AEB - Basal ganglia and limbic system anat

Putamen

receives input from the cerebral cortex and helps initiate and select appropriate movements through the basal ganglia motor loop.

Globus pallidus external (GPe)

inhibits the subthalamic nucleus and helps regulate activity in the indirect pathway.

Globus pallidus internal (GPi)

main output nucleus of the basal ganglia; tonically inhibits the thalamus to suppress unwanted movements.

Subthalamic nucleus (STN)

excites the GPi, increasing thalamic inhibition and reducing movement.

Substantia nigra

pars compacta (SNc) releases dopamine to modulate striatal activity and facilitate appropriate movement; the pars reticulata (SNr) provides inhibitory output similar to the GPi.

Disinhibition

process that reduces inhibition of a neuron, thereby increasing its likelihood of generating an action potential.

Basal ganglia motor loop

signal from motor cortex is sent to the putamen initiates a sequence of inhibitory and excitatory neurons in the basal ganglia to suppress baseline activity from cortex and initiate intended movement.

Disinhibition of thalamus

key disinhibition occurring in the direct pathway.

Global pallidus internal

What basal ganglion is directly or indirectly targeted by the putamen in the motor loop?

Direct pathway

motor loop required for execution of intended motor behaviours.

Indirect pathway

motor loop for suppressing or terminating unwanted motor behaviours.

Disinhibition of subthalamic nucleus

key disinhibition occurring in the indirect pathway.

Pars compacta

part of the substantia nigra, contains dopaminergic neurons that project to the putamen, influencing the dominance of direct and indirect pathways.

Cortex + putamen - GPI - thalamus + cortex

Describe the direct pathway.

Cortex + putamen - GPE - subthalamus + GPI - thalamus + cortex

Describe the indirect pathway.

Dopamine produced by pars compacta

excites direct pathway putamen neurons and inhibits indirect pathway putamen neurons.

Hypokinetic disorder

reduced movement; excessive suppression of movement due to greater dominance of indirect pathway.

Postural instability, gait difficulty, and akinetic rigidity

Parkinson's motor subtype, characterised by a range of symptoms such as bradycardia and hypertonia.

Tremor dominant

Parkinson's motor subtype, characterised by constant resting tremor or pill-rolling.

Parkinson’s disease

progressive neurodegenerative disorder degeneration of dopaminergic neurons in the substantia nigra pars compacta leading to bilateral hypokinetic motor symptoms.

Hyperkinetic disorder

increased movement; excessive stimulation of movement due to greater dominance of direct pathway.

Athetosis

slow, continuous, involuntary, and writhing movements of hands and feet due to degeneration of putamen neurons in the indirect pathway.

Chorea

irregular, jerky, involuntary movements of hands, feet, limbs, and face that worsens with movement, can seem to move between body parts due to degeneration of putamen neurons in the indirect pathway.

Helliballismus

uncontrollable, flinging, forceful movements of the arm or leg on one side of the body due to damage to contralateral subthalamic neurons in the indirect pathway.

Huntington’s disease

inherited neurodegenerative disorder commonly causing degeneration of putamen neurons of the indirect pathway leading to bilateral hyperkinetic motor symptoms like athetosis and chorea

Limbic system

network of interconnected cortical and subcortical structures involved in emotion, motivation, learning, memory and aspects of autonomic and endocrine regulation.

Papez circuit

loop of interconnected brain structures originally proposed to explain how emotional experiences are processed and expressed.

Hippocampus

receives information about sensory stimulus from the cortex and other structures for processing and consolidation of memories. Output carried via fornix in the Papez circuit

Mammillary bodies

received hippocampal output to relay limbic information in the Papez circuit; responsible for emotional expression by enacting behavioural and autonomic functions associated with memory. Output carried via mammillothalamic tract.

Thalamus anterior nuclei

receives information from the mammillary bodies, passing information onto the cingulate gyrus in the Papez circuit.

Cingulate gyrus

receives information from the thalamus anterior nuclei; integrates emotional and cognitive information to initiate conscious emotional experience based on memories and returns information to hippocampus.

Hippocampus, mammillary bodies, thalamus anterior nuclei, cingulate cortex

What are the 4 major relay stations in the Papez circuit.

Amygdala

group of nuclei in anterior aspect on the ventromedial temporal lobe involved in processing emotions, particularly fear, emotional learning, and emotional memory.

Corticomedial nuclei

amygdala nuclei; process olfactory information and contribute to innate behaviours, including feeding, reproduction, and responses to pheromones.

Basolateral nuclei

amygdala nuclei; receive sensory information from cortex and thalamus and integrates it with emotional significance, supporting emotional learning and fear conditioning.

Central nucleus

main output region of the amygdala; coordinates autonomic, endocrine, and behavioural responses to emotional stimuli, particularly fear.

Anxiety

impaired prefrontal regulation causes amygdala hyperactivity contributing to negative emotional bias, persistent fear, and hypervigilance.

Post-traumatic stress disorder (PTSD)

impaired prefrontal regulation causes amygdala hyperactivity with exaggerated fear responses to neutral stimuli.

Klüver–Bucy syndrome

caused by lesion of the amygdala; causing hypersexuality, docile/placid behaviour, lack of fear response, and inability to recognise fear or anger in the facial expression of others.

Emotional significance, emotional learning, behavioural/autonomic responses

What are the 3 key roles of the amygdala.

Olfactory bulb, prefrontal cortex, temporal cortex, thalamus, hypothalamus

List 5 key inputs to the amygdala.

Olfactory bulb

provide smell information to the amygdala and hippocampus, which can trigger emotional responses and memories.

Prefrontal cortex and septal area

provides information involved in evaluating emotional stimuli and regulating emotional responses to the amygdala.

Hippocampus and temporal cortex

provides remembered contextual and spatial information to the amygdala, helping the assess whether a stimulus is threatening in a particular environment.

Thalamus

provide rapid sensory information to the amygdala, allowing identification of threatening stimuli.

Hypothalamus

provides information about internal bodily states and physiological responses relevant to emotional processing and memory formation to the amygdala and hippocampus

Temporal cortex, prefrontal cortex, septal area, hypothalamus, brainstem

List 5 key outputs from the amygdala.

Hippocampus and temporal cortex

receives amygdala output; modulates the formation and retrieval of emotional memories and contextual fear memories. Key in emotional experience.

Prefrontal cortex

receives amygdala output; influences emotional evaluation, decision-making and behavioural responses. Key in emotional experience.

Septal area, hypothalamus, brainstem

List 3 structures receiving amygdala output for emotional behaviour and autonomic regulation in response to stimuli.

Dorsal amygdalofugal pathway (stria terminalis)

travels from amygdala along the dorsolateral surface of the thalamus to reach hypothalamus and septal area.

Ventral amygdalofugal pathway

travels from amygdala reaching hypothalamus and brainstem.

Hippocampal formation

structure comprised of hippocampus and subiculum.

Hippocampus

structure comprised of hippocampal gyrus and dentate gyrus.

Hippocampus

ventral medial temporal lobe structure within inferior horn of the lateral ventricle; essential for forming and consolidating new declarative memories and supporting spatial navigation.

Archicortex

evolutionarily ancient type of cortex containing three layers present in the hippocampus.

Hippocampal and dentate gyrus

gyri with 3-layered archicortex making up the hippocampus.

Subiculum

zone of hippocampal formation transitioning archicortex of hippocampus to neocortex of adjacent structures; parahippocampal gyrus and entorhinal cortex.

Formation/consolidation of new memories, spatial navigation, context learning

List the 3 main functions of the hippocampus.

Alzheimer’s disease

disorder with early degeneration of entorhinal cortex and hippocampus impairing the formation and recall of declarative memories.

Korsakoff syndrome

damage to hippocampus and connecting structures causes severe anterograde amnesia.

Other hippocampus, amygdala, olfactory bulb, parahippocampal gyrus

List 4 key inputs for the hippocampus.

Parahippocampal gyrus

relays sensory, spatial and contextual information from entire neocortex to the hippocampus; allows linkage of information from different cortical areas into unified memories.

Other hippocampus, amygdala, hypothalamus, parahippocampal gyrus

List 4 key outputs from the hippocampus.

Parahippocampal gyrus

receives hippocampal output and relays processed memory information back to widespread cortical regions for storage and retrieval.