Basal Ganglia Flashcards
basal ganglia: 2 definitions
deep grey matter structures that develop from the telencephalon
a series of grey matter structures that are interconnected and serve a common function (this is the one we will use)
corpus striatum
-subdivisions
neostriatum or striatum
- caudate nucleus
- putamen
- globus pallidus
neostriatum
- divisions
- divided by…
one nucleus divided into 2 parts by anterior limb of internal capsule
putamen and caudate make up the…
dorsal striatum
caudate nucleus
-composed of…
head
body
tail
globus pallidus (GP)
- what are the parts
- separated by…
external (GPe - lateral)
internal (GPi - medial)
separated by internal medullary lamina
amygdaloid nuclear complex
- develops from…
- functionally associated with…
develops from telencephalon
functionally associated with Limbic System
other structures functionally associated with Basal Ganglia
subthalamic nucleus (ST nuc.)
Substantia nigra (SN)
thalamic nuclei: VA, VL, DM, CM
pedunculopontine nucleus
substantia nigra
-parts
zona or pars compacts (SNc)
zona or pars reticulata (SNr)
pars compacta
- neural neurotransmitter
- contains…
dopamine neurons
contains black pigment: neuromalanin
pars reticulata
- neural neurotransmitter
- does not contain…
- functionally similar to…
GABA neurons
no neuromelanin
functionally similar to medial GP (GPi)
pedunculopontine nucleus
- relation to Basal Ganglia
- function
RF nucleus that sets up a rhythmic cholinergic input to the striatum
plays a role in the coordination of synergistic movement
structures anatomically related to corpus striatum
lenticular nucleus
claustrum
lenticular nucleus
-what is it?
name given to GP plus putamen
claustrum
-bounded by…
external and extreme capsules
function of basal ganglia
collection of sub-cortical (suprasegmental) masses of gray matter that serve to modulate cortical control of
- motor function
- cognition
- motivation
basal ganglia pathways
-form _____ that start in _____ and end in _____
form several circuits or loops that start in widespread areas of cortex and end in more circumscribed parts of motor cortex, limbic cortex or frontal lobe association cortex
from a functional point of view, the basal ganglia and related nuclei have been divided into…
dorsal and ventral striatum
dorsal striatum
-consists of…
consists of pathways involving the caudate and putamen
caudate is involved in…
cognitive processing
putamen involved in…
involved more with sensorimotor processing
ventral striatum
-function
involvement with limbic system and emotion
dorsal striatum
-general pathways
afferents
interconnections
efferents
dorsal striatum afferents
-location of the structures that project to the dorsal striatum
widespread cortex
intralaminal nucleus of thalamus
raphe nuclei fibers
pedunculopontine nuclei fibers
dorsal striatum afferents: widespread cortex
- neurotransmitter
- projects to…
glutamate
projects to striatum
smaller inputs to SNr (pars reticulata) and ST nuclei (subthalamic nucleus)
dorsal striatum afferents: intralaminal nucleus of thalamus
- another name
- projects to…
centromedial thalamic nucleus (CM)
-projects to striatum
dorsal striatum afferents: raphe nuclei fibers
- neurotransmitter
- projects to…
serotonin
projects to all parts of basal ganglia
dorsal striatum afferents: pedunculopontine nuclei of RF
- neurotransmitter
- projects to…
ACh
projects to SNr and GP
dorsal striatum interconnections
-can be categorized as…
direct (main) circuit
indirect (auxillary) circuit
nigro-striatal-nigral pathway
dorsal striatum interconnections: direct circuit
- pathway
- neurotransmitter associated with each
widespread areas of cortex (glutamate) –> stiratum (GABA and substance P) –> GPi and SNr (GABA) –> thalamic nuclei (glutamate) –> frontal lobe cortex
dorsal striatum interconnections: indirect circuit
- pathway
- neurotransmitter associated with each
widespread areas of cortex –> striatum –> GPe (GABA) –> subthalamic nuclei (glutamate) –> SNr and GPi (GABA) –> thalamic nuclei –> frontal lobe cortex
dorsal striatum interconnections: nigrostriatal pathway
- neurotransmitter
- from
- to
dopamine-containing fibers from SNc to striatum
GABA fibers from striatum back to SNc
dorsal striatum efferents
-no direct output of…
basal ganglia to brainstem or spinal cord LMNs
dorsal striatum efferents
- major efferents are from…
- to
- function of each area they go to
GPi (largest number) and SNr to the
- VA and VL
- -motor function
- DM
- -cognitive function
- CM
dorsal striatum efferents from GPi and SNr directed through the thamalus
-relayed to _____ as part of _____
relayed to frontal lobe cortex and supplementary motor cortices as part of the direct and indirect circuits
dorsal striatum efferents: cerebellar connections running through the thalamus end primarily in…
lateral premotor cortex
dorsal striatum efferents
- other efferents
- function
SNr to tectum
-modulates tectospinal path
SNr and GPe to the pedunculopontine nucleus (RF nucleus)
the primary mechanism underlying the function of the basal ganglia is…
-explain
disinhibition
-inhibition of a tonically active inhibitory pathway; an inhibitiroy neuron inhibiting a tonically active inhibitory neuron
disinhibition
-how is it accomplished
accomplished through a balance of signals from the direct and indirect loops converging on the output nuclei, GPi and SNr
disinhibition
- groups of cells in the GPi are strongly linked to…
- the initiation in from _____ rather than _____
remembered motor tasks coupling them to an internally generated initiation of movement
-initiation is more from an internal direction of deciding to do something, rather than from sensory cued stimuli such as vision or proprioception
disinhibition
-when are different groups of GPi cells active?
some cells are associated with specific phases of complex movements, active only during a portion (single joint) of a complex activity
other groups of cells are active throughout the entire sequence of the movement, programming sequential multi-joint activity
disinhibition: cells of the GP
- when are they active
- controlled by…
spontaneously active
controlled by cortical or nigral activation of the relatively quiet striatal cells (caudate and putamen)
what general things will be noted with lesions in the basal ganglia
abnormal movement and posture
how is the basal ganglia involved in movement and posture
basal ganglia activity coupled to areas of the cortex that are involved in planning and execution of motor activity
secondary proposed function of the basal ganglia
part of the procedural learning of motor activity
describe procedural learning
more task-oriented
-i.e. ability to learn and replicate automatic motor skills
procedural and declarative learning relation to Alzheimer’s patients
they can learn new motor tasks (procedural), but not new facts (declarative)
aside from disinhibition and procedural memory, basal ganglia also involved in…
cognitive function
describe basal ganglia role in cognitive function
head of caudate nucleus
- recieves a large projection from frontal lobe assocation cortex
- projects back to the same cortical area via VA and DM thalamic nuclei
putamen role in basal ganglia cognitive function
primarily a motor function nucleus
functions more in habit formation and procedural or implicit memory
basal ganglia blood supply
- from…
- -each supplies…
striatal or ganglionic arteries (small deeply penetrating brahcnes of Circle of Willis)
-supply bulk of caudate nucleus
-anterior globus pallidus
-putamen
-internal capsule
thalamo-geniculate branch of posterior cerebral artery
-subthalamic nucleus (plus thalamus and adjacent posterior limb of internal capsule)
diffuse diseases of the CNS with multiple sites of damage
- examples
- produce…
- -as a result
encephalitis and CP
produce a variety of dyskinesias (disorders of movement)
-makes localization of lesions difficult
the idea that individual components of the basal ganglia and related motor areas have certain distinct functions is based on…
observations of two types of dyskinesias
-hyper- and hypo-kinetic in nature
kyperkinetic disorders
-what are they
athetoses
choreas
ballismus
athetoses
- describe
- often seen in…
- lesion location
involuntary, ceaseless, slow, writhing movements (like an “oriental dancer”)
often seen in CP
lesion location is unclear, but probably involves striatum
choreas
- describe
- lesion location
jerking, dancing, grimacing movements of varying duration and latency
-frequently appear “purposive”
when not moving, patients’ muscles exhibit hypotonia
lesions are typically in striatum or VL of thalamus
ballismus
- describe
- lesion location
violent flinging movements due to involuntary contractions, especially of proximal limb muscles
usually on one side only = hemiballism
caused by localized lesion of subthalamic nucleus contralateral to affected limb
why is ballismus caused by a contralateral lesion?
I don’t know
hypokinetic disorder
- lesion location
- example
lesions usually in striatum and SN
Parkinsonism
Parkinson’s disease
- caused by…
- characteristic
- -caused by…
caused by degeneration of nigrostriatal neurons that use dopamine as their neurotransmitter
deficit may be worse on one side than the other, in which case dopamine loss is greater on the side contralateral to the worst deficits
hyperkinesias: hypothesized mechanisms
- best interpretation from…
clinical observations and primate research
hyperkinesias
- explain the mechanism
- -function of indirect and direct circuits
- -what would cut the indirect circuit and what would the result be
basal ganglia normally has an inhibitory influence on UMNs through the indirect circuit and an excitatory influence through the direct circuit
lesions of the subthalamic nucleus would cut the indirect circuit and permit the direct circuit to drive movements unopposed
hyperkinesias
-explanation for choreas and athetoses
still unknown but may involve selective loss of striatal GABA neurons that normally inhibit motor activity
hypokinesia with rigidity
-current mechanism hypothesis
dopamine normally enhances the direct (excitatory) circuit and inhibits the indirect (inhibitory) circuit
loss of SNc dopaminergic neurons results in a greatly reduced ability of the cortex to initiate movement through the activation of cortical UMNs
loss of control over UMNs results in loss of voluntary control of alpha LMNs (akinesia) and decreased inhibition of the gamma loop relfex (rigidity)
