Types of muscles:
Cardiac:
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 specialised. It is under the control of the autonomic nervous
system, however, even without a nervous input 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.
The heart muscle is an example of a cardiac muscle and it exhibits many structural and functional
characteristics intermediate between those of skeletal and smooth muscle. Like skeletal muscle,
cardiac muscle contractions are strong, and utilise a great deal of energy. Like some smooth
muscle, cardiac muscle can contract without nervous stimulation so it is myogenic, and this enables
the heart to be transplanted. Muscle in different parts of the heart show different intrinsic rhythms
- isolated myocardium from the ventricles for example, beat very slowly whereas isolated atrial
fibres beat more rapidly. Like smooth muscle, cardiac contractions are continuous and initiated by
inherent mechanisms - although they can be modified by external nervous and hormonal stimuli, the
cardiac cells still cannot regenerate. Cardiac muscle fibres are essentially long, cylindrical cells with
one (or sometimes two) nuclei. These are centrally located within the cell. The ends of the fibres are
split longitudinally into a small number of branches, the ends of which abut onto similar branches of
adjacent cells giving the impression of a continuous three-dimensional cytoplasmic network.
Between the muscle fibres, delicate connective tissue, analogous to the endomysium of skeletal
muscle so this supports the extremely rich capillary network necessary to meet the high metabolic
demand of strong continuous activity. Also like the skeletal muscle, the sarcomere is the contractile
unit of the myocardial cell. As it contains myosin and actin filaments as well as troponin and
tropomyosin. Therefore the shortening of sarcomeres causes contraction by the sliding filament
theory.
Skeletal:
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. Also not all fibres within skeletal muscles are the same. Different fibre types
contract at different speeds, are suited to different types of activity and vary in colour depending on
their Myoglobin content.
Smooth:
Smooth muscle is also sometimes known as involuntary muscle due to our inability to control its
movements, 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, Oesophagus, 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. Smooth muscle is found in the walls of hollow
organs like your intestines and stomach. They work automatically without you being aware of them.
Smooth muscles are involved in many housekeeping functions of the body. For example the
muscular walls of your intestines contract to push food through your body and the muscles in your
bladder wall contract to expel urine from your body. Smooth muscles in a woman's uterus help to
push babies out of the body during childbirth.
Types of muscle fibres:
Type 1:
Type 1 fibres are also known as slow twitch fibres. They are red in colour due to the presence of
large volumes of myoglobin and so oxygen and high numbers of Mitochondria. Due to this fact they
are very resistant to fatigue and are capable of producing repeated low-level contractions by
producing large amounts of ATP through an aerobic metabolic cycle. They are also used for
endurance based activities such as 10,000m so they can contract repeatedly as they exert minimal
force and they have a high concentration of myoglobin and mitochondria. Having a high
concentration of myoglobin in type 1 muscle fibres would be good because there would be a lot of
oxygen stores within them and they would be transported to the mitochondria and this would cause
the muscle to work harder and longer due to the constant oxygen and energy being delivered to the
large muscle group being used. The reason why it would be good for type 1 muscle fibres to have a
high concentration of mitochondria would be because they are responsible for energy production
and they are an important part of aerobic energy production. They also have a large capillary
network and this would be good because the blood, oxygen and nutrients can be transported much
faster and the waste products can be removed much quicker and this would suite the endurance
type of activity that would be performed.
Type 2a:
Type 2a fibres are also sometimes known as fast oxidative fibres and are a hybrid of type 1 and 2
fibres. These fibres contain a large number of mitochondria and Myoglobin, hence their red colour.
They manufacture and split ATP at a fast rate by utilising both aerobic and anaerobic metabolism
and so produce fast, strong muscle contractions, although they are more prone to fatigue than type
1 fibres. They are used for aerobic energy systems. They would normally be used for middle distance
type of activities such as 400m and they are also fairly resistant to fatigue. They exert medium force
and they have a medium concentration of myoglobin and mitochondria. Having a medium
concentration of myoglobin and mitochondria in this muscle fibre would be suited to 400m because
the performer wouldn’t be running for as long as a marathon runner so they would need less
myoglobin and mitochondria because the muscles being used wouldn’t be needing a lot of oxygen
and energy because the events would last as long as type 1 muscle fibre activities would and the
muscles wouldn’t need as much oxygen and energy to cope with the race because the race would be
fairly short lasting between 2-3 minutes. Type 2a muscle fibres also have a large capillary network so
they can transport the right amount of energy and oxygen needed on time so the performer
wouldn’t suffer from fatigue so that why type 2a muscle fibres are fairly resistant to fatigue. This
would also make the person running finish the race quicker and there muscle wouldn’t be built up
with a lot of lactic acid due to the large capillary network.
Type 2b:
Type 2b are also often known as fast glycolytic fibres they are white in colour due to a low level of
myoglobin and also contain few mitochondria. They produce ATP at a slow rate by anaerobic
metabolism and break it down very quickly. This results in short, fast bursts of power and rapid
fatigue. Type 2b muscle fibres are white and they also contract rapidly but they are used for
anaerobic energy systems. They are used for speed and strength based activities such as 100m. They
fatigue easily and they exert great force, they have a low concentration of myoglobin and
mitochondria due to them being anaerobic based muscle fibres. They also have few capillaries due
to type 2b muscle fibres being used for anaerobic based activities and the muscles wouldn’t need
large quantities of oxygen and energy because the race would only last only 10 seconds and most
athletes don’t breath during this period because it’s so fast and this enables them to use these fast
burst of power to their advantage and there muscle suffer from fatigue much easier due to them not
getting a lot of oxygen and nutrients transported to the active muscle being used during the race.