Overview
This lecture introduces the three types of muscle tissue—skeletal, cardiac, and smooth—describing their structure, function, and unique characteristics.
Types of Muscle Tissue
- The body contains three muscle types: skeletal, cardiac, and smooth.
- All muscle tissue enables movement through contraction of specialized muscle cells.
Skeletal Muscle
- Skeletal muscles cover the skeleton, shape the body, and number over 650.
- Attach to bones directly or via tendons (connective tissue).
- Produce voluntary movements, maintain posture, and form sphincters for digestive and urinary control.
- Help regulate body temperature by releasing heat during contraction.
- Skeletal muscle cells (muscle fibers) are multinucleated, formed from fused myoblasts.
- Muscle fibers contain myofibrils, which are made of myofilaments arranged into sarcomeres.
- Sarcomeres give skeletal muscle a striated appearance and are the contractile unit.
- Myofilaments are actin (thin) and myosin (thick); their sliding causes contraction.
- Muscle fibers bundle into fascicles (surrounded by perimysium), grouped to form a muscle (surrounded by epimysium).
- Muscles attach to bones directly or indirectly (via tendons or aponeuroses).
- Skeletal muscle is controlled by the somatic (voluntary) nervous system.
Cardiac Muscle
- Cardiac muscle is only found in the heart and contracts to pump blood.
- Cells (cardiomyocytes) are short, branched, usually with 1–2 centrally located nuclei.
- Cardiac muscle is striated due to sarcomeres, like skeletal muscle.
- Intercalated discs between cells allow electrical signals to pass quickly for coordinated contraction.
- Controlled involuntarily by the autonomic nervous system; pacemaker cells regulate heartbeat.
Smooth Muscle
- Smooth muscle is found in most organs, blood vessels, airways, digestive tract, bladder, and reproductive system.
- Regulates blood pressure, air flow, material movement (peristalsis), urination, and childbirth.
- Organized into longitudinal and circular layers for coordinated movement.
- Cells are short, spindle-shaped (fusiform), with a single central nucleus.
- Not striated; myofilaments scattered in the cytoplasm.
- Controlled automatically by the autonomic nervous system.
Key Terms & Definitions
- Skeletal Muscle — Muscle attached to bones, under voluntary control.
- Cardiac Muscle — Striated muscle found only in the heart, contracts involuntarily.
- Smooth Muscle — Non-striated muscle found in organs, contracts involuntarily.
- Sarcomere — The smallest functional unit of muscle, responsible for contraction.
- Myofibril — Bundles of myofilaments within muscle fibers.
- Myofilaments — Protein filaments (actin & myosin) enabling muscle contraction.
- Intercalated Disc — Specialized structure in cardiac muscle for rapid electrical communication.
- Peristalsis — Wave-like contraction in smooth muscle to move material through organs.
- Somatic Nervous System — Part of the nervous system controlling voluntary muscles.
- Autonomic Nervous System — Controls involuntary muscle activity.
Action Items / Next Steps
- Prepare to learn about muscle contraction at the molecular level in upcoming lessons.