3.5.9Inquiry Process
Neurones in the Brain — IB Biology HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 140 of 160
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.
Section 1 of 5Organisation in the Brain
Cerebral cortex
- Cerebral cortex This outer layer processes sensory information, controls voluntary movement and is involved in thinking, language and memory.
Convergence
- Convergence A single neurone may receive thousands of synaptic inputs, and adds them together before deciding whether to fire.
Divergence
- Divergence One neurone can pass its message to many others, allowing a signal to spread through large areas of the brain.
Networks
- Networks Memory and thought depend on pathways of connected neurones rather than on any single cell.
Section 2 of 5Synaptic Plasticity
1
When a pathway is used repeatedly, the synapses along it are strengthened and respond more strongly.
2
Strengthening can involve more receptors on the postsynaptic membrane or more neurotransmitter being released.
3
Synapses that are rarely used may become weaker and may be removed, which is called synaptic pruning.
4
New connections can also form, so the pattern of connections changes with learning and experience.
5
These changes in synaptic strength are thought to be the physical basis of learning and memory.
Section 3 of 5Pain as an Example
Pain as an Example
Nociceptors
- Nociceptors Sensory neurones with free nerve endings detect damaging stimuli such as extreme heat or tissue injury.
Pathway
- Pathway Impulses pass to the spinal cord, then relay neurones carry them up to the brain where pain is perceived.
Endorphins
- Endorphins The body releases endorphins, which bind opioid receptors and reduce pain signalling by inhibiting transmitter release.
Drugs
- Drugs Opioid drugs such as morphine act on the same receptors, while local anaesthetics block voltage-gated sodium channels.
| Process | Change in synapse | Result |
|---|---|---|
| Learning | Strengthened | Easier transmission |
| Disuse | Weakened or removed | Pathway fades |
Section 4 of 5Worked Example
Question
- A neurone in the cortex receives 4 excitatory inputs of +5 mV and 2 inhibitory inputs of −6 mV.
- The resting potential is −70 mV and threshold −55 mV.
- After practice, each excitatory input grows to +7 mV.
- Does the neurone fire before and after?
- Before4 × 5 = +20 mV and 2 × (−6) = −12 mV, net +8 mV, giving −62 mV, so no firing.
- After4 × 7 = +28 mV, minus 12 mV, net +16 mV, giving −54 mV.
- −54 mV is above the threshold of −55 mV.
Answer It does not fire before practice but does fire after, illustrating strengthened synapses.
Section 5 of 5Exam Checklist & Tips
3.5.9 – Key Points for the Exam
- Synaptic plasticity The ability of synapses to strengthen or weaken in response to activity.
- Cerebral cortex Outer layer of the brain involved in higher functions.
- Nociceptor A sensory receptor that detects painful stimuli.
- Endorphin Natural opioid peptide that reduces the perception of pain.
Common Mistakes
- Saying that new neurones are needed for every memory; synaptic changes are central.
- Thinking pain is felt at the receptor; perception occurs in the brain.
- Confusing convergence (many inputs) with divergence (many outputs).
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