Week 9 - Motor Neurons and Movement Flashcards
What are the 5 general steps involved in movement?
- Plan movement
- Initiate movement
- Co-ordinate multiple muscles in space and time
- Refine movements using sensory feedback
- Optimise movements when repeated
Can one motor neuron innervate multiple muscle fibres?
yes
and each muscle fibre only receives input from one neuron
What are the 3 sources of input to LMNs?
- Input from spinal interneurons
- Sensory input from muscle spindle fibres
- Input from UMNs in brain
Where are the cell bodies of LMNs found?
- within brainstem of motor nuclei of cranial nerves
- ventral horn of spinal cord
What are 2 descending pathways and what they do?
Corticospinal tract -> supplies musculature of body
Corticobulbar tract -> supplies musculature of head and neck
Distinction between lateral and anterior corticospinal tract?
Lat CST -> moves limbs and muscles contralaterally
Ant CST -> moves limbs in proximity to midline
What percentage of fibers decussate to form lateral CST? and how many remaining for anterior CST?
90% fibers cross at caudal medulla in a bundle of axons called pyrimidal decussation and form Lat CST
10% continue down ipsilaterally to form Ant CST
What are the motor systems involved in motor control? and how do they work in regard to motor function?
Posterior Parietal Cortex -> sens integration centre informing premotor cortex of sensory input
Prefrontal Cortex -> decision-making to execute action
Premotor Cortex -> receives info from prefrontal -> plans movement
Primary Motor Cortex -> receives info from pre-motor -> executes movement through muscle contraction and relaxation
What are the types of Unilateral Lesions and how do they affect the motor pathways?
UMN lesions above pyramidal decussation:
-> affect contralateral side
UMN lesions below pyramidal decussation:
-> affect ipsilateral side
LMN lesions:
-> produce ipsilateral paralysis and atrophy
What are symptoms of LMN lesions?
- Loss of motor control (flaccid paralysis)
- Weakness (Paresis)
- Muscle fibres lose contractile proteins (muscle atrophy)
- Loss of reflexes (Areflexia)
What are short and long-term symptoms of UMN lesions?
Short term:
- Flaccidity
- Hypotonia (less spinal cord activity
- Areflexia
Long term:
- Loss of fine movements
- Spasticity
- Babinski sign
What does the cerebellum do?
helps refine movements (planning movement // doesnt affect LMNs)
Functions:
- Gait coordination
- Maintenance of balance and posture
- Muscle tone control and voluntary muscle activity
What are the 3 functionally distinct cerebellar regions and what do they do?
What are symptoms of Cerebellar damage?
Ataxia -> uncoordinated movements
Dysenergia -> decomp of synergistic multi-joint movements (eg touching finger to nose)
Dysemetria -> lack of coordination -> results in overshoot/undershoot
Does cerebellum control ipsilateral or contralateral movements?
ipsilateral
What do the basal ganglia do?
modulate motor function and control movement
What is the basal ganglia?
Interconnected nuclei below cerebral cortex
What nuclei does the Basal Ganglia consist of?
- Striatum (Caudate and Putamen)
- Globulis pallidus
- Substantia nigra
- Subthalamic nucleus
Direct and Indirect pathway of Basal Ganglia diagram
GPI = Globulis pallidus internal
-> this is inhibitory in nature so when you inhibit it via striatum, you are disinhibiting it therefore increasing stimulus to thalamus
What are D1 and D2 expressing neurons and where are they?
D1-expressing neurons = excited by dopamine
D2-expressing neurons = inhibited by dopamine
What produces dopamine?
Substantia nigra
How does dopamine facilitate motor loops?
- excites direct pathway
- inhibits indirect pathway
What happens when something goes wrong in basal ganglia like degeneration or lesion?
Disorders of Basal Ganglia characterised by limited or excessive movement.
Hypokinetic Disorders:
= overactivity in indirect pathway
- eg Parkinson’s
Hyperkinetic Disorders:
= underactivity of indirect pathway
- eg Huntington’s
