Lecture 8 Flashcards
(16 cards)
Skeletal muscle is a compound tissue
muscle fibres, connective tissue, supply and other. Fused myoblasts form a syncytium. Muscles aren’t the only thing able to contract.
Extrafusal muscle fibres
red slow, aerobic or white fast, anaerobic (T1 or T2 muscle types)
Organised at 4 levels. Myofibres have some CT associated with them (endomyosin) and they are surrounded by a basement membrane. There are small cells associated with the outside of the muscle called satellite cells. Generally, skeletal muscles dont divide once established. It can hypertrophy. Satellite cells can give rise to replacement myofibres in mature muscles. Skeletal muscle starts off as individual myoblasts and they fuse. This is sometimes referred to as syncytium.
intrafusal muscle fibres
bag and chain. innovated by proprioception
Myofibrils
Sarcomeres joined end to end bundled. Run the length of muscle.
A-band
Dark band in middle of sarcomere. Runs from Z line to Z line. Runs Horizontally
I band
Light band that crosses 2 sarcomere. Runs horizontally
Z line
Line passing through middle of I-band. Runs vertically.
Contraction
When muscle contracts, overlap increases and the I-band decreases in length but A band remains the same length
Nerve innovation
Neuromuscular junctions allow muscles to be innervated by nerves
Sarcolemma
AKA junctional folds. Part of cell membrane. Vesicles contain acetylcholine so when nerve is activated, acetylcholine crosses over and binds to receptors on junctional complexes. Sarcolemma have t-tubules that assist with signal transduction and sit next to the SER cisternae containing Ca2+.
Triads
t-tubule and two cisternae. Triads are at A-I junction. Two sets of triads per sarcomere. T tubules take the conduction from the neuromuscular junction deep into the muscle, activates the Ca2+ inside the SER and the Ca2+ causes the actin and myosin to couple. Ca2+ pumps allow process to be repeated.
Heart
Endocardium inner, myocardium and epicardium outer
cardiac muscles
made up of individual muscle cells that are joined end-to-end by intercalated discs. Each cell has a single, centrally located nucleus and contains sarcomeres, which organise into myofibrils, giving the muscle a striated appearance. The cells are also branched and closely associated with capillaries for blood supply. They have diads which are located adjacent to the Z-lines (unlike in skeletal muscle, where triads are found at the A–I band junctions). Cardiac muscle contracts involuntarily, and although it can spontaneously contract, its natural rhythm is relatively slow, so it depends on electrical signals (from the heart’s conduction system) to increase the rate and coordinate contractions.
Purkinje fibres
In the subendocardium. Larger than cardiac cells. Pale as there’s less myofibrils. Throughout ventricle wall and conduct signals. Sinuate the AV node and bundle. Gap junctions here very important for heart rate
Smooth muscle
Fusiform shape (circular cross-section), single central nucleus when muscles contracts, nucleus takes on spiral appearance. Actin and myosin are contractile element, but, they arent arranged in sarcomeres but rater dense bodies. Contractile filaments do not run along the muscle like CM and SM, they run in all directions. No branches, but can be in sheets with gap junctions or individually. Particularly found in structures in lumen like a tube or bag (changes tube diameter and volume of bags). They are activated by many pathways e.g endocrine, mechanical, electrical. Nerves are not in close proximity to muscles, they are distal in varicosities (nerve swellings) which uses diffusion to activate muscles.
Intercalated disks
A transverse component, which contains fascia adherens and desmosomes. These provide strong mechanical connections between cells. A longitudinal component, which contains gap junctions that allow electrical signals to pass quickly between cells.
