Muscular tissue is used for movement, stability of the body, control of body passages and openings, and heat production.
Summary
Muscular tissue is used for
movement, stability of the body, control of body passages and openings, and
heat production. Muscle cells are able to carry out excit-ability,
conductivity, contractility, extensibility, and elasticity. A muscle fiber is a
long, slender cell with multiple nuclei just inside the sarcolemma. The sar-coplasm is
occupied mainly by myofibrils, which are thread-like
bundles of protein filaments. A muscle fiber is a long, slender cell with
multiple nuclei just inside the sarcolemma. The sarcoplasm is occupied mainly
by myofibrils, which are thread-like bundles of protein filaments. Each
myofibril is a bundle of protein myofilaments. The thick filaments are made up
mostly of myosin and the thin filaments mostly of actin.
Nerves and muscle fibers meet at
a complex of synapses called a neuromuscular junction. Each tip of a nerve
fiber ends in the synaptic knob. A narrow gap, the synaptic cleft, separates
the synaptic knob from the sarcolemma. The synaptic knob contains synaptic
ves-icles. An enzyme called acetylcholinesterase, found in the synaptic cleft
and as part of the sarcolemma, breaks down ACh to terminate stimulation of the
muscle fiber.
Smooth muscle fibers are much
smaller than skeletal muscle fibers. Smooth muscle does not have the
striations that skeletal muscle has. A different type of myosin exists in
smooth muscle. There are two types of smooth muscle: multiunit (found in the
eyes and blood vessels) and visceral (found in hollow organs). The wave-like
motion of many tubular organs, known as peristalsis, is caused by visceral
smooth muscles. Smooth muscle, unlike skeletal muscle, is affected by the
neurotransmitter called norepinephrine. Smooth muscle takes approximately 30
times longer than skel-etal muscle to contract and relax, but uses much less
energy. Smooth muscle contraction is regulated by nerves, hormones, and local
chemical changes.
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