Chapter 1 Flashcards
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 _____.
- epimysium
- fasciculi
Fasciculi is surrounded by ______ and consists of individual muscle cells called _____.
- perimysium
- muscle fibres
Muscle fiber is surrounded by ______ and consists of ______.
- endomysium
- myofibrils divided into sarcomeres
Name the 5 parts of muscle fibres.
- plasmalemma
- satellite cells
- sarcoplasm
- 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.
Ca2+ storage
Describe myofibrils.
- Muscle –> fasciculi –> muscle fiber –> myofibril
- Hundreds to thousands per muscle fiber
Describe sarcomeres.
- Basic contractile element of skeletal muscle
- End to end for full myofibril length
Myosin is _____ filament.
thick
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 _____.
titin
Actin is ______ filament.
thin
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 ______.
Z-disk
Actin is equally spaced out by ______.
titin
_____ _____ innervate muscle fibres.
α-motor neurons
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.
- Action potential (AP) starts in brain
- AP arrives at axon terminal, releases acetylcholine (ACh)
- ACh crosses synapse, binds to ACh receptors on plasmalemma
- AP travels down plasmalemma, T-tubules
- Triggers Ca2+ release from sarcoplasmic reticulum (SR)
- Ca2+ enables actin-myosin contraction
The sliding filament theory is a process of …
actin-myosin contraction
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
ATP =
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
50%
For type I muscle fibres, peak tension is in _____ ms.
- 110 ms
- slow twitch
The average muscle consists of roughly ___% of type IIa fibres
25%
The average muscle consists of roughly ___% of type IIx fibres
25%
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
- SR
- 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?
type I
Power athletes predominantly have what muscle fibre type?
type II
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
- aging
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
- motivation
- 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
Describe the speed-force relationship.
- Concentric: maximal force development decreases at higher speeds
- Eccentric: maximal force development increases at higher speeds
