TABLE 1.
Membrane currents in motoneurons, their proposed function, and modulation by transmitters
| Current (Ions) | Proposed Function | Transmitter Modulation | Transmitter Reference No. |
|---|---|---|---|
| INa i (Na+) | Action potential | ||
| INa p (Na+) | Acceleration of membrane potential to spike threshold, amplify EPSP, linearize firing with increased current input | 5-HT | 527 |
| IK leak (K+) | Resting Vm | TRH, SP, NE, 5-HT, Glu (metabotropic) | 77, 287, 302, 367, 526, 703, 958, 1039 |
| IKir (K+) | Resting Vm, stabilize Vm around rest | ||
| IKdr (K+) | Action potential repolarization, fAHP | ||
| Ih (K+, Na+) | Resting Vm, stabilize Vm around rest, rebound potentials | 5-HT, NE | 526, 702, 959 |
| IA (K+) | Resting Vm, control onset of firing | NE | 958 |
| ICl leak (Cl−) | Resting Vm | ||
| IK Ca(BK) (K+) | Action potential repolarization | ||
| IK Ca(SK) (K+) | AHP | ||
| ICa HVA (Ca2+) | ADP, AHP, plateau potentials | 5-HT Adenosine, Glu (metabotropic) | 73, 285, 287, 521, 796, 882 |
| ICa LVA (Ca2+) | ADP, action potential repolarization | 5-HT | 93 |
| INa Ca (Na+) | Plateau potentials, afterdepolarization in specialized motoneurons | ||
| IK Na (K+) | Postdischarge hyperpolarization |
EPSP, excitatory postsynaptic potential; Vm, membrane potential; fAHP, fast afterhyperpolarization; AHP, afterhyperpolarization; ADP, afterdepolarization; 5-HT, 5-hydroxytryptamine; TRH, thyrotropin-releasing hormone; SP, substance P; NE, norepinephrine; Glu, glutamate.