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        • D.1 PHARMACEUTICAL PRODUCTS AND DRUG ACTION
        • D.2 Aspirin and penicillin
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        • D.5 Antiviral Medications
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    • Biology SL >
      • Tips & Guides
      • TOPIC 1: CELL BIOLOGY >
        • 1.1 Introduction to cells
        • 1.2 Ultrastructure of Cells
        • 1.3 Membrane Structure
        • 1.4 Membrane Transport
        • 1.5 Origin of Cells
        • 1.6 Cell Division
      • TOPIC 2: MOLECULAR BIOLOGY >
        • 2.1 Molecules to metabolism
        • 2.2 Water
        • 2.3 Carbohydrates and Lipids
        • 2.4 Proteins
        • 2.5 Enzymes
        • 2.6 Structure of DNA and RNA
        • 2.7 DNA Replications, Transcription and Translation
        • 2.8 Cell Respiration
        • 2.9 Photosynthesis
      • Topic 3: Genetics >
        • 3.1 Genes
        • 3.2 Chromosomes
        • 3.3 Meiosis
        • 3.4 Inheritance
        • 3.5 Genetic Modification and Biotechnology
      • Topic 4: Ecology >
        • 4.1: Species, Communities and Ecosystems
        • 4.2 Energy Flow
        • 4.3 Carbon Cycling
        • 4.4 Climate Change
      • Topic 5: Evolution and Biodiversity >
        • 5.1 Evidence for evolution
        • 5.2 Natural Selection
        • 5.3 Classification and Biodiversity
        • 5.4 Cladistics
      • Topic 6: Human Physiology >
        • 6.1 Digestive System
        • 6.2 The blood system
        • 6.3 Defense against infectious disease
        • 6.4 Gas Exchange
        • 6.5 Neurons and Synapses
        • 6.6 Hormones, Homeostasis and Reproduction
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      • Topic 6: Circular Motion & Gravitation
      • Topic 7: Atomic, Nuclear, & Particle Physics
      • Topic 8: Energy Production
      • Option D: Astrophysics
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      • Unit 1: Changing population
      • Unit 2: Global climate—vulnerability and resilience
      • Unit 3: Global resource consumption and security
      • Unit 4: Power, Places and Networks
      • Unit 5: Human Development and Diversity
      • Unit 6: Global Risks and Resillience
      • Option A: Freshwater
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      • Option C: Extreme Environments
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      • Unit 1: Business Organization and Movement >
        • 1.1 Nature of Business
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        • 1.6 Growth and evolution
      • Unit 2: Human Resource Management >
        • 2.1 The functions and evolution of human resource management
        • 2.2 Organizational structure
        • 2.3 Leadership and management
        • 2.4 Motivation
      • Unit 3: Finance and Accounts >
        • 3.1 Sources of Finance
        • 3.2 Costs and Revenues
        • 3.3 Break-even analysis
        • 3.4 Final accounts
        • 3.5 Profitability and liquidity ratio analysis
        • 3.7 cash flow
      • Unit 4: Marketing >
        • 4.1 The role of marketing
        • 4.2 Marketing Planning
        • 4.4 Market Research
        • 4.5 The four ps
        • 4.8 E-commerce
      • Unit 5: Operations Management >
        • 5.1 The role of operations Management
        • 5.2 Production methods
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      • Topic 1: Measurements and Uncertainties
      • Topic 2: Mechanics
      • Topic 3: Thermal Physics
      • Topic 4: Waves
      • Topic 5: Electricity and Magnetism
      • Topic 6: Circular Motion and Gravitation
      • Topic 7: Atomic, Nuclear and Particle Physics
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6.5 Neurons and Synapses

6.5 Syllabus
Picture

U1. Neurons transmit electrical impulses.

  • One form of internal communication in the body occurs through nerve impulses in the nervous system
  • Neurons transmit electrical impulse nu allowing the passage of charged ions across their membranes in response to stimuli
  • Neurons consist of a cell body with a nucleus and cytoplasm, an elongated nerve fibre called an axon, and short-branched nerve fibres called dendrites. 
Picture

U2. ​The myelination of nerve fibres allows for salutatory conduction.

  • Nerve fibres conduct electrical impulses along the length of their axons. Some of these axons such as interneurons are unmyelinated, and therefore the impulse travels much slower
  • The greater the diameter, the greater the speed of the nerve impulse
  • Some axons are surrounded by a mixture of protein and phospholipids called myelin that collectively form a myelin sheath
  • Many layers of myelin are deposited around the axon by special cells called Schwann cells
  • The myelin sheath insulates the axon and greatly increases the speed of nerve impulse
  • In between the myelin are gaps called the nodes of Ranvier
  • In Myelinated neurons, the impulse can jump from one node to the next. This is called saltatory conduction
  • This allows myelinated neurons to conduct impulses up to 100 x faster than unmyelinated axons. 
​

U3. ​Neurons pump sodium and potassium ions across their membranes to generate a resting potential.

Picture
  • The time period when a neuron that is not conducting a nerve impulse, but is ready to conduct one, is called the resting potential
  • This membrane potential is due to an imbalance of positive and negative charges across the membrane
  • Sodium-potassium pumps pump Na+ out of the axon and K+ into the axon
  • Sodium-potassium pumps pump Na+ out of the axon and K+ into the axon
  • Three Na+ are pumped out of the neuron and two K+ are pumped into the neuron
  • This creates a concentration gradient of Na+ (outside to in) and of K+ (inside to out)
  • The membrane is also much more permeable to K+ as Na+, so K+ leaks back out of the neuron through leak channels
  • This means the Na+ concentration is much greater outside the neuron
  • There are also negatively charged ions permanently located in the cytoplasm of the neuron
  • These conditions create a resting membrane potential of -70mv inside the neuron. 
​

U4. ​An action potential consists of depolarization and repolarization of the neuron.

Picture
  • Action potentials are rapid changes in membrane potentials
  • This consists of rapid depolarization (change from negative to positive when sodium diffuses into the neuron) and a rapid repolarization (change from positive to negative when potassium diffuse out of the neuron
  • The arrival of an action potential caused by a stimulus causes a depolarization of the membrane as Na+ channels begin to open
  • If the membrane potential reaches a threshold level of -50mv. Many more voltage gated Na+ channels open and Na+ rapidly diffuses into the neuron
  • The inside of the neuron becomes more positively charged than the outside of the neuron (depolarization) 
  • K+ channels open and K+ ions diffuse out of the neuron making the inside negative again (repolarization) 
  • After the action potential, there is a refractory period where the impulse cannot go back in the same direction. This ensures a one-way nerve impulse 
​

U5. ​Nerve impulses are action potentials propagated along the axons f neurons.

  • As a depolarization occurs in one part of the neuron, the positive charge triggers the Na+ channels to open in the nearby regions causing an action potential to occur
  • This action potential will cause a depolarization in the next region
  • The propagation of action potentials will continue along the axon of the neuron
  • Nerve impulses move in one direction along the neuron from one end of the neuron to the other end
  • A refractory period occurs after depolarization which prevent the electrical impulses from traveling backwards along the axon
​

U6. ​Propagation of nerve impulses is the result of local currents that cause each successive part of the axon to reach the threshold potential.

  • Propagation of nerve impulses along the axon results from the diffusion of Na+ ions from the area that was just depolarized to the neighbouring area that is still polarized inside the axon
  • When a part of the axon depolarizes, the localized are inside the axon become more positive as Na+ diffuses into the axon through voltage gated channels
  • Outside the axon the concentration of Na+ is less in the depolarized region, so sodium diffuses from the polarized region towards the depolarized region. 
  • The adjacent area inside the axon that is still polarized (more negative) 
  • The higher the concentration of Na+ inside the depolarized region region diffuses towards the polarized (more negative) region inside the axon
  • When this happens, the membrane potential of the adjacent region becomes more positive from -70mv to -50mv (threshold potential) 
  • This results in a depolarization in the neighbouring region, as Na+ voltage-gated channels open and Na+ diffuses into the axon. 
​
Picture


U7. ​Synapses are junctions between neurons and between neurons and receptors or effector cells.

  • Synapses are junctions or structure between the pre-synaptic and post-synaptic membrane of two cells in the nervous system
  • The junction can be between a neuron and an effector such as a muscle or a gland
  • It can be between two different neurons. Many of these connections occur in the CNS (brain and spinal cord) 
  • A junction also exists between the sense receptor cells and the sensory neurons 
  • Neurotransmitters are chemicals diffuse across a synapse from pre-synaptic membrane to post-synaptic membrane to send a signal to the next cell 
​

u8. When presynaptic neurons are depolarized they release a neurotransmitter into the synapse.

  • As the nerve impulse reaches the axon terminal of the presynaptic neuron, the positive charge from the depolarization causes voltage-gated channels permeable to Ca2+ to open
  • Ca2+ flows into the presynaptic neuron increasing the amount of Ca2+ in the presynaptic neuron
  • This Ca2+ causes vesicles containing neurotransmitters to bind to the membrane and release their neurotransmitters into the synaptic cleft (space between pre and post synaptic neuron) 
  • These neurotransmitters diffuse across the synaptic cleft and bind to receptor sites on the membrane of the post synaptic neuron
  • The binding of these neurotransmitters open ion channels allowing ions such as Na+ to diffuse into the post synaptic neuron
  • This influx of positive charge possibly leads to an action potential and a depolarization in the post synaptic neuron
  • The neurotransmitter is reabsorbed by the presynaptic neuron or broken down in the synapse by enzymes 
​

U9. ​A nerve impulse is only initiated if the threshold potential is reached.

  • The threshold potential is the critical level to which a membrane potential must be reach in order to initiate an action potential
  • Neurons fire or a nerve impulse is generated by an 'all or nothing'
  • When a stimulus occurs, some Na+ channels open causing the membrane potential to become more positive 
  • If enough Na+ diffuses into the neuron(-50mv to -70mv) and action potential is generated
  • At a synapse, binding of a neurotransmitter at the post-synaptic membrane causes Na+ to diffuse into the neuron
  • This can cause a depolarization of the neuron if enough neurotransmitters are released 
​
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  • Home
  • IB STUDY MATERIALS
    • Psychology SL/HL >
      • Tips & Guide
      • Biological Approach >
        • Brain and Behaviour
        • Hormones and Pheromones
        • Genetics and Evolution
        • HL Animal Research
      • Sociocultural Approach >
        • Individual and the group
        • Cultural Origins
        • Cultural Influences
        • HL Globalization
      • Cognitive Approach >
        • Cognitive Processing
        • Reliability of Cognitive Processes
        • Emotion and Cognition
        • HL Digital World
      • B. Human Relationships >
        • Personal Relationships
        • Group Dynamics
      • D. Developmental >
        • Developing as a Learner
        • Developing an Identity
      • Studies >
        • Biological Approach
        • Sociocultural Approach
        • Cognitive Approach
        • B. Human Relationships
        • D. Developmental
    • Chemistry SL/HL >
      • Tips & Guide
      • All Vocab Definitions
      • ALL EQUATIONS
      • Unit 1,2 & 12
      • Unit 3 &13
      • Unit 4 &14
      • Unit 5,6,7 & 15,16,17
      • Unit 8 & 18
      • Unit 9 & 19
      • Unit 10 & 20
      • Unit 11 & 21
      • Option D: Medicinal Chemistry >
        • D.1 PHARMACEUTICAL PRODUCTS AND DRUG ACTION
        • D.2 Aspirin and penicillin
        • D.3 Opiates
        • D.4 pH Regulation of the Stomach
        • D.5 Antiviral Medications
        • D.6 Environmental impact of some medications
        • D.7 Taxol- A Chiral Auxiliary Case Study
        • D.8 Nuclear Medicine
        • D.9 Drug Detection and Analysis
    • Biology SL >
      • Tips & Guides
      • TOPIC 1: CELL BIOLOGY >
        • 1.1 Introduction to cells
        • 1.2 Ultrastructure of Cells
        • 1.3 Membrane Structure
        • 1.4 Membrane Transport
        • 1.5 Origin of Cells
        • 1.6 Cell Division
      • TOPIC 2: MOLECULAR BIOLOGY >
        • 2.1 Molecules to metabolism
        • 2.2 Water
        • 2.3 Carbohydrates and Lipids
        • 2.4 Proteins
        • 2.5 Enzymes
        • 2.6 Structure of DNA and RNA
        • 2.7 DNA Replications, Transcription and Translation
        • 2.8 Cell Respiration
        • 2.9 Photosynthesis
      • Topic 3: Genetics >
        • 3.1 Genes
        • 3.2 Chromosomes
        • 3.3 Meiosis
        • 3.4 Inheritance
        • 3.5 Genetic Modification and Biotechnology
      • Topic 4: Ecology >
        • 4.1: Species, Communities and Ecosystems
        • 4.2 Energy Flow
        • 4.3 Carbon Cycling
        • 4.4 Climate Change
      • Topic 5: Evolution and Biodiversity >
        • 5.1 Evidence for evolution
        • 5.2 Natural Selection
        • 5.3 Classification and Biodiversity
        • 5.4 Cladistics
      • Topic 6: Human Physiology >
        • 6.1 Digestive System
        • 6.2 The blood system
        • 6.3 Defense against infectious disease
        • 6.4 Gas Exchange
        • 6.5 Neurons and Synapses
        • 6.6 Hormones, Homeostasis and Reproduction
    • Physics SL >
      • Must-have Resources
      • Full Study Resources
      • Other Resources
      • Tips & Guide
      • IA, Lab Report
      • Topic 1: Measurements & Uncertainties
      • TOPIC 2: MECHANICS
      • TOPIC ​3: THERMAL PHYSICS
      • Topic 4: Waves
      • Topic 5: Electricity & Magnetism
      • Topic 6: Circular Motion & Gravitation
      • Topic 7: Atomic, Nuclear, & Particle Physics
      • Topic 8: Energy Production
      • Option D: Astrophysics
    • Geography SL/HL >
      • Tips & guide
      • Unit 1: Changing population
      • Unit 2: Global climate—vulnerability and resilience
      • Unit 3: Global resource consumption and security
      • Unit 4: Power, Places and Networks
      • Unit 5: Human Development and Diversity
      • Unit 6: Global Risks and Resillience
      • Option A: Freshwater
      • Option B: Ocean and Coastal Margins
      • Option C: Extreme Environments
      • Option E: Leisure, tourism and sport
    • Business SL/HL(pending) >
      • Tips & guides
      • Unit 1: Business Organization and Movement >
        • 1.1 Nature of Business
        • 1.2 Types of Organizations
        • 1.3 Organizational objectives
        • 1.4 Stakeholders
        • 1.5 External Environment
        • 1.6 Growth and evolution
      • Unit 2: Human Resource Management >
        • 2.1 The functions and evolution of human resource management
        • 2.2 Organizational structure
        • 2.3 Leadership and management
        • 2.4 Motivation
      • Unit 3: Finance and Accounts >
        • 3.1 Sources of Finance
        • 3.2 Costs and Revenues
        • 3.3 Break-even analysis
        • 3.4 Final accounts
        • 3.5 Profitability and liquidity ratio analysis
        • 3.7 cash flow
      • Unit 4: Marketing >
        • 4.1 The role of marketing
        • 4.2 Marketing Planning
        • 4.4 Market Research
        • 4.5 The four ps
        • 4.8 E-commerce
      • Unit 5: Operations Management >
        • 5.1 The role of operations Management
        • 5.2 Production methods
        • 5.4 Locations
    • Economics SL/HL (pending) >
      • Tips & guides
      • MICROECONOMICS >
        • 1.1 Competitive Markets: Demand and Supply
      • macroeconomics
    • Chinese B SL >
      • Oral Example
    • Extended Essay (EE) >
      • General Tips
      • Physics EE
    • Internal Assessment (IA) >
      • General Tips
    • Theory of Knowledge >
      • Essay Example
      • Presentation Example
    • Other notes >
      • Topic 1: Measurements and Uncertainties
      • Topic 2: Mechanics
      • Topic 3: Thermal Physics
      • Topic 4: Waves
      • Topic 5: Electricity and Magnetism
      • Topic 6: Circular Motion and Gravitation
      • Topic 7: Atomic, Nuclear and Particle Physics
      • Topic 8: Energy Production
      • Option D: Astrophysics
    • Other Citations
  • UNI application
    • United States
    • United Kingdom >
      • Academic Schools
      • Art & Design Schools
    • China
    • Japan
    • Hong Kong
    • Canada (pending)
    • Australia (pending)
  • our warm advice
    • academic advice!
    • Toxic Productivity
    • Finding Your Balance
    • Giving Up
    • YOLO?
    • Are grades important
    • Danger of Quotes
    • How to Destress
  • About us