Histology of Muscle
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What are the 4 classes of muscle?
• Cardiac • Skeletal • Smooth • Myoepithelial
How is myosin made? What does this form?
It is made as cells fuse together. The myoblast is made by the fusion of many cells and is therefore multi nucleated.
What connects muscle to the tendon? What connects muscle to bone?
Connective tissue Tendons
What is a myotendinous junction?
A site of connection between tendon and muscle. The epimysium merge with the dense collagenous connective tissue of the tendon.
How do we recognise skeletal muscle under a microscope?
Peripheral nuclei of fibres Multi nucleated Endomysium separating individual fibres Blood vessels Striations
What is the correct name for a muscle cell? What is this name made up of?
Myofibre Made up of myofibrils
Explain all the bands present in a sarcomere
A Band - overlap of myosin and actin I band - actin filament] H band - myosin filament Sarcomeres divided by Z lines
Where does a myofibre receive innervation from? What is formed at a neuromuscular junction? What does motor unit size dictate?
• one motoneuron • a synapse • the degree of muscle control (smaller ones in eyes for more control)
Give a definition of a motor unit
The set of muscle fibres which are innervated by the axonal branches of a single motor neuron of the CNS
What is found in white and red muscle fibres?
White = fast myosin isoform. They contain small amounts of myoglobin and contract rapidly, hence quickly fatigued. Red = slow myosin isoform. is found in red muscle. They contract slowly (endurance) and contains a lot of myoglobin.
Give details on satellite cells found in skeletal muscle including what they form and where they are found
Found on the surface of muscle fibres. They are a population of stem cells. Usually quiescent (not dividing) Can be activated and enter the cell cycle to become myoblasts. The myoblasts can then differentiate and fuse to form new myofibres. Satellite cells can renewq to maintain the stem cell population Important for muscle growth after birth, muscle maintenance, muscle repair and regeneration.
Give details on the nuclei of cardiac cells. How do cardiac cells connect together?
• mono nucleated • nuclei centrally located • cells connect via intercalated discs • cells have gap junctions to allow transmission of action potentials
Cardiac tissue has functional syncytium. What is this? Why does it form?
A single cell with multiple nuclei formed by the fusion of cells or nuclei division. Forms due to intercalated discs between cells.
Why is regeneration of cardiac muscle cells not possible?
There are no satellite cells
What is the function of a desmosome and a gap junction during muscle contraction? What does the last sarcomere have at the end instead of a Z - line?
Desmosome - holds the sarcomeres together when contracting Gap junction - allows the calcium to flow It has actin bound to the end.
Why does the heart not rely on for contraction and why?
It does not rely on neurons to coordinate contraction because the muscle cells do this themselves due to conductive myocytes called Purkinje fibres. These fibres ensure that the atria contract from the top down and ventricles from the bottom up,
Where is smooth muscle usually found? What formation is it found in?
Found in walls of the gut, blood vessels, respiratory tract Usually found in rings
Give details on the histology of smooth muscle fibres
• each cell surrounded by a basal lamina • small amount of connective tissue between cells • spindle - shaped cells • no myofibrils so no striations
What is in the cytoplasm of smooth muscle cells? What allows electrical excitation to spread from cell to cell? What is contraction controlled by?
Filaments of actin and some myosin but more actin Gap junctions Hormones or the balance between the sympathetic and parasympathetic system