Reflexive and Voluntary Activation of Muscle Flashcards
What are some signs of faulty motor control?
Paralysis Weaknss Stiffness Increased reactivity Ticks, twitches, and jerks Fibrillations and fasciculations Loss of coordination and smoothness Loss of effectiveness of movements
Define motor signs
Observable/measurable motor abnormalities/
Presence of abnormalities/
Absence of normal motor actions
Define motor symptoms
Problems of motor function reported by patients
Define motor syndromes
Associated/clustered signs and symptoms
Where are motor neurons found?
Ventral part of spinal cord
Brainstem
What is a motor pool?
Cluster of motor neurons in spinal cord innervating a muscle group
What are the characteristics of a motor neuron?
Large
Cholinergic
Fast conducting
Where do motor neurons synapse with muscle?
At neuromuscular junction (NMJ)
What is the ratio of motor neurons to muscle fibres?
1:many
What is a motor unit?
Motor neuron + all muscle fibres it innervates
Are motor units all the same size?
No
How much force is applied when 25% of a motor pool is activated? Why?
5% of force because smaller motor units recruited first
How is the force applied by a muscle increased?
Larger and larger motor units recruited
What kind of fibres are those that are first activated?
Slow - don’t fatigue over long periods of time
What kind of fibres are activated after slow fibres?
Fast fatigue-resistant
What kind of fibres are activated last?
Fast fatiguable
What is the neurotransmitter released at the NMJ?
ACh
What is a fibrillation?
Tiny contraction caused by activity of single muscle cell
What can fibrillations be due to?
Hypersensitivity
Increased AChR expression - including extra-junctional
What is a fasciculation?
Groups of muscle fibres contracting involuntarily
Can be measured on surface
What does long-term denervation cause?
Atrophy and degeneration of muscle
When can atrophy occur?
In catabolic states
- Diabetes
- Cushing’s disease
What will complete denervation lead to?
Progressive irreversible muscle loss
When at rest, are muscles inactive?
No, have resting tone
What do muscle spindles do?
Report back on length of muscle
Are muscle spindles in series or parallel with muscle?
Parallel
How do muscles spindles work?
The longer a muscle stretches > more activity in these stretch receptors
What do Golgi tendon organs do?
Report back on amount of force transmitted through tendon?
Are Golgi tendon organs in series or parallel with muscle?
In series
What is the role of muscle spindles in the monosynaptic reflex?
Activate motor neurons of same muscle
Returns muscle to original state after stretch detected
What are the signs of lower motor neuron lesions?
Weakness/paralysis Decreased superficial reflexes Hypoactive deep reflexes Decreased tone Fasciculations and fibrillations Severe muscle atrophy
What are the three main types of input onto lower motor neurons?
Sensory input from muscles Secondary information from interneurons - Most of input Input from brain - Come from various regions - Most don't make direct synaptic contact but via interneurons
What are the two groups of descending pathways in the spinal cord?
Lateral
Ventromedial
What tracts are in the lateral part of the spinal cord?
Corticospinal tract
Rubrospinal tract
Where does the corticospinal tract come from?
Cerebral cortex
What is the corticospinal tract sometimes called?
Lateral corticospinal tract
Do the corticospinal and rubrospinal tracts overlap?
Yes
Where does the rubrospinal tract come from?
Red nucleus in brainstem
Which tracts are in the ventromedial part of the spinal cord?
Tectospinal tract
Vestibulospinal tract
Pontine and medullary reticulospinal tracts
Where does the tectospinal tract come from?
Superior colliculus
What else is the tectospinal tract called?
Colliculospinal tract
Where does the vestibulospinal tract come from?
Vestibular nuclei in brainstem
What are the two reticulospinal tracts?
Pontine
Medullary
Which reticulospinal tract is more lateral?
Medullary
Where are the motor neurons for distal muscles in the ventral horns?
More lateral
Why is it important that the motor neurons for distal muscles are more lateral?
Lateral descending tracts make most connections with lateral motor neurons > control more distal muscles
Because distal muscles involve more voluntary control
Where are the motor neurons for proximal muscles in the ventral horns?
More medial
Why is it important that the motor neurons for proximal muscles are more medial?
Ventromedial descending tracts make most connections with medial motor neurons > control more medial muscles
Because medial muscles involve more involuntary control
What does corticobulbar tract refer to>
Cerebral inputs to motor nuclei in brainstem
Cerebral inputs to LMNs in brainstem (cranial nerves)
Where does the corticospinal tract decussate?
Medullary pyramids
How much of the descending projections from the cerebral cortex decussate at the medullary pyramids?
90%
Where do the 10% of descending projections from the cerebral cortex that don’t decussate in the brainstem travel?
In ventromedial pathway
Which ventromedial pathways don’t decussate?
Vestibulospinal tract
Reticulospinal tract
Which ventromedial pathways decussate, and where?
Colliculospinal tract
Decussates immediately
What kinds of connections do ventromedial tracts have in the spinal cord?
Synapse with interneurons that spread information ipsilaterally and contralaterally
What kinds of connections do ventromedial tracts have in the spinal cord?
Synapse with interneurons that spread information ipsilaterally and contralaterally
What happens when the brain can no longer influence the spinal cord?
Spinal locomotor circuits can’t be activated
Most of inputs from brain inhibitory > now hyper-excitable
Spinal reflex circuits become oversensitive and muscle tone above normal levels
What is spinal shock?
After lesion when spinal cord doesn’t really respond
Variable
Unknown pathophysiology
What are upper motor neuron lesion signs?
Weakness Spasticity - Increased tone - Hyperactive deep reflexes - Clonus Babinski's sign Loss of fine voluntary movements
What is clonus?
Rhythmic response to stimulus for long time after stimulus gone
