14.1.4Coordination and Response
The Synapse — Cambridge IGCSE Biology 0610 Revision Notes & Topical Questions
5 min read 5 parts Lesson 6 of 7 Unit quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 5Structure of a Synapse
Neurones do not touch each other; a tiny gap separates the end of one from the next.
Synaptic gap
- Synaptic gap This is the narrow space between the end of one neurone and the start of the next, across which chemicals must diffuse.
Vesicles
- Vesicles Small sacs in the first neurone store neurotransmitter molecules until an impulse arrives.
Neurotransmitter
- Neurotransmitter A chemical that carries the signal across the gap, released when the impulse reaches the end of the axon.
Receptor proteins
- Receptor proteins Proteins on the membrane of the next neurone have a shape that is complementary to the neurotransmitter,
- so only the right chemical can bind.
Mitochondria
- Mitochondria Mitochondria in the first neurone supply the energy needed to make and release neurotransmitter.
Part 2 of 5Passing the Impulse
The signal changes from electrical, to chemical, and back to electrical.
1
An electrical impulse travels along the axon of the first neurone and arrives at its ending.
2
The impulse triggers vesicles to fuse with the membrane and release neurotransmitter into the synaptic gap.
3
Neurotransmitter molecules diffuse across the gap, which is a short distance, so this happens very quickly.
4
The neurotransmitter binds to receptor proteins on the membrane of the next neurone.
5
Binding stimulates a new electrical impulse in the next neurone, which then travels along it.
6
The neurotransmitter is then removed, for example by being broken down by enzymes, so the signal does not continue indefinitely.
Part 3 of 5One-Way Transmission and Roles
One-Way Transmission and Roles
Direction
- Direction Only the first neurone has vesicles of neurotransmitter and only the second has receptors, so impulses can travel in one direction only.
Importance
- Importance One-way transmission prevents signals going backwards and confusing the nervous system, so messages reach the right place.
Reflex arc
- Reflex arc Synapses link sensory neurones to relay neurones and relay neurones to motor neurones in a reflex arc.
Delay
- Delay The chemical step takes a little time, so a synapse slightly slows a message compared with an electrical connection.
Part 4 of 5Synapses and Drugs
Synapses and Drugs
Target for drugs
- Target for drugs Because transmission across the gap is chemical, some drugs can affect how synapses work.
Heroin
- Heroin Heroin acts at synapses in the nervous system, changing how messages are passed and producing its effects on the body.
Dependence
- Dependence Drugs that alter synapses can lead to dependence, and the user then needs more of the drug to get the same effect.
Part 5 of 5Exam Checklist & Tips
14.1.4 – Key Points for the Exam
- Synapse A junction between two neurones.
- Neurotransmitter A chemical that diffuses across a synapse to pass a signal.
- Receptor A protein on a membrane that a specific chemical can bind to.
- Vesicle A small membrane-bound sac containing stored substances.
- Impulse An electrical signal that passes along a neurone.
Common Mistakes
- Saying an electrical impulse jumps across the synapse, when a chemical crosses the gap.
- Stating that neurotransmitter is released by the second neurone rather than by the first.
- Forgetting that receptor shape must be complementary to the neurotransmitter.
- Writing that neurotransmitters travel by active transport, when they diffuse across the gap.
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