Basal nuclei & Parkinson’s disease Flashcards
What is the lentiform nucleus and it’s structures?
The lentiform nucleus is wedge-shaped and consists of the outer part putamen (shell) and the globus pallidus (pallidum) which is divided to lateral (outer) and medial (inner) segments. The pallidum is so named because of its pale appearance in comparison to the caudate nucleus and putamen due to the presence of myelinated fibres forming the internal connections of the basal ganglia.
What is the corpus striatum subdivided into? HINT: anatomically and functionally different
The corpus striatum is subdivided to:
Anatomically = caudate nucleus + lentiform nucleus
Functionally= pallidum + Striatum
What are the two functional zones of the basal nuclei
There are two functional zones based upon afferent and efferent connections.
The striatum (caudate nucleus and putamen) is the‘input’ portion of the basal ganglia which receives projections from the overlying cerebral cortex. The putamen and caudate nucleus have a common embryological origin, identical histological appearances, and similar connections.
The pallidum (internal segment of the globus pallidus) is the ‘output’ portion of the basal ganglia which projects to the thalamus.
What are the brain functions that are regulated by the basal nuclei
The basal nuclei regulate different brain functions through three pathways (loops):
-Voluntary motor control (motor cortex), motor movement loop
-Emotional functions (cingulate gyrus), limbic loop
-Cognitive functions (prefrontal cortex), Prefrontal loop/Cognitive-executive loop
Describe the voluntary motor loop of the basal ganglia
Disturbed in movement disorders such as Parkinson’s disease. Projections arise from the motor area of frontal lobe into the putamen (motor part of the striatum). The putamen gives rise to direct and indirect connections that converge on the internal pallidum. This projects in turn to the thalamus, which completes the loop via a thalamocortical projection back to the supplementary motor area (SMA).
Dopamine deficiency in Parkinson’s disease leads to under-activity of the motor loop and SMA, interfering with the initiation of voluntary actions.
Voluntary motor loop regulates body movements by:
-Enabling desired movements to occur.
-Inhibiting undesired movements from occurring.
-The regulation happens via two parallel pathways, direct and indirect pathway.
Direct pathway disinhibits (facilitates) desired movements and indirect pathway inhibit undesired (competing movements).
Describe the limbic loop of basal ganglia
The projections arise in the limbic lobe or amygdala which then project to the ventral striatum (nucleus accumbens) and ventral pallidum. The ventral striatum is rich in opiate receptors and has been implicated in motivation, reward-based learning and addictive behaviours.
Note: The caudate nucleus and putamen are fused underneath of the internal capsule to form the nucleus accumbens.
Limbic loop may regulate:
-Emotional and motivated behaviour
-Reward based learning and addiction
-Transition from one mood to another
Describe the Prefrontal loop/ Cognitive-executive loop of basal ganglia
This loop passes through the caudate nucleus. It arises and terminates in the prefrontal cortex and influences cognition and behaviour. Over-activity in caudate-prefrontal connections has been implicated in obsessive-compulsive disorder.
Prefrontal loop regulates initiation and termination of cognitive process such as:
-Planning
-Working memory
-Attention.
What are the input and output zones of basal nuclei?
The caudate and putamen (striatum) comprise the input zone of the basal ganglia which receive input from different parts of cortex and the substantia pars compacta.
The globus pallidus and substantia nigra pars reticulata are the main sources of output from the basal ganglia complex
Describe Obsessive-compulsive disorder (OCD) and what is the cause of this in the brain
This is an anxiety disorder that affects around 2% of the population. Obsessions are recurring unwanted thoughts, ideas and sensations whereas compulsions are irrational urges to carry out particular acts or rituals. Pathological doubt is also common, leading to repetitive behaviors, such as hand washing, checking on things or cleaning which can significantly interfere with a person’s daily activities and social interactions.
Neuroimaging suggests that there may be overactivity in connections between the caudate nuclei and prefrontal cortex, which appears to normalize after successful treatment using serotonin-selective reuptake inhibitors (SSRIs).
What is the difference between positive and negative movement signs when there are abnormalities in the basal nuclei
The positive signs are ‘spontaneous’ actions the patient does not want to perform but cannot prevent such as:
-Tremors are rhythmic or oscillatory movements in the distal parts of the limbs, such as the hands.
-Chorea is rapid, spastic dance-like movements in the more distal parts of the limbs and in the face.
-Ballismus is violent throwing movements of the entire limb as a result of contractions of the more proximal muscles.
The negative signs are actions the patient wants to perform but cannot such as:
-Postural instability (common in Parkinson patients).
-Akinesia: hesitancy in starting a movement.
-Bradykinesia: slowness in execution of Movements
Describe Parkinson’s disease
It is a neurodegenerative disease that results in a decrease in the initiation of movements (hypokinetic) and a resting tremor. It is characterized by a loss of the dopaminergic neurons of the substantia nigra. The confirmation of the diagnosis upon autopsy shows the pallor of the substantia nigra.
The pathological hallmark of Parkinson’s disease is the Lewy body. This is a type of pathological protein aggregation found in the cytoplasm of surviving neurons. The main constituent of Lewy bodies is alpha-synuclein. This is a synaptic protein that is present in presynaptic terminals in association with synaptic vesicles.
Describe Huntington’s disease. What can be found in CT/MRI? What are the symptoms (physical, cognitive, emotional)?
It is an autosomal dominant disease characterized by the progressive loss of selective neurons in the basal ganglia. Patients with HD experience hyperkinetic movements.
Protein aggregates of huntingtin can be found in neurons of the striatum. The MR and CT imaging show prominent atrophy of the caudate nucleus with secondary atrophy of the putamen and dilation of the lateral ventricles.
CT and MRI findings:
-Marked cortical thinning.
-Extensive loss of subcortical white matter.
-Dilation of the lateral ventricle.
-Atrophy in caudate nucleus.
Symptoms:
1. Physical symptoms:
-Twitching of the fingers and toes
-Walking difficulties
-Dance-like or jerky movements of the arms or legs (chorea)
-Speech and swallowing difficulties
- Cognitive symptoms:
-Short-term memory loss
-Difficulties in concentrating and making plans. - Emotional and behaviors:
-Depression
-Mood swings, apathy and aggression
Explain why patients with Parkinson’s disease difficulty in decision-making and executive functions having (be sure to include the affected circuit)
John is a 56-year-old man who presents to a psychiatrist for treatment. His symptoms started slowly; he mentioned that he was always described as an anxious person and remembers being
worried about a lot of things throughout his life. He said he was washing his hands excessively and checking doors/ window’s lock several times during day and at night.
a) What would be the diagnosis?
b) What basal nuclei circuit might be affected
