Control of Movement 1 Flashcards
What is Henneman’s size principle?
Henneman’s size principle describes the way which we recruit motor units - we first recruit small slow twitch fatigue resistant motor units for a small amount of force and then recruit bigger and bigger motor units as we go, recruiting fast twitch fatigue resistant and then fast twitch fatiguable fibres - leaving the biggest motor unit until last to achieve the most force
Why is the neuromuscular junction described as a secure synapse?
because there is a 1:1 relationship between an action potential and muscle contraction
What feature of the neuromuscular junction ensure a secure synapse?
post junctional folds, large area, lots of synaptic vesicles
What is Myasthenia Gravis?
a type II hypersensitivity where antibodies attack the ACh nicotinic receptors and the 1:1 relationship between action potentials and muscle contraction is lost
What happens if muscles remain un-activated?
the muscle will up regulate its ACh receptors which will result in a response to circulating ACh which will activate a muscle cell - these small activations are called fibrillations - there is also spontaneous activity of the degenerating motor neurons which creates fasciculations - over time without activation the muscle will irreversibly degenerate
What are the signs of lower motor neuron syndrome?
weakness or paralysis, decreased superficial reflexes, hypoactive deep reflexes, decreased tone, fasciculations and fibrillations, severe muscle atrophy
What are upper motor neurons?
neurons that control the excitability of lower motor neurons
What causes involuntary muscle activation?
lower motor neurons
What causes voluntary muscle activation?
upper motor neurons
What are the two motor control pathways in the spinal cord and what do they control?
the lateral pathways control more lateral motor neurons for voluntary muscle control and skilled movement, the ventromedial pathways control more medial motor neurons for postural control
What are the lateral pathways for motor control?
corticospinal tract and the rubrospinal tract
Where does the lateral cortico-spinal tract decussate?
at the pyramidal decussation
What are the 3 pathways that contribute to the ventromedial pathway?
colliculospinal tract (also called tectospinal), reticulospinal tract (pontine and medullary) and vestibulospinal tract (lateral and medial)
What is the role of colliculospinal tract?
postural adjustment with visual looming - e.g. when falling towards the floor respond by stepping out
What are the signs of upper motor neuron syndrome?
weakness, spasticity, increased tone, hyper reactive deep reflexes, clonus, babinski’s sign, loss of fine voluntary movements
