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There are four characteristics associated
with muscle tissue:
• Tissue can receive and respond to stimulation
• Tissue can shorten and thicken
• Tissue can lengthen
• Tissue can return to its resting state
The characteristics of muscle tissue enable it to
perform some important functions, including:
Movement (both voluntarily and involuntarily)
Supporting soft tissues within body cavities
Guarding entrance and exits of the body
Maintaining body temperature
Skeletal Muscle Tissue features and characteristics:
Fibers are multinucleated with peripheral nuclei
Actin and myosin filaments form distinct cross- striation patterns
Muscle is surrounded by connective tissue epimysium
Muscle fascicles surrounded by connective tissue perimysium
Each muscle fiber surrounded by connective tissue endomysium
Voluntary muscle under conscious control
Sensitive stretch receptors called neuromuscular
spindles are present within nearly all skeletal
These spindles consist of a connective tissue
capsule, in which are found modified muscle fibers
called intrafusal fibers and numerous nerve endings
Neuromuscular spindles monitor the changes in the
muscle lengths and activate complex reflexes to
regulate muscle activity
Functions of Skeletal Muscle Tissue
Skeletal muscles function in pairs to
bring about the coordinated movements
of the limbs, trunk, jaws, eyeballs, etc.
Skeletal muscles are directly involved in
the breathing process.
Smooth Muscle Tissue features and characteristics:
Found in hollow organs and blood vessels
Fibers are fusiform in shape and contain single nuclei
Each cell is filled with a specialized cytoplasm, the
sarcoplasm and is surrounded by a thin cell membrane,
Contain contractile actin and myosin filaments; however,
they are not arranged in the regular, cross-striated
patterns that are visible in both the skeletal and cardiac
As a result, these muscle appear smooth or nonstriated
Smooth muscle fibers are also involuntary muscles and
are, therefore, under autonomic nervous system and
Functions of Smooth Muscle Tissue
Smooth muscle controls slow, involuntary
movements such as the contraction of the
smooth muscle tissue in the walls of the
stomach and intestines.
The muscle of the arteries contracts and
relaxes to regulate the blood pressure and
the flow of blood.
Cardiac Muscle Tissue features and characteristics:
Primarily located in the walls and septa of the heart and in the walls of the large
vessels attached to the heart(aorta and pulmonary trunk)
Similar to skeletal muscle, cardiac muscle fibers exhibit distinct cross-striations as a
result of the arrangement of actin and myosin filaments.
Transmission electron microscopy reveals similar A bands, I bands, Z lines, and
repeating sacromere units
Exhibits only one or two central nuclei, are shorter, and are branched
The terminal ends of adjacent cardiac muscle
fibers show characteristic and dense-staining,
end-to-end junctional complexes called
Located in the intercalated disks are the gap
junctions that enable ionic communication and
continuity between adjacent cardiac muscle
Exhibit autorhythmicity and spontaneously
Functions of Cardiac Muscle Tissue
Cardiac muscle tissue plays the most
important role in the contraction of the
atria and ventricles of the heart.
It causes the rhythmical beating of the
heart, circulating the blood and its
contents throughout the body as a
The heart is influenced by the autonomic nervous system which can
increase or decrease the heart rate in line with the requirements of
the body. However, due to an intrinsic regulating system, called the
conduction system it is possible for the heart to go on beating without
any direct stimulus from the nervous system.
This system is composed of
specialized muscle tissue that
generates and distributes the
conduction that causes contraction
of the cardiac muscle. These tissues
are found in the sinus (or sinoatrial)
node, atrioventricular node, bundle
of His, bundle branches, and
When stimulated by electrical activity, muscle fibers
contract and produce motion. In the heart, this
electrical activity is referred to as depolarization.
The contraction causes the blood to be pumped around
the body. Contracted chambers within the heart are
Relaxation of the heart muscle is caused by
electrical repolarisation. Relaxed chambers within the
heart are termed diastolic.
Heartbeat Origination in the Sinus Node
Atrioventricular Nodal Depolarization
Early Ventricular Depolarization
Late Ventricular Depolarization
Atrial and Ventricular
• Skeletal muscles require stimulation from the nervous
system in order to contract
• Motor neurons are the cells that cause muscle fibers to
(synaptic end bulbs)
•Once an action potential (AP) is generated
at the motor end plate it will spread like an
electrical current along the sarcolemma of
the muscle fiber
• The AP will also spread into the T-tubules,
exciting the terminal cisternae of the
•This will cause Calcium (Ca+2 ) gates in the
SR to open, allowing Ca+2 to diffuse into the
•Calcium will bind to troponin (on the thin
myofilament), causing it to change its
shape. This then pulls tropomyosin away
from the active sites of actin molecules.
•The exposure of the active sites allow the
sliding of the filaments
• If there are no longer APs generated on
the motor neuron, no more Ach will be
• AchE will remove Ach from the motor end
plate, and AP transmission on the muscle
fiber will end
• Ca+2 gates in the SR will close & Ca+2 will
be actively transported back into the SR
• With Ca+2 removed from the sarcoplasm
(& from troponin), tropomyosin will re-cover
the active sites of actin
• No more cross-bridge interactions can
• Thin myofilaments slide back to their
Skeletal muscle fibers shorten as thick filaments interact with
thin filaments (“cross bridge”) and sliding occurs (“power
The trigger for contraction is the calcium ions released by the
SR when the muscle fiber is stimulated by its motor neuron
Contraction is an active process; relaxation and the return to
resting length is entirely passive.
Calcium ions regulate contraction in smooth muscle, but they do it in a slightly different
way than in skeletal muscle:
Calcium ions come from outside of the cell.
Calcium ions bind to an enzyme complex on myosin, called calmodulin-myosin
light chain kinase.
The enzyme complex breaks up ATP into ADP and transfers the Pi directly to
This Pi transfer activates myosin.
Myosin forms crossbridges with actin (as occurs in skeletal muscle)
When calcium is pumped out of the cell, the Pi gets removed from myosin by
The myosin becomes inactive, and the muscle relaxes.
This process is called myosin-regulated contraction.
Cardiac-muscle contraction is actin-regulated,
meaning that the calcium ions come both from
the sarcoplasmic reticulum (as in skeletal muscle)
and from outside the cell (as in smooth muscle).
Otherwise, the chain of events that occurs in
cardiac-muscle contraction is similar to that of
DE SAGUN, CRISTINE ANNE
HORTIZUELA, JOYCE ANNE