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Reflex Arcs

Reflex Arcs. SNAB Topic 8 Grey Matter Lesson 3. Learning Objectives. Describe the path of nerve impulses in reflex arcs Describe the pupil reflex Explain the process by which the pupil reflex is controlled. Key Notes. Interesting Facts. Questions. Reflex Actions.

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Reflex Arcs

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  1. Reflex Arcs SNAB Topic 8 Grey Matter Lesson 3

  2. Learning Objectives • Describe the path of nerve impulses in reflex arcs • Describe the pupil reflex • Explain the process by which the pupil reflex is controlled Key Notes Interesting Facts Questions

  3. Reflex Actions • Many of the actions we carry out every day are done without conscious thought • These are call Reflex Actions • The nerve impulses in reflex actions do not follow the same path as those in conscious actions • The path they follow is called the Reflex Arc

  4. GCSE Review Question • What neuron is unique to the Reflex Arc? • Effector • Motor • Relay • Sensory

  5. Examples of Reflex Arcs • Knee Jerk Reaction – Involved in keeping standing • Pupil Dilation – Protect eyes from light • Vomit Reflex • Cough Reflex • Sneeze Reflex • Eye tracking Reflex

  6. Nervous Impulse Pathway in a Reflex Arc

  7. Interlink/Relay Neurons • These neurons are the vital part of the reflex arc • They connect the Sensory neuron to the Motor/Effector neuron • They can be found in the grey matter of the spinal cord and in the midbrain

  8. Advantage of Reflexes • The reflex arc allows a much quicker response to stimuli • This is especially important where the stimuli is a source of potential damage e.g. a hot object, a sharp pin

  9. Inhibition of the Reflex Response • The reflex response is considerably inhibited in several situations: • Exposure to Noradrenalin (Parasympathetic nervous system) • Tiredness • High Blood Alcohol • Effect from Sedative Drugs (e.g. Cannabis)

  10. Stimulation of the Reflex Response • The speed of the reflex response can be increase by several factors: • Exposure to adrenaline (Sympathetic Nervous System) • Exposure to stimulant drugs (Caffeine, Beta Amphetamines/Speed)

  11. The Pupil Reflex Response • The pupil response allows the iris to contract and dilate • This changes the size of the pupil • In the eye the pupil acts like an aperture • It controls the amount of light which enters the eye.. • … and protect the retina from “overexposure”

  12. Bright Light, Bright Light • When light levels are high Circular muscles in the iris contract • This causes the pupil to become smaller • This is controlled by the parasympathetic nervous system

  13. In the Dark… • When light levels are low Radial muscles contract • This causes the pupil to increase in size • This is caused by the sympathetic nervous system

  14. Diagram of Pupil Response

  15. Control of the Pupil Reflex: In Detail • When high levels of light strike photoreceptors in the retina they cause nervous impulses to be sent along the Sensory neuron (Optic Nerve) • These impulses are co-ordinated by relay neurons in the Midbrain • Signals are then sent along the parasympathetic nervous system

  16. Diagram of the Pupil Reflex Arc

  17. Eye Dilation Videos • http://video.google.co.uk/videoplay?docid=-4513396283977692296&q=pupil • http://video.google.co.uk/videoplay?docid=-2586168005397990196&q=pupil • http://video.google.co.uk/videoplay?docid=-6096473483443032157&q=pupil+reflex

  18. Atropine • Atropine is a sedative drug made from the deadly nightshade plant (Atropa belladonna) • It was apparently used in the middles ages by women to dilate there pupils • This is the source of the word belladonna in Latin and Belle in French

  19. Check Point • What muscle contracts when the pupil dilates? • Optic • Radial • Ocular Motor • Circular

  20. Check Point • What nervous system is involved in pupil contraction? • Somatic • Sympathetic • Central • Parasympathetic

  21. Correct!

  22. Try Again!

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