Nervous System Study Guide

Q: What is the difference between the CNS and PNS?

The central nervous system (CNS) is the brain and spinal cord — the control center for processing and decision-making. The peripheral nervous system (PNS) is everything outside the CNS: the cranial nerves, spinal nerves, and ganglia. The PNS is further divided into the somatic nervous system (voluntary motor control) and autonomic nervous system (involuntary control of organs, divided again into sympathetic and parasympathetic branches).

Q: How do the sympathetic and parasympathetic nervous systems differ?

The sympathetic system is your "fight or flight" — it speeds heart rate, dilates pupils, increases blood pressure, slows digestion, and dilates airways. The parasympathetic system is your "rest and digest" — it slows heart rate, constricts pupils, lowers blood pressure, stimulates digestion, and constricts airways. Many nursing medications target one of these systems (beta blockers, anticholinergics, cholinergics).

Q: Which cranial nerve controls vision and which controls eye movement?

CN II (Optic) controls vision — it transmits visual information from the retina to the brain. CNs III, IV, and VI control eye movement: CN III (Oculomotor) moves the eye in most directions and controls the pupil and eyelid; CN IV (Trochlear) is tested with downward-inward gaze and innervates the superior oblique muscle; CN VI (Abducens) controls lateral (outward) gaze. A common mnemonic is "On Old Olympus' Towering Tops" for the first six cranial nerves.

Q: What are the signs of increased intracranial pressure (ICP)?

Early signs of increased ICP include headache, restlessness, irritability, and decreased level of consciousness. Late signs make up Cushing's triad: increased systolic blood pressure with widened pulse pressure, bradycardia, and irregular respirations. Pupil changes (unilateral dilation, sluggish reaction) are also late signs. Position the head of bed at 30° and avoid anything that increases pressure — coughing, straining, neck flexion, suctioning longer than 10 seconds.

Nervous System Overview

The body's master control system — sensing, processing, and responding.

The nervous system is the body's communication and control network. It detects changes inside and outside the body, processes that information, and coordinates responses to keep us alive and functioning. It works closely with the endocrine system, but the nervous system is much faster — responses happen in milliseconds versus minutes to hours for hormones.

Three Main Functions

Sensory input — gathering information about changes in the environment (internal and external) via sensory receptors
Integration — processing sensory information and deciding what to do about it
Motor output — sending signals to muscles or glands to produce a response

Major Anatomical Divisions

Central Nervous System (CNS): Brain and spinal cord. Integration and command center.
Peripheral Nervous System (PNS): Cranial nerves, spinal nerves, ganglia. Carries signals between CNS and the rest of the body.

Functional Divisions of the PNS

Sensory (Afferent)Somatic Sensory: Carries signals from skin, muscles, joints to CNS.
Sensory (Afferent)Visceral Sensory: Carries signals from internal organs to CNS.
Motor (Efferent)Somatic Motor: Voluntary control of skeletal muscle.
Motor (Efferent)Autonomic (ANS): Involuntary control of smooth muscle, cardiac muscle, glands.

Why This Matters Clinically

Nearly every nursing assessment touches the nervous system — level of consciousness, pain perception, motor strength, sensation, reflexes, pupil response, swallow function, breathing patterns. Understanding the anatomy lets you predict what symptoms a stroke, head injury, or spinal cord injury will produce based on which area is affected.

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Neurons & Glial Cells

The cells that do the signaling and the cells that support them.

Neuron Anatomy

Neurons are the functional cells of the nervous system that transmit electrical and chemical signals.

Cell body (soma): Contains the nucleus; main metabolic center.
Dendrites: Branch-like extensions that receive signals from other neurons.
Axon: Long projection that sends signals away from the cell body.
Myelin sheath: Fatty insulating layer around axons that speeds up signal transmission.
Nodes of Ranvier: Gaps in the myelin where the signal "jumps" (saltatory conduction).
Axon terminals: End of the axon where neurotransmitters are released into the synapse.
Synapse: Junction between two neurons where chemical signals are passed.

Three Types of Neurons

Sensory (afferent) neurons — carry signals FROM receptors TO the CNS
Motor (efferent) neurons — carry signals FROM the CNS TO muscles or glands
Interneurons — connect neurons within the CNS; most of the brain's neurons are interneurons

Glial Cells (Support Cells)

AstrocytesCNS: Most abundant; form the blood-brain barrier, regulate environment around neurons.
OligodendrocytesCNS: Produce myelin in the CNS (one cell myelinates many axons).
MicrogliaCNS: Immune defense in the CNS; phagocytose pathogens and debris.
Ependymal cellsCNS: Line ventricles; produce and circulate cerebrospinal fluid (CSF).
Schwann cellsPNS: Produce myelin in the PNS (one cell myelinates one axon segment).
Satellite cellsPNS: Surround and support neuron cell bodies in ganglia.

Demyelinating Diseases

When myelin is damaged, signals slow down or fail. Two key conditions to know: Multiple Sclerosis (MS) — autoimmune destruction of CNS myelin (oligodendrocytes affected); causes weakness, vision changes, fatigue, coordination problems. Guillain-Barre Syndrome — autoimmune destruction of PNS myelin (Schwann cells affected); causes ascending paralysis starting in the legs; can progress to respiratory failure.

How Neurons Communicate

Action potential (electrical signal) travels down the axon.

At the axon terminal, the signal triggers release of neurotransmitters into the synapse.

Neurotransmitters cross the synaptic cleft and bind to receptors on the next neuron.

This can either excite (depolarize) or inhibit (hyperpolarize) the next neuron.

If enough excitation occurs, the next neuron fires its own action potential.

Brain Anatomy

The control center — each region has specific functions that show up in clinical assessment.

Three Major Divisions

Cerebrum: Two hemispheres (right and left); four lobes per hemisphere.
Cerebellum: Below the cerebrum at the back of the skull.
Brainstem: Midbrain, pons, medulla oblongata.

The Four Cerebral Lobes

Frontal Lobe: Functions: Executive function, decision-making, personality, voluntary movement (motor cortex), Broca's area (speech production). If damaged: Personality changes, poor judgment, hemiparesis on opposite side, expressive aphasia.
Parietal Lobe: Functions: Sensory perception (touch, temperature, pain, position), spatial awareness. If damaged: Loss of sensation, spatial neglect, problems with body awareness.
Temporal Lobe: Functions: Hearing, memory, smell, Wernicke's area (language comprehension). If damaged: Hearing problems, memory loss, receptive aphasia (can't understand language).
Occipital Lobe: Functions: Vision processing. If damaged: Visual deficits, cortical blindness.

Deep Brain Structures

Thalamus: "Relay station" for sensory information going to the cortex (except smell).
Hypothalamus: Controls body temperature, hunger, thirst, sleep cycles, hormones (links to pituitary). Master regulator of homeostasis.
Basal Ganglia: Coordinates voluntary movement; damaged in Parkinson disease.
Limbic System: Emotion, memory formation; includes hippocampus and amygdala.
Hippocampus: Memory formation; first area damaged in Alzheimer disease.

The Cerebellum

Coordinates voluntary movement, balance, and posture
Fine-tunes movements for smoothness and precision
Important for motor learning
Damage causes ataxia (clumsy, uncoordinated movements), problems with balance

The Brainstem — Vital Functions

Midbrain: Visual and auditory reflexes (pupillary reflex, head turning toward sound).
Pons: Connects cerebrum to cerebellum; regulates breathing rhythm with the medulla.
Medulla Oblongata: Controls heart rate, breathing, blood pressure, swallowing, coughing, vomiting. Damage is often fatal.

Meninges and CSF

The brain and spinal cord are protected by three layers called the meninges:

Dura mater — outermost, tough layer
Arachnoid mater — middle layer; CSF flows in the subarachnoid space below it
Pia mater — innermost layer; directly adheres to brain tissue

Cerebrospinal Fluid (CSF) circulates around the brain and spinal cord, providing cushioning, nutrient delivery, and waste removal. Produced in the ventricles by ependymal cells.

The Blood-Brain Barrier

The blood-brain barrier (BBB), formed by astrocytes and tight junctions in brain capillaries, protects the brain by blocking most substances from crossing from the bloodstream into the brain. This protects the brain from toxins but also makes it hard for many drugs to reach the brain — including some antibiotics. Only small, lipid-soluble molecules cross easily (oxygen, CO₂, alcohol, anesthetics, glucose via transporters).

Cerebral Blood Supply

The brain receives about 15-20% of cardiac output despite weighing only 2% of body weight
The Circle of Willis at the base of the brain provides collateral circulation through interconnected arteries
The brain cannot store oxygen or glucose — even brief interruptions cause damage
Strokes occur when blood flow is blocked (ischemic) or vessels rupture (hemorrhagic)

Spinal Cord & Spinal Nerves

The communication highway between the brain and the rest of the body.

Spinal Cord Anatomy

Extends from the medulla through the foramen magnum to about the level of L1-L2 in adults
Below L1-L2, the cord becomes the cauda equina (horsetail of spinal nerves)
Gray matter (cell bodies) is in the center, shaped like an "H" or butterfly
White matter (myelinated axons) surrounds the gray matter and carries signals up and down

31 Pairs of Spinal Nerves

Cervical (C1-C8): 8 pairs
Thoracic (T1-T12): 12 pairs
Lumbar (L1-L5): 5 pairs
Sacral (S1-S5): 5 pairs
Coccygeal: 1 pair

Each Spinal Nerve Has Two Roots

Dorsal (posterior) root — carries SENSORY information INTO the spinal cord
Ventral (anterior) root — carries MOTOR information OUT of the spinal cord

Dermatomes

Each spinal nerve serves a specific area of skin called a dermatome. Key landmarks:

C4 — shoulders
T4 — nipple line
T10 — umbilicus (belly button)
L1-L2 — inguinal area
L4 — medial leg, big toe
S1 — lateral foot

Why Dermatomes Matter

Dermatomes help identify which spinal nerve or cord segment is affected. Shingles (herpes zoster) typically erupts along a single dermatome — following the path of a single spinal nerve. Sensation testing in spinal cord injury maps to dermatomes to identify the level of injury (e.g., "sensation intact to T4 level").

Spinal Cord Injury Levels — What's Lost

Above C4: Loss of diaphragm function — requires ventilator support.
C5-C7: Quadriplegia; arm function varies; breathing usually intact but weak.
T1 and below: Paraplegia; arms intact, varying degrees of trunk and leg weakness.
L1 and below: Bowel, bladder, and lower extremity weakness; cauda equina syndrome possible.

The 12 Cranial Nerves

They emerge from the brain directly — mostly serve the head and neck.

I — OlfactorySensory: Smell.
II — OpticSensory: Vision.
III — OculomotorMotor: Most eye movements, pupil constriction, eyelid opening.
IV — TrochlearMotor: Tested with downward-inward gaze; innervates the superior oblique muscle.
V — TrigeminalBoth: Facial sensation (3 branches: ophthalmic, maxillary, mandibular); chewing.
VI — AbducensMotor: Lateral eye movement (lateral rectus muscle).
VII — FacialBoth: Facial expression, taste (anterior 2/3 of tongue), tears, salivation.
VIII — VestibulocochlearSensory: Hearing and balance.
IX — GlossopharyngealBoth: Taste (posterior tongue), swallowing, gag reflex.
X — VagusBoth: Parasympathetic to heart, lungs, GI tract; swallowing, voice, gag reflex.
XI — AccessoryMotor: Shrugging shoulders, turning head (sternocleidomastoid, trapezius).
XII — HypoglossalMotor: Tongue movement.

Classic Mnemonics

Names: "On Old Olympus' Towering Tops A Finn And German Viewed Some Hops" (Olfactory, Optic, Oculomotor, Trochlear, Trigeminal, Abducens, Facial, Acoustic/Vestibulocochlear, Glossopharyngeal, Vagus, Spinal Accessory, Hypoglossal)

Type (S=Sensory, M=Motor, B=Both): "Some Say Marry Money But My Brother Says Big Brains Matter More"

? Which cranial nerve controls vision — and which ones control eye movement?

CN II (Optic) controls vision. CN III, IV, and VI control eye movement: III (Oculomotor) — most directions; IV (Trochlear) — superior oblique muscle, tested with downward-inward gaze; VI (Abducens) — lateral gaze.

The Vagus Nerve (CN X) — Special Importance

Longest cranial nerve; "wanders" through the body to many organs
Main parasympathetic nerve to the heart, lungs, and most of the GI tract
Slows heart rate when stimulated (vagal stimulation by bearing down, carotid massage, vomiting)
Stimulates GI motility and acid secretion
Vagal nerve stimulation devices are used to treat refractory epilepsy and depression

Key Cranial Nerve Assessments at the Bedside

Pupil response (II, III) — pupillary light reflex; checks brainstem function
Extraocular movements (III, IV, VI) — the "H" pattern eye movement test
Facial symmetry (VII) — smile, raise eyebrows, puff cheeks (asymmetry suggests stroke or Bell's palsy)
Swallow and gag reflex (IX, X) — assesses risk of aspiration before feeding
Tongue protrusion (XII) — tongue should be midline; deviation indicates weakness

The Autonomic Nervous System (ANS)

Two opposing systems that keep your body in balance.

The autonomic nervous system controls involuntary functions — heart rate, blood pressure, digestion, respiration, pupil size, sweating, and more. It has two divisions that often work in opposition.

Sympathetic vs Parasympathetic — Side by Side

Main Neurotransmitter: Sympathetic: Norepinephrine (NE) · Parasympathetic: Acetylcholine (ACh)
Heart Rate: Sympathetic: Increases · Parasympathetic: Decreases
Blood Pressure: Sympathetic: Increases (vasoconstriction) · Parasympathetic: Decreases
Bronchi: Sympathetic: Dilates (more air) · Parasympathetic: Constricts
Pupils: Sympathetic: Dilates (mydriasis) · Parasympathetic: Constricts (miosis)
GI Motility: Sympathetic: Decreases (slows digestion) · Parasympathetic: Increases (stimulates digestion)
Salivation: Sympathetic: Decreases (dry mouth) · Parasympathetic: Increases
Sweating: Sympathetic: Increases · Parasympathetic: No effect
Bladder: Sympathetic: Relaxes (retention) · Parasympathetic: Contracts (voiding)
Blood Glucose: Sympathetic: Increases (glucose released) · Parasympathetic: Decreases (storage)
Origin: Sympathetic: Thoracic and lumbar spinal cord (T1-L2) · Parasympathetic: Cranial nerves (especially vagus) and sacral spinal cord

Receptor Types — The Foundation of Pharmacology

Alpha-1Sympathetic: Vasoconstriction, increased BP, mydriasis.
Alpha-2Sympathetic: Feedback inhibition (decreases NE release); used in BP medications like clonidine.
Beta-1Sympathetic: Increases heart rate and contractility ("1 heart").
Beta-2Sympathetic: Bronchodilation, uterine relaxation ("2 lungs").
MuscarinicParasympathetic: Most parasympathetic effects (slow HR, GI motility, etc.).
NicotinicBoth: At all autonomic ganglia and the neuromuscular junction.

Why Receptors Matter for Medication Class Knowledge

Beta-blockers (-olol): block beta receptors. Selective (beta-1) for cardiac effects; nonselective also affect beta-2 (caution in asthma). Beta-2 agonists: albuterol — bronchodilator for asthma. Anticholinergics (block muscarinic): atropine (raises HR), Benadryl, scopolamine; cause "red, hot, dry, blind, mad" (anticholinergic toxicity). Cholinergic agonists: bethanechol (urinary retention); cholinesterase inhibitors (Alzheimer disease).

Neurotransmitters & Their Roles

The chemicals that drive every signal across every synapse.

Acetylcholine (ACh): Effect: Excitatory at neuromuscular junction; parasympathetic; memory in CNS. Conditions: Decreased in Alzheimer disease; targeted by myasthenia gravis (antibodies block ACh receptors).
Dopamine: Effect: Reward, motivation, voluntary movement. Conditions: Decreased in Parkinson disease; increased activity linked to schizophrenia (positive symptoms).
Norepinephrine (NE): Effect: Alertness, attention, fight-or-flight. Conditions: Decreased in depression; increased in mania.
Serotonin (5-HT): Effect: Mood, sleep, appetite, satiety. Conditions: Decreased in depression and anxiety; targeted by SSRIs.
GABA: Effect: Main inhibitory neurotransmitter in CNS. Conditions: Enhanced by benzodiazepines, alcohol, barbiturates — produces sedation.
Glutamate: Effect: Main excitatory neurotransmitter in CNS. Conditions: Involved in learning and memory; excess linked to seizures and excitotoxicity.
Endorphins: Effect: Natural pain relief; pleasure. Conditions: Targeted by opioid analgesics.

Neurotransmitter Imbalances Drive Major Conditions

Understanding which neurotransmitter is involved helps make sense of why certain medications work. Depression is treated with SSRIs (serotonin), SNRIs (serotonin and NE), MAOIs, and TCAs. Parkinson disease is treated with levodopa to increase dopamine. Schizophrenia is treated with antipsychotics that block dopamine. Alzheimer disease is treated with cholinesterase inhibitors to preserve acetylcholine. Anxiety and seizures respond to drugs that enhance GABA.

Reflexes & Sensory Pathways

Automatic responses that bypass the brain — and the pathways that bring sensation in.

The Reflex Arc

A reflex is an involuntary, predictable response to a specific stimulus. It involves five components:

Receptor — detects the stimulus.

Sensory neuron — carries signal toward the CNS.

Integration center — usually in the spinal cord (allows fast response).

Motor neuron — carries signal to the effector.

Effector — muscle or gland that produces the response.

Deep Tendon Reflexes (DTRs)

Tested with a reflex hammer to assess spinal cord and peripheral nerve function. Graded 0-4+:

0 — no response (abnormal)
1+ — diminished
2+ — normal
3+ — brisker than average
4+ — hyperactive with clonus (abnormal)

Common Deep Tendon Reflexes

Biceps: C5-C6
Triceps: C7-C8
Brachioradialis: C5-C6
Patellar (knee jerk): L2-L4
Achilles (ankle jerk): S1-S2

Common Reflexes Tested in Newborns

Moro (startle)disappears 3-6 mo: Sudden movement causes arms to fling out then bring in.
Rootingdisappears 3-4 mo: Stroking cheek causes baby to turn head toward stimulus.
Suckingbecomes voluntary 3-4 mo: Inserting finger in mouth elicits sucking.
Palmar Graspdisappears 3-4 mo: Placing object in palm causes grip.
Babinskidisappears ~12 mo: Stroking sole of foot causes toes to fan out (normal in infants, ABNORMAL in adults).
Tonic Neckdisappears 3-4 mo: Turning head causes same-side arm extension.
Steppingdisappears ~4 weeks: Holding baby upright with feet touching surface elicits stepping.

The Babinski Reflex Is Different

The Babinski reflex (toes fanning out when sole is stroked) is NORMAL in infants under about 12 months because the corticospinal tract is not yet fully myelinated. After that age, a positive Babinski (toes fan out instead of curling down) indicates an upper motor neuron lesion — possibly stroke, spinal cord injury, or multiple sclerosis.

Sensory Pathways — Quick Overview

Sensory information travels up the spinal cord in distinct tracts:

Dorsal columns — carry fine touch, vibration, and proprioception (sense of body position). Cross over in the medulla.
Spinothalamic tract — carries pain, temperature, and crude touch. Crosses over almost immediately at the spinal cord level.
This is why certain spinal cord injuries can cause loss of pain/temperature on one side but loss of vibration/position on the other (Brown-Sequard syndrome).

Clinical Applications

How neuro anatomy and physiology connect to nursing practice every day.

Glasgow Coma Scale (GCS)

Standardized assessment of level of consciousness. Total score: 3-15. Lower scores indicate more severe impairment.

Eye Opening1-4: 4: spontaneous, 3: to voice, 2: to pain, 1: none.
Verbal Response1-5: 5: oriented, 4: confused, 3: inappropriate words, 2: sounds, 1: none.
Motor Response1-6: 6: obeys commands, 5: localizes pain, 4: withdraws, 3: flexion (decorticate), 2: extension (decerebrate), 1: none.

15 — fully alert and oriented
13-14 — mild impairment
9-12 — moderate impairment
8 or less — severe impairment; typically requires intubation to protect airway
3 — deep coma or death

Decorticate vs Decerebrate Posturing

Decorticate: Position: Arms flexed in toward CORE (chest), legs extended. Indicates: Damage above the brainstem (cerebral hemispheres or thalamus).
Decerebrate: Position: Arms extended outward, wrists rotated, legs extended. Indicates: Damage to the brainstem — WORSE prognosis.

Increased Intracranial Pressure (ICP)

Normal ICP is 5-15 mmHg. Pressures above 20 mmHg require urgent intervention to prevent brain damage.

Signs of Increased ICP

Early signs: Decreased level of consciousness (FIRST sign — restlessness, confusion), headache, pupil changes (sluggish reaction to light), nausea/vomiting, vision changes. Late signs — Cushing triad (ominous): Hypertension with widened pulse pressure, bradycardia, irregular respirations. The Cushing triad indicates brainstem compression and is a medical emergency.

ICP Nursing Interventions

Elevate head of bed 30 degrees to promote venous drainage
Keep head and neck in neutral alignment (avoid flexion or rotation)
Avoid Valsalva maneuver — no straining at stool (stool softeners), no breath holding, no suctioning longer than 10-15 seconds
Cluster nursing care to allow rest periods
Avoid hip flexion — impedes drainage
Quiet, dim environment
Monitor for seizures; have suction available

Stroke (Cerebrovascular Accident)

Ischemic~85%: Blood clot blocks artery (thrombotic or embolic).
Hemorrhagic~15%: Blood vessel ruptures (intracerebral or subarachnoid).

FAST Stroke Assessment

F — Face drooping
A — Arm weakness
S — Speech difficulty
T — Time to call 911

Aphasia Types

Broca's (expressive) aphasia — cannot produce speech; understands; from frontal lobe damage
Wernicke's (receptive) aphasia — can speak fluently but doesn't make sense; cannot understand; from temporal lobe damage
Global aphasia — both expressive and receptive deficits

Common Neurological Conditions Tied to A&P

Parkinson disease — loss of dopaminergic neurons in basal ganglia; tremor, rigidity, bradykinesia
Alzheimer disease — degeneration starting in the hippocampus; memory loss, eventual global impairment
Multiple sclerosis — CNS demyelination; relapsing-remitting symptoms
Myasthenia gravis — antibodies block ACh receptors at neuromuscular junction; muscle weakness that worsens with use
Guillain-Barre syndrome — PNS demyelination; ascending paralysis; respiratory failure possible
Seizures — abnormal excessive neuronal firing; can be focal or generalized
Meningitis — inflammation of the meninges; fever, severe headache, nuchal rigidity, photophobia

Pupillary Response Is a Brainstem Check

The pupillary light reflex tests CN II (sensing the light) and CN III (constricting the pupil). It also depends on intact brainstem function. A unilateral fixed dilated pupil ("blown pupil") indicates pressure on CN III, often from a herniating brain — a true neurosurgical emergency. Always check pupil size, equality, and reaction in any client with altered mental status or head injury.

Frequently Asked Questions

Common student questions on this topic.

What is the difference between the CNS and PNS?

The central nervous system (CNS) is the brain and spinal cord — the control center for processing and decision-making. The peripheral nervous system (PNS) is everything outside the CNS: the cranial nerves, spinal nerves, and ganglia. The PNS is further divided into the somatic nervous system (voluntary motor control) and autonomic nervous system (involuntary control of organs, divided again into sympathetic and parasympathetic branches).

What is the function of the medulla oblongata?

The medulla oblongata is part of the brainstem and controls vital involuntary functions: respiratory rate, heart rate, blood pressure, swallowing, coughing, sneezing, and vomiting. Damage to the medulla is often incompatible with life because these automatic functions cease. On the NCLEX-PN, medulla questions usually focus on respiratory and cardiovascular regulation.

How do the sympathetic and parasympathetic nervous systems differ?

The sympathetic system is your "fight or flight" — it speeds heart rate, dilates pupils, increases blood pressure, slows digestion, and dilates airways. The parasympathetic system is your "rest and digest" — it slows heart rate, constricts pupils, lowers blood pressure, stimulates digestion, and constricts airways. Many nursing medications target one of these systems (beta blockers, anticholinergics, cholinergics).

What does the Glasgow Coma Scale measure?

The Glasgow Coma Scale (GCS) measures level of consciousness on a scale of 3–15, scoring three categories: eye opening (1–4), verbal response (1–5), and motor response (1–6). A score of 15 is fully alert and oriented; 8 or below typically indicates coma and the need for airway protection. The GCS is used to track neurological status over time after head injury, stroke, or altered mental status.

Which cranial nerve controls vision and which controls eye movement?

CN II (Optic) controls vision — it transmits visual information from the retina to the brain. CNs III, IV, and VI control eye movement: CN III (Oculomotor) moves the eye in most directions and controls the pupil and eyelid; CN IV (Trochlear) is tested with downward-inward gaze and innervates the superior oblique muscle; CN VI (Abducens) controls lateral (outward) gaze. A common mnemonic is "On Old Olympus' Towering Tops" for the first six cranial nerves.

What are the signs of increased intracranial pressure (ICP)?

Early signs of increased ICP include headache, restlessness, irritability, and decreased level of consciousness. Late signs make up Cushing's triad: increased systolic blood pressure with widened pulse pressure, bradycardia, and irregular respirations. Pupil changes (unilateral dilation, sluggish reaction) are also late signs. Position the head of bed at 30° and avoid anything that increases pressure — coughing, straining, neck flexion, suctioning longer than 10 seconds.

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