Topic 6—B: Nervous Coordination-1. Neurones Flashcards

1
Q

What are nervous impulses?

A
  • They are electrical charges transmitted along a neurone
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2
Q

How are nervous impulses created?

A
  • By the movement of sodium and potassium ions
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3
Q

The resting membrane potential

A
  • In a neurone’s resting state (when it’s not being stimulated) the outside of the membrane is positively charged compared to the inside.
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4
Q

How is the outside of the membrane polarised?

A
  • There are more positive ions outside the cell than the inside
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5
Q

What does it mean when the membrane is polarised?

A
  • There is a difference in charge (called a potential difference or voltage) across it.
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6
Q

Resting potential

A
  • Voltage across the membrane when it’s at rest
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7
Q

How is the resting potential created and maintained?

A
  • By the sodium-potassium pumps and potassium ion channels in a neurones membrane
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8
Q

Sodium potassium pumps

A
  • they use active transport to move three sodium ions out of the neurone for every two potassium ions moved in
  • ATP is needed
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9
Q

Potassium ion channels

A
  • They allow facilitated diffusion of potassium ions out of the neurone down their concentration
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10
Q

Sodium ion channels

A
  • Diffusion of sodium ions into the neurone
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11
Q

Movement of sodium and potassium ions across a resting cell membrane

A
  • The sodium potassium pumps move sodium ions out of the neurone but the membra isn’t permeable to sodium ions so they can’t diffuse back in - this creates a sodium ion electro chemical gradient. ( A concentration gradient of ions) because there are more positive sodium ions outside the cell than inside
  • The sodium potassium pumps also move potassium ions into the membrane
  • When the cells at rest, most potassium ion channels are open. This means that the membrane is permeable to potassium ions, so some diffuse back out through potassium ion channels
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12
Q

How is the outside of the cell positively charged compared to the inside?

A
  • More positive ions move out of the cell than enter
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13
Q

What happens when a neurone is stimulated?

A
  • Other ion channels in the cell membrane called sodium ion channels open
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14
Q

What happens if the stimulus is big enough?

A
  • It will trigger a rapid change in the potential difference which causes the cell membrane to become depolarised (action potential)
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15
Q

Stimulus

A
  • This excites the neurone cell membrane
  • This causes sodium ion channels to open
  • The membrane becomes more permeable to sodium, so sodium ions diffuse into the neurone down their sodium ion electrochemical gradient.
  • This makes the inside of the neurone less negative
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16
Q

Resting potential

A
  • There is a positive charge on the outside of the neurone due to the presence of sodium and potassium ions
  • There is a negative charge in the inside of the neurone due to the presence of anions
  • Gated sodium ion channels are closed so little diffusion of sodium into the neurone
  • Gated potassium ion channels are open so potassium can diffuse out of neurone
  • Sodium potassium pump returns the membrane to it’s resting potential by pumping 3 sodium ions out for every 2 potassium ions in
  • Resting potential is maintained until the membranes excited by another stimulus
17
Q

Depolarisation

A
  • The outside of the neurone gets more negative due to the loss of sodium and potassium ions
  • The inside of the neurone is more positive due to the presence of sodium and potassium ions
  • If potential a difference reaches threshold more gated sodium ion channels open increasing permeability to sodium ions
  • 2 potassium ions are pumped in for every 3 sodium ions pumped out.
    -They diffuse down its concentration gradient into the neurone making potential difference more positive
  • If there is enough sodium ions diffusing across membrane then threshold potential is reached and neurone membrane is depolarised.
18
Q

Generator potential

A
  • The same as depolarisation but less sodium ion channels are open compared to action potential
19
Q

Repolarisation

A
  • Outside the neurone is more positive due to the presence of sodium and potassium ions
  • Inside of the neurone is negative
  • Gated sodium ion channels close so less diffusion of sodium ions into the neurone
  • Potassium ion channel open allow potassium ions to diffuse out of neurone
  • Sodium-potassium pump removes sodium from neurone cytoplasm
  • The membrane is more permeable to potassium so potassium ions diffuse out of neurone down the potassium ion concentration gradient
  • This starts to get the membrane back to it’s resting potential
20
Q

Hyperpolarisation

A
  • Potassium ion channels are slow to close so there’s a slight ‘overshoot’ where too many potassium ions diffuse out of the neurone
  • The potential difference becomes more negative than the resting potential
21
Q

What happens to the membrane when sodium ion channels are open?

A
  • The permeability of membrane to sodium ions increase
22
Q

What happens to the membrane when sodium ion channels are closed?

A
  • The permeability of membrane to sodium ions decrease
23
Q

Refractory period

A
  • The time taken before a new depolarisation (action potential) can occur (during Repolarisation and Hyperpolarisation)
  • It acts as a time delay between one action potential and the next
  • This makes sure that action potentials don’t overlap but pass along as discrete (separate) impulses.
24
Q

Waves of depolarisation

A
  • When an action potential happens some of the sodium ions that enter the neurone diffuse sideways.
  • This causes sodium ion channels in the next region of the neurone to open and sodium ions diffuse into that part.
  • This causes waves of depolarisation to travel along the neurone.
  • The wave moves way from the parts of the membrane in the refractory period because these parts can’t fire an action potential
25
Q

All or nothing principle

A
  • Once the threshold is reached, an action potential will always fire with the same change in voltage, no matter how big the stimulus is
  • If the threshold isn’t reached an action potential wont fire
  • A bigger stimulus wont cause a bigger action potential, but it will cause them to fire more frequently
26
Q

What three factors affect the speed of conduction of action potentials?

A
  1. Myelination
  2. Axon diameter
  3. Temperature