summary on Muscle Tissue

Muscle tissue is a soft tissue that composes
muscles in animal bodies, and gives rise to
muscles' ability to contract. This is opposed to
other components or tissues in muscle such as
tendons or perimysium . It is formed during
embryonic development through a process
known as myogenesis . [1]
Muscle tissue varies with function and location
in the body. In mammals the three types are:
skeletal or striated muscle ; smooth or non-
striated muscle; and cardiac muscle , which is
sometimes known as semi-striated. Smooth
and cardiac muscle contracts involuntarily,
without conscious intervention. These muscle
types may be activated both through interaction
of the central nervous system as well as by
receiving innervation from peripheral plexus or
endocrine (hormonal) activation. Striated or
skeletal muscle only contracts voluntarily, upon
influence of the central nervous system.
Reflexes are a form of non-conscious activation
of skeletal muscles, but nonetheless arise
through activation of the central nervous
system , albeit not engaging cortical structures
until after the contraction has occurred. [1]
The different muscle types vary in their
response to neurotransmitters and endocrine
substances such as acetyl-choline ,
noradrenalin , adrenalin, nitric oxide and among
others depending on muscle type and the exact
location of the muscle. [1]
Sub-categorization of muscle tissue is also
possible, depending on among other things the
content of myoglobin, mitochondria, myosin
ATPase etc.
Structure
Muscle (myocytes ) are elongated cells ranging
from several millimetres to about 10
centimetres in length and from 10 to 100
micrometres in width. [2] These cells are joined
together in tissues that may be either striated
or smooth, depending on the presence or
absence, respectively, of organized, regularly
repeated arrangements of myofibrillar contractile
proteins called myofilaments . Striated muscle is
further classified as either skeletal or cardiac
muscle. [3] Striated muscle is typically subject
to conscious control, while smooth muscle is
not. Thus, muscle tissue can be described as
being one of three different types:
Skeletal muscle , striated in structure and
under voluntary control, is anchored by tendons
(or by aponeuroses at a few places) to bone
and is used to effect skeletal movement such
as locomotion and to maintain posture.
(Though postural control is generally
maintained as an unconscious reflex—see
proprioception —the muscles responsible also
react to conscious control like non-postural
muscles.) An average adult male is made up of
42% of skeletal muscle and an average adult
female is made up of 36% (as a percentage of
body mass). [4] It also has striations unlike
smooth muscle.
Smooth muscle , neither striated in structure
nor under voluntary control, is found within the
walls of organs and structures such as the
esophagus , stomach , intestines , bronchi , uterus ,
urethra , bladder, blood vessels, and the arrector
pili in the skin (in which it controls erection of
body hair).
In vertebrates, there is a third muscle tissue
recognized:
Cardiac muscle (myocardium), found only in
the heart, is a striated muscle similar in
structure to skeletal muscle but not subject to
voluntary control.
Cardiac and skeletal muscles are "striated" in
that they contain sarcomeres and are packed
into highly regular arrangements of bundles;
smooth muscle has neither. While skeletal
muscles are arranged in regular, parallel
bundles, cardiac muscle connects at branching,
irregular angles (called intercalated discs).
Striated muscle contracts and relaxes in short,
intense bursts, whereas smooth muscle
sustains longer or even near-permanent
contractions.