week 16: Motor systems L3 Flashcards
General Motor system components and interactions Descending Pathways and motor cortex Reticulospinals
what threshold and receptor type are large diameter, rapidly conducting afferents associated with
low threshold mechanoreceptors
what receptor type are small diameter, low conducting afferents associated with
nociceptors and thermoreceptors
how is conduction velocity related to axon diameter
positvely correlated
what do joint receptors respond to
extreme flexion and extension
why do reflexes always have a monosynaptic and dysnaptic component
monosynaptic component ensures speed
dysnptic component fine tunes response by inhibiting antagonist or recruiting additional motor units
what event is stretch always
IA
how is motor output often affected in disease
affects way motor neurons fire
what are the 5 primary descending pathways
reticulospinal
vestibulospinal
rubrospinal
tectospinal
corticospinal
what are monamines and what release them
neuromodulators released by slow motor pathways (involving reticulospinal, vestibulospinal, dopaminergic systems)
modulate excitability of neurons, makes them high or low threshold
corticospinal
precise voluntary control of distal muscles
rubrospinal function
facilitates flexor muscles of upper limb, some role in motor control
rubrospinal origin, decussation and target
red nucleus
midbrain (immediately after leaving red nucleus)
cervical spinal cord
corticospinal origin and target
primary motor cortex
spinal cord and motor neurons
reticulospinal tract function
controls posture, locomotion and muscle tone
reticulospinal tract origin, decussation and target
reticular formation (pons and medulla)
mostly ipsilateral, some bilateral projections
axial and proximal limb muscles
vestibulospinal tract function
maintains balance, posture and head stabilisation
vestibulospinal origin, decussation and target
vestibular nuclei (brainstem)
lpsilateral (lateral tract)
bilateral (medial tract)
spinal motor neurons controlling extensors
tectospinal function
reflexive head, neck and eye movements in response to visual, auditory and somatosensory stimuli
tectospinal origin, decussation and target
superior colliculus
midbrain
cervical spinal cord
what part of the corticospinal tract stays ipsilateral
anterior corticospinal
10%
what part of the corticospinal tract decussate and where
lateral corticospinal
medullary pyramids
what type of movements does lateral corticospinal tract control
contralateral
what is the reticular formation
network of interconnected nuclei in brainstem
connects to cortex, spinal cord, cerebellum
regulate arousal, motor control, autonomic functions and reflexes
what is the basal ganglia
group of subcortical nuclei involved in motor control, movement initiation, habit formation
modifies movement indirectly
deep within forebrain
connected to thalamus, cortex and brainstem
2 roles of basal ganglia in motor control
regulates movement by modulating motor cortex activity
facilitates desired movements and inhibits undesired movements
inputs of the basal ganglia
main input site: striatum (caudete and putamen nucleus)
from:
cerebral cortex
substantia nigra pars compacta
thalamus
basal ganglia outputs
ventroanterior and ventrolateral areas of thalamus
feeds to motor cortex (motor modulation)
second output from SNpr to superior colliculus (eye and head movement)
hyperkinesia
excessive movement e.g Huntington’s disease
hypokinesia
limited movement e.g Parkinson’s disease
role of GPi and GPe
regulate motor signals
STN
role in modulating movement via excitatory input
SN
contains dopamine producing neurons that modulate striatum
how does the basal ganglia work to allow or supress movement
modulates inhibition levels
what does the direct pathway of basal ganglia do
inhibits GPi, less inhibition on thalamus, more movement
what does the indirect pathway of the basal ganglia do
excited GPi, more inhibition on thalamus, less movement
what does cerebellum keep track of
real time, monitors sensory inputs, from every source, monitors real time feedback
what does basal ganglia remember
what was good and beneficial, does not keep track of what is happening real time, reward prediction mechansim
