Guide
How to Use This (Study Guide)
Learn → Differentiate → Apply
Checklist for each section
| Do this | What “mastery” looks like |
|---|---|
| Scan the summary table | You can recite each row from memory |
| Read the arrow-flow | You can redraw it from first principles |
| Quiz mode | Blurred answers, still correct |
| Apply a clinical anchor | Localize/choose pathways from findings |
1
Association Cortices & Motor Planning
PMA/SMA/M1 roles; population vectors; lateralization; association cortex
Functions by area (high-yield)
| Area | Core Role | Activity Pattern | Lesion Anchor |
|---|---|---|---|
| PMA (area 6) | Plan from external cues; sensory→motor goals; proximal/axial bias | Cue-locked rise; wanes on execution | Stimulus-guided planning / apraxia-like deficits |
| SMA (area 6) | Internally generated sequences; bimanual; set-shifting | Cue-related ramping > execution | Poor self-initiated sequential/bimanual acts |
| M1 (area 4) | Execution via corticospinal; contralateral; direction-tuned | Peak near onset/trajectory | Pure motor deficits by somatotopy (hand knob) |
Population vectors in M1 — derivation
Preferred direction (PD) fixed vector = (unit PD) × firing magnitude
Σ across neurons
Population vector (angle ≈ movement direction; length ≈ confidence/drive)
Lateralization & association cortex
| Domain | Hemisphere | Clinical Anchor |
|---|---|---|
| Language; analytic | Left | Aphasia with L perisylvian lesions |
| Spatial attention; faces; prosody | Right | R parietal → persistent left neglect |
| Parietal association | — | Multimodal spatial maps; neglect; spatial apraxia |
| Prefrontal association | — | DLPFC exec/WM; OFC/VMPFC value/affect; dysexecutive/disinhibition |
2
Descending Pathways — Overview → Details
Direct vs indirect; tract table; abnormal posturing
Direct vs Indirect (condensed)
| Route | Source | Synapses | White-matter bias → Motor pools | Job |
|---|---|---|---|---|
| Direct (cortico-) | M1, premotor, SMA | Mono/oligo (hand↑) | Lateral funiculus → lateral (limb) | Precise fractionated movement |
| Indirect (rubro/reticulo/vestibulo-) | Brainstem (cortex/cerebellum/BG/sensory-shaped) | Polysynaptic networks | Anterior/anterolateral → medial (axial/prox) | Posture, tone, gait, reflex gain |
Tracts (origin → crossing → termination → role)
| Tract | Origin | Crossing | Synapse Bias | Termination | Cord Location | Role |
|---|---|---|---|---|---|---|
| LCST | M1/PM/SMA → IC → crus → pyramids | Pyramidal decussation | Interneurons ± direct digits | All; cervical/lumbar↑ | Posterolateral lat. funiculus | Distal limb fractionation |
| ACST | M1/PM (axial/prox) | Segmental AWC; some uncrossed | Interneurons → medial LMNs | Cervical/upper thoracic | Anterior funiculus paramedian | Trunk/postural set |
| Rubrospinal | Red nucleus | Ventral tegmental (immediate) | Lateral LMNs; arm flexor bias | Mainly cervical | Lateral funiculus (ant. to LCST) | Facilitate upper-limb flexors |
| Medial RST | Pontine RF | Predominantly ipsi | Broad → extensors | All | Anterior funiculus medial | Antigravity tone/posture |
| Lateral RST | Medullary RF | Bilateral | Mixed; extensor tone mod | All | Anterior lateral funiculus | Tone/posture modulation |
| LVST | Vestibular nuclei | Ipsi | Axial/prox extensors | All | Anterior funiculus (lateral) | Strong extension drive |
| MVST | Vestibular nuclei | Bilateral | Neck/upper-T LMNs | Cervical/upper thoracic | MLF (anteromedial) | Head–neck stabilization |
| Corticobulbar (VII) | Face motor ctx → IC genu | — | Upper face bi; lower face contra | CN motor nuclei | Brainstem | UMN vs LMN facial patterns |
Abnormal posturing
| Pattern | Lesion Level | Mechanism | Signal |
|---|---|---|---|
| Decorticate (flexor) | Above red nucleus | RST intact/disinhibited arms; reticulo/vestibulo legs extensor | Rostral to midbrain tegmentum |
| Decerebrate (extensor) | At/below red nucleus | Loss of RST flexor bias → extension predominates | More caudal; worse prognosis |
3
Spinal Nerves — Rapid Q→A
Segments, counts, roots/rami, DRG, dermatomes, injuries
| Q | A (condensed) |
|---|---|
| Spinal cord segment? | Cord region giving rootlets/roots for one nerve pair |
| How many pairs? | 31 (C8, T12, L5, S5, Co1). C1–C7 exit above vertebra; C8 between C7–T1 |
| Ventral vs dorsal roots | Ventral = motor; Dorsal = sensory |
| Rami | Dorsal → deep back & skin; Ventral → plexuses & anterolateral trunk/limbs |
| DRG contains | Sensory neuron cell bodies |
| Cauda equina | Bundle of lumbosacral roots in lumbar cistern |
| Conus medullaris level | Adults ~L1–L2 disc; newborns ~L2–L3 |
| GVE chain? | Always 2-neuron (pre + postganglionic) |
| Dermatome | Skin by one spinal nerve; 30 dermatomes (C2–Co1; C1 none) |
| Paraplegia vs tetraplegia | Para: lower limbs (e.g., T1–T9). Tetra: upper+lower (e.g., C4–C5) |
4
Cerebellum + Cranial Nerves (High-Yield Tables)
Anatomy/circuits/zones; CN components & nuclei locations
Cerebellar anatomy & blood
| Topic | Key Points |
|---|---|
| Morphology | Anterior/posterior lobes; cortex folia; vermis/hemispheres |
| Peduncles | SCP (efferent), MCP (afferent from pons), ICP (mixed) |
| Deep nuclei | Dentate, interposed (globose+emboliform), fastigial |
| Blood | SCA, AICA, PICA |
| Layers | Molecular, Purkinje, Granular; white-matter core |
Inputs/outputs & circuit
| Stream | Synopsis |
|---|---|
| Climbing | Inferior olive → strong Purkinje drive (1 CF/PC) |
| Mossy | Pontine/spinal/vestibular/reticular → granule → parallel fibers → Purkinje |
| Outputs | Purkinje (GABA −) → deep nuclei; deep nuclei → thalamus (VA/VL) → cortex |
| Ipsilateral signs | Spinal/vestibular inputs ipsi; cerebellar lesions → ipsi deficits |
Longitudinal zones → roles
| Zone → Nucleus | Role |
|---|---|
| Cerebrocerebellum → Dentate | Plan/program skilled rapid movements |
| Spinocerebellum → Interposed | Adjust ongoing limb movements; sensorimotor match |
| Vermis/Vestibulo → Fastigial/vestibular | Posture, equilibrium, vestibulo-collic |
Cranial nerves: components & key functions
| Nerve | Components | Key Functions (targets) |
|---|---|---|
| I | SSA | Smell |
| II | SSA | Vision |
| III | GSE,GVE | SR,IR,MR,IO,levator; pupil/ciliary (ciliary ganglion) |
| IV | GSE | SO (intort, depress in adduction) |
| V | GSA,BE | Facial somatosensation; mastication + tensors |
| VI | GSE | LR (abduction) |
| VII | BE,GVE,GSA,GVA,SSA | Facial expression; glands; taste ant 2/3; small ear sensation |
| VIII | SSA | Hearing & balance |
| IX | BE,GVE,GSA,GVA,SSA | Stylopharyngeus; parotid; taste post 1/3; carotid body/sinus |
| X | BE,GVE,GSA,GVA,SSA | Phonation/swallow; PSNS thoracoabdominal; taste epiglottis |
| XI | BE | SCM & trapezius |
| XII | GSE | Tongue (except palatoglossus) |
CN nuclei: where they live
| Region | Nuclei |
|---|---|
| Midbrain | III (oculomotor, Edinger–Westphal), IV; V (mesencephalic) |
| Pons | V (principal, motor), VI, VII (motor, sup. saliv.), VIII (junction) |
| Medulla | IX/X ambiguus; DMX; solitarius; XII; inf. saliv.; spinal trigeminal; parts of VIII |
| Upper C-spine | XI spinal accessory nucleus |
5
Eye Movements & Deficits
Muscles/axes; movement types; calorics; CN III GVE
Muscles & actions (LR6 SO4 R3)
| Muscle | Nerve | Actions |
|---|---|---|
| Medial rectus | III | Adduction |
| Lateral rectus | VI | Abduction |
| Superior rectus | III | Elevation, intorsion, adduction |
| Inferior rectus | III | Depression, extorsion, adduction |
| Superior oblique | IV | Intorsion, depression, abduction |
| Inferior oblique | III | Extorsion, elevation, abduction |
MLF lesion → INO: adduction failure on gaze, convergence spared.
Movement types & calorics (COWS)
| Type | Notes |
|---|---|
| Saccades | Fast foveation; transient suppression |
| Smooth pursuit | Voluntary tracking; needs stimulus |
| VOR | Stabilize during brief head motion |
| OKN | Slow follow + fast reset |
| Vergence | Convergence/divergence for near/far |
Calorics (awake, cortex-intact): COWS
Cold → Opposite (fast phase),
Warm → Same.
CN III GVE (parasympathetic)
Edinger–Westphal
CN III
ciliary ganglion
short ciliary nerves
| Target | Effect |
|---|---|
| Pupillary sphincter | Miosis (light, near) |
| Ciliary muscle | Accommodation (near focus) |
6
Hypothalamus & Limbic System
Core functions; divisions; pituitary control; inputs/outputs
What it does
| Bucket | Details |
|---|---|
| Homeostasis | BP/electrolytes; temp; energy; reproduction; stress |
| Behaviors | Feeding, fighting, fleeing, mating |
| Limbic partners | Cingulate/parahippocampal ctx; hippocampus; amygdala |
Divisions & high-yield nuclei
| Nucleus | Role |
|---|---|
| SON/PVN (magnocellular) | Oxytocin; ADH → posterior pituitary |
| PVN (parvocellular) | Releasing factors for anterior pituitary |
| Arcuate | Portal releasing/inhibiting factors |
| SCN | Circadian pacemaker |
| Mammillary | Memory loops (mammillothalamic/tegmental) |
Pituitary control
Posterior (neurohypophysis): Magnocellular neurons
axons
direct hormone release (ADH/oxytocin).
Anterior (adenohypophysis): Parvocellular factors portal veins control gland cells (ACTH/TSH/GH/LH/FSH/prolactin).
Anterior (adenohypophysis): Parvocellular factors portal veins control gland cells (ACTH/TSH/GH/LH/FSH/prolactin).
Inputs & Outputs
| Path | Direction | Payload |
|---|---|---|
| MFB | ↔ | Limbic/brainstem drives |
| Fornix | ↔ | Hippocampus ↔ mammillary |
| Amygdala | ↔ | Stria terminalis & ventral amygdalofugal |
| DLF | ↔ | Brainstem autonomic centers |
| Retinohypothalamic | → | Light → SCN |
| Circumventricular | → | Blood chemistry/temperature/osmolality |
7
Stress Systems — HPA vs SAM, Allostasis, Brain Effects
Definitions → cascades → structural changes → PTSD
Definitions
| Term | Self-definition |
|---|---|
| Stress | Challenge to homeostasis → adaptive energy mobilization |
| Allostasis | Stability via change; adaptive set-point shifts |
| Allostatic load | Cumulative wear from chronic responses |
Two-system view (arrow flows)
SAM (fast): Threat appraisal
amygdala
hypothalamus
adrenal medulla
Epi/NE (seconds)
↑BP/CO, ↑glucose.
HPA (slow): PVN CRH pituitary ACTH adrenal cortex cortisol (min–hrs) sustained energy, immune modulation.
Negative feedback: hippocampal GRs suppress CRH; circadian modulation.
HPA (slow): PVN CRH pituitary ACTH adrenal cortex cortisol (min–hrs) sustained energy, immune modulation.
Negative feedback: hippocampal GRs suppress CRH; circadian modulation.
Structural brain changes (chronic stress)
| Region | Effect |
|---|---|
| Hippocampus | ↓spines/branching; ↓neurogenesis; CA1 vulnerability → memory/LTP hits |
| PFC | Volume/function reductions; executive down-shift |
| Amygdala | Reactivity/volume changes; heightened salience |
PTSD clusters (condensed)
| Bucket | Examples |
|---|---|
| Re-experiencing | Intrusions; distressing dreams |
| Control imbalance | Impaired extinction; hyper-reactive amygdala; ↓mPFC control |
| Endocrine tone | Often low basal cortisol with high CRH |
| Hippocampus | Possible volume reductions |
8
Autonomic Nervous System — Master Table
Divisions; ganglia; transmitters; receptors; reflexes; tissue effects
Divisions, effectors, chain lengths
| Item | Key |
|---|---|
| Divisions | SNS (thoracolumbar), PSNS (craniosacral), ENS |
| Effectors | Cardiac, smooth muscle, glands |
| Chain length | SNS: short pre/long post; PSNS: long pre/short post |
Ganglia & transmitters
| Topic | High-yield |
|---|---|
| SNS ganglia | Paravertebral chain; prevertebral (celiac, SM, IM) |
| PSNS ganglia | Terminal/intramural near targets |
| Preganglionic | ACh → N2 (both SNS/PSNS); adrenal medulla is modified ganglion |
| Postganglionic SNS | NE → α/β; sweat glands are ACh → M3 |
| Postganglionic PSNS | ACh → muscarinic (M1–M5) |
Receptors (where/effects)
| Receptor | Where | Effect |
|---|---|---|
| N2 | All autonomic ganglia; adrenal medulla | Fast EPSP |
| M1 | Glands/parietal | ↑Secretion |
| M2 | SA/AV | ↓HR/AV conduction |
| M3 | Smooth m., glands, eye circular | Contraction/secretion; miosis; detrusor ↑ |
| α1 | Vessels (skin/viscera), iris radial | Vasoconstriction; mydriasis; sphincters ↑ |
| α2 | Presynaptic; GI | ↓NE release; ↓GI motility |
| β1 | Heart | ↑HR/contractility |
| β2 | Bronchi; skeletal muscle beds | Bronchodilation; vasodilation |
| β3 | Adipose | Lipolysis |
Reflexes & tissue effects
Baroreflex:
↑BP ↑baro firing
↑PSNS (↓HR) & ↓SNS (vasodilation);
inverse for ↓BP.
| Tissue | SNS | PSNS |
|---|---|---|
| Heart | β1 ↑HR/↑inotropy | M2 ↓HR/↓AV |
| Vessels | α1 constrict skin/viscera; β2 dilate muscle beds | Minimal direct |
| Lungs | β2 bronchodilation | M3 bronchoconstriction + secretions |
| GI | α2/α1 ↓motility; sphincters contract | M3 ↑motility; sphincters relax |
| Bladder | β2/β3 relax detrusor; α1 sphincter ↑ | M3 detrusor ↑; sphincter relax |
| Eye | α1 radial → mydriasis | M3 circular → miosis + accommodation |
| Sweat | SNS cholinergic M3 → sweating | — |
9
Basal Ganglia — Wiring → Behavior → Disease
Disinhibition logic; direct vs indirect; clinical anchors
Canonical wiring (staircase)
Cortex (+) Striatum
D1 (−) GPi/SNr ↓ Thalamus disinhibited (+) Cortex ↑ (facilitates movement)
D2 (−) GPe ↓ STN ↑ (+) GPi/SNr ↑ Thalamus inhibited Cortex ↓ (suppresses movement)
SNc dopamine: D1 ⬆, D2 ⬇ ⇒ net ↓GPi/SNr ⇒ movement promoted
D1 (−) GPi/SNr ↓ Thalamus disinhibited (+) Cortex ↑ (facilitates movement)
D2 (−) GPe ↓ STN ↑ (+) GPi/SNr ↑ Thalamus inhibited Cortex ↓ (suppresses movement)
SNc dopamine: D1 ⬆, D2 ⬇ ⇒ net ↓GPi/SNr ⇒ movement promoted
Effects of node manipulation
| Node | ↑ Activity | ↓ Activity |
|---|---|---|
| GPi/SNr | ↓ movement (thalamus more inhibited) | ↑ movement |
| STN | ↓ movement | ↑ movement (hemiballismus if lesioned) |
| GPe | ↑ movement (via STN ↓) | ↓ movement |
| D1-MSNs | ↑ movement | ↓ movement |
| D2-MSNs | ↓ movement | ↑ movement |
| SNc dopamine | ↑ movement | ↓ movement (Parkinsonian) |
Clinical anchors
| Disorder | Path | Net |
|---|---|---|
| Parkinson’s | ↓SNc dopamine → direct↓ + indirect↑ | GPi/SNr ↑ → hypokinetic |
| Huntington (early) | Loss of D2-MSNs | GPi/SNr ↓ → hyperkinetic (chorea) |
| Hemiballismus | STN lesion | GPi/SNr ↓ → hyperkinetic (ballism) |
10
Brainstem Lesions — Crossed Findings → Vascular Territories
Map symptoms → structures → PICA/vertebral; differentials; risks/management
Case synthesis → Why lateral medulla (right)
| Finding | Structure | Side |
|---|---|---|
| Ipsi face pain/temp loss | Spinal trigeminal n./tract | Right |
| Contra body pain/temp loss | Spinothalamic tract | Left |
| Dysphagia/dysarthria; uvula away | Nucleus ambiguus (IX/X) | Right |
| Ipsi limb ataxia | Inferior cerebellar peduncle/cerebellum | Right |
| Vertigo/N/V | Vestibular nuclei | Right |
Summary:
PICA/vertebral territory Wallenberg (lateral medullary) syndrome.
Differentiate: AICA (lateral pontine) & ASA (medial medullary)
| Syndrome | Key Distinguishers |
|---|---|
| Lateral pontine (AICA) | Often LMN facial paralysis (VII nucleus) ± hearing loss/tinnitus; lacrimation/salivation changes |
| Medial medullary (ASA) | Contra hemiparesis (pyramids) + contra DCML loss + ipsi tongue weakness (XII → toward lesion) |
| Lateral medullary (PICA) | Crossed pain/temp; nucleus ambiguus involvement; facial movements typically preserved |
Immediate risks & early management priorities
| Risk | Priority Action |
|---|---|
| Aspiration (bulbar) | NPO + swallow screen; SLP early; suction/aspiration precautions |
| Posterior fossa worsening | Close neuro checks; ICU if needed |
| Autonomic/respiratory instability | Symptom control (antiemetics/vestibular suppressants); fluids |
| Reperfusion window | CT/MRI; CTA/MRA; consider IVT if eligible; thrombectomy if LVO suitable |
| Secondary prevention | Antiplatelet/anticoag as indicated; BP & risk factors; DVT ppx; early rehab |