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Summary Neuronal Network and Behaviour; motor systems
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Summary Neuronal Network and Behaviour; movementLecture 1, movement & central control
Today: Conceptual background, stretch reflexes, lower motor neurons, eye movements.
After today’s lecture you will be able to:
• Explain how stretch reflexes work.
• Describe the anatomical organization of spinal innervation of muscles.
• Explain how saccadic eye movements are controlled.
Movement is fundamental
- Nothing in biology makes sense unless it is in the light of evolution, which is certainly
true for the brain.
- How more the brain develops, the more mobile the animals become, they have more
complex movements. The primates can do very complex things with their hands and
fingers, this is due to our motor systems being elaborate and complex.
- Seasquirts move towards a place and then digest their brain for energy. Thus we have
a brain for movement.
,All neuronal networks and behaviours arise from feedback circuits
How many types of movement are there? What are some examples?
- Voluntary: hitting a tennis ball
- Involuntary: reflexes
- Rhythmic: walking, breathing
- Learned: piano
- Habitual: scratching
→ this implies there are different circuits in the brain for this
Systems overview: Neural control of movement
Lower motor neurons innervate skeletal muscles causing them to contract together with
local circuit neurons that make up the spinal cord circuits→ low level motor control.
The higher level is in the brain proper inside your head and those we call upper motor
neurons which are located in the primary motor cortex as well as in the brainstem.
Modulatory systems like the basal ganglia and cerebellum are connected to the upper motor
neurons and also cortical areas.
The hypothalamus controls a lot of involuntary movements.
,Control circuits for movement
When we talk about movement, we have to pay attention to local control circuits
What happens in ballistic control is that the driver is very simple, you have a controller
(neurons) and a plant (muscle). In ballistic control, there is not that much control after you
send the commands. Therefore it is very prone to noise.
Noise in the movement system: something hits your arm while making a movement or the
weights put on your leg muscle changes.
Ballistic control can be improved with parametric adjustment (learning)
To control noise we have ballistic control with a parametric adjustment
- Feedforwards→ adjusting by measuring the new weight
- Feedback→ here you can introduce a comparator which is essential to nervous
control of the motor system. From the actual result, you learn and you adjust the
parameters. You learn from each preceding trial.
o It is not ideal if the noise changes before the next cycle as you then first have
to know again the actual result before you can adjust
, Feedback guidance is best
Feedback guidance has a comparator before the desired result will go into the controller. The
error between the actual and desired result will control the controller and plant.
- The actual result is compared all the time to the desired result
- The command becomes an error
Thus guided feedback is better than ballistic due to guided feedback control that compares
the actual and desired result all the time without a delay minimizing noise.
The simplest feedback circuit for movement
• Stretch reflex (e.g., knee-jerk reflex )
- You have some kind of sensor in the flexor of the bicep.
This sensor sends input of the stretch of the muscle into
the spinal cord, it comes through the dorsal root
ganglion (as usual for sensory input) and contacts
directly the alpha motor neurons that control the
muscles and increase their firing which then increases
the tone of the muscle, how hard it is pushed.
- If you hold a cup for example and you pour some soda
into it, the muscle is stretched as there is more load on it
and it activates the motor neurons which then increases
the tone of the muscle by bringing the cup upwards.
- Also if you go to the doctor and the doctor chacks your
reflex of your leg by hitting below your knee with a
rubber mallet the leg will extend.
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