HMC| Sofie Nooijen
Human Motor Control
Hoorcollege 1
From muscle contraction to action
Levels of description
Fibers→muscles→antagonists→actions
Contractile proteins: actine and myosine
- Training increases the number of actine-myosine bridges (bigger muscles)
- Non-use results in muscle atrophy
Warming up increase:
- Muscle temperature
- Muscle metabolism (supply of energy through breakdown of glycogen)
Motion planning→ mental image of ‘planned action/movement’
Coordination→ coordinating movements to your own and others movements
Saccade→ ‘fastest’ movement (eye movements), which is kind of a picture (moment opname)
Smooth pursuit→ following a moving ‘object’ with your eyes; so that’s different from saccade
Redundancy→ movements can be generated by different combinations of contracting muscles
Bi-articular muscle→ over 2 joints/gewricht
Poli-articular→ multiple joints; generating force
Mono-articular→ over one joint; body position
Executing movements in different ways, with different muscle combinations is necessary, to prevent
strain and tiredness when performing repetitive movements.
Control Muscles
More about positions and posture, not about the control over specific muscles
Joint space→ posture
Parameter space→ with force (‘how’ the movement should be)
Work space→ the environment; you should use a specific ‘area’
Interpersonal space→ with ‘teamsports’; your place relative to the rest (place, timing, reaction to..
etc.)
Muscle as springs?
Cyclic movements/repetitive movements→ walking is movement like a ‘spring’ you can adapt the
frequency or speed (sinusoidal velocity profile)
- Harmonic oscillator:
o walking is subcortical controlled, so it is unconscious
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Oscillatory movements→ ‘automatic’ movements; subcortical controlled from when you started the
movement (you turned the movement ‘on’)
They need energy, adjustment and monitoring
Sports that require oscillatory movements:
- Horseback riding
- Swimming
- Running
▪ Oscillatory movements need energy, adjustment and monitoring
Sport: also need to (implicitly) understand the laws of motion…, think about figure skating…
Damped oscillator→ the resistance increases, when energy/tiredness increases (like with snorkelling)
Mass spring system
When a movement has started / the force is released: you can’t really stop the movement anymore
(the same with a spring)
boxers know how to exploit their mass-spring system to generate high forces
at top speed.
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Redundancy→ movements can be performed by contractions of many muscle combinations
Experts know how to exploit this redundancy
Sensory information originating from muscles contraction provides proprioception: awareness
(feeling and knowing) of one’s own body position in the world; which is essential for many sports
Control level 1:
Spinal sensory-motor loop
Alpha primary motor neurons→ Makes muscle contract ;
project onto the muscle; final part of the muscles
that cause muscle contraction, they are in the
spinal cord.
Gamma neurons→ project on the connection parts of the
spindles (which are spinals) in the sensory
parts in the muscles; depending on how
these ‘spindle/spiral’ is stretched→ on the
end parts of the spindle, and with the gamma
motor neuron, you somehow change the
stiffness of the muscle/spindle, which then sensors
detect etc. etc. → Gamma equilibrium-point model by Feldman et al.
Voluntary control of muscle contraction compared with movements of mass-spring system
When muscles are contracted, kinetic energy is stored in the actine-myosine bridges and this
energy is exploited when the muscle relaxes. Indeed, the sensorimotor loop responsible for muscle
contraction has spring-like features which is the key claim of the equilibrium-point model
Stretch reflex; spinal level
Change the sensory thresholds of muscle spindles and a target movement to a new equilibrium
follows automatically?
You set the threshold of the muscle in a new state; and then this muscle goes automatically to the
equilibrium of this muscle state
- Practicing proprioception improves motor control
“golgi organ in the tendon tapped starts firing and this neural afferent signal is connected at the
spinal level with alfa motor neuron that sends an efferent signal to your leg muscle, which then
automatically contracts”
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Spinal level; Stretch Reflex
Also known as ‘knee-jerk reflex’ and ‘myotatic reflex’. In its simples form it is a 2-neuron loop,
one afferent neuron and one efferent neuron. The afferent neuron is connected to a muscle spindle;
which detects stretch in the muscle. The efferent neuron is the motor neuron; which causes the
muscle to twitch.
1. When stretch receptors fire, the alfa-motor neuron is excited, and the muscle contracts
2. When the golgi tendon organ fires, the alfa-motor neuron is inhibited, and the muscle
relaxes.
- The purpose here is that the stretch receptors tell the muscle when it needs a little more
force – that despite intending to contract the muscle is lengthening. This helps you to
maintain the correct muscle tone. The golgi tendon organs, on the other hand, begin to
fire when the tension on the tendon is so great, that you are in danger of injury. They
have a protective function, and therefore they tell the muscle to ease off before it tears.
Several pathways which innervate alfa-motor neurons
1. Voluntary pathways: include lateral and anterior corticospinal systems (basis motor
section)
2. Postural pathways: do not originate in cortex; their function is to maintain an upright
posture against gravity; requires hundreds of little muscular adjustments that we are not aware
of
- Practising proprioception improves motor control
At the lowest motor control level (muscles) we have a clever sensory motor mechanism that takes
care of discrete but targeted movement.
Control level 2:
Brain stem
Movement is controlling imbalance due to displacement of center of gravity
Crucial in relating vision to balance: “when you put a child in a room, standing upward and
facing the wall of the room and you suddenly move the room towards the child, the visual
flowfield change will induce the child to fall backward: demonstration of direct link
between vision and balance”
Medial – proximal: Whole body movements; vision – balance – reticular formation
Reticular formation; integrate a lot of information from the visual system and vestibular
system, and project to the motor system.
Lateral – distal: arm – hand – leg – foot;
Control level 3:
Cerebellum
- Sensorimotor
- Feedforward; you gain time, you’re faster in controlling
- Learning
- Timing stiffness
- Smoothness
Co-contraction→ increases stiffness of the arm
Sport: stiffness control and co-contraction is important in many sports contexts
Collorary discharge ; efference copy; whenever I plan a movement and I send the information from
my cortical area to my muscles, there will be a copy (feedforward) of those signals stored in the
Cerebellum, and this copy has in it, expected sensory consequences of this movement that’s about to
be made. That copy is compared to the sensory information that comes in, when the movement is
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