CH 9 Smooth Muscle Tissue J.F. Thompson, Ph.D.

Smooth Muscle Cells nonstriated = smooth uninucleate

Smooth Muscle Tissue Lacks the dense fibrous connective tissue sheaths of skeletal muscles, but have delicate endomysium Found in the walls of hollow internal organs (except the heart) Often organized into two antagonistic layers (longitudinal and circular) oriented perpendicular to each other

Characteristics of Smooth Muscle Found in the walls of hollow internal structures (digestive, respiratory, reproductive tracts, blood vessels) Arrector pili, pupil of the eye, etc. Involuntary (unconscious) Long, slow contractions, non-fatigable

Smooth Muscle Tissue

May be autorhythmic May have gap junctions Dense bodies are cytoskeletal anchors Myosin and Actin myofilaments are responsible for contraction

Smooth Muscle Tissue When the longitudinal layer contracts, the organ dilates and shortens When the circular layer contracts, the organ constricts and elongates

Contractions of Smooth Muscle Peristalsis – alternating contractions and relaxations of smooth muscles that squeeze substances through the lumen of hollow organs Segmentation – contractions and relaxations of smooth muscles that mix substances in the lumen of hollow organs

Contractions of Smooth Muscle Some smooth muscle cells: –Act as pacemakers and set the contractile pace for whole sheets of muscle –Are self-excitatory and contract without external stimuli Whole sheets of smooth muscle exhibit slow, synchronized contractions –They contract in unison, reflecting their electrical coupling with gap junctions

Regulation of Smooth Muscle Contracts under the influence of: –Autonomic Nervous System –Hormones –Local regulatory factors

End CH 9 Smooth Muscle Tissue