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Biology > M6 - Muscles > Flashcards

M6 - Muscles Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

How does an action potential pass along a neurone?

A

Depolarisation of axon membrane with Na+ establishes local currents.

This opens Na+ gates of adjoining region. Adjoining region depolarises.

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2
Q

Describe what happens at a neuromuscular junction.

A
  1. AP arrives causing the uptake of Ca2+ ions. Vesicles containing ACh fuse with a presynaptic membrane and release ACh into the synaptic cleft.
  2. ACh binds to receptors on the sarcolemma. Na+ channels open and Na+ moves in. Membrane is depolarised - this spreads across the membrane.
  3. Depolarisation of sarcolemma spreads down T-tubule.
  4. Ca2+ channels open and Ca2+ diffuse out of sarcoplasmic reticulum (equivalent to SER).
  5. Ca2+ binds to protein in the muscle fibre which triggers contraction.
  6. ACh in synaptic cleft is rapidly broken down by acetylcholinesterase so contraction only occurs when impulses arrive continuously.
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3
Q

Compare synapses to neuromuscular junctions.

A

SYNAPSE
- preS neurone to postS neurone
- postsynaptic stimulation leads to AP in postS neurone.
- synaptic knob appears smooth and rounded
- excitatory or inhibitory
- motor, sensory and intermediate neurones

NEUROMUSCULAR JUNCTION
- motor neurone to sarcomere.
- postsynapstic stimulation leads to depolarisation of sarcolemma.
- end plate appears like microvilli and is flattened up to muscle fibre.
- only excitatory
- only involved motor neurones

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4
Q

The brain controls the _______ of each contraction because many neurones stimulate a single ______ _______.

Each one branches to neuromuscular junctions, causing the contraction of a cluster of _____ cells - known as a ______ ______.

The more stimulated the greater the _______ of contraction. This is known as a _________ of ________.

A

strength
muscle fibre

muscle
motor unit

force
graduation of response

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5
Q

What are the 3 types of muscle?

A

Smooth, skeletal and cardiac

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6
Q

Describe skeletal muscles.

A

Can be moved voluntarily and are connected to bones by tendons. Exerts its force via tendons to move bones around points called joints.

Work in antagonistic pairs - one contracts and the other relaxes.
Contracting muscle = agonist
Relaxing muscle = antagonist

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7
Q

Explain the advantage of muscles being organised in antagonistic pairs.

A

Muscle can only contract/pull.

As one muscle contracts the other relaxes.

1st muscle moves arm up, the 2nd muscle required to reverse movement.

Maintenance of posture requires contraction of both muscles.

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8
Q

Describe fast twitch muscle fibres.

A

Fast speed of contraction
More powerful
Short length of contraction time
Good for intense bursts of activity
White in colour.
Energy from anaerobic respiration.

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9
Q

How are fast twitch muscle fibres adapted to anaerobic respiration?

A
  • thicker filaments
  • higher conc of glycogen
  • higher conc of enzymes involved in anaerobic respiration (lactase dehydrogenase)
  • high levels of phosphocreatine that generates ATP from ADP in anaerobic conditions
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10
Q

Describe slow twitch muscle fibres.

A

Slow speed of contraction.
Less powerful
Long length of contraction time
Good for maintaining body position
Red in colour
Energy from aerobic respiration

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11
Q

How are slow twitch muscle fibres adapted to aerobic respiration?

A
  • large stores of myoglobin
  • rich supply of blood vessels
  • many mitochondria
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12
Q

What are skeletal muscles made out of?

A

Myofilaments (protein structures) –> myofibrils (organelle) –> muscle fibre (cell) –> muscle fibre bundle –> muscle

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13
Q

How are skeletal muscles made?

A

Skeletal muscles are made up of bundles of thousands of elongated cells (called muscle fibres).

They are bound together by connective tissue containing blood vessels and nerves. Muscle fibres form via the fusion of muscle cells forming long cylindrical cells that are highly specialised to perform their function.

These cells form muscle fibre bundles.

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14
Q

What does each muscle fibre contain?

A

Sarcolemma - muscle fibre membrane
Sarcoplasm
Multiple Nuclei
Many mitochondria

Transverse tubules - bits of sarcolemma that fold inwards across muscle fibre and help spread electrical impulses throughout sarcoplasm.

Sarcoplasmic Reticulum - a network of internal membranes that store and release Ca2+ ions.

Myofibrils - structures containing actin and myosin.

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15
Q

What is skeletal muscle also known as and why?

A

Striated muscle
- because muscle fibres show a pattern of cross-banding (under light microscope)

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16
Q

Under an ______ microscope, we can see that myofibrils contain thin and thick __________ that move past each other when the muscle contracts.

Thick filaments = _______
Thin filaments = _______

A

electron
myofilaments

Myosin
Actin

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17
Q

Describe Myosin

A

Consists of long rod-shaped tails (fibrous protein) with bulbous heads (globular protein) that project to the side.

Thick filaments are made up of many myosin molecules.

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18
Q

Describe Actin.

A

Actin molecules joined end to end and are thinner than myosin.

Thin filaments consist of 2 strands of actin molecules twisted around each other and associate with tropomyosin forming fibrous strands.

19
Q

Describe the bands in muscle fibre and what they are made of.

A

Dark bands: A bands - myosin and actin filaments overlap.

Light bands: I bands - thin actin filaments only

H zone : only thick myosin filaments

Z line found in the middle of I bands.

Sarcomere = one Z line to the next.

20
Q

What is the Sliding Filament Theory?

A

Suggests that actin and myosin filaments slide past each other to contract the sarcomere.
I band narrows, sarcomere shortens, H band becomes narrow, A band remains the same.

21
Q

Where does Ca2+ ions come from in muscle contraction?

A

The sarcoplasmic reticulum.

22
Q

What does Phosphocreatine do?

A

Releases phosphate group and becomes creatine - catalysed by creatine Kinase.

Phosphate group added to ADP to make instant (but small) supply of ATP.

23
Q

Describe the contraction of muscle cycle at a molecular level (Sliding Filament theory).

A
  1. Ca2+ binds to troponin causing myosin binding sites to be exposed.
  2. ADP binds to myosin head
  3. This causes the formation of a cross-bridge between myosin head and actin molecule (only when myosin binding sites are exposed).
  4. Once myosin head attaches it changes its angle, pulling actin filament along and releasing ADP molecule.
  5. ATP binds to myosin head causing detachment from actin filament.
  6. ATP hydrolase enzyme is activated by Ca2+ and the energy from ATP hydrolysis provides energy for myosin to return to original shape.
24
Q

Describe muscle relaxation.

A

NS stimulation ceases and Ca2+ are actively transported back into the sarcoplasmic reticulum.
Ca2+ conc decrease causes tropomyosin to block myosin binding sites on actin filaments.
Myosin heads unable to bind to actin filaments and muscle relaxes.

(Troponin promotes muscle contraction, while tropomyosin blocks muscle contraction)

25
Q

What is Homeostasis?

A

The maintenance of a constant internal environment.

26
Q

What is negative feedback?

What is positive feedback?

A

NF: A response to a change that reverses the change (brings back to normal).

PF: When feedback causes the corrective measures to remain switched on, causing further deviation from the original level (e.g. labour-oxytocin).

27
Q

What is the advantage of having separate negative feedback mechanisms to control deviations away from normal values?

A

Gives a greater degree of homeostatic control.

28
Q

How is too high or low temperature controlled?

A

Too high:
- vasodilation
- sweating - (H2O has high LHV)

Too low:
- vasoconstriction
- shivering (respiration)

29
Q

How is low pH controlled?

A

Increased heart rate and breathing rate - removes CO2.

30
Q

What is the summary of when a parameter falls?

A

Parameter falls
Receptor Detects
Effector Responds
Parameter Rises
Regulated Parameter

31
Q

The heart stimulates its own contraction. What is this called?

A

Myogenic

32
Q

What is the equation from A1 of cardiac output?

A

Cardiac output = stroke vol x heart rate (bpm)

33
Q

What generates the first electrical impulse in a heart beat?
Where is it located? What does it cause?

A

Sino-atrial node (SAN)
- group of cells in wall of right atrium
- causes atrial systole

34
Q

What generates the second electrical signal in a heart beat?
Where is it located? What does it cause?

A

Atrio-ventricular node (AVN)
- group of cells between the atria
- causes ventricular systole

35
Q

How is the contraction of the ventricles stimulated?

A

AVN impulses pass down the septum between the ventricles and down mucle fibres called bundle of His.

Fibres divide into 2 branches called purkyne tissue.

36
Q

What causes the delay in electrical signals and what does it allow?

A

Electrical signals cannot pass directly from atria to ventricles, so SAN stimulates separate signal.

This allows atria to empty completely before ventricles contract.

37
Q

Describe how the cardiac cycle is controlled by the SAN and AVN - 6 marks.

A

1) SAN initiates impulse
2) SAN sends impulse across atria causing atrial contraction - atrial systole.
3) AVN delays impulse…
4) …allowing atria to empty before ventricles contract
5) AVN sends impulse down Bundle of His and Purkyne fibres
6) Causing ventricles to contract from base up - ventricular systole

38
Q

What does the sympathetic and Parasympathetic nervous system do?

A

SYMPATHETIC
- generally stimulates effectors so speeds up activity.
- heightens awareness and prepares for activity (fight and flight).

PARASYMPATHETIC
- generally inhibits effectors so slows down activity
- involved with conserving energy and maintaining resting conditions.

39
Q

Where is the cardiovascular centre? What is it connected to and how?

A

In the Medulla (oblongata)

Connected to the SAN via the accelerator nerve and vagus nerve.

40
Q

What does the accelerator nerve do?

A

Part of the sympathetic NS.

When stimulated, releases neurotransmitter at the SAN to increase heart rate.

Numerous sympathetic nerves also link to the walls of the ventricles to increase the force of contraction of these chambers.

41
Q

What does the Vagus Nerve do?

A

Part of the parasympathetic NS.

When stimulated, releases neurotransmitter at the SAN to decrease heart rate.

42
Q

What does the cardiovascular centre do?

A

Receives information from receptors about:
- blood pH (chemoreceptors in carotid arteries)
- blood pressure (stretch receptors in wall of carotid arteries)

43
Q

How do chemoreceptors control heart rate?

A

Increased respiration increases CO2 conc in blood, lowering the pH.

Chemoreceptors in the carotid arteries increase the frequency of impulses to the medulla.

The cardiac centre in the medulla increases frequency of impulses to the SAN via the sympathetic NS. This increases the heart rate, increasing blood flow, removing CO2 faster and returning CO2 conc and pH to normal.

Chemoreceptors in the carotid arteries decrease the frequency of impulses to the SAN node - reducing HR.

44
Q

How do pressure receptors control HR.

A

When blood pressure is high, pressure receptors transmit more nervous impulses to the part of the medulla that decreases HR. This then sends impulses via the parasympathetic NS to the SAN of the heart which lead to a decrease in HR.

When blood pressure low, pressure receptors transmit more impulses to the apart of medulla that increases HR. This then sends impulses via the sympathetic NS to the SAN of the heart, increasing HR.

Biology (17 decks)

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