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(143) 14. Coordination and response(Part 1)(Cambridge IGCSE Biology 0610 for exams in 2023, 2024 and 2025)

Introduction to Coordination and Response

  • Importance of coordination between organs and systems for survival.

  • Organisms sense environmental changes and respond accordingly.

  • The nervous system plays a crucial role in coordinating and regulating body functions.

  • Key function: maintaining homeostasis (stable internal environment).

The Nervous System

  • Structure of the nervous system:

    • Central Nervous System (CNS): Comprises the brain and spinal cord.

    • Peripheral Nervous System (PNS): Includes all nerves outside the CNS.

Neurons

  • Three types of neurons:

    1. Sensory Neurons

      • Carry impulses from sense organs to the CNS.

    2. Relay Neurons

      • Found within the CNS and connect sensory and motor neurons.

    3. Motor Neurons

      • Carry impulses from the CNS to effectors (muscles or glands).

  • Distinguishing features of neurons:

    • Sensory neurons: Long with a cell body in the middle of the axon.

    • Relay neurons: Short with a small cell body and many branching dendrites.

    • Motor neurons: Large cell body with long branched dendrites.

Key Concepts

Stimulus, Receptor, and Effector

  • Stimulus: Change in the environment detected by sensory neurons (e.g., light, sound, touch).

  • Receptor: Structure that detects a stimulus and generates an impulse (e.g., skin receptors for heat).

  • Effector: Muscle or gland that responds to signals from the CNS (e.g., muscles pulling away from a fire).

Voluntary vs. Involuntary Responses

  • Voluntary Response:

    • A deliberate action initiated by the brain (e.g., raising a hand).

  • Involuntary Response:

    • Automatic reaction to a stimulus without brain involvement (e.g., pulling away from heat).

    • Faster than voluntary responses and crucial for survival.

Reflex Arc

  • Definition: The pathway of a nerve impulse during an involuntary response.

  • Example process (touching fire):

    1. Stimulus: Fire detected.

    2. Receptor: Skin receptors respond to the heat.

    3. Sensory Neuron: Sends impulse to the spinal cord.

    4. Relay Neuron: Connects sensory neuron to motor neuron in the spinal cord.

    5. Motor Neuron: Carries impulse to arm muscles (effector).

    6. Response: Arm pulls away from fire.

  • Diagramming the reflex arc:

    • Impulse flow:

      • Stimulus → Receptor → Sensory Neuron → Relay Neuron → Motor Neuron → Effector → Response.

Synapses

  • Definition: Junctions between two neurons where signals are transferred.

  • Structure of a synapse:

    • Vesicles with neurotransmitters, synaptic gap, receptor proteins.

  • Function at a synapse:

    • Neurotransmitters are released from one neuron,

    • Diffuse across the synaptic gap and bind to receptors on the next neuron,

    • Stimulates an impulse in the next neuron.

  • Impulses travel in one direction at synapses.

Conclusion

  • Recap of the nervous system's role in coordination and response.

  • Importance of understanding voluntary and involuntary responses and reflex arcs in biology.

  • Engaging viewers to subscribe and join for more educational content on biology.