Neuronal communication (5.1.3)
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Delivery guides are designed to represent a body of knowledge about teaching a particular topic and contain:
- Content: A clear outline of the content covered by the delivery guide;
- Thinking Conceptually: Expert guidance on the key concepts involved, common difficulties students may have, approaches to teaching that can help students understand these concepts and how this topic links conceptually to other areas of the subject;
- Thinking Contextually: A range of suggested teaching activities using a variety of themes so that different activities can be selected which best suit particular classes, learning styles or teaching approaches.
|Content (from A-level)
The content from the specification that is covered by this delivery guide is:
|5.1.3 Neuronal communication|
|(a)||the roles of mammalian sensory receptors in converting different types of stimuli into nerve impulses||To include an outline of the roles of sensory receptors (e.g. Pacinian corpuscle) in responding to specific types of stimuli and their roles as transducers.|
|(b)||the structure and functions of sensory, relay and motor neurones||To include differences between the structure and function of myelinated and non-myelinated neurones.|
|(c)||the generation and transmission of nerve impulses in mammals||To include how the resting potential is established and maintained and how an action potential is generated (including reference to positive feedback) and transmitted in a myelinated neurone
AND the significance of the frequency of impulse transmission.
|(d)||the structure and roles of synapses in neurotransmission||To include the structure of a cholinergic synapse
AND the action of neurotransmitters at the synapse and the importance of synapses in summation and control.
This topic covers detection of stimuli by sensory receptors, the three types of neurone, transmission of electrical impulses and events at the synapse. Students need to be careful to distinguish between the events in sensory receptors where one type of energy is transduced into electrical energy giving a generator potential and the events of the action potential. It should be stressed that all cells have a resting potential but only neurones and muscle cells are electrically excitable, that is able to change the potential difference across their membranes. This can be related to the presence of voltage-gated and ligand-gated channels on their cell surface membranes. As some candidates may have less physics background than others, terms like potential difference and transduction may need to be carefully explained.
- Wordsearch (link to Learner resource 1)
- Solution (link to Teacher resource 1)
- Key words worksheet (link to Learner resource 2)
Students can research the meanings of words themselves but careful checking of the definitions either as a class exercise or by the teacher is necessary for it to become a reliable resource for learning.
Customised word search puzzles for classroom use can be generated using this quick and easy website tool.
These can be linked to a worksheet providing either the words for students to define (as above), or the definitions for students to match to the terms. In the latter case teachers have more control over the quality of the definitions provided.
The speed of the nerve impulse in humans can be estimated through this simple exercise.
- The class members stand up and link hands in a circle.
- One student, or the teacher, stands aside and acts as timer using a precise stopclock (laboratory stopclock or stopclock provided on mobile phone).
- On the word ‘Go’ the stopclock is started and a designated starting student squeezes their right hand.
- When the adjacent person feels the squeeze (on their left hand) they immediately squeeze their right hand.
- This continues around the circle.
- The starting student shouts ‘Stop’ when they feel their left hand squeezed and the timer stops the clock and reveals the time taken for the impulse to transmit around the circle.
- To estimate a speed for nerve impulse transmission students need to consider the length of the combined neurones allowing detection of the pressure stimulus in the left hand, conduction to the brain and then impulse transmission to the muscles of the right hand. They must then consider the number of people in the circle to estimate the total length of neurones involved in transmitting the impulses round the circle.
- Development of this idea can include investigating the effect of practice on the speed, sending the message in the opposite direction round the circle, and comparing the speed of transmission in boys versus girls.
Approaches to teaching the content
Examination of the list of problems students have with this topic, and the many areas in which it links to other areas of the syllabus, suggest several approaches to teaching the content.
- Start with revision of the physico-chemical terminology and mechanisms of moving substances across membranes before teaching receptors, the action potential and synapses, i.e. build up from the basics.
- Start with the structure of the nervous system (perhaps involving dissection), and use light and electron micrographs of neurones and plan diagrams of reflex arcs supported by experiment, before explaining how sensory receptors, nerve impulses and synapses work, i.e. work down from the whole body level).
- Start with an open-ended list of questions for a project using a comprehensive website such as Neuroscience for Kids, or a case study scenario such as investigating what spinal cord injuries do and why.
Common misconceptions or difficulties students may have
- Logical sequencing: Students struggle to see the overview between separately taught sequences of events such as those occurring to generate a receptor potential, an action potential and synaptic transmission. A question about how an action potential is transmitted may produce answers that deal mostly with irrelevant parts of neurone function. After teaching each element separately students need to put the elements back in order to see an overview of nervous system function.
- Errors in understanding and terminology: It is common for students to think that vesicles cross the synapse. Some students incorrectly refer to the post-synaptic dendrite as a ‘knob’. The terms ‘sensory receptor’ and ‘membrane receptor’ can be confused, as can receptor potential and action potential.
- Use of inappropriate terms. The terms stimuli, action potential and impulse should be used in preference to ‘signal’, ‘message’, etc. Candidates should choose carefully when qualifying ‘protein channel’ as voltage-gated or ligand-gated as the terms are often used in the wrong context.
- Chemistry: Students use terms like ion, molecule and atom loosely and misrepresent symbols for ions.
- Physics: The concept of receptors acting as energy transducers requires candidates to be familiar with different forms of energy such as mechanical energy (Pacinian corpuscle and hair cells in ear), electromagnetic or light energy (rods and cones), chemical energy (tastebuds, olfactory receptors), thermal energy (temperature receptors) and electrical energy (the nerve impulse).
- Scale: Students have difficulty in grasping the relationship between large-scale nervous system structure and behavioural psychology and micro-level events such as ion movements. It is worth pointing out how the molecular level events relate back up to nerves, the brain and behaviour. Students also confuse the terms nerve and neurone.
Conceptual links to other areas of the specification
Links should be made to earlier topics to reinforce and extend understanding of these topics and to place the new material into context.
- 2.1.1 Cell Structure. The neurone is a specialised cell and estimating the dimensions of a motor neurone running from the human big toe to the spinal cord makes students re-consider their idea of cell size and shape.
- 2.1.2 Biological Molecules. The properties conferred by the phospholipid structure of the neurone surface membrane, the lipid nature of the myelin sheath and the precise folding of ligand-gated and voltage-gated protein receptors could be highlighted.
- 2.1.4 Enzymes. Acetylcholinesterase could be added to a glossary list of important enzymes.
- 2.1.5 Biological Membranes. The key areas here are 2.1.5(d), where understanding the nerve impulse extends understanding of active transport (the sodium-potassium pump), facilitated diffusion (of ions through specific protein channels) and exocytosis (of neurotransmitter), and 2.1.5(b), the role of receptors to which neurotransmitter and drug molecules bind.
- 2.1.6 Students could be given an open-ended brief to consider why damaged nervous tissue, for example spinal cord injuries, has limited capability for re-growth and repair.
- 3.1.1(g) Dissection of a bony fish to reveal the gas exchange surfaces is also an opportunity to show students the white matter of the fish’s spinal cord by cutting through the spine of the fish. It should be explained that the bright white colour is due to the myelin sheaths of millions of neurones.
- 3.1.2(g) The myogenic nerve impulses initiating heart muscle contraction and ECG analysis introduces the concept of electrical excitation.
- 4.1.1(m) Plant and microbial origins of some drugs that act at synapses include curare (Curarea toxicofera), atropine (Atropa belladonna) and nicotine (Nicotiana tabacum) which act at acetylcholine releasing synapses and botulinum toxin (Clostridium botulinum) at the neuromuscular junction.
In teaching later modules the following synoptic links could be made:
- 5.1.1(b) The synapse is an example of cell signalling between adjacent cells.
- 5.1.1(d) The role of temperature receptors and nerve impulses in homeostatic control of body temperature in mammals can be used as a case study example of autonomic reflexes.
- 5.1.2(d) The features of neurosecretory cells involved in ADH secretion could be examined to list their structural and functional similarities to both neurones and endocrine cells.
- 5.1.4(d) Students could be asked to consider whether there are similarities between neurotransmitter release and the control of the release of insulin from β cells of the islets of Langerhans in the pancreas.
- 5.1.5(g – l) These learning outcomes (animal responses) build on the foundations of section 5.1.3 and could be taught directly after the neuronal communication topic or, if started later, begun with a careful review of the principles of 5.1.3 via class discussion, student PowerPoint presentations or a revision test.
- 5.2.2(a) Cellular respiration for ATP for active transport can be linked to the role of sodium-potassium pumps establishing and restoring resting potential in neurones.
- 6.1.1(a) Gene mutations affecting the nervous system include Friedreich’s Ataxia, Tay-Sachs disease and Huntington’s disease.
- 6.1.2 Friedreich’s Ataxia and Tay-Sachs can be used as examples of autosomal recessive disorders and Huntington’s as an autosomal dominant disorder in genetic crosses and pedigree diagrams for (b). They can also be linked to patterns of variation (d), Hardy-Weinberg calculations (f) and factors affecting evolution (e), questioning the persistence of genetic disorders and whether there might be a hidden selective advantage for carriers of recessive alleles. Alleles for variant forms of neurotransmitter receptors (eg. DRD 4) provide a link between the molecular level of brain synapses and human personality traits.
- 6.1.2(h) It is possible to artificially select for behavioural traits such as tameness in silver foxes.
- 6.1.3(f) Neurotoxin genes have been introduced into plants by genetic engineering. Gene therapy (h) for the brain disease Parkinson’s places gene therapy in a nervous system context.
Contexts in which knowledge of neuronal communication can be extended and applied include:
- linking images and films of real neurones to text book diagrams
- experimenting with simple somatic reflexes
- understanding the action of psychoactive drugs and poisons in medical, recreational and warfare contexts
- researching degenerative motor neurone disease and spinal cord injuries
- comparing the working of the mammalian nervous system with artificial intelligence systems.
Can neurones undergo mitosis? Can physical injury to nerves be repaired? Why does damage to the spinal cord affect so many areas of the body?
The actor Christopher Reeve played Superman in the 1978 movie and its sequels. After being paralysed by a spinal cord injury he founded an organisation campaigning for stem cell research into nervous system repair. Students can consider the questions above through researching the life of Christopher Reeve.
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