Scenario 25: David's Weakness Flashcards
Where does the internal carotid artery enter the cranium?
Through the carotid canal
What are the major branches of the internal carotid artery?
Anterior and middle cerebral, ophthalmic, central artery of the retina
What are the major branches of the vertebral artery?
Posterior cerebral artery, basilar artery
Where does the vertebral artery enter the cranium?
Foramen magnum
Where do the vertebral arteries branch off?
The subclavian artery
Describe the course of the internal carotid artery after it enters the cranium
Enters into the middle cranial fossa then has a sinus course, lateral to the body of the sphenoid bone, emerging adjacent to the optic chiasm
Describe the course of the vertebral artery after it enters the cranium
Runs along the lateral surface of the medulla before fusing together on the ventral surface of the pons to form the basilar artery
Where is the circle of Willis found?
Surrounding the optic chiasm and pituitary on the base of the brain
What are the arteries which make up the circle of Willis?
L and R anterior and posterior cerebral arteries, L and R internal carotid arteries, anterior communicating artery and L and R posterior communicating arteries
What are the arteries coming off the circle of Willis? (which are not necessarily part of it)
Middle cerebral artery, superior cerebellar artery, posterior and anterior inferior cerebellar arteries, basilar artery with pontine branches, ophthalmic artery, anterior choroidal artery, labyrinthine artery
Where does the middle cerebral artery supply?
Parts of frontal, temporal and parietal lobes incl primary motor area, first somatosensory area, auditory area, receptive speech area and Broca’s expressive speech area.
What will occlusion of the MCA result in?
Contralateral paralysis and sensory detects of lower face, arm, aphasia if dominant area, contralateral hemianopia
Where does the anterior cerebral artery supply?
Midline portions of frontal and superior medial parietal lobes as well as corpus callosum and parts of internal capsule
What will occlusion of the ACA result in?
Paralysis and sensory defects to contralateral leg and perineum, mental confusion and dysphasia, may be defects in face, tongue and upper limb contralaterally due to internal capsule damage
Where does the posterior cerebral artery supply?
Occipital lobe and inferior temporal lobe
What will occlusion of the PCA result in?
Blindness in contralateral visual field, hippocampal memory affected temporarily
Why is the medial rim of lateral hemispheres particularly vulnerable following occlusion of cerebral arteries?
Because, although it is supplied by PCA and ACA, it is far away from the source so if BP drops it is more likely to become ischaemic
What is the blood supply of the basal ganglia and internal capsule?
Small central or perforating arteries from ACA (Recurrent artery of Heuber) or MCA (lenticulostriate arteries)
What will occlusion of blood supply to the basal ganglia and internal capsule cause?
Contrallateral sensory and motor defects
What is the blood supply of the ventral midbrain?
Posterior central or perforating arteries
What can happen if vertebral and/or basilar arteries are occluded?
Death due to coma, loss of respiratory control, cerebellar defects, cranial nerve defects, deafness and vertigo (if labyrinthine artery affected) infarction of ventral pons leads to locked in syndorme
Where does the basilar artery supply?
Pons and cerebellum
Where does the vertebral artery supply?
Upper spinal cord, brainstem, cerebellum and posterior brain
What are the pros and cons of anastomoses?
They provide a route for blood when there is a blockage but are prone to aneurysms
What is a common type of aneurysm in the circle of Willis?
A berry aneurysm
What are dural venous sinuses?
Lying between periosteal and meningeal layers of the dura mater, they valveless vessels best thought of as collecting pools of blood which drain the intracranial veins from CNS and veins of face and scalp.
Where do dural venous sinuses ultimately drain?
Into the internal jugular vein via jugular foramen in posterior cranial fossa
Can you name the venous sinuses?
Superior and inferior sagittal sinuses, straight, transverse, sigmoid, cavernous and superior and inferior petrosal sinuses
Where are the straight, superior and inferior sagittal sinuses found?
In the falx cerebri
Where is the cavernous sinus?
Either side of the sella turnica
Which venous sinus leaves the skull through the jugular foramen?
Sigmoid sinus
Where does the middle meningeal artery branch off?
The maxillary artery
Where does the middle meningeal artery enter the intracranial region?
Through the foramen spinosum
Where is the middle meningeal artery most vulnerable?
As it runs beneath the pterion where the bone is thin
What is the arterial supply of the spinal cord?
2 x posterior spinal arteries and 1 x anterior (from vertebral arteries) radicular arteries (from spinal segmental arteries)
What is the venous drainage of the spinal cord?
Posterior, anterior and posteriolateral spinal veins, radicular veins and intervertebral venous plexus
Where is an extradural haemorrage?
Between skull and dura
Where is an subdural haemorrage?
Between dura and arachnoid
Where is an subarachnoid haemorrage?
Between arachnoid and pia
Where is an intracerebral haemorrage?
Within brain tissue
Why does the brain require so much glucose?
High ATP demand due to density of synapses (Na+K+ATPase for repolarisation, ATP linked glutamate removal into astrocytes and ATP linked degradation to glutamine)
What is flow-metabolism coupling?
Increased blood flow in brain linked to increased activity due to increased demand for glucose and oxygen
How is glucose metabolised in the brain?
Taken up from blood into astrocytes and neurones, the converted into glucose-6-phosphate (locked in cell) and metabolised or stored
Where are the glycogen stores in the CNS?
Astrocytes
Which anastomoses would limit the damage caused by an MCA occlusion by atheroma with thrombus or embolus?
Recurrent artery of Heuber or anterior choroidal artery may allow collateral blood supply, leptomeningeal collateral circulation will allow limited degree of compensation
What is the infarct core of a stroke?
Dead, unsavable tissue after stroke
What is the ischaemic penumbra of a stroke?
Tissue at risk of death if not reperfused quickly, kept alive by recruited anastomoses. Increased BP here prevents further damage
Why would an MCA occlusion cause cell death?
Interrupts supply of glucose and O2 to cells, decreased ATP production, energy failure leads to death
What are the phases of cell death following MCA occlusion?
Initially there would be electrical silence followed by sequalae of Na+K+ATPase, spreading depolarisations, intracellular Na+ accumulation and H2O influx causing cytotoxic oedema
Why would there be an influx of Ca2+ into cells following MCA occlusion?
Failure of ATP dependant glutamate transporter means it is not removed from the synapse, activating the postsynaptic neurone continually
What causes spreading depolarisations in MCA occlusion?
Na+K+ATPase and Ca2+ pump failure leads to imbalance of currents, neurones have sustained depolarisation of -10mV and repolarisation is impossible if energy not restored
Why are spreading depolarisations dangerous?
Can cause vasodilation or vasconstriction caused by spreading depolarisations. Vasodilation may use up blood in one area needed by another, vasoconstriction will exacerbate ischaemia
What is cytotoxic oedema?
Swollen neurone with H2O accumulation due to breakdown of ionic gradients due to insufficient sodium pump
What are the consequences of glutamate build up in stroke?
Binds to NMDA receptor and triggers Ca2+ influx. This causes: cytotoxic oedema, activation of destructive enzymes, production of inflammatory mediators, platelets, leucocytes and free radicals leading to cell death, BBB breakdown, increased intracranial pressure, and ischaemia
How do we treat a ischaemic stroke?
Rencanalisation is the priority. Intravenous thrombolysis by recombinant plasminogen activator or mechanical extraction of clot
What is interventional neuroradiology for a stroke?
Intra-arterial catheter to remove clot or apply thrombolysis directly
How can ischaemic penumbra be recused?
Reperfusion of MCA with O2 and glucose, recruitment of leptomeningeal collateral supply, compensatory increase of blood flow through recurrent artery of Heuber and anterior choroidal artery, increase in cerebral perfusion pressure
What are the risks of recanalisation?
Bleeding events, reperfusion injury (exacerbation of inflammation and vasogenic oedema)
Why can patients deteriorate after thrombolysis?
Vasogenic oedema exacerbated by reperfusion, infarction progression, too low BP for collateral perfusion, depolarisations still spreading
What is a decompressive hemipraniectomy? When can it be used?
Remove part of skull to allow pressure to subside, used if stroke score above 6, up to 60 years of age, onset of stroke less than 48 hours, no haemorrhage, pupillary reflexes must be present, infarction of 2/3 MCA territory
Which part in the embryo will go on to form forebrain?
Prosencephalon (later splits into telencephalon and diencephalon)
Which part in the embryo will go on to form midbrain?
Mesencephalon
Which part in the embryo will go on to form hindbrain?
Rhombencephalon
Where is the insular cortex?
Folded deep within the lateral sulcus
What is the function of the insular cortex?
Emotion, consciousness and body homeostasis
What are the parts of the diencephalon?
Thalamus, hypothalamus, epithalamus and subthalamus
What are the parameters of brain shrinkage?
Atrophy of gyri, widened sulci, enlarged ventricles. Grey matter and connecting white matter both lost.
What are the two cell types of the cortex?
Stellate and pyramidal cells
What are the superlayers that the cortex can be divided into?
Granular layer with infragranular below and supragranular above (outer surface of cortex)
What connections does the infragranular layer have?
Efferents to brainstem and spinal cord
What connections does the supragranular layer have?
Efferent and afferent connections to other parts of the cortex
What are intercortical connections that project ipslaterally called?
Association projections
What are intercortical connections that project contralaterally or to corpus callosum called?
Commissural projection
What connections does the granular layer have?
Afferents from the principal thalamic nuclei
What is the only connection to the cortex which does NOT come via the thalamus?
Olfaction
Where is the primary motor cortex?
In the precentral gyrus anterior to the central sulcus
Where is the primary somatosensory cortex?
In the postcentral gyrus, posterior to central sulcus
Where is the supplementary motor cortex?
On medial area (midline) with bilateral representation, anterior to primary motor cortex
Where is the premotor cortex?
On the lateral surface just anterior to primary motor cortex
What is the premotor cortex important for?
Trunk muscle innervation for posture
Where is the secondary somatosensory cortex?
In parietal lobe on the ceiling of lateral sulcus posterior to the primary somatosensory cortex
Which side are Broca’s area, Wernicke’s area, the language and speech centre generally on?
The left
What woudl be the consequence of damage to the primary somatosensory cortex?
Loss of touch contralaterally, pain intact
What would be the consequence of damage to the superior parietal lobule?
Contralateral somatosensory agnosia (recognising objects by touch alone)
What would be the consequence of damage to the inferior parietal lobule?
If dominant hemisphere: loss of language
If non-dominant hemisphere: body image disturbances (can’t recognise own limbs)
Where in the thalamus would visual input from the retina project to?
The lateral geniculate nucleus
Where in the thalamus would auditory input from the cochlea project to?
The medial geniculate nucleus
Where in the thalamus would taste input project to?
Ventro posteriomedial thalamus (VPM)
Where in would olfaction input project to?
Directly into olfactory cortex
Where is the primary visual cortex?
Posterior cortex either side of the calcarine sulcus
How much of the visual cortex is dedicated to the fovea alone and how much to the whole peripheral vision?
50-50
What is the dorsal stream of visual processing associated with?
Visual-spatial function, movement
What is the ventral stream of visual processing associated with?
Form and colour recognition for object recognition
What will result from damage of primary visual cortex?
Blindness
What can result from damage of the secondary visual cortices?
Visual agnosia- can’t recognise objects
Visual neglect of half of visual field (if non-dominant side lesion)
What is Broca’s area?
Speech motor area
What is Wernicke’s area?
Speech sensory area
Where is the auditory cortex?
On the superior temporal gyrus
How is language processed through Broca’s and Wernicke’s area?
Written language into visual cortex, sounds in midbrain. Sent to Wernicke’s area first for processing. Crude linguistic outline formed in Wernicke’s. Sent to Broca’s area to be refined into grammatical form then sent to motor cortex for speech.
What is the result of damage to Broca’s area?
Know what want to say but have no grammar, stuttering
What is the result of damage to Wernicke’s area?
Have grammar but speaking meaningless sentences
What connects Wernicke’s and Broca’s area?
Arcuate fasciculus
What forms the brainstem?
Medulla oblongata, pons, midbrain
What runs along the medulla oblongata ventrally?
Anterior fissure, with pyramids on either side and the two olivary nuclei more laterally
What do the olivary nuclei do?
Form connections between cerebellum and medulla oblongata
What connects cerebellum to pons?
Medial cerebellar peduncle
What does the crus cerebri connect?
Cerebral hemispheres and cerebellum
Where are the superior and inferior colliculi?
On the dorsal aspect of the mid brain
What is the function of superior and inferior colliculi?
Visual processing and auditory processing respectively
What lies in between superior and inferior peduncles in the pons?
The floor of the 4th ventricle
Where are the gracile and cuneate tracts?
On the dorsal aspect of the medulla
Where does the corticospinal tract dessucate?
At the level of the pyramids on the ventral surface of the medulla
Which cranial nerves attach to the brain stem?
III-XII
Where do the olfactory tracts project to CNS?
Directly projects into cortex
Where does the optic nerve attach to the brain?
Lateral geniculate nucleus of thalamus
Which nuclei fibres contribute to the oculomotor nerve?
Oculomotor nucleus and Edinger-Westphal nucleus
Where is the trochlear nucleus found?
At the level of inferior colliculus
What is unique about the course of the trochlear nerve?
Project dorsally and wrap around cerebral aqueduct of the midbrain and exits the brainstem on the dorsal surface (only nerve exit dorsally)
Where is the abducens nuclei found?
Embedded in floor of 4th ventricle at the level of mid pons
How does the oculomotor nerve leave the brainstem?
Projects ventrally between midbrain and pons
How does the abducens nerve leave the brainstem?
Projects ventrally between pons and medulla obongata
How do the III, IV and VI cranial nerves reach the eye?
Through the superior orbital fissure
Why are III, IV and VI cranial nerves prone to injury?
Run through cavernous sinus so if there is vascular injury here then pressure may damage these nerves
What will result from III, IV and VI injury?
Paralysis of eye lid (can’t open eye) and eye muscles
Where do parasympathetic fibres of the oculomotor nerve run?
In the Edinger- Westphal nucleus
Which reflex does the parasympathetic component of the oculomotor nerve control?
Pupillary light reflex
What does the trigeminal nerve provide?
Main sensory innervation of face
What are the three branches of the trigeminal nerve and where do they supply?
Opthalamic, forehead, bridge of nose and superior face, maxillary, cheeks, mandibular, ear, jawline and inferior face
Where does the opthalamic nerve exit?
Superior orbital fissure
Where does the maxillary nerve exit?
Foramen rotundum
Where does the mandibular nerve exit?
Foramen ovale
Where does the trigeminal nucleus run in the brain stem?
All the way from midbrain to medulla oblongata, very large
Where is the major sensory nucleus of trigeminal nerve? What does it process?
Level of pons, touch and pressure of face
Where is the mesencephalic sensory nucleus of trigeminal nerve? What does it process?
Level of midbrain, proprioception of face
Where is the spinal sensory nucleus of trigeminal nerve? What does it process?
Level of medulla, pain and temperature of face
What is special about the mesencephalic sensory nucleus of trigeminal nerve?
Sensory cell body lies within CNS. Only place in the whole CNS where this happens, all other sensory cell bodies lie outside the CNS
Where does the facial nerve connect to the brainstem?
At the cerebellar pontine angle (CPA)
What are the sensory nuclei of the facial nerve?
Nucleus solitarius
What are the motor nuclei of the facial nerve?
Facial motor nucelus
What are the parasympathetic nuclei of the facial nerve?
Superior salivatory nucelus
Where can we find the facial nerve in the brainstem?
Embedded in floor of fourth ventricle deeper than abducens
Which muscles does the facial muscle innervate for motor control?
Facial muscles (via stylomastoid foramen) and stapeddus
Which muscles does the facial muscle innervate for sensation?
Anterior 2/3 tongue and palate
Which muscles does the facial muscle innervate for parasympathetic control?
Lacrimal gland and salivary glands
What nucleus does the vestibulocochlear nerve attach to?
Vestibulocochlear nucleus
Which nerve is the vestibulocochlear nerve closely associated with? Why is this important clinically?
Facial nerve in internal auditory meatus, if an acoustic neuroma forms (not uncommon) facial nerve will be affected
Where does the glossopharyngeal nerve join the brainstem?
Level of lateral upper medulla
Which sensory nuclei are associated with glossopharyngeal nerve?
General sensation: trigeminal sensory nucleus
Taste (posterior 1/3 tongue) and visceral sensation: nucleus solitarius, hypoglossal nucleus
Which motor nuclei are associated with glossopharyngeal nerve?
Nucleus ambiguous- for stylopharyeus muscle
Inferior salivary nucleus for parotid salivary glands
Where does the vagus nerve join the brainstem?
Lateral upper medulla level
Which sensory nuclei are associated with vagus nerve?
Trigeminal sensory nucleus- general sensation
Nucleus solitarius- visceral sensation
Which motor nuclei are associated with vagus nerve?
Nucleus ambiguous- soft palate, pharynx, larynx, upper oesophageal tract
Dorsal motor nucleus- parasympathetic innervation to most internal organs
Where does the accessory nerve join the brainstem?
Level of lateral medulla
What are the two roots of the accessory nerve?
Cranial root- nucleus ambiguous
Spinal root- outside of neurocranium (must enter via foramen magnum to join cranial root)
What do the spinal root of the accessory nerve control?
Sternomastoid and trapezius muscle
What do the cranial root of the accessory nerve control?
Larynx and pharynx
Where do cranial nerves IX-XI exit the skull?
Through jugular foramen
Where does the hypoglossal nerve attach to the brainstem?
Between olives and pyramids, ventral on surface of medulla oblongata
Where does the hypoglossal nerve give motor supply?
Vast majority of extrinsic and intrinsic muscles of tongue
Where does the hypoglossal nerve exit the skull?
Hypoglossal canal
What would compression of cranial nerves IX-XII result in?
Dysphonia, dysphagia, dysarthria, gag reflex suppression, weakness of tongue, unilateral wasting of sternomastoid and trapezius muscles
What is the reticular formation?
Found in centre of brainstem, characterised by sending different kinds of projections from brain stem throughout cortex, cerebellum and whole brain.
What do noradrenergic projections from the reticular formation regulate?
Arousal, attention, awareness, sleep, homeostatic control
What do dopaminergic projections from the reticular formation regulate?
Reward, cognition, motivation, emotional processing, motor control, saccadic eye movement
What do serotonergic (raphe nuclei) projections from the reticular formation regulate?
Reward (drug abuse), sleep, nociception
What is going on before we initiate a movement?
Muscle tone holds posture, balance counteracts momentum, visual, vestibular and proprioception systems set idea of body in space
What is going on as we initiate a movement?
Basal ganglia and supplementary motor cortex work together to initiate voluntary movement
What will happen if there is a lesion in the supplementary motor cortex?
Initiation of movement nearly impossible
What is going on during a movement?
The cerebellum monitors messages and actual position and compares cerebral and peripheral signals to detect mismatches and error correct them before they happen. This provides a smooth movement
What is going on as we stop a movement?
Basal ganglia and cerebellum form the ‘brakes’ and feed back to predict the end point
What goes on after a movement has finished?
Resting state, tone posture and balance all still being controlled
Where does the idea or motivation for a movement come from?
The prefrontal cortex
What can cause damage to the prefrontal cortex?
Head injury or ACA occulsion
What does the premotor cortex do before a movement?
Motivation and conceptualisation, realises goal and formulates plan for movement
What is the blood supply of the premotor cortex?
MCA
What is the blood supply of the supplementary motor cortex?
ACA
What does the supplementary motor cortex do before a movement?
Work out the function, strategy and plan of how to achieve that goal
What is the function of the posterior parietal cortex?
Analyses sensory information related to hypothetical movement (particularly visual), activates supplementary and premotor cortex to write programme for movement
What is the function of the cerebellum in movement?
Balance, coordination, muscle memory. Monitors and compares the plan of action (motor cortex command) to what is actually happening (propprioceptive feedback)
what is the blood supply of the cerebellum?
The anterior and posterior inferior and superior cerebellar arteries branching off the basilar
What would result from a clinical lesion of the cerebellum?
Cerebellar ataxia
What is the blood supply of the basal ganglia?
MCA via lenticulostriate arteries, ACA and anterior choroidal
Why are leticulostriate arteries at risk of a stroke?
They enter the basal ganglia at sharp right angles making them a target for atherosclerosis
What is the function of the basal ganglia in movement?
Timing and rhythm of movement, amplitude of movement
What clinical conditions affect the basal ganglia?
Parkinson’s, chorea (involuntary dancing), athetosis (involuntary writhing)
What is the blood supply of the primary motor cortex?
MCA and ACA
What is the blood supply of the internal capsule?
Upper anterior limb by MCM
Lower anterior limb by ACA
Upper genu by lenticulostriate branches of MCA.
Lower genu directly from internal capsule and from ACA
Upper posterior limb by lenticulostriate branches from MCA.
Lower posterior limb by anterior choroidal artery
