Download Sheet#6 Motor system

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* Action potential being through nerve then acetylcholine is released which effect
postsynaptic on muscle and contraction is accomplished.
*Motor neurons are present in the anterior gray horn of the spinal cord (where a
neuron cell body is found), the axon of each neuron then travels to muscles for
excitation.
-Small motor unit >>>control small fibers and big motor unit>>>control big fibers.
*There are several ways a motor neuron can be activated:
1) Spinal cord reflexes:
Not all movements come from orders from the brain, some movement circuits
are found in other parts of the brain and one important example is reflexes in the
spinal cord. The most vital function of reflexes is the protection of our body, by:
a) Doing fast actions that do not require processing from the brain.
b) Away from danger.
*Examples of spinal cord reflexes that activated motor neuron:
Muscle stretch reflex:
*IF brain gets order for spinal cord: maintain muscle length 5Cm and muscle
tension 100 Newton and environmental factor change length and tension of
muscle So ,spinal cord back muscle to normal state which the manger (brain)
order it.
**Remember: muscle length receptor is called muscle spindle.
*A change length in the muscle stimulates sensory receptors located in the muscle
called muscle spindles, in response a muscle spindle generates impulses (action
potentials) through afferent sensory neurons (first order neuron) into a PCML
pathway to brain for conscious response. If change in length not from brain order
but by environmental factor a branch go to spinal cord to do a reflex and back
normal length (muscle contraction ) by excitation motor unit (excitation of action
potential).
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*If I want to contract biceps muscle at the same time the opposite triceps muscle
is relaxed.
*how we can do relaxation for a muscle?
By decreased number of action potential through motor neuron or don’t send
action potential so, Ach releasing is decreased also contraction is decreased
(relaxation).
Now, we should do inhibition of motor neuron of opposite muscle >>>sensory
neuron ( blue color) can't do inhibition >>>this sensory neuron excitants
inhibitory interneuron(purple) >>>which cause inhibition for motor neuron to
reciprocal (opposite) muscle then decrease action potential that why relaxation is
happen (This phase is known as the reciprocal inhibition).
**This is commonly known as Knee jerk reflex (made of two phases the muscle
stretch reflex and the reciprocal inhibition), however this can be done to other
joints to test the stretch reflex but the most commonly known is the knee jerk
reflex.
**you should when doc hit knee tendon is stretched (not nerve ) then muscle that
bind this tendon also is stretched.
When you hold a cup of tea its weighted 100 gram this is conscious behavior >>
brain get order to biceps for potential contraction equivalent the weight of cup.
If anyone pour tea >>weight become more than double at least 250 gram if weight
more than tension your hand will descend. When weight increased your hand is
descended so, biceps muscle length is increased that get order for spinal cord to
do a reflex (a reflex is muscle contraction that back muscle to normal state and
fixed your hand) also , for brain to increase tension to equivalent new weight .
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**Notice when holding object weight increase suddenly your hand will vibrate,
this vibration is happened through spinal cord reflex which prevent hand to
descend.
Tendon reflex (autogenic inhibition reflex):
Another type of spinal cord reflex is the tendon reflex. This reflex is caused by
extra tension on a muscle whether it’s caused from an external source or from a
brain order (wanting to lift a heavy object for example) that might damage the
muscle, so the muscle must have a sensor to protect it and keep track of the
allowable tension levels by decrease action potential. This sensor is the Golgi
tendon organ, extra tension will stimulate this receptor that will send information
to spinal cord also will give a branch to the brain through "PCML" pathway also,
include an inhibitory interneuron cause fast muscle relaxation.
Tendon
Reflex
Nociceptive reflex:
Another type of reflex that the body uses to protect itself from pain and harm is
the withdrawal reflex, for instance if you step on glass, touch a hot object, your
leg knock against table ect, in response to such painful stimuli the body tends to
withdraw the leg to stop the pain immediately and involuntary and this is done by
the spinal cord reflexes.
**Remember: pain receptor is called free nerve ending (nociceptor receptor).
Stepping on a sharp object by right leg for example will stimulate the nociceptor
receptors (pain receptor), these receptors generate an impulse to spinal cord
which do synapses in the grey matter and the second neuron do crossing then to
cortex through "ALS" pathway.
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*If pain in right leg >>>right leg should rise and do reflection for far away pain
source. Pain neuron gets three branches: one of them brain branch, inhibitory
interneuron which causes inhibition of the extension muscles and excitatory
interneuron to the flexion muscles to remove the leg from the source of pain.
**The strong question:
Although pain neuron itself is excitatory neuron it doesn't cause excitation to the
flexion muscle but using excitatory interneuron which brain get excitatory order
through it?
Because we have many flexor muscles that more logically and faster using
interneuron instead of pain neuron get a branch for each muscle!!
Crossed Extension Reflex:
After withdrawing the leg in pain from the source of harm, an order to the other
leg is also sent to prepare it bear the weight of the body and prevent the person
from falling. So from the same neuron there is also a crossing circuit in spinal cord
to the other leg causes activation to the other site through an interneuron (using
both inhibitory and excitatory interneuron) Which causes the opposite action in
the other leg; inhibition of the flexor muscles and activation of the extensor
muscles. (This cycle requires 4 neurons).
**NOTE:
-Both crossed extension reflex and nociceptive reflex sends impulses to more than
one muscle (complex muscle).
-The smallest body reflex (in the number of neurons) is the muscle stretch reflex,
requiring only a sensory and a motor neuron (NO intermediate neurons).
- All of these reflexes happen on different levels (segments) of the spinal cord.
-we talked about spinal cord reflex as a way for motor unit excitation also; we
have two ways conscious through cortex and unconscious through sub cortical.
Motor System Division:
1) Tracts: send orders to motor neurons
-Voluntary(conscious) tracts>>> come from motor cortical area then to
spinal cord so is called Corticospinal tract ….when this tract reach medulla
it will pass pyramid area so is called (pyramidal Tracts)you should know it's
get conscious order from cortex to muscle.
-Involuntary (unconscious) tracts>>>Extra_pyramidal tract: all tracts that
send direct orders to motor neurons but not from cortex and do not pass
through the pyramid.
*usually first part of name of tract (area that comes from it) and second
part (area that will go to it).
a) Tectospinal tract
b) Rubrospinal tract
c) vestibulospinal tract
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d) Reticulospinal tract
2) Receptors (Regulators)
Basal ganglia
Cerebellum
Tract
Tectospinal tract
Pathway
Runs from Superior &
Inferior collicili in
midbrain (tectum of the
brain) to the spinal cord.
Function
Feedback from the ear and the eye,
so when doc hit table the majority
look to sound source because
sound that we are hearing caused
localize of brainstem then signal
transfer to superior colliculus or
when doc walk a visual stimuli
transfer to superior colliculus then
as a reflex all turning of the head,
(muscles of the neck and trunk) in
response to visual or auditory
stimuli.
Rubrospinal tract
(Ruby: red) This tract runs
from a region in the
brainstem called the red
nucleus to the anterior
horn of the spinal cord
vestibulospinal tract
from vestibular system to
the spinal cord
Helps in fine delicate movement,
thus usually innervates distal parts
of the limbs especially upper limbs
in human and both upper and lower
limbs in monkeys. When moving
our fingers, there’s already a
baseline of activation from the red
nucleus, control of further
movement is by additional
activation of basal tone (for delicate
and precise movement), which
makes it much easier to move than
starting from zero impulses.
(the main order comes from the
cortex to move your fingers,
however the delicate movement
comes from the red nucleus).
Maintains balance of the body and
posture. Also innervates ear, that
sends information to the brain as a
result of tilting of the head,
processes this information and
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correct the movement, but also
branches to synapse with motor
neurons that innervates muscle of
the trunk, since it is the major
region to control body’s posture.
(Also innervate and sends signals to
the eyes, since it also helps in
body’s balance.
Reticulospinal Tract:
reticular formation in
brain stem (net-like of
cells don’t have nucleus
and definite shape) to the
spinal cord
* In corticospinal have two neurons:
1) Upper motor neuron: from cortex to spinal cord.
2) Lower motor neuron: from spinal cord to muscle.
Gives the muscle tone (baseline of
tension found in the muscles (not
completely relaxed)
Innervates all body muscles but
most importantly muscles of
posture and trunk that hold weight
because they require higher muscle
tone.
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*If cutting occur in upper motor neuron and lower motor unit, I can't do voluntary
movement because pathway is damaged so, no movement and cause weakness or
completely paralysis to muscles in two cases.
*If cutting occur in lower motor neuron>>>absolutely I can't do excitation because
no spinal cord and reflexes also, no muscle tone (muscle don’t receive activators
by any way) so, paralysis in this case is called (flaccid paralysis). But If cutting occur
in lower motor neuron >>>I can do excitation because spinal cord and reflexes are
found although fine movement is canceled, muscle tone is increased because
muscle is agog for activation so, paralysis in this case is called (tonic paralysis).
* Babinski sign:
 This movement comes from sensation, recognisation and some control
from upper motor neurons, if upper motor neuron is not found or damaged
which cause fanning reflex (A positive Babinski sign).
Don’t compare yourself with
Anyone in this world. If you
Compare, you are insulting
Yourself 
Done by:
Samar Al-mazone ^_^
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