Muscle
There are three types of muscle, Cardiac, smooth and striated.
Skeletal Muscle
Muscle tissue is made of myoblasts, that are embryonically uninucleate. They fuse to form a long multinucleate syncytium.
In a bundle of skeletal muscle the entire muscle is covered by the epimysium, each fascicle (large grouping of fibres) is covered by a perimysium, and individual fibres are covered by endomysium.
Muscle fibers/cells contain the contractile elements or myofilaments. Myofilaments are organized into myofibrils, each muscle cell can contain many myofibrils.
Myofibrils exhibit a banding pattern or striation pattern that can be resolved into A (anisotropic) bands or I (Isotropic) bands and the Z line. Repetition of these units is a sarcomere.
Sarcomeres are composed of thin and thick filaments. Thick filaments are myosin and thin are composed of actin, troponin and tropomyosin.
Muscle Spindle
An encapsulated sensory receptor that branches off from a skeletal muscle fibre. the spindle contains 8-10 modified muscle cells called intramural fibres. Nervous innervation includes annulospiral nerve endings (afferent-detect rate of stretch), the flower spray nerve endings (afferent- detect duration of stretch ) on either side and the y-efferent motor neurons.
Cardiac Muscle
Blood vessel
Striations
Bladder
Intercalated Disc
Bifurcating cell
Cardiac Muscle is striated like skeletal and is rich in mitochondria. Here the muscle cells are branched and uninucleate. The cells are joined by intercalated discs. The Intercalated discs are formed by desmosomes and gap junctions to allow for the electrical signal to pass through the heart.
The other specialization of the heart consists of the SA and AV node that create impulses and the purkinje fibres.
Purkinje fibres are modified cardiac muscle cells that specialize in generating and conducting electrical impulses to all areas of the ventricles. They contain fewer and more disorganized myofibrils than cardiac muscle cells, and possess rich glycogen stores (extracted during processing, leaving large spaces in the cells). These cells are found between the myocardium and the endocardium.
Smooth Muscle
Nuclei of single muscle cell
Smooth Muscle lightly stains with no striations, the central nucleus is often spirally contrasted in cells. Cells are fusiform in shape and vary in length. These cells are connected electrically and metabolically vis gap junctions.
The mechanism of contraction is also different in smooth muscle in that it involves calmodulin and myosin light chain kinase (MLCK) rather than troponin and tropomyosin (skeletal and cardiac muscle use those)
This single muscle cell shows the fusiform shape and the single nuclei of the smooth muscle cell.