IGCSE Biology: Coordination and Response (Chapter 14)

Introduction

• Coordination and Response: Chapter covers electrical impulses, nervous system parts, mechanisms like reflex arc, synapse.
• Syllabus Core vs. Extended: Core requires basic understanding; extended includes synapse processes and effects.

Nervous System

Electrical Impulses

• Travel along neurons: Key concept, often a simple exam question.

Parts of the Nervous System

• Central Nervous System (CNS): Brain and spinal cord; coordination centers.
• Peripheral Nervous System (PNS): Nerves and neurons; coordinates/regulates bodily functions.

Actions

• Voluntary Actions: Conscious control actions.
• Involuntary Actions: Automatic, quick actions, e.g., reflexes.

Nerve Impulses

• Definition: Electrical signals passed along neurons (nerve cells).

Types of Neurons

• Motor Neuron: Cell body at one end, covered with myelin sheath.
• Sensory Neuron: Smaller cell body, in the middle.
• Relay Neuron: More branched, shorter axon.

Reflex Arc

• Definition: Automatic, rapid integration and coordination of stimuli with effector responses.
  • Stimuli: Environmental changes (e.g., temperature).
  • Effectors: Body parts that react (e.g., muscles, glands).
• Involves: Sensory, relay, and motor neurons.
• Synapse: Gap between neurons; neurotransmitters transmit signals.
• Simple Reflex Arc: Stimulus affects receptor -> Sensory neuron -> CNS (Relay neuron) -> Motor neuron -> Effector.

Synapse

• Function: Ensures one-directional impulse travel.
• Events at Synapse: Impulse arrives -> Vesicles release neurotransmitters -> Diffuse across synaptic cleft -> Attach to receptor molecules.
• Drug Effects: Can prevent neurotransmitter diffusion, e.g., heroin.

Sense Organs

Eye Anatomy

• Parts: Cornea, iris, lens, retina, optic nerve.
• Functions:
  • Cornea: Refracts light.
  • Iris: Controls light entry.
  • Lens: Focuses light.
  • Retina: Contains light receptors (rods and cones).
  • Optic Nerve: Carries impulses to brain.

Pupil Reflex

• Function: Adjusts pupil size for light intensity.
  • Low Light: Radial muscles contract, circular muscles relax.
  • High Light: Circular muscles contract, radial muscles relax.

Accommodation

• Near Objects: Ciliary muscles contract, lens thickens.
• Distant Objects: Ciliary muscles relax, lens thins.

Light Receptors

• Rods: Low detail, black & white, low light.
• Cones: High detail, color, high light intensity.

Hormones

Definition

• Hormone: Chemical substance by glands, carried by blood, affects target organs.

Types of Hormones

• Adrenaline: Produced in adrenal gland; fight-or-flight response.
• Insulin: Produced in pancreas; reduces blood glucose.
• Testosterone & Estrogen: Development of sexual characteristics.

Adrenaline

• Effects: Increases pulse, converts glycogen to glucose, diverts blood.

Nervous vs. Endocrine Systems

• Speed: Nervous is quick; Endocrine is slow.
• Message Type: Nervous is electrical; Endocrine is chemical.
• Duration: Nervous short-lived; Endocrine can last long.
• Area: Nervous local; Endocrine widespread.

Homeostasis

Definition

• Homeostasis: Maintenance of constant internal environment.

Glucoregulation

• Insulin: Lowers glucose by storing as glycogen.
• Glucagon: Raises glucose by converting glycogen to glucose.
• Diabetes: Failure in glucoregulation; Type 1 requires insulin injections.

Thermoregulation

• Vasodilation: Blood vessels dilate to release heat.
• Vasoconstriction: Blood vessels constrict to retain heat.

Tropic Responses

Gravitropism

• Response: Growth towards or away from gravity.
• Positive: Roots grow down.
• Negative: Shoots grow up.

Phototropism

• Response: Growth towards or away from light.
• Positive: Shoots grow towards light.

Weed Killers

• Plant Hormones: Used to disrupt normal growth, kill weeds.

Exam Practice

• Example Questions: Applying knowledge of muscle contractions and eye parts.