Pupil dilation and contraction (Edexcel SNAB)

This lesson describes how the antagonistic action of the radial and circular muscles of the iris causes the pupil to dilate or contract. The PowerPoint has been designed to cover point 8.2 (ii) of the Pearson Edexcel A-level Biology A (Salters Nuffield) specification.

The students may have encountered this concept at GCSE, so this lesson has been written to build on that knowledge and includes key A-level details such as the innervation of the smooth muscles by divisions of the autonomic nervous system. Students will learn how the contraction of the radial muscles pulls the iris radially and enlarges the pupil, allowing more light to enter when an individual is in a room with dim light and that this contraction is the result of the conduction of an electrical impulse along a sympathetic motor neurone.