The shape of the lesson
By the end of the lesson, learners can
- Hormones or nerves?: Click each part of the motor neurone (top, yellow) and the sensory neurone (bottom, green).
- A receptor cell in a taste bud: Press Next step to follow salt from the tongue to the brain.
- Hormones reach every cell; only target cells with receptors respond.
- Motor cell body in the CNS; sensory cell body in a ganglion.
- Receptor potential is graded; action potential is all-or-nothing.
- Taste: Na+ in, depolarise, Ca2+ in, transmitter out.
One picture every idea returns to
The endocrine system is made of ductless glands that secrete hormones into the blood; only target cells with the matching receptor respond. Examples: ADH from the posterior pituitary acts on collecting duct cells; insulin (beta cells) and glucagon (alpha cells) from the islets of Langerhans in the pancreas act on liver and other cells. The nervous system sends electrical impulses along neurones to specific effectors: it is faster, more precise and shorter-lived. A sensory neurone carries impulses from a receptor to the CNS; an intermediate (relay) neurone connects it to a motor neurone, which carries impulses to an effector. Sensory receptor cells are transducers: a stimulus changes the permeability of their membrane, producing a receptor potential; if this is big enough, an action potential starts in the sensory neurone. In a taste bud, Na+ from salt enters a chemoreceptor cell, depolarising it, so Ca2+ channels open and neurotransmitter is released onto a sensory neurone.
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, Two ways to send a message.. Mammals coordinate their organs with two systems. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Hormones or nerves? | Click each part of the motor neurone (top, yellow) and the sensory neurone (bottom, green). Project tab 1 of the lab (Control and coordination lab, neurones) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: A receptor cell in a taste bud | Press Next step to follow salt from the tongue to the brain. Project tab 2 of the lab (Control and coordination lab, a taste receptor) and let a student drive it while the class predicts. | Corners |
| 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, 21 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 A receptor cell in a taste bud, 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.
Corners
Put one answer or viewpoint in each corner of the room. Students move to the corner they agree with, justify the choice to a partner there, then hear one voice from each corner before the reveal.
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 |
|---|---|
| Do not say hormones travel only to their target organ. | Hormones are carried in the blood to every tissue; only target cells respond, because only they have receptors with a shape complementary to the hormone. |
| A receptor potential is graded: its size depends on the stimulus strength. | An action potential is all-or-nothing. Only when the receptor potential pushes the sensory neurone past threshold does an action potential start. |
Nervous and endocrine systems: worksheet
6 questions, 21 marks. Written in the style of the papers; no past paper question is reproduced.
Name the endocrine gland that secretes each of ADH, insulin and glucagon, and give one target cell for each.
Compare the ways the nervous system and the endocrine system transmit information.
Describe the structure of a motor neurone and state how it differs from a sensory neurone.
Describe the sequence of events by which salt on the tongue leads to an action potential in a sensory neurone.
A hormone circulates in the blood and reaches every organ, but only cells in the liver respond to it. Suggest why.
Explain why a very weak stimulus on a receptor cell may produce no action potential at all in the sensory neurone.
Answer key and marking notes
- ADH: posterior pituitary gland; target: cells of the collecting duct (and distal convoluted tubule) in the kidney.
- Insulin: beta cells of the islets of Langerhans in the pancreas; target: liver / muscle / fat cells.
- Glucagon: alpha cells of the islets of Langerhans in the pancreas; target: liver cells.
- Nervous: electrical impulses along neurones (and chemical neurotransmitter across synapses); endocrine: chemical hormones.
- Nervous signals go along specific neurones to one effector; hormones are carried in the blood to the whole body.
- Nervous transmission is fast (milliseconds); hormonal is slower.
- Nervous effects are short-lived and localised; hormonal effects are often long-lasting and widespread (any cell with receptors).
- Cell body (with nucleus, many mitochondria and rough ER) in the CNS, with many dendrites.
- Long axon, usually myelinated by Schwann cells with nodes of Ranvier, ending in motor end plates on an effector.
- A sensory neurone has a long dendron carrying impulses from a receptor to its cell body.
- Its cell body is in a ganglion to one side, outside the CNS, and a short axon carries impulses into the CNS.
- Na+ ions from the salt reach the microvilli of a chemoreceptor cell in a taste bud.
- Na+ diffuses into the receptor cell through Na+ channels, down the electrochemical gradient.
- The membrane depolarises, producing a receptor potential.
- This opens voltage-gated Ca2+ channels; Ca2+ enters and causes vesicles to release neurotransmitter by exocytosis.
- Neurotransmitter binds to receptors on the sensory neurone and depolarises it; if threshold is reached, an action potential is set up.
- Only liver cells have receptors (on the cell surface membrane) with a shape complementary to the hormone.
- Other cells lack the receptor, so the hormone cannot bind and no response is triggered.
- A weak stimulus gives only a small receptor potential (the receptor potential is graded).
- Little or no neurotransmitter is released, so the sensory neurone is depolarised only slightly.
- Threshold is not reached, so no action potential is set up (all-or-nothing).
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 hormone is released from the posterior pituitary gland and acts on cells of the collecting ducts in the kidney?
- AADH
- Binsulin
- Cglucagon
- Dadrenaline
Where are intermediate (relay) neurones found?
- Aentirely within the brain or spinal cord
- Bin ganglia just outside the spinal cord
- Cat the junction between a motor neurone and a muscle
- Din the skin, next to the sensory receptors
A neurone has its cell body in the spinal cord, many short dendrites, and a long myelinated axon that ends on fibres of a leg muscle. What type of neurone is it?
- Aa motor neurone
- Ba sensory neurone
- Can intermediate neurone
- Da receptor cell
What is a receptor potential?
- Aa graded change in the membrane potential of a receptor cell caused by a stimulus
- Ban all-or-nothing action potential produced in a receptor cell
- Cthe resting potential of a sensory neurone before stimulation
- Dthe minimum stimulus that a receptor cell can detect
Which row correctly compares the nervous system with the endocrine system?
- Anervous: impulses along neurones, fast, short-lived; endocrine: hormones in blood, slower, longer-lasting
- Bnervous: hormones in blood, fast, long-lasting; endocrine: impulses along neurones, slower, short-lived
- Cnervous: impulses along neurones, slow, widespread; endocrine: hormones in blood, fast, localised
- Dnervous: impulses in blood plasma, fast, localised; endocrine: hormones along neurones, slow, widespread
A drug blocks the voltage-gated Ca2+ channels of taste receptor cells but has no other effect. Salt is placed on the tongue. What happens?
- Athe receptor cell depolarises, but little neurotransmitter is released, so no action potentials pass to the brain
- BNa+ cannot enter the receptor cell, so there is no receptor potential
- Cthe sensory neurone fires action potentials, but they are smaller than normal
- Dthe receptor cell releases more neurotransmitter, because Ca2+ cannot leave it
Glucagon circulates in the blood and reaches liver cells and skeletal muscle cells. Liver cells respond by breaking down glycogen; muscle cells do not. Which is the best explanation?
- Aliver cells have glucagon receptors in their cell surface membranes; muscle cells lack them
- Bglucagon cannot leave the capillaries that supply skeletal muscle
- Cmuscle cells contain no glycogen to break down
- Dglucagon enters liver cells and binds to DNA, but cannot cross muscle cell membranes
The graph shows the receptor potential of a taste receptor cell at four salt concentrations, and the size of receptor potential needed for action potentials in its sensory neurone. What is the lowest concentration tested that produces action potentials?
- A0.20 mol dm−3
- B0.05 mol dm−3
- C0.10 mol dm−3
- D0.40 mol dm−3
Quiz key
ADH (antidiuretic hormone) is released from the posterior pituitary and makes collecting duct cells more permeable to water. Insulin and glucagon come from the islets of Langerhans in the pancreas and act mainly on liver, muscle and fat cells to control blood glucose. Adrenaline comes from the adrenal glands and does not target the collecting ducts in this way.
Intermediate neurones lie entirely within the CNS and connect sensory neurones to motor neurones. Ganglia outside the spinal cord hold the cell bodies of sensory neurones. The neuromuscular junction is where a motor neurone meets a muscle fibre. Receptors in the skin connect to the endings of sensory neurones, not intermediate ones.
A motor neurone has its cell body inside the CNS and carries impulses out along its axon to an effector, here a muscle. A sensory neurone has its cell body in a ganglion outside the CNS and a long dendron from a receptor. An intermediate neurone lies wholly in the CNS. A receptor cell detects stimuli and does not have a long axon to a muscle.
A receptor potential is a change in membrane potential, usually a depolarisation, whose size depends on the strength of the stimulus. It is not all-or-nothing, which is what distinguishes it from an action potential. It is not the resting potential, which is the unstimulated state. The smallest detectable stimulus is the threshold stimulus, not the receptor potential itself.
Nervous signals are electrical impulses along neurones, very fast and short-lived; hormones are chemicals carried in the blood, slower and usually longer-lasting. The second row swaps the signals. The third row gets the speeds and the spread the wrong way round. The fourth puts impulses in the blood and hormones along neurones, which mixes up the routes.
Na+ still enters through its own channels, so a receptor potential forms. But Ca2+ entry is what triggers vesicles to release neurotransmitter, so the sensory neurone is not stimulated and no action potentials are sent. The Na+ channels are not affected by this drug. Action potentials cannot be smaller: they are all-or-nothing. Blocking Ca2+ entry reduces, not increases, transmitter release.
A hormone affects only target cells with receptors complementary to it; muscle cells do not have glucagon receptors, so they cannot respond. Glucagon reaches tissue fluid around all capillaries. Muscle cells do store glycogen, so lack of substrate is not the reason. Glucagon is a peptide hormone that binds to a receptor on the cell surface; it does not enter the cell to bind DNA.
The receptor potential rises with concentration because it is graded. Only at 0.20 mol dm−3 (about 18 mV) does it pass the dashed line at 15 mV, so this is the lowest concentration that triggers action potentials. At 0.05 and 0.10 mol dm−3 the receptor potentials (5 and 10 mV) are below the level needed. 0.40 mol dm−3 also works, but it is not the lowest; a stronger stimulus gives a higher frequency of impulses, not the first ones.
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.