Part 3 of 6 Anatomy Flashcards
Describe the location of the circle of Willis as well as these major arteries in the brain:
- Anterior cerebral artery
- Middle cerebral artery
- Posterior cerebral artery
- Circle of Willis: In the region of interpeduncular fossa (With in interpeduncular cistern) encircling the Optic chiasm, Pituitary and Mamillary bodies.
- Anterior cerebral artery: In the longitudinal fissure runing around the corpus callosum.
- Middle cerebral artery: Lateral sulcus and onto the lateral surface of brain
- Posterior cerebral artery: Around the cerebral peduncle into the transverse fissure on the base of temporal and occipital lobes.
F650 - Location of cerebral arteries and Circle of Willis.
Describe the parts of the MCA and major branches.
What main functional areas does the MCA innervate?
Parts of MCA
- M1: arises from internal carotid and runs towards the lateral sulcus. Called M1, i.e. first aprt of MCA. M1 gives off branches caled lenticulostriated branches - tiny branches compared to size of MCA (1mm diameter), but very important function, supplies structures, i.e. internal capsule and basal ganglia.
- M2: Called the ‘Sylvian Part’ has 2 subsets, inferior (temporal lobe) and superior (frontal and parietal lobe).
- M3: Cortical branches
Major Branches
- Just know the rolandic artery is located in the central sulcus, henceforth also known as the ‘rolandic fissure’
F651 - Middle cerebral artery parts.
Describe the posterior cerebral artery and its relation to other major arteries in the area.
- Terminal branch of basilar artery
See F652 -
Posterior cerebral artery and relations.
Describe the anterior cerebral artery and its major branches.
F653 - Anterior cerebral artery and its relations
Draw a diagram summarising the main areas of cortical blood supply.
F654 -
Summary of main areas cortical blood supply.
List the structural and functional supplied by these cerebral arteries: MCA, PCA, ACA.
F656 - Structural functional areas supplied by cerebral arteries
Describe different types of infarctions and their effect on the visual pathway.
Posterior Limb Internal Capsule Lesion
- Contralateral homonymous hemianopia
Temporal Lobe Anterior Lesion
- Superior Quadrantonopia
Parietal Lobe (Anterior) Lesion
- Inferior Quadrantonopia
Occipital Lobe Lesion
- Contralateral homonymous hemianopia
F656 - Reference diagram for visual loss types.
What mechanisms are in place in the brain to optimise blood flow?
- Autoregulation - Vasodilation and constriction in response to local factors such as CO2, K+, ICP, regulate blood flow according to demand
- Collateral circulation - chronic ischaemia due to atheromatous plaques may lead to establishment of effective collateral circulations, e.g. external carotid artery, opthalmic artery
- Large vessel anastamoses - usually not effective in preventing infarctions during acute obstruction
See MM 116.
What is a cerebrovascular accident? Explain the types that exist.
- Cerebrovascular accident- outdated term, but refers to what happens when the brain is deprived of blood due to an event such as a vessel bursting or blocking
Classifications
Clinically
- Transient ischaemic attack
- Stroke
Pathophysiologically
- Haemorrhagic
- Subarachnoid haemorrhage, e.g. hypertension, berry aneurysms
- Intracerebral haemorrhage, e.g. chronic hypertensive vascular damage.
- Occlusive
- Thrombotic
- Atherosclerosis
- Embolic
- Atherosclersis/ AF/ endocarditis/ Valvular defects/ Fat or air embolism
- Thrombotic
What is the most common site for a berry aneurysm?
- Anterior communicating artery (30-35%)
F657 - Sites of berry aneurysms
What is an anterior circulation CVA?
List the clinical features and recognise the CT/MRI images showing the ACA infarcts.
Anterior Circulation CVA
What is it?
- ACA obstruction, proximal to the anterior communicating artery.
- Presence of collateral circulation may help
Clinical Features
- Paralysis of contralateral leg and foot
- Sensory loss in contralateral leg and foot
- Bilateral lesions may cause urinary incontinence
F658 -
CT-MRI of ACA CVA.
Describe the possible presentations of a distal MCA occlusion.
(MM 117) M3 Occlusion
General Signs
- 1ry motor/ sensory areas: contralateral arm & face > leg paralysis and sensory loss (impairment)
- Optic radiation
- Posterior - homonymous hemianopia
- Anterior - superior or inferior quadrantonopia
- Parietal cortex
- Astererognosis/ agraphaesthesia/ loss of 2-point discrimination
Hemisphere-Specific Signs
- Left-side occlusion
- Aphasia - global, receptive, expressive
- Agraphia (can’t write), acalculia, finger agnosis (can’t recognise things)
- Right-side occlusion
- Sensory inattention - hemineglect
- Constructional apraxia
Describe the possible presentations of a proximal MCA infarct.
- Leads to a massive infarct involving both cortex and deep cerebral structures.
- Involvement of posterior limb and genu of the internal capsule leads to
- Contralateral hemiparesis and hemisensory loss involving face, arm, leg equally (WHY?)– dense hemiplegia
- Homonymous hemianopia
(MM 117)
Describe the possible presentations of the obstruction of the internal carotid.
- If the opposite circulation is adequate – asymptomatic.
- Symptoms are very similar to proximal MCA occlusion
- Complete contralateral hemiparesis and hemisensory loss.
- Contralateral homonymous hemianopia
- Larger lesions (if not compensated)
- Cerebral oedema and herniation (coning)
(MM 117)
Describe the presentation of lenticulostriate arteries obstruction.
- These arteries arise right angle to the main artery.
- Small caliber vessels, commonly ruptures due to hypertension.
- Leads to smaller infarcts in the deep grey and white matter – Lacunar infarcts/stroke
- Symptoms and signs depends on the structures involved.
- May cause pure sensory or motor deficits.
Describe the possible presentations of a PCA obstruction.
- Leads to infarcts in
- Occipital
- Medial temporal
- Cerebral peduncles
- Commonest are the visual symptoms
- Occipital lobe - homonymous hemianopia.
- Hippocampus - Defects in forming new memories – usually with bilateral lesions
- Cerebral peduncles - Contralateral hemiparesis – Not common
(MM 118)
Describe the presentation of a cerebellar CVA.
- Less commoner than cerebral hemispheric strokes.
- Commonest sign is Ataxia.
- Note that ataxia may occur as a result of brainstem infarct, because pathways carrying information co-ordiation involve peduncles brainstem.
Describe the presentation of a brainstem CVA.
- As this is cross sectionally a small area, vascular lesions affect multiple structures, both grey and white matter.
- Typically, unilateral lesions lead to ipsilateral cranial nerve palsy and contralateral long tracts signs.
- Altered level of consciousness and vomiting is common.
- Ataxia may occur if the cerebellum or cerebellar pathways are involved.
- Occlusion of a large vessel may cause severe disability or death (80%).
- Quadriplegia (large lesion involving both sides)
- Hemiplegia/hemisensory loss
- Dysphagia
- Dysarthria
- Other CN palsies
- Ataxia
- Vertigo
- Gaze abnormalities
- Visual field defects
(MM 119)
Describe the blood supply of the spinal cord.
F666 -
Spinal cord blood supply.
How many cranial nerves are there?
Explain their rough locations.
There are 12 cranial nerves.
I: extension of olfactory cortices
II: extension of visual centres in the brain
III-XII: part of midbrain + brainstem
Describe the functional classification of cranial nerves.
Sensory
- I - olfactory
- II - optic
- VIII - vestibulocochlear
Motor
- III Oculomotor
- IV Trochlear
- VI Abducens
- XI Accessory
- XII Hypoglossal
Mixed Sensory & Motor (Both)
- V Trigeminal
- VII Facial
- IX Glossopharyngeal
- X Vagus
Hint: Some say marry money but my brother says big brains matter more
Parasympathetic
- III Oculomotor
- VII Facial
- IX Glossopharyngeal
- X Vagus
Name the cranial nerves as well as their associated foramina.
- I - Olfactory: Cribiform plates of ethmoid bone
- II - Optic: Optic canal
- III, IV, V(1), VI - Abducens, Trochlear, Opthalmic branch of the trigeminal, Abducens: Superior orbital fissure
- V(2) - Maxillary branch of the trigeminal: Foramen rotundum
- V(3) - Mandibular branch of trigeminal: Foramen ovale
- VII, VIII - Facial, vestibulocochlear: internal acoustic meatus to stylomastoid foramen
- IX, X, XI - Glossopharyngeal, vagus, accessory: jugular foramen
- XII - Hypoglossal: hypoglossal canal
F667 - Inferior surface brain cranial nerves.
Where do the cranial nuclei sit in the brain?
Explain the clinical relevance of this.
4-4 Rule
- Bottom 4: 12,11, 10, and 9 –> found in medulla
- Next 4: 8, 7, 6, 5 –> found in the pons
- 4 and 3 lie under the inferior and superior colliculi
- 2 is the optic nerve
- 1 is the olfactory
Refer for further reference to F668 - Cranial nerve nuclei locations
Clinical Relevance
Knowledge of this brainstem anatomy really helps you localize a lesion. For example, if the patient has a 6th nerve palsy and problems with hearing (CN7), the lesion is probably in the pons. If all the eye nerves 3,4,6 are gone and the patient is otherwise “OK,” then this lesion is probably NOT in the brainstem as any lesion big enough to hit BOTH the pons and midbrain would cause other systemic problems.
Describe the location of the olfactory nerve and its path.
See F669 - Olfactory Nerve Location and Path
Explain how the visual vield of the eye actually translates to the retinal areas of the eye, linking quadrants between the two.
F670 - Visual field and retinal quadrants correlation
Image is inverted both horizontally and vertically.
Describe the visual pathways of the eye, mentioning the different nerve loops involved.
Visual Fields and the Retina
- You have 2 retinas, one in each eye
- Each retina has 2 halves:
- Nasal retina (medial half)
- Temporal retina (lateral half)
- Images are inverted as they pass through the lens to the retina, this means that in the right eye:
- Nasal retina sees the right half of the world
- Temporal retina sees the left half of the world
- More specifically,
- Right hemifield consists of:
- Right nasal retina
- Left temporal retina
- Left hemifield hence consists of:
- Left nasal retina
- Right temporal retina
- Right hemifield consists of:
Contralateral Control of the Visual Field (L & R)
- Right half of brain controls left visual field
- Left half of brain controls right visual field
- Hence:
- Fibres of temporal retinas do not cross, as they already receive information from the opposite hemifield, e.g. the left temporal retina receives information from the right hemifield
- Fibres of the nasal retinas do cross, at an area called the optic chiasm as they receive information from the hemifield of the same side.
Control of the Upper and Lower Parts of Visual Field
- Meyer’s loop of a certain side controls the upper part of the contralateral hemifield, e.g. the right Meyer’s loop if affected will cause loss of vision in the upper quadrant of the left hemifield in both eyes.
- Baum’s loop or parietal loop of a certain side controls the lower part of the contralateral hemifield, e.g. the right Meyer’s loop if affected will cause loss of vision in the upper quadrant of the left hemifield in both eyes.
Pathway Terminology
- Information leaves the retinas of the eye as the optic nerve and there is partial crossing of fibres at the optic chiasm
- After the chiasm, the fibres are known as the optic tract, the tract then wraps around the midbrain to form a structure known as the lateral geniculate nucleus, where all the axons synapse
- The fibres then fan out via optic radiations into the deep white matter of the brain and these radiations include the Meyer’s loop and the Baum’s loop (parietal loop) until they eventually reach the primary visual cortex at the back of the brain
F671 - Visual pathways and visual fields
It would also be useful to learn to draw this pathway.
Describe the expected damage to the visual field from the following insults:
- Damage before the optic chiasm
- Damage after the optic chiasm but before the lateral geniculate nucleus
- Damage of the Meyer’s loop
- Damage of the parietal loop
See F672 - Examples of lesions in the optic pathways.
Describe the location of the cranial nerves III, IV, VI as well as their functions.
Location
- Superior orbital fissure
- F673- Location of III, IV and VI cranial nerves and functions
Functions
- The trick to remembering which muscles are innervated by which nerves: LR(6)(SO4)3
- Lateral rectus = CN 6
- Superior oblique = CN 4
- All others = CN 3
- Inferior rectus
- Inferior oblique
- Superior rectus
- Medial rectus
What are the possible movements of the eye?
F674 - Movements of the eye.
Name the muscles of the eye and describe their functions.
Movement along 1 axis
- Medial and lateral recti
- Medial rectus = adducts eye
- Lateral rectus = abducts eye
Movement along 3 axes
- Superior rectus
- Elevation of eye, especially in abducted position, adduction of eye, intortion of eye
- Superior oblique
- Depression of eye, especially in adducted position, abduction of eye, intortion of eye
- Inferior rectus
- Depression of eye, especially in abducted position, adduction of eye, extortion of eye
- Inferior oblique
- Elevation of eye, especially in adducted position, abduction of eye, extortion of eye
See F675 - Eye muscles and their movements
Be able to label the ocular muscles in a sagittal section of the eye.
F676 - Labelled sagittal section of ocular muscles.
Name the major muscles found on the lid and the iris of the eye.
Levator Palpebrae Superioris
- 2 parts
- Skeletal muscle
- Function: elevates the superior (upper) eyelid.
- Innervation: oculomotor nerve (Cranial Nerve III)
- Malfunction: Damage to this muscle, or its innervation, can cause ptosis, the drooping of the eyelid.
- Smooth muscle, aka ‘Muller’s muscle’
- Skeletal muscle
Smooth Muscles of the Eye
- Muller muscle
- Iris
- Ciliary muscle
See F677 - Muller, iris and ciliary smooth muscles of the eye.
What are some general causes of cranial nerve palsies?
Causes
- Central Lesions
- Brainstem infarcts/ haemorrhage/ tumours
- Commonly associated with long tract signs, i.e. spasticity, hyperreflexia, and abnormal reflexes such as Babinski or Hoffman’s sign
- Peripheral Lesions
- Tumours/ Herniation/ Raised ICP/SAH/Aneurysms/Injuries/Neuropathies (Diabetes/Hpt)
Possible Presentations
- Can either present as isolated or multiple, depending on pathology or anatomic location
- Causes of multiple cranial nerve palsies:
- Subarachnoid haemorrhage
- Cerebellopontine angle tumour
- Cavernous sinus thrombosis
- Base of skull fracture
- Nasopharyngeal tumour
Describe and explain the presentation of right CN III palsy.
Presentation
- R - Complete ptosis
- R - abducted & depressed, pupil dilated
Explanation
- Recall that the oculomotor nerve (CN III) innervates the following ocular muscles:
- Superior rectus
- Medial rectus
- Inferior oblique
- Inferior rectus
- It also innervates the levator palpebrae m.
- Ciliary ganglion also is affected
F678 - Right CNIII nerve palsy.
Know the important relations of the cranial nerve III.
See F679 - Important relations of CN III – oculomotor nerve.
Describe and explain the presentation of cranial nerve IV palsy.
Presentation
- Complains of diplopia when walking down steps, when tilt head to left = okay, but when tilt head to right, eye rolls upwards
F680 - Trochlear nerve CN IV palsy presentation.
Explanation
- Causes:
- Trauma, e.g. base of skull fracture following MVA
- Congenital
- Vasculopathies
- CN IV has the longest intracranial course, nuclear lesions cause contralateral SO paralysis
Describe and explain the presentation of right CN VI palsy
Presentation
- Patient can look right only with left eye
- Can look left with both eyes
Explanation
- Damage to the nerve due to several causes:
- Diabetes and hypertension - vasculopathy
- Raised ICP
- Tumours, e.g. cerebello-pontine angle (CN VI, VII, VIII are common sites for tumours)
F681 -
Abducens nerve CN VI palsy presentation.
Describe the locations of the 3 branches of the trigeminal nerve, CN V as well as the relevant nuclei.
F682 - Location of branches of trigeminal nerve, CN V.
What are the muscles of mastication? Describe their innervation and locations.
Mastication Muscle Innervation
- Trigeminal nerve (or CN V). More specifically, they are innervated by the mandibular branch, or V3.
F684 - Muscles of Mastication
Describe the sensory distribution of the trigeminal nerve.
F683 -
Sensory distribution of trigeminal nerve.
Describe the function and location of CN VII.
Understand the pathway of the facial nerve.
CN VII Facial Nerve
- Motor = muscles of facial expression (CNVII –> stylomastoid foramen –> muscles of facial expression)
- Sensory = taste to anterior 2/3 of tongue
- Parasympathetic = salivary glands (submandibular & sublingual) + lacrimal gland
F725 - Facial nerve pathway and location.
What are some common sites for CNVII tumours?
F726 - Common sites for CN VII tumours.
What are the muscles of facial expression?
See 727 - Facial expression muscles.
Describe the effect of UMN vs LMN lesions on facial weakness.
- Left LMN type facial weakness = hemifacial weakness (e.g. like Bell’s palsy)
- Loss of forehead wrinkles
- Dry eyes
- Deviation of mouth
- Loss of nasolabial fold
- Salivary drooling
- Left UMN type facial weakness = lower facial weakness
F728 - UMN and LMN facial weakness.
Describe the locations and functions of CN IX.
CN IX = Glossopharyngeal Nerve
- Jugular foramen, along with CNX and CN XI and jugular vein
Functions
- Sensory = post. 1/3 of tongue (sensation and taste), oropharynx and soft palate, tonsil, carotid bodies
- Motor = pharynx (palatopharyngeus muscle)
- Parasympathetic = parotid gland
F729 - Glossopharyngeal nerve location.
Describe the functions of the vagus nerve.
See F730 - Functions of the vagus nerve.
What cranial nerves are involved in the gag reflex?
- CN IX = afferent
- CN X = motor
Describe the location and functions of the accessory nerve.
See F731 - Location and function of the accessory nerve.
Describe the location and functions of the hypoglossal nerve.
See F732 - Hypoglossal nerve location.
Function
- Supplies all muscles of the tongue except for the palatoglossus
- F733 - Muscles of tongue
Note that in a left hypoglossal nerve palsy, the tongue would be pulled to the right.
Explain the anatomy of the corneal reflex.
See F734 - Corneal reflex anatomy.
Explain the anatomy of the pupillary light reflex and the relevance of the rapid swinging light test.
F735 - Pupillary light reflex and RAPD.
Explain the anatomy of the accommodation convergence test.
See F736 - accommodation convergence test anatomy.
Describe some common head and neck clinical manifestations where the sympathetic nerves are affected.
See F737 - Head and neck sympathetic NS clinical syndromes.
