lecture 31 Flashcards
1
Q
Learning objectives?
A
- structure and function of skeletal muscle
- pathologic processes affecting human skeletal muscle
→ model: the human muscular dystrophies - clinical presentation of the muscular dystrophies
→ model: duchenne muscular dystrophy, most common MD, affecting 1/3500 boys - treatment of the muscular dystrophies
- advances in therapeutics of the muscular dystrophies
2
Q
objectives for this lecture?
A
- the structure of human skeletal muscle
- myofibrils
- sarcomeres
- the contractile function of human muscle
- the ‘sliding filament’ theory
- different fibre types in human skeletal muscle
3
Q
What are muscle diseases?
A
- muscle tissue consists of highly specialised cells/fibres which contract to actively generate force
- shortening of muscles moves joints, resulting in motion
- because of this characteristic, muscle tissue enables motion and maintenance of posture
- muscle tissue also engenders heat production
- based on structural and function characteristics, muscle tissue is classified into three types: cardiac, smooth, and skeletal
- muscle disorders affect one or more of these tissue types
4
Q
What are myopathies?
A
- genetic and acquired disorders of the muscle contractile apparatus
- myopathies are disorders of the muscle contractile apparatus, with characteristic pathologic changes which do not generally change greatly over time i.e. are usually static
5
Q
What are muscular dystrophies?
A
- genetic disorders of the supporting structures e.g. sarcolemmal proteins and protiens which anchor the contractile apparatus in place cause muscular dystrophies
- dystrophies are progressive disorders in which muscle pathology is characterised by degeneration and regeneration of muscle fibres
6
Q
What is skeletal muscle?
A
- by definition, is attached to bone
- can be made to contract or relax by conscious control (voluntary)
– extra-ocular (muscles around eyes super specialised), limbs, truncal (vary in structure according to function) - it is striated: fibres (cells) contain alternating light and dark bands (striations) perpendicular to their long axes
- skeletal muscle fibres vary in structure and function
– variable colour depending on myoglobin content
→ myoglobin: a protein, stores oxygen for mitochondria
– fibres contract with different velocities, depending on their ability to split ATP
– variable metabolic processes used to generate energy
7
Q
How are smooth and skeletal muscle similar? different?
A
- both are multinucleated and contractile
smooth muscle: dense bodies, intercalated
skeletal muscle: parallel fibres, separate from each
8
Q
What is the structure of skeletal muscle?
A
- each muscle belly is made up of muscle cells, or fibres
- each individual fibre consists of a membrane (sarcolemma) containing muscle tissue (myofibrils) and sarcoplasm
- myofibrils are surrounded by sarcoplasm and together make up the contractile components of muscle
- muscle fibres are striated and multinuclear, and grouped into bundles (called fasciculi) of myofibrils
- fibres within each bundle are surrounded by connective tissue called endomysium
- each fasciculus (bundle) is surrounded by connective tissue (perimysium)
9
Q
What is the substructure of skeletal muscle?
A
- each myofibril is organised into sections along its length
- each section is called a sarcomere
- sarcomeres are repeated along the length of muscle fibres
- the sarcomere is the smallest contractile portion of a muscle fibre
10
Q
What is the sarcomere?
A
- the basic unit of skeletal muscle
- Z disc to Z disc
- dark and light represents areas of overlapping actin and myosin filaments
- during contraction this bands move relative to each other and work to short the distance between z discs thus shortening the muscle overall
- 80 or 100 proteins in each sarcomere and mutations in any one can lead to myopathies
11
Q
What is the I band?
A
- region of the sarcomere that contains only actin filaments
- isotropic
- aligned actin filaments
12
Q
What is the A band?
A
- overlapping/aligned actin and myosin filaments
- anisotropic
13
Q
What is the H zone?
A
- myosin only
- centre of sarcomere
14
Q
What is the sarcoplasm?
A
- the sarcoplasm contains glycogen, fat particles, enzymes and mitochondria which support muscle contraction
15
Q
What is the Z disc?
A
- limit of sarcomere, sited within I band