Neuro physiology Flashcards by Fearghal O'Brien

Give the four morphological regions of a neurone

Dendrites 
Soma 
Axon hillock and initial segment
Axon
(synapse)

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What are dendrites and what is the function of them?

Form tree like structures projecting close to the soma and increase SA. Receive input and pass graded electrical signals to the soma

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Dendrites transmit actively to the soma - true/false

false - dendrites transmit passively to the soma.

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On average how many synapses does each cell receive information from?

1000+

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What is the soma and what is it’s function?

It is the body and core of the cell, it is the synthetic and metabolic part of the neurone. It integrates signals from the dendrites and passes a net signal, depolarising or hyper polarising to the axon hillock.

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What is the nissl substance?

This is the endoplasmic reticulum of the neurone.

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passing of the net signal from the soma to the axon hillock is a passive/active process

Passive

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The axon hillock is the most excitable part of the cell - true/false

True - this is where initiation of the AP occurs.

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What determines an APs generation?

Size and magnitude of the signal arriving - is it hyperrpolarizing/depolarising and of sufficient magnitude

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What determines the axon output intensity?

Frequency of APs is variable

Size is fixed - therefore frequency decides the intensity of the output

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What does the axon do in a neurone?

It conducts output signals as APs to other neurones or cells.
Also mediates transport of materials from the soma and presynaptic membrane to each other.

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What is anterograde transport in a neurone?

It is transport from the soma to the presynaptic membrane

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What is retrograde transport in a neurone?

Transport from the presynaptic membrane to the soma.

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What is the issue with retrograde transportation in neurones?

Some viruses hijack it to infect the neurone.

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Which viruses hijack retrograde transportation in a neurone?

Polio
Rabies
Herpes

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Describe a synapse

Point of (usually) chemical transmission between neurones or neurones and other cells.

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What are the tree parts of a neurone?

presynaptic terminal
Synaptic cleft
Postsynaptic dendrites

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What is the purpose of the synapse?

It allows “neurone decision making.” - there is a chance for the chain of transmission to either continue or break it is not hardwired to continue.

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The general premise of synaptic transmission is __________

Electrical -> Chemical -> Electrical

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Describe a neurite

A process arising from a soma.

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Describe a unipolar neurone

Only one neurite. Soma at one end, axon at the other.

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Give an example of a unipolar neurone.

Peripheral autonomic neurone.

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Describe a pseudounipolar neurone

Appears to have two axons but the neurite bifurcates - therefore there are two a central axon and a peripheral one.

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Give an example of a pseudo unipolar neurone

Dorsal root ganglion neurone

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Describe a bipolar neurone

two true neurites leaving the soma.

Give an example of a bipolar neurone

Retinal bipolar neurones

What is a multipolar neurone

3 or more neurite passing from one soma.

Give an example of a multipolar neurone

lower motor neurones

When a cell is resting its concentration of sodium is greater inside/outside the cell

outside

When a cell is resting its concentration of potassium is greater inside/outside the cell

inside

What causes the charge separation in a cell?

The sodium/potassium antiporter removes 3 sodium for every 2 potassium it brings in. therefore the inside of the cell has a less positive charge than outside.

What is the typical resting potential of a standard cell?

-70mV.

When a stimulus is perceived an AP is set up if ____

the threshold potential is reached

Threshold potential causes an opening of which type of channel?

Voltage activated sodium channels.

When voltage activate sodium channels open there is a positive/negative feedback which cause more channels to open/close

Positive feedback | More channels open

When the membrane potential reaches a certain size, the upstroke ends and the downstroke begins - what magnitude is that at?

+40mV

When the membrane potential begins the downstroke, which channels open and which close?

Voltage gate potassium channels open and sodium channels close

Which way does sodium move during the generation of an AP?

Sodium influxes

Which way does potassium move during the generation of an action potential?

Potassium effluxes.

What causes the refractory period?

The cell undershoots and ends up with a more negative potential that it started with and becomes hyper polarised.

What causes hyper polarisation?

this is caused by potassium channels remaining open which sodium channels are closed so potassium effluxes while sodium remains constant and the cell becomes much more negative.

What is the purpose of action potentials?

they allow an electrical signal to be conducted across very large distances without decaying.

Why will passive signals decay as they travel along an axon?

the axon membrane is leaky and therefore there will be current lost across it.

What is the relationship between the membrane distance and potential change across the membrane?

For given current I, change in potential increases linearly with membrane resistance.

The membrane potential change in a passive neuronal process decays linearly/exponentially with distance?

Exponentially

What is the length constant?

It is the length along a given neurone a passive charge may travel before it reaches 37% of its original amplitude

What is the length constant proportional to?

the ratio of the resistance in the membrane to the axoplasmic resistance

at the point of the AP the charges on the membrane are normal - true/false

false they are reversed (negative outside positive inside).

Due to the +-+ or -+- pattern inside and outside the cell at the point of the AP, the charges will move linearly without decaying along the axon - true/false

true

how does myelin increase the conduction velocity of an AP?

Increases the resistance of the membrane.

What provides myelin in the CNS?

oligodendrocytes

What provides myelin in the PNS?

Schwann cells

the cells that provide myelin are both what type of cell?

Macroglia

Describe the difference between the two types of myelin generating cells

Schwann - multiple Schwann cells surround one axon in many layers Oligodendrocytes - one oligodendrocytes surrounds multiple axons

conduction in myelinated/unmyelinate axons is faster

Myelinated

What are the nodes of ranvier?

They are gaps between the myelin on an axon.

Describe saltatory conduction

It is a process whereby an AP jumps from one node of ranvier to the next.

What causes saltatory conduction?

this is caused as the charges cannot leave the cell at any other point except at the nodes so the AP moves from node to node

in an unmyelinated cell, the voltage activated transporters are not clustered. where do they cluster in myelinated cells?

At the nodes of Ranvier.

Compare myelinated and unmyelinated conduction velocities

Unmyelinated; 0.5-3m/s | Myelinated; up to 120m/s

Give two example of diseases which cause demyelination and what area they affect

Guillain Barré syndrome - PNS | Multiple Sclerosis - CNS

Give the three morphological classes of synapse

Axo-dendritic Axo-somatic Axo-axonic

Which type of synapse is most common?

Axo-dendritic

Which type of synapse is least common?

Axo-axonic

Describe each of the types of synapse?

Axo-dendritic - axon synapses with the dendrite of the other cell(s) Axo-somatic - axon synapse directly with the soma of the other cell(s) Axo-axonic - axon synapses directly with the axon of the other cell(s).

What are the two functional classes of synapse?

Excitatory | Inhibitory.

what is the most common transmitter for an excitatory synapse in the CNS?

Glutamate is most common

What receptors are activated in CNS excitatory synapses?

Post-synaptic cation selective, ionotropic glutamate receptors.

What happens when post-synaptic cation selective ionotropic glutamate receptors are activated?

A local, graded, excitatory response (the excitatory post synaptic potential or EPSP) is generated.

Inhibitory synapse usually have what two neurotransmitters in the CNS?

gamma-aminobutyric acid (GABA) or glycine

What receptors are activated by inhibitory synapses in the CNS?

Post-synaptic anion selective, ionotropic, GABA2 or glycine receptors

What happens when Post-synaptic anion selective, ionotropic, GABA2 or glycine receptors are activated?

A local, graded, inhibitory (hyperpolarising) response (the inhibitory postsynaptic potential IPSP)

What type of neurotransmitter are glutamate/GABA/glycine?

Amino acid neurotransmitter

How far separates the presynaptic and postsynaptic membranes?

20-50nm.

What holds the pre and post synaptic clefts together?

A matrix of fibrous extracellular proteins

Where are the neurotransmitters normally stored?

Vesicles approximately 50nm in diameter

What is the active zone of the presynaptic membrane?

the area the vesicles cluster around

What is the postsynaptic density?

It is an area of the post-synaptic membrane which contains the receptors

How does glutamate cause depolarisation in excitatory synapses?

When glutamate binds to glutamate receptors, Na channels are opened which cause influx and depolarisation

How do GABA or glycine cause inhibition?

Inhibition is brought about when GABA or glycine bind to GABA2 or glycine receptors which causes chloride channels to open and influx; this causes hyper-polarisation.

What is spatial summation?

Multiple inputs add together/subtract from each other to get a net excitation or inhibition with a larger or smaller EPSP or IPSP.

What is temporal summation?

the same input(s) summate but not due to multiple sources; this is due to the higher frequency of EPSPs or IPSPs to give a larger EPSP or IPSP.

Temporal and spatial summation are entirely separate; true/false

false - they work together and are complimentary in reality.

Glycine/GABA and glutamate are only present in neurones - true/false

False - GABA is only found in neurones but Glutamate and glycine are part of the 20 amino acids used to synthesise proteins and so are found in all cells.

GABA and amines are synthesised, as needed, by enzymes - true/false

True

Where are the enzymes formed in the neurone to form GABA and amines?

the soma

Where are the enzymes for forming GABA and amines transported to and how are they transported?

they are transported to the presynaptic terminal by microtubules using axoplasmic transport.

What decides if an EPSP is going to generate an action potential?

The summed potential of all of the EPSPs and IPSPs arriving at its axon hillock.

Neuro physiology Flashcards

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