Coordination & Response & Homeostasis - Notes

Cambridge (CIE) IGCSE Biology Coordination, Response & Homeostasis

Contents

• Mammalian Nervous System

• Types of Neurones

• The Reflex Arc

• The Synapse

• Sense Organs

• The Eye

• Hormones in Humans

• Homeostasis: Definition

• Homeostasis

• Homeostasis: Temperature Control

• Tropisms

Mammalian Nervous System

Structure & Role

• Nervous System Components:

  • Central Nervous System (CNS): Brain and spinal cord.

  • Peripheral Nervous System (PNS): All nerves in the body.

• Functions:

  • Coordination and regulation of body functions.

  • Interpretation and response to surroundings.

• Nerve Impulses:

  • Information is transmitted as electrical signals through nerve cells (neurones).

  • A bundle of neurones is referred to as a nerve.

Types of Neurones

Types Overview

• Three Main Types:

  • Sensory Neurones: Carry impulses from sense organs to the CNS.

  • Relay Neurones: Connect sensory and motor neurones within the CNS.

  • Motor Neurones: Carry impulses from the CNS to effectors (muscles/glands).

Neurone Structure

• Axons: Long fibres that facilitate quick impulse transfer by allowing the impulse to jump along at nodes.

• Dendrites: Extensions in the cell body that receive impulses from other neurones.

The Reflex Arc

Reflexes Overview

• Types of Responses:

  • Voluntary: Conscious actions initiated by the brain.

  • Involuntary (Reflex): Automatic reactions not processed by the brain (e.g., touching something sharp).

• Function: Reflex responses are crucial for survival and occur rapidly to prevent injury.

Reflex Response Sequence

1. Stimulus detected by a receptor.

2. Sensory neurone transmits impulse to the spinal cord.

3. Relay neurone passes impulse to motor neurone.

4. Motor neurone directs muscle contraction (effector).

The Synapse

Synaptic Function

• Definition: Junction where two neurones meet; critical for impulse transmission.

• Mechanism:

  • Electrical Impulse: Triggers neurotransmitter release from the presynaptic neurone.

  • Neurotransmitter Action: Diffuses across the synaptic cleft, binding to receptors on the postsynaptic neurone, leading to electrical impulse generation in the second neurone.

  • Directionality: Impulses are unidirectional due to synaptic structure.

Sense Organs

Function of Receptors

• Definition: Specialized groups of cells detecting environmental changes.

• Response Process:

  • Receptor stimulation generates an impulse.

  • Sensory neurone conveys the impulse to the CNS for response decision-making involving motor neurones and effectors.

The Eye

Structure Overview

• Main Components:

  • Cornea: Transparent front for light refraction.

  • Iris: Controls light entry via the pupil.

  • Lens: Focuses light onto the retina.

  • Retina: Contains light receptor cells for vision.

  • Optic Nerve: Transmits impulses to the brain.

Pupil Reflex

• Function: Adjustments to control light entry—dilates in dim light and constricts in bright light.

Hormones in Humans

Hormonal Function

• Definition: Chemical substances produced by glands, conveyed via blood to alter activity of specific target organs.

• Endocrine System: Glands responsible for hormone production and regulation.

Blood Glucose Regulation

• Insulin & Glucagon: Control blood sugar levels through conversion of glucose.

  • Insulin: Reduces blood glucose by promoting its storage as glycogen.

  • Glucagon: Raises blood glucose by converting glycogen back into glucose.

Homeostasis

Definition & Importance

• Homeostasis: Maintenance of stable internal conditions (temperature, pH, glucose levels) vital for proper body function.

• Negative Feedback Mechanisms: React to deviations from set points to restore normalcy (e.g., blood glucose regulation).

Temperature Control

• Skin receptors detect temperature changes, prompting responses via nervous impulses to regulate heat retention or loss (vasoconstriction & vasodilation).

Tropisms

Plant Responses to Stimuli

• Types of Tropisms:

  • Phototropism: Growth towards light.

  • Gravitropism: Growth towards gravity.

• Auxin: Plant hormone controlling growth direction by stimulating cell elongation.

Investigating Tropisms

• Experimentation: Involves placing plants in different orientations to observe responses in light and gravity.

Key Concepts and Summary

• The nervous system coordinates responses using neurones, synapses, and reflex arcs.

• Hormones are critical for maintaining homeostasis via the endocrine system, particularly exemplified in blood glucose regulation through insulin and glucagon.

• Plants exhibit responsive growth behaviors (tropisms) that are vital for survival and adaptation.