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Module 202 Neuroscience & behaviour > T1 L5 Physiology of neurons > Flashcards

T1 L5 Physiology of neurons Flashcards

1
Q

Describe an electrical synapse

A 
Faster
Bidirectional
Smaller gap = 3.5nm
No plasticity
No amplification
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2
Q

What is spatial summation

A

Neuron determines whether to fire based on add-together of all the tiny signals from several neutrons synapsing on it.

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3
Q

What is temporal summation?

A

One input neuron is firing fast enough so the receiving neuron can add together the many tiny signals to reach threshold

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4
Q

What allows temporal summation to occur?

A

Receiving neuron must recover slowly from the previous signal

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5
Q

Briefly describe the 4 stages of action potential

A

1) At rest, K+ going out of the cell clamps the membrane negative
2) External factor causes the membrane to depolarise slightly
3) Na+ conductance shoots, Na+ current goes into cell, membrane depolarises
4) After a time delay, Na+ conduction diminishes, K+ conductance increases, K+ leaves cell & voltage returns to resting potential

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6
Q

What happens during initial depolarisation?

A

Inward rectifier K+ channels are open

Something causes cell to become less negative

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7
Q

State the 4 stages of the action potential

A 
Initial depolarisation
Positive feedback of depolarisation
Repolarisation
Refractory period 
After-hyperpolarisation
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8
Q

What can cause the cell to become less negative

A

A nearby cell depolarising

Synaptic transmission where a neurotransmitter opens a ligand-gated channel

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9
Q

What happens during positive feedback of depolarisation?

A

Initial depolarisation causes a few Na+ channels to open
Additional current of Na+ going into cell –> more depolarisation
Acts as a positive feedback loop

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10
Q

What happens during repolarisation?

A

Na+ channel inactivation –> decreased Na+ current going in
Delayed rectifier K+ channels open –> increases K+ going out

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11
Q

What is the refractory period?

A

The period of time where a neuron is unable to reinitiate an action potential
Amount of time it takes for neuron’s membrane to be ready for a second stimulus once it returns to its resting state following an excitation

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12
Q

What is the definition of after-hyperpolarisation?

A

At the end of an action potential the voltage inside temporarily goes slightly more negative than at rest followed by a return to resting membrane potential

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13
Q

What happens during after hyperpolarisation?

A

Inward rectifier K+ open again
The K+ permeability increases
Decrease in Na+ permeability
Membrane potential moves closer to Ek

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14
Q

How do neutrons code the intensity of their synaptic input?

A

Firing frequency

Different neurons for different strength stimuli

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15
Q

Describe how firing frequency represents the intensity of activity

A

Increasing the threshold lowers firing frequency
Increasing excitatory synaptic activity increases firing frequency
Small, length synaptic currents create a higher threshold potential for AP generation than larger currents

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16
Q

What is excitability?

A

How easy it is to start nervous signalling

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17
Q

What does a high excitability increase the risk of?

A

Seizures or spasms

18
Q

What happens to membrane potential when Na+ channels open?

A

The membrane becomes positive inside as Na+ concentration is higher outside the cell

19
Q

What happens to membrane potential when K+ open?

A

The membrane becomes more negative inside

K+ travel from inside to outside

20
Q

What happens to membrane potential when Ca2+ channels open?

A

Membrane becomes more positive inside

Calcium passively goes inward

21
Q

What is lidocaine?

A

Lignocaine

Local anaesthetic

22
Q

How does lidocaine work?

A

Blocks Na+ channels, which raises threshold & lowers excitability to locally stop action potentials

23
Q

What is carbamazepine?

A

Anticonvulsant

24
Q

How does carbamazepine work?

A

Inactivates sodium channels

Raises action potential threshold & lowers excitability

25
Q

What are the 2 forces on an ion?

A

Chemical force

Electrical force

26
Q

What is chemical force?

A

Also known as diffusional force

Based upon the difference in concentration across the membrane

27
Q

What is electrical force?

A

Based on Vm

Affects every ion in that area

28
Q

What is used to calculate equilibrium potential?

A

Nernst equation

29
Q

What is the equilibrium potential of Na?

A

+60mV

30
Q

What is the equilibrium potential of K?

A

-90mV

31
Q

What is the equilibrium potential of Ca?

A

+123mV

32
Q

What is the equilibrium potential of Cl?

A

-40mV

33
Q

What happens to the membrane potential if the membrane is equally permeable to Na+ & K+ ?

A

The membrane potentials will be the average between their equilibrium potentials
-15mV

34
Q

Describe the properties of an action potential

A

Stereotyped electrical signal
Short duration
In most neurons, skeletal & cardiomyocytes
Spike
Always the same - ‘‘all or none’’
Require time to start because of conformational changes

35
Q

Describe the properties of a graded potential

A

Electrically localised
Last a long time
Much flatter in shape
Conducted almost instantly

36
Q

What is saltatory conduction?

A

When the action potential jumps from node to node

37
Q

What is the net effect of saltatory conduction?

A

Faster conduction velocity

38
Q

What is the typical conduction velocity for alpha motor fibres (myelinated, 15um diameter)?

A

100m/s

39
Q

What is the typical conduction velocity for C nociceptive fibres (unmyelinated, 0.2-1.5um)?

A

1m/s

40
Q

What are the clinical uses of conduction velocity?

A

Nerve conduction studies to evaluate paresthesias

Evaluation of weakness of the arms & legs

41
Q

What conditions can conduction velocity diagnose?

A 
Peripheral neuropathy
Carpal tunnel syndrome
Ulnar neuropathy
Guillain-Barre syndrome
Spinal disc herniation

Module 202 Neuroscience & behaviour (39 decks)

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