dNdx t quark

Clear[tb1, tn1, tc2, tp, tq, tl]; 
tb1[M_] := (ta1b1*M^tb1b1 + ta2b1*M^tb2b1)*UnitStep[349.999 - M]*UnitStep[M - 200] + 
    tab1*M^tbb1*UnitStep[1000 - M]*UnitStep[M - 350]; 
ta1b1 = 9.32; 
tb1b1 = 0.0507; 
ta2b1 = 11.*10^6; 
tb2b1 = -2.91; 
tab1 = 16.4; 
tbb1 = -0.04; 
tn1[M_] := (ta1n1*M^tb1n1 + ta2n1*M^tb2n1)*UnitStep[M - 200]*UnitStep[299.999 - M] + 
    tan1*M^tbn1*UnitStep[M - 300]*UnitStep[1000 - M]; 
ta1n1 = 21.4; 
tb1n1 = -0.818; 
ta2n1 = 0.00867; 
tb2n1 = 0.589; 
tan1 = 0.559; 
tbn1 = -0.0379; 
tc2[M_] := tac2*M^tbc2*UnitStep[M - 200]*UnitStep[1000 - M]; 
tac2 = 8910; 
tbc2 = -3.23; 
tp[M_] := tap*M^tbp*UnitStep[M - 200]*UnitStep[1000 - M]; 
tap = 5.78/10^5; 
tbp = 1.89; 
tq[M_] := taq*M^tbq*UnitStep[M - 200]*UnitStep[1000 - M]; 
taq = 0.133; 
tbq = 0.488; 
tl[M_] := tal*M^tbl*UnitStep[M - 200]*UnitStep[1000 - M]; 
tal = 21.9; 
tbl = -0.302; 
Clear[ttotal, x]; 
ttotal[M_, x_] := 290.*Exp[(-tb1[M])*x^tn1[M] - 1.61/x^0.19 - tc2[M]/x^0.845]*
    (Log[tp[M]*(1. - x^tl[M])]/Log[tp[M]])^tq[M];

Clear[tTotal,M]
tTotal[M_,x_]:=Piecewise[{{0.000001,M<200},{ttotal[M,x],200≤M≤1000},{ttotal[1000,x],1000<M<50000}}];
Plot[tTotal[5000,x],{x,0.0001,1.03},PlotRange->All]