Functional hierarchy of the motor system Flashcards
What is the direct control of muscles via?
alpha motorneurons in the spinal cord
What 2 tracts give descending inputs to incorporate the trunk and limb muscles into reflexes?
vestibulospinal and reticulospinal
What are the 3 higher brain centres controlling brainstem nuclei instructing voluntary movement?
cerebral cortex
basal ganglia
cerebellum
Lesions of LMN results in?
flaccid paralysis and muscle atrophy
How is alpha motor neuron activity regulated?
UMN in brainstem or cortex synapse with multiple lower circuit neurons
Lesion in UMN
spasticity, high tone eg Parkinsons
Corticospinal tract lesion
weakness rather than paralysis
Paresis
muscle weakness
How is the body musculature mapped in spinal cord?
medio-laterally
If there is damage to sensory inputs what happens?
paralysis as if the motor neurons themselves were damaged
In the stretch reflex which muscle is innervated by a monosynaptic synapse and which by a polysynaptic reflex?
the extensor is monosynaptic and the flexor is polysynaptic
Name the 4 main stretch reflexes and their cord segment which they align with
biceps - C6
triceps - C7
patellar - L4
Achilles tendon - S1
How can reflexes help detect level of spinal cord damage?
reflexes can be evoked above but not below level of damage
In diabetes which reflex may be lost?
Achilles tendon - ankle jerk
Why must patients be distracted when testing their reflexes?
avoid voluntary interference
What are nociceptors?
pain receptors
nociceptor - 3 P’s
protective, polysynaptic and pain
Do nociceptive fibres have a large or small diameter?
small
Flexor reflex - is there contralateral or ipsilateral flexion?
ipsilateral
Flexor reflex - is there contralateral or ipsilateral extension?
contralateral
Why does the contralateral limb extend?
prevent falling over
In the flexor reflex how does sensory information ascend to the brain?
spinothalamic tract
This basic circuitry for the flexor withdrawl and contralateral extension is the same for what simple day to day activity?
walking
Why is the flexor crossed extensor reflex much slower than the stretch reflex?
several interneurons with synaptic delay
nociceptive fibres have small diameter = slow conduction
Excessive load on a muscle activates what to protect the muscle from tearing?
Golgi tendon organ
What can override the GTO?
descending voluntary excitation of alpha motor neurons
High activity of gamma motor neurons can lead to what?
muscles becoming resistant to stretch –> spastic
What Is altered gamma motor neuron discharge to spindles associated with?
neurological disorders
What is facilitation of reflexes?
increases effects of sensory inputs
Pain fibre input facilitates action of muscle spindles by maintaining alpha motor neurons in which state?
depolarised
When the lateral aspect of sole is stroked what should happen?
plantar flexion
What is babinski’s sign?
disruption to corticospinal tract causes plantar extension
What group of non pathological patients is babinski’s sign found in?
children < 1 years old as their motor system is not fully developed
What is spinal shock?
spinal cord injury leading to loss of reflexes for a month which come back gradually and are often exaggerated
Clonus
stretch causes oscillatory muscle contraction and relaxation
