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Week 6 Lecture 2
Muscle System Part 1
| Question | Answer |
|---|---|
| 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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