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Neuromuscular junction college
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Exercise physiology college
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Neuromuscular junction college blok 2.3Drive and design together make the plan.
Design and motor patterns together make the program. Some of the motor patterns are innate:
already there at birth.
Neuromuscular system from bottom to top
The muscle fibers are 1-40 mm long, and 10-100 microns wide.
Actin is the thin filament, and myosin is the thick filament.
There is also a third filament: titin. This is very big, because it goes from one Z disc to the other: it is
at least 2 microns, and when the actin myosin complex is stretched, it can go to 3 microns. The titin
zorgt ervoor dat myosine op zn plaats blijft. Daarnaast kan het zijn eigenschappen veranderen, het
kan stijf worden bijv.: hierbij inhibeert het spierfunctie (verandering bij ziekte of bij exercise bijv.).
Myosine bestaat uit kopjes, die kunnen binden aan actine. Elk van deze filamenten bestaat uit 2
heavy chains, and at the end each of the 2 chains has 2 light chains.
Bij activatie trekt het myosine het actine over zichzelf heen: power stroke.
By the rowing action of the myosin heads, the muscle can get shorter. Besides there is force
developed.
The force developed is dependent on the length of sarcomere. You want to have a sarcomere length
of ongeveer 2 mm.
The maximum overlap is when all the myosin can act at the same actin.
In the body all the muscles have sarcomere lengths of 2.2 (C) or less (tussen A en C).
The heavier you load your muscle, the lower the maximal velocity of contraction is. Wanneer je een
hele zware tas op tilt kun je deze minder snel optillen. The stronger you are, the stronger the hill
relation is.
Every crossbridge between myosin and actin consists out of a crossbridge cycle.
Attached state: myosin is attached to actin, but doesn’t develop forced.
then you need ATP. It binds the myosin head, causing the dissociation of the actin-myosin complex.
When crossbridge is being released. This means, ATP leads to relaxation of the muscle. This relaxation
enables a next contraction cycle.
ATP is being broken down to ADP. With ADP you can make the next cross bridge connection. The
phosphate is moving out. Then you have the powerstroke. Afterwards, even the ADP is being
released: this is the attached state again.
For this, you need energy. Besides the cycle runs as long as the calcium level in the muscle is high.
Excitation-contraction coupling
In between the muscle fibers you see small fibers: the T-tubules. These are little tiny channels running
through the muscle. The action potential on the outer membrane on de muscle cell, causes a DHP
receptor to open calcium channel. Eventually the calcium is being released out of channel in the
Sarcoplasmic reticulum. Afterwards, the calcium channel is being closed again.
The conduction in the nerves going to your muscle is fast: Swann cells, myeline sheets, around your
nerves allow very fast conduction.
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