Introduction to Coordination and Control
Overview
Living organisms continuously respond to changes in their internal and external environments. For appropriate responses, multiple body parts must work together in a coordinated manner. This coordination is achieved through two main systems:
Nervous System
Rapid coordination via nerve impulses
Endocrine System
Slower coordination via chemical messengers (hormones)
Steps in Nervous Coordination
- Stimulation: Environmental changes detected by receptors
- Reception: Sensory receptors convert stimuli into nerve impulses
- Transmission: Impulses travel via sensory neurons to CNS
- Processing: CNS interprets information and makes decisions
- Response: Motor neurons carry signals to effectors
- Action: Effectors (muscles/glands) execute the response
Three Basic Components of Nervous System:
- Receptors: Detect stimuli (e.g., photoreceptors, mechanoreceptors)
- Neurons: Transmit nerve impulses
- Effectors: Execute responses (muscles and glands)
Nervous Coordination
Basic Organization
| System | Components | Functions |
|---|---|---|
| Central Nervous System (CNS) | Brain and Spinal Cord | Processing center, integration, decision making |
| Peripheral Nervous System (PNS) | Nerves and Ganglia | Connects CNS to receptors and effectors |
Sensory Receptors
| Type | Location | Function | Examples |
|---|---|---|---|
| Photoreceptors | Retina of eyes | Detect light stimuli | Rod cells, Cone cells |
| Mechanoreceptors | Skin, Blood vessels | Detect pressure, position, acceleration | Meissner’s corpuscles, Pacinian corpuscles |
| Thermoreceptors | Skin, Hypothalamus | Detect temperature changes | Cold receptors, Warm receptors |
| Chemoreceptors | Nasal epithelium, Tongue | Detect chemical stimuli | Olfaction receptors, Gustation receptors |
| Nociceptors | Skin, Joints, Internal organs | Detect pain | Free nerve endings |
Peripheral Nervous System Divisions
| Feature | Somatic Nervous System | Autonomic Nervous System |
|---|---|---|
| Control | Voluntary | Involuntary |
| Effectors | Skeletal muscles | Smooth muscles, Cardiac muscles, Glands |
| Pathways | One neuron pathway | Two neuron pathway (ganglion) |
| Neurotransmitter | Acetylcholine | Acetylcholine and Norepinephrine |
| Examples | Walking, Talking, Writing | Heartbeat, Digestion, Breathing |
Neurons: Structural and Functional Units
Structure of a Neuron
Cell Body (Soma)
Contains nucleus and organelles, metabolic center
Dendrites
Receive signals from other neurons, carry impulses toward cell body
Axon
Transmits impulses away from cell body
Myelin Sheath
Insulating layer, increases impulse speed (saltatory conduction)
Types of Neurons
| Type | Function | Direction | Location |
|---|---|---|---|
| Sensory Neurons | Carry impulses from receptors to CNS | Afferent (toward CNS) | PNS (except cell bodies in dorsal root ganglia) |
| Motor Neurons | Carry impulses from CNS to effectors | Efferent (away from CNS) | CNS and PNS |
| Interneurons | Connect sensory and motor neurons | Within CNS | Entirely within CNS |
Nerve Impulse Transmission
Resting Membrane Potential (-70mV)
- Inside of neuron is negatively charged relative to outside
- Maintained by Na⁺/K⁺ pump (3 Na⁺ out, 2 K⁺ in)
- K⁺ leakage contributes to negative interior
Action Potential (+50mV)
Depolarization
Na⁺ channels open → Na⁺ influx → inside becomes positive
Repolarization
Na⁺ channels close, K⁺ channels open → K⁺ efflux
Hyperpolarization
Brief overshoot of K⁺ efflux
Refractory Period
Neuron cannot fire again immediately
Myelination Effect:
- Non-myelinated fibers: 1-3 m/s conduction speed
- Myelinated fibers: up to 120 m/s conduction speed
- Saltatory conduction: impulse jumps between nodes of Ranvier
Reflexes and Reflex Arc
Reflex Action
- Definition: Immediate, automatic, involuntary response to stimuli
- Examples: Knee-jerk reflex, withdrawal reflex, blinking
- Importance: Protective mechanism, rapid response without brain involvement
Reflex Arc Components
Receptor
Detects stimulus
Sensory Neuron
Carries impulse to CNS
Interneuron
In spinal cord, processes information
Motor Neuron
Carries impulse from CNS to effector
Effector
Muscle or gland that responds
Classification of Reflexes
| Basis | Type | Characteristics | Examples |
|---|---|---|---|
| Origin | Unconditioned (Inborn) | Present from birth, no learning required | Sucking reflex, knee-jerk |
| Conditioned (Acquired) | Developed through experience | Salivation to bell (Pavlov) | |
| Synapses | Monosynaptic | Only one synapse in arc | Stretch reflex |
| Polysynaptic | Multiple synapses in arc | Withdrawal reflex | |
| Function | Somatic | Involves skeletal muscles | Knee-jerk, blinking |
| Autonomic | Involves smooth/cardiac muscles, glands | Salivation, pupillary reflex |
Synapse: Neural Communication
Structure of Synapse
- Presynaptic Neuron: Neuron sending the signal
- Synaptic Cleft: Gap between neurons (20-40 nm)
- Postsynaptic Neuron: Neuron receiving the signal
- Synaptic Vesicles: Contain neurotransmitters
Synaptic Transmission Process
Action Potential Arrival
Depolarizes presynaptic terminal
Calcium Influx
Voltage-gated Ca²⁺ channels open
Vesicle Fusion
Synaptic vesicles fuse with membrane
Neurotransmitter Release
Exocytosis into synaptic cleft
Receptor Binding
NT binds to postsynaptic receptors
Postsynaptic Potential
EPSP or IPSP generated
Neurotransmitters
| Type | Neurotransmitter | Function | Disorders Related |
|---|---|---|---|
| Excitatory | Acetylcholine | Muscle contraction, memory | Myasthenia gravis |
| Glutamate | Learning, memory | Stroke damage | |
| Inhibitory | GABA | Reduces neuronal excitability | Anxiety, epilepsy |
| Glycine | Spinal cord inhibition | Startle disease | |
| Modulatory | Dopamine | Reward, movement, mood | Parkinson’s, Schizophrenia |
| Serotonin | Mood, sleep, appetite | Depression, migraine |
Synaptic Integration: The postsynaptic neuron integrates signals from thousands of synapses. Spatial and temporal summation determine whether an action potential is generated.
Human Brain: Structure and Function
Major Brain Divisions
| Division | Main Structures | Key Functions |
|---|---|---|
| Forebrain | Cerebrum, Thalamus, Hypothalamus, Limbic System | Conscious thought, memory, emotion, homeostasis |
| Midbrain | Tectum, Tegmentum | Visual and auditory reflexes, motor control |
| Hindbrain | Pons, Cerebellum, Medulla Oblongata | Coordination, balance, vital functions (breathing, heartbeat) |
Cerebral Lobes and Functions
| Lobe | Location | Primary Functions | Key Areas |
|---|---|---|---|
| Frontal | Anterior | Reasoning, planning, movement, speech | Motor cortex, Broca’s area |
| Parietal | Superior | Sensory processing, spatial awareness | Somatosensory cortex |
| Temporal | Lateral | Hearing, memory, emotion | Auditory cortex, Wernicke’s area |
| Occipital | Posterior | Vision processing | Visual cortex |
Protection of CNS
Bony Protection
Skull (brain), Vertebral column (spinal cord)
Meninges
Three protective membranes: Dura mater, Arachnoid mater, Pia mater
Cerebrospinal Fluid (CSF)
Cushions brain, provides nutrients, removes waste
Blood-Brain Barrier
Selective permeability protects brain from toxins
Endocrine System: Chemical Coordination
Hormones: Chemical Messengers
- Definition: Chemical substances secreted by endocrine glands
- Transport: Via bloodstream to target cells
- Action: Bind to specific receptors, alter cellular activity
- Characteristics: Specific, potent, regulate rather than initiate reactions
Major Endocrine Glands and Hormones
| Gland | Hormone(s) | Target | Main Functions | Disorders |
|---|---|---|---|---|
| Pituitary | GH, TSH, ACTH, FSH, LH, Prolactin | Various tissues | Master gland, regulates other glands | Gigantism, Dwarfism |
| Thyroid | Thyroxine (T₄), Triiodothyronine (T₃), Calcitonin | Most body cells | Metabolism, growth, development | Goiter, Cretinism, Myxedema |
| Parathyroid | Parathormone (PTH) | Bone, Kidney, Intestine | Calcium homeostasis | Tetany, Kidney stones |
| Pancreas | Insulin, Glucagon | Liver, Muscle, Fat cells | Blood glucose regulation | Diabetes mellitus |
| Adrenal | Cortisol, Aldosterone, Adrenaline | Various tissues | Stress response, metabolism, electrolyte balance | Addison’s, Cushing’s |
| Gonads | Testosterone, Estrogen, Progesterone | Reproductive tissues | Sexual development, reproduction | Infertility, Hormonal imbalances |
Mechanisms of Hormone Action
1. Protein/Peptide Hormones (Water-soluble)
Receptor Binding
Bind to membrane receptors (1st messenger)
Second Messenger Activation
Activate cAMP or other second messengers
Cellular Response
Alter enzyme activity, gene expression
Examples
Insulin, Glucagon, ADH
2. Steroid Hormones (Lipid-soluble)
Diffusion
Diffuse through cell membrane
Receptor Binding
Bind to intracellular receptors
Gene Activation
Hormone-receptor complex activates genes
Examples
Testosterone, Estrogen, Cortisol
Feedback Mechanisms
| Type | Mechanism | Effect | Example |
|---|---|---|---|
| Negative Feedback | Response reduces the original stimulus | Maintains homeostasis | Blood glucose regulation (insulin/glucagon) |
| Positive Feedback | Response enhances the original stimulus | Amplifies processes | Childbirth (oxytocin), Blood clotting |
Nervous System Disorders
Common Neurological Disorders
| Disorder | Causes | Symptoms | Treatment |
|---|---|---|---|
| Parkinson’s Disease | Dopamine deficiency in substantia nigra | Tremors, rigidity, slow movement | L-dopa, Deep brain stimulation |
| Alzheimer’s Disease | Amyloid plaques, Neurofibrillary tangles | Memory loss, confusion, personality changes | Cholinesterase inhibitors, Memantine |
| Epilepsy | Abnormal electrical activity in brain | Seizures, loss of consciousness | Anticonvulsants, Surgery |
| Multiple Sclerosis | Autoimmune attack on myelin sheath | Fatigue, numbness, coordination problems | Immunomodulators, Physical therapy |
Endocrine Disorders
| Disorder | Gland/Hormone | Causes | Symptoms |
|---|---|---|---|
| Diabetes Mellitus | Pancreas (Insulin) | Insulin deficiency or resistance | Hyperglycemia, polyuria, polydipsia |
| Graves’ Disease | Thyroid (Hyperthyroidism) | Autoimmune stimulation of thyroid | Exophthalmos, weight loss, tachycardia |
| Cushing’s Syndrome | Adrenal (Cortisol excess) | Tumor or medication | Moon face, buffalo hump, hypertension |
| Addison’s Disease | Adrenal (Cortisol deficiency) | Autoimmune destruction | Fatigue, hyperpigmentation, hypotension |
Study Guidelines for Coordination & Control
1
Understand the Two Systems
Clearly distinguish between nervous system (fast, electrical) and endocrine system (slow, chemical) coordination mechanisms.
2
Master Neuron Structure
Draw and label a neuron diagram with all components: dendrites, cell body, axon, myelin sheath, nodes of Ranvier.
3
Trace Signal Pathways
Practice tracing reflex arcs and hormone pathways from stimulus to response.
4
Use Comparative Tables
Create comparison tables for: CNS vs PNS, somatic vs autonomic, sympathetic vs parasympathetic, excitatory vs inhibitory neurotransmitters.
5
Connect Structure-Function
For each brain region and endocrine gland, learn both structure and specific functions.
6
Practice Action Potential
Memorize the sequence: resting potential → depolarization → repolarization → refractory period with exact mV values.
7
Clinical Applications
Relate disorders to specific system malfunctions: Parkinson’s (dopamine), Diabetes (insulin), Myasthenia gravis (acetylcholine receptors).