BASAL NUCLEI Flashcards
What are the components of the BASAL NUCLEI?
1 * Caudate nucleus
2 * Putamen
3 * Globus pallidus
4 * Nucleus accumbens
5* Subthalamic nucleus
6* Substantia nigra
BLOOD SUPPLY TO THE BASAL NUCLEI?
MAJORITY = MIDDLE CEREBRAL ARTERY
ALSO
- ANTERIOR CEREBRAL ARTERY
- INTERNAL CAROTID ARTERY
DIRECT PATHWAY VS INDIRECT PATHWAY
Direct pathway facilitate target- oriented & efficient behaviour.
Indirect pathway suppresses superfluous behaviours that are not related to the targeted behaviour.
ANATOMICAL TERMS OF BASAL NUCLEI PATHWAYS
1.THALAMIC FASICULUS
2. SUBTHALAMIC FASCICULUS
3.NIGROSTRIATAL
4.CORTICOSTRIATAL
CORTICOSTRIATAL = Fibres projecting from cortex to the striatum
NIGROSTRIATAL: Fibres projecting from substantia nigra to the striatum
SUBTHALAMIC FASCICULUS : Fascicle of fibres projecting to and from the globus pallidus & subthalamic nucleus
THALAMIC FASICULUS Fascicle of fibres projecting from globus pallidus internus to thalamus
C/P = caudate nucleus/putamen = striatum SN = substantia nigra
STN = subthalamic nucleus
GPe = globus pallidus externus
GPi = globus pallidus Internus
DIRECT PATHWAY STEPS
- CORTEX TO CAUDATE/PUTAMEN (STRIATUM)
- EXCITATORY projections from the cortex to the striatum synapse with inhibitory neurons
NIGROSTRIATAL NEURONS INCREASE EXITATORY INPUT TO STRIATUM BY BINDING TO D1 RECEPTORS
- Inhibitory neurons project directly to GLOBUS PALLIDUS internus
- from GPi inhibitory neurons project to the THALAMUS
- Inhibition of the inhibition releases tonic inhibition of the thalamus, resulting in INCREASED OUTPUT
- The THALAMUS sends EXICTATORY FINRES TO THE CORTEX
- the SUBTHALAMIC nucleus (DTN) provides tonic stimulation to the SN, influencing output to the SN
- N enhances the excitatory input from the cortex.
SIMPLIFIED:
* Nigrostriatal neurons increase excitatory input to striatum by binding to D1 receptors.
- Striatopallidal neurons project to GPi. Pallidothalamic neurons release thalamus from tonic inhibition => increased excitation of cortex.
INDIRECT PATHWAY STEPS
- Excitatory projections from the cortex to the striatum synapse with inhibitory neurons
- Dopaminergic neurons inhibit (via D2 RECEPTORS) excitatory cholinergic interneurons in the striatum.
- inhibitory neurons project to the GPe
- From the GPe, an inhibitory projection goes to the SUBTHALAMIC NUCLEUS (STN)
***the SN has an inhibitry effect on the STN, whcih in turn sends excitatory projections to SN. This reciprocal connection controls the input to the Basal ganglia as wel as the output to the THALAMUS - The STN in turn sends an excitatory projection to the globus pallidus internal segment (GPi). This excites the inhibitory neurons in the GPi.
- This excitation of the inhibition by the STN projection increases the tonic inhibition of the THALAMUS.
- The thalamus then sends excitatory fibres to the cortex.
SIMPLIFIED:
- Corticostriatal neurons synapse with inhibitory neurons which project to GPe.
- Nigrostriatal neurons inhibit excitatory cholinergic neurons.
Striatopallidal neurons project to GPe which release the inhibition of the subthalamic nucleus. - Subthalamic neurons excite the GPi to increase the inhibition of the thalamus ultimately resulting in less movements (or the suppression of unwanted movements).
OVERVIEW OF THE BASAL NUCLEI FUNCTION
- Input from cortex (COGNITIVE, LIMBIC, MOTOR) => striatum.
BASAL GANGLIA; integration of associative, limbic and motor input in the striatum.
- THALAMUS
PROCESSING THROUGH THE DIRECT AND INDIRECT PATHWAYS RESULTS IN AN INTEGRATED OUTPUT TO THE THALAMUS.
Output from globus pallidus internus => thalamus.
- Basal nuclei integrate the sum of cortical activity into one behavioural output.
- Back to CORTEX with OUTPUT
UNDERSTANING BASAL NUCLEI AND MOTOR CIRCUIT
- During acquisition of habits and skills, dopaminergic input reinforces behaviours that result in a desired goal-oriented outcome.
- Motor circuit becomes active once habits and skills are well established and are no longer dopamine-dependent.
- Supplementary motor, premotor, primary motor
- DIRECT AND INDIRECT PATHWAY
- THALAMUS: VA/VL
- PRIMARY SENSORY AND SENSORY ASSOCIATION
COGNITIVE CIRCUIT AND BASAL NUCLEI
- Cognitive circuit participates in the planning of complex motor activity.
- When habits and skills have been practised and well- learned, and dopaminergic input has strengthened these behaviours, cognitive circuit activity decreases and motor circuit increases.
- Cortex (each lobe)
- nucleus accumbens
- Direct and indirect pathways
- THALAMUS VA/CM
- frontal lobe
BASAL NUCLEI AND LIMBIC CIRCUIT
- Limbic circuit is important in the motor expression (postures, gestures, facial expressions) of emotions.
- AMYGDALA, HIPPOCAMPUS, FRONTAL ASSOCIATION AREAS, ANTERIOR CINGULATE ORBITOFRONTAL LOBE
- NUCLEUS ACCUMBENS
- DIRECT AND INDIRECT
- THALAMUS: VA/DM
- ANTERIOR CINGULATE, ORBITOFRONTAL LOBE AND OR FRONTAL ASSOCIATION AREAS
UNDERSTANDING HUNTINGTONS DISEASE
- Autosomal dominant.
Degeneration of the striatum (caudate nucleus and putamen) gives the appearance of enlarged ventricles
- HD gene on chromosome 4.
- Incidence of 6 / 100,000 people in Australia, Europe & North America.
- Significantly lower incidence in Asia: 0.4 / 100,000 people.
SYMPTOMS: irritability, depression, small involuntary movements, poor coordination, and trouble learning new information or making decisions.
UNDERSTANDING PARKINSONS DISEASE:
- 1 in 308 people living with PD in Australia in 2018.
- 37 new cases diagnosed daily.
- Degeneration of dopaminergic neurons in the substantia nigra.
SYMPTOMS
Tremor. Rhythmic shaking, called tremor, usually begins in a limb, often your hand or fingers. …
Slowed movement, known as bradykinesia. …
Rigid muscles. …
Impaired posture and balance. …
Loss of automatic movements. …
Speech changes. …
Writing changes.
