Functional Hierarchy System Flashcards
What is direct control of muscles via?
alpha motoneurones in the spinal cord
Where do reflexes occur?
Autonomously at each segmental spinal level
What 4 systems control movement?
Descending control pathways from UMN
Basal ganglia
cerebellum
Local spinal cord and brain stem circuits
What do LMN at spinal levels directly innervate?
Muscles to initiate reflex and voluntary movements
What do lesions to LMN cause?
Flaccid paralysis
Muscles atrophy
Decreased reflexes
Where do UMN synapse with?
With multiple lower circuit neurons to regular alpha moto neurone activity
Where does the spinal cord receive descending input from?
Neurons in the brainstem
And directly from the corticospinal tract
At which level does sensory input enter?
At all levels
Name a stretch reflexes
Patellar tendon
Knee jerk reflex
What is the simplest segmental reflex?
Stretch reflex
What needs to contract and relax with the knee jerk reflex?
Contract the quadriceps
Relax the hamstrings
Why do pathways occur in the knee jerk reflex?
Because one is needed to contract the quadriceps
And the other is needed to relax the hamstrings
Which level is the biceps jerk?
C6
Which level is the triceps jerk?
C7
Which level is the patellar tendon reflex?
L4
What level is the achilles tendon reflex?
S1
Where are proximal shoulder muscles mapped to?
Medial motoneurones
Where are distal muscles mapped to?
Lateral motoneurones
What happens if there is damage to sensory inputs?
Paralysis as if the motoneurons themselves have been damaged
What is the significance of reflex testing?
Can help to detect spinal cord damage
Can evoke reflexes above but not below the level of damage
Why must patients be distracted during reflex testing?
To avoid voluntary influencing of response
What are the steps of the pain reflex?
Increased sensory AP from pain receptors cause
Increased activity in the flexor muscle
Antagonists extensors are inhibited
What happens to the contralateral limb in the pain reflex?
Increased activity in extensors
Decreased activity in flexors
Opposite to the other limb
Why is the contralateral limb extended in pain reflex?
Protective mechanism to protect falling over
Through which tracts does sensory information ascend to the brain?
In the spinothalmic tract
What is babinskis sign a sign of clinically?
The Babinski sign can indicate upper motor neuron lesion constituting damage to the corticospinal tract.
Why is the flexors crossed extensor reflex slower than the stretch reflex?
Because nociceptive sensory fibres have smaller diameter than muscle spindle fibre and so conduct more slowly
How are reflexes overidden?
Descending voluntary excitation of alpha motoneurones can override the inhibition from the GTO’s and maintain contraction
What is the normal response when stroking the lateral aspect of the foot?
Causes plantar flexion (downwards curling of the big toe)
When does the foot reflex only work?
If the Corticospinal tract is intact
What does damage to the CST cause in the foot reflex?
Causes extension and not flexion so toes fan up and out
Why is babinski sign seen in children?
Because their motor system is not fully developed
What is there a loss of in spinal shock?
Supraspinal excitation
How long does it take for the gradual return of reflexes in spinal shock?
2-6 weeks
