Functional hierarchy of the motor system and motor control Flashcards
What does it mean that the motor system is organized as a hierarchy?
Voluntary brain control of muscles is via alpha motorneurones in the spinal cord- they are the “final common path”
But
Reflex control of muscles is autonomous and hard-wired into motorneurone circuit at each segmental spinal level
But
Brainstem nuclei control spinal reflexes and integrate them into higher-order reflexes that control posture and balance
- For example, descending inputs from vestibulospinal and reticulospinal tracts regulate trunk and limb muscle reflexes
But
Brainstem nuclei themselves receive control inputs about voluntary movements from higher centers- from the cerebral cortex (motor, premotor and supplementary motor cortex), the basal ganglia, and the cerebellum
What controls movement?
Four system control movement
1 Descending control pathways
2 Basal ganglia
3 Cerebellum
4 Local spinal cord/ brain stem circuits
Describe the motor system
Explain the spacial map of the bodies musculature
Muscles also map spatially where?
Higher brain centres are
Functionally interdependent and control different aspects of voluntary movements
The spinal cord recieves
Descending input via the brainstem and direct cortical input via the Corticospinal (Pyramidal) tract
Sensory input is crucial and enters at all levels
1 at the spinal cord in the form of proprioceptors, touch, pain etc
2 at the brainstem the vestibular system informs about balance
3 at cortical level, we make movements in response to visual, olfactory, auditory, emotional, intellectual cues
Damage to sensory inputs (at spinal level)
Results in paralysis as if the motorneurones themselves had been damaged
Tell the tale of Ian Waterman
Viral infection caused loss of proprioception therefore unable to move
Autoimmune attack on sensory neurones in the dorsal root ganglia (DRG) causing loss of large myelinated fibres and sensory neuropathy - very rare. DRGs don’t regenerate
So he lost the sens of his body in space and his motor control and was effectively paralysed
Taught himself to mentally visualise the movements he needed to make and the sequence of muscle contractions needed for them
So he used visual system instead of his proprioceptive system to provide feedback on where the parts of his body were
Spinal cord reflexes
Spinal reflexes are simple building blocks for movement
The simplest reflex is the stretch reflex
EG patellar tendon or knee-jerk reflex
Uses information from muscle spindles which monitor muscle length
Describe the reflex arc
Explain how the stretch reflex work
- Force transmitted to the muscle fibres- they are more elastic than tendons and so are more able to stretch
- Stretch activates 1a afferent sensory nerves in the muscle spindle:
- → this increases the number of action potentials in 1a afferents projecting through the dorsal horn into the spinal cord
Spindle sensory afferents divide to make…
3 types of connections
2 spinal cord one brain
- Monosynaptic reflex
- Reciprocal inhibition
- Thalamus and somatosensory cortex
Explain Monosynaptic reflex
many directly contact a-motoneurones in the stretched muscle : causing rapid contraction of the AGONIST muscle.
this is a MONOSYNAPTIC REFLEX – one synapse, no interneurones involved – it is the only such connection known.
Describe the pathways in a diagram for motor control
Describe the pathways in a diagram for motor control
Stretch reflex in arms
Inverse stretch reflex
Inverse stretch reflex
Why the clasp-knife reflex?
Golgi tendon organ refkex
Flexor/Withdrawal reflex with crossed extension
Circuitry of flexor reflex
Spinal cord circuitry for flexor and crossed extensor reflex
Can the stretch reflex be overridden
