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Wk 3 Neurophysiology - Coggle Diagram

- - - - :chart_with_upwards_trend: in Cl ions
      - :chart_with_upwards_trend: in NA ions
      - :chart_with_downwards_trend: in K ions
      - similar to seawater
      - usually assigned 0V
    - - :chart_with_downwards_trend: in NA ions
      - :chart_with_downwards_trend: in Cl ions
      - :chart_with_upwards_trend: in K ions
      - resting potential
        of -70mV
      - :heavy_minus_sign: charged proteins
        in ion form
  - - - acted on by both diffusion
        and electrostatic pressure
    - - Diffusion pushes from extra to intra
        Electrostatic pressure pushes from intra to extra
    - - increased potassium concentration in extracellular cells
        
        increases resting
        potential of cell
        
        depolarisation inactivates sodium channels and stops signalling
      - used for lethal injections
        
        administered with barbiturate painkiller due to extreme pain it causes
  - - - :one: Voltage-dependent Na+ channels open and Na+ enters the cell rapidly
        
        :two: Intracellular fluid now more :heavy_plus_sign: than extracellular fluid
        
        :three: Voltage-dependent K+ channels have delayed response and K+ leaves the cell
        
        :four: Intracellular fluid
        becomes :heavy_minus_sign: again
        
        :five: Hyperpolarises
    - - open quickly :zap:
      - open for a short
        period of time
      - Tetrodotoxin
        
        blocks sodium channels responsible for rising phase of action potential
        
        can be found in pufferfish
    - - open slowly :snail:
      - remain open
        longer
    - - Absolute
        
        period when no stimulus can
        produce action potential
        
        because sodium channels are closed until membrane is polarised to near resting levels
      - Relative
        
        period when larger than normal input is necessary to produce action potential
        
        sodium channels regain
        ability to reopen at -50mV
        
        hyperpolarised state
        
        fewer active
        sodium channels
    - - ion channels needed to
        produce action potentials
        
        found in initial segment
        and nodes of Ranvier
        
        Density of ion channels at NOR is 10x that of unmyelinated axon
      - saltatory conduction
        
        can conduct action potentials
        at about 120m/s
  - - - :two: Binding in
        Postsynaptic
        
        Receptors
        
        control ion channels
        directly or indirectly
        
        have binding sites that
        selectively interact with
        neurochemicals
        
        Ionotropic
        
        binding site is
        on ion channel
        
        quick reaction to
        neurochemicals
        (order of ms)
        
        effect is small
        and localised
        
        Metabotropic
        
        binding site is on receptor
        
        G protein
        
        found on receptor's
        intracellular end
        
        binds to ion channels
        causing them to open
        
        can also activate second messengers inside the postsynaptic cell
        
        slow reaction
        (hundreds of ms to seconds)
        
        diverse
        functionality
        
        initiate changes in gene expression
        
        control magnitude of
        neurochemicals released
        
        maintain resting potential
        
        :three: Termination
        
        Enzyme
        Deactivation
        
        enzymes in the synaptic gap break neurochemicals into components
        
        components are collected by presynaptic neuron to make
        more neurochemicals
        
        Reuptake
        
        Receptors in presynaptic membrane recapture neurochemicals
        
        Neurochemicals can be packaged in vesicles for future use
        
        Receptors also known as
        transporters
        
        Simple
        Diffusion
      - Action potential at axon terminals triggers opening of VD calcium channels
        
        Ca2+ enters the
        presynaptic neuron
        
        Ca2+ triggers release of neurochemicals within 0.2 ms
        
        amount of neurochemicals directly proportional to amount of Ca2+
        
        Ca2+ frees vesicles from protein anchors so they can move to release sites
        
        Ca2+ stimulates fusion of vesicle with axon membrane for exocytosis
        
        Restoring initial
        state of neuron
        
        Ca2+ pumps return calcium to extracellular fluid
        
        Recycling of vesicle material to prevent thickening of the axon membrane
        
        after positive action
        potential has receded
        
        Ca2+ more prevalent in extracellular fluid
  - - - caused by depolarisation of postsynaptic membrane
        
        depolarisation due to opening of chemically-gated sodium channels
      - more common at dendritic sections further from soma
    - - caused by opening of chemically-gated channels
        
        allow inward
        movement of Cl-
        
        Hyperpolarisation
        of the cell
        
        allow outward
        movement of K+
      - more common at soma and dendritic shafts closer to soma
    - - being able to vary in size and shape as opposed to action potentials
      - last about 5 to 10 ms
    - - Spatial Summation
      - Temporal
        Summation
    - - measures large pyramidal output cells in layers 3 and 5 of cortex
      - postsynaptic potentials last longer than action potentials
        
        generate field potentials
        which EEG can measure
  - - - increases neurochemical amounts released by target axon
    - - decreases neurochemical amounts released by target axon
- - - - Cell Membrane
        
        Made of a double layer
        of phospholipids
        
        Fatty molecules
        containing phosphates
        
        Water insoluble
        
        Width of 2 molecules
        
        Protein Structures
        
        Ion Channels
        
        allow passive :zzz: ion movement without energy expenditure
        
        Opening
        Mechanisms :door:
        
        Voltage-Dependent
        Channels :zap:
        
        Chemically / Ligand -
        gated Channels :male-scientist:
        
        Ion Pumps
        
        require energy expenditure :zap:
        for ion movement
        
        Sodium-Potassium Pumps
        
        Make up 20-40% of energy
        expenditure in the brain
        
        move 2 potassium ions
        from extra to intra
        
        move 3 sodium ions
        from intra to extra
        
        Calcium Pumps
        
        Move calcium ions
        out of the cell
        
        separates intracellular fluid (cytoplasm) from extracellular fluid surrounding the neuron
      - Cytoskeleton
        
        Microtubules
        
        transport various
        materials within the cell
        
        anterograde = :house: :arrow_right:
        
        retrograde = :house: :arrow_left:
        
        range from 8mm/day :snail:
        to 400mm/day :zap:
        
        Hollow tubes with a
        diameter of about 25nm
        
        Tau
        
        microtubule-associated protein that connects adjacent microtubules and holds them in place
        
        :one: Increased levels of tau
        due to Alzheimer's disease
        
        :two: Neuron adds phosphate molecules to tau, causing it to disconnect from microtubules
        
        :three: Disconnected tau forms
        neurofibrillary tangles
        
        1 more item...
        
        Intermediate
        Filaments
        
        provide structural
        support for the neuron
        
        most common fibre
        in the neuron
        
        diameter of
        about 10nm
        
        run parallel to the axon
        
        Microfilaments
        
        diameter of between
        3 to 5 nm
        
        located in
        neuron branches
        
        Involved in changing shape and length of neuron branches
      - Dendrites
        
        receive signals
        from other neurons
        
        Dendritic Spines
        
        provide more locations
        for synaptic sites
        
        can change shape
        based on synaptic activity
        
        abnormalities linked to ASD, Alzheimer's, schizoprenia
      - Axons
        
        responsible for carrying
        messages to other neurons
        
        action potential starts in the initial segment (between hillock and first myelin segment)
        
        varying diameter
        (1µm - 25µm)
        
        :chart_with_upwards_trend: diameter = :chart_with_upwards_trend: speed
        
        varying length
        
        local circuit neurons
        
        projection neurons
        
        Myelin
        
        Allows for smaller diameter without compromising transmission speed
        
        Reduces energy
        requirements of neurons
        
        Myelin sheaths wrap
        tightly around axon membrane
        
        No need for ion channels
        under myelin sheaths
      - Synapses
        
        Types
        
        Gap Junctions
        
        direct stimulation of adjacent neurons through protein channels that touch
        
        Functions
        
        synchronise hormone release
        from hypothalamus activity
        
        Synchronisation of hippocampus and cortex for learning and memory
        
        3.5nm width
        
        rapid transmission
        of excitatory signals
        
        requires large :building_construction: presynaptic neuron to influence small :peanuts: postsynaptic neuron
        
        strength of signal decreases from one cell to the next
        
        Chemical
        Synapses
        
        from 0.3 ms to
        several ms
        
        20nm width
        
        ability to send greater
        variety of messages
        
        small presynaptic neuron can still influence a large postsynaptic neuron
        
        correlation between synapse size and signalling strength
    - - Unipolar
        
        singular branch
        extending from
        the cell body
        
        splits in 2 with 1 end
        to PNS and one to CNS
        
        found in sensory systems
        and in invertebrates
      - Bipolar
        
        two branches extending
        from cell body
        
        dendrite and axon
        
        Von Economo
        Neuron
        
        found in the anterior
        cingulate cortex (ACC) and dorsolateral prefrontal cortex
        
        provide fast, intuitive
        assessments of
        complex situations
        
        useful in
        social situations
      - Multipolar
  - - - Astrocytes
        
        found in the CNS
        
        Functions
        
        Structural matrix for neurons
        by holding them in place
        
        Debris cleanup
        (eg. dead neurons)
        
        Transfers nutrients to neurons
        
        form neurovascular units through close connections with brain capillary cells
        
        Regulate blood flow
        based on synaptic activity
        
        due to ability to contact
        synapses and blood vessels
        
        Form blood-brain barrier
        
        Stops movement of circulating toxins into neural tissue
        
        done by covering capillary
        with their endfeet
        
        Isolate synapses
        
        can envelope more
        than 100,000 synapses
        
        prevent neurotransmitters released at synapses from leaving restricted areas
        
        Facilitate brain
        development
        
        signal neurons
        to build synapses
        
        Reactive
        Astrocytes
        
        Play a role in chronic diseases
        
        change physically and functionally in response to ageing, injury and disease
        
        form glial scars
        
        release chemicals that inhibit
        repair of damaged connections
        
        release large amounts of
        the neurotransmitter glutamate
        
        Excessive glutamate kills neurons
        
        reduce inflammation
        
        promote healing of the
        blood-brain barrier
      - Ependymal Cells
        
        lines ventricles and the
        central canal of the spinal cord
        
        Functions
        
        Firewall to prevent
        viruses from attacking CNS
        
        Destroyed in the process
        
        Malfunction may
        lead to hydrocephalus
        
        Move CSF
        
        whip-like motion
        of the cilia
        
        QC for CSF
        
        because cilia
        absorb some CSF
        
        Production of CSF
        at the choroid plexus
        
        special ependymal cells filter fluid from CP capillaries to produce CSF
      - Oligodendrocytes
        
        Functions
        
        provide myelin covering for the
        central nervous system (CNS)
        
        Provides structural stability
        for the brain and spinal cord
        
        has a number of branches that
        wrap around the axons of neurons
        
        a single oligodendrocyte can
        myelinate 15 axons on average
        
        Release
        exosomes
        
        Protect the neuron
        
        Facilitate transport
        in the neuron
      - Schwann Cells
        
        provide myelin covering in the
        peripheral nervous system (PNS)
        
        1 Schwann cell myelinates
        a single myelin segment
        
        Release
        exosomes
        
        Help regeneration
        of damaged axons
      - originate in the
        ectoderm layer
    - - Functions
        
        Clean up brain debris
        (when cells die)
        
        Synaptic Pruning
      - Complications
        
        Uncontrolled
        microglia activation
        
        inflammation from
        microglia activation
        suspected contributor to
        
        Alzheimer's Disease
        
        Parkinson's
        
        Multiple Sclerosis
        
        digesting healthy cells
        adjacent to damaged ones
        
        excessive synaptic removal possible cause for Alzheimer's Disease
        
        Highly sensitive to changes
        in gut microbiota
        
        Dysbiosis
        
        imbalances in gut microbiota linked to microglia dysfunction and neurological problems
        
        possible treatment for neurological problems using prebiotics