PY10.1-20 | Central Nervous System Physiology — Summary & Reflection

REFLECT

KEY TAKEAWAYS

Key Takeaways — Central Nervous System Physiology

Foundations (PY10.1-PY10.6):
- CNS = brain + spinal cord; PNS = somatic + autonomic (sympathetic + parasympathetic + enteric)
- Major neurotransmitters: ACh (NMJ, autonomic), glutamate (excitatory), GABA (inhibitory in brain), glycine (inhibitory in spinal cord), catecholamines (dopamine, noradrenaline, adrenaline), serotonin
- Synapses: chemical (unidirectional, modifiable) vs electrical (gap junctions, no delay)
- Reflex arc: receptor, afferent, integration centre, efferent, effector. Stretch reflex = monosynaptic; withdrawal = polysynaptic
- Receptors encode stimulus by frequency coding and population coding; classified by modality, location, and adaptation rate

Sensory Pathways (PY10.7, PY10.8):
- DCML (fine touch, proprioception, vibration): DRG to ipsilateral dorsal columns to nucleus gracilis/cuneatus to contralateral medial lemniscus to VPL thalamus to S1 cortex. Crosses in medulla
- Anterolateral/Spinothalamic (pain, temperature, crude touch): DRG to dorsal horn to contralateral anterolateral column (crosses within 1-2 segments) to VPL thalamus to S1 cortex
- Pain: fast (A-delta) vs slow (C fibres); gate control theory (A-beta touch closes gate); descending modulation via PAG to raphe magnus to dorsal horn (serotonin, enkephalins)
- Referred pain: convergence of visceral and somatic afferents on the same dorsal horn neuron

Motor Pathways (PY10.9, PY10.10):
- Pyramidal: cortex to posterior limb of internal capsule to crus cerebri to pyramid to decussation (85-90% cross) to lateral corticospinal tract to alpha motor neuron
- UMN lesion: spastic paralysis, hyperreflexia, Babinski positive, clonus, no atrophy
- LMN lesion: flaccid paralysis, areflexia, Babinski negative, atrophy, fasciculations
- Brown-Sequard (hemisection): ipsilateral DCML loss + ipsilateral UMN signs + contralateral pain/temperature loss
- Syringomyelia (central cord): bilateral cape-like loss of pain and temperature, preserved DCML

Cerebellum (PY10.11):
- Vestibulocerebellum (flocculonodular): balance, eye movements. Lesion: truncal ataxia, nystagmus
- Spinocerebellum (vermis): axial coordination. Lesion: gait ataxia
- Cerebrocerebellum (lateral hemispheres): planning, motor learning. Lesion: intention tremor, dysmetria, dysdiadochokinesia
- Cerebellar signs are ipsilateral (double-crosser rule)

Basal Ganglia (PY10.12, PY10.13):
- Direct pathway (D1, facilitates movement): cortex to striatum to GPi (inhibition) = thalamic disinhibition
- Indirect pathway (D2, inhibits movement): cortex to striatum to GPe to STN to GPi = thalamic inhibition
- Parkinson's (SNc dopamine loss): TRAP — resting Tremor, Rigidity, Akinesia, Postural instability
- Huntington's (striatal degeneration): chorea. Hemiballismus (STN lesion): violent flinging
- Decerebrate rigidity: intercollicular transection. Decorticate: above red nucleus

Thalamus (PY10.14):
- VPL: body sensation. VPM: face sensation. LGN: vision. MGN: hearing. VL/VA: motor (cerebellar + basal ganglia output). Anterior: limbic (Papez circuit)
- Dejerine-Roussy syndrome: thalamic stroke to VPL causing contralateral thalamic pain

Hypothalamus and Limbic System (PY10.15):
- Hypothalamus: temperature (anterior = cooling, posterior = heating), appetite (lateral = feeding, ventromedial = satiety), ADH/oxytocin (supraoptic/paraventricular), circadian rhythm (SCN), pituitary control (arcuate)
- Hippocampus: declarative memory consolidation. Amygdala: fear and emotion. Mammillary bodies: Papez circuit, Wernicke's encephalopathy

Cerebral Cortex (PY10.16):
- Motor cortex (area 4): precentral gyrus, motor homunculus
- Broca's (areas 44-45): non-fluent aphasia. Wernicke's (area 22): fluent aphasia
- Prefrontal: executive functions, personality (Phineas Gage)
- Left hemisphere dominant for language in 95% of right-handed people

Sleep and EEG (PY10.17):
- NREM: N1 (theta), N2 (spindles, K-complexes), N3 (delta, growth hormone, restorative)
- REM: paradoxical sleep, dreaming, muscle atonia, EEG like waking
- Flip-flop switch: VLPO (sleep) vs ARAS (wake), stabilised by orexin. Narcolepsy = orexin loss
- EEG: beta (active), alpha (relaxed, eyes closed), theta (drowsy), delta (deep sleep)

Learning, Memory, Speech (PY10.18):
- Declarative memory: hippocampus-dependent, consolidated during SWS
- Procedural memory: basal ganglia + cerebellum, hippocampus-independent
- LTP: NMDA receptors, Ca2+ influx, AMPA receptor insertion, CREB for long-term
- Aphasias: Broca's (non-fluent), Wernicke's (fluent, no comprehension), conduction (can't repeat), global (both)

Clinical Examination (PY10.19, PY10.20):
- Systematic: higher functions to motor to sensory to reflexes to cranial nerves
- Key UMN vs LMN signs at the bedside differentiate cortical from spinal from peripheral lesions