Motor control Flashcards
In terms of motor control, what is meant by hierarchical organisation?
High order areas of hierarchy are involved in more complex tasks (programme and decide movements, coordinate muscle activity), lower level areas perform lower level tasks (execution of movement)
In terms of motor control, what is meant by functional segregation?
Motor system organised in as number of different areas that control different aspects of movement
In terms of motor control, what is meant by the motor system hierarchy?
Different parts of the brain interact with each other in order to bring out voluntary or involuntary movement
What are the three broad principles of motor control?
Hierarchical organisation, functional segregation and motor system hierarchy
What are the two types of major descending tracts associated with motor control?
Pyramidal tracts and extrapyramidal tracts
What are the two major descending pyramidal tracts?
The corticospinal (movement from the neck down) and corticobulbar tracts (movement of the head and neck)
Why are pyramidal tracts called pyramidal tracts?
Pass through the pyramids of the medulla, whereas the extrapyramidal tracts do not
Outline the path of the major descending pyramidal tracts
Motor cortex to spinal cord or cranial nerve nuclei in brainstem
What is the function of the major descending pyramidal tracts?
Voluntary movements of the body and face
What are the 4 major descending extrapyramidal tracts?
Vestibulospinal, tectospinal, reticulospinal, rubrospinal
Outline the path of the major descending extrapyramidal tracts
Brainstem nuclei to spinal cord
what is the function of the major descending extrapyramidal tracts?
Involuntary movements for balance, posture and locomotion
What is the function of the premotor area?
Involved in the planning of movements, regulates externally cued movements
The premotor area is located where?
Anterior to primary motor cortex
What is the function of the supplementary motor area?
Planning complex movements, becomes active prior to voluntary movement
Where is the supplementary motor area located?
Anterior and medial to the primary motor cortex
Outline the pathway of the corticobulbar tract
Upper motor neurones in the primary motor cortex synapse with brainstem nuclei to provide voluntary movement of the face and neck
Outline the pathway of the corticospinal tract
Upper motor neurones in the primary motor cortex descend and converge to form the corona radiata. The fibres then pass through the midbrain, the pons, into the medulla. The majority of fibres dessucate in the medulla forming the lateral tract, both tracts run along the spinal cord synapsing with lower motor neurones.
What is the function of the Vestibulospinal tract?
Stabilise head during body movements, coordinate head movements with eye movements. Mediate postural adjustments.
What is the function of the reticulospinal tract?
Changes in muscle tones associated with voluntary movement. Postural stability
What is the function of the tectospinal tract?
Orientation of the head and neck during eye movements
What is the function of the rubrospinal tract?
Mainly taken over by corticospinal tract, innervates lower motor neurones of flexors of the upper limb
What path does the reticulospinal tract take?
From medulla to pons
Where does the tectospinal tract originate?
From superior colloculus of midbrain
Where does the rubrospinal tract originate?
From red nucleus of midbrain
Outline the negative signs associated with a upper motor neurone lesion
Loss of voluntary motor function. Paresis (graded weakness of movements). Plegia of voluntary muscle activity
Outline the positive signs associated with an upper motor neurone lesion
Increased abnormal motor function due to loss of inhibitory descending inputs. Spasticity. Hyper-reflexia. Clonus. Babinskis sign.
What is spasticity?
Where a muscle is over-active
What is hyper-reflexia?
Exaggerated reflexes
What is clonus?
Abnormal oscillatory muscle contraction
What is babinskis sign?
Abnormal Dorsi flexion of toes with plantar stimulation
What is apraxia?
Disorder of skilled movement. Patients are not paretic but have lost information about how to perform skilled movements
Why does a lower motor neurone lesion result in hypotonia and not spasticity?
No signal from brain for contraction
What are the causes of apraxia?
Lesion of inferior parietal lobe, the frontal lobe. Stroke and dementia are the most common causes
What are the signs of a lower motor neurone lesion?
Weakness, hypotonia, hyporeflexia, muscle atrophy, fasciculations, fibrillations
What is hypotonia?
Reduced muscle tone
What is hyporeflexia?
Reduced reflexes
What are fasciculations?
Damaged motor units produces spontaneous action potentials resulting in a visible twitch
What are fibrillations?
Spontaneous twitching of individual muscle fibres, recorded during needle electromyography examination
What is motor neurone disease?
Progressive neurodegenerative disorders of the motor system.
What are the signs associated with upper motor neurone disease?
Spasticity, brisk limbs and jaw reflexes, babinskis sign, loss of dexterity, dysarthria, dysphagia,
What is dysarthria?
Difficulty speaking
What is dysphagia?
Difficulty swallowing
What are the signs associated with lower motor neurone disease?
Weakness. Muscle wasting. Tongue fasciculations and wasting. Nasal speech. Dysphagia
What is the function of the basal ganglia?
Makes decision to move, elaborating associated movements, moderating and coordinating movements, performing movements in order
What are the major structures located in the basal ganglia? (CPGTAccAmAc)
Caudate nucleus, putamen, globus pallidus, thalamus, nucleus accumbens, Amyglada, anterior commisure
What is Parkinson’s disease?
Degeneration of the dopaminergic neurones that originate in the substantia nigra and project to the striatum
What are the symptoms associated with Parkinson’s disease?
Bradykinesia, tremor at rest, rigidity, hypomimic face, akinesia
What is bradykinesia?
Slowness of small movements
How does a tremor develop in Parkinson’s?
Starts as a ‘pill-rolling tremor’ in one hand then spreads to other parts of the body
In Parkinson’s, what is meant by rigidity as a symptom?
Muscle tone increase causing resistance to externally imposed joint movements
What is a hypomimic face?
Expressionless, mask-like face
What is akinesia?
Difficulty in the initiation of movements because cannot initiate movements internally
What is huntingtons disease?
Degeneration of GABAergic neurons in the striatum, caudate and putamen.
What signs and symptoms are associated with Huntingtons disease?
Choreic movements, speech impairment, dysphagia, unsteady gait, cognitive decline and dementia
What is the cause of Huntington’s disease?
Is a genetic neurodegenerative disorder caused by autosomal dominant CAG repeats of chromosome 4
What is Ballism?
Sudden uncontrolled flinging of the extremities
What usually causes Ballism?
A stroke affecting the subthalmic nucleus, symptoms occur contralaterally
Where is the cerebellum located?
Posterior cranial fossa, separated from the cerebrum by tentorium cerebelli
What is the function of the cerebellum?
Coordination and prediction of movement
What are the three functional regions of the cerebellum?
Vestibulocerebelum, spinocerebelum, cerebrocerebelum
what is the function of the vestibulocerebellum?
regulation of gait, posture, and equilibrium. coordination of head and eye movements.
what occurs as a result of damage to the vestibulocerebellum?
gait ataxia, and tendency to fall
what is the function of the spinocerebellum?
coordination of speech, adjustment of muscle tone, coordination of limb movements.
what occurs as a result of damage to the spinocerebellum?
affects mainly the legs, causes abnormal gait and stance (wide-based)
what would be the most likely cause of damage to the vestibulocerebellum?
tumour
what would be the most likely cause of damage to the spinocerebellum?
degeneration and atrophy associated with chronic alcoholism
what is the function of the cerebrocerebellum?
coordination of skilled movements, cognitive function, atention, processing of language. emotional control
what occurs as a result of damage to the cerebrocerebellum?
affects mainly arms and skilled coordinated movements causing tremor and abnormal speech
when are the main signs of cerebellar dysfunction most present?
apparent only on movement
What are the five cardinal signs of cerebellar dysfunction? (ADIDyS)
ataxia, dysmentria, intention tremor, dysdiadochokinesia, scanning speech
Dysmetria is the inability to control the distance, speed, and range of motion necessary to perform smoothly coordinated movements.
what is ataxia?
general impairments in movement coordination and accuracy. disturbances of posture or gait
what is dysmetria?
innapropriate force and distance for target-directed movements
what is intention tremor?
increasing oscillatory trajectory of a limb in a target-directed movement
what is dysdiadochokinesia?
inability to perform rapidly alternating movements
what is meant by ‘scanning speech’?
speaking in short, choppy sentences due to impaired coordination of speech muscles
What are alpha motor neurones?
the lower motor neurons of the brainstem and spinal cord
what do alpha motor neurones innervate?
the extrafusal muscle fibres of the skeletal muscles
what results as alpha motor neurons are activated?
muscle contraction
what is a motor unit?
a single motor neuron along with all the muscle fibres it innervates
what is the name of the smallest motor unit able to produce force?
a motor unit
what happens when a motor unit is stimulated?
contraction of all muscle fibres in that unit
what are the three types of motor unit?
Slow (S, type 1), fast fatigue resistant (FR, type 2a), fast fatiguable (FF, type 2B)
what is the difference between slow and fast type motor units?
slow = smallest diameter cell bodies, small dendritic trees, thinner axons, slowest conduction velocity
which type of motor unit produces the most force in response to a single motor neuron action potential?
type 2b (fast fatiguable)
what are the two mechanisms by which the brain regulates the force that a single muscle can produce?
recruitment and rate coding
In terms of motor control, what is recruitment?
smaller units are recruited first, as more force is required, more units are recruited, this allows for fine control
which of the two regulatory mechanisms for muscle force allows for fine control?
recruitment
in terms of motor control, what is rate coding?
a motor unit can fire at a range of frequencies, as the firing rate increases, the force produced by the unit increases
when does summation occur?
when units fire at frequency too fast to allow the muscle to relax between arriving action potentials
what are neurotrophic factors?
growth factor that prevents neuronal death and promotes growth of neurons after injury
What muscle fibre switch could you expect to see following training?
type 2B to 2A
what muscle fibre switch would you expect to see following severe deconditioning or spinal cord injury?
type 1 to type 2
what switch in muscle fibres occurs with aging?
preferential loss of type 2 fibres, larger proportion of type 1 fibres in aged muscle
Define reflex
automatic, stereotyped response to a peripheral stimulus resulting in involuntary coordinated pattern of muscle contraction and relaxation without reaching the level of consciousness
what is the Jendrassik manoeuvre?
pulling against locked fingers when having a patellar tendon tapped makes the reflex larger
explain the role of the CNS in reflex movement
higher centers of CNS exert inhibitory and excitatory regulation upon the stretch reflex. inhibitory control dominates in normal conditions, decerebration reveals the excitatory control from supraspinal areas
what are the five pathways that make up the descending control of reflexes?
activating alpha motor neurons, activating inhibitory interneurons, activating propiospinal neurons, activating gamma motor neurones, activating terminals of afferent fibres
What is hyper-reflexia?
overeactive reflexes with loss of descending inhibition, associated with upper motor neurone lesions
