  \begin{tikzpicture}

	\node (input0) at (9,-0.1)  {$x_{1}$};
	\node (input1) at (10,-0.1)  {$x_{2}$};
	\node (input2) at (11,-0.1)  {$x_{3}$};
	\node [hidden_neuron] (neuron1) at (10,2)  {$\sigma$};
	\node (output0)  at (10,3.5) {$y$};

	\draw [->] (input0) -- (neuron1);
	\draw [->] (input1) -- (neuron1);
	\draw [->] (input2) -- (neuron1);
	\draw [->] (neuron1) -- (output0);

	\node (formula)[scale=.8] at (9.1,0.6) {$w_{1}$};
	\node (formula)[scale=.8] at (9.8,0.6) {$w_{2}$};
	\node (formula)[scale=.8] at (10.4,0.6) {$w_{3}$};
  \end{tikzpicture}