Motor systems: the higher level Flashcards
what set of subcortical nuclei make up the basal ganglia?
the striatum, the subthalamic nucleus, the SN and the amygdala
what are the components of the striatum of the basal ganglia?
the putamen and caudate nucleus
information is drawn from all areas of the cortex to the basal ganglia via the
striatum
the striatum feeds information from the cortex to the
globus pallidus and substantia nigra
the globus pallidus is
an output target of the (striatum of the) basal ganglia
information from the globus pallidus and SN feed into which nucleus?
the ventroanterior nucleus of the thalamus
information that has gone through the BG to the VA nucleus of the thalamus then feeds back into the
cortex
the information loop involving the cortex, BG and thalamus can be described as
reentrant as it then goes round again
what is the supplementary area concerned with?
movement planning and selection of motor programs
the fact that info is drawn from all areas of the cortex to the BG allow the BG to select programs according to all
sensory areas an behavioural needs
what are the 2 functions of the BG?
- selection of motor programs
2. appropriate scaling of programs and hence of muscular output
what are the 2 major classes of BG disorder?
Akinesia (because of failure to select motor program) and dyskinesia (because of inappropriate scaling/selection of programs)
akinesia is
decreased movement and rigidity, also referred to as parkinsonism
dyskinesia is
involuntary movement
what are the 5 main symptoms of parkinsonism
- shuffling/festinating gait
- tremor (increases with agitation)
- rigidity (due to increased muscular hypertonus)
- Akinesia
- bradykinesia
in parkinsons akinesia is seen especially in the
face, so is associated with an expresssionless face with reduced blinking
bradykinesia is
slowness of movement and inappropriate scaling of movements
inappropriate scaling of movements in parkinsons results in
the need for repeated agonist and antagonist activity to achieve simple movements, where normally a simple ag.–>antag.–>ag. (triphasic emg pattern) is used
the 5 parts of the BG involved in motor control are the
- putamen
- caudate nucleus
- globus pallidus
- subthalamic nucleus
- SN
the caudate nucleus and putamen are anatomically similar and so can be distinguished by
the fact that they are separated by the internal capsule
the globus pallidus can be separated into the
- GPe (external/lateral part)
2. GPi (internal/medial part)
the SN can be divided into 2 parts:
- SNpc (pars compacta)
2. SNpr (pars reticulata)
which of the 2 parts of the SN is darker?
the SNpc
what are the 2 afferent projections into the striatum?
corticostriatal projection and thalamic projection
the corticostriatal projection is organised
topographically (diff. areas of cortex project into diff. areas of striatum)
projections from cortex to striatum come from which parts of the cortx?
all of them including ex visual, limbic, etc
examples of the functions of the caudate nucleus:
eye movements and cognitive function
examples of functions of the putamen:
general motor function and limbic function
which parts of the putamen are associated with limbic function?
the most ventral parts
where do fibres of the corticospinal tract terminate?
on distal parts of medium sized cells with spiny dendrites
which cells make up 98% of striatal neurones?
the medium sized cells with spiny dendrites that the corticospinal fibres terminate on
what is the NT used between the fibres of the corticostriatal projection and the dendrites on to which they terminate, and where do the latter receive input from?
glutamate, cortex and striatum
which thalamic nuclei project into the basal ganglia?
intralaminar
what is the thalamic projection of particular interest in motor control?
motor cortex to thalamic centromedian nucleus to putamen
spiny neurones of the striatum project either to the :
globus pallidus or SNpr
striatopallidal pathway=
striatum to globus pallidus
striatonigral pathway=
striatum to SNpr
how are the striatopallidal and striatonigral pathways organised?
topographically, so functional organisation is maintained in GP and SN
the GPe inhibits the
subthalamic nucleus
the GPi inhibits the
thalamus (ventrolateral and centromedial nuclei of)
GPi inhibition of thalamus occurs in direct or indirect?
both
GPe inhibition of STN occurs in direct or indirect?
indirect only
the NT of striatum to GPi (in direct) is
GABA and substance P (inhib)
the NT of striatum to GPe (in indirect) is
GABA and ekephalin (inhib)
is the direct route excited by DA?
yes
is the indirect route excited or inhib by DA?
inhib
what is the effect of deplettion of DA on the routes through BG?
removes 1 excitatory from direct and removes 1 inhib from indirect
whats the difference between direct and indirect routes of BG?
indirect has 1 more inhibitory neuron
what does excitation of striatal neurones lead to?
inhibition of pallidal targets, and therefore disinhibition of thalamic targets, and therefore net excitation of cortex
what does the thalamocortical projection allow the BG to do?
activate motor areas of the cerebral cortex
