Motor Control Flashcards
What are broad principles of motor control
Hierarchical organisation
Functional segregation
What is meant by hierarchical organisation
High order areas of hierarchy are involved in more complex tasks (programme and decide on movements, coordinate muscle activity)
lower level areas of hierarchy perform lower level tasks (execution of movement)
What is meant by functional segregation?
Motor system organised in a number of different areas that control different aspects of movement
What are 2 major descending tracts?
Pyramidal tracts
Extrapyramidal tracts
What are 2 pathways of the pyramidal tracts
Corticospinal
Corticobulbar
(pass through pyramids in medulla)
What are pathways of the extrapyramidal tracts
Vestibulospinal
Tectospinal
Reticulospinal
Rubrospinal
(do not pass through pyramids in medulla)
What are the functions of the pyramidal tract?
Motor cortex to spinal cord or cranial nerve nuclei in brainstem
Voluntary movements of body and face
What are the functions of the extrapyramidal tracts?
Brainstem nuclei to spinal cord
Involuntary (automatic) movements for balance, posture and locamotion
Where is the primary motor cortex located?
What does the it do?
Located in precentral gyrus, anterior to the central sulcus
Controls fine, discrete, precise voluntary movements.
Provides descending signals to execute movements.
Where is the premotor area?
What does it do?
Located anterior to primary motor cortex
involved in planning movements
Regulates externally cued movements
e.g. seeing an apple and reaching out for it
Where is the supplementary area?
What does it do?
Located anterior and medial to primary motor cortex
Involved in planning complex movements (e.g. internally cued, speech)
Becomes active prior to voluntary movement
Describe the path of the corticospinal tract?
What are two tracts it split into and where ?
Where doe they then innvervate?
What does homunculus show?
What does the somatotopic representation show?
How much brain is needed for parts to work?
Where innervates where
What does the corticobulbar tract do
Principal motor pathway for voluntary movements of the face (and neck)
What do moto neurons from the following nuclei do?
Oculomotor and trochlear ?
Trigeminal?
Abducens?
Facial?
Hypoglossal?
Eye movements
Muscles of the jaw
Muscles of the face
The tongue
What do the vestibulospinal tract do?
Stabilise head during body movements, or as head moves
Coordinate head movements with eye movements
Mediate postural adjustments
What does the reticulospinal tract do?
Most primitive descending tract - from medulla and pons
Changes in muscles tone associated with voluntary movement
Postural stability
What does the tectoospinal tract do?
From superior colliculus of midbrain
Orientation of the head and neck during eye movements
What does the rubrospinal tract do?
From red nucleus of midbrain
In humans mainly taken over by corticospinal tract
Innervate lower motor neurons of flexors of the upper limb
What are negative signs of upper motor neurone lesions?
Loss of voluntary motor function
Paresis: graded weakness of movements
Paralysis (plegia): complete loss of voluntary muscle activity
What are positive signs of upper motor neurone lesions?
Increased abnormal motor function due to loss of inhibitory descending inputs
Spasticity: increased muscle tone
Hyper-reflexia: exaggerated reflexes
Clonus: abnormal oscillatory muscle contraction
Babinski’s sign
What is apraxia
What causes it
A disorder of skilled movement. Patients are not paretic but have lost information about how to perform skilled movements
Lesion of inferior parietal lobe, the frontal lobe (premotor cortex, supplementary motor area - SMA)
Any disease of these areas can cause apraxia, although stroke and dementia are the most common causes
What happens with a low motor neuron lesion
Weakness
Hypotonia (reduced muscle tone)
Hyporeflexia (reduced reflexes)
Muscle atrophy
Fasciculations: damaged motor units produce spontaneous action potentials, resulting in a visible twitch
Fibrillations: spontaneous twitching of individual muscle fibres; recorded during needle electromyography examination
What is motor neurone disease?
Progressive neurodegenerative disorder of the motor system
Also known as Amyotrophic Lateral Sclerosis (ALS)
What are upper motor neurone signs of MND?
Spasticity (increased tone of limbs and tongue)
Brisk limbs and jaw reflexes
Babinski’s sign
Loss of dexterity
Dysarthria (difficulty speaking)
Dysphagia (difficulty swallowing)
What are lower motor neurone signs of MND?
Weakness
Muscle wasting
Tongue fasciculations and wasting
Nasal speech
Dysphagia
Describe the structure of basal ganglia
Caudate nucleus
Lentiform nucleus (putamen + external globus pallidus) – together caudate and putamen are known as the striatum
Nucleus accumbens
Subthalamic nuclei
Substantia nigra (midbrain)
Ventral pallidum, claustrum, nucleus basalis (of Meynert)
Describe the function of basal ganglia
Decision to move
Elaborating associated movements (e.g. swinging arms when walking; changing facial expression to match emotions)
Moderating and coordinating movement (suppressing unwanted movements)
Performing movements in order
What is Parkinson’s disease?
Name some signs of Parkinsons disease
Degeneration of the dopaminergic neurons that originate in the substantia nigra and project to the striatum
Bradykinesia - slowness of (small) movements (doing up buttons, handling a knife)
Hypomimic face - expressionless, mask-like (absence of movements that normally animate the face)
Akinesia - difficulty in the initiation of movements because cannot initiate movements internally
Rigidity - muscle tone increase, causing resistance to externally imposed joint movements
Tremor at rest - 4-7 Hz, starts in one hand (“pill-rolling tremor”); with time spreads to other parts of the body
What is Huntington’s disease
What are the signs
Degeneration of GABAergic neurons in the striatum, caudate and then putamen
Choreic movements (chorea - dance)
rapid jerky involuntary movements of the body; hands and face affected first; then legs and rest of body
Speech impairment
Difficulty swallowing
Unsteady gait
Later stages, cognitive decline and dementia
Genetic neurodegenerative disorder
Chromosome 4, autosomal dominant
CAG repeat
What is ballism
Usually from stroke affecting the subthalamic nucleus.
Sudden uncontrolled flinging of the extremities
Symptoms occur contralaterally.
Where is the cerebellum
What is its function
Located in posterior cranial fossa
Separated from cerebrum above by tentorium cerebelli
Coordinator and predictor of movement
What is the function of the vestibulocerebellum
What does damage cause to it
Regulation of gait, posture and equilibrium
Coordination of head movements with eye movements
Damage (tumour) causes syndrome similar to vestibular disease leading to gait ataxia and tendency to fall (even when patient sitting and eyes open)
What is the spinocerebellum
What does damage cause
Coordination of speech
Adjustment of muscle tone
Coordination of limb movements
Damage (degeneration and atrophy associated with chronic alcoholism) affects mainly legs, causes abnormal gait and stance (wide-based)
What does cerebrocerebellum do
What does damage to it do
Coordination of skilled movements
Cognitive function, attention,
processing of language
Emotional control
Damage affects mainly arms/skilled coordinated movements (tremor) and speech
What is ataxia
General impairments in movement coordination and accuracy. Disturbances of posture or gait: wide-based, staggering (“drunken”) gait
What is dysmetria
Inappropriate force and distance for target-directed movements (knocking over a cup rather than grabbing it)
What is an intention tremmor
Increasingly oscillatory trajectory of a limb in a target-directed movement (nose-finger tracking)
What is dysdiadochoikensia
Inability to perform rapidly alternating movements (rapidly pronating and supinating hands and forearms)
What is scanning speech
Staccato, due to impaired coordination of speech muscles
What are the main signs of cerebellar dysfunction and when are they apparent
Apparent only on movement
Ataxia
General impairments in movement coordination and accuracy. Disturbances of posture or gait: wide-based, staggering (“drunken”) gait
Dysmetria
Inappropriate force and distance for target-directed movements (knocking over a cup rather than grabbing it)
Intention tremor
Increasingly oscillatory trajectory of a limb in a target-directed movement (nose-finger tracking)
Dysdiadochokinesia
Inability to perform rapidly alternating movements (rapidly pronating and supinating hands and forearms)
Scanning speech
Staccato, due to impaired coordination of speech muscles
What are alpha neurones
They are lower motor neurons of the brainstem and the spinal cord
Innervate the extrafusal muscle fibres of the skeletal muscles
Activation causes muscle contraction
What is the motor neuron pool
Motor neuron pool contains all alpha motor neurons innervating a single muscle
What is a motor unit
a single motor neuron together with all the muscle fibres that it innervates. It is the smallest functional unit with which to produce force
Stimulation of one motor unit causes contraction of all the muscle fibres in that unit.
What are the types of motor units?
Slow (S, type I)
smallest diameter cell bodies
small dendritic trees
thinnest axons
slowest conduction velocity
e.g.posture
Fast, fatigue resistant (FR, type IIA)
larger diameter cell bodies
larger dendritic trees
thicker axons
faster conduction velocity
e.g.sprinting
Fast, fatiguable (FF, type IIB)
larger diameter cell bodies
larger dendritic trees
thicker axons
faster conduction velocity
Different portions based on genetics and environment
How are the 3 different motor unit types classified?
amount of tension generated
speed of contraction
fatiguability
What are the 2 mechanisms by which the brain regulates the force that a single muscle can produce
Recruitment
Motor units are not randomly recruited. There is an order to this.
Governed by the “size principle”. Smaller units are recruited first (these are generally the slow twitch units).
As more force is required, more units are recruited.
This allows fine control (e.g. when writing), under which low force levels are required.
Rate coding
A motor unit can fire at a range of frequencies. Slow units fire at a lower frequency.
As the firing rate increases, the force produced by the unit increases.
Summation occurs when units fire at frequency too fast to allow the muscle to relax between arriving action potentials.
What are neurotrophic factors
Are a type of growth factor
Prevent neuronal death
Promote growth of neurons after injury
What is hypo-reflexia
Below normal or absent reflexes
Associated with lower motor neuron diseases
Explain the plasticity of motor units
Fibre types can change properties under many different conditions.
Type IIB to IIA most common following training
Type I to II possible in cases of severe deconditioning or spinal cord injury. Microgravity during spaceflight results in shift from slow to fast muscle fibre types
Ageing associated with loss of type I and II fibres but also preferential loss of type II fibres. This results in a larger proportion of type I fibres in aged muscle (evidence from slower contraction times).
What is the function of 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.
An involuntary coordinated pattern of muscle contraction and relaxation elicited by peripheral stimuli.
“…….the magnitude and timing of which are determined respectively by the intensity and onset of the stimulus”.
Reflexes differ from voluntary movements in that once they are released, they can’t be stopped.
What is the Jendrassik manoeuvre
Try clenching the teeth, making a fist, or pulling against locked fingers when having patellar tendon tapped. The reflex becomes larger
Descending (supraspinal) control of reflexes
Higher centres of the CNS exert inhibitory and excitatory regulation upon the stretch reflex.
Inhibitory control dominates in normal conditions (N).
Decerebration reveals the excitatory control from supraspinal areas (D).
Rigidity and spasticity can result from brain damage giving over-active or tonic stretch reflex.
What is hyper-reflexia
Overactive reflexes
Loss of descending inhibition
Associated with upper motor neuron lesions
What is clonus
Involuntary and rhythmic muscle contractions
Loss of descending inhibition
