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NAS > WEEK 1 > Flashcards

WEEK 1 Flashcards

1
Q

What is the nervous system made of?

A

Cells-neurones and glia

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2
Q

How do neurones work?

A 
within the neurone=electrical activity
between neurones (+other cells)=synapses
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3
Q

How is the nervous system organised?

A

Central vs Peripheral NS
Motor/Efferent vs Sensory/Afferent neurones
Somatic vs Autonomic NS

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4
Q

`What is an electrical signal?

A

A change in the balance of +ve and -ve charges due to ion transfer through ion channels

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5
Q

What are ions?

A

Charged particles (eg. Na+, K+, Cl-, Ca2+)

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6
Q

What controls ion movement in and out of a cell?

A

Cell membrane

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7
Q

General ion concentrations inside and outside of cells

A

K+=high conc. inside, low conc. outside
Na+=low conc. inside, high conc. outside
Ca2+=extremely low conc. inside, low conc. outside
Cl-=low conc. inside, high conc. outside

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8
Q

Basic electrical property of membranes

A

Inside of cell contains slight excess of anions->negative voltage

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9
Q

What is membrane potential (Em)?

A

The voltage inside a cell determined by the balance of charges

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10
Q

What are ion channels?

A

Membrane proteins which are essential for controlling Em

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11
Q

What is the difference between active and passive transport?

A

Active requires energy (ATP), passive doesn’t

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12
Q

Is ion movement active or passive?

A

Passive

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13
Q

Ion channel gating mechanism classification

A

Non-gated (leak): set Em of resting membrane
Voltage-gated: generate AP
Ligand-gated (chemical): generate Em changes at synapse

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14
Q

What is the resting membrane potential in neurones?

A

-65mV (excess -ve charge inside)

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15
Q

What is the permeability value of each ion dependent on?

A

The number of open channels for that ion

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16
Q

What factors influence ion movement (flux)?

A

Chemical gradient: unequal ion distribution (concentration gradient)
Electrical force: attraction/repulsion of ions by voltage inside the cell (Em)

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17
Q

How does the chemical gradient affect K+ and Na+ movement?

A

K+ drive to leave cell (efflux) due to high conc. inside, Na+ drive to enter cell (influx) due to high conc. outside

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18
Q

How does the electrical force affect K+ and Na+ movement?

A

both Na+ and K+ drive to enter cell (influx) due to negative Em

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19
Q

What is a property of chemical gradient?

A

It is ‘constant’-small changes are irrelevant fluctuations

20
Q

When is an ion in equilibrium (no net flux)?

A

When the chemical gradient and electrical force are in balance

21
Q

What is the Nernst equation used to define?

A

The equilibrium potential of an ion (Eion)

22
Q

What is the equilibrium potential of K+ (Ek)?

A

-80mV

23
Q

What is the equilibrium potential of Na+ (Ena)?

A

+62mV

24
Q

What does Em>Ek tell us about K+ movement?

A

At -65mV, chemical influence (efflux)>electrical influence (influx)->K+ efflux (trying to reach -80mV)

25
Q

What does Em

A

At -65mV, both chemical and electrical influences cause Na+ influx (trying to reach +62mV)

26
Q

What is the ionic driving force?

A

The net force resulting from chemical and electrical influences, which is present whenever Em differs from equilibrium potential

27
Q

Where does Em rest between?

A

Ena and Ek-closer to Ek as Pk is much higher (more open leak K+ ion channels-Pk=40xPna)

28
Q

What is the Goldman equation used to define?

A

The membrane potential taking into account all ions permeant through that membrane

29
Q

What does Em being at rest tell us?

A

Na+ influx=K+ efflux

30
Q

What causes the maintenance of ionic gradients?

A

Ion pumps operating continuously (especially: Na+/K+ pump-Na+ efflux/K+ influx and Calcium pump-Ca2+ efflux)

31
Q

What are the stages of an action potential?

A

Generator potential, depolarisation, repolarisation, hyperpolarisation and return to resting Em

32
Q

What is required for action potential to occur?

A

Em less negative than threshold potential

33
Q

How is depolarisation achieved?

A

Na+ influx due to increased Pna (opening of V-gated Na+ channels)

34
Q

How is repolarisation achieved?

A

K+ efflux due to increased Pk (opening of V-gated K+ channels)-and terminating activity of ‘extra’ Na+ channels (decreased Pna)

35
Q

What does conductance of ion channels relate to and why is it used?

A

Permeability and due to it being proportional to the number of ion channels open

36
Q

Conductance (g)=

A

1/R(resistance due to membrane)

37
Q

How do depolarisation and repolarisation affect V-gated ion channels?

A

Open due to depolarisation, Close due to repolarisation

38
Q

Summary of AP events

A

Initial stimulus (depolarisation) which reaches threshold, opening of V-gated Na+ channels (increased gNa), Na+ influx-further depolarisation, Em approaches Ena, Na+ channels inactivate (decreased gNa), Na+ influx stops, delayed opening of V-gated K+ channels (increased gK), K+ efflux-repolarisation, but increased gK after Em returns to rest, Em approaches Ek-hyperpolarisation, V-gated K+ channels close (decreased gK), Em returns to resting potential via leak channels

39
Q

What is threshold potential and what does it cause?

A

The Em value where Na+ influx (due to leak and V-gated channels)>K+ efflux (leak) and causes AP to be all-or-nothing event

40
Q

What is the absolute refractory period?

A

The period after AP where no further AP can be caused by any stimulus

41
Q

What causes the absolute refractory period?

A

Most V-gated Na+ channels being inactivated and many V-gated K+ channels being open

42
Q

What is the relative refractory period?

A

The period after AP where a stronger stimulus is required to overcome increased gK/remaining K+ efflux

43
Q

What causes the relative refractory period?

A

V-gated Na+ channels recovering from inactivation and some V-gated K+ channels still being open

44
Q

Describe AP propagation along an unmyelinated axon

A

Electrotonic spread due to local current flow to adjacent membrane

45
Q

Describe AP propagation along myelinated axon

A

Saltatory conduction-ion flow, therefore depolarisation, from node to node where V-gated channels are located-increasing speed of AP conduction

NAS (9 decks)

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