Functional Systems and Pathways

Sensory Pathways - Info Superhighways

• Dorsal Column-Medial Lemniscus (DCML): 📌 "Dorsal Columns Carry Very Precious Sensations"
  • Functions: Fine touch, vibration, conscious proprioception.
  • Key: 1st neuron (DRG) ascends ipsilaterally; decussates in Medulla (2nd neuron: N. Gracilis/Cuneatus) → VPL (Thalamus) → Cortex.
• Spinothalamic Tract (STT): 📌 "Spinothalamic Transmits Pain, Temperature, Crude touch"
  • Functions: Pain, temperature, crude touch.
  • Key: 1st neuron (DRG) → 2nd neuron (Dorsal Horn) decussates in Spinal Cord (Anterior White Commissure) → VPL (Thalamus) → Cortex.
• Spinocerebellar Tracts (SCT):
  • Functions: Unconscious proprioception for coordination.
  • Key: Input to Cerebellum. Dorsal SCT (uncrossed), Ventral SCT (crossed).

⭐ Lesion of dorsal columns results in ipsilateral loss of fine touch, vibration, and proprioception below the lesion level.

Motor Pathways - Action Command Central

• Pyramidal (Corticospinal) Tracts: Execute voluntary, skilled movements.
  • Origin: Primarily motor cortex (precentral gyrus).
  • Decussation: 85% fibers at medullary pyramids (forming lateral CST).
  • Termination: Anterior horn cells (AHCs) or interneurons.
• Extrapyramidal Tracts: Modulate posture, balance, muscle tone, gross movements.
  • Key Tracts: Rubrospinal (flexor tone), Vestibulospinal (extensor tone, balance), Reticulospinal (posture, muscle tone), Tectospinal (head/eye orientation to stimuli).

Limbic System - Emotion & Memory Hub

• Key Structures & Functions:
  • Hippocampus: Memory (new declarative memories, spatial navigation).
  • Amygdala: Emotion (fear, anxiety, aggression), emotional learning & memory.
  • Fornix: Connects hippocampus to mammillary bodies.
  • Cingulate Gyrus: Emotional processing, learning, motivation, pain perception.
  • Mammillary Bodies: Memory relay (key in Papez circuit).
  • Septal Nuclei: Reward, pleasure reinforcement.
• Core Functions: The limbic system integrates emotion, learning, memory (consolidation of new memories), motivation, olfaction, and autonomic/endocrine responses. 📌 Mnemonic for functions: HOME (Homeostasis, Olfaction, Memory, Emotion).
• Papez Circuit (Memory & Emotion): Key pathway for memory consolidation. 📌 Mnemonic for core structures: "Hippo For Ma And CiEnHi" (Hippocampus → Fornix → Mammillary body → Anterior thalamic nucleus → Cingulate gyrus → Entorhinal cortex → Hippocampus).

⭐ Kluver-Bucy Syndrome: Results from bilateral amygdala lesions. Presents with hyperorality, hypersexuality, placidity (↓ fear/aggression), visual agnosia (psychic blindness), and amnesia (anterograde).

Cortical Functions - Language & Logic Zones

• Broca's Area (Inferior Frontal Gyrus, dominant hemisphere): Motor speech production. Lesion → Expressive (non-fluent) aphasia. 📌 'Broca's = Broken speech'.
• Wernicke's Area (Superior Temporal Gyrus, dominant hemisphere): Language comprehension. Lesion → Receptive (fluent) aphasia. 📌 'Wernicke's = Wordy but makes no sense'.
• Arcuate Fasciculus: Connects Wernicke's to Broca's area. Lesion → Conduction aphasia (impaired repetition; fluency & comprehension relatively intact).
• Prefrontal Cortex (PFC): Executive functions (e.g., planning, decision-making, working memory).
• Hemispheric Specialization:
  • Dominant (usually Left): Language (Broca's, Wernicke's), logic, calculations.
  • Non-Dominant (usually Right): Spatial skills, facial recognition, emotional prosody, music.

Aphasia Comparison:

High‑Yield Points - ⚡ Biggest Takeaways

• DCML pathway: Fine touch, vibration, proprioception; decussates in medulla.
• Spinothalamic tract: Pain, temperature, crude touch; decussates in spinal cord.
• Corticospinal tract: Voluntary motor control; decussates at medullary pyramids.
• Basal ganglia: Modulate movement via direct (facilitatory) & indirect (inhibitory) pathways.
• Cerebellum: Motor coordination, balance, learning; lesions cause ipsilateral ataxia.
• Limbic system (Papez circuit): Key for emotion, behavior, and memory.
• Thalamic nuclei: LGN for vision, MGN for audition, VPL/VPM for sensation.