoneurons from the nucleus of the solitary tract was confirmed; monosynaptic pathways from upper cervical spinal cord, spinal trigeminal nucleus, medical and lateral vestibular nuclei, and medial pontine tegmentum were not verified. Locations of third-order neurons were consistent with described projections to the ventral respiratory group, from contralateral ventral respiratory group, Botzinger complex, A5 noradrenergic cell group, and the following nuclei; solitary, raphe, Kolliker-Fuse, parabrachial, retrotrapezoid, and paragigantocellular. Novel findings included a projection from locus coeruleus to respiratory premotoneurons and the lack of previously described pathways from area postrema and spinal trigeminal nucleus. These second- and third-order neurons from the output network for diphragm motor control which includes numerous behaviors (e.g., respiration, phonation, defecation). Of the premotoneurons, the rostral ventral respiratory group is the primary population controlling phrenic motoneurons.

Brainstem network controlling descending drive to phrenic motoneurons in rat.

The sections in this article are:


1
Respiratory Homeostasis and Control of Respiratory Movements
1.1
Effectors of Ventilation

1.2
Respiratory Muscles and Their Innervation

1.3
Summary




2
Central Location of Respiratory Controller
2.1
Historical Background

2.2
Summary

2.3
Modern View

2.4
Brain Stem Anatomy

2.5
Classification of Respiratory Neurons

2.6
Connections Between Respiratory Neurons

2.7
Location and Mechanisms for Generation of Respiratory Patterns

2.8
Production of Respiratory Pattern

2.9
Central Pattern Generation and Respiration

2.10
Hypothesis for Role of Dorsal and Ventral Respiratory Groups in Generating Respiratory Pattern




3
Sensors
3.1
Time Course of Responses to Respiratory Afferent Stimulation

3.2
Integrated Responses to Changes in Carbon Dioxide

3.3
Integrated Responses to Changes in Oxygen

3.4
Summary




4
Mechanoreceptors
4.1
Pulmonary Stretch Receptors

4.2
Summary




5
Exercise—An Example of an Integrated Response
5.1
Critique




6
State Dependence

7
Conclusion

Neurophysiology of Breathing in Mammals

Synaptic connections between medullary respiratory neurons and considerations on the genesis of respiratory rhythm.

Research on descending motor pathways to caudal brainstem and spinal cord in the spinal motor system is reviewed. Particular attention is given to somatic and autonomic motoneurons in the spinal cord and brainstem, local projections to motoneurons, bulbospinal interneurons projecting to motoneurons, descending pathways of somatic motor control systems, and descending pathways involved in limbic motor control systems.

/pdf/descending-motor-pathways-and-the-spinal-motor-system-limbic-3kcca6gtar.pdf

Descending motor pathways and the spinal motor system: limbic and non-limbic components

Anterograde transport of tritiated amino acids (leucine, lysine, and proline) was used to examine the spinal projections of respiratory premotor neurons in the ventral respiratory group (VRG) of cats. This population of neurons corresponds anatomically with the nucleus ambiguus-retroambigualis. Small volumes (20 to 50 nl) of tritiated amino acids were pressure ejected into the middle of the VRG through a micropipette which permitted simultaneous recording of respiratory modulated activity. In two cats injections were made caudal to the obex in regions which contained expiratory modulated neurons. In five cats injections were made rostral to the obex in regions containing inspiratory neurons. After a 2-week survival period, cats were anesthetized and perfused. The entire neuraxis was removed and processed using standard autoradiographic techniques. Transport of tritiated amino acids revealed a marked bilateral projection to lamina IX of the spinal cord at the C4 to C6 level and a primarily contralateral projection to laminae VIII and IX in the thoracic spinal cord. Distinct descending pathways to the phrenic motor neurons were observed in the lateral funiculus and in the ventral funiculus; descending fibers to the intercostal motoneurons in the thoracic cord appeared to be restricted to the ventral funiculus. Labeling of axon terminals in both the cervical and thoracic cords was confined to ventral horn regions which contain motoneurons. These results suggest that monosynaptic projections from brainstem bulbo-spinal neurons to spinal motoneurons are important in controlling respiratory movements of the diaphragm and intercostal muscles.

https://www.jneurosci.org/content/jneuro/5/8/1993.full.pdf

Dexter F. Speck

Papers

Projections from the ventral respiratory group to phrenic and intercostal motoneurons in cat: an autoradiographic study.