Is every map $N \to \mathbb{S}^m$ null-homotopic if $N$ is a compact $n$-dimensional manifold and $n < m$?

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We know that $\pi_n(\mathbb{S}^m) \cong 0$ for $n < m$, i.e every map from $\mathbb{S}^n \to \mathbb{S}^m$ is null-homotopic. From this can we conclude that every map from $N \to \mathbb{S}^m$ is null-homotopic if $N$ is a compact $n$-dimensional manifold?

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Every compact manifold is homotopy equivalent to a CW complex, so your statement follows from the theorem of cellular approximation.