Muscles Flashcards
Classify the 3 histology all forms of muscle
Skeletal Muscle (striated), Cardiac Muscle (striated), Smooth Muscle (non-striated)
Describe, in ascending order of size, the structure of muscle.
Many myofilaments in a myofibril, many of which, make up
a single muscle fibre (cell) wrapped in endosmysium. Arranged into fascicles wrapped in perimysium. Arranged into whole muscles wrapped by epimysium.
Describe the ultrastructure appearance of skeletal muscle. (Bands)
MHAZI. M line is in the H band which is in the A band. The Z line is in the I band
In sarcomeres which filament is thick and which is thin
Actin is Thin
Myosin is Thick
Name the constituent parts of actin filaments
Actin wrapped in tropomyosin, interspersed with troponin complexes
Describe the structure of the thick, myosin, filament.
Many myosin molecules, whose heads protrude at opposite ends.
Describe stage 1 of 4 of muscle contraction (Cocking)
Hydrolysis of the ATP attached to the myosin head cocks the head into a high energy state.
Describe stage 2 of 4 of muscle contraction (Binding)
In the presence of Ca+, which binds to troponin exposing binding sites on the tropomyosin, the myosin head binds lightly to the actin filament.
Describe stage 3 of 4 of muscle contraction (power stroke)
The release of the ADP and Pi causes the myosin head to bind tightly moving the actin filament 5nm (the head is now uncocked)
Describe stage 4 of 4 of muscle contraction (detachment)
ATP binds to the myosin head, releasing it from the actin filament.
The cycle then repeats
Describe the the mechanism of innervation of muscle. (~6 steps)
- Nerve impulse arrives at neuromuscular junction
- This releases Acetyl Choline causing depolarisation of sarcolema
- Voltage gated Na Channels open, Na enters cell
- Depolarisation spreads through T tubules
- The gated Ca channels open and Ca enters sarcolemoplasm
- Ca allows muscle contraction (exposes myosin binding sites)
Explain the attachment of muscle to tendons
Skeletal muscle fibres interdigitate with tendon collagen bundle at myotendenous junction.
The sarcolema always lies between collagen bundles and microfilaments.
Describe the nature of repair in skeletal muscle
Cells cannot divide but tissue can regenerate by mitotic activity of satellite cells, the can fuse with existing muscle cells to increase mass.
Gross damage is repaired with connective tissue, which leaves scars
Describe the nature of repair in cardiac muscle
Incapable of regeneration.
Following damage, fibroblasts invade and lay down scar tissue.
Describe the nature of repair in smooth muscle
Cells undergo mitosis
Particularly evident in the pregnant uterus where the muscle wall becomes thicker.
Define muscular hyperplasia
The increase in muscle size due to mitotic division (exclusive to smooth muscle)
Define muscular hypertrophy
The increase in muscle size due to swelling of individual cells. Often caused by an increase in number of myofibrils.
Describe the histology of cardiac muscle
Striated Branching Central nuclei Intercalated disks (for mechanical and electrical coupling) Gap junctions T tubules are in line with the Z disk
Describe the histology of smooth muscle
Cells are fusiform (like a bronchasuharus with no legs)
Non striated
Contraction is slower and requires less ATP
Can be stretched
Responds to hormones, nerves, drugs, [blood gasses]
Filaments spiral along the cell
Outline the structure and function of the Purkinje fibres
Abundant glycogen
Sparse myofilaments
Extensive gap junction sites
Rapid conduction of action potentials
How long does the remodeling of skeletal muscle take?
2 weeks
Define muscular atrophy
Muscular atrophy is the loss of muscular tissue caused by a greater rate of destruction than replacement.
List the causes of muscular atrophy
Disuse of muscle (muscle fibres shrink)
Age
Denervation reduced nervous activity leads to disuse
Outline the role of acetyl choline in the neuromuscular junction
Acetyl choline (ACh) is released across the junction.
25% of ACh receptors need to be occupied to…..
Open sodium channels to…..
Start depolarisation of sarcolema
