Basal Nuclei Flashcards
what does baseline activity allow for?
- common throughout the nervous system, allows for increase and decrease in activity (activity never completely turned off)
- allows for fine tuning
- sensitivity
what does baseline activity allow for?
- common throughout the nervous system, allows for increase and decrease in activity (activity never completely turned off)
- allows for fine tuning
- sensitivity
basal ganglia
- directly effect UMN cortex through modulation.
- determine appropriateness of actions, emotions, cognition: decide what behavior is most likely to be “Correct”
- “basal nuclei” is more appropriate name, they are subcortical grey matter
basal ganglia
- directly effect UMN cortex through modulation.
- determine appropriateness of actions, emotions, etc.
- “basal nuclei” is more appropriate name, they are subcortical grey matter
what forms striatum of basal nuclei?
caudate nucleus and putamen
- note: caudate nucleus forms lateral wall of ventricle
- called “striatum” because they have myelinated axons passing through causing them to look striated.
what forms lentiform nucleus?
putamen
+
globus pallidus (internal and external)
(have a lens like appearance together)
what is globus pallidus composed of?
GPe (external) or “lateral” segment
GPi (internal) or “medial” segment
- globus pallidus lies just medial to putamen
substantia nigra involvement in basal ganglia?
pars compacta (SNc): releases dopamine
pars reticulata (SNr)
substantia nigra involvement in basal ganglia?
pars compacta (SNc): releases dopamine
pars reticulata (SNr)
Disinhibtion
= removal of an inhibitory effect by a stimulus
- “inhibition of an inhibition”
- inhibitory = gabaminergic
- disinhibitory = glutamatergic
basal ganglia
- directly effect UMN cortex through modulation.
- determine appropriateness of actions, emotions, etc.
- “basal nuclei” is more appropriate name, they are subcortical grey matter
what forms striatum of basal nuclei?
caudate nucleus and putamen
- note: caudate nucleus forms lateral wall of ventricle
- called “striatum” because they have myelinated axons passing through causing them to look striated.
what forms lentiform nucleus?
putamen
+
globus pallidus (internal and external)
(have a lens like appearance together)
what is globus pallidus composed of?
GPe (external) or “lateral” segment
GPi (internal) or “medial” segment
- globus pallidus lies just medial to putamen
what portions of thalamus are involved in the in basal ganglia?
subthalamic nucleus
thalamus
substantia nigra involvement in basal ganglia?
pars compacta (SNc): releases dopamine
pars reticulata (SNr)
what are the two paired circuits of the basal nuclei?
- Direct pathway: “yes” loop
- indirectly pathway: “no”/don’t loop
- determine Motor, cognition and affect
- there are two paired circuits in each hemisphere that run in a parallel manner
where does output/input from basal nuclei come from? how do they influence the cortex?
input: from striatum (pyramidal cells and motor cx always project in through striatum)
output: globus pallidus internus and substantia nigra
final projection is into the thalamus. the thalamus ultimately influences the cortex (though this is technically not part of the basal nuclei )
draw out direct and indirect pathways.
do it now.
and memorize it.
direct loop: actions of ACH and dopamine
ACH: cholinergic neurons of striatum are inhibitory. ACH is released and ultimately results in decreased cortical activity of direct loop.
Dopa: released from SNc and binds D1 receptors: results in depolarization: facilitates cx through increasing thalamic activity (thalamus is disinhibited)
indirect loop: actions of ACH and dopamine
ACH: cholinergic neurons of striatum are excitatory and decreases cortical activity of indirect loop
Dopa: released from SNc binds to D2: results in hyperpolarization: facilitates cx through increasing thalamic activity (subthalamic is disinhibited)
what is role of substantia nigra compacta?
releases dopamine
- Dopa depolarizes (excitatory) to D1 receptors of direct loop, results in facilitating cortex
- dopa hyperpolarizes (inhibitory) to D2 receptors of indirect loop, thus facilitating cortex
- this is what is damaged in Parkinson’s disease* thus increased cortical activity is lost with parkinson’s disease
what does ACA supply to basal nuclei?
head of caudate
nucleus accumbens
what does branches of MCA (lenticulostriate) supply of basal nuclei?
Lentiform (putamen and GP)
majority of caudate***
what does branches of PCA supply?
- substantia nigra
- subthalamic nucleus
*** this is the most common place for stroke lesions, will produce hemiballismus symptoms = decrease in activity of the subthalamic nucleus of the basal ganglia, resulting in the appearance of flailing, ballistic, undesired movements of the limbs.
what do pathologies of the basal nuclei usually present through?
- movement disorders
- not directly affecting strength, coordination or sensation
- VOLUNTARY movmt systems are affected
- will see abnormalities of tone (increased or decreased) depending on lesion
- akinetic or hyperkinetic depending on lesion
negative vs. positive signs
neg = reduced mvmt pos = increased/inappropriate mvmt
four different types of kinesias…
akinesia = no mvmt hypokinesia = reduced mvmt bradykinesia = slow mvmt dyskinesia = inappropriate/incorrect mvmt
tremor
- oscillatory mvmt (4-6 Hz)
- greatest at rest, they are decreased with voluntary mvmt
athetosis
slow writhing mvmt
chorea
abrupt, rapid, jerking dance like (often distal limbs and orofacial mm)
choreoathetosis
mixture of slow writhing mvmt and abrubt jerking.
ballism
violent flinging
- usually unilateral = hemiballismus
Parkinson’s disease cause
- late onset disease (<50 y/o)
- unknown cause
- results in degeneration of SNc and loss of Dopa neurons
- substantia nigra looks severely lesioned
- results in decreased activity of cortical motor neurons - cx is inhibited
Parkinson’s disease symtpoms: negatives and positives?
Negative signs:
- hypokinesia/bradykinesia
- Gait is small, shuffling steps
- facial masking
- loss of postural reflexes (flexed stooped posture)
- late cognitive defects
- difficulty initiating gait
Positive signs:
- Tremor that occurs at rest (pill rolling)
Therapy for Parkinson’s disease
- Replace missing L-dopa (effectiveness decreases over time)
- replace missing cells of SNc via stem cell transplant (will eventually die just as predecessors did)
- reduce the activity of indirect loop
huntington’s disease cause?
- earlier onset: age 30-40y/o
- due to multiple CAG repeats on chromosome 4 “huntington protein”
- autosomal dominante
- results in degeneration of striatum (caudate) of indirect loop
symptoms of huntington’s disease
positive changes:
- hyperkenisias
- choreoathetosis “huntingtono’s chorea”
negative symptoms:
- dementia and cognitive changes (caudate is important part of “cognitive loops”)
- psychoses (hallucinations and paranoia)
- very little treatment. developes earlier than parkinson’s disease
