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AQA A-Level Biology > Y2: Nervous coordination and muscles > Flashcards

Y2: Nervous coordination and muscles Flashcards

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1
Q

How is a resting membrane potential established?

4

A
  • The sodium-potassium pump actively transports 3 Na+ out of the axon per 2 K+ in
  • Sets up electrochemical gradient
  • Sodium channels are mostly closed and potassium channels mostly open
  • Means the inside of the axon is more negative than outside the membrane
  • Sets up potential difference/ axon is polarised
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2
Q

Action potential steps? Full

8

A
  • Neuron is at resting membrane potential
  • A stimulus depolarises the nerve to threshold and Na+ moves in by facilitated diffusion
  • Voltage-gated Na+ Channels open
  • Na+ floods in and the membrane potential depolarises
  • Voltage-gated K+ Channels open
  • Potassium floods out of the cell (repolarisation)
  • The membrane potential falls past the threshold (hyperpolarisation) and the voltage gated K+ channels close
  • The membrane potential is restored to resting by the sodium-potasssium pump
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3
Q

Action potential steps? brief

7

A
  • Resting membrane potential
  • Threshold
  • Depolarisation
  • Peak
  • Repolarisation
  • Hyperpolarisation
  • Recovery/ resting membrane potential
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4
Q

What is the all or nothing principle?

3

A
  • An impulse has to surpass a threshold value to generate action potential
  • size/strength of stimulus does not affect size/strength of impulse
  • However, stronger impulses lead to significantly more frequent stimulations.
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5
Q

What is the refractory period?

5

A
  • After action potential
  • Where inward movement of Na+ ions is prevented
  • Na+ voltage gated channels closed
  • Impossible for another action potential to be generated
  • however, huge stimulus can stimulate action potential in refractory period
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6
Q

Propagation/ unmyelinated axon: how is action potential conducted/ propagated? full
8

A
  • Resting potential- more positive inside
  • Stimulus causes influx of Na+ and depolarisation of first region
  • Voltage-gated Na+ channels allow influx of Na+ in next region depolarising next region
  • Voltage-gated Na+ channels in first region close and voltage gated K+ channels open and K+ leave
  • The second region induces depolarisation in the next region
  • First region hyperpolarises
  • Third region induces depolarisation in next region
  • First region returns to resting membrane potential
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7
Q

What is important about the all or nothing principle?

3

A
  • Action potentials can only be propagated in one direction
  • Produces discrete impulses (no overlap)
  • Limits number of action potentials
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8
Q

Saltatory conduction in myelinated axons: steps?

3

A
  • Action potentials occur at nodes of ranvier
  • Localised circuits occur between adjacent nodes of ravier,
  • Causes electrical charge to ‘jump’ from one node to the other.
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9
Q

Which is better saltatory conduction or propagation? Why?

A

Saltatory conduction

It is faster

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10
Q

Factors in the speed of an impulse?

A

-Myelin sheath
-Diameter of axon- bigger means membrane potentials
are easier to maintain, so less leakage of ions, so faster
speed of conduction
-Temperature- enzymes, diffusion, rate

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11
Q

Synapses part 1?
Up to synaptic cleft
5

A
  • Resting- Ca2+ actively transported out of synapse
  • Depolarisation- voltage gated Ca2+ ion channels open and Ca2+ enter
  • Calcium causes vesicles containing neurotransmitters to travel to the pre-synaptic membrane
  • Vesicles fuse w/ pre-synaptic membrane
  • Release neurotransmitters into synaptic cleft by exocytosis
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12
Q

Synapses: two options after neurotransmitters released into synaptic cleft?

A

Excitatory- depolarises next neuron

Inhibitory - hyperpolarises next neuron

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13
Q

Excitatory synapse steps?

5

A
  • NT diffuses from pre-synaptic membrane to post-synaptic membrane
  • NT binds to Na+ ion channels on postsynaptic membrane
  • Opens the Na+ ion channels
  • Na+ enter down electrochemical gradient
  • If enough enter, generates action potential in postsynaptic neuron
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14
Q

Inhibitory synapse steps?

6

A
  • NT diffuses from presynaptic membrane to postsynaptic membrane
  • NT binds to Cl- or K+ ion channels on postsynaptic membrane
  • Channels open
  • Cl- enter or K+ leave –> makes membrane potential more -ive
  • Makes it more difficult to meet threshold for an action potential
  • Lots of Na+ need to enter
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15
Q

What happens to the neurotransmitters after synapse stuff?

3

A
  • They must be removed
  • Then hydrolysed and recombined so can be used again
  • Taken up by presynaptic membrane and reused
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16
Q

Why is summation needed?

A

Frequency of action potentials can be too low to release enough NT to depolarise post-synaptic membrane
-Need to increase amount of NT in cleft

17
Q

What are the two ways to increase amount of NT in synaptic cleft? ie: summation

A

Temporal

Spatial

18
Q

What is temporal summation?

4

A
  • Increase frequency of AP’s in one neuron
  • Constant stimulus
  • More NT released
  • More Na+ channels open so more Na+ into postsynaptic membrane
19
Q

What is spatial summation?

3

A
  • Multiple neurons release NT together on one postsynaptic membrane (into synaptic cleft)
  • Enough Na+ channels open on postsynaptic membrane
  • To trigger opening of voltage-gated Na+ channels so more Na+ enters
20
Q

What is the terminal bouton?

A

Axon terminal

21
Q

Neuromuscular junction steps? Remember different names
Cholinergic receptor
6

A
  1. Action potential depolarises neuron
  2. Voltage gated Ca2+ channels open and Ca+ enters
  3. Ca2+ causes vesicles containing acetylcholine move to presynaptic membrane
  4. Vesicle fuses w/ membrane and releases acetylcholine into synaptic cleft by exocytosis
  5. Acetylcholine binds to voltage gated Na+ channels on sarcolemma
  6. If enough Na+ enters into the sarcoplasm depolarises so causes sarcoplasmic reticulum to release calcium ions- for muscle contraction
22
Q

What are the three types of muscle?

A
  • Skeletal- move bones/ whole limbs, antagonistic pairs
  • Cardiac- heart
  • Smooth- lines tubes
23
Q

Structure of skeletal muscle?

5

A

-Surrounded by a membrane called the sarcolemma
-Have thousands of myofibrils that are made up of thick
and thin filaments
-Myofibrils are divided into sarcomeres
-Have cytoplasm called sarcoplasm
-Have a specialized network of tubules that store calcium
called sarcoplasmic reticulum

24
Q

Structure of muscle fibres?

3

A
  • Multi-nucleiated
  • Bundles of fibres
  • Myofibrils
25
Q

Structure of sarcomeres?

5

A
  • Between two successive Z-disks.
  • Each comprises of two I bands surrounding an A band in the center.
  • I band= just actin
  • A band= actin and myosin- length of the myosin
  • H zone= just myosin in the centre of the sarcomere
26
Q

What are z-disks?

A

Z-disks are the filamentous proteins to which actin filaments are attached.

27
Q

Sliding filament theory? full Dr Stones explaination

8

A
  1. Ca2+ released from the SR causes a change in the
    tertiary structure of tropomyosin, exposes the
    binding sites on the actin
  2. The globular myosin head forms a cross bridge with
    the actin.
  3. The myosin head changes angle, which pulls the actin
    along the myosin (the power stroke)
  4. ADP detaches from the myosin head, and is replaced
    with an ATP molecule.
  5. This causes the actin-myosin cross-bridge to break.
  6. ATP is hydrolysed to ADP + Pi. The energy that is
    released is used to reset the myosin head back to its
    original position.
  7. This continues - Actin is pulled inwards over the
    myosin causing an overall shortening of the sarcomere
  8. When the stimulus finishes, the Ca2+ are actively
    transported back into the sarcoplasmic reticulum
  9. tertiary structure of tropomyosin changes and it blocks
    the binding sites on the actin
    again.
28
Q

Sliding filament theory? brief

6

A
  • Ca2+ ions bind to troponin, uncovering the myosin-binding sites
  • Charging of myosin heads
  • Binding of globular myosin heads to actin filaments forming cross-bridges
  • Power stroke that pulls the actin filaments towards the center - myosin head changes angle
  • Release of cross-bridges after the ADP detaches and ATP binds to myosin head
  • ATP hydrolysed, energy used to reset head to original position
29
Q

What happens to structure of sarcomere when muscle contracts?
4

A
  • I band decreases
  • H zone decreases
  • A band stays the same
  • Z disks move closer together

AQA A-Level Biology (11 decks)

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