Functional components of the brain, vascular supply and stroke syndromes
Frontal Lobe
- Motor and pre-mortor cortex (somatomotor)
- Broca's area (motor speech)
- Pre-frontal cortex ('personality' = initiative, concentration,
judgement, foresight, emotion)
- Association cortex
- Olfactory nerve (smell)
- Optic chiasm (vision)
Blood supply
- Lateral surface - Middle cerebral artery
- Medial (para-saggital) surface - Anterior cerebral artery
Clinical assessment and signs of dysfunction
Broca's area
- Difficulties naming objects, repeating phrase
- Difficulty writing words
Pre-frontal cortex
- Abnormal mental state - lack of concentration, distractible, lack of
planning and initiative
- Preserved grasp reflex - unconsciously will grasp fingers brushed across
palm
- Pout and snout reflex - stroking above upper lip causes unconscious
pouting
- Concrete thinking - gives literal interpretations of proverbs
- Gait apraxia - widely placed shuffling feet glued to the floor
Olfactory cortex
- Unable to identify smells e.g. clove oil
- Optic chiasm
- Bitemporal hemianopia
Parietal lobe (General)
- Somatosensory (e.g. pain, touch, prioprioception)
- Posterior parietal association cortex (sensory integration -
somatosensory, auditory, visual)
Blood supply
- Lateral surface - Middle cerebral artery
- Medial (para-saggital) surface - Anterior cerebral artery
Parietal lobe (Dominant - language hemisphere) - usually left side even in
left-handed people
Clinical assessment and signs of dysfunction
- Acalculia - can't count backwards by 7s e.g. 100, 93. 86, 79, 72....
- Agraphia - can't write
- Left-right disorientation - unable to place left hand on right ear or
vice versa
- Finger agnosia - can't name each finger
- Agnosognosia - unaware of illness (e.g. one side of body is paralysed)
- Tactile agnosia - can't recognise objects by touch
- Astereognosis - can't describe shapes by touch
- Apraxia - unable to execute learned movements
Parietal lobe (Non-dominant)
Clinical assessment and signs of dysfunction
- Dressing apraxia - unable to put an inside-out PJ top on properly
- Spatial neglect - can't arrange numbers properly when asked to draw a
clock face
Temporal lobe
- Olfactory cortex (smell)
- Auditory cortex (hearing)
- Wernicke's area (language comprehension)
- Association cortex (e.g. face recognition)
- Memory
- Optic radiaiton (lower fibres)
Blood supply
- Lateral and anterior surface - Middle cerebral artery
- Medial (para-saggital) surface - Posterior cerebral artery
- Posterior-Inferior surface - Posterior cerebral artery
Clinical assessment and signs of dysfunction
Wernicke's area (receptive speech)
- Auditory-verbal agnosia - unable to recognise words e.g. cannot repeat
phrases or follow commands
- Difficulty naming objects
- Difficulty recognising faces
- Alexia - can't read
- Auditory agnosia - unable to recognise sounds
- Upper quadrant homonymous hemianopia
- Antegrade amnesia - can't form new memories (e.g. remember a list of
objects)
- Retrograde amnesia - can't recollect old memories (e.g. remember your
address)
Occipital lobe - (vision)
Blood supply
- Posterior cerebral artery
Clinical assessment and signs of dysfunction
- Visual agnosia - can't recognise images
- various lobar syndromes occur when space occupying masses (e.g.
haemorrhage or tumour) involve discrete areas of the brain.
- generalised processes e.g. hepatic encephalopathy have more diffuse
effects on brain function
SUMMARY OF VASCULAR SUPPLY
- Anterior circulation (Carotid artery)
- Ophthalmic artery - retina
- Anterior cerebral artery (ACA) - Medial surface of frontal, parietal
lobe
- Middle cerebral artery (MCA) - with deep sub-cortical branches to
internal capsule - Lateral surface of frontal, parietal and temporal lobe
- Posterior circulation (Vertebral-Basilar system) - with median and
paramedian branches
- Cerebellar arteries - cerebellum and brainstem (includes cranial nerve
nuclei)
- Posterior cerebral arteries (PCA) - occipital lobe, infero-posterior
temporal lobe
STROKE SYNDROMES
Anterior circulation infarct
Any of face, arm (MCA) or leg (ACA) weakness WITH sensory loss
+/- Dysphasia
+/- Homonymous hemianopia
+ loss of cortical function (e.g. agnosia, apraxia)Lacunar circulation
infarct (sub-cortical infarct)
Involves corticospinal or thalamocortical fibres of the internal capsule
supplied by perforating branches of MCA
Any of the following:
- Face, arm or leg weakness
- Face, arm or leg sensory loss
- Arm or leg incoordination
Posterior cerebral artery infarct
- Visual loss
- Visual agnosia
Brainstem / Cerebellar infarct
Any number of the following
- Depressed consciousness (reticular activating system)
- Incoordination / vertigo / nystagmus / ataxia (CN VIII, vestibular
system / cerebellum)
- Diplopia (incoordinate eye movement (CN II, III, VI, medial longitudinal
fasciculus)
- Abnormal face sensation (CN V)
- Abnormal facial movement (CN VII)
- Dysphagia / Loss of gag reflex (CN IX, X)
- Loss of shrug / head turning (CN XI)
- Abnormal tongue movement (CN XII)
- Hemiplegia/hemisensory loss (descending and ascending motor/sensory
tracts)
NB subcortical infarcts have motor &/or sensory changes without cortical
dysfunction (e.g. dysphasia, agnosia, apraxia)