Chapter 12: Coordination and Response in Humans

Learning Objectives

By the end of this chapter, you should be able to:

• Describe the structure and function of the nervous system
• Explain the components of neurons and nerve impulse transmission
• Understand the process of nerve impulse transmission across synapses
• Identify major parts of the human brain and their functions
• Compare nervous and endocrine coordination systems

Overview

Coordination and response are essential for maintaining homeostasis and adapting to environmental changes. The human body coordinates its activities through two main systems: the nervous system for rapid, short-term responses and the endocrine system for slower, long-term regulation. This chapter explores how these systems work together to control bodily functions and maintain internal balance.

Coordination Systems

Nervous vs. Endocrine Coordination

Two complementary systems coordinate body functions:

Integration of Systems

Complementary Functions:

• Nervous system provides rapid, precise control
• Endocrine system provides sustained, widespread regulation
• Neuroendocrine integration: Some neurons produce hormones (neurohormones)

Did You Know? The human nervous system contains about 86 billion neurons, and each neuron can form connections with thousands of other neurons, creating an incredibly complex network with over 100 trillion connections!

Neural Network Complexity:

$$\text{Connections} = \text{Neurons} \times \text{Connections per Neuron}$$ $$100\text{ trillion} = 86\text{ billion} \times \text{1,164 connections per neuron}$$

The Nervous System

Components of the Nervous System

Central Nervous System (CNS):

• Brain: Controls body functions and processes information
• Spinal Cord: Conducts nerve impulses, coordinates reflexes

Peripheral Nervous System (PNS):

• Somatic Nervous System: Controls voluntary muscle movement
• Autonomic Nervous System: Controls involuntary functions
  • Sympathetic: "Fight or flight" responses
  • Parasympathetic: "Rest and digest" responses

Neuron Structure and Function

Neuron (Nerve Cell): The basic functional unit of the nervous system

Structural Components:

Conduction Velocity Equation:

$$\text{Velocity} = \frac{\text{Distance}}{\text{Time}} = k \times \text{Diameter}$$

where $k$ = conduction constant

Neuron Types:

Nerve Impulse Transmission

Resting Potential:

• State: Neuron not transmitting impulse
• Membrane Potential: -70mV (negative inside)
• Ions: High Na⁺ outside, high K⁺ inside
• Maintained by: Sodium-potassium pump

Action Potential:

• Depolarization: Na⁺ channels open, Na⁺ enters
• Repolarization: K⁺ channels open, K⁺ exits
• Refractory Period: Neuron cannot fire again temporarily

Myelin and Saltatory Conduction:

• Myelin sheath insulates axon
• Nodes of Ranvier allow ion exchange
• Saltatory conduction: Impulse jumps between nodes, increasing speed

Speed of Nerve Impulse:

• Unmyelinated fibers: 0.5-2 m/s
• Myelinated fibers: Up to 120 m/s
• Factors affecting speed: Fiber diameter, myelination, temperature

Saltatory Conduction Velocity:

$$\text{Velocity} = \frac{\text{Distance Between Nodes}}{\text{Time for Node Depolarization}}$$ $$\text{Speed Increase} = \frac{\text{Myelinated Velocity}}{\text{Unmyelinated Velocity}} = \frac{120\text{ m/s}}{2\text{ m/s}} = 60\times$$

The Synapse

Synapse Structure

Junction between two neurons or between neuron and effector cell

Components:

• Presynaptic neuron: Neuron sending signal
• Postsynaptic neuron: Neuron receiving signal
• Synaptic cleft: Gap between neurons
• Synaptic vesicles: Contain neurotransmitters
• Receptors: Bind neurotransmitters on postsynaptic membrane

Synaptic Transmission Equation:

$$\text{Signal Strength} = \frac{\text{Neurotransmitter Released}}{\text{Receptor Affinity} \times \text{Distance}}$$

Neurotransmission Process

Steps:

1. Nerve impulse reaches axon terminals
2. Calcium channels open, C$a^2$⁺ enters
3. Vesicles fuse with presynaptic membrane
4. Neurotransmitters released into synaptic cleft
5. Neurotransmitters bind to receptors on postsynaptic membrane
6. Signal transmission occurs in postsynaptic neuron

Common Neurotransmitters:

Neurotransmitter Balance Equation:

$$\text{Neural Signaling} = \frac{\text{Excitatory Input} - \text{Inhibitory Input}}{\text{Total Synaptic Activity}}$$

Synaptic Integration

Spatial Summation: Multiple synapses firing simultaneously Temporal Summation: Single synapse firing rapidly Excitatory Postsynaptic Potential (EPSP): Depolarization, promotes firing Inhibitory Postsynaptic Potential (IPSP): Hyperpolarization, prevents firing

Reflex Actions

Definition and Characteristics

Reflex: Rapid, automatic response to stimuli that does not require conscious thought

Characteristics:

• Automatic: No conscious control
• Rapid: Fast response time
• Protective: Prevents injury
• Involuntary: Cannot be voluntarily controlled

Reflex Arc Components

Neural pathway for reflex actions:

1. Receptor: Detects stimulus
2. Sensory Neuron: Transmits signal to spinal cord
3. Interneuron: Processes signal in spinal cord (may be absent)
4. Motor Neuron: Transmits signal from spinal cord
5. Effector: Responds to signal (muscle or gland)

Types of Reflex Arcs:

Examples of Reflexes

Stretch Reflexes:

• Knee-jerk reflex: Muscle stretch receptor detects stretch, causes contraction
• Purpose: Maintains muscle tone and posture

Withdrawal Reflexes:

• Hand withdrawal: Pull hand away from painful stimulus
• Purpose: Prevents tissue damage

Protective Reflexes:

• Blink reflex: Protects eyes from foreign objects
• Cough reflex: Clears airways of irritants
• Gag reflex: Prevents choking

Autonomic Reflexes:

• Pupil reflex: Adjusts pupil size to light
• Heart rate reflex: Regulates cardiovascular function

The Human Brain

Major Brain Regions

Brain: Control center of the nervous system

Cerebrum:

• Structure: Largest part of brain, divided into hemispheres
• Functions: Higher cognitive functions, consciousness, memory
• Lobes: Frontal, parietal, temporal, occipital
• Corpus Callosum: Connects hemispheres

Cerebellum:

• Structure: Second largest part, located behind brainstem
• Functions: Coordinates movement, balance, posture
• Cerebellar Cortex: Outer layer with folia (folds)

Brainstem:

• Structure: Connects brain to spinal cord
• Components: Midbrain, pons, medulla oblongata
• Functions: Vital life functions, relay station

Specific Brain Functions

Cerebral Cortex Functions:

Brainstem Functions:

• Midbrain: Visual and auditory reflexes, motor control
• Pons: Respiratory control, facial movement
• Medulla Oblongata: Vital functions (heart rate, breathing, blood pressure)

Limbic System:

• Components: Amygdala, hippocampus, hypothalamus
• Functions: Emotion, memory, motivation, basic drives

Protection of the Brain

Meninges: Protective membranes around brain and spinal cord

• Dura Mater: Tough outer layer
• Arachnoid Mater: Middle layer with web-like appearance
• Pia Mater: Inner layer adherent to brain surface

Cerebrospinal Fluid (CSF):

• Function: Cushions brain, removes waste
• Circulation: Produced in ventricles, circulates around brain and spinal cord
• Protection: Absorbs shocks, maintains buoyancy

Blood-Brain Barrier:

• Structure: Tight junctions between capillary cells
• Function: Protects brain from harmful substances
• Selective permeability: Allows essential nutrients, blocks toxins

The Endocrine System

Overview of the Endocrine System

Endocrine System: Network of glands that produce hormones

Hormones: Chemical messengers that regulate body functions

Key Characteristics:

• Long-distance signaling: Travel via bloodstream
• Slow but sustained effects: Last minutes to days
• Specificity: Bind to specific receptors
• Amplification: Small amounts cause large effects

Major Endocrine Glands

Pituitary Gland:

• Location: Base of brain, below hypothalamus
• Structure: Anterior and posterior lobes
• Functions: "Master gland" controlling other glands

Thyroid Gland:

• Location: Neck, below larynx
• Hormones: Thyroxine (T4), Triiodothyronine (T3)
• Functions: Regulates metabolism, growth, development

Parathyroid Glands:

• Location: On thyroid gland
• Hormone: Parathyroid hormone (PTH)
• Function: Regulates calcium levels

Adrenal Glands:

• Location: On top of kidneys
• Structure: Cortex and medulla
• Cortex hormones: Cortisol, aldosterone, sex hormones
• Medulla hormones: Epinephrine, norepinephrine

Pancreas:

• Endocrine functions: Insulin, glucagon from islets of Langerhans
• Functions: Regulates blood sugar levels

Gonads:

• Testes: Testosterone, inhibin
• Ovaries: Estrogen, progesterone, inhibin

Other Glands: Pineal gland, thymus, hypothalamus

Hormone Types and Actions

Chemical Classes:

Mechanism of Action:

Peptide Hormones:

1. Bind to cell surface receptors
2. Activate second messenger systems
3. Trigger cellular responses

Steroid Hormones:

1. Diffuse through plasma membrane
2. Bind to intracellular receptors
3. Form hormone-receptor complex
4. Bind to DNA and regulate gene expression

Hormone Regulation:

• Feedback loops: Negative feedback maintains homeostasis
• Hierarchical control: Hypothalamus → Pituitary → Target glands
• Circadian rhythms: Hormone release follows daily patterns

Nervous and Endocrine Integration

Coordinated Responses

Stress Response Example:

Temperature Regulation:

• Nervous system: Sensory input, motor control
• Endocrine system: Thyroid hormones (basal metabolism)

Neuroendocrine Integration

Hypothalamus-Pituitary Axis:

• Hypothalamus: Produces releasing hormones
• Pituitary: Responds to hypothalamic signals
• Target glands: Produce final hormones

Examples:

• Stress response: CRH → ACTH → Cortisol
• Growth: GHRH → GH → Growth factors
• Reproduction: GnRH → FSH/LH → Sex hormones

Practice Tips for SPM Students

Key Concepts to Master

1. Neuron structure and nerve impulse transmission
2. Synapse function and neurotransmission
3. Reflex arc components and types
4. Brain regions and their specific functions
5. Hormone types and endocrine gland functions

Experimental Skills

1. Identify brain structures from diagrams and models
2. Design nerve impulse experiments with proper stimulation and recording
3. Interpret neurological test results and reflex responses
4. Apply knowledge to coordination and integration scenarios

Problem-Solving Strategies

1. Neural pathway analysis: Trace signal transmission through reflex arcs
2. Hormonal regulation: Understand feedback loops and hierarchies
3. Coordination scenarios: Analyze how nervous and endocrine systems interact
4. Clinical applications: Apply knowledge to neurological and endocrine disorders

Environmental and Health Connections

Environmental Impact on Coordination

• Stress affects both nervous and endocrine systems
• Pollutants can disrupt neurotransmitter function
• Electromagnetic fields may influence neural activity
• Diet affects neurotransmitter production and hormone synthesis

Public Health Significance

• Neurological disorders affect millions worldwide
• Endocrine diseases impact metabolism, growth, and reproduction
• Mental health involves complex coordination systems
• Aging affects both nervous and endocrine function

Biomedical Applications

• Neuropharmacology uses drugs to target specific neurotransmitters
• Hormone replacement therapy for endocrine deficiencies
• Neuroprosthetics restore nervous system function
• Gene therapy for neurological disorders

Summary

• The nervous system provides rapid, precise coordination through electrical signals
• Neurons transmit nerve impulses via action potentials across synapses
• Reflexes provide automatic protective responses without conscious thought
• The brain coordinates higher cognitive functions and maintains vital functions
• The endocrine system provides slower, longer-term regulation through hormones
• Both systems work together to maintain homeostasis and coordinate body functions

Related Topics

• Chapter 10: Transport in Humans and Animals
• Chapter 11: Immunity in Humans
• Chapter 13: Homeostasis and the Human Urinary System
• Chapter 1: Organisation of Plant Tissues and Growth (Form 5)