The shape of the lesson
By the end of the lesson, learners can
- Brain, spinal cord and nerves: Switch between the whole system, the central nervous system and the peripheral nervous system, then pick the types of neurone.
- The reflex arc: Press Touch the hot plate and follow the impulse.
- Across the synapse: Extended.
- CNS: brain and spinal cord. PNS: all the nerves outside them.
- Reflex arc: receptor, sensory neurone, relay neurone, motor neurone, effector.
- Effectors are muscles or glands; receptors detect stimuli.
- Synapse (Extended): release from vesicles, diffusion across the gap, binding to receptor proteins, new impulse.
One picture every idea returns to
Electrical impulses travel along neurones. The mammalian nervous system is the central nervous system (brain and spinal cord) plus the peripheral nervous system (all the nerves outside them); together they coordinate and regulate body functions. A reflex action automatically and rapidly links a stimulus to the response of an effector (a muscle or gland) through a reflex arc: receptor, sensory neurone, relay neurone, motor neurone, effector. A synapse is a junction between two neurones.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Impulses, reflexes and synapses.. Your body is coordinated by electrical impulses that race along neurones to and from the brain and spinal cord. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 13 min | Teach and check: Brain, spinal cord and nerves | Switch between the whole system, the central nervous system and the peripheral nervous system, then pick the types of neurone. Project tab 1 of the lab (The human nervous system) and let a student drive it while the class predicts. | Whole class, then pairs |
| 13 to 21 min | Teach and check: The reflex arc | Press Touch the hot plate and follow the impulse. Project tab 2 of the lab (A reflex arc from a hot plate to the biceps) and let a student drive it while the class predicts. | Pairs |
| 21 to 30 min | Teach and check: Across the synapse | Extended. Project tab 3 of the lab (Events at a synapse) and let a student drive it while the class predicts. | Anticipation / Reaction Guide |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 24 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Across the synapse, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Anticipation / Reaction Guide
Before the lesson, students mark five statements true or false. After the teaching they mark them again and justify any change of mind in one sentence each. The statements come from the examiner traps below.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| A nerve and a neurone are not the same thing. | A neurone is a single nerve cell; a nerve is a bundle of many neurone fibres. |
| In a spinal reflex the response does not wait for the brain. | Impulses do also travel up to the brain, which is why you feel the pain a moment after the hand has moved. |
| Neurotransmitter crosses the gap by diffusion, not as an electrical impulse and not by active transport. | The impulse itself never crosses the gap. |
The nervous system: worksheet
6 questions, 24 marks. Written in the style of the papers; no past paper question is reproduced.
Describe the mammalian nervous system in terms of the central nervous system and the peripheral nervous system, and state its role.
A person steps on a drawing pin and lifts their foot away. Describe the pathway of the impulse in this reflex arc.
A diagram shows three neurones. Neurone A has a long fibre that starts at a receptor and its cell body is on a side branch. Neurone B is short and lies entirely inside the spinal cord. Neurone C has its cell body inside the spinal cord and a long axon that ends in a muscle. Identify A, B and C.
Students tested their reaction time by catching a falling ruler. The ruler fell further before being caught when the student was tired.
| Condition | Mean distance fallen / cm |
|---|---|
| rested | 14 |
| tired | 21 |
(a) Calculate the percentage increase in distance fallen when tired. (b) Catching a ruler is not a reflex action. Suggest why, and state one variable that should be controlled.
Extended. Describe the structure of a synapse.
Extended. Explain how an impulse passes from one neurone to the next across a synapse, and why it can only travel in one direction.
Answer key and marking notes
- The central nervous system (CNS) consists of the brain and the spinal cord.
- The peripheral nervous system (PNS) consists of the nerves outside the brain and spinal cord.
- Its role is the coordination and regulation of body functions, using electrical impulses that travel along neurones.
- Pain (pressure) receptors in the skin of the foot detect the stimulus.
- An impulse travels along a sensory neurone to the spinal cord.
- In the spinal cord a relay neurone passes the impulse to a motor neurone.
- The motor neurone carries the impulse to the effector, a muscle in the leg.
- The muscle contracts, lifting the foot away from the pin.
- A: sensory neurone (carries impulses from a receptor to the CNS).
- B: relay neurone (inside the CNS, links sensory and motor neurones).
- C: motor neurone (carries impulses from the CNS to an effector).
- (a) (21 − 14) ÷ 14 × 100 = 50% increase.
- (b) The student decides to catch the ruler: the response involves the brain and is a voluntary action, not automatic.
- It is slower than a reflex because the impulse passes through the brain and more synapses.
- Control: same ruler, same starting height or hand position, same hand used (also accept same number of practice attempts).
- A synapse is a junction between two neurones.
- The ending of the first neurone contains vesicles holding neurotransmitter molecules.
- There is a narrow synaptic gap between the two neurones.
- The membrane of the next neurone has receptor proteins that the neurotransmitter binds to.
- The impulse arriving at the end of the first neurone stimulates vesicles to release neurotransmitter molecules into the synaptic gap.
- The neurotransmitter molecules diffuse across the gap.
- They bind with receptor proteins on the membrane of the next neurone.
- This stimulates an impulse in the next neurone.
- Only the first neurone has vesicles of neurotransmitter and only the next neurone has receptor proteins, so the impulse can only travel one way.
8 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
Which row correctly describes the two parts of the mammalian nervous system?
- ACNS: brain and spinal cord; PNS: nerves outside the brain and spinal cord
- BCNS: brain only; PNS: spinal cord and all the nerves
- CCNS: brain and all the nerves; PNS: spinal cord only
- DCNS: spinal cord and nerves; PNS: brain and sense organs
The diagram shows three neurones in a reflex arc. Which row identifies X, Y and Z?
- AX sensory, Y relay, Z motor
- BX motor, Y relay, Z sensory
- CX relay, Y sensory, Z motor
- DX sensory, Y motor, Z relay
Which of these is an effector?
- AA salivary gland
- BA heat receptor in the skin
- CA relay neurone
- DThe spinal cord
Dust touches the surface of the eye and the person blinks before they are aware of it. Why is this described as a reflex action?
- AIt is an automatic, rapid response to a stimulus
- BIt is a response the person decides to make
- CIt is controlled by a hormone in the blood
- DIt is a learned response that needs practice
How does information travel along a neurone?
- AAs an electrical impulse
- BAs a hormone in the blood
- CAs neurotransmitter diffusing along the axon
- DAs a wave of muscle contraction
Extended: what is found inside the vesicles at the end of the first neurone at a synapse?
- ANeurotransmitter molecules
- BReceptor proteins
- CElectrical impulses
- DHormones for the blood
Extended: a drug blocks the receptor proteins on the second neurone at a synapse. What is the most likely effect?
- ANeurotransmitter cannot bind, so no impulse starts in the second neurone
- BNeurotransmitter is no longer released from the vesicles
- CImpulses now cross the synapse in both directions
- DThe impulse jumps the gap without needing neurotransmitter
Extended: what is the correct order of events at a synapse? 1 neurotransmitter binds with receptor proteins; 2 an impulse arrives at the end of the first neurone; 3 neurotransmitter diffuses across the gap; 4 vesicles release neurotransmitter; 5 an impulse is stimulated in the next neurone.
- A2, 4, 3, 1, 5
- B2, 3, 4, 1, 5
- C4, 2, 3, 1, 5
- D2, 4, 1, 3, 5
Quiz key
The central nervous system is the brain and the spinal cord; the peripheral nervous system is all the nerves outside them. The spinal cord is part of the CNS, not the PNS, so the options that place it in the PNS or leave it out are wrong. Nerves are always peripheral, and sense organs contain receptors rather than forming part of the CNS.
X runs from the receptor to the spinal cord, so it is the sensory neurone. Y is short and lies entirely inside the spinal cord, so it is the relay neurone. Z carries impulses from the spinal cord to the muscle (the effector), so it is the motor neurone. The other options reverse the direction of the arc or put the relay neurone outside the CNS, where relay neurones are never found.
Effectors are muscles and glands; a salivary gland responds by secreting saliva. A heat receptor detects the stimulus rather than responding to it. A relay neurone only passes impulses on, and the spinal cord is part of the CNS, which coordinates the response but does not carry it out.
A reflex action is automatic (no conscious decision) and rapid, coordinating a stimulus with an effector response; here the eyelid muscles contract. A decided response is a voluntary action, which is slower. Hormones act too slowly for a blink. Reflexes are not learned: they work the first time.
Electrical impulses travel along neurones. Hormones travel in the blood, not inside neurones. Neurotransmitter diffuses only across the small gap at a synapse, not along the whole neurone. Muscle contraction is the response of an effector, not the way the message travels.
The vesicles hold neurotransmitter molecules, which are released into the synaptic gap. Receptor proteins are on the membrane of the next neurone, not inside vesicles. An impulse is an electrical event and cannot be stored in a vesicle. Hormones are secreted by glands into the blood, not by neurones into a synaptic gap.
Neurotransmitter must bind with receptor proteins to stimulate an impulse in the next neurone; if they are blocked, binding fails and no impulse is set off. Release from vesicles happens in the first neurone and does not depend on the receptors. Blocking receptors cannot make transmission two-way, and impulses never jump the synaptic gap.
The impulse arrives (2), stimulating vesicles to release neurotransmitter (4); the molecules diffuse across the gap (3), bind with receptor proteins (1), and an impulse is stimulated in the next neurone (5). Diffusion cannot happen before release, release is triggered by the impulse so cannot come first, and binding cannot happen before the molecules have crossed the gap.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.