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Biology > Section 6- Nervous co-ordination and muscles > Flashcards

Section 6- Nervous co-ordination and muscles Flashcards

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1
Q

When is a neuron ‘at rest’?

A

When a neuron is not transmitting an action potential

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2
Q

What does the sodium/ potassium ion pump do?

A

Actively transports 3 Na+ out of the cell and 2 K+ from the tissue fluid into the cell

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3
Q

At a resting potential, what are the voltage gated Na+ channels like?

A

Some are open

Most are closed

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4
Q

How is the membrane differentially permeable?

A

Many more K+ channels open than Na+ channels

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5
Q

What is a typical resting potential?

A

-70mV

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6
Q

How is there a negative potential difference across the membrane?

A

More positive ions in the tissue fluid than in the cytoplasm

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7
Q

What is the action potential in response to a stimulus?

A

Na+ channels open allows Na+ to enter cytoplasm by facilitated diffusion, makes potential difference across the membrane less negative

If threshold is reached, more Na+ channels open so more facilitated diffusion causing membrane to become depolarised

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8
Q

At what voltage is the action potential achieved?

A

+40mV

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9
Q

What happens after the membrane is repolarised in the action potential?

A

At resting potential, the K+ channels are slow to close allowing too many K+ out of the cell

This hyperpolarises the membrane and causes the refractory period

Once K+ channels close the Na+/K+ pump reinstates the resting potential

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10
Q

What is the ‘all or nothing principle’?

A

If stimulus is too small to open sufficient Na+ channels to meet the threshold, there is no action potential

If the stimulus is big enough the action potential will be +40mV

Action potential doesn’t change regardless of size of stimulus

Larger stimulus will generate more frequent action potentials

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11
Q

What is the refractory period in the action potential?

A

Because membrane is hyperpolarised during refractory period, it cannot be stimulated, and cannot generate action potential

Makes sure that action potentials are uni-directional and discreet (stay separate)

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12
Q

What does the refractory period ensure?

A

Makes sure that action potentials are uni-directional and discreet (stay separate)

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13
Q

What is the myelin sheath composed of?

A

Composed of Schwann cells that wrap around the axon

Myelin in their membranes which along with phospholipids prevent ions from diffusing across it

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14
Q

What are the nodes of Ranvier stimulated by?

A

By extended localised circuits of Na+

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15
Q

When do the localised circuits of Na+ form?

A

When Na+ flood into cytoplasm and diffuse down the concentration gradient through the cytoplasm

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16
Q

What is the saltatory conduction?

A

Movement of the action potential from node of Ranvier to node of Ranvier

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17
Q

How does temperature affect the action potential speed?

A

Increasing temperature increases the kinetic energy of the ions

Increases the rate of diffusion

As action potential relies on facilitated diffusion this is increased too

If temperature goes too high, the proteins can become denatured so action potentials cannot be transmitted

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18
Q

What does the diameter of the axon affect the action potential speed?

A

Wider axon provides less resistance in the cytoplasm to the lateral movement of sodium ions

Increase in the speed of the action potential along the membrane

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19
Q

How is the membrane repolarised in an action potential?

A

At 40mV Na+ channels close and K+ opens allowing K+ to flood out of the cell into the tissue fluid, repolarising membrane

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20
Q

What is the process of synaptic transmission?

A
  1. Ca2+ channels open when action potential arrives at synaptic knob
  2. Ca2+ flood into synaptic knob by facilitated diffusion causing vesicles to move towards presynaptic membrane where they fuse
  3. Acetylcholine is released from vesicles by exocytosis
  4. Ach diffuses across synaptic cleft and binds to complementary receptors opening Na+ channels
  5. Na+ flood into the axon causing depolarisation of post-synaptic membrane
  6. Enzyme acetylcholinesterase hydrolyses acetylcholine into acetyl and choline which is actively transported back into synaptic knob
  7. Energy from ATP used to recycle and repackage into vesicles and Ca2+ are actively transported back out of synaptic knob
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21
Q

What is the benefits of a synapse?

A

Allow for control

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22
Q

What is temporal summation?

A

A SINGLE presynaptic neurons releases neurotransmitter MANY TIMES over a very short period

Temporarily builds up in the synaptic cleft to pass the threshold of the post synaptic membrane

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23
Q

What is spatial summation?

A

Number of DIFFERENT presynaptic neurons together release enough neurotransmitter to exceed threshold value

TOGETHER they trigger new action potential

24
Q

What are inhibitory synapses?

A

Release a neurotransmitter that will bind to receptors on the post synaptic membrane that will open K+ channels and Cl- channels

K+ out of postsynaptic neurone
Cl- into postsynaptic neurone

Membrane potential increases making it less likely that a new action potential is created

25
Q

What do inhibitory synapses allow for?

A

Allows for the facilitated diffusion of K+ out of the post-synaptic neurone and Cl- into it

Has the effect of making the potential difference across the membrane more negative, meanings action potentials cannot be generated

26
Q

What are excitatory synapses?

A

All synapses are unidirectional

Neurotransmitter is only made in the synaptic knob, and complementary receptors are only found on the post synaptic membrane

27
Q

How do synapses ensure that nerve impulses only travel towards muscle fibres?

A

Neurotransmitter only made in the pre-synaptic neurone

Complementary receptor only on the post-synaptic membrane

28
Q

What are the 3 types of muscles?

A

Cardiac: myogenic

Smooth: typically involuntary control, found in airways

Straited: voltutary muscles, connected to bone

29
Q

What is the neuromuscular junction?

A

When an action potential arrives at a neuromuscular junction, the neurotransmitter is released from the synaptic knob

It diffuses to the sarcolemma where it binds to complementary receptors that open Na+ channels

Depolarising sarcolemma

Wave of depolarisation travels through the sarcoplasm in t-tubules to the sarcoplasmic reticulum which releases Ca2+ by facilitated diffusion

30
Q

What is myosin?

A

Thick fibrous protein with globular head (——o )

Many of these combine together with globular head facing out in all directions

—–o-
–o—-
——-o
o——
-

31
Q

What is actin?

A

Globular protein arranged into fibrous chains

Thin fibrous protein with another fibrous protein called tropomyosin wrapped around it

32
Q

What is the A band?

A

where myosin is present

33
Q

What is the I band?

A

Where ONLY actin is present

34
Q

What is the H zone?

A

Where ONLY myosin is present

35
Q

What is a neuromuscular junction?

A

The point where a motor neuron meets a skeletal muscle fibre

36
Q

What are the differences between cholinergic synapses and neuromuscular junctions?

A

Neuromuscular junction:
Only excitatory
Only motor neurons
Action potential ends here

Cholinergic synapse:
Excitatory or inhibitory
Motor, sensory or relay
Ach bind to receptor on post-synaptic membrane

37
Q

What is a slow-twitch muscle?

A

Endurance

Aerobic

Contracts slowly for longer
Fatigues slowly

High mitochondria density

38
Q

What is a fast-twitch muscle?

A

Burst of activity

Contacts quickly and relaxes rapidly

Low mitochondria density

High concentration of glycogen

Anaerobic

39
Q

What is the phosphocreatine system?

A

Relies on the phosphocreatine attaching a Pi to ADP very quickly, leaving ATP and creatine

Provides just a few seconds of energy suitable for very high intense exercie

40
Q

Where is excess creatine excreted?

A

In urine

Can be an indicator of kidney failure

41
Q

What is the process of muscle contraction?

A
  1. Tropomyosin protein is wrapped around the actin filament blocking the myosin binding sites
  2. Ca2+ released from sarcoplasmic reticulum causes change in shape of tropomyosin revealing the myosin binding sites
  3. Myosin head has an ADP and Pi attached to it which are released when it bind to the myosin binding site, forming an actin-myosin crossbridge
  4. Myosin head changes shape pulling the actin molecule along - power stroke
42
Q

What is the sarcomere?

A

Distance between adjacent z-lines

43
Q

What is tropomyosin?

A

Fibrous strand around the actin filament

44
Q

What is the sliding filament mechanism?

A

Actin and myosin filaments slide past each other

45
Q

What happens during muscle contraction?

A

I band becomes shorter

Z lines move closer to one another

H zone becomes shorter

A band doesn’t change as it’s determined by the length of mysoin

46
Q

What is the energy needed for during a muscle contraction?

A

Movement of myosin head

Reabsorption of Ca2+ in sarcoplasmic reticulum by active transport

46
Q

Why is the effects of drugs that stimulate the nervous system?

A

Create more action potentials

Mimicking neurotransmitter

Stimulating release of more neurotransmitter

Inhibiting enzyme that breaks down neurotransmitter

47
Q

How do endorphins affect sensory nerve pathways?

A

They block the sensation of pain

Drugs bind to specific receptors in the brain used by endorphins so mimic the effect of endorphins

48
Q

Why can damage to the myelin sheath cause problems controlling the contraction of muscles?

A

Action potential ‘leaks’ to adjacent neurons

So wrong muscle fibres contract

49
Q

How can hydrophobic molecules easily pass into neurons?

A

Lipid soluble so pass through phospholipid biplayer

50
Q

What is the process of muscle relaxation?

A
  1. ATP binds to myosin head causing myosin head to detach from the actin
  2. Myosin head contains ATPase that hydrolyses ATP into ADP and Pi
    Energy released returns the myosin head to its original position (recovery stroke)
  3. Sarcomere shortens: I-band and H-zone shorten, A-band remains same length
  4. Ca2+ are actively transported back into the sarcoplasmic reticulum and the muscle stops contracting
51
Q

What is the effect of myelination on the rate of conduction of an action potential?

A

Speed of conduction is slower with non-myelinated

No saltatory conduction

Axon potentials along axon, constant depolarisation

Myelin sheath as electrical insulator

Lack of Na+ and K+ gates in myelinated region

52
Q

How many milliseconds are in a second?

A

1000

53
Q

What are 2 reasons why an increased concentration of calcium ions inside the the cell could increase the contractility of the heart muscle?

A

More myosin heads revealed

Increase rate at which energy for muscle contraction is released as Ca2+ needed to activate ATP hydrolase

54
Q

What causes the thick and thin myofilaments to slide past each other when the myofibril contracts?

A

Myosin heads bind to actin molecules

Myosin heads bend pulling thin filament along the length of the thick filament

Myosin heads detach and re-attach further along thin filament

55
Q

Describe the role of calcium ions in the concentration of a sarcomere? [4]

A

Binding with tropomyosin causing active binding sites to be revealed

Allows myosin to bind to actin

Releasing ATP

Biology (25 decks)

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