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Anatomy - BPT04 > Muscle physiology > Flashcards

Muscle physiology Flashcards

1
Q

Extensibility

A

Ability to be able to stretch without sustaining damage.

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2
Q

Excitability

A

Muscle responds to stimulus by producing electrical signal.

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3
Q

Elasticity

A

Able to return to it’s original shape.

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4
Q

Conductivity

A

Muscles ability to be able to propagate(spread and promote) signals. Electrical signals will have to be transmitted at different levels.

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5
Q

Contractility

A

Muscles ability to shorten, thicken, thus producing force, in response to a specific stimulus.

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6
Q

How do striations appear on skeletal muscles?

A

Skeletal muscle fibers have A-bands(dark) and I-bands(light).
One A-band in the middle and an I-band on each side.

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7
Q

Sarcomere

A

Consists of an A-band and half an I-band on each side.
In the middle of an A-band is H-zone, in the middle of H-zone is M-line.
In the middle of an I-band is Z-disc.
Sarcomere is from one Z-disc to another.

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8
Q

Triad

A

Consist of one T-tubule and a terminal cisternae on each side.

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9
Q

Terminal cisternae

A

Enlarged areas of the sarcoplasmic reticulum, on each side of T-tubules.
Store Ca2+ (calcium ions).

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10
Q

Sliding filament theory

A

The explanation for how muscles contract to produce force. Actin and myosin filaments within the sarcomeres of muscle fibers bind to create cross-bridges and slide past one another, creating a contraction.
9 steps.

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11
Q

Sliding filament theory - Step 1

A 
Nerve impulse (action potential) reaches the end of a motoneuron - Release of neurotransmitter Acetylcholine (ACh). 
Ca2+ needed for this, as for the contraction it self.
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12
Q

Sliding filament theory - Step 2

A

ACh diffuses across neurotransmitter junctions and binds to receptors on the motor endplate of the muscle fiber.

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13
Q

Sliding filament theory - Step 3

A

Stimulation of receptors initiates impulses that travel along sarcolemma, through T-tubules, to the sacs of the Sarcoplasmic reticulum.

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14
Q

What is the functional unit of skeletal muscles?

A

Sarcomere

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15
Q

Sliding filament theory - Step 4

A

Ca2+ is released from the SR into the sarcoplasm, where it binds to troponin molecules in the thin myofilaments.

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16
Q

Sliding filament theory - Step 5

A

Tropomyosin is displaced.

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17
Q

Sliding filament theory - Step 6

A

Actin’s active sites are exposed.

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18
Q

Sliding filament theory - Step 7

A

Myosin binds to actin forming cross bridges. Myosin pull actin towards the center (M-line) and release, binding to another actin further down.
1 action potential is needed for each myosin - actin bond.

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19
Q

Sliding filament theory - Step 8

A

This cycle repeats itself many times per second, as long as adenosine triphosphate (ATP) is available.

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20
Q

Sliding filament theory - Step 9.

A

As the filaments slide across each other the muscle shortens.

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21
Q

How are sodium(Na+) and potassium(K+) involved in muscle contractions?

A

When ACh binds to receptors in the sarcolemma, they open ion channels that allow passage of Na+ into the muscle and K+ out of the muscle. More Na+ enters the muscle, than K+ leaves which causes a depolarization.
Leading to an action potential in the sarcolemma.

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22
Q

Muscle metabolism

A
  • Direct phosphorylation
  • Anaerobic pathway
  • Aerobic pathway
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23
Q

Direct phosphorylation

A

Energy source: Creatine phosphate
Not producing a lot of energy.
15 second activity.
No oxygen use, 1 ATP.

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24
Q

Anaerobic pathway

A

Glycolysis, lactic acid fermentation.
Energy source: Glucose, no oxygen.
60-120 second activity.
2 ATP.

25
Q

Aerobic pathway

A

Cellular respiration. Oxygen required.
Energy source: Glucose, pyruvic acid, free fatty acids, amino acids.
32 ATP, CO2, H2O.
Hours of activity.

26
Q

Static stabilizers

A
  • Ligaments
  • Meniscus (in knee)
  • Capsules
  • Labrum (hip/shoulder, expands the articular surface for more
    stability)
27
Q

Dynamic stabilizers

A

When muscles contract they stabilize by proximating 2 bones.
Important in glenohumeral articulation.

28
Q

Motor neuron

A

Located in the spinal cord.
Activate the contraction of muscles.
Motoneurons release the neurotransmitter acetylcholine at a synapse called the neuromuscular junction.

29
Q

Muscle tension

A

Force exerted by a contracting muscle on an object.

30
Q

Muscle load

A

Opposing force exerted on the muscle by the weight of

the object to be moved.

31
Q

Motor unit

A

Functional unit of the neuromuscular system that allows the production of force and movement.
One motor unit consists of:
Alpha (α)-motor neuron and the muscle fibers it innervates.

32
Q

Alpha-motoneuron

A

Innervate skeletal muscle that will cause muscle contraction that will generate movement.
Clustered in the spinal cord or in the brainstem.

33
Q

3 Types of motor units

A

Slow
Large
Intermediate

34
Q

Slow motor units

A

Sustained, slow activity, prolonged time. Sustained muscular contractions. Standing upright.

35
Q

Large motor units

A

Fast fatigable.
Fast activity, a lot of force needed.
Fibers have sparse mitochondria and are easily fatigued.
Running, jumping.

36
Q

Intermediate motor units

A

Fast fatigue resistant.
Not as fast as fast fatigable MUs but generate twice the force of slow MUs.
Half as fatigable as large.

37
Q

Muscle twitch

A

A single action potential from a MN will produce a single contraction in the muscle fibers of its MU.
Muscle contraction is an accumulation of muscle twitches.
3 phases:
- Lag/Latent period
- Contraction phase
- Relaxation phase

38
Q

Lag/Latent period

A

Impulse initiated by the stimulation travels through sarcolemma and T tubules to the SR - release of Ca2+ into the sarcoplasm.

39
Q

Contraction phase

A

Cross bridge activity.

40
Q

Relaxation phase

A

Reentry of Ca2+ into the SR.

41
Q

Tetanus

A

Coordinated contractions of different motor units within the muscle organ. Sustained contraction.
Contraction exhibited by normal skeletal muscle organs most of the time.

42
Q

Fused (complete) Tetanus

A

High stimulation frequency.

43
Q

Unfused (incomplete) Tetanus

A

Low stimulation frequency.

44
Q

Size principle recruitment or Henneman principle

A

Not random.

Weakest motor units recruited first, than the stronger.

45
Q

Skeletal muscle fiber types

A

Slow twitch fibers (type 1)
Fast twitch fibers (type 2)
Intermediate fibers

46
Q

Slow twitch fibers (type 1)

A

Slow oxidative fibers: contract slowly but resistance to

fatigue.

47
Q

Fast twitch fibers (type II)

A

Fast glycolytic fibers: generate fast powerful contractions

but quickly fatigable.

48
Q

Intermediate fibers

A

Fast oxidative glycolytic fibers: characteristics of both fibers.
Will adapt to the body’s demand.

49
Q

Small motoneurons

A 
Muscle fibers innervation: Few
Thresholds: Low
Recruitment: First 
Force: Small
Smaller membrane surface area with fewer ion channels, larger input resistance.
50
Q

Why does orderly recruitment occur?

A

Ohm’s Law:
V (membrane voltage) = I (current) .R (resistance)
Small MNs: small amount of synaptic current will be sufficient to cause the membrane potential of a small motor neuron to reach firing threshold.
Large MNs: stays below threshold and when amount of current increases, the membrane potential of the larger MNs also increases, until it also reaches firing threshold.

51
Q

Large motoneurons

A 
Muscle fibers innervation: Many
Thresholds: High
Recruitment: Last 
Force: Great
Larger membrane surface and more ion channels,
smaller input resistance.
52
Q

What is a muscle contaction?

A

Bringing the insertion of a muscle towards it’s origin.

53
Q

Types of muscle activity

A

Dynamic: Contraction with limb movement. Three types:
- Concentric (isotonic)
- Eccentric (isotonic)
- Isokinetic
Static: Contraction with no limb movement. One type:
- Isometric

54
Q

Static/Isometric

A

Contraction with no limb movement.
Not changing length of muscle nor joint angle.
Not able to hold for a long time, f.ex. plank.
No change in load on joints, good for beginning of rehab.
Stabilize joint rather movement.
Pushing or pulling against immovable object.

55
Q

Isokinetic

A

Dynamic.
Contraction with movement of the limb at a constant speed.
Often used for strength assessment.
Sometimes called accommodating resistance exercise
because of the change in resistance given throughout a range of motion.
Used with great success in rehab of: ACL reconstruction, jumping capacity, osteoarthritis, muscle weakness caused by Parkinson’s.

56
Q

Concentric

A

Dynamic - Isotonic (contraction with movement of limb at varied speed).
Shortening of the muscle.
Initiates or accelerates movement and overcome some external resistance (gravity). Starting to walk, masticating, going up stairs.
Decreases the joint angle.

57
Q

Eccentric

A

Dynamic - Isotonic (contraction with movement of limb at varied speed).
Lengthening of the muscle.
Movement with gravity.
It exerts a braking action against a downward movement
and to maintain balance.
Causes delayed muscle soreness, believed to be bad for rehabilitation because of the pain related but that has been disproved.
Used in ACL reconstruction and Parkinson’s rehab.

58
Q

What are the different properties of skeletal muscle?

A 
Extensibility
Elasticity
Excitability 
Conductivity
Contractility

Anatomy - BPT04 (28 decks)

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