Basal Ganglia and Thalamic Pathways Quiz

Basal Ganglia

• Basal ganglia are a collection of masses of gray matter located within each cerebral hemisphere.
• These structures include the caudate nucleus, putamen, and globus pallidus.
• Basal ganglia are involved in the control of movement.
• They do not directly control movement, but modulate, and help coordinate motor commands initiated by the cortex.

Brain Components

• Cerebral cortex is the outer layer of the brain, responsible for higher-level functions like thought, language, and memory.
• Basal nuclei, also called basal ganglia, are located deep within the cerebral hemispheres and are vital for motor control.
• Thalamus is a relay station that processes sensory information before it reaches the cortex.
• Cerebellum is responsible for coordinating movement and balance.
• Brain stem, consisting of the midbrain, pons, and medulla oblongata, controls basic life functions like breathing and heart rate.
• Spinal cord transmits signals between the brain and the rest of the body.
• Hypothalamus is involved in regulating various bodily functions, including homeostasis, and links the nervous system and endocrine system.

Traditional Concepts of Basal Ganglia

• Corpus Striatum: Comprising of the Caudate Nucleus, Putamen, and Globus Pallidus.
• Neostriatum: Composed of the Caudate Nucleus and Putamen.
• Paleostriatum: Forms the Globus Pallidus.
• Archistriatum: Not detailed in the provided text.
• Corpus Amygdaloideum: Distinct structure, part of the system, not part of corpus striatum.

Components of Basal Ganglia

• Corpus Striatum: Receives information from the cortex and other structures.
• Caudate Nucleus: One of the components of the Corpus Striatum.
• Putamen: One of the components of the Corpus Striatum.
• Nucleus Accumbens: Part of the striatum, implicated in reward-related processes.
• Pallidum: Includes the Globus Pallidus segments.
• Globus Pallidus: Output nucleus of the basal ganglia.
• Substantia Nigra: Plays a critical role in motor control.
• Pars Compacta (SNc): dopaminergic, essential component.
• Pars Reticulata (SNr): inhibitory output.
• Subthalamic Nucleus (STN): Excitatory output to the basal ganglia.
• Ventral Striatum/Nucleus Accumbens: Implicated in reward and motivation.
• Ventral Pallidum: Involved in the output of the basal ganglia.

Caudate Nucleus

• C-shaped structure.
• Located next to the lateral ventricle.
• Situated laterally to the thalamus.
• Located next to (lateral to) the internal capsule and lentiform nucleus.
• The head of the caudate nucleus continues into the putamen (below).
• The tail of the caudate nucleus extends to the amygdala, a structure associated with emotion.

Amygdala

• Consists of three nuclear groups.
• Corticomedial nuclear group
• Basolateral nuclear group
• Central
• Plays a role in processing emotional responses, particularly fear, and influencing behavior.
• Influences the body's responses to environmental changes through connections with other brain regions.

Subthalamus

• Located inferior to the thalamus.
• Located between the thalamus and the tegmentum.
• Craniomedially located to the hypothalamus.
• Part of the diencephalon.
• Contains nuclei that project to the corpus striatum, globus pallidus, and other structures.
• Its neurons utilize glutamate, acting as an excitatory neurotransmitter.

Zona Incerta

• Elongation of the reticular formation within the subthalamus.
• Connected to the tectum, tegmentum, and red nucleus.
• Evaluates optic and vestibular impulses and relays them to the globus pallidus.

Afferents Fibers of Corpus Striatum

• Corticostriate fibers extend from the cortex to the putamen and caudate nucleus.
• The sensory-motor cortex's afferent signals are a major source of input (larger input).
• Thalamostriate fibers connect the thalamus to the caudate and putamen.
• Nigrostriate fibers connect the substantia nigra to the caudate and putamen (important for dopamine transmission).
• Intralaminar nuclei are also related to afferent signals.

Efferents of Corpus Striatum

• Striatopallidal fibers project from the caudate and putamen to the globus pallidus.
• Striatonigral fibers connect the caudate and putamen to the substantia nigra.

Afferents Fibers of Globus Pallidus

• Striatopallidal fibers carry signals from the striatum (caudate and putamen) to the globus pallidus.

Efferents of Globus Pallidus

• Ansa lenticularis: Afferent fibers to the thalamus.
• Fasciculus lenticularis: Afferent fibers to the subthalamus.
• Pallidotegmental fibers: project to the tegmentum.
• Pallidosubthalamic fibers: Project to subthalamic nuclei.

Nucleus Accumbens

• Part of the basal forebrain.
• Receives dopamine signals from the ventral tegmental area (VTA).
• Implicated in reinforcement, motivation, behavior and potentially rewarding experiences.

Pedunculopontine Nucleus

• Part of the basal ganglia.
• Located in the mesopontine tegmentum, between the posterior pole of the substantia nigra and the superior cerebellar peduncle.
• Involved in sleep, learning, sensory processing, reaction time, performance, and locomotion.

Oculomotor Circuit

• Crucial for regulating eye movements and gaze.
• Inputs from prefrontal and posterior parietal areas to the caudate nucleus.
• Signals travel from caudate to GPi and SNr (striatal output nuclei) which project to the thalamus (ventral anterior and dorsomedial nuclei).
• Ventral anterior nucleus to cortical eye fields for initiating movement.
• Dorsomedial nucleus to the limbic system for directing gaze toward salient stimuli.
• Substantia nigra pars reticulata (SNr) to superior colliculus coordinate movement.

Association Circuit

• Plays a critical role in cognitive functions.
• Receives signals from frontal, parietal, and temporal association areas, directing them to the caudate and nucleus accumbens.
• Output from the globus pallidus internal (GPi) and substantia nigra pars reticulata (SNr) reaches the thalamus (especially the ventral anterior (VA) and centromedian (CM) nuclei).
• The VA contributes to motor and prefrontal areas.
• The CM impacts overall cortical arousal and function.

Planning of complex motor activity

• Circuit activity decreases after practicing well-learned activities.
• Impacts cognitive processes and learning significantly.
• Aids in differentiating stimuli to guide goal-directed behavior.

Limbic Circuit

• Regulates emotional, motivational, and affective behaviors.
• Involves motor expression of emotions (e.g., postures, gestures, facial expressions).
• Contains a dopaminergic rich circuit, regulating and influencing facial muscles.
• Regulated by the circuitry from the cingulate gyrus to face related muscles.

Motor Circuit

• Balance between direct and indirect pathways is critical to proper motor function.
• Imbalance can lead to either insufficient, excessive, or uncoordinated movements.
• Dysfunction may lead to motor disorders.

Parkinson's Disease

• Loss of dopaminergic neurons in the substantia nigra.
• Characterized by resting tremors, slow movements, rigidity, and postural instability (motor symptoms).

Huntington's Disease

• Genetic disorder affecting the basal ganglia, particularly the caudate and putamen, leading to neuronal loss.
• Involves uncontrolled, involuntary movements (chorea).

Blood Supply to Basal Ganglia

• Blood supply arises primarily from the internal carotid artery (ACA), middle cerebral artery (MCA), and posterior cerebral artery (PCA).
• Specific branches like anterior choroidal arteries and lenticulostriate arteries are critical providers to the different regions of the basal ganglia.