TABLE 1.
Glossary and key to abbreviations for neuronal populations
| Neuronal Population | Description |
|---|---|
| I-Driver (I-EI) | Excitatory inspiratory neurons in the pre-BotC region that excite other I neurons. During eupnea, they are usually activated before the expiratory-inspiratory phase transition. In our models these neurons have intrinsic, persistent sodium current-dependent pacemaker bursting properties which may be released under certain conditions. |
| I-Aug (BS) | Inspiratory neurons with an augmenting firing pattern during the inspiratory phase. BS–a subset of bulbospinal I-Aug neurons with axonal projections to spinal cord; does not exclude collateral axons in the brain stem. |
| I-Dec | Inhibitory inspiratory neurons with a decrementing firing pattern. |
| ILM | Inspiratory laryngeal motoneuron |
| IE | Neurons with average peak of firing rate at the inspiratory-to-expiratory (I-to-E) phase transition or at the end of inspiration (“late I”). |
| EI | Neurons with average peak of firing rate at the expiratory-to-inspiratory (E-to-I) phase transition. |
| E-Aug (-early, -late, -BS, -HT) | Expiratory neurons with an augmenting discharge pattern. “Early” − onset of activity begins early in the phase and continues throughout the phase; includes E-“constant” firing rate pattern (Ezure 1990). “Late” − activity onset is delayed and may be limited primarily to the later half of the expiratory interval (stage 2 expiration). BS − bulbospinal. High-threshold (HT) neurons are a subset of the E-Aug-late population with activity evoked by cough and chemoreceptors. |
| ELM | Expiratory laryngeal motoneuron |
| E-Other | Additional expiratory pontine population in initial model |
| E-Dec (-T, -P) | Expiratory neurons with a decrementing firing rate; most active during the early-expiratory (post-inspiratory) interval: -T and -P represent such populations with tonic and phasic discharge pattern, respectively |
| NRM (+, −) | Neurons with non-respiratory-modulated activity as judged by statistical methods; (excitatory or inhibitory, respectively). |
| PRG I | Pontine neuron with a peak firing rate during the second half of the inspiratory phase and with a generally augmenting activity profile during the phase. |
| PRG E | Pontine neuron with a peak firing rate during the second half of the expiratory phase and with an augmenting activity profile during the phase. |
| PRG IE | Pontine neuron with a peak firing rate during the I-to-E phase transition and with a decrementing activity profile in the latter phase. |
| PRG EI | Pontine neuron with a peak firing rate during the E-to-I phase transition and with a decrementing activity profile in the latter phase. |
| Pump+ and Pump− | Neurons located in the NTS that are excited by pulmonary stretch receptors during lung inflation; do not receive direct central respiratory drive. Pump+ neurons are excitatory; Pump− neurons are inhibitory. |
| Phrenic (Phr) | Phrenic motoneuron |
| Lum (Exp MN) | Spinal (Lumbar) motoneurons controlling expiratory muscle. |
| PSR | Slowly adapting pulmonary stretch receptors |
| Second order (cough) | Second-order NTS neurons that affect respiratory neurons in both VRC and PRG, causing reconfiguration of the respiratory network to produce the cough motor pattern |
Heterogeneity within classes of respiratory neurons was considered and some “types” of neurons described in the literature were grouped together, either for simplicity or because different terminology has been used for neurons with similar discharge patterns and proposed functions as noted elsewhere (e.g., Ezure 1990).