Lecture10 Flashcards
What is Sensory Feedback crucially important for modulating?
The output of the motor system
What is the order of the descending motor circuits;
Feedback circuits travel which way?
Association cortex, secondary cortex, primary motor cortex, brain stem motor nuclei, spinal motor circuits;
In the opposite direction beginning with the muscles (parallel hierarchy)
What are the lowest hierarchical level of the sensorimotor spinal circuits?
Where is the point of innervation?
Motor neurones & the muscle fibres they innervate;
Neuromuscular junction
From the primary motor cortex, signals descend to muscles through which two pairs of tracts in the spinal cord?
Dorsolateral (terminate in contralateral half of 1 spinal cord segment & sometimes directly on a motor neuron) & Ventromedial (more diffuse, with axons innervating interneurones in several segments of the spinal cord)
Which pair of dorsolateral tracts travel the direct route?;
After reaching the medullary pyramid, what do they do?
Corticospinal tracts;
Decussate to the dorsolateral portion of the spinal cord, then to contralateral distal limb muscles
Which pair of dorsolateral tracts travel the indirect route?;
After reaching the red nucleus, what do they do?
Corticorubrospinal tracts;
Decussate to nuclei of cranial nerve motor neurons, where some fibres decussate & travel to contralateral facial muscles, & others descend straight to contralateral distal limb muscles
What do dorsolateral tracts control?
Movement of the limbs (especially independent movement)
When dorsolateral corticospinal tracts in medullary pyramids of monkeys were transected, what occurred?
After surgery, monkeys could stand, walk & climb but couldn’t use limbs for other activities, such as reaching for things or moving fingers independently
Which pair of ventromedial tracts travel the direct route?;
How do they descend?
Ventromedial corticospinal tracts;
Ipsilaterally to the ventromedial portion of the spinal cord, then to the trunk & proximal limb muscles
Which pair of ventromedial tracts travel the indirect route?;
At the tectum, what happens?
Cortico-brainstem-spinal tracts;
Fibres travel bilaterally via the Reticular formation & vestibular nucleus, then continue through the motor nuclei of cranial nerves to the trunk & proximal limb muscles
What do ventromedial tracts control?
Posture & whole body movements, & the limbs involved in these activities
When ventromedial tracts were transected in monkeys, what was found?
They had postural abnormalities; impaired walking & sitting
From where does the Cerebellum receive its input?;
From where does it receive motor response feedback?;
What does it control?;
What does Cerebellar Ataxia result in?
From primary & secondary motor cortex;
Somatosensory & vestibular systems;
Gait, speech & balance; learning new motor sequences; fine-tuning & learning functions;
Inability to output appropriate movement; difficulty in grasping objects in the environment
What is the Basal Ganglia made up of?;
What do they modulate?
Complex, heterogenous interconnected nuclei;
Movement; cognitive functions; habitual responses & implicit learning
Information can pass from primary motor cortex straight to the supplementary motor area. This direct pathway governs…;
The indirect pathway travels…;
And governs…;
Therefore, the supplementary area acts as a…
Selection of actions;
From primary motor cortex to basal ganglia, thalamus, supplementary motor & back to primary motor cortex;
Inhibition of actions;
Gatekeeper, selecting what’s appropriate or suppressing what’s not wanted
Imbalance of the system, where selection & inhibition of actions is impaired, can lead to what condition?
Parkinson’s disease
Activity in the basal ganglia can be direct or indirect, & depend on what?;
In an intact system there is a fine balance between what?;
An imbalance leads to…
Dopaminergic connections from Substantia Nigra;
Nuclei activation & deactivation (excitation & inhibition);
Extra or reduced movements (as seen in PD)
What are some positive symptoms of Parkinson’s disease?
Tremor &/or rigidity (resistance to passive movement leading to postural problems/loss of righting reflexes); akinesia; forward or backward leaning; postural hypotension leading to falls; sometimes cognitive dysfunction, dementia & depression
What are some negative symptoms of Parkinson’s disease?
Hypokinesia (reduction in spontaneous movement); Akinesia (slow initiation of movement); progressive slowing or freezing during movement; reduced range & scale of movement (e.g. micrographia, gait); dull, weak voice w/o inflections; mask-like expression
What are some side effects of L-Dopa?
Name some paradoxical movement problems once the system gets used to L-Dopa
Hypotension; arrhythmias; nausea; disorientation; confusion; affect; auditory/visual hallucinations; poor working memory; eventual drug failure;
Dyskinesias at peak dose; end-of-dose dysfunction; on-off cycles; freezing
Name the 3 peculiarities of Huntington’s disease
Hereditary nature (autosomal dominance with complete lifetime penetrance, chromosome 4); manifestation in adulthood; tendency to insanity & suicide
How is Huntington’s disease caused?
Destruction of GABAergic (& some cholinergic neurones in striatum); progressive striatal atrophy (medial caudate, then putamen, then tail of caudate); enlargement of ventricles; defective metabolism precedes loss of tissue
The first signs of Huntington’s disease is usually…
Affective (depression, anxiety, irritability, aggression);
The 2nd stage of Huntington’s includes…
Restlessness, clumsiness, poor coordination, forgetfulness & personality changes; altered speech & writing, saccadic changes; bradyphrenia (slow thinking), bradikinesia (slow movement); poor motor dexterity, unsteadiness, reduced speed; athetosis & chorea
Last stages of Huntington’s include…
Involuntary movements stop because of upper limb flexion & lower limb extension
In regards to movement disruption, how is Huntington’s disease characterised?;
Jerky, rapid, uncontrollable movements (choreiform), starting with minor tics & twitches, developing into abrupt, random jerks, interspersed with silence
The jerky movements of Huntington’s, often appear to be fragments of what?;
They involve multiple…;
They increase with…
Quasi-undulating character is…
Normal behaviours (suppressible & decrease during sleep)
Joints & thus resemble voluntary action;
Stress & with voluntary movements like walking;
Idiosyncratic to individuals
Where is the Primary Motor Cortex situated?;
What is its main role?;
What can damage here lead to?
In the precentral gyrus of the frontal lobe;
Major hub of convergence of cortical motor signals & a major point of outgoing signals;
Hemiplegia (weakness/loss of power in the body part represented by that site)
From where does the Secondary Motor Cortex receive its input?;
Where does it send its output?;
What does it consist of?
Association cortex;
Primary motor cortex;
Pre-supplementary motor area, SMA, dorsal premotor, ventral premotor & at least 2 cingulate motor areas
What is the role of the secondary motor cortex?
Programming of specific patterns of movement, with input from the dorsolateral prefrontal cortex
In which area is the Sensorimotor association cortex found?;
From where does it receive its input?;
What is its role?;
What do deficits after damage include?
Superior & inferior posterior parietal lobes;
From more than one sensory system;
Integrates knowledge of position of objects & position of body parts; directs attention;
Ataxia & impaired body representation
Where does the sensorimotor association cortex send its output?;
What do deficits after damage include?
Dorsolateral prefrontal association cortex; secondary motor cortex & frontal eye fields;
Apraxia & contralateral neglect
What is the dorsolateral prefrontal cortex involved in?
The decision to make an action; not the action itself or the processing of the target objects
What is Ataxia?;
What does it result in?;
Where is the deficit most severe?
The inability to use visual information to guide movement of hands
Incorrect/awkward movements; errors in accuracy (over/under shoots)
Periphery of the visual field (visual fixation preserved)
When patient A.T had an eclamptic attack at 34 y.o, MRI scans when she was 46 showed what?;
When trying to reach for dots in the periphery of her visual field, she…
Haemorrhagic softening in parieto-occipital territory;
Misjudged; her depth perception was impaired
What is Apraxia?;
What is the deficit?
A disorder of skilled movement resulting from neurologic dysfunction (not due to sensory loss, weakness or ataxia);
An inability to act; i.e. to move the moveable parts of the body in a purposeful manner (ability to move is intact)
What are the deficits in Ideational Apraxia?;
Elements of an action may be intact but there is a disruption of…;
Which body parts are effected?
Inability to carry out a complex gesture/multistep action (e.g. strike match/blow out candle);
The logical sequence, the overall action is incorrect;
General & bilateral (rather than specific body parts)
What is Ideomotor Apraxia a disorder of?;
In which regions does the damage occur?;
How is it tested?
Representation or execution of action (inability to gesture or pantomime object);
Left frontoparietal regions;
Using verbal commands & imitation
What is Intrinsic Spatial Coding?;
When is it essential?
Knowing what our own body parts are doing (maintaining internal representations);
When a body part is going to be obscured at some stage in the movement planning & execution
Patient P.J suffered a head injury at 43, with a 30 min loss of consciousness. She was assessed at 48 after having focal seizures & jerking of the right arm. What did MRI scans show?;
What symptoms did she complain of?
A cyst encroaching on the cortex & subcortical white matter of the left superior parietal lobe (no visual neglect, extinction or other visual deficits);
Perceived her arm & leg to drift & fade unless able to see them; loss of knowledge of limb position in bed; people on public transport tripping over her drifting leg in aisle
What is the Superior Parietal Lobe critical for?
Sensorimotor integration by maintaining an internal representation of the body’s state
Describe the basic components of the Motor Control system;
How do each of these stages communicate with each other?;
Where does the predictor reside?
Goal (desired state); affordances/controllers (perception of goal to movement); predicted state via predictors (movement to perception); motor commands; movement, actual state, sensory feedback; estimated actual state;
Via Comparators;
Parietal lobe (predicts what should be happening & if on right track based on experience)
What is the crucial deficit in Alien/Anarchic syndrome?
Activation of actions by irrelevant affordances which are not suppressed by intended actions; no inhibition of unwanted action; system doesn’t recognise what it’s doing & can’t compare if on right track or not
Explain the phenomenon of Mirror Neurones
Action observation system; Observing, imagining or in any way representing action excites the programs involved in that action
What did Gallesse et al. find mirror neurones in monkeys respond to?
To sight of goal-directed actions only, as long as goal is achieved even if out of sight; to the sound of an action (multimodal); when action is performed by an agent (hand-object interactions - not to tools)
Which cortical areas are activated by perception of action & execution?;
When is activation greater?;
What does the mirror neuron system facilitate?
Premotor & parietal cortices;
When movements are to be replicated later;
Action understanding, allowing planning of our actions & understanding of others’ actions
There appears to be a similar cortical network associated with mirror neurones in humans as monkeys. What main areas do these include?
Inferior parietal lobe; premotor area; inferior frontal gyrus; superior temporal sulcus/middle temporal gyrus
What did Ferrari et al. find with neonatal rhesus macaque (monkeys)?;
What does this suggest?
They showed imitative responses in extremely early age of development (even on the first day of life);
That imitative capacities are not limited to human & ape lineage, & that their evolutionary origins may be traced to affiliative gestures with communicative functions
