Basal Ganglia Flashcards
What is the basal ganglia?
A group of subcortical nuclei located in the inferior cerebral hemisphere, lateral to the thalamus, with crucial motor and behavioral functions.
What are the 5 main components of the basal ganglia?
Caudate nucleus.
Putamen.
Globus pallidus (external and internal segments).
Substantia nigra (pars compacta and pars reticulata).
Subthalamic nucleus.
What are the related structures of the basal ganglia and their function?
Amygdala: Anatomically part of the basal ganglia but functionally part of the limbic system; processing emotions and memories related to fear
Claustrum: Function unknown
What is the overall function of the basal ganglia?
Regulation of voluntary motor control, procedural learning, and habit formation.
Role in emotion and cognition.
What are the anatomical components of the basal ganglia?
Striatum: Caudate nucleus and putamen.
Globus pallidus: External (GPe) and internal (GPi).
Subthalamic nucleus (STN).
Substantia nigra: Pars compacta (dopaminergic) and pars reticulata (output nucleus).
Which basal ganglia structure has an unknown function?
Claustrum: Function unknown.
Why is the amygdala part of the basal ganglia anatomically but not functionally?
Developmentally part of the basal ganglia, but it primarily functions in the limbic system (emotion and fear processing).
What are the two main motor pathways involving the basal ganglia?
Direct pathway: Facilitates movement by reducing thalamic inhibition.
Indirect pathway: Inhibits movement by increasing thalamic inhibition.
“Direct pathway - acts like a green light, promoting movement by reducing the inhibition of the thalamus ‘Traffic’, while the Indirect pathway acts like a red light, inhibiting movement by increasing thalamic inhibition”
What role does dopamine play in basal ganglia pathways?
Released by the substantia nigra pars compacta.
Enhances the direct pathway and suppresses the indirect pathway, promoting voluntary movement.
What happens in Parkinson’s disease?
Cause: Loss of dopaminergic neurons in the substantia nigra pars compacta.
Symptoms: Bradykinesia, resting tremor, rigidity, postural instability.
What happens in Huntington’s disease?
Cause: Degeneration of the striatum (mainly the caudate nucleus).
Symptoms: Chorea (involuntary jerky movements), cognitive decline, psychiatric disturbances.
What is the clinical importance of the subthalamic nucleus?
Lesion: Hemiballismus (flailing, involuntary limb movements).
Which basal ganglia structure is primarily affected in hemiballismus?
Subthalamic nucleus: Lesion results in reduced inhibition of movement.
What are the two divisions of the Corpus Striatum?
Dorsal division: Includes caudate nucleus, putamen, globus pallidus.
Ventral division: Includes ventral striatum (nucleus accumbens, olfactory tubercle) and ventral pallidum.
What is the Lentiform Nucleus?
Lentiform nucleus = Putamen + Globus Pallidus.
What are the parts of the caudate nucleus?
Head, body, and tail.
What lies above and medial to the caudate nucleus?
Above: Corpus callosum.
Medial: Thalamus
What structures are located between the thalamus and the caudate nucleus?
Stria terminalis and thalamostriate vein.
What separates the caudate nucleus from the lentiform nucleus?
The anterior limb of the internal capsule.
What components make up the striatum functionally?
Striatum = Caudate nucleus + Putamen.
What is the pallidum?
Pallidum = Globus pallidus.
Which nucleus is part of both the basal ganglia and the limbic system?
Amygdala: Anatomically basal ganglia, functionally limbic system.
What are the components of the substantia nigra?
Pars Reticulata (receives afferents) and Pars Compacta (sends efferents, dopaminergic).
What is the role of the subthalamic nucleus?
Integrates and smoothens movements, key in the indirect pathway.
What neurotransmitter is key in the direct and indirect pathways?
Dopamine: Stimulates the direct pathway and inhibits the indirect pathway.
What are the four circuits of the basal ganglia?
Motor, Cognitive, Limbic, and Oculomotor loops.
What happens in Parkinson’s Disease?
Loss of dopaminergic neurons in the substantia nigra pars compacta, leading to bradykinesia and rigidity.
Which pathway is overactive in Huntington’s Disease?
Direct pathway, resulting in excessive movements (chorea)
What is the functional role of the limbic loop?
Links emotions to motor expressions (e.g., smiling, gesturing).
What is hemiballismus?
Damage to the subthalamic nucleus.
Reduced indirect pathway activity → Violent, involuntary limb movements.
What is the cause of Huntington’s Disease?
Degeneration of striatum (especially in the indirect pathway).
Reduced inhibitory output → Excessive movements (chorea).
Describe the limbic loop pathway
Pathway:
Prefrontal Cortex → Ventral Striatum (Nucleus Accumbens) → Ventral Pallidum → Thalamus (Mediodorsal Nucleus) → Prefrontal Cortex.
What is the function of the limbic loop and what are the symptoms of dopaminergic decline?
Assigns motor expressions to emotions (e.g., smiling, gestures).
Clinical Insight:
Dopaminergic decline in this loop results in mask-like facies, as seen in Parkinson’s disease.
Describe the Direct Pathway
Pathway:
Cerebral Cortex → Corpus Striatum (dorsal) → Globus Pallidus (medial segment) → Thalamus (Ventral anterior/lateral nuclei) → Cerebral Cortex.
What neurotransmitter sare involved in the direct pathway?
Neurotransmitters:
Corticostriate fibers: Glutamate (excitatory).
Striatopallidal fibers: GABA (inhibitory).
Pallidothalamic fibers: GABA.
Describe the mechanisms of the direct pathway
Mechanism:
Inhibition of the inhibitory neurons (disinhibition), leading to increased motor activity.
Dopamine (from substantia nigra pars compacta) stimulates this pathway.
Describe the Indirect Pathway
Pathway:
Cerebral Cortex → Corpus Striatum (dorsal) → Globus Pallidus (lateral segment) → Subthalamus → Globus Pallidus (medial segment) → Thalamus → Cerebral Cortex.
What neurotranmitters are involved in the Indirect pathway?
Corticostriate fibers: Glutamate (excitatory).
Striatopallidal fibers: GABA (inhibitory).
Subthalamopallidal fibers: Glutamate (excitatory).
Pallidothalamic fibers: GABA (inhibitory).
Describe the mechanism of the Indirect Pathway
Mechanism:
Excitation of inhibitory neurons reduces motor activity.
Dopamine inhibits this pathway.
Explain the role of Dopamine in both Indirect and Direct Pathways
Dopamine’s Role
Stimulates the direct pathway (via D1 receptors).
Inhibits the indirect pathway (via D2 receptors).
Net effect: Increases motor activity
Describe the SUBTHALAMIC NUCLEUS
Shape: Biconvex lens.
Location: Subthalamic region, at the junction of the internal capsule and crus cerebri.
Function: Integrates and smoothens movements by relaying signals in the indirect pathway.
Describe the functions of the basal ganglia
Motor Refinement:
Prevents unwanted or exaggerated movements.
Refines cortical activation by reducing excitatory input to the cortex.
Cognitive and Emotional Modulation:
Ventral striatum plays a role in emotional responses via limbic inputs.
Pathways:
Direct Pathway: Facilitates motor activity.
Indirect Pathway: Inhibits motor activity.
Overall Goal: Influence the ipsilateral cerebral cortex, which controls the contralateral side of the body.
What is the goal of the direct pathway?
Facilitates movement by disinhibiting the thalamus and increasing motor cortex activity.
What are the main steps in the direct pathway?
Motor cortex → Corpus striatum (Caudate + Putamen).
Striatum inhibits globus pallidus (medial segment) using GABA.
Reduced globus pallidus inhibition of the thalamus.
Thalamus excites the motor cortex.
Which connections are excitatory in the direct pathway?
Corticostriate fibers: Glutamate excites the striatum.
Thalamocortical fibers: Glutamate excites the motor cortex.
Which connections are inhibitory in the direct pathway?
Striatopallidal fibers: GABA inhibits the globus pallidus (medial segment).
Pallidothalamic fibers: Normally, GABA inhibits the thalamus (disinhibited in this pathway).
How does dopamine influence the direct pathway?
Dopamine binds to D1 receptors in the striatum → Increases activity of the striatopallidal (GABAergic) neurons → Enhances disinhibition of the thalamus → More movement.
What is the goal of the indirect pathway?
Inhibits movement by increasing inhibition of the thalamus, reducing motor cortex activation.
What are the main steps in the indirect pathway?
Motor cortex → Striatum.
Striatum inhibits globus pallidus (lateral segment) using GABA.
Reduced globus pallidus inhibition of the subthalamic nucleus.
Subthalamic nucleus excites the globus pallidus (medial segment).
Globus pallidus inhibits the thalamus.
Reduced thalamic excitation of the motor cortex.
Which connections are excitatory in the indirect pathway?
Corticostriate fibers: Glutamate excites the striatum.
Subthalamopallidal fibers: Glutamate excites the globus pallidus (medial segment).
Which connections are inhibitory in the indirect pathway?
Striatopallidal fibers: GABA inhibits the globus pallidus (lateral segment).
Pallidosubthalamic fibers: Normally, GABA inhibits the subthalamic nucleus (disinhibited in this pathway).
Pallidothalamic fibers: GABA inhibits the thalamus
How does dopamine influence the indirect pathway?
Dopamine binds to D2 receptors in the striatum → Reduces activity of the striatopallidal (GABAergic) neurons → Less inhibition of the globus pallidus (lateral segment) → Decreases suppression of movement.
What are dyskinesias?
Abnormal, involuntary movements that can be categorized as hyperkinesia (excessive movement) or hypokinesia (reduced movement).
What are examples of hyperkinetic and hypokinetic disorders?
Hyperkinesia: Tremors, athetosis, chorea, ballism.
Hypokinesia: Parkinson’s disease.
What is a tremor?
A rhythmical, alternating involuntary movement with relatively regular frequency and amplitude.
What is the key tremor associated with Parkinson’s disease?
Resting tremor, typically described as a “pill-rolling” movement.
What characterizes athetosis?
Involuntary, slow, writhing movements.
Involves distal muscles of the extremities.
What is the common anatomical association with athetosis?
Lesions in the corpus striatum, particularly the putamen.
What characterizes chorea?
- Quick, jerky, irregular involuntary movements.
- Non-repetitive in nature.
What are the two primary types of chorea, and how do they differ?
Sydenham’s chorea:
Disease of childhood.
Associated with rheumatic fever and heart disease.
Huntington’s chorea:
Autosomal dominant.
Overactivation of dopaminergic neurons in the substantia nigra.
Involves degeneration of the caudate nucleus, leading to enlarged lateral ventricles (visible on CT scans).
What is hemiballismus?
Violent, forceful, unilateral movements involving the proximal extremities (e.g., shoulder or pelvic girdle muscles).
What lesion causes hemiballismus?
Damage to the subthalamic nucleus, often due to a posterior cerebral artery thrombosis.
What are the hallmark features of Parkinsonism?
Hypokinesia: Reduced voluntary movement, delay in initiation, lack of precision.
Rigidity: Cogwheel rigidity.
Resting tremor: Often “pill-rolling” tremor.
Expressionless face: Mask-like facies.
Stooped posture.
What is the primary pathological cause of Parkinson’s disease?
Loss of dopaminergic neurons in the substantia nigra pars compacta.
What happens to the nigrostriatal pathway in Parkinson’s disease?
Reduced dopamine → Overactivation of the indirect pathway → Inhibition of motor activity.
Underactivation of the direct pathway → Reduced facilitation of movement.
What is seen histologically in Parkinson’s disease?
Cellular loss and depigmentation of the substantia nigra.
What does a CT or MRI show in Huntington’s disease?
Enlarged lateral ventricles due to degeneration of the caudate nucleus.
What structure is primarily affected in hemiballismus?
The subthalamic nucleus.
Which part of the basal ganglia degenerates in Parkinson’s disease?
The substantia nigra pars compacta.
What are the key anatomical landmarks around the caudate nucleus?
Medial: Thalamus.
Above: Corpus callosum.
Separated from the lentiform nucleus by: Internal capsule (anterior limb).
