Fig 021 Muscle

Skeletal Muscle

Skeletal muscles are connected to bone (or cartilage) by way of tendons and produce all movements of parts of the body.

• Long cylindrical cells
• Multinucleated cells with many peripheral nuclei
• Striated muscle - exhibit cross-striations
• Voluntary control - innervated by the somatic nervous system (motor neurons)
• Respond quickly to stimuli
• Satellite cells - skeletal muscle stem cells

Cardiac Muscle

Cardiac muscle makes up the walls of the heart and pumps blood throughout the body.

• Short, branched cells that form a syncytium (coupled by gap junctions)
• Generally single centrally located nucleus (occasionally binucleate)
• Striated muscle - exhibit cross-striations
• Intercalated discs join cells end-to-end
• Involuntary control - innervated by the autonomic nervous system
• Automatic rhythmic contractions for life
• Long-lived cells
• Lipofuscin pigment - end-stage lysosomes containing undigested material
• Poor capacity for regeneration

Smooth Muscle

Smooth muscle is used by various systems to apply pressure to organs (such as the stomach, intestines and uterus) and blood vessels.

• Spindle-shaped cells of variable size
• Single centrally located nucleus
• Non-striated muscle - do not exhibit cross-striations
• Involuntary control - innervated by the autonomic nervous system
• Responds slowly to stimuli and are capable of long-time sustained contractions
• Retain the ability to divide