Description

CHAPTER TWO: COORDINATION IN MAMMALS
Complete Study Notes & Revision Guide
📚 What This Document Covers
This comprehensive chapter breakdown covers everything you need to master coordination in mammals — from the fundamental concepts of stimuli and response to the intricate workings of the nervous system, the structure and function of neurones, the brain and spinal cord, sense organs, and the effects of drugs on nervous coordination.

🔬 SECTION 1: FOUNDATIONS OF COORDINATION IN ANIMALS
Understanding Coordination
Coordination is the linking together of different parts or organs in the body so that they work at the appropriate time and required rate. Without coordination, body activities would be disorganized and the body would fail to function properly.

The Three Requirements of Coordination
Detect changes in the environment

Transmit information to appropriate body parts

React to changes in a way that ensures survival

Stimuli and Responses
Stimuli = changes in the environment to which organisms respond

Irritability/Sensitivity = the ability to sense, interpret, and respond to stimuli

Response = a behavioral, physiological, or muscular activity initiated by a stimulus

Type of Stimulus Description Examples
External stimuli From the surrounding environment Wind, cold, heat, light, odor, vibration, pressure, pain, water, gravity
Internal stimuli From within the organism Sense of body position, glucose level, blood pressure
Why Coordination Matters — The Evolutionary Perspective
Predator avoidance: Rapid reflex responses prevent injury

Food acquisition: Coordinated movement allows hunting and foraging

Homeostasis: Maintains stable internal conditions

Reproduction: Coordinated behaviors are essential

🔑 Key Concept: The nervous system is the fast coordination system (electrical impulses, milliseconds), while the endocrine system is the slow coordination system (hormones, minutes to hours).

🧠 SECTION 2: NERVOUS COORDINATION IN HUMANS
Overview of the Nervous System
Division Components Function
Central Nervous System (CNS) Brain and spinal cord Integration, processing, decision-making
Peripheral Nervous System (PNS) Nerve fibres branching from CNS Communication between CNS and body
Homeostasis = the body’s ability to maintain stable internal conditions through feedback mechanisms.

Components of Nervous Coordination
Component Definition Examples
Stimulus Change in environment Touch, pain, temperature, light
Receptors Specialized cells that detect changes Eye, ear, nose, skin, tongue
Coordinator Receives and interprets messages Brain and spinal cord
Effectors Receive motor impulses and bring about response Muscles and glands
Response Change shown by organism Pulling hand from hot object
Feedback Animal decides what to do in response —
The Coordination Pathway
text
Stimulus → Receptor → Coordinator (CNS) → Effector → Response
↑ |
└──────────── Feedback ────────────────┘
🔑 Key Concept: The coordinator uses messages called nerve impulses — electrical signals transmitted along neurones.

🔬 SECTION 3: STRUCTURE OF NEURONES
What Are Neurones?
Neurones are the conducting cells of the nervous system — the basic structural and functional units found between receptors and effectors.

Distinguishing properties:

Highly responsive to stimuli

Capable of conducting nerve impulses rapidly over long distances

General Structure of a Neurone
Part Description Function
Cell body Contains nucleus; angular/oval/star-shaped Processes nerve impulses it receives
Dendrites One or more extensions from cell body Receive signals and direct them to cell body
Axon Long, stem-like part Sends signals to other cells
Axoplasm Space inside axon with charged ions Conducts electrical impulses
Myelin sheath Fatty layer covering some axons Protects, insulates, facilitates rapid transmission
Neurilemma Cellular layer inside myelin sheath Nourishes and insulates the axon
Nodes of Ranvier Periodic gaps in myelin sheath Facilitate rapid transmission by allowing “leaping”
Axon terminal Terminal end of axon Transmits signals to next neurone or effector
Why the Myelin Sheath Matters — Saltatory Conduction
Unmyelinated axons: Impulse travels continuously — relatively slow

Myelinated axons: Impulse “leaps” from node to node — saltatory conduction (from Latin saltare = to leap)

Advantages: Much faster and more energy-efficient (fewer ion movements = less ATP used)

Clinical note: Multiple sclerosis (MS) — myelin sheath damaged → saltatory conduction fails → muscle weakness, coordination problems

Types of Neurones
Feature Sensory Neurone Motor Neurone Interneurone
Other name Afferent neurone Efferent neurone Relay/intermediate neurone
Structure Long dendron, short axon Short dendrites, long axon Short dendrites, short/long axon
Cell body location Outside CNS Inside CNS Inside CNS
Function Receptor → CNS CNS → Effector Connects sensory to motor
Direction of impulse Toward CNS Away from CNS Within CNS
Adaptations of a Neurone to Its Function
Myelin sheath — protection, insulation, rapid transmission

Schwann cells — secrete myelin sheath

Many dendrites — large surface area for receiving impulses

Elongated axons — carry information over long distances

Tiny branches at end — facilitate receiving impulses from other neurones

High metabolic rate — requires glucose and oxygen for ion gradients

Long lifespan — most formed before birth, must last a lifetime

🔗 SECTION 4: THE SYNAPSE
Definition
A synapse is the gap at the point where the axon terminals of one neurone are in association with the dendrite or cell body of another neurone, or an effector organ. The gap is called the synaptic cleft.

Mechanism of Synaptic Transmission
Impulse arrives at axon terminal of presynaptic neurone

Calcium ions (Ca²⁺) enter → trigger exocytosis of synaptic vesicles

Neurotransmitter (e.g., acetylcholine) released into synaptic cleft

Neurotransmitter binds to receptors on postsynaptic membrane

Ion channels open → Na⁺ enters → depolarization → new impulse generated

Neurotransmitter broken down (e.g., by acetylcholinesterase) or taken back up → synapse reset

Why Synapses Matter
Unidirectional transmission: Impulses travel only from presynaptic to postsynaptic → one-way flow

Integration: A single neurone may receive thousands of inputs and “decide” whether to fire

Modulation: Site of learning, memory, and drug action

Key Neurotransmitters
Neurotransmitter Function Location
Acetylcholine Muscle contraction, parasympathetic NS Neuromuscular junction, autonomic ganglia
Dopamine Reward, motivation, motor control Brain (substantia nigra, VTA)
Serotonin Mood, sleep, appetite Brain (raphe nuclei)
Noradrenaline Fight-or-flight response Sympathetic nervous system
GABA Inhibitory neurotransmitter Brain
Glutamate Excitatory neurotransmitter Brain
Drug Connections
Cocaine blocks dopamine reuptake → dopamine accumulates → prolonged reward → addiction

SSRIs block serotonin reuptake → mood improvement

Organophosphate pesticides inhibit acetylcholinesterase → acetylcholine accumulates → continuous muscle contraction → paralysis and death

🧠 SECTION 5: CENTRAL NERVOUS SYSTEM (CNS)
Overview
The CNS consists primarily of the brain and spinal cord. It processes received information, coordinates, and influences activities of all body parts.

The Brain — Protection
Encased in skull (cranium)

Meninges — system of membranes

Cerebrospinal fluid — cushions, provides nutrients, removes waste

The Three Main Parts of the Brain
(a) Forebrain
Composed of: olfactory lobes, cerebrum, hypothalamus, pituitary gland

Cerebrum:

Largest part; divided into right and left hemispheres

Connected by corpus callosum

Outer portion: grey matter (cell bodies); inner portion: white matter (axons)

Folds (gyri and sulci) increase surface area

Functions: Voluntary activities, speech, reasoning, memory, decision-making, behavior, vision, imagination

Localization of function:

Lobe Function
Frontal lobe Motor control, planning, decision-making, personality
Parietal lobe Somatosensory processing (touch, temperature, pain)
Temporal lobe Hearing, language comprehension, memory
Occipital lobe Vision
Hypothalamus:

Homeostasis: Regulates temperature, fluid balance, metabolism, hormones

Involuntary activities: Appetite, sleep, thirst

Link between nervous and endocrine systems: Controls pituitary gland

Thermoregulation centre and osmoregulation centre

Pituitary gland:

“Master gland” — controls activity of most other hormone-secreting glands

Anterior pituitary: Secretes TSH, ACTH, FSH, LH, GH, Prolactin, MSH

Posterior pituitary: Stores and releases ADH and oxytocin

(b) Midbrain
Smallest part of the brain

Connects hindbrain with forebrain

Functions: Conveys information, controls involuntary activities and reflex movements of head/neck/eyes, visual and auditory reflexes

(c) Hindbrain
Composed of: cerebellum and medulla oblongata

Cerebellum:

Cauliflower-shaped structure

Functions: Body movements, balance, posture; receives impulses from skeletal muscles, tendons, inner ear

Clinical note: Damage → ataxia (loss of coordination, unsteady gait)

Medulla oblongata:

Most posterior part; connects to spinal cord

Controls involuntary and reflex activities: Breathing, heartbeat, digestion, blood vessel dilation/constriction, swallowing, sneezing, vomiting, secretion of juices, temperature regulation

Clinical note: Damage → death (controls breathing and heartbeat)

Cranial Nerves
Pairs of nerves connecting brain to head, neck, and trunk:

Olfactory nerves — smell

Optic nerves — vision

Vestibulocochlear nerves — hearing and balance

Vagus nerve — mixed motor and sensory (heart, gut, respiratory tract)

Oculomotor nerve — eye movement, pupil constriction

Spinal Cord
Structure:

Runs from head to end of trunk; encased in meninges

Lies in canal of vertebral column

Cross-section: Two identical halves enclosing spinal canal (filled with cerebrospinal fluid)

Inner region: Grey matter (cell bodies)

Outer region: White matter (myelinated axons)

Spinal nerves: Dorsal root (sensory) and ventral root (motor)

Functions:

Coordinating centre — controls involuntary actions (reflex actions)

Nerve impulse conduction pathway — between brain and rest of body

Reflex centre — fast, automatic responses

Reflex actions controlled by spinal cord:

Coughing, sneezing, blinking

Removing hand or leg when touching hot or sharp object

Clinical note: Spinal cord injury → loss of function below injury level (paralysis, loss of sensation)

Comparison of Grey Matter and White Matter
Feature Grey Matter White Matter
Colour Grey White
Composition Cell bodies of neurones Myelinated axons
Location in spinal cord Inner region Outer region
Location in brain Outer region (cortex) Inner region
Function Processing, integration Conduction of impulses
✅ QUICK REVISION CHECKLIST
□ I can define coordination and explain why animals need it
□ I can describe the coordination pathway (stimulus → receptor → coordinator → effector → response)
□ I can name the three types of neurones and their functions
□ I can label the structure of a neurone
□ I can explain saltatory conduction and why myelin matters
□ I can describe the mechanism of synaptic transmission
□ I can name key neurotransmitters and their functions
□ I can describe the three main parts of the brain and their functions
□ I can explain the structure and function of the spinal cord
□ I can compare grey matter and white matter
□ I can describe the reflex arc and its components
□ I can distinguish between simple and conditioned reflexes
□ I can describe the structure of the skin and its receptors
□ I can explain the mechanism of hearing
□ I can explain the mechanism of body balance
□ I can describe the structure of the eye and its functions
□ I can explain accommodation (near vs. distant objects)
□ I can describe common eye defects and their corrections
□ I can describe the nose (smell) and tongue (taste) mechanisms
□ I can categorize drugs and describe their effects
□ I can explain how drugs affect the synapse
□ I can describe preventive measures against drug abuse
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