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ALL NERVES IN THE HUMAN BODY - Exam Notes (15 Marks)

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OVERVIEW - CLASSIFICATION OF NERVES

1. Central Nervous System (CNS) - Brain + Spinal cord
2. Peripheral Nervous System (PNS) - All nerves outside the CNS

• Cranial Nerves (12 pairs) - exit the skull
• Spinal Nerves (31 pairs) - exit the vertebral column
• Autonomic Nerves - sympathetic + parasympathetic

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PART 1 - CRANIAL NERVES (12 Pairs)

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MNEMONIC for Names:

MNEMONIC for Type (Sensory/Motor/Both):

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CN I - OLFACTORY NERVE

• Type: Purely Sensory (Special Afferent - smell)
• Origin: Olfactory mucosa of nasal cavity
• Exit: Cribriform plate of ethmoid bone
• Function: Sense of smell
• Lesion: Anosmia (loss of smell) - common in basal skull fracture

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CN II - OPTIC NERVE

• Type: Purely Sensory (Special Afferent - vision)
• Origin: Retinal ganglion cells
• Exit: Optic canal
• Function: Vision
• Lesion: Blindness in one eye (ipsilateral); AFFERENT defect in pupil reflex

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CN III - OCULOMOTOR NERVE

• Type: Motor (GSE + GVE/parasympathetic)
• Origin: Midbrain (anterior to cerebral aqueduct)
• Exit: Superior orbital fissure
• Motor function: Moves eyeball (SR, MR, IR, IO muscles); raises eyelid (levator palpebrae)
• Parasympathetic: Constricts pupil (sphincter pupillae) + ciliary muscle for accommodation
• Ganglion: Ciliary ganglion
• Lesion: Ptosis, "down and out" eye, dilated pupil (CN III palsy)

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CN IV - TROCHLEAR NERVE

• Type: Purely Motor (GSE)
• Origin: Midbrain (dorsal surface - only cranial nerve to exit from the back of brainstem)
• Exit: Superior orbital fissure
• Function: Superior oblique muscle - depresses, intorts, abducts the eye
• Lesion: Diplopia on looking downward (e.g., going down stairs); head tilt to opposite side

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CN V - TRIGEMINAL NERVE (Largest cranial nerve)

• Type: Both (Sensory + Branchial Motor)
• Origin: Pons
• Three divisions:

• Motor (V3 only): Muscles of mastication (temporalis, masseter, pterygoids)
• Ganglion: Trigeminal (Gasserian/semilunar) ganglion
• Lesion: Loss of corneal reflex; loss of facial sensation; jaw deviates to lesion side; Trigeminal Neuralgia (tic douloureux)

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CN VI - ABDUCENS NERVE

• Type: Purely Motor (GSE)
• Origin: Pons (floor of 4th ventricle)
• Exit: Superior orbital fissure
• Function: Lateral rectus muscle (ABDucts the eye)
• Lesion: Medial squint (convergent strabismus); cannot abduct eye

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CN VII - FACIAL NERVE

• Type: Both + Parasympathetic (mixed)
• Origin: Pons
• Exit: Internal acoustic meatus → facial canal → stylomastoid foramen
• Functions:
  • Motor: Muscles of facial expression
  • Parasympathetic: Lacrimal gland (via pterygopalatine ganglion); submandibular + sublingual glands (via submandibular ganglion)
  • Sensory: Taste from anterior 2/3 of tongue (via chorda tympani)
• Lesion - LMN (Bell's palsy): Entire face paralyzed on same side (cannot close eye, drooping of mouth corner)
• Lesion - UMN (cortical stroke): Only lower face paralyzed (forehead spared - bilateral cortical representation)

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CN VIII - VESTIBULOCOCHLEAR NERVE

• Type: Purely Sensory (Special Afferent)
• Two parts:
  • Cochlear nerve: Hearing
  • Vestibular nerve: Balance and head position
• Origin: Inner ear
• Exit: Internal acoustic meatus
• Lesion: Sensorineural deafness; vertigo; tinnitus

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CN IX - GLOSSOPHARYNGEAL NERVE

• Type: Both + Parasympathetic
• Origin: Medulla
• Exit: Jugular foramen
• Functions:
  • Motor (branchial): Stylopharyngeus muscle
  • Sensory: Posterior 1/3 of tongue (taste + general); pharynx; carotid sinus/body
  • Parasympathetic: Parotid gland (via otic ganglion)
• Lesion: Loss of taste from posterior tongue; loss of gag reflex (afferent limb)

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CN X - VAGUS NERVE (Longest cranial nerve)

• Type: Both + Parasympathetic (most extensive distribution)
• Origin: Medulla
• Exit: Jugular foramen
• Distribution: Descends into thorax and abdomen
• Functions:
  • Motor: Pharynx + larynx (speech, swallowing)
  • Parasympathetic: Heart (slows rate), lungs (bronchoconstriction), gut (peristalsis) down to splenic flexure
  • Sensory: Viscera (thorax + abdomen), skin near ear
• Lesion: Hoarseness, dysphagia, loss of gag reflex (efferent limb); uvula deviates away from lesion

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CN XI - ACCESSORY NERVE

• Type: Purely Motor (Branchial Efferent)
• Unique: Only cranial nerve with a spinal root (C1-C5)
• Exit: Jugular foramen
• Functions:
  • Cranial root: Joins vagus to supply larynx/pharynx
  • Spinal root: Sternocleidomastoid + Trapezius muscles
• Lesion: Cannot turn head to opposite side (SCM); dropped shoulder (trapezius weakness)

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CN XII - HYPOGLOSSAL NERVE

• Type: Purely Motor (GSE)
• Origin: Medulla
• Exit: Hypoglossal canal
• Function: All intrinsic + extrinsic muscles of tongue (except palatoglossus which is CN X)
• Lesion - LMN: Tongue deviates TOWARD lesion side (paralyzed side pushes it); wasting + fasciculations
• Lesion - UMN: Tongue deviates AWAY from lesion side

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QUICK REFERENCE TABLE - All 12 Cranial Nerves

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PART 2 - SPINAL NERVES (31 Pairs)

Total Count:

• Cervical: 8 pairs (C1-C8)
• Thoracic: 12 pairs (T1-T12)
• Lumbar: 5 pairs (L1-L5)
• Sacral: 5 pairs (S1-S5)
• Coccygeal: 1 pair (Co1)

Key Rule for Cervical Nerves:

• C1-C7 exit ABOVE their respective vertebra.
• C8 exits BETWEEN C7 and T1 vertebrae.
• T1 onwards exit BELOW their vertebra.

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PART 3 - NERVE PLEXUSES

A. CERVICAL PLEXUS

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B. BRACHIAL PLEXUS

• Roots → Trunks → Divisions → Cords → Branches

• Superior trunk = C5 + C6
• Middle trunk = C7 (alone)
• Inferior trunk = C8 + T1

• Lateral cord (anterior divisions of superior + middle trunks)
• Medial cord (anterior division of inferior trunk)
• Posterior cord (all 3 posterior divisions)

• Erb's palsy (C5, C6): "Waiter's tip" position - arm adducted, medially rotated, forearm pronated
• Klumpke's palsy (C8, T1): Intrinsic hand muscles paralyzed - claw hand; Horner's syndrome if T1 root avulsed

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C. LUMBAR PLEXUS

• Forms within the substance of psoas major muscle

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D. SACRAL PLEXUS

• Lies on piriformis muscle (anterior surface) on pelvic wall

• Largest nerve in the body
• Exits through greater sciatic foramen, below piriformis
• Divides into tibial + common fibular (usually at apex of popliteal fossa)
• Tibial nerve injury: Foot inverted + plantarflexed ("claw foot"); loss of sensation on sole
• Common fibular nerve injury: Foot drop; cannot dorsiflex or evert foot; loss of sensation on dorsum of foot

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PART 4 - AUTONOMIC NERVOUS SYSTEM NERVES

SYMPATHETIC ("Fight or Flight")

• Origin: Thoracolumbar (T1-L2) - also called thoracolumbar outflow
• Preganglionic: Short; synapse in paravertebral or prevertebral ganglia
• Postganglionic: Long; travel with blood vessels or spinal nerves
• Effects:
  • Heart: Increases rate + force
  • Pupils: Dilation (mydriasis)
  • Bronchi: Dilation
  • Gut: Decreases peristalsis
  • Sweat glands: Increases sweating

PARASYMPATHETIC ("Rest and Digest")

• Origin: Craniosacral outflow
  • Cranial part: CN III, VII, IX, X
  • Sacral part: S2, S3, S4 (pelvic splanchnic nerves)
• Preganglionic: Long; synapse in ganglia near or in target organ
• Postganglionic: Short

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PART 5 - IMPORTANT INDIVIDUAL NERVES (High Yield)

Radial Nerve

• Root: C5-T1 (posterior cord of brachial plexus)
• Injury sites:
  • Axilla (crutch palsy): All triceps, wrist, finger extension lost
  • Spiral groove of humerus (Saturday night palsy): Triceps spared; wrist drop
  • Elbow: Posterior interosseous nerve - finger drop only

Median Nerve

• Root: C6-T1 (lateral + medial cords)
• Injury sites:
  • Elbow (carpal tunnel syndrome): Thenar wasting; sensory loss over thumb, index, middle, lateral half ring finger
  • "Ape hand" deformity - thumb cannot oppose
  • LOAF muscles spared in ulnar injury but affected in median: Lateral 2 lumbricals, Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis

Ulnar Nerve

• Root: C7-T1 (medial cord)
• Injury at elbow (medial epicondyle):
  • Claw hand (more prominent in ring + little fingers)
  • Loss of intrinsic hand muscles (except LOAF)
  • Sensory loss on medial 1.5 fingers + medial palm

Sciatic Nerve

• Root: L4-S3 (largest nerve in body)
• Common injury: Hip fracture/dislocation, buttock injection (avoid upper medial quadrant)
• Loss of all muscles below knee; hamstrings affected too

Phrenic Nerve

• Root: C3, C4, C5
• Motor to diaphragm
• Injury: Diaphragm paralysis on same side; elevated hemidiaphragm on X-ray

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PART 6 - SPINAL NERVE ROOTS - REFLEXES (Exam High Yield)

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PART 7 - DERMATOMES (Key ones for Exam)

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EXAM TIPS SUMMARY

1. 12 cranial nerves = "Some Say Marry Money But My Brother Says Big Brains Matter More" (S/S/M/M/B/M/B/S/B/B/M/M)
2. Brachial plexus = Roots-Trunks-Divisions-Cords-Branches = C5 to T1
3. Erb's palsy (C5,C6) = "Waiter's tip" | Klumpke's (C8,T1) = Claw hand
4. Radial nerve = Wrist drop | Ulnar = Claw hand | Median = Ape hand
5. Femoral nerve = Cannot extend knee | Sciatic = Foot drop + loss of sensation below knee
6. Phrenic nerve = C3,4,5 keeps the diaphragm alive
7. Parasympathetic ganglia in head = Ciliary, Pterygopalatine, Submandibular, Otic
8. Vagus (CN X) = longest cranial nerve; Trigeminal (CN V) = largest cranial nerve
9. CN IV (Trochlear) = only CN to exit from dorsal midbrain
10. CN IV lesion = cannot go down stairs (diplopia looking down)

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