Functional Hierarchy of the Motor System Flashcards
What allows direct control of muscle
Motor neurones in the spinal cord
in the final common path
Where doe reflex occur
Autonomously at each segmental spinal levels
Where does input to trunk and limbs arise from
Vestibulospinal and reticulospinal tracts
What is the function of the basal ganglia in the motor system
Gating proper initiation of movement
What is the function of the cerebellum in motor system
Sensory motor coordination of ongoing movement
-refinement
What is the function of the cerebral cortex in the motor system
Planning, initiating and directing voluntary movements
What is the function of brainstem in the motor system
Controls spinal reflexes and integrates them into higher order reflexes controlling posture and balance
What controls the brainstem nuclei and stimulates voluntary movement
Cerebral cortex
(motor cortex, premotor and supplementary motor areas)
Basal ganglia
Cerebellum
What four system control movement
Descending control pathway (motor cortex and brainstem)
Basal ganglia
Cerebellum
Local spinal cord and brainstem circuits
Where are the Lower motor neurones found and what is their function
at spinal levels directly innervate muscles to initiate reflex and voluntary movements
What is the result of lower motor neurones lesions
Flaccid paralysis
muscle atrophy - as no longer metabolically active
What is the function of the upper motor neurones
synapse with multiple lower circuit neurones to regulate motoneurone activity
Where are upper motor neurones located
Brainstem or cortex
What do the upper motor neurones from the cortex control
Spatiotemporal skilled movement
Lesion is upper motor neurones in the cortex causes
Spasticity, some paralysis, may be transient
Lesion specifically in the brainstems posture -regulating pathway causes
Spastic paralysis
Lesion in the Corticospinal tract (cortex) result in
weakness (paresis), rather than paralysis
What does it mean that there is a spatial map of the body musculature in the spinal cord
Muscles closer to the trunk (shoulders) are more medial motor neurones and muscle located further away from the trunk (fingers) are lateral motor neurones
How does body musculature in the spinal cord refer to arms and legs
Medio-laterally
How does the spinal cord receive descending input
via neurons in the brainstem AND direct cortical input via Corticospinal / Pyramidal tract.
How does ascending sensory input enter the spinal cord
at any level and in the from of proprioceptors, touch, pain etc
Why and How does the sensory input reach brainstem
via the vestibular system to inform about balance
What occurs when sensory input is at the level of the cortex
We make movements in response to visual, olfactory, auditory, emotional, intellectual cues
If their is damage to sensory input at spinal level what can occur
paralysis as if the motoneurones themselves had been damaged
What is the affect of sensory neuropathy
Loose all proprioception (lost sense of body in time and space and motor control so effectively paralysed)
How does sensory neuropathy occur
autoimmune attack on sensory neurones in the dorsal root ganglia cause loss of large myelinated fibres
What occurs in the stretch reflex
Initial stimulus causes the muscle to stretch and stimulates muscle spindles
afferent Impulses from muscle spindle acting as stretch receptor travel to spinal cord via dorsal route
efferent/motor impulses leave via ventral route and travel to to alpha motor neuones leading to contraction of the stretched muscle resulting in extension
whilst efferent impulses travel to antagonist muscle and cause relation
(= reciprocal inhibition)
What is the crucial cord segment in the biceps jerk tricep jerk patellar tendon Achilles tendon reflex
C6
C7
L4
S1
What is the significance of testing reflexes
Helps to detect level of spinal cord damage
Impaired reflexes indicate areas of nerve damage
In spinal cord damages where can reflects be evoked
Above spinal cord damage
How do you avoid voluntary influencing of reflex response
Distract patient
What occurs in the process of the flexor (withdrawal) reflex
Uses information from pain receptors (nociceptors) in skin, muscle and joint and through a polysynaptic and protective process to withdraw body away from painful stimulus and toward the body
=ipsilateral flexion in response to pain
What is activated by the nociceptive fibres that controls all the flexor muscle of the affected limb
activate interneurones in spinal cord segment which in turn activates α motoneurones
In the flexor withdrawal reflex if you withdraw the limb and do nothing else, you would fall over, so what additional process occurs to prevent this
The Contralateral limb extends - maintain an upright postures by extending the limb to bear body weight
How does the contralateral limb extend
By excitatory interneurones crossing the spinal cord
What is the affects of increase sensory AP from nociceptors
Increases activity of the flexor muscle of the affected part
Inhibits the antagonist extensors
Excite contralateral extensors
Inhibit contralateral flexors
How does sensory information ascend to the brain
Via the contralateral spinothalamic tract
What is the two reasons the flexor crossed extensor reflex far slower than the stretch reflex
The process has several interneurones in the pathways each with a small synaptic delay (slow down process)
Nociceptive fibres have smaller smaller than muscle spindle afferents (conduct more slowly)
What occurs in the golgi tendon reflex
There is an excessive load on muscle, activates GTO reflex
Neurones from golgi tendon organ flies, motor neurone is inhibited causing the muscle to relax and release the load in an aim to protect the arm
How do you maintain contraction of the GOT reflex if you are holding something important and heavy
Reflexes are over-ridden consciously
by Descending voluntary excitation of motoneurones overriding the inhibition from the GTOs
Where does a motor neurones receive its synpases
Many are from descending cortical excitatory and inhibitory inputs, with continual integration of EPSPs and IPSPs
How is the stretch reflex over-ridden
strong descending inhibition hyperpolarizes α-motoneurones and the stretch reflex can not be evoked.
Where do the muscle spindles get their motor innervation
Gamma motor neurones innervating both poles of the intrafusal pathway and maintain spindles sensitivity t stretch
What occurs with high gamma motoprneruone activation of spindle fibres
Muscles become extremely resistant to stretch and become spastic
What is the clinical relevance of the stretch reflex
reflexes can be evoked above, but not below given level may localise a problem eg. segmental trauma to the spine.
Why does a more painful stimulus give a larger response
Due to facilitation which increases the effects of sensory inputs
How do pain fibres input facilitate the action of muscle spindles
By maintaining the alpha motor neurones in a more depolarised state
What can mild cutaneous stimulation provoke (give an example)
Flexor reflex
eg mild stoking of the sole of your foot causes plantar flexion - downward curling of big toe)
What is it called when the toe extends and doesn’t flex (fans up and out)
Babinskis sign
What is the cause of Babinskis sign
Damage or disruption to the Corticospinal tract (upper motor leison) meaning their is an imbalance between extensor and flexor reflexes
Where else is babinskis sign seen in
Seen in children < 1 year old motor system not fully developed
After epileptic seizures - transient cortical function disruption
What is the affect does spinal transection (complete tear of spinal cord) have on the function of higher centres in maintaining normal reflexes
immediate sensory and autonomic effects - loss of sensation;
loss of bowel, bladder and sexual regulation
What Occurs in spinal shock
Loss of supraspinal excitation (no control from higher centres)
hyporeflexia, as all reflexes below the point of injury
are not evoked
This lasts 2-6 weeks - then gradual return of reflexes
What is the second stage of symptoms seen after spinal shock
Reflexes return
Reflexes are exaggerated = hyperflexia
- Light touch provokes powerful withdrawl
- extensor reflex support body weight briefly
Clonus
Define clonus
stretch causes oscillatory muscle contraction/relaxation
