Motor Control and Movement Disorders Flashcards
What are the 2 principles of motor control?
- Hierarchical organisation
- Functional segregation
What is hierarchical organisation?
- higher order areas are involved in complex tasks (programming and deciding on movements, co-ordinating muscle activity)
- lower order areas are involved in lower level tasks (execution of movement)
What is function segregation?
Different areas control different aspects of movement
What are pyramidal tracts?
tracts that pass through the pyramids of the medulla
What are extrapyramidal tracts?
tracts that do NOT pass through the pyramids of the medulla
What are the 2 pyramidal tracts?
- Corticospinal
- Corticobulbar
What is the output of neurons of the pyramidal tracts?
From the motor cortex to the spinal cord or cranial nerve nuclei in the brainstem
What is the output of the extrapyramidal tracts?
Brainstem nuclei to spinal cord
What are the pyramidal tracts responsible for?
The voluntary movements of the body and face
What are the 4 extrapyramidal tracts?
- Vestibulospinal
- Tectospinal
- Reticulospinal
- Rubrospinal
What are the extrapyramidal tracts responsible for?
Involuntary (automatic) movements for balance, posture and locomotion
Where are the motor neurons of the extrapyramidal tracts?
- UMN = motor cortex
- LMN = brainstem nuclei to the spinal cord
Where is the primary motor cortex?
In the precentral gyrus, anterior to the central sulcus
What does the primary motor cortex control?
Controls voluntary movement
Where is the premotor area located?
anterior to the primary motor cortex
What does the premotor area do?
- involved in planning voluntary movements
- regulates externally cued movements
Where is the supplementary motor area?
anterior and medial to the primary motor cortex
What does the supplementary motor area do?
- involved in planning complex movements (internally cued, speech)
- becomes active prior to voluntary movement
What is the proportion of crossed fibres in the corticospinal tract?
85%-90% crossed fibres
10%-15% uncrossed fibres
What is the vestibulospinal tract responsible for?
- stabilise the head during body or head movements
- co-ordinate head movements with eye movements
- mediate postural adjustments
What is the reticulospinal tract responsible for?
- changes in muscle tone associated with voluntary movements
- postural stability
What is the tectospinal tract responsible for?
orientation of the head and neck during eye movements
What is the rubrospinal tract responsible for?
- from the red nucleus of the midbrain
- In humans mainly taken over by the corticospinal tract
- Innervate lower motor neurons of flexors of the upper limb
What are the negative signs of the effect of a upper motor lesion?
- loss of voluntary motor function
- paresis: graded weakness of movements
- paralysis (plegia): complete loss of voluntary muscle activity
What are the positive signs of an upper motor lesion?
- Babinski’s sign
- Clonus (abnormal oscillatory muscle contraction)
- Hyper-reflexia (exaggerated reflexes)
- Spasticity (increased muscle tone)
- Increased abnormal motor function due to loss of inhibitory descending inputs
What is apraxia?
A disorder of skilled movement, not paretic but have lost information on how to perform skilled movements
What are the causes of apraxia?
lesions at: - inferior parietal lobe - the frontal lobe (premotor cortex, supplementary motor area) - stroke - dementia
What are the impacts of the lower motor neuron lesion?
- weakness
- hypotonia (reduced muscle tone)
- hyporeflexia (reduced reflexia)
- muscle atrophy
- fasciculations (damage motor units produce spontaneous action potentials, resulting in a visible twitch)
- fibrillation (spontaneous twitching of individual muscle fibres, recorded during needle electromyography examination)
What motor spinal tract is responsible for the voluntary movements of the head/neck?
corticobulbar
What motor spinal tract is responsible for motor information to the trunk?
anterior corticospinal tract
What motor spinal tract is responsible for motor information to the limbs?
lateral corticospinal tract
What cranial nerves are controlled by the corticobulbar tract?
- oculomotor
- trochlear
- abducens
- trigeminal
- facial
- hypoglossal
what is the route of the corticospinal tracts?
- motor cortex
- cerebral peduncle (midbrain)
- pyramids of medulla
- corticospinal tracts
- synapse with LMN in the ventral horn of spinal cord
- LMN via the ventral root to effector
Which part of the corticospinal tract decussates at the pyramids?
- anterior stays ipsilateral
- lateral goes contralateral
Where do upper motor neurones travel to?
from the brain to the spinal cord
Where do the lower motor neurones travel to?
from the spinal cord to the effector
What happens when there is upper motor neurone lesion?
- increased tone
- reduced power
- increased reflexes
How do you examine patients?
- inspection
- tone
- power
- reflexes
- sensation
- co-ordination
What happens when there is lower motor neurone lesion?
- muscle atrophy and fasciculations (twitch)
- reduced tone
- reduced power
- reduced reflex
What is a nucleus?
collection of neurones in the brain that have a similar function
What is Parkinson’s disease?
- degeneration of dopaminergic neurones projecting from the substantia nigra (midbrain) to the striatum (basal ganglia)
- basal ganglia cannot process motor programmes correctly
What are the symptoms of Parkinson’s?
- rigidity
- tremor at rest
- hypomimic face
- bradykinesia
- akinesia
- shuffling gait
What is Huntington’s disease?
- degeneration of GABA and acetylcholine neurones in the striatum
- leads to hyperexcitability because GABA is inhibitory
What are the symptoms of Huntington’s disease?
- choreic movements
- speech difficulty
- dementia
- dysphagia
- unsteady gait
- hallucinations
What lies in the posterior cranial fossa?
cerebellum (below the tentorium cerebelli)
What is the role of the vestibulocerebellum ?
regulation of gait, posture and coordination of head/eye movement
What is the role of the spinocerebellum?
Coordination of speech, adjustment of muscle tone and coordination of limb movements.
What is the role of the cerebrocerebellum?
co-ordination of skilled movements and cognitive functions (attention, language processing and emotions)
What happens when the vestibulocerebellum is damaged?
- gait ataxia
- tendency to fall
What happens when the cerebrecerebellum is damaged?
- Damage to arms/skilled coordinated movements and speech
- tremor
What are the general cerebellar dysfunction signs?
D - Dysdiadochokinesia (inability to perform rapidly alternating movements) A - Ataxia N - Nystagmus I - Intention Tremors S - slurred staccato speech H - Hypotonia (Dysmetria)
Where are the effects of cerebellar disease seen?
In the limbs ipsilateral to the lesion
What is a motor unit?
- basic unit of motor control
- involves a single lower motor neurone and all the motor fibres that it innerveates
What are the three different types of fibres?
- slow (1)
- fast, fatigue resistant(2a)
- fast, fatiguable (2b)
What is the fatiguability of slow (1) fibres?
minimal
What is the maximum force of slow (1) fibres?
small
What type of motor units are needed to function in day to day living?
a combination of fast, fatigue resistant (2a) and slow (1)
What motor unit transition happens in spinal injury?
from fast, fatigue resistant (2a) to fast, fatiguable (2b)
What colour do slow neurones tend to be?
red
What is the fatiguability of fast, fatigue resistant (2a) fibres?
medium
What is the maximum force of fast, fatigue resistant (2a)fibres?
large amount
What are reflexes?
automatic protective responses to dangerous stimuli that don’t reach consciousness and are unstoppable
What is descending control?
descending pathways (UMN) that can inhibit or increase reflexes
What is the Jendrassik Manoeuvre?
- to relax the UMN effect - LMN reflexes more obvious
- clench teeth, lock hands and pull hard
- increased UMN firing overflows to increase excitability of LMNs
Describe the path of the lateral corticospinal tract from the brain?
- precentral gyrus
- cerebral peduncle
- midbrain
- medulla (cross over)
- lower motor nuerones
What makes up the lateral corticospinal tract?
decussated upper motor neurones
What makes up the anterior corticospinal tract?
ipsilateral upper motor neurones (innervate trunk muscles)
Where do UMN in the corticobulbar tract synapse?
the brainstem cranial nuclei
What is motor neurone disease?
progressive neurodegenerative disorder of the motor system characterised by progressive muscle weakness
What is motor neurone disease also known as?
amyotrophic lateral sclerosis (ALS)
What causes upper motor signs in motor neurone disease?
damage to the UMN which extend from the primary motor cortex via the pyramids of the medulla and down the corticospinal tract
What are the upper motor neurone disease signs?
- spasticity
- brisk limbs
- babinski’s sign
- loss of dexterity
- difficulty speaking (dysarthria)
- dysphagia
What are the lower motor neurone disease signs?
- weakness
- muscle wasting
- tongue fasciculations and wasting
- nasal speech
- dysphagia
What is the basal ganglia?
a number of subcortical nuclei primarily responsible for motor control
What is the role of the basal ganglia?
- decision to move and conduct voluntary movements including elaborating associated movements
- Moderating and coordinating movement through suppression
- Performing movements in order.
What does the basal ganglia consist of?
.
What causes Huntington’s disease?
- due to excessive (>35) CAG repeats in the HTT gene on chromosome 4
- elongated polyglutamine tail of the huntington protein, interfering with normal cellular function
What happens when the spinocerebellum is damaged?
affects mainly the legs
- abnormal gait
- wide based stance
What can cause damage to the spinocerebellum?
chronic alcoholism
What is an intraparenchymal bleed?
within the substance of the brain
What are the clinical features of an Intraparenchymal bleed?
- rapid onset headache
- Hx of hypertension
- no trauma
How do you treat a Intraparenchymal bleed?
- anti-hypertensives
- ?surgical intervention
What is an alpha motor neurone?
LMN of the brainstem and spinal cord
What do alpha motor neurones innervate?
extrafusal muscle fibres of skeletal muscles (contractile)
What is an innervation ratio?
the number of muscle fibres innervated by a single motor neurone (inversely proportional to the level of control)
What is the innervation ratio of fine control?
low (nuanced movement)
What is the innervation ratio of coarse control/ strong movements?
high
Describe slow twitch (T1) motor units?
- small diameter
- slow conduction velocity
- minimal fatiguability
- small force
Describe fast, fatigue resistant (T2a) motor units?
- larger diameter
- faster conduction velocity
- increased ATP hydrolysis
- eg: oxidative fibres
- fatigues in minutes
- moderate force
Describe fast, fatigable (T2b) motor units?
- largest diameter
- insignificant amount of myoglobin
- Glycolytic fibres generate ATP through anaerobic glycolysis
- fatigues in seconds
- large force
What motor units are prevalent in the muscles for postural stability?
slow type muscle fibres
What is recruitment?
the activation of additional motor units to accomplish an increase in contractile strength in muscle
In what order are motor units recruited?
from slow to fast
What is rate coding?
the concept that the force produced by a single motor unit is determined by the number of muscle fibres that it innervates and the frequency of innervation
What are neurotrophic factors?
growth factors that support growth, survival and differentiation of developing/mature neurones
What do neurotrophic factors do?
- prevent neuronal death
- promotes the growth of neurone post-injury
What is the palsticity of motor units?
Muscle fibres can change types under different conditions
What can cause the conversion of motor units from type 2b to type 2a?
post-training
What can cause the conversion of motor units from type 1 to type 2?
severe deconditioning or spinal cord injury
What is the impact of microgravity on the type of muscle fibre types?
from slow (T1) to fast (T2)
How does microgravity cause a change in the muscle fibre types?
- diminished load on the MSK system
- hydrostatic pressure difference
- muscular atrophy of postural muscles
What happens to muscle fibre types in ageing?
- loss of type 1 and type 2 (2 preferentially)
- larger proportion of T1 therefore slower contraction time
What are the steps involved in a reflex arc?
- sensory receptor
- sensory neuron
- integrating center (spinal cord)
- motor neurone
- effector
What is decerebration?
Loss of inhibtion due to motor neurone damage causes hyper-excitability of relflexes
What can cause an over-active or tonic stretch reflex?
- rigidity
- spasticity
(due to brain damage)
What causes hyper-reflexia?
- loss of descending inhibition
- UMN lesions
What causes clonus?
- loss of descending inhibition
- UMN lesions
What is Babinski’s sign?
- stimulate sole with blunt instrument
- normal: curls downwards
- positive: curls upwards
- in infants, upwards normal
