Biology Lecture: Control and Coordination

Introduction

• Focus on Topic 15: Control and Coordination
• Comparison between nervous system and endocrine system
  • Nervous system: rapid response
  • Endocrine system: gradual response
• Hormones: insulin, glucagon, ADHD, adrenaline
• Endocrine glands: ductless, release hormones into bloodstream

Nervous System

• Composed of neurons: sensory neurons, relay neurons, motor neurons
• Neuron structure:
  • Cell body
  • Axon
  • Dendrons
• Myelinated neurons: myelin sheath formed by Schwann cells
  • Myelin sheath: insulates axon, speeds up impulse transmission
  • Nodes of Ranvier: gaps that facilitate saltatory conduction

Types of Neurons

• Sensory Neurons
  • Carry impulses from sensory receptors to relay/motor neurons and brain
  • Long dendron and short axon
• Relay Neurons
  • Connect sensory and motor neurons
  • Multiple short axons and dendrons
• Motor Neurons
  • Carry impulses from relay neurons to effectors (muscles/glands)
  • Long axon and multiple short dendrons

Sensory Receptors

• Detect stimuli and convert to electrical impulses
• Types:
  • Photoreceptors: light (e.g., rod and cone cells)
  • Thermoreceptors: temperature
  • Mechanoreceptors: pressure, taste, smell, balance

Resting Potential and Action Potential

• Resting Potential
  • Neuron at rest: -70 mV
  • Na+ and K+ ions create electrochemical gradient
• Action Potential
  • Stimulus induces depolarization
  • Threshold: -55 mV for action potential initiation
  • Depolarization: Na+ influx, voltage becomes positive
  • Repolarization: K+ efflux, voltage decreases
  • Hyperpolarization: overshoot, refractory period
  • Saltatory conduction: "Mexican wave" movement through axon

Synapse and Neurotransmission

• Synapse Definition: Gap between neurons
• Transmission Process
  • Action potential triggers neurotransmitter release
  • Neurotransmitters cross synaptic cleft, bind to receptors
  • Binding depolarizes post-synaptic neuron
  • Neurotransmitter degradation prevents constant firing

Neuromuscular Junction

• Specialized synapse at muscle fibers
• Acetylcholine as neurotransmitter
• Muscle depolarization leads to contraction

Muscle Contraction

• Sarcomere Structure
  • Thick filaments: myosin
  • Thin filaments: actin
• Sliding Filament Theory
  • Myosin heads bind to actin, causing sliding
  • ATP involved in crossbridge cycling and myosin head movement

Plant Responses

• Venus Flytrap: rapid closure mechanism via electrical impulses
• Tropisms
  • Phototropism: growth towards light
  • Gravitropism: growth towards/against gravity
• Hormones in Plants
  • Auxins: cell elongation
  • Gibberellins: germination, stem elongation

Summary

• Control and coordination via nervous system and hormones
• Plant responses to environmental stimuli via hormones
• Importance of understanding biological mechanisms