1. Smooth and Cardiac Muscle
Ch. 9a Part 4 Notes
Smooth and Cardiac Muscle
Interactive Notes pages

2. Smooth Muscle
Compared to skeletal muscle fibers, smooth muscle fibers are:
Shorter.
Single, centrally located nucleus.
Elongated with tapering ends.
Myofilaments randomly organized.
Lack striations.
Lack transverse tubules.
Sarcoplasmic reticulum (S R) not well developed.

3. Types of Smooth Muscle 2 types of smooth muscle:
Multi-unit Smooth Muscle:
Cells are less organized.
Function as separate units.
Fibers function independently.
Iris of eye, walls of blood vessels.
Stimulated by neurons, hormones.
Visceral Smooth Muscle:
Single-unit smooth muscle; cells respond as a unit.
Sheets of spindle-shaped muscle fibers.
Fibers held together by gap junctions.
Exhibit rhythmicity.
Conduct peristalsis.
Walls of most hollow organs.
More common type of smooth muscle.

4. Smooth Muscle Contraction
Resembles skeletal muscle contraction in these ways:
Interaction between actin and myosin.
Both use calcium and A T P.
Both are triggered by membrane impulses.
Different from skeletal muscle contraction in these ways:
Smooth muscle lacks troponin; uses calmodulin instead.
Two neurotransmitters affect smooth muscle: Acetylcholine (A c h) and norepinephrine (N E).
Hormones can stimulate or inhibit smooth muscle.
Stretching can trigger smooth muscle contraction.
Smooth muscle slower to contract and relax.
Smooth muscle more resistant to fatigue.
Smooth muscle can change length without changing tautness.

5. Cardiac Muscle Cardiac Muscle: Located only in the heart.
Striated muscle cells.
Muscle fibers joined together by intercalated discs.
Fibers branch, contain a single nucleus.
Network of fibers contracts as a unit (syncytium).
Self-exciting and rhythmic.
Longer refractory period than skeletal muscle.
No sustained or tetanic contractions.

7. Table 9.3 Characteristics of Muscle Tissues
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Skeletal
Smooth
Cardiac
Dimensions
Length
Diameter
Up to 30 cm µm
30–200 µm
3–6 µm
50–100 µm
14 µm
Major location
Skeletal muscles
Walls of hollow organs
Wall of the heart
Major function
Movement of bones at joints; maintenance of posture
Movement of walls of hollow organs; peristalsis; vasoconstriction
Pumping action of the heart
Cellular characteristics
Striations
Nucleus
Special features
Present
Multiple nuclei
Transverse tubule system is well developed
Absent
Single nucleus
Lacks transverse tubules
Transverse tubule system is well developed; intercalated discs connect cells
Mode of control
Voluntary
Involuntary
Contraction characteristics
Contracts and relaxes relatively rapidly
Contracts and relaxes relatively slowly; some types self-exciting; rhythmic
Network of cells contracts as a unit; self-exciting; rhythmic; remains refractory until contraction ends