Flashcards in Chapter 1 Deck (82):
Name and describe the 3 types of muscle tissue.
- Smooth muscle: involuntary, hollow organs
- Cardiac muscle: involuntary, heart
- Skeletal muscle: voluntary, skeleton
The entire muscle is surrounded by _____ and consists of many bundles called _____.
Fasciculi is surrounded by ______ and consists of individual muscle cells called _____.
- muscle fibres
Muscle fiber is surrounded by ______ and consists of ______.
- myofibrils divided into sarcomeres
Name the 5 parts of muscle fibres.
- satellite cells
- transverse tubules (t tubules)
- sarcoplasmic reticulum (SR)
Describe the plasmalemma (cell membrane).
- Fuses with tendon
- Conducts action potential
- Maintains pH, transports nutrients
Describe satellite cells.
- Muscle growth, development
- Response to injury, immobilization, training
Describe the sarcoplasm.
- Cytoplasm of muscle cell
- Unique features: glycogen storage, myoglobin
Describe t tubules.
- Extensions of plasmalemma
- Carry action potential deep into muscle fiber
Describe the SR.
- Muscle --> fasciculi --> muscle fiber --> myofibril
- Hundreds to thousands per muscle fiber
- Basic contractile element of skeletal muscle
- End to end for full myofibril length
Myosin is _____ filament.
What does myosin look like?
Two intertwined filaments with globular heads
Describe the globular heads on myosin.
- Protrude 360° from thick filament axis
- Will interact with actin filaments for contraction
Myosin is stabilized by _____.
Actin is ______ filament.
Actin is composed of 3 proteins. Name and describe them.
- Actin: contains myosin-binding site
- Tropomyosin: covers active site at rest
- Troponin: anchored to actin, moves tropomyosin
Actin is anchored at ______.
Actin is equally spaced out by ______.
_____ _____ innervate muscle fibres.
A motor unit consists of:
Single α-motor neuron + all fibers it innervates
More operating motor units =
more contractile force
What is the neuromuscular junction?
Site of communication between neuron and muscle
What does the neuromuscular junction consist of?
synapse between α-motor neuron and muscle fiber
Name and describe the steps in muscle fibre contraction: excitation-contraction coupling.
1. Action potential (AP) starts in brain
2. AP arrives at axon terminal, releases acetylcholine (ACh)
3. ACh crosses synapse, binds to ACh receptors on plasmalemma
4. AP travels down plasmalemma, T-tubules
5. Triggers Ca2+ release from sarcoplasmic reticulum (SR)
6. Ca2+ enables actin-myosin contraction
The sliding filament theory is a process of ...
Describe what is happening during the relaxed state of the sliding filament theory.
- No actin-myosin interaction at binding site
- Myofilaments overlap a little
Describe what is happening during the contracted state of the sliding filament theory.
- Myosin head pulls actin toward sarcomere center (power stroke)
- Filaments slide past each other
- Sarcomeres, myofibrils, muscle fiber all shorten
Describe what is happening after the power stroke ends in the sliding filament theory.
- Myosin detaches from active site
- Myosin head rotates back to original position
- Myosin attaches to another active site farther down
The sliding filament theory process continues until:
- Z-disk reaches myosin filaments or
- AP stops, Ca2+ gets pumped back into SR
Energy for muscle contraction comes from:
Adenosine triphosphate (ATP)
ATP binds to ______ for muscle contraction.
- Binds to myosin head
- ATPase on myosin head
ADP + Pi + energy
When does muscle relaxation occur?
AP ends, electrical stimulation of SR stops
What happens to Ca2+ during muscle relaxation?
- Ca2+ pumped back into SR
- Stored until next AP arrives
- Requires ATP
Without Ca2+, what happens to troponin and tropomyosin?
- returns to resting conformation
- Covers myosin-binding site
- Prevents actin-myosin cross-bridging
The average muscle consists of roughly ___% of type I fibres
For type I muscle fibres, peak tension is in _____ ms.
- 110 ms
- slow twitch
The average muscle consists of roughly ___% of type IIa fibres
The average muscle consists of roughly ___% of type IIx fibres
For type II muscle fibres, peak tension is in ____ ms.
- 50 ms
- fast twitch
What are the 5 ways in that type I muscle fibres differ from type II muscle fibres?
- speed of myosin ATPase varies
- muscle biopsy
- gel electrophoresis
- motor units
Describe how the speed of myosin ATPase varies between type I and type II muscle fibres.
- Fast myosin ATPase = fast contraction cycling
- Slower myosin ATPase = slower contraction cycling
Describe how muscle biopsy can be used to tell the difference between type I and type II muscle fibres.
- Small (10-100 g) piece of muscle removed
- Frozen, sliced, examined under microscope
Describe how gel electrophoresis can be used to tell the difference between type I and type II muscle fibres.
- Type I versus II fibers have different types of myosin
- Separates different types of myosin by size
Describe how the SR is different between type I and type II muscle fibres.
- Type II fibers have a more highly developed SR
- Faster Ca2+ release, 3 to 5 times faster Vo
Describe how motor units differ between type I and type II muscle fibres.
- Type I motor unit: smaller neuron, <300 fibers
- Type II motor unit: larger neuron, >300 fibers
Describe the following for type I muscle fibres: oxidative capacity, glycolytic capacity, contractile speed, fatigue resistance, motor unit strength.
- oxidative capacity: high
- glycolytic capacity: low
- contractile speed: slow
- fatigue resistance: high
- motor unit strength: low
Describe the following for type IIa muscle fibres: oxidative capacity, glycolytic capacity, contractile speed, fatigue resistance, motor unit strength.
- oxidative capacity: moderately high
- glycolytic capacity: high
- contractile speed: fast
- fatigue resistance: moderate
- motor unit strength: high
Describe the following for type IIx muscle fibres: oxidative capacity, glycolytic capacity, contractile speed, fatigue resistance, motor unit strength.
- oxidative capacity: low
- glycolytic capacity: highest
- contractile speed: fast
- fatigue resistance: low
- motor unit strength: high
Describe the distribution of fibre types (type I : type II ratios).
- Each person has different ratios
- Arm and leg ratios are similar in one person
- Soleus: type I in everyone
Endurance athletes predominantly have what muscle fibre type?
Power athletes predominantly have what muscle fibre type?
Describe the following for type I muscle fibres: fibres per motor neuron, motor neuron size, motor neuron conduction velocity, contraction speed (ms), type of myosin ATPase, SR development.
- fibres per motor neuron: < or equal to 300
- motor neuron size: smaller
- motor neuron conduction velocity: slower
- contraction speed (ms): 110
- type of myosin ATPase: slow
- SR development: low
Describe the following for type II muscle fibres: fibres per motor neuron, motor neuron size, motor neuron conduction velocity, contraction speed (ms), type of myosin ATPase, SR development.
- fibres per motor neuron: > or equal to 300
- motor neuron size: larger
- motor neuron conduction velocity: faster
- contraction speed (ms): 50
- type of myosin ATPase: fast
- SR development: high
Describe type I fibres during exercise.
- high aerobic endurance
- efficiently produce ATP from fat, carbohydrate
Type I fibres have high aerobic endurance, meaning:
- Can maintain exercise for prolonged periods
- Require oxygen for ATP production
- Low-intensity aerobic exercise, daily activities
Describe type II fibres in general during exercise.
- Poor aerobic endurance, fatigue quickly
- Produce ATP anaerobically
Describe type IIa fibres during exercise.
- More force, faster fatigue than type I
- Short, high-intensity endurance events (1,600 m run)
Describe type IIx fibres during exercise.
- Seldom used for everyday activities
- Short, explosive sprints (100 m)
Name 3 fibre type determinants.
- genetic factors
- training factors
Describe how genetic factors can influence fibre type determinants.
- Determine which α-motor neurons innervate fibers
- Fibers differentiate based on α-motor neuron
Describe how training factors can influence fibre type determinants.
- Endurance versus strength training, detraining
- Can induce small (10%) change in fiber type
Describe how aging can influence fibre type determinants.
muscles lose type II motor units
Muscle fibre recruitment is also called ...
motor unit recruitment
Less force production means...
fewer or smaller motor units
More force production means...
more or larger motor units
Type ___ motor units smaller than type _____.
type I smaller than type II
What is the recruitment order for muscle fibre types?
- Smallest (type I) motor units recruited first
- Midsized (type IIa) motor units recruited next
- Largest (type IIx) motor units recruited last
What is the size principle?
order of recruitment of motor units directly related to size of α-motor neuron
Name factors (other than muscle fibre type) that can be a predictor of success.
- cardiovascular function
- training habits
- muscle size
Name the 2 types of muscle contraction.
- static (isometric contraction)
- dynamic contraction
Describe static (isometric) contraction.
- Muscle produces force but does not change length
- Joint angle does not change
- Myosin cross-bridges form and recycle, no sliding
Describe dynamic contraction.
- Muscle produces force and changes length
- Joint movement produced
What are the 2 subtypes of dynamic contraction?
- concentric contraction
- eccentric contraction
Describe concentric contraction.
- Muscle shortens while producing force
- Most familiar type of contraction
- Sarcomere shortens, filaments slide toward center
Describe eccentric contraction.
- Muscle lengthens while producing force
- Cross-bridges form but sarcomere lengthens
- Example: lowering heavy weight
Describe the generation of force in different types of motor units.
- type I motor units: less force
- type II motor units: more force
What are the 3 words used to describe the frequency of stimulation (rate coding)? Describe them.
- twitch: 1 stimulation
- summation: 3 stimuli
- tetanus: continual stimulation
Describe the length-tension relationship.
- Optimal sarcomere length = optimal overlap
- Too short or too stretched = little or no force develops