Session 6: Muscle tissues Flashcards
Describe the process of skeletal muscle contraction
- Nerve impulse arrives at the neuromuscular junction
- Action potential from a motor neuron triggers the release of acetylcholine into the motor end plate
- The sarcolemma undergoes depolarisation
- Calcium ions are released from the sarcoplasmic reticulum and bind to troponin, exposes binding site, actin and myosin can form a bridge.
- Muscle contraction begins
- ATP, on myosin head, is hydrolysed to ADP and phosphate
- Myosin and actin fibres separate and their cross bridge is lost. Contraction stroke ends, machinery resets for next contraction
Compare the features of red and white skeletal muscle fibres
look at notes
Compare the 3 different twitch fibres
look at notes
Describe the difference between hypertrophy and atrophy
Hypertrophy: heart is bigger than normal
Atrophy: heart is smaller than normal
State the structure and function of Purjinke fibres
Purjinke fibres are large cells with: more glycogen, less myofibrils, more gap junction. They help to conduct action potentials rapidly, allowing ventricles to contract in a synchronous manner. Will appear white in H+E due to presence of glycogen.
Differentiate between cardiac and skeletal muscle
Both are striated muscles and have similar contraction mechanisms. But:
1. Nuclei in cardiac muscle are central not peripheral, some cardiac may have 2 nucei per cell
2. Cardiomyocytes communicate through gap junctions in intercalated disk
3. Only has one contractile cell type- cardiomyocyte vs 3 in smooth muscle
Is mature muscle repair possible?
Skeletal muscle: cannot divide. Regenerate by mitotic activity of satellite cells, cell development follows muscle injury. Satellite cells can also fuse with existing muscle cells to increase mass- hypertrophy
Cardiac muscle: incapable of regeneration. After damage, fibroblasts invade, divide, and lay down scar tissue
Smooth muscle: retain mitotic activity, form new smooth muscle cells. Good at repairing themselves. Eg: muscle wall in uterus becomes thicker by hypertrophy( cell enlargment)
How does smooth muscle contract?
Unlike striated muscle, contraction occurs along microtubules that run between dense bodies. When stimulated to contract, myosin and actin filaments interact like in striated muscles and slide over each other, but instead of pulling the z lines together, different sides of the cell are pulled together by the dense plaques.
What is the similarity between cardiac muscle cells and smooth muscle cells?
Like cardiomyocytes, smooth muscle cells are joined at numerous points so that as one cell contracts, the entire tissue can act and contract as one. This occurs through gap junction interaction.
What is the difference between hypertrophy and hyperplasia?
Tissues and muscles may increase in size by:
1. Hypertrophy: enlargement of individual cells
2. Hyperplasia: multiplication of their cells
Describe the origin and insertion of a muscle and relate to its actions
Muscle: biceps brachii muscle
Origin: proximal bone which has a greater mass and is more stable during contraction than muscle’s insertion
Insertion: the structure the muscle attaches to. Tends to be moved by contraction, usually tendon to bone. Greater motion than origin during contraction.
Explain the different roles muscles can play in coordinated movement
Agonists: responsible for a particular movement. eg. Biceps brachii, brachialis
Antagonists: oppose agonists. eg. triceps brachii
Synergists: they cannot perform movement, but will assist with angle with agonists
Neutralisers: prevent unwanted actions of muscle caused by agonists
Fixators: stabilise joint, hold body part immobile whilst another part is moving
Describe the process of skeletal muscle remodelling
Destruction>replacement: atrophy, decrease in fibre number and fascicle size
Replacement>destruction: hypertrophy
Untrained muscle to trained muscle: involves fusion of satellite cells and growth
What is the mechanism behind hypertrophy?
Overstretching so that A and I bands can no longer re-engage. New muscle fibrils are produced from bone marrow. New sarcomeres are added in the middle of existing sarcomere. New muscle fibres arise, overstretching can lead to cardiac issues like enlarged ventricles
What is the mechanism behind atrophy?
- Disuse: sedentary behaviour, age etc
- Surgery: denervation of muscle, nerve regeneration will take 3 months
- Disease: muscular dystrophies
leads to loss of protein, reduced fibre diameter, loss of muscle power