MEC322: Muscle system Flashcards
Name the three muscle types
cardiac, smooth and skeletal
Which is the most abundant muscle type?
skeletal
40-45% of total weight
more than 430 pairs of skeletal muscle
Where will you find skeletal muscles?
attached to bones or for some facial muscles to skin
Where will you find cardiac muscles?
walls of the heart
Where will you find smooth muscles?
mostly in walls of hollow visceral organs (other than heart)
Describe the shape of skeletal muscle
single, very long, cylindrical, multinucleate cells with very obvious striations
Describe the shape of cardiac muscle
branching chains of cells, uninucleate, striations, intercalated discs
Describe the shape of visceral muscle
single, fusiform, uninucleate, no striations
What are the five key functions of muscles?
producing body movements stabilizing body positions regulating organ volume moving substances within the body producing heat
What is a tendon?
extensions of connective tissue beyond muscle fibers that attach muscle to bone
What are skeletal muscles well supplied with?
nerves and blood vessels, which provide nutrients and oxygen for contraction
Skeletal muscles are separate organs made up of….
muscles fiber (cell)
What does each muscle fiber contain?
myofibrils that contain thin filament and thick filament
What are the filaments in the myofibrils arranged in?
sarcomeres
What do thick filaments in myofibril composed of?
mysoin
What do thin filaments in myofibril composed of?
actin, tropomyosin and troponin
How are sarcomeres separated from each other?
zig-zagging zones of dense protein material called z discs
What is an A band?
within each sarcomere a darker area called an a band extends the entire length of the thick filament
What is at the centre of each a band?
h zone, which contains only the thick filaments
Describe the i band
lighter coloured area either side of the a band contains the rest of the thin filament
what is the contraction cycle?
Repeating sequence that causes sliding of filaments
Describe the contraction cycle
Splitting ATP – myosin ATPase splits ATP and becomes energized
Forming cross-bridges – the myosin head attaches to actin, forming a cross-bridge
Power stroke – the cross-bridge generates force as it swivels or rotates toward the center of the sarcomere
Binding ATP & detaching – myosin detaches from actin. The myosin head again splits ATP, returns to its original position, and binds to a new site on actin as the cycle continues
What is the sliding filament mechanism of muscle contraction?
the sliding of filaments and shortening of sarcomeres that cause the shortening of muscle fibers.
What is ATP?
ATP (adenosine triphosphate) is the energy-carrying molecule used in cells because it can release energy very quickly.
What is needed for muscle contraction?
Ca2+ and energy in the form of ATP
What must happen before a skeletal muscle fibre can contract?
It must be stimulated by an electrical signal called a muscle action potential delivered by its neuron called a motor neuron.
What is a motor unit?
A single motor neuron along with all the muscle fibres it stimulates
What is the neuromuscular junction (NMJ)?
the synapse between a motor neuron and a skeletal muscle fiber.
What does the neuromuscular junction (NMJ) include?
the axon terminals, synaptic end bulbs of a motor neuron and the adjacent motor end plate of the muscle fiber sarcolemma.
How does a motor neuron excite a skeletal muscle fiber at the NMJ?
- acetylcholine (ACh) release from synaptic vesicles
- ACh diffuses across synaptic cleft
- binds to ACh receptors
- muscle action potential initiated
- the flow of Na+ generates .a muscle action potential
- breakdown of ACh by enzyme called acetylcholinesterase
What is a record of a contraction called?
myogram
consists of latent period, contraction period and relaxation period
What is wave summation?
the increased strength of a contraction that occurs when a second stimulus arrives before the muscle has completely relaxed
What can repeated stimuli produce?
unfused (incomplete) tetanus
What can rapid repeated stimuli produce?
fused (complete) tetanus
What is motor unit recruitment?
the process of increasing the number of active motor units
What increases force potential?
synchronisation
large number of fibres in motor units
type IIA and IIB
Which type of motor unit decrease force potential?
Type I
What are the three types of skeletal muscle fibres?
slow oxidative (SO) fibers, fast oxidative-glycolytic (FOG) fibers, fast glycolytic (FG) fibers
Which fibre do most skeletal muscle contain?
most contain a mixture of all three fibres in varying proportions
fibre type distribution is genetically determined
what is the order the motor units of a muscle are recruited?
first SO fibers,
then FOG fibers,
and finally FG fibers.
What is type I muscles fibre?
slow oxidative (SO) fibers
What is type IIA muscles fibre?
fast oxidative-glycolytic (FOG) fibers
What is type IIB muscles fibre?
fast glycolytic (FG) fibers
When do sarcomeres produce maximal tension?
when thick and thin filaments overlap 100-120%
What are muscles designed to do?
Optimise the force produced during contraction through sarcomere contraction
What happens when a sarcomere is stretched too far?
Force reduced due to insufficient overlap of myofibrils
What happens when the muscle is over contracted?
force reduce as potential for further contraction reduced
What must the force of contraction for the whole muscle account for?
active (contractile) and passive (series and parallel elastic elements) components
What is isometric contraction?
muscle contracts but does not shorten (held at position)
often used for measurements as safer to conduct
What is concentric contraction?
shortening
What is eccentric contraction?
lengthening
Is the force greater during eccentric or concentric contraction?
eccentric
Greater concentric velocity…..
smaller the force
When can the largest force be applied?
fastest eccentric motion
Why are fibres in fusiform muscle parallel to the long axis of the muscle?
advantage for length of contraction
What does fusiform mean?
Fusiform means having a spindle-like shape that is wide in the middle and tapers at both ends (think long lemon)
How are fibres arranged in pennate muscle?
Fibers arranged obliquely to long axis of muscle
uni-, bi-, and multi-
How is the arrangement of pennate fibres advantageous?
advantage for force of contraction
Which fibre arrangement tends to have a larger physiological cross-sectional area?
pennate
What is the force of muscle contraction proportional to?
physiological cross-sectional area
What is the velocity and excursion of muscle proportional to?
length of myofibril
