Page 34 - Demo 1

Skeletal muscles move the bones of the skeleton. The cells of the
skeletal muscle, called fibers, are cylindrical and long – at mes, running the
whole length of the muscle. They develop from the fusion of several cells,
resulng in one fiber with mulple nuclei. The nuclei are located at the edge of
the cell, just inside the plasma membrane. The alternang light and dark bands
running across the cell give the fibers a striated appearance. These bands are
due to the regular arrangement of the acn and myosin in the cell. Because
skeletal muscles are under voluntary control, contracon occurs much faster
than the other two muscle types.

Cardiac muscles, like skeletal muscles are striated in appearance but
their contracon is involuntary. The cardiac muscle is found only in the walls of
the heart; its contracon is responsible for the heartbeat. The heart muscle is
composed of chains of single cells, each with its own nucleus. Cardiac muscle
cells are organized into fibers that branch and interconnect, forming a
lacework.
Smooth muscles lack the striaons that skeletal and cardiac muscles
have. Smooth muscle cells are long and spindle-shaped, each containing a
single nucleus. Smooth muscle ssue is organized into sheets of cells in which
the thick middle poron of one cell is opposite the thin ends of adjacent cells,
forming an irregular paern. Like cardiac muscle, smooth muscle is involuntary.
It contracts more slowly than skeletal muscle but can remain contracted for a
longer duraon. Smooth muscle is also referred to as visceral muscle because it
is found in the walls of the viscera (intesnes, stomach, and other internal
organs) and blood vessels. The contracon of smooth muscles in the intesnes
moves food along its lumen, while the contracon of blood vessels helps raise
blood pressure.

Nervous Tissue

Nervous ssue receives smuli and conducts nerve impulses. It
coordinates the funcons of the different body parts in humans and animals,
allowing them to respond to smuli from the external and internal environment.
The nervous system depends on (1) sensory input, (2) integraon of data, and
(3) motor output to carry out its funcons. Nervous ssue in vertebrates consists
of two kinds of cells: neurons and supporng neuroglia.

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