Lesson overview
Nerves and reflexes: How fast can you react?
Catch a falling metre rule five times, read where you caught it and turn each distance into a reaction time, then decide which times go into the mean. Follow your catch through the nervous system, then a reflex that pulls your hand from a hot plate before you feel it, and (Supplement) watch an impulse cross the gap between two neurones.
Suggested sequence
- Lesson 1 · How fast can you react? How fast can you react? Impulses along neurones, the central and peripheral nervous systems, and measuring a reaction time with a falling rule. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- Lesson 2 · Reflexes. Reflexes: sensory, relay and motor neurones, the reflex arc, and why a reflex is automatic and rapid. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- Lesson 3 · Synapses. Synapses: the junction between two neurones; (Supplement) its structure, the events that pass an impulse on, and why impulses go one way only. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- End of module · final check. 11 new questions, 20–30 min, without hints or notes; pupils check their answers once they have answered them all.
- One to two weeks later · return questions. 11 questions, 15 min, lesson closed.
Learning goals
Part 1: How fast can you react?
- State that electrical impulses travel along neurones, and describe the mammalian nervous system: the central nervous system (CNS) is the brain and spinal cord, the peripheral nervous system (PNS) is the nerves outside them (14.1.1, 14.1.2)
- Describe the role of the nervous system as coordination and regulation of body functions (14.1.3)
- Measure a reaction time with a falling ruler: turn each catch into a time from a table, repeat, identify an anomalous catch and leave it out of the mean or repeat it, and find a mean (practical skills)
Part 2: Reflexes
- Identify in diagrams and images sensory, relay and motor neurones (14.1.4)
- Describe a simple reflex arc in terms of receptor, sensory neurone, relay neurone, motor neurone and effector (14.1.5)
- Describe a reflex action as a means of automatically and rapidly integrating and coordinating stimuli with the responses of effectors (muscles and glands) (14.1.6)
Part 3: Synapses
- Describe a synapse as a junction between two neurones (14.1.7)
- Supplement: describe the structure of a synapse, including the presence of vesicles containing neurotransmitter molecules, the synaptic gap and receptor proteins (S14.1.8)
- Supplement: describe the events at a synapse: an impulse stimulates the release of neurotransmitter from vesicles into the synaptic gap; the molecules diffuse across the gap and bind with receptor proteins on the next neurone; an impulse is then stimulated in the next neurone (S14.1.9)
- Supplement: state that synapses ensure that impulses travel in one direction only (S14.1.10)
Misconceptions to listen for
- “The brain, the spinal cord and the arm nerves.” — The nerves in the arms are outside the brain and spinal cord, so they are part of the PNS.
- “The brain only, with nothing else.” — The spinal cord is part of the CNS too, together with the brain.
- “The spinal cord and the backbone.” — The backbone is bone that protects the spinal cord; it is not part of the nervous system. And the brain is missing.
- “As a chemical diffusing along the cell.” — Diffusion is far too slow to carry a message a metre in a fraction of a second. Along a neurone the message is an electrical impulse.
- “As a liquid flowing along inside the cell.” — Nothing flows along a neurone. The message is an electrical impulse passing along the cell.
- “As a hormone carried along inside the cell.” — Hormones are chemicals carried in the blood, not inside neurones. Along a neurone the message is an electrical impulse.
- “The spinal cord is PNS.” — The spinal cord is part of the CNS, together with the brain.
- “A nerve that joins the brain is part of the CNS.” — The nerve lies outside the brain, so it is part of the PNS. Only the brain and the spinal cord are the CNS.
- “The receptor is the muscles in the hand.” — The muscles carry out the response, so they are the effectors. The receptors detect the stimulus: here, in the ear.
- “0.30 s.” — That turns 30 cm into 0.30 s, as if 1 cm were 0.01 s. Read the time from the table instead: 0.25 s.
Scope
The nervous system (14.1.1–14.1.10): electrical impulses along neurones; the central nervous system (the brain and the spinal cord) and the peripheral nervous system (the nerves outside them); the role of the nervous system in coordinating and regulating body functions; sensory, relay and motor neurones; the simple reflex arc and the reflex action; the synapse as a junction between two neurones; and, for the Supplement, the structure of a synapse, the events at a synapse and why synapses make impulses travel in one direction only. The eye and the pupil reflex are in the module on sense organs, hormones in the module on hormones, and drugs that act at synapses are not covered.