8. Muscle Tissue and Physiology.pdf - 3/19/2020 Human...

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Human Anatomy and Physiology I:
Muscle Tissue and Physiology
Focusing Primarily on Skeletal Muscle
and Smooth Muscle
Functions of Muscle Tissue
• Functional characteristics of all muscle tissues:
– Excitability (electrical) – the ability to receive and respond to
an electrochemical stimulus; some muscle cells can generate
an action potential (such as certain types of cardiac and
smooth muscle cells).
– Contractility – the ability to shorten when an adequate
stimulus is present (separates muscle from all other tissues);
possess a highly specialized cytoskeleton for generation of
force; requires calcium ions for contraction.
– Extensibility – the ability to be stretched or extended (due to
the relaxation of the myofibrils).
– Elasticity – the ability of a muscle to resume resting length
after it has contracted or been stretched (probably due to
passive tension from the connective tissues).

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Functions of Skeletal Muscle Tissue
• Movement/locomotion:
– Most voluntary movements are due to skeletal muscular
contraction; with the exception of amoeboid, ciliary, and
flagellar movements.
• Posture Maintenance:
– Due to posture containing muscles, such as the soleus and
erector spinae muscles.
• Stabilizing Joints:
– Increasing the muscle tone (the resting levels of contraction)
will stabilize joints.
• Heat Generation:
– About 50% of the energy from ATP hydrolysis is heat energy.
– Skeletal muscle is most important; about 40% of body mass.
Introduction to Skeletal Muscle Tissue
• There are three different types of muscle tissues: 1) skeletal, 2) cardiac, and 3) smooth.
• Individual muscle cells are also called fibers .
• Skeletal Muscle Tissue:
– Typically, has the longest fibers (unbranched) and composes 40% of the total body
mass.
– Multinucleated cells (derived from unicellular precursor cells that fuse) or fibers.
– Striated (myofibrils/contractile machinery – the myofilaments – are regularly arranged
to show bands, layers, or lines).
– Often called “voluntary muscle;” controlled by the somatic nervous system .
– Can contract rapidly and vigorously, but tires easily (when compared to cardiac and
smooth muscles).

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Gross Anatomy of a Skeletal Muscle
• A skeletal muscle is a discreet organ.
– Each muscle also contains substantial amounts of connective tissue, blood
vessels, and nerve fibers.
• There are probably over 600 skeletal muscles in the body.
• Each skeletal muscle is typically composed of hundreds to
thousands of muscle cells (or fibers); however, this is variable.
• Skeletal muscles develop embryonically by fusion of many
uninucleate myoblasts .
Anatomy of a Skeletal Muscle
• Each fiber is surrounded by a thin basal lamina with a loss mesh of
reticular fibers; this wrapping called the endomysium .
• Between the endomysium and the muscle fibers are scattered
satellite cells .