Neuroanatomy Neuroanatomy MCEM Revision

ObjectivesObjectives

Review the BASICS of neuroanatomyRevise the clinical presentation of stroke

diseaseUnderstand the Munro-Kelly Doctrine.Revise the effects of certain cranial nerve

defectsTouch upon spinal anatomy

Curriculum contentsCurriculum contents

Huge topicGeneral: Structural arrangement of the

brain and spinal cord. Divided into

– Lobar anatomy– Neurovascular anatomy– Cranial Nerves & Nuclei– Spinal Anatomy

Clinical ConsiderationsClinical Considerations

Stroke diseaseSubarachnoid HaemorrhageIntracranial Pathology Cranial Nerve defectsSpinal lesions

Considering the NeocortexConsidering the Neocortex

Complex visual functions are processed within the occipital lobe

The motor homunculus lies posterior to the central sulcus

Division of the cortical tracts within the corpus callosum prevents processing of speech

Infacrtion of Broca’s area will cause receptive dysphasia

Considering the NeocortexConsidering the Neocortex

Complex visual functions are processed within the occipital lobe

The motor homunculus lies posterior to the central sulcus

Division of the cortical tracts within the corpus callosum prevents processing of speech

Infacrtion of Broca’s area will cause receptive dysphasia

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The Neocortex - Cerebral The Neocortex - Cerebral HemispheresHemispheres Frontal lobe: anterior to central sulcus

– Motor strip, eye control, speech motor function

Parietal lobe: behind central sulcus

– Sensory strip, motor and sensory projections, interpretations of motor input

Occipital Lobe: complex visual functions

Temporal Lobe:

– Auditory projection, memory, smell(medial)

Cortical LinksCortical Links

The cortices are linked by the Corpus Callosum– Division leaves both cortices capable of memory and

emotional responses Cortical connections to the body

– Motor, including links to cerebellum– Sensory– Special sensory

Intra cortical connections– Integration of sensory inputs with memory areas

Motor tracts Motor tracts Sensory Tracts

In relation to neurovascular anatomyIn relation to neurovascular anatomy

The circle of Willis is an anastamosis of the vertebral and external carotid end arteries

The middle cerebral artery supplies all of the parietal lobe

Occlusion of the anterior cerebral artery causes leg weakness

10% of Berry Aneurysms arise from congenital defects

In relation to neurovascular anatomyIn relation to neurovascular anatomy

The circle of Willis is an anastamosis of the vertebral and external carotid end arteries

The middle cerebral artery supplies all of the parietal lobe

Occlusion of the anterior cerebral artery causes leg weakness

10% of Berry Aneurysms arise from congenital defects

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Cerebrovascular AnatomyCerebrovascular Anatomy

Neurovascular AnatomyNeurovascular Anatomy

4 Arteries supply the brain and it’s extensions– 2 Internal Carotid Arteries

– 2 Vertebral Arteries

– Connect together to form the Circle of Willis. Branches of the External Carotid Arteries supply

the Meninges and Skull. Venous drainage via dural sinuses into the IJV.

– Communicate with the diplopic veins of the skull into the facial venous circulation.

Circle of WillisCircle of Willis

Internal Carotid BranchesInternal Carotid Branches

Anterior Cerebral Artery

Middle Cerebral Artery– Divides at the

trifurcation to form penetrating branches to the basal ganglia

Vertebral Artery BranchesVertebral Artery Branches

2 vertebrals merge to form Basilar– Basilar supplies

cerebellum and brain stem structures

Basilar ends in formation of Posterior Cerebral

Cortical SupplyCortical SupplySensory Homunculus Motor Homunculus

Stroke PatternsStroke Patterns

TACI Total Anterior circulatory infarctPACI Partial Anterior circulatory infarctPOCI Posterior circulation infarctLACI Lacunar infarct

Stroke PatternsStroke Patterns

Anterior Cerebral Artery– Leg weakness

Middle Cerebral Artery– Upper limb and face– Perforators cause lacunar stroke (20% of all)

Posterior Cerebral Artery– Short term memory– Smell & Visual defects

Lacunar StrokeLacunar Stroke

Localised lesion within the internal capsule and basal ganglia– Pure motor (50-60%)– Pure sensory (6-7%)– Sensory-motor (20%)– Ataxic Hemiparesis

Lower limb weakness, and loss of co-ordination

Sub Arachnoid HaemorrhageSub Arachnoid Haemorrhage

Berry Aneurysm– 1% congenital defect

Found at the branch points of arteries– Posterior Communicating– Anterior Communicating– Middle Cerebral– Basilar

With regards to cerbrospinal fluidWith regards to cerbrospinal fluid

Approximate production equates to 200ml/day

Reabsorption occurs through the arachnoid granulations within the venous sinuses

The CSF flows from the 3rd to 4th ventricle via the foramen of Munro

There is a fixed volume of CSF within the subarachnoid space

With regards to cerbrospinal fluidWith regards to cerbrospinal fluidApproximate production equates to

200ml/dayReabsorption occurs through the

arachnoid granulations within the venous sinuses

The CSF flows from the 3rd to 4th ventricle via the foramen of Munro

There is a fixed volume of CSF within the subarachnoid space

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VentriclesVentricles

Lateral ventricle as a C-shaped cavity: – Divided into a body, anterior, inferior and

posterior horns3rd ventricle as a slit-like space in the

sagittal plane4th ventricle as lying around the pons and

upper medulla. Contain CSF (subarachnoid space)

Cerebrospinal FluidCerebrospinal Fluid CSF is secreted by the choroid plexuses.

– Vascular conglomerates of capillaries, pia and ependyma cells. Majority from the plexuses of the lateral ventricles.

– Flows through the foramen of Munro into the 3rd Ventricle– Passes into 4th via Sylvian aqueduct.

300-500 ml/24hours Reabsorption via arachnoid granulations in venous

sinuses. Function:

– Protect from mechanical damage– Maintains a constant chemical environment– Can help maintain CPP in relation to rising ICP.

Munro-Kelly DoctrineMunro-Kelly Doctrine

Ven.Vol.

Art.Vol.

Brain CSFMass

ArterialVolume

Brain CSF75 mL

Mass75 mL

VenousVolume

Art.Vol.

Brain CSF

VolumeVolume –– Pressure CurvePressure Curve

©ACSVolume of Mass

60-55-50-45-40-35-30-25-20-15-10- 5-

ICP(mm Hg)

Compensation

Herniation

Point ofDecompensation

Causes of Mass EffectCauses of Mass Effect

Intracranial Bleed– Traumatic

– Primary Obstructive Hydrocephalus

– Primary or post shunt Tumour

– Often associated with oedema Generalised Oedema

– Infection/ Infarction

Intracerebral HaematomasIntracerebral Haematomas

In relation to the cranial nervesIn relation to the cranial nerves

A lesion across the right optic tract will lead to a homonymous hemianopia

Dilatation of the pupil is controlled by the 3rd cranial nerve

A 4th cranial nerve palsy causes diplopia on lateral gaze

The 3rd cranial nerve has the longest intracranial pathway.

In relation to the cranial nervesIn relation to the cranial nerves

A lesion across the right optic tract will lead to a homonymous hemianopia

Dilatation of the pupil is controlled by the 3rd cranial nerve

A 4th cranial nerve palsy causes diplopia on lateral gaze

The 3rd cranial nerve has the longest intracranial pathway.

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Cranial NervesCranial Nerves Olfactory ) Extrusions of brain tissue Optic ) not “true” Cranial nerves Occulomotor Trochlear Trigeminal Equivalent of spinal nerve roots Abducens contain sensory and motor fibres Facial Ganglia in the brain stem, sensory and Vestibulo-cochlear motor equivalent of spinal DRG Glossopharyngeal Vagus Accessory Hypoglossal

II Optic NerveII Optic Nerve•Rods and Cones

•Axons

•Decussate at chiasm

•Nasal retinal fields cross

•Synapse in lateral geniculate body

•Damage to ON causes relative afferent pupillary defect

III OcculomotorIII Occulomotor

• Ganglia in Pons• Long pathway, first affected in raised ICP• Supplies pupil via ciliary ganglion• Medial rectus, superior rectus, inferior

rectus, inferior oblique, levator palpebrae superioris.• Palsy: ptosis, large down and out pupil.

Eye MovementsEye Movements

IV Trochlea– Superior Oblique

Diplopia on looking down/in

VI Abducens– Longest intracranial course, can lead to false

localising signs– Lateral rectus

Diplopia on lateral gaze.

In relation to the spinal cordIn relation to the spinal cord

Motors tracts decussate within the medulla.

The spinothalamic tract carries proprioceptive sensory signals

Hemisection of the cord causes a contralateral paralysis & senosry loss with ipsilateral pain & temp loss

Central cord syndrome results in greater motor loss within the upper limbs

In relation to the spinal cordIn relation to the spinal cord

Motors tracts decussate within the medulla.

The spinothalamic tract carries proprioceptive sensory signals

Hemisection of the cord causes a contralateral paralysis & senosry loss with ipsilateral pain & temp loss

Central cord syndrome results in greater motor loss within the upper limbs

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Spinal AnatomySpinal Anatomy

Continuation from the brain stem through foramen magnum

At birth, the conus medullaris lies at L3. By the age of 21, its sits at L1 or 2.– Below this is cauda equina

Enlargements within the cord to allow for:– C3-T1; brachial plexus

– T9-L1; lumbosacrial plexus Sympathetic chain lies between T5-9

Spinal nerve rootsSpinal nerve roots Rootlets emerge from the cord in the

subarachnoid space and amalgamate shortly afterwards into roots.

Anterior & posterior roots then emerge from their individual intervertebral foramina.– combine into mixed spinal nerves which then go off

to their respective destinations.

The lower a nerve root, the more steeply it slopes down before gaining its intervertebral foramen

Spinal LevelsSpinal LevelsMyotomes Level Dermatomes

C5 Badge area

Wrist Extensor C6 Thumb

Triceps C7 Middle Finger

Middle finger Dig Flex C8 Little Finger

Abductors of hand T1 Medial upper arm

T4 Nipple

T10 Umbilicus

Hip flexors L2 “jeans pockets”

Knee Extensor L3 Front thigh “the knee”

Knee Flexor L4 Medial lower leg

Dorsiflex big toe L5 1st web

Plantar flex S1 Lateral foot, sole

Spinal TractsSpinal Tracts

Descending motor tracts– 90% decussate at Foramen Magnum– Either pyramidal or extra-pyramidal according

to site of origin– Exit via ventral root

Ascending sensory tracts– Enter on dorsal roots

Spinal TractsSpinal Tracts

Motor cell bodies lie in anterior cord (ventral horn)

Sympathetic nerves are in intermedio-lateral column.

Ascending sensory pathways (decussate at different levels)– Spinothalamic tract (pain & temp) Anterior

– Spinocerebellar (proprioception)

– Dorsal column (proprioception, light touch, vibration).

Spinal cord lesionsSpinal cord lesions

Anterior Cord Syndrome– Loss of power and pain below level

Brown-Sequard– Hemisection: ipsilateral paralysis & sensory loss,

contralateral pain & temp. Posterior Cord Syndrome

– Loss of sensation Central Cervical Cord

– Incomplete quadrapareis, upper limbs more affected due to central location. Variable sensory deficit

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Key pointsKey points

Stroke patterns depend upon vessel affected

Munro-Kelly Doctrine is a closed boxKnowledge of the key anatomical elements

of the cord is fundamental in clinical practice

Useful linksUseful links

http://medocs.ucdavis.edu/cha/400/fineuQBS/QBS3.htm Cranial nerve MCQs

http://www.mrcophth.com/MRCOphth/physiology10.html Basic sciences