Neurons

1. 1Ion channels affect the membrane potential
   - if permeability for Na+ increases the membrane potential will shift towards the equilibrium potential for Sodium, Na+ --> this leads to [blank_start]depolarisation[blank_end] (gets positive, as sodium enters the cell)
   
   if permeability for K+, potassium increases the membrane potential will shift towards the equilibrium potential of potassium --> this leads to [blank_start]hyperpolarisation[blank_end] (gets more negative as potassium leaves the cells)

   

   1. Adepolarisation
   2. Bhyperpolarisation
2. 2How is opening/closure of ion channels controlled
   - ion channels are literally a pore in the membrane
   - ion channels mediate [blank_start]facilitated[blank_end] diffusion of ions and other metabolites
   - channels typically exist in either a close or open conformation
   - they are opened (or closed) by specific triggers, specific ligands, [blank_start]voltage[blank_end] conditions or physical association with structural elements
   - ion channel activity is the reason for electrical [blank_start]brain[blank_end] activity
   
   Ligands physically bind to channels leading to a [blank_start]conformational[blank_end] change in the ion channel leading to an influx of ions
   - mechanosensitive ion channels e.g. in ears, sound is a mechanical stimulant

   

   1. Afacilitated
   2. Bvoltage
   3. Cbrain
   4. Dconformational
3. 3[blank_start]Neurons[blank_end] > all brain activity is due to individual neurons
   - cell body has arms extending called [blank_start]dendrites[blank_end] > dendrites receive information from other neurons, this is where neurons send neurotransmitters and lots of [blank_start]ion[blank_end] channels are on the dendrites = where signal input occurs
   
   SO dendrites = receive information from other neurons
   
   the cell [blank_start]body[blank_end] contains the [blank_start]nucleus[blank_end] and most cell organelles
   
   all information collected by the dendrites is integrated in the axon [blank_start]hillock[blank_end], which generates action potentials (where all information is summed up and send far away) to be send to the axon terminal
   
   the [blank_start]axon[blank_end] = conducts action potentials away from the cell body
   
   axon [blank_start]terminals[blank_end] (pl) = synapses with a target cell
   
   Presynaptic and [blank_start]post[blank_end]synaptic cells are terms used
   

   

   1. ANeurons
   2. Bdendrites
   3. Cion
   4. Dbody
   5. Enucleus
   6. Fhillock
   7. Gaxon
   8. Hterminals
   9. Ipost
4. 4neurons morphology varies a lot, they also vary in length e.g. the Sciatic nerve is the longest spinal nerve in the human body

   

   1. AVerdadeiro
   2. BFalso
5. 5[blank_start]Cell[blank_end] body = where all information is received
   - contains the [blank_start]nucleus[blank_end] and most cell organelles
   - potentials at the cell body are called [blank_start]graded[blank_end] potentials, not an action potential
   - a graded potential is a change from the [blank_start]resting[blank_end] potential that is proportional to the magnitude of a stimulus
   - graded potentials are a means of integrating stimuli because membrane can respond with proportional amounts of [blank_start]depolarisation[blank_end] or hyperpolarisation to each stimulus, and those changes in membrane potential are summed
   - whether the membrane is depolarised or hyperpolarised depends on the ion concentrations inside and outside of the neuron, the [blank_start]equilibrium[blank_end] potentials, and the repertoire of ion channels

   

   1. ACell
   2. Bnucleus
   3. Cgraded
   4. Dresting
   5. Edepolarisation
   6. Fequilibrium
6. 6Signal reception at the cell [blank_start]body[blank_end]: stimulus strength
   - the [blank_start]stronger[blank_end] the stimulus (concentration of neurotransmitter), the greater the effect on the membrane potential of the dendrites
   - this has something to do with the concentration of ligands
   - the [blank_start]more[blank_end] neurotransmitter, the bigger the effect on ions channels, more ion channels open more effect on the membrane

   

   1. Abody
   2. Bstronger
   3. Cmore
7. 7Signal reception at the cell body: spatial and temporal [blank_start]summation[blank_end]
   - concentration is one thing that determines stimulus strength
   - problem is some cells have lots of dendrites full of synpases
   e.g. 4 synapses can occur at the cell body, parts will receive inputs of varying strength, this is spatial and temporal summation
   
   [blank_start]spatial[blank_end] summation occurs when several excitatory post-synaptic potentials (EPSPs) arrive at the axon hillock simultaneously (at the [blank_start]same[blank_end] time)
   
   [blank_start]temporal[blank_end] summation = means that post-synaptic potentials created at the [blank_start]same[blank_end] synapse in rapid succession can be summed
   
   stimulus strength depends on the [blank_start]neurotransmitter[blank_end] concentration, ligands for ion channels, spatial and temporal summation.

   

   1. Asummation
   2. Bspatial
   3. Csame
   4. Dtemporal
   5. Esame
   6. Fneurotransmitter
8. 8Signal reception at the cell body: conduction with [blank_start]decrement[blank_end]
   - the membrane potential [blank_start]decreases[blank_end] exponentially with distance
   - this allows signal integration
   - signals are integrates at the axon [blank_start]hillock[blank_end]
   
   Problem with decrement (membrane potential decreases exponentially with distance)
   -how can neurons send information over long distances? e.g. the sciatic nerve
   - solution = [blank_start]action[blank_end] potentials (spikes)

   

   1. Adecrement
   2. Bdecreases
   3. Chillock
   4. Daction
9. 9The phases of a typical action potential
   1. permeability of [blank_start]sodium[blank_end], Na+, increases > sodium channels will open
   2. then suddenly permeability [blank_start]decreases[blank_end] again
   3. the same happens for [blank_start]potassium[blank_end], increase (channels open) and then a sudden decrease at the channels close, this is a little bit delayed
   
   a few [blank_start]milli[blank_end]seconds occurs between the initial opening of sodium channels and then the secondary opening of potassium ion channels
   
   if you look at the membrane potential, the resting potential is close to the equilibrium potential of [blank_start]potassium[blank_end] (contributes most to the membrane potential)
   - if we increase the permeability of sodium by opening sodium ion channels, then the membrane potential shifts towards the [blank_start]equilibrium[blank_end] potential of sodium (which is very positive; thus [blank_start]depolarisation[blank_end]) > at this point the sodium ion channels close and the membrane potential will decrease again = [blank_start]hyperpolarisation[blank_end]
   
   the after hyperpolarisation becomes more negative (overshoots) than the resting potential due to the open potassium channels (potassium moves out), the membrane potential shifts towards the equilibrium potential for potassium
   
   the after the ion gradients are restored to the [blank_start]resting[blank_end] potential of the membrane

   

   1. Asodium
   2. Bdecreases
   3. Cpotassium
   4. Dmilli
   5. Epotassium
   6. Fequilibrium
   7. Gdepolarisation
   8. Hhyperpolarisation
   9. Iresting
10. 10[blank_start]Depolarisation[blank_end] Phase: voltage-gated sodium channels
    - voltage gated sodium channels contain an [blank_start]activation[blank_end] gate and an inactivation gate
    - the activation [blank_start]gate[blank_end] opens the channel and allows ions to pass through the pore
    - the inactivation gate '[blank_start]plugs[blank_end]' the pore, preventing ions from passing through while the activation gate is open
    
    At the membrane [blank_start]resting[blank_end] potential the voltage gated sodium channels are closed
    - they open in response to a [blank_start]nerve[blank_end] impulse, the gate opens and sodium enters the cell
    - for a brief period following activation, the channel does [blank_start]not[blank_end] open in response to a new signal

    

    1. ADepolarisation
    2. Bactivation
    3. Cgate
    4. Dplugs
    5. Eresting
    6. Fnerve
    7. Gnot

11. 11Activation of voltage gated sodium channels
    - input of summed dendrites reaches [blank_start]threshold[blank_end] of voltage > when this threshold is reached the activation gate of voltage gated sodium channels opens > causing sodium ions to [blank_start]enter[blank_end] the cell
    - the more voltage > the more channels open leading to a steep increase in membrane potential, sodium ions are entering to the membrane potential is getting more positive ([blank_start]depolarisation[blank_end])
    - the activation gate of voltage gated sodium ion channels closes as the membrane potential approaches +[blank_start]30[blank_end]mV
    
    NOTE: at more sodium enters the cell, the membrane depolarises further causing more voltage gated sodium ion channels to open, so more enter, this sets up a [blank_start]positive[blank_end] feedback loop causing rapid depolarisation of the cell membrane

    

    1. Athreshold
    2. Benter
    3. Cdepolarisation
    4. D30
    5. Epositive
12. 12Repolarisation phase: voltage-gated K+ channels
    - potassium channels work in the same way, they do not have an activation gate but they sense a membrane potential
    - potassium channels open due to voltage sensors and potassium [blank_start]leaves[blank_end] the cell, causing the membrane potential to decrease (become more negative, [blank_start]hyperpolarisation[blank_end])
    - with potassium ion channels being open, more potassium leaves the cell and the membrane potential moves towards the [blank_start]equilibrium[blank_end] potential of potassium, this overshoots the resting membrane potential
    
    so ion gradients need to be restored

    

    1. Aleaves
    2. Bhyperpolarisation
    3. Cequilibrium
13. 13Restoring ion gradients (over the overshoot from potassium ion channels)
    - ion gradients are restored using an ion pump
    - [blank_start]hydrolyses[blank_end] ATP to pump sodium out of the cell against the concentration gradient
    - called the Na+/K+-[blank_start]ATPase[blank_end]
    - [blank_start]3[blank_end] sodium are pumped out of the cell, while [blank_start]2[blank_end] potassium are pumped in from the extracellular fluid
    
    Absolute and Relative Refractory Period
    - [blank_start]absolute[blank_end] refractory period = [blank_start]no[blank_end] action potentials will be generated, even if the membrane depolarises beyond the threshold potential > this is due to the fact that voltage-gated sodium channels are [blank_start]inactivated[blank_end] > all [blank_start]sodium[blank_end] channels are blocked
    
    [blank_start]relative[blank_end] refractory period = this is the period of time after hyperpolarisation in which the membrane potential is lower (more [blank_start]negative[blank_end]) than usual (the resting potential) so if an action potential is to be generated it would require [blank_start]more[blank_end] depolarising power to reach the threshold potential
    > so an action potential can be generated at this point but more depolarising power is required
    
    why is this important? this determines the [blank_start]direction[blank_end] of travel

    

    1. Ahydrolyses
    2. BATPase
    3. C2
    4. D3
    5. Eabsolute
    6. Fno
    7. Ginactivated
    8. Hsodium
    9. Irelative
    10. Jnegative
    11. Kmore
    12. Ldirection
14. 14Due to the [blank_start]absolute[blank_end] and relative [blank_start]refractory[blank_end] period, action potentials travel only in one [blank_start]direction[blank_end]; away from the axon and towards the synapse
    

    

    1. Aabsolute
    2. Brefractory
    3. Cdirection
15. 15Action potentials vs. Graded potentials
    
    [blank_start]Graded[blank_end] potentials
    - vary in magnitude
    - vary in duration
    - decay with distance
    - occur in [blank_start]dendrites[blank_end] and the [blank_start]cell[blank_end] body
    - caused by opening and closing of many kinds of ion channels
    
    [blank_start]Action[blank_end] potentials
    - always the [blank_start]same[blank_end] size and shape (in a given cell type)
    - always the same duration (in a given cell type)
    - do [blank_start]not[blank_end] decay with distance
    - occur in [blank_start]axons[blank_end] of neurons (also in muscle cells)
    - caused by opening and closing of voltage gated ion channels
    
    there are major differences between graded potentials and action potentials
    - graded potentials allow integration of multiple input signals into action potentials
    - how can this information be modulated > this is achieved through the [blank_start]frequency[blank_end] of action potentials, the frequency of action potentials encodes information

    

    1. AGraded
    2. Bdendrites
    3. Ccell
    4. DAction
    5. Esame
    6. Fnot
    7. Gaxons
    8. Hfrequency
16. 16Frequency of action potentials
    - [blank_start]graded[blank_end] potentials allow integration of multiple input signals into potentials
    - how can this information be modulated? > stimulus characteristics (e.g. brief, sustained, suprathreshold) are encoded by action potential [blank_start]frequency[blank_end]
    
    can we increase the frequency of action potentials to unlimited? [blank_start]no[blank_end], due to the [blank_start]refractory[blank_end] period, where the ion channels are closed so cannot be activated (absolute refractory period), this [blank_start]absolute[blank_end] refractory period in which the sodium voltage gated ion channels are inactive dictates the speed of action potentials
    - generation of axon potentials follows the 'all-or-none' principle
    - if the depolarisation [blank_start]threshold[blank_end] is reached, an action potential is generated
    - this action potential always has the [blank_start]same[blank_end] magnitude

    

    1. Agraded
    2. Bfrequency
    3. Cno
    4. Drefractory
    5. Eabsolute
    6. Fthreshold
    7. Gsame
17. 17All-or-none principle of action potential generation

    1. Aonce threshold depolarisation is reached, an action potential will be generated
    2. Bthe action potential always has the same magnitude
18. 18Glial cells; cells in the brain that are not neurons
    - [blank_start]glial[blank_end] cells surround neurons and provide [blank_start]support[blank_end] for and insulation between neurons
    - the most abundant cell types in the central nervous system = [blank_start]glial[blank_end] cells
    - [blank_start]astrocytes[blank_end] = maintain homeostasis
    - [blank_start]microglial[blank_end] cells = are similar to macrophages, so involved in the immune system, microglial cells removed damaged neurons, involved in the health of the CNS
    - [blank_start]oligodendrocytes[blank_end] - oligodendrocytes wrap around axons (as insulation, in the [blank_start]central[blank_end] nervous system)
    - in the peripheral nervous system oligodendrocytes are called [blank_start]Schwann[blank_end] cells > schwann cells wrap around axons to produce the [blank_start]Myelin[blank_end] sheath, a greatly extended and modified [blank_start]plasma[blank_end] membrane wrapped around the axon in a spiral fashion

    

    1. Aglial
    2. Bsupport
    3. Cglial
    4. Dastrocytes
    5. Emicroglial
    6. Foligodendrocytes
    7. Gcentral
    8. HSchwann
    9. IMyelin
    10. Jplasma
19. 19Vertebrate axons: myelin-producing Schwann cells
    - [blank_start]Scwhann[blank_end] cells produce the [blank_start]myelin[blank_end] sheath > a greatly extended and modified plasma membrane wrapped around the axon in a spiral fashion
    
    

    

    1. ASchwann
    2. Bmyelin
20. 20[blank_start]Saltatory[blank_end] conduction of action potentials
    - in long axons (e.g. those projecting to the periphery) membrane depolarisation and action potential generation occurs only in parts of the axons which are [blank_start]not[blank_end] insulated by the [blank_start]myelin[blank_end] sheath (made of schwann cells)
    - these parts of the axon which are not insulated are called the [blank_start]nodes[blank_end] of Ranvier
    - it is only at the nodes of [blank_start]Ranvier[blank_end] that you find voltage-gated sodium and [blank_start]potassium[blank_end] channels
    
    Myelination and Action potential speed
    - myelination [blank_start]increases[blank_end] the speed of action potential propagation in neurons (up to 100m/s)
    - myelination as an evolutionary prerequisite to increased body size (is a hypothesis)
    - please note: [blank_start]not[blank_end] all axons are myelinated (especially in invertebrates)
    

    

    1. ASaltatory
    2. Bnot
    3. Cmyelin
    4. Dnodes
    5. ERanvier
    6. Fpotassium
    7. Gincreases
    8. Hnot
21. 21Not all axons are myelinated (especially in [blank_start]invertebrates[blank_end])
    - an [blank_start]increase[blank_end] in the diameter of an axon effectively decreases the internal resistance of current flow (similar to giant transatlantic cables)
    - the wider the axon = the lower the [blank_start]resistance[blank_end]
    - the explains why giant axons evolved in invertebrates, and why rapidly conducting axons in animals tend to be bigger than slowly conducting ones
    
    

    1. Ainvertebrates
    2. Bincrease
    3. Cresistance
22. 22Synapses: electrical and [blank_start]chemical[blank_end] synapses
    - electrical synapses have protein structures called [blank_start]GAP[blank_end] junctions which physically connect the 2 synapses
    - electrical synapses are [blank_start]faster[blank_end] than chemical synapses
    - chemical synapses can be [blank_start]excitatory[blank_end] or inhibitory, electrical synapses only link cells
    
    why do we have both?
    - [blank_start]electrical[blank_end] synapses are for transmitting information fast
    - chemical synapses can be [blank_start]modulated[blank_end], depending on transmitter/ion channels > more complex regulation
    
    

    

    1. Achemical
    2. BGAP
    3. Cfaster
    4. Dexcitatory
    5. Eelectrical
    6. Fmodulated
23. 23[blank_start]Chemical[blank_end] synapses = can be modulated, depending on neurotransmitter/ion channels > more complex regulation
    
    1. action potential arrives in the pre-synaptic cell and [blank_start]depolarises[blank_end] the membrane
    2. this depolarisation in the pre-synaptic cell causes voltage-gated [blank_start]calcium[blank_end] ion channels to open > calcium ions, Ca2+ enter the cell
    3. the entry of calcium ions causes vesicles containing neurotransmitter to be released into the synapse via [blank_start]exocytosis[blank_end]
    
    

    1. AChemical
    2. Bdepolarises
    3. Ccalcium
    4. Dexocytosis
24. 24Acetylcholine chemical synapse
    1. acetyl CoA is synthesized in the [blank_start]mitochondria[blank_end] and combines with choline to produce acetylcholine
    2. acetylcholine (ACh) is packaged into vesicles
    3. arrival of action potential to pre-synaptic cells causes [blank_start]depolarisation[blank_end] of the membrane, opening voltage gated calcium channels > calcium ions enter the cell causing vesicles containing ACh to be released into the synapse via exocytosis
    4. ACh binds to its receptor on the post-synaptic cell
    
    switching off = neurotransmitters are removed from the synaptic cleft and often are recycled
    - e.g. ACh is broken down by [blank_start]acetylcholinesterase[blank_end]
    
    FACT: deadly nerve agent [blank_start]Novichok[blank_end] is a likely inhibitor of acetylcholinesterase, so acetylcholine builds up in synapses leading to disregulated neuronal activity
    
    there are lots of forms of synapses, they have a huge variety

    

    1. Amitochondria
    2. Bdepolarisation
    3. Cacetylcholinesterase
    4. DNovichok

Descrição

Physiology Quiz sobre Neurons, criado por sophie waddington em 10-01-2019.

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sophie waddington

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