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College Notices/Lectures BBS2001 Threats And Defence Mechanisms
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Lecture notes of 210 pages for the course BBS2001 Threats And Defence Mechanisms at UM (.)
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Lecture 9: Neuromuscular control of movementBut now, if you contract the muscle, you work with an external force on the tendon.
During passive stretch, the tendon will also experience a bit of force, the collagen fibres will
have less room. The golgi tendon organ (: 1b golgi) will increase in frequency but after the
stretch is completed, it will return to the low frequency just as before the stretch.
If the muscle is contracted, then there is a very large external force on the tendon. During
the active contraction, the golgi tendon organ will fire with higher frequency. If you then
stretch more and more, the 1b golgi will assure that there is not a force which is too high to
prevent tendon injury by stopping the contraction.
• Passive stretch → only slight stretch of the tendon (weak Golgi organ signal)
• Active muscle contraction → stretch of the tendon (Golgi organ high frequency
signals)
→ shortening of muscle spindle) no signaling of muscle spindle)
,With a passive stretch, it is assured that the muscle is reshortened via the muscle
contraction. Muscle contractions (active) are used to produce a movement. If the
muscle spindle would always interfere with this, it would cause a mess and inhibit
normal movement production.
The alpha- motor neuron contracts the whole muscle. In addition to that, the
gamma- motor neuron contracts the outer parts of the muscle spindle. The outer
parts of the muscle spindle are small mini-muscles and only the inner part is the
sensory. During contraction, the outer and inner parts are stretched. This is a
possibility to activate the signals of the inner part of the muscle spindle. This is used
to assure that even when the large muscle contracts which will shorten, the sensitive
inner parts of the spindle stay sensitive, since in parallel the outer parts of the muscle
spindle contract which may lengthen the inner sensory part.
If we have the activation of the alpha motoneurons without the gamma
motoneurons
→ The muscle shortens because the alpha motoneuron to the muscle it must
contract but this results in the silencing of the spindle. The spindle will be shortened
(seen in reflex) and then the spindle will not fire any longer. The frequency will be
very low. Also in the state of contraction, the muscle spindle should be able to sense
if there is a stretch of the muscle. The gamma motoneurons will contract the outer
parts of the muscle spindle and because the inner parts are aligned to the two ends
,of the outer parts; when contracting the outer parts of the muscle spindle there will
be an elongation of the inner parts of the muscle spindle which are the receptor
parts. By contracting the spindle, during the contraction of the whole muscle, it is
assured that the spindle maintains its sensitivity. Otherwise it would be too short to
sense information. Activation of both alpha and gamma motoneurons assures the
maintenance of spindle sensitivity.
Completely different signals from the sole of your foot as well as tendons and
muscles are received. The tracts of touch and proprioception of tendons and muscles
are discussed. In addition, there are different signals from the joints (different
positions of the foot) and different signals from the vestibular system.
→ All these signals have to be taken into account when planning a movement/
adjustment of movement depending on position of body/ producing movement.
, The cerebellum has memory (macro) of trained movements. The proprioceptive
signals reach the cerebellum and cortex (aware of it). The cerebellum can take into
account: what the position of the body is, what is the balance, what is the movement
which is planned from the cortex. The cerebellum gets the information what the
movement is what the cortex has decided. It receives information about the
nonconscious proprioception (body position and balance). Cerebellum can integrate
the desire to move with the necessity of the proprioception of the body and can sent
an adjusted motor program to the cortex. It coordinates the movement taking
proprioceptive input into account.
The basal nuclei decides how far, strong and fast a movement should be. The basal nuclei
are a group of nuclei which are located in the cortex at the lower areas of telencephalon.
They are also located in the diencephalon. The nucleus caudatus belongs to the
telencephalon. The putamen, globus pallidus and Nucleus subthalamicus belongs to the
diencephalon.
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