The nervous system is the most challenging topic in anatomy — cranial nerves, spinal tracts, neuron types, and reflex arcs. These mnemonics cut through the complexity and help you remember what matters most for exams.
All 12 cranial nerves in order — the most tested sequence in neuroscience
Each word starts with the same letter as the cranial nerve it represents. I=Olfactory (smell), II=Optic (vision), III=Oculomotor (eye movement), IV=Trochlear (superior oblique), V=Trigeminal (face sensation/chewing), VI=Abducens (lateral eye), VII=Facial (expression/taste), VIII=Auditory/Vestibulocochlear (hearing/balance), IX=Glossopharyngeal (throat/taste), X=Vagus (parasympathetic), XI=Spinal Accessory (SCM/trapezius), XII=Hypoglossal (tongue).
CN I
Olfactory — smell. Passes through cribriform plate of ethmoid.
CN II
Optic — vision. Only CN that is actually brain tissue (not true nerve).
Central Nervous System · Peripheral Nervous System
Two divisions of the nervous system and their key differences
CNS = brain and spinal cord — protected by bone (skull and vertebral column) and meninges. PNS = all nervous tissue outside the CNS — cranial nerves, spinal nerves, ganglia. Key difference: CNS uses oligodendrocytes for myelination. PNS uses Schwann cells. PNS can regenerate after injury — CNS generally cannot.
SAM — Sensory Afferent · Association · Motor Efferent
Sensory (Afferent) · Interneurons · Motor (Efferent)
Three functional neuron types — and how to remember which direction they travel
Sensory (afferent) neurons carry signals TOWARD the CNS — from receptors. Interneurons (association neurons) are entirely within the CNS — they process and integrate information. Motor (efferent) neurons carry signals AWAY from the CNS — to effectors (muscles and glands). Memory trick: Afferent = Arrive (toward CNS). Efferent = Exit (away from CNS).
Sensory
Afferent — carries signals TO the CNS. Arrive = Afferent.
Interneuron
Within CNS only — integrates sensory and motor signals.
Motor
Efferent — carries signals FROM CNS to muscles/glands. Exit = Efferent.
99% of neurons
Are interneurons — the brain is mostly integration, not input/output.
Spinal Cord Tracts
DCML Up · Spinothalamic Up · Corticospinal Down
Dorsal Column = fine touch · Spinothalamic = pain/temp · Corticospinal = voluntary movement
The three major spinal cord tracts — what each carries and which direction
Dorsal Column-Medial Lemniscal (DCML): fine touch, vibration, proprioception — travels ipsilateral up to medulla then crosses. Spinothalamic: pain and temperature — crosses immediately at spinal level then travels up contralateral. Corticospinal: voluntary motor — descends from cortex, crosses in medulla (pyramidal decussation). This is why a brain lesion on the LEFT causes weakness on the RIGHT.
DCML
Fine touch, vibration, proprioception — ipsilateral then crosses at medulla.
Spinothalamic
Pain and temperature — crosses at spinal level, travels contralateral.
Corticospinal
Voluntary motor — crosses at medulla (pyramidal decussation).
Clinical
Left brain lesion = right body weakness. Left brain lesion = left fine touch loss.
Meninges
DAP — Dura · Arachnoid · Pia
Dura Mater · Arachnoid Mater · Pia Mater
Three meningeal layers from outside to inside
The three meninges surround and protect the CNS. Dura mater = tough outer layer (dura = tough). Arachnoid mater = middle spider-web layer — CSF flows in the subarachnoid space beneath it. Pia mater = thin delicate layer directly on brain surface (pia = delicate). Meningitis = inflammation of meninges. Epidural hematoma = arterial blood between skull and dura. Subdural hematoma = venous blood between dura and arachnoid.
Dura Mater
Outermost, toughest. Epidural space above it (epidural injections here).
Arachnoid
Middle layer. Subarachnoid space below it — filled with CSF.
Pia Mater
Innermost, thinnest — directly on brain and spinal cord surface.
Epidural
Arterial bleed between skull and dura — lens-shaped on CT.
Subdural
Venous bleed between dura and arachnoid — crescent-shaped on CT.
Lobes of the Brain
FTOP — Frontal · Temporal · Occipital · Parietal
4 cerebral lobes and their primary functions
Four lobes of the cerebral cortex — location and primary function
Frontal lobe: voluntary motor control (primary motor cortex), executive function, personality, Broca's area (speech production). Temporal lobe: hearing, Wernicke's area (speech comprehension), memory (hippocampus). Occipital lobe: vision — all visual processing. Parietal lobe: somatosensory (touch, pressure, pain, temperature), spatial awareness. Damage to Broca's = can't speak. Damage to Wernicke's = can't understand speech.
Frontal
Motor cortex, personality, judgment, Broca's area (speech production).
Temporal
Hearing, Wernicke's area (comprehension), memory (hippocampus).
A reflex arc is the neural pathway for a reflex — it does NOT require conscious thought because it is processed in the spinal cord, not the brain. The five components in order: Receptor detects stimulus → Afferent neuron carries signal to spinal cord → Integration center (spinal cord) → Efferent neuron carries signal to → Effector (muscle or gland) responds. The knee-jerk reflex is a monosynaptic reflex — only one synapse between afferent and efferent.
Receptor
Detects the stimulus — stretch receptor, pain receptor, etc.
Afferent neuron
Carries signal TO spinal cord — sensory neuron.
Integration
Spinal cord processes signal — interneuron (except monosynaptic).
Six types of glial cells — the support cells of the nervous system
Glial cells outnumber neurons 10:1 and are responsible for support, protection, and myelination. Astrocytes: blood-brain barrier, nutrient support. Microglia: CNS immune cells — phagocytose debris. Oligodendrocytes: myelinate CNS axons (one cell myelinates multiple axons). Ependymal cells: produce CSF, line ventricles. Schwann cells: myelinate PNS axons (one cell per axon). Satellite cells: support neurons in PNS ganglia.
Astrocytes
Blood-brain barrier, structural support, nutrient delivery to neurons.
Microglia
CNS macrophages — phagocytose pathogens and dead cells.
Oligodendrocytes
CNS myelin — one cell wraps multiple axons. Damaged in MS.
Ependymal
Line ventricles, produce and circulate CSF.
Schwann cells
PNS myelin — one cell per axon segment. Allow PNS regeneration.
📝 Exam Prep
5 Common Exam Questions
Frequently tested concepts — know these cold before your exam.
❓ What is the difference between CNS and PNS?
✅ CNS = brain + spinal cord. Protected by skull and vertebral column. Uses oligodendrocytes for myelination. Limited regeneration after injury. PNS = all nerves outside CNS (cranial and spinal nerves, ganglia). Uses Schwann cells for myelination. Better regenerative capacity than CNS.
❓ What are the 12 cranial nerves and a quick way to remember them?
✅ On Old Olympus' Towering Top A Finn And German Viewed Some Hops: Olfactory (I), Optic (II), Oculomotor (III), Trochlear (IV), Trigeminal (V), Abducens (VI), Facial (VII), Auditory/Vestibulocochlear (VIII), Glossopharyngeal (IX), Vagus (X), (Spinal) Accessory (XI), Hypoglossal (XII).
❓ What is the significance of a positive Babinski sign in adults?
✅ A positive Babinski = great toe extends (goes up) and other toes fan out when the sole is stroked. Normal in infants (up to ~2 years). Positive in adults = upper motor neuron lesion (stroke, MS, spinal cord injury, brain tumor). In adults the normal response is plantar flexion (toes curl down).
❓ What are the meninges and what is found between each layer?
✅ Dura mater (outer, tough) → Epidural space (site of epidural anesthesia) → Arachnoid mater (middle) → Subarachnoid space (contains CSF and major arteries — site of lumbar puncture) → Pia mater (innermost, adheres to brain surface). Epidural hematoma = arterial bleed between skull and dura. Subdural hematoma = venous bleed between dura and arachnoid.
❓ What does the sympathetic nervous system do to the body?
✅ The 4 D's: Dilates pupils, Dilates bronchi, increases cardiac output (rate and force), Decreases GI motility. Also: vasoconstriction to skin/gut, vasodilation to skeletal muscle, releases glucose from liver, inhibits bladder contraction. Neurotransmitter = norepinephrine (postganglionic). Pre-ganglionic = acetylcholine.