What you need to know
- 8.1–8.9Original mixed practice. Not medical advice.
No doses and no mark allocations.
By the end, you should be able to…
- Keep the axon spike distinct from rod hyperpolarisationWhen the membrane potential becomes more negative than the resting potential..
- Place grey matter, myelin and acetylcholineA neurotransmitter used at many synapses and at neuromuscular junctions. correctly.
- Match each drug to one site.
Build your understanding
Three electrical stories
Axon: sodium in, spike, potassium out. Rod: light closes sodium channels, hyperpolarisationWhen the membrane potential becomes more negative than the resting potential.. Synapse: calcium in, acetylcholineA neurotransmitter used at many synapses and at neuromuscular junctions. out, sodium channels on the next cell. Mixing them is the usual error.
Structures
Sensory in, motor out, relay in the grey matter. Myelin from Schwann cellA cell that wraps around an axon to form the myelin sheath., jumps at nodes. Circular muscle constricts the pupil. habituationA reduced response to a repeated stimulus that is harmless. is less transmitter, tested with a new stimulus.
Make your reasoning visible
Direction of sodium
Into the axon during the spike. Less sodium into the rod in the light.
No advice
Mechanisms only. Do not add a dose.
Avoid this misconception
The claim: Myelin, acetylcholineA neurotransmitter used at many synapses and at neuromuscular junctions. and rhodopsin are three names for the transmitter.
The correction: Myelin insulates. Acetylcholine is a transmitter. Rhodopsin is the rod pigment.
Check your understanding
Try each question before opening the suggested answer.
Check your understanding (continued)
Practice question
Retrieval and explanation · suggested answer
State one structural difference between a sensory neurone and a motor neurone.
Show suggested answer
The sensory cell body is on a side branch. The motor cell body is at the end of the cell, inside the CNS, with a long axon to the effector.
Practice question
Retrieval and explanation · suggested answer
Which ion’s entry causes the rising phase of an action potential?
Show suggested answer
Sodium.
Practice question
Retrieval and explanation · suggested answer
Name the enzyme that stops acetylcholine acting for long.
Show suggested answer
Acetylcholinesterase.
Practice question
Retrieval and explanation · suggested answer
Lidocaine and cobra alpha toxin both stop signals. How do their targets differ?
Show suggested answer
Lidocaine blocks voltage-gated sodium channels. The toxin blocks acetylcholine receptors on the muscle.
Take the idea further
Apply the same specification knowledge to an unfamiliar problem. Any extra assumptions are supplied in the question.
Stretch question
A bright light shines into an eye. Describe one event in a rod and one event in the iris. Then say which of those two is an action potential. Assume both pathways work.
Show a hint
Hyperpolarisation versus a muscle.
Explore the reasoning
In the rod, retinal changes shape, sodium channels close and the rod hyperpolarises, so less transmitter is released. In the iris, circular muscles contract and the pupil constricts. Neither of those two events is the action potential. Action potentials occur in the neurones that link them, including optic neurones. The muscle response is contraction after its own synapses.
Recall this lesson
Lesson recall questions
Question 1 of 5: How is a myelinated motor neurone adapted to carry impulses a long distance to a muscle?
Neurone types and myelin
Practice question
Retrieval and explanation · suggested answer
How is a myelinated motor neurone adapted to carry impulses a long distance to a muscle?
Lesson: 8A 1: The Structure of Neurones
Try this from memory first.
Put your biology to work
Explore where these ideas appear in the world. Enrichment, not extra required recall.
Dopamine loss is not an axon sodium story
8A · Exam PracticeThe NHS account of Parkinson’s is loss of substantia nigra cells and reduced dopamine, with effects on movement. That is an 8.7 synapse problem. It is not a…Specification 8.7Read & use the scienceClose article
Why this matters
The NHS account of Parkinson’s is loss of substantia nigra cells and reduced dopamine, with effects on movement. That is an 8.7 synapse problem. It is not a failure of myelin or of rod pigment. Do not treat the health page as a drug list. 8.1–8.9 reviewed as structures and transmission. A behaviour or symptom is the output of a pathway, not a direct recording of ion movement in one axon or synapse.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.7 How specified drugs alter nerve impulse transmission.
Use the science
Which named substance in 8.7 is the one linked to that cell loss, and what does it become?
Explore a possible response
L-DOPA. It can cross into the brain and be converted to dopamine. It does not restore the missing cells.
Explore the source
The NHS account of Parkinson’s is the cell loss
8A · The Effect of Drugs on the Nervous SystemThe NHS says Parkinson’s disease is caused by a loss of nerve cells in the substantia nigra, which reduces dopamine, and that people may have tremor, slow movement…Specification 8.7Read & use the scienceClose article
Why this matters
The NHS says Parkinson’s disease is caused by a loss of nerve cells in the substantia nigra, which reduces dopamine, and that people may have tremor, slow movement and stiff muscles. That supports the reason L-DOPA exists in the specification. The page is a health overview. It is not a dose chart, and it does not describe nicotine, lidocaine or MDMA. 8.7: L-DOPA is used because dopamine signalling has fallen. The other four substances are different synaptic or channel effects.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.7 How specified drugs alter nerve impulse transmission.
Use the science
Why is “the NHS says take L-DOPA with MDMA” an unacceptable sentence?
Explore a possible response
The NHS page describes the disease, not a combination with MDMA. MDMA is not a treatment. This lesson only explains mechanisms. Medical decisions belong with a clinician, not a revision note.