(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.