Case 7 - extra Flashcards
what does the cerebellum monitor
monitors and regulates motor control
what is the result of the cerebellum modulating movement
neuronal activity in the cerebellum changes continually during the course of a movement
what is this action controlled by
the purkinje fibres and the deep cerebellar nuclear cells
what are these fibres like during rest
both are tonically active during rest and change their frequency of firing as movements occur
what happens when there are lesions in the cerebellum
patients find it difficult to produce smooth, well coordinated movement - cerebellar ataxia
what does the cerebellum contribute to in the oculomotor system
contributes to the motor error reduction in the oculomotor system
this is done when a small part of the tendon of the lateral rectus is cut which weakens horizontal eye movement
the nervous system corrects the error in the saccades mode by the weak eye by increasing the gain in the saccade motor system
lesions in the vermis of the spin cerebellum eliminate this ability to reduce the motor error
what does the cerebellum also contribute to
error reduction in the vestibule-ocular reflex system:
if the cerebellum is damaged or removed, the ability of theVOR to adapt to the new conditions is lost
what does the basal ganglia facilitate
the initiation of motor programs that express movement and the suppression of competing motor programs that would otherwise interfere with the expression of sensory drive or goal directed behaviour
what are the nuclei in the basal ganglia that are concerned with motor movement
corpus striatum (caudate and putamen)
globus pallidus
how does the BG influence movement
by regulating the activity of upper motor neurones
what does the loop including the BG, substantia nigra and sub thalamic nucleus do
the neurones in this loop respond in anticipation of and during movements, and their effects on upper motor neurones are required for the normal course of voluntary movements
what happens when one of the components of this loop is compromised
the patient cannot switch between commands smoothly that initiate a movement and those that terminate a movement
what is the largest source of input to the BG
the corticostriatal pathways, from the cortex. these tackle through the internal capsule to reach the caudate and putamen directly
what is the only cortical area that does not project to the corpus striatum
the primary visual and auditory cortices
what are cortical projections topographically mapped within
rostrocaudal bands
what is the output from the basal ganglia from
the corpus striatum.
the destinations pf the incoming axons form the cortex are the dendrites of medium spiny neurones in the corpus striatum
what is most cortical input from the striatum
excitatory and uses glutamate
where do the axons arising from the medium spiny neurones convert on neurones
in the globus pallidus and the substantia nigra pars reticulate, the main sources of output from the basal ganglia compel
how is dopamine produced
by the action of DOPA decarboxylase on L-DOPA
following its synthesis in the cytoplasm of presynaptic terminals, what happens to the dopamine
is loaded into synaptic vesicles via a vesicular monoamine transporter (VMAT)
what is dopamine action in the synaptic cleft terminated by
reuptake of dopamine into nerve terminals or surrounding glial cells by a Na_ dependent dopamine transporter - termed DAT
what do both neurones and glia contain
mitochondrial MAO and COMT
where do the dopaminergic systems arise
in the midbrain
what are the two structures in the midbrain that give rise to the dopaminergic systems
substantia nigra
ventral tegmental ares
why is the substantia nigra darker than neighbouring areas
due to high levels of neuromelanin in dopaminergic neurones
where does the nigrostriatal pathway arise form
the substantia nigra pars compacta and projects into the caudate and putamen. this pathway serves as the primary inout into the basal ganglia system
what does dysfunction of this pathway produce
movement disorders such as PD
what are the two pathways in the ventral tegumental area
mesolimbic pathway
mesocortiyal pathway
features of the mesolimbic pathway
arises mainly from the ventral tegumental area and projects to limbic structures. this pathway plays a major role in the reward circuitry and addiction
features of the mesocortiyal pathway
arises mainly from the ventral tegumental area and projects to the prefrontal cortex. this pathway is involved in working memory and attentional aspects of motor ignition
how does dopamine act once release
exclusively by activating G protein coupled receptors
how do most dopamine receptor subtypes act
by either activating or inhibiting adenylyl cyclase
