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Module 204 MSK & Immune system > T2 L5 Physiology of skeletal muscle contraction > Flashcards

T2 L5 Physiology of skeletal muscle contraction Flashcards

1
Q

How many thin filaments are adjacent to 1 thick filament?

A

6

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2
Q

How many thick filaments are adjacent to 1 thin filament?

A

3

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3
Q

In the sarcomere, which bands become shorter during contraction?

A

H and I

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4
Q

What 3 proteins are on thin filaments?

A

F actin
Tropomyosin
Troponin

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5
Q

What ions travel across membrane during skeletal action potential?

A

Na+ goes in during depolarisation
k+ goes out during repolarisation
Ca2+ goes in during depolarisation

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6
Q

What process connects action potential to muscle contraction?

A

Excitation-contraction coupling

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7
Q

What microscopic structures anchor the thick and thin filaments?

A

Thick filaments are anchored by M band (minor proteins of thick filament)
Thin filaments are anchored to Z disc

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8
Q

What happens when calcium binds to troponin C?

A

Troponin C changes conformation which shuts off troponin I. Tropomyosin-troponin leaves F-actin groove which unmasks myosin binding site on actin

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9
Q

What is troponin C?

A

Calcium binding

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10
Q

What is troponin I?

A

Inhibitory

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11
Q

What is the marker for muscle breakdown?

A

Total troponin I

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12
Q

What is the marker for myocardial infarct?

A

Cardiac troponin I

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13
Q

What is cross-bridge cycling?

A

Molecular cycle of actin-myosin interaction

Mechanism of control at molecular level

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14
Q

What is F-actin?

A

Filamentous actin

Long polymer chain of actin

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15
Q

What is G-actin?

A

Globular actin

Single subunit

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16
Q

What are the 4 steps of cross bridge cycling?

A

1) Myosin releases actin
2) Myosin head cleaves ATP
3) Myosin binds actin
4) Power stroke

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17
Q

What is the effect of increased overlap of thin and thick filaments?

A

Increased force

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18
Q

Describe the creatine found in muscle fibres

A

Small, organic, nitrogen-containing molecule

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19
Q

What happens when creatine accepts high energy phosphate bonds from ATP?

A

Phosphorylated to creatine phosphate which stores energy in muscle

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20
Q

Why can’t energy be stored as excess ATP?

A

The ATP levels must be kept stable

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21
Q

What is creatine phosphokinase?

A

Also known as creatine kinase
Enzyme that adds a phosphate to creatine
Plasma marker of muscle destruction
Large molecule detected by antibodies

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22
Q

What is creatinine?

A

Breakdown of creatine - marker of kidney function

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23
Q

What are the 2 calcium gradients involved in contraction?

A

Extracellular vs cytosolic free Ca2+

Sarcoplasmic reticulum vs cytosolic free Ca2+

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24
Q

What is excitation contraction (EC) coupling?

A

Molecular mechanism for how depolarisation of plasma membrane leads to release of Ca2+ into cytoplasm following contraction

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25
Describe the ryanodine receptor (RyR)
In sarcoplasmic reticulum membrane Releases calcium from sarcoplasmic reticulum RyR channels in terminal cistern of SR are in contact with L-type calcium channels in T-tubule membranes
26
What triggers the release of calcium through RyR?
Voltage sensor on Ca2+ channel
27
Describe SERCA
Smooth endoplasmic reticulum calcium ATPase In SR membrane Pumps Ca2+ back into sarcoplasmic reticulum using ATP
28
Describe L-type calcium channels
Most common calcium selective channel Voltage gated so opens when cell is depolarised In plasma membrane
29
Describe how tetany occurs
Single AP --> sufficient Ca2+ released from SR --> twitch Ca2+ pumped back into SR --> end of twitch Frequent APs --> time interval between APs is shortened --> insufficient Ca2+ re-sequestered --> summation of contraction
30
What are the 2 main types of muscle fibres?
Slow twitch - type 1 | Fast twitch - type 2
31
Describe slow twitch fibres
Red, oxidative, small diameter High myoglobin Many mitochondria Postural or weight bearing muscles
32
Describe fast twitch fibres
White, non oxidative, wide diameter Lower myoglobin Increased energy from glycolysis
33
What are the differences between the muscle fibre types?
Aerobic (slow), anaerobic (fast) Faster calcium re-uptake in fast twitch Maximum tension produced in fast twitch Fatigue resistance in slow twitch
34
What does the fibre type distribution depend on?
Muscle action
35
Describe the fibre type distribution in soleus muscle
80% type I (slow) | 20% type IIA
36
Describe the fibre type distribution in vastus lateralis
Mixture of type I, IIA, IIX
37
Describe the characteristics of type I fibres
``` Sub-name: slow-oxidative ATP generation: aerobic Contraction rate: slow Fatigue resistance: high Fibre diameter: small Myoglobin: high Mitochondria: many Capillaries: many Fuel for storage: triglycerides ```
38
Describe the characteristics of type IIA
``` Sub-name: fast oxidative-glyoclytic ATP generation: aerobic / anaerobic Contraction rate: fast Fatigue resistance: intermediate Fibre diameter: intermediate Myoglobin: high Mitochondria: many Capillaries: many Fuel for storage: creatine phosphate, glycogen ```
39
Describe the characteristics of type IIB (IIX) fibres
``` Sub-name: fast, glycolytic ATP generation: anaerobic Contraction rate: fastest Fatigue resistance: low Fibre diameter: high Myoglobin: low Mitochondria: few Capillaries: few Fuel for storage: creatine phosphate, glycogen ```
40
What are the 3 types of coordination?
Motor units Tetany Fusion of myocytes into long myofibres
41
What is a motor unit?
Single alpha motor neuron and all the muscle fibres it innervates
42
How many motor units in a peripheral muscle?
100-500
43
How many muscle fibres per motor unit in a biceps branch?
500
44
How many muscle fibres per motor unit in gastrocnemius?
2000
45
What is the percentage of slow twitch in gastrocnemius in sprinters?
25%
46
What is the percentage of slow twitch in gastrocnemius in marathoners?
93-99%
47
How many muscle fibres per motor unit in extrinsic eye muscles?
9
48
What determines the muscle fibre?
Type and function of lower motor neuron
49
What is isometric?
Generates variable force while length of muscle remains unchanged
50
What is isotonic?
Generates constant force while length of muscle changes
51
Describe the steps for picking up a glass
Stage 1 - isometric - force increases, joint doesn't move - muscle force < force of gravity --> force increases - biceps and brachioradialis generate force by isometric contractions as muscles haven't yet shortened Stage 2 - isotonic - force remains same, arm moves - glass moves upward in response to force - isotonic contraction starts as force generated by muscle exceeds gravitational and inertial forces keeping glass on table
52
What is concentric?
Force during contraction e.g. tossing a ball into air
53
What is eccentric?
negatives Force during muscle elongation Eg when braking or when weight of object is overwhelming such as when catching a ball
54
Describe the recruitment size principle
As initial isometric contraction occurs: - more motor units are recruited (start with smaller ones and progressively add larger ones) - allows fine gradation of force for small movements
55
Describe lower motor neurons
Signal starts in spinal cord and extends to effector muscles in periphery
56
Describe the signs of lower motor neuron disease
Weakness | Muscle atrophy
57
Describe upper motor neurons
Signal starts in brain and extends to spinal cord to synapse with lower motor neuron
58
Describe upper motor neuron disease
Inhibits normal inhibitory input to spinal interneurons | Spindle becomes oversensitive and attempts to contract muscle all the time
59
What are the signs of upper motor neuron disease?
Spasticity | hypertonia
60
What does the stretch reflex do?
Controls muscle length | Increases muscle force
61
What is Westphal's sign and what causes it?
``` Lack of patellar reflex Damage to: - femoral nerve - receptor damage - peripheral nerve disease e.g. peripheral neuropathy -cerebellar damage ```
62
Describe sensory intrafusal fibres
Skeletal muscle fibres that serve as specialised sensory organs (proprioceptors) that detect amount and rate of change in length of muscle Constitute muscle spindle and don't generate contractile force associated with muscles
63
Describe contraction extrafusal fibres
Skeletal muscle fibres innervated by alpha motor neurons Generate tension by contracting which allows skeletal movement Attached to bone by fibrous tissue extensions
64
What is the function of the patellar reflex?
Posture and balance
65
What spinal cord level does flexion for patellar reflex occur?
L4
66
Describe a muscle spindle
Consists of 3-12 intrafusal fibres | Gamma motor neurons to increase sensitivity
67
Describe gamma motor neurons
Drive contraction of edge of intrafusal fibres Sensory from muscle spindle: - type 1a and type 2 - wrap around intrafusal fibre - detect stretch of central non-contracting region using stretch receptors
68
What is the function of the tendon reflex?
Prevents overloading Decreases muscle force to drop load - sensor fires to decrease contraction
69
Describe the steps of the Golgi tendon reflex
1) Neuron from Golgi tendon organ fires 2) Motor neuron is inhibited 3) Muscle relaxes 4) Load is dropped

Module 204 MSK & Immune system (44 decks)

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