Download Smooth muscle

NAME: ONI HERITAGE TOLULOPE
MATRIC NO: 14/MHS01/114
COURSE CODE: ANA 203
DEPT: PHYSIOLOGY
HISTOLOGY OF MUSCLE AND ITS TYPES
Muscle cells, also known as muscle fibers or myocytes, are the fundamental units
of your muscles. Humans have three types of muscle: skeletal, smooth and
cardiac. Your skeletal muscles are under conscious control, while your smooth
muscle -- found in the walls of your blood vessels and your hollow organs -- and
cardiac muscle are not. All muscle cells share four primary properties that
distinguish them from other cells.
Skeletal muscle
Skeletal Muscles are those which attach to bones and have the main function of
contracting to facilitate movement of our skeletons. They are also sometimes
known as striated muscles due to their appearance. The cause of this 'stripy'
appearance is the bands of Actin and Myosin which form the Sarcomere, found
within the Myofibrils. Skeletal muscles are also sometimes called voluntary
muscles, because we have direct control over them through nervous impulses
from our brains sending messages to the muscle. Contractions can vary to
produce powerful, fast movements or small precision actions. Skeletal muscles
also have the ability to stretch or contract and still return to their original shape.
Smooth muscle
Smooth muscle is also sometimes known as involuntary muscle due to our
inability to control its movements, or Unstriated as it does not have the stripy
appearance of skeletal muscle. Smooth muscle is found in the walls of hollow
organs such as the Stomach, Esophagus, and Bronchi and in the walls of blood
vessels. This muscle type is stimulated by involuntary neurogenic impulses and
has slow, rhythmical contractions used in controlling internal organs, for example,
moving food along the Oesophagus or constricting blood vessels during
Vasoconstriction.
Cardiac muscle (heart muscle)
The three types of muscle (skeletal, cardiac and smooth) have significant
differences. However, all three use the movement of actin against myosin to
create contraction. In skeletal muscle, contraction is stimulated by electrical
impulses transmitted by the nerves, the moto neurons (motor nerves) in
particular. Cardiac and smooth muscle contractions are stimulated by internal
pacemaker cells which regularly contract, and propagate contractions to other
muscle cells they are in contact with. All skeletal muscle and many smooth muscle
contractions are facilitated by the neurotransmitter acetylcholine.
Function
When sarcomere contracts, the Z lines move closer together, and the I band
becomes smaller. The A band stays the same width. At full contraction, the thin
and thick filaments overlap.
The action a muscle generates is determined by the origin and insertion locations.
The cross-sectional area of a muscle (rather than volume or length) determines
the amount of force it can generate by defining the number of sarcomeres which
can operate in parallel.[citation needed] The amount of force applied to the
external environment is determined by lever mechanics, specifically the ratio of
in-lever to out-lever. For example, moving the insertion point of the biceps more
distally on the radius (farther from the joint of rotation) would increase the force
generated during flexion (and, as a result, the maximum weight lifted in this
movement), but decrease the maximum speed of flexion. Moving the insertion
point proximally (closer to the joint of rotation) would result in decreased force
but increased velocity. This can be most easily seen by comparing the limb of a
mole to a horse - in the former, the insertion point is positioned to maximize
force (for digging), while in the latter, the insertion point is positioned to
maximize speed (for running).
This type of muscle is found solely in the walls of the heart. It has similarities with
skeletal muscles in that it is striated and with smooth muscles in that its
contractions are not under conscious control. However this type of muscle is
highly specialized. It is under the control of the autonomic nervous system,
however, even without a nervous impute contractions can occur due to cells
called pacemaker cells. Cardiac muscle is highly resistant to fatigue due to the
presence of a large number of mitochondria, myoglobin and a good blood supply
allowing continuous aerobic metabolism Anatomy
Function of Muscle Tissue
The main function of the muscular system is movement. Muscles are the only
tissue in the body that has the ability to contract and therefore move the other
parts of the body.
Related to the function of movement is the muscular system’s second function:
the maintenance of posture and body position. Muscles often contract to hold the
body still or in a particular position rather than to cause movement. The muscles
responsible for the body’s posture have the greatest endurance of all muscles in
the body—they hold up the body throughout the day without becoming tired.
Another function related to movement is the movement of substances inside the
body. The cardiac and visceral muscles are primarily responsible for transporting
substances like blood or food from one part of the body to another.
The final function of muscle tissue is the generation of body heat. As a result of
the high metabolic rate of contracting muscle, our muscular system produces a
great deal of waste heat. Many small muscle contractions within the body
produce our natural body heat. When we exert ourselves more than normal, the
extra muscle contractions lead to a rise in body temperature and eventually to
sweating. The Four Properties of Muscle Cells
Muscle cells, also known as muscle fibers or myocytes, are the fundamental units
of your muscles. Humans have three types of muscle: skeletal, smooth and
cardiac. Your skeletal muscles are under conscious control, while your smooth
muscle -- found in the walls of your blood vessels and your hollow organs -- and
cardiac muscle are not. All muscle cells share four primary properties that
distinguish them from other cells.
Excitability
For a muscle to contract and do work, its cells must be stimulated, most often by
the nerves supplying them. Nervous impulses cause the release of the
neurotransmitter acetylcholine at the nerve-muscle junction, and the
acetylcholine activates receptors on the surface of the muscle cell. This results in
an influx of positively charged sodium ions into the muscle cell and a
depolarization of the muscle cell membrane, which in the resting state is quite
negatively charged. If the membrane becomes sufficiently depolarized, an action
potential results; the muscle cell is then "excited" from an electrochemical
standpoint.
Contractility
In the case of skeletal muscles, muscle cells contract when stimulated by neural
input; smooth and cardiac muscles do not require this input. When a muscle cell
is excited, the impulse travels along various membranes of the cell to its interior,
where it leads to the opening of calcium channels. Calcium ions flow toward and
bind to a protein molecule called troponin, leading to sequential changes in shape
and position of the associated proteins tropomyosin, myosin and actin. The
upshot is that myosin binds to small strands within the cell called myofilaments
and pulls them along, causing the cell to shorten, or contract. Since this is going
on simultaneously and in a coordinated fashion in many thousands of myocytes at
the same time, the muscle as a whole contracts.
Extensibility
Most of your body's cells lack the capacity to stretch; attempting to do so only
damages or destroys them. Your long, cylindrical muscle cells, however, are a
different story. Muscle cells contract, and in order for them to retain this ability,
they must accordingly possess extensibility, or the capacity to lengthen. Your
muscle cells can be stretched to about three times their contracted length
without rupturing. This is important because in a lot of coordinated movements,
so-called antagonistic muscles operate such that one is lengthening while the
other is contracting. For example, when you run, the hamstring in the back of
your thigh contracts while your quadriceps are extended and conversely.
Elasticity
When something is described as elastic, this is simply a statement that it can be
stretched or contracted by some amount above or below its resting or default
length without damaging it, and that it will return to this resting length once the
stimulus for stretching or contraction is removed. Your muscles require the
property of elastic recoil for them to be able to do their jobs. If, say, your biceps
muscles failed to recoil to their resting length after being stretched during a series
of curling exercises, they would become slack, and slack muscles with no tension
are unable to generate any force and are therefore useless as levers.
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