Neuroanatomy untangled

Dr. Martin Turner MA MB BS MRCP PGCAP PhD turnermr@doctors.org.ukSpecialist Registrar in Neurology (Oxford Deanery)5th Year Undergraduate Medical Students

Localisation•Brain (stroke, MS, tumour)

•Cerebellum (stroke,MS, alcohol)•Spinal cord (tumour, MS)

•Neuromuscular junction (MG)

•NB always ask why not?•Muscle (dystrophy, myositis)•NB muscle wasting think nerve first•Autonomic nervous

system

•Peripheral nerve (GBS, vasculitis)

•Brain-stem (stroke, MS)

•Anterior horn (MND)

Big clues

•Brain (hemi-body, cognitive involvement)•Brain-stem (CN involvement)•Cerebellum (ataxia, NB remember dorsal columns)•Spinal cord (legs not arms, sensory level)•Anterior horn (upper and lower motor neurone)•Peripheral nerve (asymmetrical, patchy)•Neuromuscular junction (non-specific, fatiguable)•Muscle (symmetry, family history)•Autonomic nervous system (postural hypotension,

diarrheoa, sweating)

Upper vs. Lower Motor Neuron

UMN*

LMN

Brain

Brain-stem

Spinal cord

Peripheral nerves (including some CNs)

* Pyramidal (corticospinal) tract

Common UMN/LMN conditions

UMN (central) conditions

Stroke

MS (demyelination)

Head injury

Cerebral palsy

LMN (“peripheral”) conditions

Entrapment neuropathies

Guillain-Barré

Diabetes

Vasculitis

UMN and LMN = anterior horn = MND

Much rarer, but don’t forgetNeuromuscular junction

•Myasthenia Gravis

•Lambert-Eaton myasthenic syndrome (LEMS)

Clues:

•Generalised, fatiguable weakness

•Unexplained ptosis, bulbar problems

1º Muscle disease

•Dystrophies: Duchenne, FSH

•Inflammatory

Clues:

•Symmetrical wasting

•Retained reflexes

The Examination elements

•The central nervous system–cranial nerve testing (brain-stem and brain)

–(cognitive testing – cortex: grey matter)•The peripheral nervous system

–limb function (spinal cord, neuromuscular junction, muscle)

•The autonomic nervous system–control of heart rate, BP, blood flow

Cranial nerves

Twelve pairs

The origins of the CNs

III, IVV, VI, VII, VIIIIX, X, XI, XII

III

The course of the CNs

I – back of nose (trauma), frontal lobe (tumour)

II – visual fields

III, IV, VI,II, VI – cavernous sinus

V, VII, VIII – cerebellopontine angle (CPA)

VI – long, easily trapped under brain (false-localising)

IX, X, XI, XII – base of skull (jugular/hypoglossal foramina)

II - Optic

Optic chiasm – bitemporal hemianopia – e.g. pituitary tumour

Optic radiation – homonymous hemianopia or quadrantanopia (lower parietal, upper temporal) – e.g. stroke

Pupillary response to light•Inbound (afferent):

•II to midbrain

•Outbound (efferent):

•Parasympathetic on surface of III to both eyes

•So, testing the left pupil:

•Direct (left II and III working)

•Consensual (right II and left III working)

•“Pupil-sparing” III lesion:

•localises origin of pathology

Eye movements – III, IV and VIVI (Abducens) – Lateral rectus: abducts eye

IV (Trochlear) – Superior oblique: depresses abducted eye

III (Oculomotor) – “everything else” and eyelid retraction

So, III palsy: “down and out” and ptosis:

Left complete IIIrd nerve palsy

V - Trigeminal

Sensation to face and muscles of mastication

Corneal reflex, Jaw jerk (UMN sign)

VII - Facial

Right LMN facial nerve palsy

•Muscles of facial expression

•(Taste to front 2/3 tongue)

•UMN e.g. stroke: only lower part of face affected (opposite side to stroke) as “back-up” supply from other side

•LMN e.g. Bell’s palsy: whole of face as lesion beyond point of back-up supply

•NB remember the close association to the ear (Ramsay-Hunt syndrome)

The Cavernous

Sinus

Uncal herniation

Right abducens palsy

VI

Cerebello-pontine angle

VVIII

VII

Right acoustic neuroma

VI

IX - Glossopharyngeal, X - Vagus

•XI - taste to back 1/3 tongue, pharyngeal sensation, afferent pathway for gag reflex, some palatal elevation

•X – efferent pathway for gag reflex,vocal cords, and main parasympathetic supply

XI - Accessory

Motor to trapezius and sternocleidomastoid muscles

Right trapezius weakness

XII - Hypoglossal

Right tongue wasting – LMN sign

Tongue movements

The Peripheral Nervous System

Spinal cord anatomy

•Terminates at L1 bone (LP below here)

•Everything below is LMN (cauda equina)

•Peripheral nerves enter like “Christmas tree” to centre (LL lateral to UL fibres)