Motor learning and neurological syndromes Flashcards
Hierarchy of motor control
- Level
- Function
- Structures involved
Low: Execution
- Brainstem and spinal cord
Medium: Tactic
- Motor cortex, cerebellum
High: Strategy
- Association areas of neocortex
- Basal ganglia
Ventromedial pathways
Descending pathways, involuntary:
- Reticulospinal
- Tectospinal
- Vestibulospinal
Uses sensory information about balance, body position and vision
- Maintains balance and posture
Pyramidal/ corticospinal tract
Lateral descending motor pathway
- Initiates at the motor cortex
- Brodman areas 4 +6
- Cells are mainly from layer V [Betz cells]
Travels through internal capsule and cerebral peduncle
90% of the fibres cross in lateral tract, the rest are ipsilateral in anterior tract.
Fibres synapse directly onto motor neurones.
Rubrospinal tract
- Function
- Path
Lateral descending motor pathway
- Stimulates the flexor muscles in the upper limb.
Path:
- Initiates at red nucleus
- Crosses at the midbrain
- Travels down the lateral columns of the spinal cord
Vestibulospinal tract
- Function
- Path
Ventromedial descending motor pathway
- Tract originates in vestibular nuclei of the medulla [medial and lateral]
- Sensory information originates from vestibular labyrinth in the ear.
Medial vestibulospinal tract
- Controls neck and back muscle to guide head movements
- Keeps eyes stable as body moves
Lateral vestibulospinal [projects ipsilaterally]
- Stimulates extensor motor neurones in the legs
- Maintains upright and balanced posture.
Tectospinal tract
- Function
- Path
Ventromedial descending motor pathway
- Controls muscles of the neck, upper trunk and shoulders.
- Co-ordinates head and eye movements
Path:
- Originates in the superior colliculus of the tectum.
- Receives visual information from retina and visual cortex. - Fibres cross in the midbrain and travels down the anterior white column of the spinal cord- contralateral control
Reticulospinal tract
- Function
- Path
Ventromedial descending motor pathway
- Facilitates extension of the limbs
- Locomotion and postural control
Path:
1. Originates in reticular formation of the brainstem
- Descends down the spinal cord to form medial [pontine] and lateral [medullary] tract
Decorticate posturing in coma
Stimulation from: - Supraorbital pressure - Nail bed - Sternum Causes extension of legs and flexion of arms.
Due to lesion above the red nucleus
- Rubrospinal tract intact and more active as regulation from cortex is disrupted [disinhibition]
Decerebrate posturing in coma
- Description
- Pathophysiology
Stimulation from: - Supraorbital pressure - Nail bed - Sternum Causes extension in all limbs.
Mechanism:
- Lesion below the red nucleus, rubrospinal tract is inhibited due to disruption
- Upper limbs are extended due to activation of lateral vestibulospinal and reticulospinal tract
Stroke and posture
Stroke in middle cerebral artery can affect motor cortex and corticospinal tract
- Lower limb extension
- Upper limb flexion
Other features:
- Plasticity
- Brisk reflex [overactive reflex due to upper motor neurone lesion]
- Babinski reflex
- Clonus
Babinski reflex
Extension of the feet when stimulated.
- Seen in those who have lost corticospinal tract [loss of descending inhibition]
- Normal response is to flex feet
- Corticospinal tract is not developed in humans until around the age od 2
Brisk reflex
Spasticity caused by a loss of descending inhibition
- Spinal inhibitory interneurones have been altered
- Increased tone
Corticobulbar pathway
Axons project from
- Cingulate motor area
- Primary motor area
- Layer 5 of the motor neurones inn brainstem
Facilitates
- Mastication via CN V
- Vocal cords/ swallowing via CN IX and X
- Tongue movements via CN XII
Facial palsy and Bell’s palsy
The top half of the face is innervated by CN 7 bilaterally
- Damage in one CN 7 can still give sensation to top half of face
Lower half of the face is contralaterally innervated
- Lesion causes loss of control on lower face
Lesion in upper motor neurone affects the entire half of the face
Parasagittal meningioma
Non benign [usually] neoplasm of the meninges
- Can press on specific areas of the motor cortex, the the one controlling the legs
Can represent as bilateral leg weakness and spasticity
Middle cerebral occlusion and its effects
Proximal lesion = complete hemiparesis
- As it affects the internal capsule, connected to the cortical area of leg motor supply
Distal lesion can allow legs to still have function
- But affect hand and face
Anterior cerebral artery stroke
ACA supplies medial cortex and frontal lobe
- Includes motor control of legs
Stroke can cause:
- Leg paresis [leg motor cortex lesion]
- Abulia: inability to make decisions or act independently [frontal lobe lesion]
Jacksonian mark
Partial seizure
- Associated with lesion close/ in motor cortex
- Progression starting distally from hands to legs.
Posterior parietal cortex
Contains:
- Somatosensory afferent paths [area 5]
- Visual afferent paths [area 7]
Function:
- Body and environmental image
- Exploratory movements
- Lesion causes neglect
Premotor area
Structure
- Inputs from the cerebellum
Controls/ plans visually guided movements
- Prehension [grasping and object via orientation of hand]
- Controls postural and proximal limb muscles
Damage:
- Perseveration of motor activity despite lack of success
- Disrupts learned response to visual cues
Supplementary motor area function
Involved in mental rehearsal of movement
Bereithschaftspotential
Measured the activation of the supplementary motor area before performing an action.
This potential preceded potential from the motor cortex 500-1000ms in self-initiated movements
Apraxia
The inability to carryout purposeful movements
- In absence of paralysis or paresis
- Inability to sequence and execute movements successfully
Ideational
- Cannot report sequence
- Damage to parietal
Ideomotor
- Unable to perform action despite reporting sequence
- damage to SMA
Task specific dystonia
Repeated use of the hand can cause changes in functional organisation of the brain areas that process and execute motor control
- Causes sustained muscle contraction [twisting, abnormal posture]
