Motor Systems Flashcards
Which regions of the cortex are involved in motor control?
All of the frontal lobe
What happens to the cortical region’s role in movement as you move more and more anatomically anterior?
It becomes more and more complex and abstract.
What is area 4?
What anatomical landmark is it immediately anterior to?
Primary motor cortex - the lowest level of motor hierarchy
Central sulcus
What do local lesions to area 4 cause?
Paralysis or paresis of specific muscle groups
What do strokes involving occlusion of the middle cerebral artery affect? Is the effect contra or ipsilateral?
Almost all of one side of the frontal lobe
They produce severe motor disability in all parts of the contralateral body (except the lower limb as this region of motor cortex is supplied by anterior cerebral artery).
Which is more severe - blockage of M1 or M3 (parts of the MCA)? Why?
Blockage of M1, as it is more proximal and affects the blood supply to the basal ganglia (via the lenticulostriate arteries) as well as the blood supply to the motor cortex.
What is area 6? What is area 8?
Premotor cortex
Supplementary motor cortex
Damage to areas 6 and 8 leads to what clinical syndrome? Explain this syndrome.
Apraxia.
Patients with apraxia have normal reflexes and no muscle weakness but have difficulty performing complex motor tasks.
What else can damage to areas 6 and 8 cause?
Does damage to one side produce mild or severe symptoms? Why?
Lesions of this cortex may also impair motor responses to visual or other sensory cues.
Only minimal symptoms - the contralateral area may be able to take over some functions.
Frontal eye fields and Broca’s area are adjacent to what area?
What two special motor systems do they control?
Premotor area
Extraocular eye muscles and the muscles regulating speech
What does damage to Broca’s area lead to?
Motor aphasia - patient has difficulty verbalising word strings such as complex sentences.
What is oculomotor apraxia?
How do patients compensate?
Patients have difficulty moving their eyes horizontally and moving them quickly to follow a moving object, due to problems with the programmes controlling voluntary eye movements.
Patients have to turn their head in order to compensate.
What is one cause of oculomotor apraxia?
Bilateral lesions of the frontal eye fields
Frontal eye fields control…
Voluntary eye movements
What does saccade mean?
Rapid eye movements between fixation points.
What 3 areas contain the somatosensory cortex? Where does this lie?
Areas 1, 2 and 3 (parietal lobe)
Immediately posterior to the central sulcus
How many % of the corticobulbospinal tract arises from the somatosensory cortex?
What do these axons do?
40%
They send commands down to the spinal cord that modulate sensory input and they can modulate reflexes.
What are areas 9 and 10? What do they do?
Dorsolateral pre-frontal cortex
Planning of movement - we evaluate different possible future actions and decide which is best (executive functions).
Which areas have the most complex relationship with movement?
Areas 9 and 10
What does a dorsolateral frontal lesion cause? (4)
Apathy
Personality changes
Lack of ability to plan
Poor memory for verbal (left hemisphere) or spatial (right) information
What is a common test for frontal lobe function?
Wisconsin card sorting test
What cortex is commonly damaged by road traffic accidents/blows to the head that cause contusions?
Frontal cortex (impact with frontal bone)
What is area 11?
Orbitofrontal cortex
What is the orbitofrontal cortex concerned with?
Control/inhibition of motor responses associated with the limbic system - e.g. hunger, thirst, sexual drive
What type of behaviour is caused by orbital damage?
Pseudo-psychopathic (due to disinhibition)/acquired sociopathy = ORBITAL PERSONALITY
What does puerile mean?
Childish, silly, immature
Which areas feed into the corticobulbospinal tract? (5)
Areas 1, 2 and 3 Area 4 Areas 6 and 8 Frontal eye fields Broca's
Which areas feed into areas 6 and 8? (2)
Area 9 and 10
Area 11
What area does 6 and 8 feed into?
Area 4 - primary motor cortex
What do both the basal ganglia and cerebellum project on to (route for motor commands)?
Motor thalamus projects onto…?
Motor thalamus (VL thalamic nucleus) Motor cortex
The corticobulbospinal tract courses through what structure on its way to the brainstem? What is it especially vulnerable to damage by here?
Internal capsule
Stroke
What are the two components of the corticobulbospinal tract?
Corticobulbar
Corticospinal
Where does the corticobulbar component terminate? (4)
Cranial nerve nuclei (for control of muscles of head and neck)
Cells of pontine nuclei
Reticular formation
Red nucleus (in midbrain, next to oculomotor nuclei)
Where does the corticospinal component decussate?
What two tracts does it form?
Lower medulla
Large lateral and small anterior corticospinal tracts
Where does motor decussation occur? What level?
Upper spinal cord (C1-C5)
If the brain is injured above the spinal cord, on what side is the motor deficit?
Opposite side
If the spinal cord is injured, on what side is the motor deficit?
Same side
The lateral corticospinal tract is in the ____ quadrant of the cord, near the motor neurons supplying the _____ muscles.
Dorsal
Distal
What is the only place the corticospinal tract has mono-synaptic connections with?
What are the motor actions in other muscles mediated by?
Thumb and digits
Spinal inter-neurons
Where does the anterior corticospinal tract terminate?
What does it control?
Cervical cord.
It controls voluntary movements of the neck.
Damage to the corticospinal tract in the spinal cord causes loss of control of hands and fingers, but NOT…
Loss of posture or locomotion and gait (mediated by extra-pyramidal systems)
What are the main components of the extra-pyramidal system? (2)
Lateral vestibulospinal tract
Reticulospinal tract
Lateral vestibulospinal tract - where does it originate?
What does it control?
(IPSILATERAL)
Vestibular nuclei in upper medulla/lower pons
Posture and balance - anti-gravity muscles
Reticulospinal tract - where does it arise? What is it responsible for? (3)
(BILATERAL)
Reticular formation of pons and medulla
Autonomic control (sympathetic preganglionic neurones)
Drive to respiration (phrenic nerve)
General ‘arousal’ of spinal cord
Rubrospinal tract - where does it originate? What does it carry?
Red nucleus in midbrain
Carries cerebellar motor commands to spinal cord
What do rubrospinal lesions cause?
Slowness in movement (temporary)
Where does the red nucleus receive most of its input from?
Cerebellum
What does activation of the rubrospinal tract in animals cause?
Excitation of flexor muscles
Inhibitor of extensor muscles
What does the tectospinal tract coordinate?
Voluntary head and eye movements - postural movements of the head in response to visual and auditory stimuli
Where does the tectospinal tract originate?
Where does it receive afferents from?
What does it project to?
Superior colliculus/optic tectum
Retina
Contralateral cervical spinal cord (terminates in rexed laminae VI, VII, and VIII)
What is the medial vestibulospinal tract a continuation of?
Medial longitudinal fasciculus
What does the medial vestibulospinal tract mediate?
Involuntary (reflex) co-ordination of the head and neck muscles with the extraocular eye muscles
The major descending motor tracts act on ______ to modulate the strength and activity of ____ pathways.
Interneurones
Reflex
What does spasticity mean? What is it characteristic of?
Abnormally increased muscle tone
Increased tendon reflexes
Characteristic of upper motor neuron lesions
What does clonus mean?
Series of jerky contractions of a particular muscle
What is hyper-reflexia?
Abnormally brisk tendon reflex seen in one or more muscles
What is decorticate posturing (talk about arms, wrists, fingers, legs and feet)?
Arms are adducted and flexed
Wrists and fingers flexed on the chest
Legs may be internally rotated and stiffly extended
Plantar flexion of the feet
What does decorticate posture indicate?
Damage to corticospinal tract in midbrain
What is decerebrate posturing (talk about arms, wrists, fingers, legs and feet)?
Arms are adducted and extended
Wrists pronated and the fingers flexed
Legs may be internally rotated and stiffly extended
Plantar flexion of the feet
What does decerebrate posturing indicate?
Severe injury to the brain at the level of the brainstem, including damage to corticospinal and rubrospinal tracts.
What is decerebrate posture thought to be due to? Which particular tract? Which nucleus is damaged?
Excessive activity (disinhibition) in the extrapyramidal system Vestibulospinal tract (normally under tonic inhibition by corticobulbospinal tract and red nucleus) Red nucleus
Which tract is predominantly affected in decorticate posture?
Corticospinal
Which is more favourable - decerebrate or decorticate posture?
Decorticate
____ posture may progress to _____ posture?
Decorticate to decerebrate
Acute effects of lesions of motor cortex - what is initially seen? (1)
What is seen during recovery? (3)
Initial paralysis
During recovery there is weakness, clumsiness & fatigue of movements.
Why does recovery occur (in terms of motor cortex lesions)?
Plasticity
Larger lesions lead to ______ recovery and _______ loss of certain movement.
Slower
Permanent
Chronic effects of lesions of motor cortex - what reflex is particularly characteristic?
Clasp-knife reflex
What is hemiplegic dystonia?
Spasticity combined with profound motor weakness - persistent flexion of arms and extension of legs
What is spinal shock?
A clinical condition that occurs after acute damage to the spinal cord (includes damage to any of the descending tracts).
What are the acute effects of spinal shock? (3)
Paralysis or paresis
Reduced reflex responses in all muscles below the region of injury
In its severest form, all reflexes at all levels of the cord below the lesion are inactive.
What are the chronic effects of spinal shock?
Weak monosynaptic reflexes reappear Crossed extensor reflexes may also recover Hyperreflexia Clonus Babinski sign
What does damage to the corticospinal tract cause? (2)
Paralysis and weakness of voluntary movement
Hyperactive tendon reflexes
Loss of bladder/bowel control, loss of temperature regulation, loss of blood pressure regulation… these are signs of damage to what tract?
Reticulospinal tract
Vestibulospinal tract damage causes…
Loss of ability to stand upright/balance properly
Damage to both reticulospinal and vestibulospinal tracts causes…? (2)
Poor gait
Loss of ability to walk, sit and move freely
What is the difference in distribution between UMN lesions and LMN lesions?
Upper motor neuron lesion - always groups of muscles, it is never individual.
Lower motor neuron - segmental, limited to muscles innervated by damaged motor neurons or their axons
What is the difference in muscle tone between UMN lesions and LMN lesions?
UMN - increased tone
LMN - decreased tone
What is the difference in reflexes between UMN lesions and LMN lesions?
UMN - hyperactive reflexes
LMN - absent or decreased reflexes
What is the difference in paralysis between UMN lesions and LMN lesions?
UMN - spastic
LMN - flaccid
