Session 6 Flashcards
When can lower motor neurones regenerate?
If the cell body is damages, then the axons cannot regenerate. If the axon is damaged, but the cell body remains intact, then some Wallerian degeneration can occur.
Give 3 examples of pyramidal upper motor neurone signs.
Weakness, spasticity, pronator drift, loss of skilled movement, hypereflexia, change in tone, plantars upgoing and loss of abdominal/cremasteric reflex.
Give 3 examples of extrapyramidal upper motor neurone signs.
Tremor, chorea, hemiballismus, athestosis and dystonia.
What is the main function of the basal ganglia?
Provides a feedback mechanism to the cerebral cortex for the initiation and control of motor responses.
What does the basal ganglia consist of?
Caudate nucleus, Putamen, globus pallidus, subthalamic nucleus and substantia nigra.
What makes up the neostriatum?
Caudate nucleus + putamen.
Describe the direct pathway through the basal ganglia.
Synapses from cortical cells excite cells in the neostriatum, which inhibit neurones in the internal globus pallidus.
This then inhibits calls in the thalamus.
The connection from the thalamus to the cerebral cortex is excitatory, and reduced inhibition of the motor thalamus, hence sending signals to the SMA of the cerebral cortex. Driving muscle contraction.
Describe the indirect pathway through the basal ganglia.
Neostriatal neurones inhibit cells of the globus pallidus externa. This then inhibits cells of the globus pallidus interna and the subthalamic nucleus.
This excites the GPi, which then inhibits the thalamus.
Subthalamic nucleus is also excited by the cortex, it excites the GPi, which again inhibits thalamic neurones.
Describe the hyperdirect pathway through the basal ganglia.
Directly from the cerebral cortex to the subthalamic nucleus, hence avoiding the neostriatum.
What makes up the substantia nigra?
Pars compacta and pars reticulata.
What is the role of the pars compacta of the substantia nigra?
Increases the activity of the direct pathway and decreases the activity of the indirect pathway.
What would dysfunction of the basal ganglia affect?
Amplitude and velocity of the planned movements. Hence results in hypokinetic or hyperkinetic disorders.
What is parkinson’s disease?
Progressive degeneration of dopaminergic neurones of the substantia nigra. Hence reduced direct pathway action and an increased indirect pathway action.
What is the triad of Parkinsonian symptoms?
Tremor at rest, hypertonia and bradykinesia. Other symptoms include akinesia, monotonous speach and micrographia.
What is Huntington’s disease?
Inherited autosomal dominant condition, that is progressive and inevitably fatal. Degeneration in the GABAergic neurones in the neostriatum of the indirect pathway. Hence excessive excitation to the thalamus and choreiform movements.
