Smooth Muscle Tissue

• Access to and use of course materials is restricted to enrolled students.
• All materials are provided with permission of the rights holder under license agreements or the Copyright Act of Canada.
• Copyright and all rights are maintained by the author(s) or copyright holder(s), in this case, B. Barbara Czaban
• Reproducing/posting course material to other websites or using it outside the course is prohibited.
• Copying material for distribution, such as uploading it to commercial third-party websites, violates copyright law.
• The lecture will focus on tissues, specifically muscle tissues.
• The lecture outline includes the study of different types of tissues.
• The types of tissues covered are: Epithelial, Connective, Muscular and Nervous tissue.

Learning objectives

• List the three types of connective tissues associated with skeletal muscle's structure.
• Describe general muscle tissue characteristics.
• Identify the three types of muscle tissue.
• Compare structural organization and locations of the three muscle tissue types.
• Compare functions of the three muscle tissue types.
• Name cells in each muscle tissue type and compare their structures.
• Explain voluntary vs. involuntary muscle control.
• Identify voluntary and involuntary muscle tissues.
• Define insertion/origin of muscle, muscle belly, flexion, extension, triceps, and biceps.
• Explain what intercalated discs are, where to find them, and their function.
• Important areas to focus on will be recognizing and identifying various tissues, knowing their structure/functions and general locations.

General Organization of Muscular Tissue

• Muscular tissue is composed of cells called muscle fibres that are contractile.
• Muscle fibres forcefully shorten in response to external stimulation, then relax and passively lengthen.
• Muscle fibres contain protein filaments: actin (thin) and myosin (thick), the main contractile proteins for muscle contraction.
• Muscle fibres are arranged in parallel arrays.
• Layers of muscles/muscular organs contract in a coordinated way.

Common Traits of Muscles

• Excitability: muscles respond to stimuli.
• Contractility: muscles have the ability to shorten.
• Extensibility: muscles have ability to stretch.
• Elasticity: muscles can return to original length after being shortened/lengthened.

Functions of Muscular Tissue

• Convert chemical energy into mechanical energy.
• Body movements involve walking, heart beating, dancing etc.
• Stabilizing body position can occur while sitting or standing.
• Regulation of organ volume involves sphincters-urinary, etc.
• Moving substances: pumping blood, moving food.
• Producing heat occurs via muscle contractions.

Types of Muscular Tissue

• Characterized by location, histology, and modes of control.
• Skeletal muscle: occurs in muscles attached to bones.
• Cardiac muscle: occurs in the wall of the heart.
• Smooth muscle: occurs in walls of arteries, sphincters, stomach, intestines, and the urinary bladder.

Skeletal Muscle: Structural Organization

• Skeletal muscles are organized in bundles; this is the central theme of muscle organization.
• Each muscle bundle consists of many bundled muscle fibres, also referred to as muscle cells.
• One bundle of muscle fibres is called a fascicle.
• Each muscle fibre contains many bundled myofibrils.
• Each myofibril consists of many bundled myofilaments.
• Each myofilament consists of many bundled contractile proteins.
  • Includes actin filaments (thin filaments) and myosin filaments (thick filaments).

Skeletal Muscles Work in Pairs

• The belly of a muscle is the thicker middle region of the muscle, located between the origin and insertion.
• Flexion relates to movements that decreases the angle between two body parts.
• Extension relates to movements that increases the angle between two body parts.

Connective Tissue "Wrappings" of Skeletal Muscle

• Epimysium covers the entire skeletal muscle and is on the outside; it consists of dense irregular fibrous CT.
• The epimysium blends into an attachment structure.
  • This structure is called a tendon, which is a cord-like "attachment" structure consisting of dense regular CT.
• Fascia lies on the outside of the epimysium, consisting of dense regular fibrous CT.
• Perimysium surrounds each fascicle (bundle) of muscle fibres, with dense irregular fibrous CT.
• Endomysium is between muscle fibres, consisting of aerolar CT and loose fibrous CT.

Sites of Muscle Attachment

• Bones, via tendons or cartilage.
• Flat sheets of connective tissues called aponeurosis (sometimes called “flat tendons”).

Skeletal Muscle Characteristics

• Attaches to bones.
• Bundles are enclosed in tough connective tissue sheaths which form "muscles."
• Muscle cells (muscle fibres) are long, cylindrical cells (tube-shaped).
• They have multiple nuclei per cell due to fused cells, and are striated (striped, alternating light/dark bands).
• Striations come as a result of orderly arrangement of myofibrils within muscle cells.
• Each myofibril contains long protein myofilaments (actin and myosin).
• Actin/myosin slide past each other during contraction/relaxation cycles.
• Muscle is under voluntary neural control, movable at will.

Skeletal Muscle

• Has many mitochondria.
• ATP produced by mitochondria provides the energy for muscle contraction.
• The alternating light/dark bands that form the striations result from an orderly arrangement of actin and myosin contractile proteins.

Cardiac Muscle: General Organization

• Located in the walls of the heart, contraction of the heart "pumps blood," which creates a heart beat.
• Cells are elongated, branching, cylindrical tubes called myocytes, myocardiocytes, or cardiocytes.
• Connected end-to-end by intercalated discs (arrows).
  • Fused cell membranes that contain gap junctions, which allow electrical current flow (via charged calcium ions).
  • Also has other cell junctions.

Cardiac Muscle Characteristics

• Striated with numerous mitochondria.
• Has only one centrally located nucleus per cell.
• The nuclei are surrounded by light-staining glycogen.
• Some cells act as "pacemakers," setting the contraction rhythm.
• Under involuntary neural control.
• There is circular and spiral arrangement of cardiac muscle in the heart.

Cardiocytes

• Cardiocytes (cardiac muscle cells) are closely packed and have either one or two nuclei.

Intercalated Disks

• The cells are joined end to end by specialized cell junctions called intercalated disks.
• Desmosomes connect the myofibril filaments (contractile units of actin and myosin) of adjacent cells.
• Gap junctions synchronize the contraction of cardiac muscle by transmission of calcium ions from one cell to another
• The cardiac muscles are branched, fused end-to-end by intercalated discs

Overview of Cardiac Muscle Fibres

• Bundles of cardiac muscle are arranged spirally around the ventricle, wringing blood from the apex to base.
• Cardiac muscle fibres branch and join via intercalated discs which contain 2 types of junctions:
  • Desmosomes mechanically hold the cells.
  • Gap junctions permit action potentials to spread from one cell to adjacent cells.

Smooth Muscle: General Organization

• Located in the walls of viscera (intestine, stomach, etc) and blood vessels.
• Lacks striations.
• Cells are spindle-shaped, narrower at ends and wider in the middle.
• Cells are in staggered arrangement, forming layers in which the thick middle portion of one cell is opposite the thin end of an adjacent cell.
• Contracts more slowly than skeletal muscle and remains contracted for a longer time.
• A ‘myocyte’ is used to refer to both smooth muscle and cardiac muscles cells.
• Also note that 'cardiocytes' is used to distinguish from smooth muscle cells alone.

Smooth Muscle Characteristics

• Located in walls of "hollow organs."
• Non-striated.
• Has a single nucleus per cell.
• Cells are tapered at both ends and held together by tight and gap junctions (transmit nerve impulses) and are under involuntary neural control.
• "Spindle Shaped" cells are narrower at the ends.

Smooth Muscle Cells

• Smooth muscle cells have three filament types: -Thick Myosin -Thin Actin -Intermediate filaments form part of the skeletal support network and supports cell shape; they do not participate during contraction.
• Dense bodies inside the cells, act as anchoring sites for actin and myosin filaments
• Cells contract in many ways, causing cells to shorten and widen
• They have no striations

Explore the characteristics and function of smooth muscle tissue. Questions cover its location in body structures, contraction mechanisms, and structural organization. Understand smooth muscle's role in involuntary movements.