Overview
This lecture introduces the three types of muscle tissue in the human body—skeletal, cardiac, and smooth—focusing on their structure, location, function, and control mechanisms.
Types of Muscle Tissue
- The three muscle types are skeletal, cardiac, and smooth muscle.
- All muscle types contain specialized cells for contraction, enabling movement.
Skeletal Muscle
- Skeletal muscle covers bones and gives the body shape.
- It enables voluntary movements and maintains posture.
- Skeletal muscle forms sphincters to control swallowing and urination.
- Muscle contractions produce heat to help regulate body temperature.
- Muscle fibers are multinucleated, formed by fusion of myoblasts, with nuclei at the periphery.
- Each muscle fiber contains many myofibrils made of actin (thin) and myosin (thick) myofilaments organized into sarcomeres.
- Sarcomeres are the basic contractile units, giving skeletal muscle its striated (striped) appearance.
- Muscle fibers are grouped into fascicles (bundles), surrounded by perimysium; groups of fascicles form the muscle, enclosed by the epimysium.
- Tendons or aponeuroses connect muscles to bones.
- Skeletal muscle is under voluntary control, innervated by the somatic nervous system.
Cardiac Muscle
- Cardiac muscle is only found in the heart and is made of cardiomyocytes.
- Its main function is to contract to pump blood throughout the body.
- Cardiac muscle cells are short, branched, with mostly one central nucleus, and have a striated appearance.
- Intercalated discs with gap junctions connect cells, enabling rapid electrical communication and coordinated contractions.
- Cardiac muscle is involuntary, controlled by the autonomic nervous system and regulated by pacemaker cells.
Smooth Muscle
- Smooth muscle is found in organs, blood vessels, airways, the digestive tract, bladder, and reproductive system.
- It regulates functions like blood pressure, digestion, urination, and childbirth.
- Smooth muscle has longitudinal and circular layers that enable peristalsis (wave-like movement).
- Cells are short, spindle-shaped (fusiform), with a single central nucleus, and are not striated.
- Smooth muscle operates involuntarily, controlled by the autonomic nervous system.
Key Terms & Definitions
- Skeletal muscle — voluntary muscle attached to bones for movement.
- Cardiac muscle — involuntary, striated muscle found only in the heart.
- Smooth muscle — involuntary, non-striated muscle found in organs and vessels.
- Sarcomere — smallest contractile unit in striated muscles.
- Myofibril — threadlike structure in muscle fiber containing myofilaments.
- Myofilament — actin (thin) and myosin (thick) filaments that slide for contraction.
- Fascicle — bundle of muscle fibers.
- Tendon — connective tissue attaching muscle to bone.
- Peristalsis — wave-like contractions moving material through organs.
- Intercalated disc — cardiac muscle junction allowing rapid cell communication.
- Autonomic nervous system — controls involuntary functions, including cardiac and smooth muscle contraction.
- Somatic nervous system — controls voluntary muscle movements.
Action Items / Next Steps
- Review muscle contraction at the molecular level in the next lesson.