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
Where are the output neurons of the pyramidal tracts?
In the motor cortex, to the spinal cord or cranial nerve nuclei in the brainstem
What is 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?
Upper motor neurons:
- motor cortex
Lower motor neurons:
- 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?
Fine, discrete, precise, voluntary movements
provides descending signals
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?
located 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
What is the precentral gyrus responsible for?
Principal motor pathway for voluntary movements of the face (and neck)
What is the vestibulospinal extrapyramidal tracts responsible for?
- stabilise the head during body movements, or as head moves
- co-ordinate head movements with eye movements
- mediate postural adjustments
What is the reticulospinal extrapyramidal tracts responsible for?
- most primitive descending tract (from medulla and pons)
- changes in muscle tone associated with voluntary movements
- postural stability
What is the tectospinal extrapyramidal tracts responsible for?
- from superior colliculus of midbrain
- orientation of the head and neck during eye movements
What is the rubrospinal extrapyramidal tracts 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 head/neck?
corticobulbar
What motor spinal tract is responsible for the trunk?
anterior corticospinal tract
What motor spinal tract is responsible for 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
- corticospinal tracts
- synapse in the ventral horn
- LMN via the ventral root
Which part of the corticospinal tract decussates at the pyramids?
- anterior stays ipsilateral
- lateral goes contralateral
What are upper motor neurones?
from the brain to the spinal cord
What are the lower motor neurones?
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 examen 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 the basal ganglia?
a group of nuclei in the brain with functions associated with motor
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)
(normally have inhibitory effect)
What are the symptoms of Parkinson’s?
- rigidity
- tremor at rest
- hypomimic face
- bradykinesia
- akinesia
What is Huntington’s disease?
degeneration of GABA neurones in the striatum, caudate and putamen
What are the symptoms of Huntington’s disease?
- chorea
- speech difficulty
- dementia
- dysphagia
- unsteady gait
What lies in the posterior cranial fossa?
cerebellum (below the tentorium cerebelli)
What is the role of the vestibulocerebellum part of the cerebellum?
regulation of gait, posture and head/eye movement
What is the role of the spinocerebellum part of the cerebellum?
Coordination of speech, adjustment of muscle tone and coordination of limb movements.
What is the role of the cerebrocerebellum part of the cerebellum?
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?
affects the arms and ckilled, co-ordinated movements (tremor) and speech
What are the general cerebellar dysfunction signs?
D - Disdiadochokinesia A - Ataxia N - Nystagmus I - Intention Tremors S - slurred staccato speech H - Hypotonia (Dysmetria)
What is a motor unit?
basic unit of motor control
involves a single 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 neurones needed to function day to day living?
a combination of fast, fatigue resistant (2a) and slow (1)
What neurone 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 happens in decerebration?
UMN that normally are inhibitory, lose control and become excitatory decerebral posture (constant tensing)
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?
- cerebral peduncle
- midbrasin
- medulla (cross over)
- lateral and anterior corticospinal tract
What is lateral corticospinal tract responsible for?
limb muscles
What is anterior corticospinal tract responsible for?
trunk muscles
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)
How is the body represented somatotopically in a coronal section of the motor cortex?
in -> out
- foot
- leg
- hipp
- trunk
- neck
- head
- arm
- eblow
- hand
- fingers
- eye
- nose
- face
- lips
- tongue
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 are the affects of motor neurone disease?
- voluntary contractions of upper and lower limb muscles
- upper and lower motor neurones (contraction of tongue)
- respiratory intercostal movements
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
- 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
- Moderate and coordinating movement through suppression
- Performing movements in order.
What does the basal ganglia consist of?
- caudate nucleus
- lentiform nucleus
- striatum (putamen and caudate)
- nucleus accumbens
- subthalamic nucleus
- substantia nigra
- ventral pallidum
- claustram
- nucleus basalis
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 is Hemiballismus?
a basal ganglia syndrome characterised by aggressive involuntary limb movements
What causes Hemiballismus?
- injury to the subthalamic nucleus of the basal ganglia (stroke)
- discharges signals down motor tracts to the contralateral skeletal muscles causing uncontrollable swinging
What is the subthalamic nucleus like in normal physiology?
- regulates motor function
- connected to the internal globus pallidus
What happens when the spinocerebellum is damaged?
affects mainly the legs
- abnormal gait
- wide based stance
What can cause damage to the spinocerebellum?
degeneration and atrophy due to chronic alcoholism
What is an intraparenchymal bleed?
within the substance of the brain
What are the symptoms of an Intraparenchymal bleed?
- rapid onset
- 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 (with contractile elements)
What is an innervation ratio?
the number of muscle fibres innervated by a single motor neurones (inversely proportional to the level of control)
What is the innervation ratio of fine control?
small (nuanced movement)
What is the innervation ratio of coarse control?
high
Describe slow (T1) motor units?
- small diameter
- slow conduction velocity
Describe fast, fatigue resistant (T2a) motor units?
- larger diameter
- faster conduction velocity
- increased ATP hydrolysis
- eg: oxidative fibres
Describe fast, fatigable (T2b) motor units?
- largest diameter
- forceful contractions
- insignificant amount of myoglobin
- Glycolytic fibres generate ATO through anaerobic glycolysis
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 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 steeps involved in a reflex arc?
- sensory receptor
- sensory neuron
- integrating center (spinal cord)
- motor neurone
- effector
What can cause an over-active or tonic stretch reflex?
- rigidity
- spasticity
(due to brain damage)
What happens in the descending control of reflexes?
- alpha motor neurones
- inhibitory interneurones
- propriospinal neurones
- gamma motor neurones (alters sensory sensitivity)
- terminals of afferent fibres
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
