Muscle Flashcards
What are the functions of muscle tissue?
Movement
Maintenance of posture
Joint stabilisation
What are the two main types of muscles?
Striated muscle
Smooth muscle
What are the types of striated muscle tissue?
Skeletal muscle - attached to bone, responsible for motor movement.
Cardiac muscle - found in the wall of the heart, and in the base of the large veins that empty into the heart.
What are the characteristics of skeletal muscle?
Attach to and move skeleton
Fibres - multinucleate cells
Have obvious striations in cells
Contractions are voluntary
What are the characteristics of cardiac muscle?
Only in the wall of the heart.
Contractions are involuntary
What are the characteristics of smooth muscle?
Lack striations
Cells are fusiform spindle shaped.
There is one central nucleus.
They are grouped into sheets perpendicular to one another.
What are the structures of the skeletal muscle?
Consists of muscle fibres which are long, cylindrical multinucleated cells.
Epimysium
Perimysium
Endomysium
What does epi mean?
Outside
What does endo mean?
Inside
What does peri mean?
Surrounding
What is epimysium?
Dense connective tissue sheath
Surrounds the whole muscle externally
What is perimysium?
Connective tissue septa
Subdivides the muscle internally into fascicles, each containing several nerve fibres.
Nerves and blood vessels penetrate.
What is endomysium?
A more delicate, looser connective tissue - surrounds individual muscle fibres.
What does skeletal muscle look like?
see image
What is the muscle fibre?
Each muscle fibre is the cell of the skeletal muscle.
It consists of myofibrils, which each have thick and thin actin and myosin myofilaments.
What is a sarcomere?
The units of contraction.
Contains actin and myosin.
Dark, transverse Z bands mark the ends of each sarcomere and anchor the thin filaments.
Titin protein binds the thick filament to the Z disc.
What is the structure of myofibrils?
Myofibrils has alternating light and dark filaments.
Light filaments are actin containing I bands.
Dark filaments are myosin containing A bands along its length.
What is the H zone?
In the centre of each A band.
It is lighter because it is not overlapped by thin filaments.
It is then bisected by a thin, dark M band.
What is the sarcoplasmic reticulum?
The SR is smooth ER.
Invagination of the cell membrane are T-tubules which surround the myofibrils.
Two terminal cisternae of SR surround each T-tubule to form a triad.
What do SR cisternae do?
Cisternae store Ca2+ and release when the muscle is stimulated to contract.
How is there simultaneous contraction?
The T tubules are continuous with the sarcolemma (cell membrane) so the whole muscle contracts simultaneously.
How does muscle contraction occur?
The depolarisation of the T tubule membrane triggers the release of Ca2+ from terminal cisternae.
This initiates muscle contraction by binding to the troponin-tropomyosin complex.
This causes horizontal sliding of thin filaments on thick filaments, which shortens the muscle.
How does muscle relaxation occur?
Results from the decrease of cytosolic free Ca2+ concentration.
What is cardiac muscle?
Branched and striated.
It consists of individual cylindrical cells, each containing one or more central nuclei, and linked by adherens and gap junctions.
Where are the nuclei in skeletal muscle?
Peripheral in the cell
What are intercalated discs?
Adjacent cardiac cells are joined to each other by intercalated discs.
These are highly specialised adhesion junctions containing fascia adherens, gap junctions and desmosomes.
Found only in cardiac muscle.
How does contraction occur in cardiac muscle?
Purkinje fibres exhibit a spontaneous rhythmic contraction.
They generate and rapidly transmit action potentials to various parts of the myocardium.
It is regulated by the autonomic nervous system.
How are cisternae arranged in cardiac muscle?
Terminal cisternae are much smaller than in skeletal muscle.
One terminal cisterna and T tubules form diads located at the level of the Z line, with one in each sarcomere.
What is the structure of smooth muscle?
Dense bodies are the main unit of contraction.
Thin filaments attach to dense bodies using a-actinin, located at the cell membrane and deep in the cytoplasm.
Dense bodies at the membrane are also attachment sites for intermediate filaments and adhesive junctions between cells.
What are the contractions of smooth muscle?
Contractions are involuntary, slow, sustained and resistant to fatigue.
Does not always require a nervous signal - can be stimulated by stretching or hormones.
Where is smooth muscle found?
The walls of hollow organs - digestive organs.
Also found in the respiratory, urinary and reproductive tracts, and are a major component of blood vessels.
How is smooth muscle adapted?
The arrangement of the cytoskeleton and contractile apparatus allows the multicellular tissue to contract as a unit, which provides better efficiency and force.
How does contraction occur in smooth muscle?
Actin-myosin binding occurs with myosin phosphorylation by myosin light chain kinase (MLCK).
This is triggered when calmodulin binds Ca2+.
How is skeletal muscle repaired?
There is a sparse population of satellite cells.
Limited regeneration capcity.
After injury, inactive reserve myoblasts become activated, proliferate and fuse to form new skeletal muscle.
How is cardiac muscle repaired?
Lacks satellite cells.
Shows very little regenerative capacity.
Damaged heart muscle is replaced by fibroblasts and growth of connective tissue, this causes scarring.
How is smooth muscle repaired?
Has similar mononucleated cells.
Has active regenerative capacity.
After injury, smooth muscle cells undergo mitosis and replace the damaged tissue.
