4 - motor disorders Flashcards
what causes cerebral palsy?
damage to motor control structures of the brain, usually the motor cortex
injury often occurs pre- or peri- fatally
what does the motor cortex do?
- issues descending motor commands for muscle activation
- regulates activity levels in spinal cord circuits
- where the upper motor neuron begins
what are the results of cerebral palsy?
- stiffness and weakness of muscles
- poor coordination
- affects upper motor neurons
- affects ~2 in every 1000 births
what causes stroke?
interruption of the blood supply to the cortex (often motor cortex)
- cerebral haemorrhage - often results for aneurism
- cerebral ischaemia - interruption of blood supply to part of brain due to blockage of blood vessel
what are the results of stroke?
- upper motor neurons affected
- symptoms depend on extend and location
- FAST (face, arms, speech, time)
how can stroke be treated?
goal is to rescue the penumbra (recoverable tissue) by reopening blocked blood vessel (time sensitive)
core - non recoverable
what are the most common symptoms of damage to the motor cortex?
fine motor control
because the homunculus has large representations for these activities, so unlikely to be missed by damage, and require co-ordination across sub-regions
what is upper motor neuron syndrome?
lack of voluntary control of muscles via lower motor neurons
lack of regulation of LMNs and spinal reflex circuits
reflexes can thus become abnormal
what is the Babinksi reflex?
fanning out of toes when the sole of the foot is stroked
indicative of upper motor neuron problem
what are conditions caused by damage to the motor cortex?
- cerebral palsy
- stroke
- upper motor neuron syndrom
what does the basal ganglia do at rest?
cortex sends signals to basal ganglia structures (striatum- globus pallidus)
this inhibits the thalamus therefore it can’t excite the cortex
causes reduced activation of motor cortex
what does the basal ganglia do when excited?
excitation in striatum, which briefly inhibits globus pallid us
thamalus is then disinhibited (excitable)
causes increases excitation of motor cortex
what do diseases related to the basal ganglia have in common?
poor selection of appropriate sequences of movement
not selecting motor programmes or inappropriate activation of motor programmes
parkinson’s statistics
2nd most common neurodegenerative disease after Alzheimers
affects 3/1000 people, 1/100 in >60s, 1/25 >80s
affects~50% more males than females
10% of cases occur due to mutation of one of several genes
what is the cause of symptoms of Parkinson’s disease?
initiation (selection) of movement is impaired, but certain cues/contexts can help
- shuffling gait
- resting tremor
- lack of movement
what happens in the basal ganglia in Parkinson’s disease?
burst of dopamine when excited doesn’t occur so no disinhibition
because neurons that produce it die off
therefore thalamus is inhibited, reduced excitation of motor cortex so unable to initiate a movement
how to treat Parkinson’s disease?
give L-dopa which increases production of dopamine in dopaminergic neurons
deep brain stimulation
how is deep brain stimulation used to treat Parkinson’s disease?
electrical stimulation of basal ganglia structures (globus pallidus) which shrinks down excessive inhibition
resulting in disinhibition of thalamus and excitation of motor cortex
what are limitations of deep brain stimulation?
- side effects
- fails to deal with non-motor symptoms (depression, anxiety)
- can make some non-motor symptoms worse
what are limitations of using L-dopa to treat Parkinson’s disease?
dopaminergic neurons are dying so eventually there are not enough neurons to make dopamine and it stops being effective
features of cerebellum
contains half number of CNS neurons
10% of total brain weight
projects to almost all upper motor neurons
what does damage to cerebellum result in?
ataxia - two types:
- disturbances of posture or gait
- decomposition of movement
voluntary movement loses fluidity and appears mechanical, slow and robot-like
intention tremor (not resting)
what is motor neuron disease?
motor neuron (upper and/or lower) degeneration and muscle wasting
- degenerative
- progressive
- incurable
10% of cases have genetic component
