{ diff(x1, t) = ((-1)*k5*(k7 + k8*k3) + 1*k4*k14*x2)/k4,
  diff(x2, t) = (1*k5*(k7 + k8*k3) + (-1)*k6*k9*x2^2/(k10^2 + x2^2) + 1*k5*k3*x3*k1/k2*x2^4/(1 + k1/k2*x2^4)*k11*x4^2/(k12^2 + x4^2) + 1*k5*k13*x4 + (-1)*k4*k14*x2)/k5,
  diff(x3, t) = ((-1)*k5*k15*x2^4*x3 + 1*k5*k16*(1 - x3))/k5,
  diff(x4, t) = (1*k6*k9*x2^2/(k10^2 + x2^2) + (-1)*k5*k3*x3*k1/k2*x2^4/(1 + k1/k2*x2^4)*k11*x4^2/(k12^2 + x4^2) + (-1)*k5*k13*x4)/k6,
  diff(x5, t) = (1*k5*k15*x2^4*x3 + (-1)*k5*k16*(1 - x3))/k5 }