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Human physiology > Cell membranes + excitation > Flashcards

Cell membranes + excitation Flashcards

1
Q

What are the 2 main types of excitable cells? + what do they do when they’re excited?

A

Muscle = smooth, skeletal, cardiac- contract

Nerve = neurones- send constant electrical signals over long/short distances = conduction

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2
Q

Describe the structure of a neuron

A
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3
Q

How many dendrites are there on each neuron?

A

5-7

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4
Q

Where does an action potential begin?

A

Axon hillock

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5
Q

What is a transmembrane resting potential?

A

The potential difference between the extracellular fluid and intracellular fluid

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6
Q

What is the transmembrane resting potential of a neuron?

A

-70mv

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7
Q

What can be utilised to generate action potentials?

A

All living cells have a chemical disequilibrium that can be used by excitable cells to generate action potentials

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8
Q

What is the main creation of a neuron transmembrane resting potential?

A

Diffusion of + charge potassium ions (K+) out of cell via potassium leak channels
- so + charge is lost = inside of cell becomes more negative

= - 70mv

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9
Q

Describe how the -70mv transmembrane resting potential is created.

A
  1. Transport protein acts as potassium channel
  2. Potassium leak channels always open
  3. More potassium inside cell
  4. K+ moves by facilitated diffusion through potassium leak channels down conc gradient, from inside to outside of cell
  5. K+ lost = inside of cell becomes more negative = -70mv
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10
Q

What are potassium leak channels aided by?

A

The sodium-potassium pump = electrogenic pump

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11
Q

Describe how the sodium-potassium pump works.

A
  1. Very few sodium leak channels
  2. 3 Na+ pumped out of cell and 2 K+ pumped inside of cell via active transport- both against conc gradient
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12
Q

How does the sodium-potassium pump help to maintain the -70mv transmembrane resting potential?

A

Intracellular conc of K+ high and Na+ low as less sodium leak channels in comparison K+ so more K+ can leak out of cell = more negative

S-P pump = net loss of one + ion from inside of cell

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13
Q

Other than S-P pump and potassium leak channels, what else helps to maintain the -70mv TMR potential?

A

Negatively charged proteins
Chloride ions

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14
Q

Describe how proteins help to maintain -70mv TMR potential

A

Negatively charged proteins more inside of cell- unable to move freely out of cell as too large

= more negative inside

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15
Q

Describe how chloride ions help to maintain the TMR potential

A

Negative chloride ions in higher conc outside than inside- membrane is permeable to Cl- so they move done their conc and electrical gradient until equilibrium

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16
Q

What channels are involved in the generation of an action potential?

A

Voltage gated potassium and sodium channels

17
Q

Name some similarities + differences in the way the different voltage-gated channels work.

A

Differences:
- Potassium ions move down conc gradient outside of cell, but sodium moves into cell down conc gradient
- Potassium voltage gated channels are slower to open + close, but sodium VG channels are faster

Similarities:
- Both are normally closed
- Voltage change = protein changes shape
- Both take time to reset so action potential travels one-way down axon

18
Q

Do nerve cells have a high or low threshold for excitation?

A

Low threshold

19
Q

What are the 2 types of response to neuron excitation?

A
  • Local non-propagated
  • Propagated
20
Q

What is a non-propagated response?
+ where do they occur on a neuron?

A

= Graded response- magnitude of response is relative to the strength of stimulus

  • usually occurs at dendrites or cell body
21
Q

Define: Depolarisation

A

Membrane potential gets less negative

22
Q

Describe how a neuron non-propagated response works

A
  1. Small strength stimulus applied
  2. Results in small depolarisation
  3. This loses strength through the cytoplasm
23
Q

Describe how a neuron non-propagated response works

A
  1. Small strength stimulus applied
  2. Results in small depolarisation
  3. This loses strength through the cytoplasm
24
Q

What is a neuron propagated response?
+ where does is begin and end?

A

= ACTION POTENTIAL = magnitude of response is always the same if there is a sufficient stimulus = ALL OR NOTHING RESPONSE:
- Begins at axon hillock where is travels in a one-way direction down axon
- Ends at terminal boutons where synapse releases neurotransmitter

25
Q

Define: Hyperpolarisation
+ what is it caused by?

A

= membrane potential becomes more negative than -70mv resting potential

  • caused by VG potassium channels slowly closing so too many K+ ions leave = more negative
26
Q

Describe how a propagated response in a neuron works.

A
  1. Large enough stimulus applied = threshold reached
  2. VG sodium channels open = influx of sodium down conc gradient, which brings + charge into cell
  3. = Depolarisation of cell membrane reaches threshold = becomes more + on inside compared to outside
  4. VG sodium channels close + VG potassium channels open
  5. Potassium ions leave cell = net loss of + charge which makes membrane more negative
  6. Hyperpolarisation = membrane goes below -70mv
  7. Repolarisation = recovery period- goes back to -70mv
27
Q

What is a refractory period?

A

When neurons reset + recover after firing an action potential

28
Q

What are the 2 types of refractory periods?

A

Absolute and relative

29
Q

What is an absolute refractory period and when does it occur?

A

= cells cannot fire anymore action potentials to ensure their one-way travel
- occurs immediately after an action potential is fired

30
Q

What is a relative refractory period and when does it occur?

A

Another action potential could be intiated if neuron recieves a large enough stimulus- stronger than previous action potential
- occurs after the absolute refractory period

31
Q

If a larger stimulus is applied does that mean a bigger action potential?

A

No, they just occur more frequently

32
Q

What is the difference between a myelinated and unmyelinated axon?

A

Myelinated = has myelin sheath produced by schwann cells

33
Q

How does an AP travel down an unmyelinated axon?

A
  1. AP generated = impermanent reversal of - charge in membrane potential
  2. negative charge from outside of membrane pulls charge from membrane ahead
  3. New action potential created in adjacent active zone and zone behind becomes refractory = no AP
34
Q

How do APs travel down a myelinated sheath?

A
  1. AP jumps between nodes of ranvier
  2. AP pulls + charge from node ahead to create new AP in node- then becomes refractory

= saltatory conduction

35
Q

Which type of axon is faster at conducting APs?

A

Myelinated

Human physiology (43 decks)

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