Eyes

• How is a generator potential produced in a Pacinian corpuscle?

  Pressure deforms lamellae, opening sodium channels
• What happens to the membrane when pressure is applied to a Pacinian corpuscle?

  It stretches, opening sodium channels
• What is the "all-or-nothing principle" in action potentials?

  Action potential is same size above threshold
• What happens to action potential frequency with a stronger stimulus?

  Frequency increases, amplitude remains constant
• What occurs to circular muscles for the pupil to narrow?

  Circular muscles contract, radial muscles relax
• How does the fovea allow an eagle to see prey in detail?

  High cone density with little convergence allows detail
• Why does a high density of rod cells in an owl’s retina help it hunt at night?

  Many rods converge onto a single bipolar cell
• What is the benefit of rod cell convergence in low light?

  Greater sensitivity allows prey detection in dim conditions
• How many optic nerves are there?

  Two, one per eye
• What happens at the optic chiasm?

  Some optic nerve fibers cross over
• Why does the fovea allow vision in colour?

  It contains a high density of cone cells
• Why does the fovea provide high visual acuity?

  Each cone connects to a single bipolar neurone