Neuro - Motor Control Flashcards
What is hierarchical organisation?
Complex tasks involve higher order areas whereas simple tasks only involve lower orders
What is functional segregation?
Different areas of motor system control different aspects of movement
What does the motor cortex do?
Receives information from other cortical areas and sends commands to the thalamus and brainstem
What do the cerebellum and basal ganglia do?
Adjust the commands received from other parts of the motor system
What does the brain stem do?
Passes commands from the cortex to the spinal cord
What are the main pyramidal tracts?
Corticospinal and corticobulbar
What are pyramidal tracts associated with
Voluntary movement
Describe the course of pyramidal tracts
Cross through the pyramids from the motor cortex going to the spinal cord or the cranial nerve nuclei in the brainstem m
What are the main extrapyramidal tracts
Vestibulo, rubro, reticulo, tectospinal
What are extrapyramidal tracts associated with?
Automatic movements for balance, posture and locomotion
Describe the course of extrapyramidal tracts
Don’t cross the pyramids, lower motor neurones found in the brainstem or cranial nerve nuclei
Where is the primary motor cortex found?
Precentral gyrus
What does the supplementary area do>
Plans complex movements such as internally cued speech, active prior to voluntary movement
What does the premotor area do
Plans movements that are externally cued e.g. seeing a cup of coffee and going to pick it up
What are the 2 fates of corticospinal neurones
Either decussate or don’t at the level of the medulla
Where do uncrossed corticospinal fibres innervate
Form the anterior tract to innervate the axial/trunk muscles
Where do crossed corticospinal fibres innervate
Form the lateral tract to innervate the limbs
What does a motor homunculus show
Homunculus shows how much of the brain is devoted to different aspects of the body
What is somatotropic representation
Body is mapped to show that different motor neurones in that area will be responsible for that particular body part
What is the role of the corticobulbar tract
Responsible for the voluntary movement of the muscles of the face (and neck)
Describe the pathway of corticobulbar neurones
Originates from the motor cortex and synapses onto the CN nuclei in the brainstem
What is the role of the vestibulospinal tract
- Stabilises the head during body/head movements
- Coordinates head movements with eye movements
- Mediates postural adjustments
What is the role of the reticulospinal tract
- From medulla and pons
- Changes in muscle tone associated with voluntary movement
- Postural stability
What is the role of the tectopsinal tract
- From superior colliculus of the midbrain
- Orientation of the head and neck during eye movements
What is the role of the rubrospinal tract
- From red nucleus of the midbrain
- Mainly taken over by corticospinal tract
- Innervates lower motor neurones of flexors of the upper limb
When does the rubrospinal tract become more involved in motor control?
When there are lesions of the CNS
What is a negative sign for motor tract lesions
Loss of movement
Paresis
Paralysis
What is a positive sign for motor tract lesions
Additional abnormal functioning Spasticity Hyperreflexia Clonus Babinski's sign
What is a negative sign indicative of
LMN lesions
What is a positive sign indicative of
UMN lesions
What is apraxia a sign of
UMN lesion
What is apraxia
Disorder of skilled movements as the patient can no longer perform them
What is a common caused of apraxia
Stroke and dementia, or lesions at the inferior parietal lobe, or the supplementary/premotor area of the fontal lobe
What are the signs of lower motor neurone lesions
Weakness Hypotonia Hyporeflexia Atrophy Fasciculations Fibrillations
What are fasciculations
Visible twitches due to damaged motor neurones producing action potentials at the NMJ
What are fibrillations
Non visible witching seen in needle electromyography examination
What is motor neurone disease (MND)
A progressively degenerative disorder affecting upper and lower motor neurones in the brainstem (also called ALS)
What is the cure for MND
There us none - it eventually causes death due to decreasing function of respiratory muscles
What are UMN signs of MND
Spasticity Brisk/exaggerated reflexes Babinski + Loss of dexterity Dysarthria (trouble speaking) Dysphagia
What are LMN signs of MND
Weakness Muscle eating Tongue fasciculations + wasting Nasal speech Dysphagia
What structures are in the basal ganglia?
Caudate nucleus Lentiform nucleus Nucleus Accumbens Subthalamic nuclei Substantia nigra Ventral pallidum, claustrum, nucleus basalis
(Some Say Vicious Lions Nor Cats Can Nap)
What are the functions of the basal ganglia?
Decisions to move
Elaborating associated movements
Moderating and coordinating movement
Performing movement in order
(Don’t Ever Make Pounces)
What is the lentiform nucleus made of?
Putamen and external globus pallidum
What is the striatum made of?
Caudate and putamen
What is the basic reason as to why the basal ganglia are commonly involved in many diseases?
There is complicated circuitry that interlinks the different structures of the basal ganglia
What is Parkinson’s?
Degeneration of dopaminergic neurones originating in the substantial nigra and projecting onto the striatum, resulting in a movement disorder with a deficiency in small dextrous movements
What are the signs of Parkinson’s
Bradykinesia Hypomimic face Akinesia Rigidity Tremor at rest
What is bradykinesia
Loss in dexterity
Describe the tremor in Parkinsons
4-7Hz - starts in 1 hand but then spreads
What is Huntingtons
Degeneration of GABA neurones in the striatum, caudate and then putamen
What are the signs of Huntingtons
Choreic movements Speech impairment Dysphagia Unsteady gait Eventually cognitive decline/dementia
What are choreic movements
Dance like movements of the hands and face, then legs and then rest of body
What is ballism
Sudden uncontrolled flinging of the extremities usually from a stroke affecting the sub-thalamic nucleus.
generally one sided and contralateral
Where is the cerebellum found in the skull
Posterior cranial fossa
What covers the cerebellum
Tentorium cerebelli
What is the rile of the cerebellum
Prediction and coordination of movement - takes descending signals and compares them with afferent signals to coordinate movement and make them fluid
What are the parts of the cerebellum
Vestibulo
Spino
Cerebro
What is the role of the vestibulocerebellum
Regulate gait, posture and equilibrium
Coordinate head movements with eye movements
What is the role of the spinocerebellum
Coordinate speech
Adjusts muscle tone
Coordinates limb movements
What is the role of the cerebrocerebellum
Coordination of skilled movements
Aspects of cognitive attention control
What are the signs of damage to the vestibulocerebellum
Gait ataxia
Tendency to fall even when spatially aware
(similar to vestibular disease)
What are the signs of damage to the spinocerebellum
Abnormal gait/ wide based stance
What are the signs of damage to the cerebrocerebellum
Affects skill/ coordinated movements
What are the main signs of cerebellar dysfunction
Dysmetria Intention tremor Scanning speech Dysdiadochokinesia Ataxia
What is key about cerebellar dysfunction
Apparent only on movement
What is dysmetria
Inappropriate force and distance for targeted movement
What is ataxia
Weide based/staggering/drunken gait
What is dysdiadochokinesia
Can’t perform rapidly alternating movements such as supination and pronation
What is scanning speech
Staccato due to speech muscle coordination loss
What is intention tremor
Oscillating trajectory of a limb in target direct movement
What do extrafusal fibres do
Have contractile elements
What do intrafusal fibres do
These have sensory organs/ detect stretch
What happens upon alpha motor neurone activation
Contraction of muscle fibres
What is the motor neurone pool
All the alpha fibres innervating a single muscle
What is a motor unit
Single motor neurone and all the fibres it is innervating
How many motor units are there
420,000 - each unit has around 600 muscle fibres
What does single unit stimulation cause
Contraction by all the innervated fibres
What does a small innervation ratio mean
The motor unit is involved with fine precise movement
What are the different types of motor unit
Slow
Fast fatiguable
Fast fatigue resistant
What do slow units do
Smallest diameter cell body and smallest dendritic trees, thinnest axons with the slowest conduction velocity - produce a very small amount of force for a long time but slow generation
What do fast fatigue resistant fibres do
Produce a bit more force but slow generation of more force
What do fast fatiguable units do
Produce much more force and generate this quickly but tire quickly
What is recruitment
Slow units recruited first but then the CNS will recruit more units including FR and FF as more and more force is required
What is rate coding
happens simultaneously with recruitment - slow motoru units fire at a low frequency but an increase in firing rate causes a greater force produced
What are neurotrophic factors
Type of growth factor preventing neuronal death and promoting neurone growth after injury
Why do we get slower contraction times as we age
Loss of muscle fibres but preferentially type 2a and 2b therefore the proportion of slow twitch units increases
What is a reflex
An automatic response to a stimulus that involves a nerve impulse passing inward from a receptor to a nerve centre and then outward to an effector (as a muscle or gland) without reaching the level of consciousness
What is the Jendrassik effect?
When we clench our first when carrying out a reflex, the reflex is much greater as the effect means that we reduce inhibitors of the reflex coming from the CNS (descending/supraspinal inhibition)
What is decerebration
This is when we detach the cortex from the lower brainstem/spinal cord to give a much greater reflex/tonic response - this is because the CNS has a baseline level of inhibition and can be related to rigidity and spasticity
What are propriospinal neurones
Interneurones that go up and down the spinal cord to activate nearby muscles
What are gamma motor neurones
Altering sensitivity of sensory organs in the muscle - they don’t produce muscle contraction however they sensitise the muscle and its sensory organs
What is clonus
UMN dysfunction demonstrated through involuntary and rhythmic muscle contraction of the foot
What is a positive Babinski sign
When we stroke the outside sole and across the ball of the feet - the toes should point downward however if Babinski positive the toes still point upwards therefore is an upper motor neurone lesion
What is a normal Babinski in infants
The toes to point upwards (a positive Babinksi sign)
What is hyporeflexia
Below normal or absent reflexes due to efferent arm being affected therefore associated with a lower motor neurone lesion
