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8.1.2Unit 6: Practical Skills in Biology II

How a Response Is Generated by Effectors — IAL Edexcel Linear Revision Notes & Topical Questions

5 min read 4 parts Lesson 36 of 48 Unit quiz

📚 IAL Edexcel Linear Hub / Topical Revision
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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
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Part 1 of 4The Response Pathway

The route is

1stimulus2receptor3sensory neurone4CNS5motor neurone6effector7response

1
A stimulus, which is a change in the internal or external environment, is detected by a receptor cell.
2
The receptor generates nerve impulses, which travel along a sensory neurone to the central nervous system.
3
The central nervous system acts as a coordinator, integrating the incoming information and deciding which parts of the body must respond.
4
Impulses are sent from the central nervous system along motor neurones to the effector.
5
The effector, which may be a muscle or a gland, carries out the response.

Part 2 of 4Effectors and Responses

Muscle effectors
  • Muscle effectors Contract to cause movement, for example withdrawing the hand from a hot surface.
Gland effectors
  • Gland effectors Secrete substances such as hormones or enzymes when stimulated by a nerve impulse.
Receptors
  • Receptors Specialised cells that detect specific stimuli, such as light, pressure, chemicals or temperature.
Survival value
  • Survival value Detecting and responding to changes helps the organism avoid damage and find food.
Example
  • Example A pain receptor in the skin of the hand fires and the arm muscle contracts, moving the hand away.

Part 3 of 4Role of the Central Nervous System

Role of the Central Nervous System
Coordination
  • Coordination The CNS links incoming sensory information with outgoing instructions to effectors.
Selection
  • Selection It decides which effector must respond and how strongly.
Relay neurones
  • Relay neurones Inside the CNS, relay neurones pass the signal between sensory and motor neurones.
Unconscious or conscious
  • Unconscious or conscious Some responses are automatic reflexes, while others involve decisions in the brain.
ComponentExample in a hot-surface response
StimulusHeat from a hot surface
ReceptorPain receptor in the skin of the hand
CoordinatorSpinal cord
EffectorMuscle in the arm
ResponseHand pulled away

Part 4 of 4Exam Checklist & Tips

8.1.2 – Key Points for the Exam

  • Stimulus A change in the environment that can be detected.
  • Receptor A cell that detects a stimulus and generates an impulse.
  • Effector A muscle or gland that produces a response.
  • Coordinator The part of the nervous system that processes information and sends instructions.

Common Mistakes

  • Saying effectors are always muscles; glands are effectors too.
  • Placing the receptor after the sensory neurone in the sequence.
  • Describing the CNS as only the brain, and forgetting the spinal cord.
  • Writing that motor neurones carry information toward the CNS.

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