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Week 6 Lecture 2

Muscle System Part 1

What are the three muscle types? Cardiac, smooth & skeletal.
What is the most abundant tissue in the human body? Skeletal muscle (40-45% of total body weight).
How many pairs of skeletal muscle are there in the human body? More than 430 (most vigorous movement produced by 80 pairs).
What is the body location of skeletal muscle? Attached to bones, or for some facial muscles, to skin.
What is the body location of cardiac muscle? Walls of the heart.
What is the body location of smooth muscle? Mostly in the walls of hollow visceral organs (other than the heart).
What is the cell shape and appearance of skeletal muscle? Single, very long, cylindrical, multinucleate cells with very obvious striations.
What is the cell shape and appearance of cardiac muscle? Branching chains of cells; uninucleate, striations; intercalated discs.
What is the cell shape and appearance of smooth muscle? Single, fusiform, uninucleate; no striations.
What are the 5 key functions of muscular tissue? Producing body movements, stabilising body positions, regulating organ volume, moving substances within the body, & producing heat.
What are tendons? Extensions of connective tissue beyond muscle fibres that attach the muscle to bone.
Why are skeletal muscles well supplied with nerves and blood vessels? To provide nutrients and oxygen for contraction.
What are skeletal muscles composed of? Hundreds of thousand of cells called muscle fibres.
Why do muscle fibres get their name? Because of their elongated shape.
What do muscle fibres consist of? Each fibre contains myofibrils that contain thin filaments and thick filaments.
How are myofibril filaments arranged? In functional units called sarcomeres.
What are thick and thin myofibril filaments composed of? Thick filaments consist of myosin; thin filaments are composed of actin, tropomyosin, and troponin.
What separates sarcomeres? Zig-zagging zones of dense protein material called Z discs (Z line to Z line ~= 1.27-3.6 nano m in length).
What are A bands? A darker area within each sarcomere which extends the entire length of the thick filaments (myosin: 15nm in diameter).
What is the H zone? H zones are at the centre of the A band. It contains only the thick filaments. At both ends of the A band, surrounding the H zone, thick and thin filaments overlap.
What is the I band? A lighter-coloured area to either side of the A band that contains the rest of the thin filaments (actin: 5nm in diameter) but no thick filaments.
What is the contraction cycle? A repeating sequence of events that causes sliding of the filaments.
What are the four steps of the contraction (a.k.a cross-bridge) cycle)? 1) Splitting ATP 2) Forming cross-bridges 3) Power stroke 4) Binding ATP & detaching
Describe the first step of the cross-bridge cycle. Splitting ATP - myosin ATPase splits ATP and becomes energised.
Describe the second step of the cross-bridge cycle. Forming cross-bridges – the myosin head attaches to actin, forming a cross-bridge
Describe the third step of the cross-bridge cycle. Power stroke – the cross-bridge generates force as it swivels or rotates toward the center of the sarcomere.
Describe the fourth step of the cross-bridge cycle. 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? The sliding of filaments and shortening of sarcomeres that cause the shortening of muscle fibres.
What is needed for muscle contraction? Ca2+ and energy, in the form of ATP.
How do Ca2+ levels affect the contraction cycle? An increase in the level of Ca2+ in the sarcoplasm, caused by the muscle action potential, starts the contraction cycle; a decrease in the level of Ca2+ turns off the contraction cycle.
What is muscle action potential and how is it delivered? An electrical signal that stimulates a skeletal muscle fibre to contract. It is delivered by a 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 fibre. It includes the axon terminals and synaptic end bulbs of a motor neuron plus the adjacent motor end plate of the muscle fibre sarcolemma.
Describe the process of contraction and relaxation of a skeletal muscle (pt 1). At the NMJ, a motor neuron excites a skeletal muscle fiber in the following way: Release of acetylcholine (ACh) from synaptic vesicles. ACh diffuses across the synaptic cleft and binds to ACh receptors, initiating a muscle action potential.
Describe the process of contraction and relaxation of a skeletal muscle (pt 2). Generation of muscle action potential. The inflow of Na+ (down its concentration gradient) generates a muscle action potential. Breakdown of ACh by an enzyme called acetylcholinesterase.
What is a myogram? A record of contraction. It consists of a latent period, a contraction period, and a 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 after a previous stimulus.
What is the effect of repeated stimuli and rapidly repeating stimuli on muscle tension? Repeated stimuli can cause unfused (incomplete) tetanus. More rapidly repeating stimuli will produce fused (complete) tetanus.
What is motor unit recruitment? The process of increasing the number of active motor units.
What is synchronisation and what is the effect on force generation? Synchronisation is when there are a number of motor units active at one time. More synchronisation -> higher force potential.
What is the effect of the size of motor units on force generation? Motor units with a larger number of fibres have greater force potential.
What is the effect of the type of motor units of force generation? Type IIA and IIB increase force potential. Type I decreases force potential.
What are skeletal muscle fibres classified as and why? Slow oxidative (SO) fibres (Type I), fast oxidative-glycolytic (FOG) fibres (Type IIA), and fast glycolytic (FG) fibres (Type IIB) on the basis of their structure and function.
What fibre types do most skeletal muscles usually contain? Normally a mixture of all three fibre types. Their proportions vary with the typical action of the muscle.
In what order are motor units of a muscle recruited? 1) SO fibres (I) 2) FOG fibres (IIA) 3) FG fibres (IIB)
What is the speed of contraction for the three fibre types? 1) SO (I) - slow 2) FOG (IIA) - fast 3) FG (IIB) - fast
What is the primary source of ATP production for the three fibre types? 1) SO (I) - oxidative phosphorylation 2) FOG (IIA) - oxidative phosphorylation 3) FG (IIB) - anaerobic glycolysis
What is the glycolytic enzyme activity for the three fibre types? 1) SO (I) - low 2) FOG (IIA) - intermediate 3) FG (IIB) - high
What is the number of capillaries for the three fibre types? 1) SO (I) - many 2) FOG (IIA) - many 3) FG (IIB) - few
What is the myoglobin content for the three fibre types? 1) SO (I) - high 2) FOG (IIA) - high 3) FG (IIB) - low
What is the glycogen content for the three fibre types? 1) SO (I) - low 2) FOG (IIA) - intermediate 3) FG (IIB) - high
What is the fibre diameter for the three fibre types? 1) SO (I) - small 2) FOG (IIA) - intermediate 3) FG (IIB) - large
What is the rate of fatigue for the three fibre types? 1) SO (I) - slow 2) FOG (IIA) - intermediate 3) FG (IIB) - fast
Are motor units made of the same fibre type? All fibres of motor unit are of the same type.
How is fibre type distribution in muscle determined? Genetically.
What is the average population fibre type distribution in muscle? 50-55% type I (SO) 30-35% type IIA (FOG) 15% type IIB (FG)
Give an example of how composition of muscle relates to function. Soleus - posture muscle, high percentage type I.
Are muscles made of the same fibre type? Muscles are mixed in fibre type composition.
What (Myofibrils/sarcomeres/A-bands) run the entire length of a muscle fibre? ?
What muscle tissue type is most abundant in the human body? Skeletal.
Rheologically, synovial fluid is best described as what (gel/sol/foam)? ?
In terms of corrosion resistance what is a more suitable class of biomaterials for metallic orthopaedic implants (Ti-alloy/stainless steel)? Ti-alloys.
Created by: cliffy



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