Neuromuscular control of movement

Question 1

main players in feedback with movement

Answer 1

• Human movement depends on combination of feedforward and feedback control in an adaptive manner.
• Output of control modified based on sensor input
  • Comparison of desired vs actual behaviour
• System elements
  • Controller (Central Nervous system)
  • Actuators (Muscle-skeletal system)
  • Sensors (Proprioceptors/Vision)

Question 2

brain areas in movement

Answer 2

• contain the upper motor neurons –> innervate lower motor neurons in of brain stem or spinal cord
  1. motor cortex –> executary
  2. dorsal premotor area –> sensory integration
  3. supplementary motor area –> internal motivation (should I move?)
  4. basal ganglia –> modulation of frequency, amplitude, and force
  5. cerebellum –> modulating and memory

Question 3

spinal cord - descending tracts

Answer 3

The pyramidal tract (goes through the pyramids of the medulla) originates in the cerebral cortex, carrying motor fibres to the spinal cord and brain stem.
They are responsible for the voluntary control of the musculature of the body and face.
• Corticospinal tracts= the upper motor neurons that project to the spinal cord –> body
• Corticobulbar tracts= the ones that project to lower motor neurons of the brainstem –> head and neck

Extrapyramidal tracts: They are responsible for the involuntary and automatic control of all musculature, such as muscle tone, balance, posture and locomotion
•	 Rubrospinal
•	 Reticulospinal
•	 Vestibulospinal
•	 Tectospinal

Question 4

NMJ

Answer 4

• Neuromuscular junctions (NMJs) or motor endplates are the junctions between axonterminals of a motor neuron and muscle fiber
• Facilitates the synaptic transmission and initiates muscle contraction
• has a basal lamina
• has juntional folds
• chemical synaps –> ACh binds to AChR

Question 5

central pattern generators (CPG)

Answer 5

• Central pattern generators (CPGs) are biological neural circuits in the spinal cord that produce rhythmic outputs in the absence of rhythmic input.
• They are the source of the tightly-coupled patterns of neural activity that drive rhythmic and stereotyped motor behaviours like walking, swimming, breathing, or chewing.
• The ability to function without input from higher brain areas still requires modulatory inputs, and their outputs are not fixed. Flexibility in response to sensory input is a fundamental quality of CPG-driven behaviour
• Higher brain areas are needed to initiate and modulate but not to propagate

Question 6

gait cycle phases

Answer 6

1. heel trike (ds)
2. loading response
3. mid-stance
4. terminal stance
5. pre-swing (ds)
6. toe off
7. mid swing
8. terminal swing

Question 7

spinal cord - ascending tracts

Answer 7

• These carry sensory information from the PNS to the brain
• They found inside the ventral, lateral and dorsal parts of the spinal cord.
• There are three types of ascending tracts:
  • Dorsal lemniscus tract –> sensory pathway that transmits delicate sensations like vibration, proprioception and touch
  • Spinothalamic (or anterolateral) tarct –> sensory pathways that transmit sensory information about crude touch from free nerve endings (nociceptors, mechanoreceptors, thermoreceptors)
  • Spinocerebellar tract –> sensory pathway that is in charge of sending sensory information that will help coordinate the muscles in the trunk and the limbs. (proprioceptors)
• They are made up of four successively connected neurons.
  1. First order neurons are found inside dorsal root ganglions from where they gather sensory input
  2. And send it to the second order neurons, usually found inside the spinal cord or brainstem. –> cross over (decussation)
  3. They further transmit it to the third order neurons found inside the thalamus
  4. And then the fourth order neurons in the cerebral cortex.

Question 8

epidurial electrical stimulation

Answer 8

epidural electrical stimulation (EES) of the spinal cord may be pivotal to regain motor function in patients that suffer from SCI

• EES enables the brain to exploit spared but functionally silent descending pathways in order to produce movements of paralysed limbs
• EES activates motor neurons by recruiting proprioceptive circuits within the posterior roots of the spinal cord
• EES tries to replicate spatial and temporal neuronal activity in the spinal cord for a given movement to replicate that movement
• EES would immediately enable voluntary locomotion despite chronic paralysis, and that the ability to sustain active movements during training would promote meaningful functional improvements with and even without stimulation. –> exploiting spared but functionally silent descending pathways to move eventually without the EES

Question 9

measuring movement

Answer 9

• Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph to produce a record called an electromyogram
  • Amplitude of the function explains the amount of activation and can be used t assess force and fatigue
  • EMG gives a live overview of muscle contractions which can be used top map complicated movements if multiple muscles are imaged
• Ground reaction force apparatus is used to measure precisely how weight is distributed during the gait cycle of patients
• the one used in sci-fi movies to map parts of the body during a movement using reflective tape and detectors

Question 10

embedded coordination

Answer 10

• Preflexes:
  • The passive mechanics of the leg & joints
  • The stiffness & damping properties of muscles
• Reflexes & CNS:
  • Central pattern generators
  • Muscle synergies
• CNS:
  • Motor programs