Anatomy and Physiology Flashcards
Neurons
- Permanent do not divide in adulthood, no progenitors
- Cell bodies and dendrites stained via Nissl substance (RER)
- If axon is injured it undergoes Wallerian degeneration (degeneration distally, retraction proximally) allows for potential PNS regeneration.
Astrocytes
function, embryo origin
- Physical support, repair, K+ metabolism, removal excess neurotransmitter, blood brain barrier, glycogen fuel reserve buffer.
- Reactive gliosis in response to neural injury
- Derived from neuroectoderm
- Astrocyte marker- GFAP
Microglia
function, embryo origin, histo description
-CNS phagocytes, scavenger cells of CNS
-Respond to damage by differentiating into phagocytic cells.
HIV infected microglia –>multinucleated giant cells in CNS
-Mesodermal origin
-Not readily discernible in Nissl stain
-Small irregular nuclei, little cytoplasm
Myelin
synthesis and effect
- Incr conduction velocity (via saltatory conduction)
- Insulating axons increases space constant
- CNS (oligodendrocytes)
- PNS (Schwann cells)
Oligodendroglia
function, disease states
- Myelinates axons of neurons in the CNS
- Each oligodendrocyte can myelinate ~30 axons
- Predominant glial cell in white matter
- Derived form neuroectoderm
- “Fried egg” appearance on H&E stain
- Injured in MS, progressive multifocal leukoencephalopathy
Schwann Cells (function, disease states)
-Myelinates (only 1) PNS axon.
-Promotes axonal regeneration
-Derived from neural crest
-Destroyed in Guillain-Barre syndrome
-Acoustic neuroma - type of schwannoma (CN VIII)
if bilateral strongly associated with neurofibromatosis 2
Free nerve endings
description, location, senses
C: slow, unmyelinated, all skin, some viscera, pain/temp
A-delta: fast, myelinated, all skin, epi, viscera, pain/temp
Meissner corpuscles
description, location, senses
Large, myelinated, adapt quickly
Glabrous (hairless) skin
Dynamic, fine/light touch; position sense
Pacinian corpuscles
description, location, senses
Large, myelinated, adapt quickly
Deep skin, ligaments and joints
Vibration, pressure
Merkel discs
description, location, senses
Large, myelinated, adapt slowly
Basal epidermal layer, hair follicles
Pressure, deep static touch (shapes, edges), position sense
Peripheral nerve layers
- Endoneurium (endo=inner): invests single nerve fiber (inflammatory infiltrate in Guillain-Barre syndrome)
- Perineurium (peri=around, permeability barrier):surrounds a fascicle of nerve fibers. Must be rejoined in microsurgery reattachment
- Epineurium (epi=outer): Dense connective tissue that surrounds entire nerve (fascicles and blood vessels)
Locus ceruleus
location, neurotransmitter synthesis, disease states
- Pons
- Norepinephrine
- “Stress and panic”
- Increased in anxiety
- Decreased in depression
Ventral tegmentum and Substantia nigra pars compacts (SNc) (location, neurotransmitter synthesis, disease states)
- Midbrain
- Dopamine
- Increased in Huntington
- Decreased in Parkinson’s
- Decreased in depression
Raphe nucleus
location(s), neurotransmitter synthesis, disease states
- Pons, medulla, midbrain
- 5 HT (serotonin)
- Increased in Parkinson’s
- Decreased in anxiety
- Decreased in depression
Basal nucleus of Meynert
Neurotransmitter synthesis, disease states
- ACh
- Increased in Parkinson’s
- Decreased in Alzheimer
- Decreased in Huntington
Nucleus accumbens and septal nucleus
Neurotransmitter synthesis, disease states
- GABA
- “reward center, pleasure, addiction, fear”
- Decreased in anxiety
- Decreased in Huntington
3 structures that make up the blood-brain barrier
- Tight junctions between nonfenestrated capillary endothelial cells
- Basement membrane
- Astrocyte foot processes
Functional consequences of blood-brain barrier
-Prevents bacterial infections from spreading into the CNS, also restricts drug delivery to brain.
-Glucose and amino acids cross slowly via carrier-mediated transport
-Non-polar/lipid soluble substances diffuse rapidly
-no blood-brain barrier in some areas:
Area postremafenestrated capillaries (vomiting w/chemo)
OVLT (organum vasculosum of lamina terminals)- osmotic
Neurohyophysis -ADH release(hypothalamus penetrates)
-Also barriers in testes, maternal-fetal placental barrier
Hypothalamus (general function mnemonic)
“hypothalamus wears TAN HATS”
- Thirst and water balance
- Adenohypophysis control (of anterior pituitary)
- Neurohypophysis releases hormones from hypothalamus
- Hunger
- Autonomic regulation
- Temperature regulation
- Sexual urges
- Inputs (OVLT, area postrema)
Posterior pituitary
hormones released and synthesizing nuclei
Oxytocin and ADH made by hypothalamus but stored and released by posterior pituitary.
Supraoptic nucleus of hypothalamus –> ADH
Paraventricular nucleus of hypothalamus –> Oxytocin
Hunger/Satiety Areas (hypothalamus)
Lateral area: hunger, inhibited by leptin
destruction = anorexia, failure to thrive (infants)
Ventromedial area: satiety, stimulated by leptin
destruction = hyperphagia (craniopharyngioma)
Temperature regulation areas (hypothalamus)
Anterior hypothalamus: cooling parasympathetic
(Anterior nucleus, cool, think A/C)
Posterior hypothalamus: heating, sympathetic
Suprachiasmatic nucleus
Circadian rhythm (you need sleep to be charismatic)
Regulation of the sleep cycle
Suprachiasmatic nucleus regulates circadian rhythm, which controls nocturnal release of ACTH, prolactin, melatonin, and NE. This is regulated by environment, e.g. light.
(light)–> SCN–> NE release–> pineal gland–> melatonin.
Drugs that influence REM sleep
benzodiazepines, barbiturates and EtOH decrease REM and delta wave sleep; NE also decr REM sleep.
Treatment of bedwetting
oral desmopressin acetate (DDAVP) mimics ADH; given to treat bedwetting (sleep enuresis) over imipramine because of the latter’s adverse effects.
Treatment of sleepwalking and night terrors
Benzodiazepines
Stages of wakefullness/sleep (description, EEG waveform)
Awake (eyes open): alert, active mental concentration
Beta (highest frequency, lowest amplitude)
Awake (eyes closed):
Alpha
Non-REM stage N1 (5%): light sleep
Theta
Non-REM stage N2 (45%): deeper sleep; bruxisms (teeth grinding) - sleep spindles and K complexes
Non-REM stage N3 (25%): deepest non-REM sleep, when sleepwalking, night terrors, and bedwetting occur
Delta (lowest frequency, highest amplitude
REM sleep (25%): loss of motor tone, incr brain O2, incr variable pulse and BP; when dreaming and tumescence (erection) occur; may serve in memory processing
Beta
Posterior pituitary (neurohypophysis)
Receives hypothalamic axonal projections from supraoptic (ADH) and paraventricular (oxytocin) nuclei
(oxys= quick, tocos=birth)
(adenohypophysis=anterior pituitary)
Thalamic nuclei (just name, function on other cards)
VPL: ventral posterolateral (body SS) VPM: ventral posteromedial (face SS) LGN: lateral geniculate nucleus (vision) MGN: medial geniculate nucleus (hearing) VL: ventral lateral (motor)
VPL
Ventral posterolateral nucleus of the thalamus:
Input from spinothalamic (pain and temp) and dorsal column/medial lemniscus (pressure, touch, vibration, proprioception) to the primary somatosensory cortex.
VPM
Ventral posteromedial nucleus of the thalamus:
Input from trigeminal and gustatory pathway (face sensation and taste) to primary somatosensory cortex
LGN
Lateral geniculate nucleus of the thalamus:
Input from CN II (vision) to the calcarine sulcus (lateral=light)
MGN
Medial geniculate nucleus of the thalamus:
Input from superior olive and inferior colliculus of tectum (hearing) to the auditory cortex of temporal lobe (medial=music)
VL
Ventral lateral nucleus of the thalamus:
Input from basal ganglia, cerebellum (motor) to the motor cortex
Limbic system
Famous 5 F’s (Feeding, Fleeing, Fighting, Feeling, Sex)
Involved in emotion, long-term memory, olfaction, behavior modulation, ANS function.
Includes hippocampus, amygdala, fornix, mammillary bodies, and cingulate gyrus.
Critical for memory and motivation
All areas receive rich monoaminergic and cholinergic innervation
Hippocampus
Memory formation
Patient H.M bilateral hippocampus lobectomy –> anterograde amnesia (no new memories) specifically explicit or declarative memory (facts/experiences)
Not implicit memory (motor procedural skill)
Hippocampus → mammillary bodies + branches to septal nuclei (via fornix)
Amygdala
Major role in fear conditioning
Lesion prevents pavlovian conditioning to painful (fearful) stimuli
Could play a role in PTSD
Amygdala → septal nucleus (via stria terminalis)
Fornix
Connects hippocampus to mammillary bodies + branches to septal nuclei (fibers over thalamus)
Mammillary bodies
Mammillary body in thalamus → anterior nucleus of thalamus (via mammillothalamic tract) → cingulate gyrus + prefrontal cortex
Cingulate gyrus
c
Cerebellar Inputs
Contralateral cortex via middle cerebellar peduncle.
Ipsilateral proprioceptive information via inferior cerebellar peduncle from the spinal cord (nerves=climbing and mossy fibers)
Cerebellar Outputs
Sends info to contralateral cortex to modulate movement.
Nerves=purkinje cells –>deep nuclei of cerebellum –> contralateral cortex via superior cerebellar peduncle.
Deep nuclei: Dentate, Emboliform, Globose, Fastigial (Don’t eat greasy food)
Dentate Nucleus
Lateral hemispheres
Cerebrocerebellum: reciprocal connections w/ cortex
Spacially and temporally complex movements requiring coordination, cognition (learn complex movements)
→contralateral VL thal→cortical motor areas
→parvocellular red nucleus→ inferior olives→climbing fibers
Interposed Nucleus (Emboliform and Globus)
Paravermis
Spinocerebellum: appendicular movements (reaching, grasping)
→VL thal→M1→lateral corticospinal tract
→Magnocellular red nucleus→rubrospinal tract
Floculonodulus
Vestibulocerebellum
Fastigial Nucleus
Vermis
Spinocerebellar outputs: midline movements (speech, posture, stance, gait, visceral function)
→superior cerebellar peduncle→VL thal→M1→ventral corticospinal tract
→superior cerebellar peduncle→superior colliculus→tectospinal tract
→inferior CP→reticular nuclei→reticulospinal tracts
→inferior CP→vestibular nuclei→vestibulospinal tracts
Lateral cerebellar lesions
Voluntary movements of extremities; when injured, propensity to fall toward injured (ipsilateral) side
Medial cerebellar lesions
Lesions of midline structures (vermal/fastigial nuclei) and/or the flocculonodular lobe result in truncal ataxia, nystagmus and head tilting. These patients also may have a wide-based (cerebellar) gate and deficits in truncal coordination. Generally, midline lesions result in bilateral motor deficits affecting axial and proximal limb musculature.
Basal ganglia
Important in voluntary movements and making postural adjustments. Receives cortical input, provides negative feedback to cortex to modulate movement.
Striatum = putamen (motor) + caudate (cognitive)
Lentiform = putamen + globus pallidus
Direct pathway of basal ganglia
Direct (D1 receptor) facilitates movement:
Cortical inputs stimulate the striatum, stimulating the release of GABA which disinhibits the thalamus via the GPi/SNr (to incr motion)
Dopamine binds to D1 stimulating the excitatory pathway (increasing motion)
substantia nigra pars compacta (SNc) houses dopaminergic neurons that project to –> putamen (D1) where dopamine activates D1 receptors that –> inhibits globus pallidus internus (usually inhibits thalamus) which –> releases GPi inhibition of the thalamus so that –> thalamus can project motor signal to primary motor cortex
Indirect pathway of basal ganglia
Indirect (D2 receptor) inhibits (unwanted) movement via:
Cortical inputs stimulate the striatum, which disinhibits STN via GPe, and STN stimulates GPi/SNr to inhibit the thalamus (decreasing motion)
Dopamine binds to D2, inhibiting the inhibitory pathway (increasing motion)
substantia nigra pars compacta (SNc) houses dopaminergic neurons that project to –> putamen (D2) where dopamine inhibits D2 receptors (normally inhibit GPe) that –> releases inhibition of GPe so that it fires and inhibits sub thalamic nucleus) which –> no longer allows STN to fire and activate GPi –> so GPi then no longer inhibits the thalamus. (loss of inhibition of movement)
Parkinson Disease
Degenerative disorder of CNS associated with Lewy bodies (composed of alpha-synuclein - intracellular eosinophiolic inclusion) and loss of dopaminergic neurons in substantial nigra pars compacta. Parkinson TRAPS your body: Tremor (at rest pill rolling) Rigidity (cogwheel) Akinesia (bradykinesia) Postural instability Shuffling gait
Huntington Disease
Autosomal dominant trinucleotide CAG repeats
Chromosome 4
Loss of Ach and Gaba (CAG=Caudate loses Ach and Gaba)
Symptoms manifest between 20-50
Chorea, aggression, depression, dementia
Often accompanied by substance abuse (mistaken for)
Neuronal death via NMDA-R binding and glutamate toxicity
Atrophy of caudate nuclei seen on imaging
Hemiballismus (presentation, lesion)
Sudden, wild flailing of 1 arm +/- ipsilateral leg
Lesion: contralateral subthalamic nucleus (eg lacunar stroke)
Chorea (presentation, lesion)
Sudden, jerky, purposeless movements
Lesion: basal ganglia (eg Huntington)
Athetosis (presentation, lesion)
Slow, writhing movements’ especially seen in fingers
Lesion: basal ganglia (eg Huntington)
Myoclonus (presentation, lesion)
Sudden, brief, uncontrolled muscle contraction
Notes: common in metabolic abnormalities such as renal failure and liver failure (e.g. jerks, hiccups)
Dystonia (presentation, lesion)
Sustained, involuntary muscle contractions
Notes: Writers cramp;blepharospasm
Essential tremor (postural tremor) (presentation, lesion)
Action tremor; exacerbated by holding posture/limb position
Note: genetic predisposition. Patients often self-medicated with EtOH, which decr tremor amplitude
Tx: beta-blockers, primidone
Resting tremor (presentation, lesion)
Uncontrolled movement of distal appendages (most noticeable in hands); tremor alleviated by intentional movement
Lesion e.g. Parkinson disease
Note: occurs at rest e.g. “pill rolling tremor”
Intention tremor (presentation, lesion
Slow, zigzag motion when pointing/extending toward a target
Lesion: cerebellar dysfunction
Spinocerebellum (vermis/paravermis)
Mossy fiber sensory/motor input info from spine, vestibular, auditory, visual info, proprioceptive from ipsilateral muscles excite deep cerebellar nuclei directly.
Dorsal: sensory, clarke’s nucleus, below C8
Ventral: motor info, ventral horn, below C8
Cuneocerebellar: sensory, cuneate nucleus, above C8
Rostral: motor info, ventral horn, above C8
Mesencephalic: nucleus face
Climbing/mossy fibers
“Climb the olive tree”
(Contralateral Inferior olive → Climbing fibers→ Purkinje cell (looks like a tree))
“Moss on rock by pons”
Mossy fiber going to granule (rock) from pontine nuclei (Pond sounds like pons)
Cerebellar peduncles (input/output)
Inferior: ipsilateral input from dorsal/rostral spinocerebellar, cuneocerebellar tracts
Middle: massive contralateral input from pontine nuclei
Superior: mostly output, input from ventral spinocerebellar tract
Spinocerebellar ataxia
Wide, staggering gait, dysmetria, action tremor, timing disorders (dysdiadochokinesia), movement decomposition, inability to adapt motor programs
Vestibulocerebellum ataxia
Problems w/ equilibrium and balance (fall toward side of lesion)
Vertigo
Visual problems (nystagmus, loss of smooth pursuit, diplopia)
Cerebrocerebellum ataxia
Fine motor control deficits (writing) Highly skilled motions (speech, sports, instruments) Cognitive deficits (language deficits after PICA, behavioral)
Urbach-Wiethe disease
Bilateral lesion of amygdala
memory loss, new info with emotional content
Impaired recognition of emotion in facial expression, inability to judge like emotions (fear vs anger)
PTSD
Triad: Re-experiencing phenomena (flashbacks), avoidance of situations that parallel initial trauma, hyperarousal (hypervigilence)
Promotes increase in anxiety
Etiology: decrease inhibition of amygdala by prefrontal cortex, increase amygdala fear activity
Schizophrenia
Fragmentation of mood, thought, and movement (1% of population)
Positive sxs: delusions, hallucinations
Negative sxs: social withdrawal
Tx:
-dopamine hypothesis block DA receptors w/ Haloperidol. May see Parkinsonian-like side effects)
-glutamate hypothesis block DA and 5-HT receptors + glutamate reuptake w/ clozapine
Kluver-Bucy Syndrome
Bilateral medial temporal lobe damage (encephalitis, stroke)
Sx: K - luver - bucy
K: (okay) neutral affect
luver: (lover) hypersexuality
Gary bucy: (has a big mouth) visual agnosia - pt puts objects in mouth to identify
Alzheimer’s Dementia
Etiology: loss of cholinergic input to hippocampus (nucleus basalis)
Presence of neurofibrillary tangles (phosphorylated tau proteins) and beta-amyloid plaques
Chronic progressive deterioration
Loss of memory → mood disorders →loss of motor function → complete loss of cognitive function
Tx: Donepezil (aricept): blocks ACh esterase → increase [ACh]
Chronic Traumatic Encephalopathy
Progressive neurodegenerative disease caused by repeated head trauma
Triad of sx:
Cognition: memory impairment (anterograde), executive dysfx (goal-directed behaviors)
Mood: depression, apathy
Behavior: decreased impulse control, aggressiveness
Etiology: generalized brain atrophy, NFTs present after exposure to multiple mild brain injuries or concussions.
Amygdala lesion (bilaterally)
Kluver-Bucy syndrome (hyperorality, hypersexuality, disinhibited behavior)
Associated with HSV-1
Frontal Lobe lesion
Disinhibition and deficits in concentration, orientation, and judgment.
May have reemergence of primitive reflexes
Right vs Left parietal-temporal cortex lesion
Rt: spatial neglect syndrome (agnosia of the contralateral side of the world)
Lt: Agraphia, acalculia, finger agnosia, and left-right disorientation
Gerstmann syndrome
Reticular activating system lesion (midbrain)
Reduced levels of arousal and wakefulness (e.g. coma)
Mammillary bodies (bilateral)
Wernicke-Korsakoff syndrome: Confusion, ophthalmoplegia, ataxia; memory loss (anterograde and retrograde amnesia), confabulation, personality changes
Associated w/ thiamine (B1) deficiency and excessive EtOH use
Can be precipitated by giving glucose without B1 to a B1-deficient patient
(CAN of beer: Confusion, Ataxia, Nystagmus)
Basal ganglia lesion
May result in tremor at rest, chorea, or athetosis (e.g. Parkinson)
Cerebellar hemisphere lesion
Intention tremor, limb ataxia, and loss of balance
Damage to cerebellum = ipsilateral deficits
Fall toward side of lesion
(Cerebellar hemispheres are laterally located - affect lateral limbs)
Cerebellar vermis lesion
Trucal ataxia, dysarthria
Vermis is centrally located - affects central body
Subthalamic nucleus lesion
Contralateral hemiballismus
Hippocampus lesion (bilaterally)
Anterograde amnesia (can’t make new memories)
Paramedian pontein reticular formation lesion
Eyes look away from side of lesion
Rt FEF –> Lt PPRF –> Lt CN VI –> Rt CN III (via MLF)
Frontal eye fields lesion
Eyes look toward lesion
Rt FEF –> Lt PPRF –> Lt CN VI –> Rt CN III (via MLF)
Central Pontine Myelinolysis
Osmotic demyelination; acute paralysis, dysarthria, dysphagia, diplopia, LOC
Can cause “locked in syndrome”
Massive demyelination of pontine white matter tracts 2/2 osmotic forces and edema.
Commonly iatrogenic, overly rapid correction of hyponatremia
(from low to high, your pons will die) -CPM Na+ correction
(from high low low, your brain will blow) - cerebral edema/herniation
Aphasia vs dysarthria
Aphasia: higher-order inability to speak (language deficit)
Dysarthria: motor inability to speak (movement deficit)
Broca Aphasia (dysphasia)
Nonfluent aphasia with intact comprehension
Broca area inferior frontal gyrus of frontal lobe
(Broca boken boca - spanish)
Wernicke Aphasia (dysphasia)
Fluent aphasia with impaired comprehension and repition
Wernicke area superior temporal gyrus of temporal lobe
(Wernicke is Wordy but doesn’t make sense)
Global Aphasia (dysphasia)
Nonfluent aphasia with impaired comprehension. Both Broca and Wernicke areas affected
Conduction Aphasia (dysphasia)
Poor repetition but fluent speech, intact comprehension.
Can be caused by damage to left superior temporal lobe and/or left supra marginal gyrus
(can’t repeat phrases “no ifs, ands, or buts”)
Transcortical Motor Aphasia
Nonfluent aphasia with good comprehension and repetition
Transcortical sensory aphasia
Poor comprehension with fluent speech and repetition
Mixed transcortical aphasia
Nonfluent speech, poor comprehension, good repetition
Circle of Willis
Rt brachiocephalic –> common–> Internal carotid Artery–>
-Middle cerebral–>lenticulostriate/anterior choroidal
-Anterior cerebral–>anterior communicating
-Posterior communicating
Sub-clavian –> Vertebral –> Basilar
-Posterior Inferior Cerebellar
-Anterior Spinal
-Anterior Inferior Cerebellar
-Superior cerebellar
-Posterior cerebral
Cerebral artery cortical distributions
Anterior cerebral artery: anteromedial surface
Middle cerebral artery: lateral surface
Posterior cerebral artery: posterior and inferior surfaces
Watershed zones between anterior/middle, posterior/middle artery zones.
Damage in severe hypotension –> upper leg/upper arm weakness, defects in higher-order visual processing
Regulation of cerebral perfusion
Tight autoregulation primarily driven by PCO2 (PO2 also modulates perfusion in severe hypoxia <50mmHg)
Therapeutic hyperventilation (decr PCO2) helps decrease intracranial pressure in cases of cerebral edema (stroke, trauma) via decreasing cerebral perfusion by vasoconstriction
Middle Cerebral Artery stroke (area of lesion and sxs)
Motor: Contralateral paralysis upper limb and face
Sensory: Contralateral loss of sensation in upper/lower limb, face
Temporal lobe (Wernicke)/Frontal lobe (Broca): Aphasia if in dominant (usually left) hemisphere. Hemineglect if lesion in non dominant.
Anterior Cerebral Artery stroke (area of lesion and sxs)
Motor: contralateral paralysis lower limb
Sensory: contralateral loss of sensation lower limb
Lenticulo-striate artery stroke (area of lesion and sxs)
Striatum, internal capsule:
- contralateral hemiparesis/hemiplegia
- common location of lacunar infarcts secondary to unmanaged hypertension
Anterior Spinal artery stroke (area of lesion and sxs)
Commonly bilateral, Medial Medullary Syndrome
Caused by infarct of paramedic branches of ASA and vertebral arteries.
Lateral corticospinal tract: contralateral hemiparesis upper and lower limbs
Medial lemniscus: decrease contralateral proprioception
Caudal medulla(hypoglossal nerve): ipsilateral hypoglossal dysfunction (deviation ipsilaterally)
Posterior Inferior Cerebellar Artery (PICA) stroke
area of lesion and sxs
Lateral Medullary Syndrome (Wallenberg)
-vestibular nuclei: Vomiting, vertigo, nystagmus;
-lateral spinothalamic tract: pain and temperature sensation
from contralateral body
-spinal trigeminal nucleus: pain and temperature sensation
from ipsilateral face
-nucleus ambiguus: dysphagia, hoarseness, decr gag reflex
-sympathetic fibers: ipsilateral Horner syndrome
-inferior cerebellar peduncle: ataxia, dysmetria
Nucleus ambiguus effects are specific to PICA lesions.
“Don’t pick a (PICA) horse (hoarseness) that can’t eat
(dysphagia).”
Anterior Inferior Cerebellar Artery (AICA) stroke
area of lesion and sxs
Lateral Pontine Syndrome—cranial nerve nuclei:
-vestibular nuclei: vomiting, vertigo, nystagmus
-facial nucleus: Paralysis of face, decr lacrimation,
salivation, decr taste from anterior 2⁄3 of tongue
-spinal trigeminal nucleus: decr corneal reflex, decr facial pain and temperature sensation.
-cochlear nucleus: ipsilateral decr in hearing
-sympathetic fibers: ipsilateral Horner syndrome
-Middle and inferior cerebellar peduncles: ataxia, dysmetria
Facial nucleus effects are specific to AICA lesions.
“Facial droop means AICA’s pooped.”
Posterior Cerebral Artery stroke (lesions and sxs)
Occipital cortex, visual cortex: contralateral hemianopia with macular sparing
Basilar artery stroke (lesion and sxs)
“Locked-in syndrome”
Pons, medulla, lower midbrain, corticospinal and corticobulbar tracts, ocular cranial nerve nuclei, paramedian pontine reticular formation:
-Preserved consciousness and blinking, quadriplegia, loss of voluntary facial, mouth, and tongue movements
Anterior Communicating stroke (lesions and sxs)
Most common lesion is aneurysm. Can lead to stroke. Saccular (berry) aneurysm can impinge cranial nerves.
- Visual field defects
- Lesions are typically aneurysms, not strokes.
Posterior Communicating stroke (lesion and sxs)
Common site of saccular aneurysm.
-CN III palsy—eye is “down and out” with ptosis and pupil
dilation.
-Lesions are typically aneurysms, not strokes.
Berry Aneurysm
-Occurs at the bifurcations in the circle of Willis
-Most common site is junction of the anterior communicating artery and anterior cerebral artery.
-Rupture (most common complication) leads to subarachnoid hemorrhage (“worst headache of life”) or
hemorrhagic stroke.
-Can also cause bitemporal hemianopia via compression of optic chiasm.
-Associated with ADPKD, Ehlers-Danlos syndrome, and Marfan syndrome.
-Other risk factors: advanced age, hypertension, smoking,
race (incr risk in blacks).
Charcot-Bouchard microaneurysm
Associated with chronic hypertension; affects small vessels (e.g., in basal ganglia, thalamus).
Central post-stroke pain syndrome
- Neuropathic pain due to thalamic lesions.
- Initial sensation of numbness and tingling followed in weeks to months by allodynia (ordinarily painless stimuli cause pain) and dysaesthesia.
- Occurs in 10% of stroke patients.
Epidural hematoma
- Rupture of middle meningeal artery (branch of maxillary)
- often 2° to fracture of temporal bone.
- Lucid interval.
- Rapid expansion under arterial pressure–> transtentorial herniation, CN III palsy.
- CT shows biconvex (lentiform), hyper dense blood collection, not crossing suture lines.
- Can cross falx, tentorium.
Subdural hematoma
-Rupture of bridging veins. Slow venous bleeding
-Seen in elderly, alcoholics, blunt trauma, shaken baby
(predisposing factors: brain atrophy, shaking, whiplash).
-Crescent-shaped hemorrhage that crosses suture lines
-Midline shift. Cannot cross falx, tentorium
Subarachnoid hemmorrhage
- Rupture of an aneurysm (berry aneurysm)
- Patients complain of “worst headache of my life (WHOML).” -Seen in Marfan, Ehlers-Danlos, ADPKD) or an AVM.
- Rapid time course.
- Bloody or yellow (xanthochromic) spinal tap.
- 2–3 days afterward, risk of vasospasm due to blood breakdown (not visible on CT, treat with nimodipine) and rebleed (visible on CT)
Intraparenchymal (hypertensive) hemorrhage
- Most commonly caused by systemic hypertension.
- Also with amyloid angiopathy, vasculitis, and neoplasm.
- Typically occurs in basal ganglia and internal capsule (Charcot-Bouchard aneurysm of lenticulostriate vessels), but can be lobar.
Ischemic brain disease/stroke
- Irreversible damage begins after 5 minutes of hypoxia.
- risk: hippocampus, neocortex, cerebellum, watershed
- Irreversible neuronal injury.
Stroke imaging:
Bright on diffusion-weighted MRI in 3–30 minutes (highest sensitivity for early ischemia),
Dark abnormality on noncontrast CT in ~ 12–24 hours.
Absence of bright areas on noncontrast CT highly accurate to exclude hemorrhage (contraindication for tPA).
Histologic features of ischemic brain disease/stroke
Red neurons: 12-48 hours Necrosis + neutrophils: 24-72 hours Macrophages: 3-5 days Reactive gliosis+vascular proliferation: 1-2 weeks Glial scar: >2 weeks
Hemorrhagic stroke
- Intracerebral bleeding, often due to hypertension, anticoagulation, and cancer (abnormal vessels can bleed). –May be 2° to ischemic stroke followed by reperfusion (vessel fragility).
- Basal ganglia are most common site of intracerebral hemorrhage.
Ischemic stroke
- Disruption of blood flow and subsequent ischemia.
- Results in liquefactive necrosis.
3 types:
- Thrombotic—due to a clot forming directly at the site of infarction (commonly the MCA), usually over an atherosclerotic plaque.
- Embolic—an embolus from another part of the body obstructs a vessel. Can affect multiple vascular territories. Often cardioembolic.
- Hypoxic—due to hypoperfusion or hypoxemia. Common during cardiovascular surgeries, tends to affect watershed areas.
Treatment—tPA (if within 3–4.5 hr of onset and no hemorrhage/risk of hemorrhage). Reduce risk with medical therapy (e.g., aspirin, clopidogrel); optimum control of blood pressure, blood sugars, and lipids; and treat conditions that incr risk (e.g., atrial fibrillation).
Transient Ischemic Attack (TIA)
Brief, reversible episode of focal neurologic dysfunction lasting < 24 hours without acute infarction (neg MRI), with the majority resolving in < 15 minutes; deficits due to focal ischemia.
Dural venous sinuses
Large venous channels that run through the dura. Drain blood from cerebral veins and receive CSF from arachnoid granulations. Empty into internal jugular vein.
Superior sagittal sinus, Inferior sagittal sinus, Straight, occipital sinus, confluence of the sinuses–>transverse–>sigmoid–>internal jugular vein
Ventricular system
CSF is made by ependymal cells of choroid plexus; it is reabsorbed by arachnoid granulations and then drains into dural venous sinuses.
Lateral ventricle –> 3rd ventricle via right and left interventricular foramina of Monro.
3rd ventricle–>4th ventricle via cerebral aqueduct (of Sylvius).
4th ventricle–>subarachnoid space via:
-Foramina of Luschka = Lateral.
-Foramen of Magendie = Medial.
Communicating hydrocephalus
Decreased Csf absorption by arachnoid granulations, which can lead to increased intracranial pressure, papilledema, and herniation (e.g. arachnoid scarring post-meningitis)
Normal Pressure Hydrocephalus
Does not result in increased subarachnoid space volume. Expansion of ventricles distorts the fibers of the corona radiata and leads to:
clinical triad of urinary incontinence, ataxia, and cognitive dysfunction (sometimes reversible). “Wet, wobbly, and wacky.”
Hydrocephalus ex vacuo
Appearance of increased CSF in atrophy (e.g., Alzheimer disease, advanced HIV, Pick disease).
Intracranial pressure is normal; triad is not seen.
Apparent increase in CSF observed on imaging is actually result of decreased neural tissue due to neuronal atrophy
Noncommunicating hydrocephalus
Caused by a structural blockage of CSF circulation within the ventricular system (e.g., stenosis of
the aqueduct of Sylvius).
Spinal nerves
There are 31 spinal nerves in total:
8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal
Nerves C1–C7 exit above the corresponding vertebra. All other nerves exit below (e.g., C3 exits above the 3rd cervical vertebra; L2 exits below the 2nd lumbar vertebra).
Vertebral disc herniation
nucleus pulpous (soft central disc) herniates through annulus fibrosus (outer ring); usually occurs posterolaterally at L4–L5 or L5–S1.
Spinal cord- lower extent
In adults, spinal cord extends to lower border of L1–L2 vertebrae. Subarachnoid space (which contains the CSF) extends to lower border of S2 vertebra. Lumbar puncture is usually performed between L3–L4 or L4–L5 (level of
cauda equina)
“To keep the cord alive, keep the spinal needle between L3 and L5.”
Ascending spinal cord tracts
Dorsal column/medial lemniscal pathway: pressure, vibration, touch, proprioception
Fasciculus gracilis: lower body, legs (medial)
Fasciculus cuneatus: upper body, arms (lateral)
Lateral spinothalamic tract: pain, temperature
Sacral (lateral)
Cervical (medial)
Anterior spinothalamic tract: crude touch, pressure)
Descending spinal cord tracts
Lateral corticospinal tract: voluntary motor (sacral lateral, cervical medial)
Anterioir corticospinal tract: voluntary motor
Dorsal column (function, cell body locations, synapses)
Function: ascending pressure, vibration, fine touch, and proprioception.
1st neuron: Sensory nerve ending–> cell body in dorsal root
ganglion–>enters spinal cord, ascends ipsilaterally in dorsal column
Synapse 1: Ipsilateral nucleus cuneatus or gracilis (medulla)
2nd neuron: Decussates in medulla, ascends contra laterally in medial lemniscus
Synapse 2: VPL thalamus
3rd neuron: Sensory cortex
Spinothalamic tract (function, cell body locations, synapses)
Ascending Lateral: pain, temperature
Anterior: crude touch, pressure
1st neuron: Sensory nerve ending (Aδ and C fibers) (cell body in dorsal root ganglion) –>enters spinal cord
Synapse 1: Ipsilateral gray matter (spinal cord)
2nd neuron: Decussates at anterior white commissure
–>ascends contra laterally
Synapse 2: VPL thalamus
3rd neuron: Sensory cortex
Lateral corticospinal tract (function, cell body locations, synapses)
Descending: voluntary movement of contralateral limbs
1st Neuron: UMN: cell body in 1° motor cortex–>descends ipsilaterally (through internal capsule), most fibers decussate at caudal medulla (pyramidal decussation)–> descends contralaterally
Synapse 1: Cell body of anterior horn (spinal cord)
2nd Nueron: LMN: leaves spinal cord
Snyapse 2: NMJ
Upper motor neuron lesion signs
Weakness, increased reflexes, increased tone, +babinski, spastic paralysis, clasp knife spasticity
Lower motor neuron lesion signs
Weakness, atrophy, fasiculations, decreased reflexes, decreased tone, (-) babinski, flaccid paralysis
Werdnig-Hoffmann disease (area affected, characteristics)
Poliomyelitis and spinal muscular atrophy
LMN lesions only, due to destruction of anterior horns; flaccid paralysis
Amyotrophic lateral sclerosis (area affected, characteristics)
Combined UMN and LMN deficits with no sensory, cognitive, or oculomotor deficits; both UMN and LMN signs.
Can be caused by defect in superoxide dismutase 1. Commonly presents as fasciculations with eventual atrophy and weakness of hands; fatal.
Riluzole treatment modestly incr survival by decr presynaptic glutamate release.
Commonly known as Lou Gehrig disease. Stephen Hawking is a well-known patient who highlights the lack of cognitive deficit.
“For Lou Gehrig disease, give rilouzole.”
Complete occlusion of anterior spinal artery
Spares dorsal columns and Lissauer tract; upper
thoracic ASA territory is a watershed area, as artery
of Adamkiewicz supplies ASA below ∼T8.
Tabes dorsalis
Caused by 3° syphilis.
Results from degeneration (demyelination) of dorsal columns and roots–>impaired sensation and proprioception and progressive sensory ataxia (inability to sense or feel
the legs–>poor coordination).
Associated with Charcot joints, shooting pain, Argyll Robertson pupils (small bilateral pupils that further constrict to accommodation and convergence, not to light).
Exam will demonstrate absence of DTRs and +Romberg.
“prostitutes pupil” - it accommodates but does not react
Syringomyelia
Syrinx expands and damages anterior white commissure of spinothalamic tract (2nd-order neurons)–> bilateral loss of pain and temperature sensation (usually C8–T1); seen with Chiari I malformation; can expand and affect other tracts.
Vitamin B12 or vitamin E deficiency
Subacute combined degeneration—demyelination of dorsal columns, lateral corticospinal tracts, and spinocerebellar tracts; ataxic gait, paresthesia, impaired position and vibration sense.
Poliomyelitis
Caused by poliovirus (fecal-oral transmission).
Replicates in the oropharynx and small intestine before spreading via the bloodstream to the CNS. Infection causes destruction of cells in anterior horn of spinal cord (LMN death).
Symptoms: LMN lesion signs—weakness, hypotonia, flaccid paralysis, fasciculations, hyporeflexia, and muscle atrophy. Signs of infection—malaise, headache, fever, nausea, etc.
Findings: CSF with incr WBCs and slight incr of protein (with no change in CSF glucose). Virus recovered from stool or throat
Spinal muscular atrophy (Werdnig-Hoffmann disease)
Congenital degeneration of anterior horns of spinal cord
–>LMN lesion. “Floppy baby” with marked hypotonia and tongue fasciculations. Infantile type has median age of death of 7 months.
Autosomal recessive inheritance.
Friedreich ataxia
Autosomal recessive trinucleotide repeat disorder (GAA) on chromosome 9 in gene that encodes frataxin (iron binding protein).
Leads to impairment in mitochondrial functioning.
Degeneration of multiple spinal cord tracts–>muscle weakness and loss of DTRs, vibratory sense, and proprioception.
Staggering gait, frequent falling, nystagmus, dysarthria, pes cavus, hammer toes, hypertrophic cardiomyopathy (cause of death). Presents in childhood with kyphoscoliosis.
Friedreich is Fratastic (frataxin): he’s your favorite frat brother, always stumbling, staggering, and falling, but has a big heart.
Brown-Séquard syndrome
Hemisection of spinal cord. Findings:
- Ipsilateral UMN signs below the level of the lesion (due to corticospinal tract damage)
- Ipsilateral loss of tactile, vibration, proprioception sense 1–2 levels below the level of the lesion (due to dorsal column damage)
- Contralateral pain and temperature loss below the level of the lesion (due to spinothalamic tract damage)
- Ipsilateral loss of all sensation at the level of the lesion
- Ipsilateral LMN signs (e.g., flaccid paralysis) at the level of the lesion
If lesion occurs above T1, patient may present with Horner syndrome due to damage of oculosympathetic pathway.
Horner syndrome
Sympathectomy of face:
- Ptosis (slight drooping of eyelid: superior tarsal muscle)
- Anhidrosis (absence of sweating) and flushing (rubor) of affected side of face
- Miosis (pupil constriction)
Associated with lesion of spinal cord above T1 (e.g., Pancoast tumor, Brown-Séquard syndrome [cord hemisection], late-stage syringomyelia).
PAM is horny (Horner)
Ptosis, Anhidrosis, Miosis
The 3-neuron oculosympathetic pathway projects from the hypothalamus to the intermediolateral column of the spinal cord, then to the superior cervical (sympathetic) ganglion, and finally to the pupil, the smooth muscle of the eyelids, and the sweat glands of the forehead and face. Interruption of any of these pathways results in Horner syndrome.
Landmark Dermatomes
C2—posterior half of a skull “cap.”
C3—high turtleneck shirt.
C4—low-collar shirt.
T4—at the nipple. (T4 teat pore)
T7—at the xiphoid process.
T10—at the umbilicus (important for early
appendicitis pain referral). (T10 belly butten)
L1—at the inguinal ligament. (L1=IL-inguinal ligament)
L4—includes the kneecaps. (down on AL L4’s)
S2, S3, S4—erection and sensation of penile and anal zones. (S2,3,4 keeps the penis off the floor)
Diaphragm and gallbladder pain referred to the right shoulder via the phrenic nerve.
Clinical reflexes
Achilles = S1 nerve root (S1,2 - buckle my shoe) Patella = L4 nerve root (L3,4 - kick the door) Biceps = C5 nerve root (C5,6 - pick up sticks) Triceps = C7 nerve root (C7,8 - lay them straight)
Also:
L1,2 cremaster reflex (testicles move)
S3,4 anal wink reflex (winks galore)
Primitive reflexes
CNS reflexes that are present in a healthy infant, but are absent in a neurologically intact adult. Normally disappear within 1st year of life. These “primitive” reflexes are inhibited by a mature/ developing frontal lobe. They may reemerge in adults following frontal lobe lesions–>loss of inhibition of these reflexes.
-Moro reflex: “Hang on for life” reflex—abduct/extend limbs when startled, and then draw together
-Rooting reflex: Movement of head toward one side if cheek or mouth is stroked (nipple seeking)
Sucking reflex: Sucking response when roof of mouth is touched
Palmar reflex: Curling of fingers if palm is stroked
Plantar reflex: Dorsiflexion of large toe and fanning of other toes with plantar stimulation
Babinski sign: presence of this reflex in an adult, which may signify a UMN lesion
Galant reflex: Stroking along one side of the spine while newborn is in ventral suspension (face down) causes lateral flexion of lower body toward stimulated side
Where do the cranial nerves emerge from brainstem structures?
CN I, II: forebrain CN III, IV: midbrain CN V: pons CN VI, VII, VIII: pons/pontine-medullary junction CN IX, X, XII: medulla CN XI: spinal cord
CN that lie medially in brain stem: III, IV, VI, XII
Motor nerves are medial
(medial nuclei= motor = basal plate)
(lateral nuclei= sensory = alar plate)
Pineal gland
Melatonin secretion, circadian rythms
Superior colliculi
Conjugate vertical gaze center
Your eyes are above your ears, and the superior colliculus (visual) is above the inferior colliculus (auditory).
Inferior colliculi
Auditory
Your eyes are above your ears, and the superior colliculus (visual) is above the inferior colliculus (auditory).
Parinaud Syndrome
Paralysis of conjugate vertical gaze due to lesion in superior colliculi (e.g., pinealoma)
Cranial Nerves (names, motor/sensory)
I: olfactory II: optic III: oculomotor IV: trochlear V: trigeminal VI: abducens VII: facial VIII: vestibulochoclear IX: glossopharyngeal X: vagus XI: accessory XII: hypoglossal
“Some say mary money, but my bros say big boobs matter more”
“Ooo, to touch and and feel very good velvet, ah ha”
Cranial Nerves (function)
I: olfactory: smell (only CN without thalamic relay to cortex)
II: optic: sight
III: oculomotor: Eye movement (SR, IR, MR, IO), pupillary constriction (sphincter pupillae: Edinger-Westphal nucleus, muscarinic receptors), accommodation, eyelid opening (levator palpebrae)
IV: trochlear: Eye movement (SO)
V: trigeminal: Mastication, facial sensation (ophthalmic, maxillary, mandibular divisions), somatosensation from anterior 2/3 of tongue
VI: abducens: Eye movement (LR)
VII: facial: Facial movement, taste from anterior 2/3 of tongue, lacrimation, salivation (submandibular and sublingual glands), eyelid closing (orbicularis oculi), stapedius muscle in ear (note: nerve courses through the parotid gland, but does not innervate it)
VIII: vestibulochoclear: Hearing, balance
IX: glossopharyngeal: Taste and somatosensation from posterior 1/3 of tongue, swallowing, salivation (parotid gland), monitoring carotid body and sinus chemo- and baroreceptors, and stylopharyngeus (elevates pharynx, larynx)
X: vagus: Taste from epiglottic region, swallowing, soft palate elevation, midline uvula, talking, coughing, thoracoabdominal viscera, monitoring aortic arch chemo- and baroreceptors
XI: accessory: Head turning, shoulder shrugging (SCM, trapezius)
XII: hypoglossal: Tongue movement
Corneal reflex loop
Afferent: V1 ophthalmic (nasociliary branch)
tirgeminal spinal nucleus–>bilateral facial nuclei–>
Efferent: VII (temporal branch: orbicularis oculi)
Lacrimation reflex loop
Afferent: V1 (loss of reflex does not preclude emotional tears)
Efferent: VII
Jaw Jerk reflex loop
Afferent: V3 (sensory - muscle spindle from masseter–> mesencephalic nuclus (only afferent system with primary cell bodies in the CNS))
Efferent: V3 (CNV motor nucleus –> masseter)
Pupillary Reflex loop
Afferent: CN II –>pretectal –> bilateral Edinger Westphal–>
Efferent: CN III–>Ciliary ganglia–>pupillary sphincter
Gag reflex loop
Afferent: IX
Efferent: nucleus ambiguous –> X
Nucleus Soltarius
Visceral Sensory information (e.g., taste, baroreceptors, gut distention).
Input from: VII, IX, X
Nucleus Ambiguus
Motor innervation of pharynx, larynx, and upper esophagus (e.g., swallowing, palate elevation).
Input from: IX, X, XI
Dorsal Motor Nucleus
Sends autonomic (parasympathetic) fibers to heart, lungs, and upper GI. Input from: X
Cranial nerve and vessel pathways
Cribriform plate (CN I).
Middle cranial fossa (CN II–VI)—through sphenoid bone:
-Optic canal (CN II, ophthalmic artery, central retinal vein)
-Superior orbital fissure (CN III, IV, V1, VI, ophthalmic vein, sympathetic fibers)
-Foramen Rotundum (CN V2)
-Foramen Ovale (CN V3)
-Foramen spinosum (middle meningeal artery)
Posterior cranial fossa (CN VII–XII)—through temporal or occipital bone:
- Internal auditory meatus (CN VII, VIII)
- Jugular foramen (CN IX, X, XI, jugular vein)
- Hypoglossal canal (CN XII)
- Foramen magnum (spinal roots of CN XI, brain stem, vertebral arteries)
Divisions of CN V exit vis Standing Room Only
Cavernous Sinus
A collection of venous sinuses on either side of the pituitary. Blood from eye and superficial cortex–>cavernous sinus–>internal jugular vein.
CN III, IV, V1, V2, and VI and postganglionic sympathetic fibers en route to the orbit all pass through the cavernous sinus. Cavernous portion of internal carotid artery is also here
Cavernous sinus syndrome
e.g., due to mass effect, fistula, thrombosis:
ophthalmoplegia and decr corneal and maxillary sensation with normal visual acuity. CN VI commonly affected.
CN V motor lesion
Jaw deviates toward side of lesion due to unopposed force from the opposite pterygoid muscle.
CN X lesion
Uvula deviates away from side of lesion. Weak side collapses and uvula points away.
CN XI lesion
Weakness turning head to contralateral side of lesion (SCM). Shoulder droop on side of lesion (trapezius).
The left SCM contracts to help turn the head to the right.
CN XII lesion (LMN)
Tongue deviates toward side of lesion (“lick your wounds”) due to weakened tongue muscles on the affected side.
Genioglossus protrudes tongue on contralateral side unopposed.
Outer ear
Visible portion of ear (pinna), includes auditory canal and eardrum. Transfers sound waves via vibration of eardrum.
Middle ear
Air-filled space with three bones called the ossicles (malleus, incus, stapes). Ossicles conduct and amplify sound from eardrum to inner ear.
Inner ear
Snail-shaped, fluid-filled cochlea. Contains basilar membrane that vibrates 2° to sound waves.
Vibration transduced via specialized hair cells–> auditory nerve signaling–> brainstem.
Each frequency leads to vibration at specific location on the basilar membrane (tonotopy):
-Low frequency heard at apex near helicotrema (wide and flexible).
-High frequency heard best at base of cochlea (thin and rigid).
Hearing loss (test used and localization)
Rinne: conductive hearing loss = bone>air
Rinne: sensorineural hearing loss= air>bone
Weber: Conductive localizes to affected ear
Weber: Sensorineural localizes to unaffected ear
Noise-induced: Damage to stereocilliated cells in organ of Corti; loss of high-frequency hearing 1st; sudden extremely loud noises can produce hearing loss due to tympanic membrane rupture.
UMN facial lesion
Lesion of motor cortex or connection between cortex and facial nucleus.
Contralateral paralysis of lower face
Forehead spared due to bilateral UMN innervation.
LMN facial lesion
Ipsilateral paralysis of upper and lower face.
Facial nerve palsy
Complete destruction of the facial nucleus itself or its branchial efferent fibers (facial nerve proper).
Peripheral ipsilateral facial paralysis (drooping smile) with inability to close eye on involved side.
Can occur idiopathically (called Bell palsy); gradual recovery in most cases.
Associated with Lyme disease, herpes simplex and (less common) herpes zoster, sarcoidosis, tumors, and diabetes.
Treatment includes corticosteroids
Muscles of mastication
3 close jaw: Masseter, teMporalis, Medial pterygoid.
1 opens: lateral pterygoid.
All are innervated by the trigeminal nerve (V3).
M’s Munch. Lateral Lowers (when speaking of pterygoids
with respect to jaw motion). “It takes more muscle to keep your mouth shut.”
Refractive errors of the eye
hyperopia, myopis, astigmatism, presbyopia
Impaired vision that improves with glasses:
Hyperopia: Eye too short for refractive power of cornea and lens–>light focused behind retina.
Myopia Eye: too long for refractive power of cornea and lens–>light focused in front of retina.
Astigmatism: Abnormal curvature of cornea resulting in different refractive power at different axes.
Presbyopia: Decrease in focusing ability during accommodation due to sclerosis and decr elasticity.
Uveitis
Inflammation of anterior uvea and iris, with hypopyon (sterile pus), accompanied by conjunctival redness). Often associated with systemic inflammatory disorders (e.g., sarcoid, rheumatoid arthritis, juvenile idiopathic arthritis, TB, HLA-B27–associated conditions).
Retinitis
Retinal edema and necrosis leading to scar. Often viral (CMV, HSV, HZV). Associated with immunosuppression.
Central retinal artery occlusion
Acute, painless monocular vision loss. Retina cloudy with attenuated vessels and “cherry-red” spot at the fovea.
Retinal vein occlusion
Blockage of central or branch retinal vein due to compression from nearby arterial atherosclerosis. Retinal hemorrhage and edema in affected area.
Diabetic retinopathy
Retinal damage due to chronic hyperglycemia. Two types:
Non-proliferative—damaged capillaries leak blood–>lipids and fluid seep into retina–>hemorrhages and macular edema.
Treatment: blood sugar control, macular laser.
Proliferative—chronic hypoxia results in new blood vessel formation with resultant traction on retina.
Treatment: peripheral retinal photocoagulation, anti-VEGF injections.
Aqueous humor pathway
Ciliary epithelium (beta) produces aqueous humor–>
Flows through the posterior chamber (behind iris)–>
Anterior chamber–>
Trabecular meshwork–>
Canal of Schlemm
Glaucoma (general findings)
Optic disc atrophy with characteristic cupping, usually with incr intraocular pressure (IOP) and progressive peripheral visual field loss.
Open angle glaucoma
Associated with age, African-American race, family history. Painless, more common in U.S.
Primary—cause unclear.
Secondary—blocked trabecular meshwork from WBCs (e.g., uveitis), RBCs (e.g., vitreous hemorrhage), retinal elements (e.g., retinal detachment).
Closed/narrow angle
Primary—enlargement or forward movement of lens against central iris (pupil margin) leads to obstruction of normal aqueous flow through pupil–>fluid builds up behind iris, pushing peripheral iris against cornea and impeding flow through trabecular meshwork.
Secondary—hypoxia from retinal disease (e.g., diabetes, vein occlusion) induces vasoproliferation in iris that contracts angle.
Chronic closure—often asymptomatic with damage to optic nerve and peripheral vision.
Acute closure—true ophthalmic emergency. Incr IOP pushes iris forward–> angle closes abruptly. Very painful, sudden vision loss, halos around lights, rock-hard eye, frontal headache. Do not give epinephrine because of its mydriatic effect.
Cataract
Painless, often bilateral, opacification of lens–>decr in vision.
Risk factors: age, smoking, EtOH, excessive sunlight, prolonged corticosteroid use, classic galactosemia, galactokinase deficiency, diabetes (sorbitol), trauma, infection.
Papilledema
Optic disc swelling (usually bilateral) due to incr intracranial pressure (e.g., 2° to mass effect).
Enlarged blind spot and elevated optic disc with blurred margins seen on fundoscopic exam
Extraocular muscles and nerves
CN VI: lateral rectus (abducens)
CN IV: superior oblique (trochlear)
CN III: all the rest (SR, IR, MR, IO)
The superior oblique abducts, intorts, and depresses while adducted.
CN III damage
eye looks down and out; ptosis, pupillary dilation, loss of accommodation
CN IV damage
eye moves upward, particularly with contralateral gaze and head tilt toward the side of the lesion (problems going down stairs, may present with compensatory head tilt in the
opposite direction).
CN VI damage
medially directed eye that cannot abduct.
Miosis
Constriction, parasympathetic:
1st neuron: Edinger-Westphal nucleus to ciliary ganglion via CN III
2nd neuron: short ciliary nerves to pupillary sphincter muscles
Mydriasis
Dilation, sympathetic:
- 1st neuron: hypothalamus to ciliospinal center of Budge (C8–T2)
- 2nd neuron: exit at T1 to superior cervical ganglion (travels along cervical sympathetic chain near lung apex, subclavian vessels)
- 3rd neuron: plexus along internal carotid, through cavernous sinus; enters orbit as long ciliary nerve to pupillary dilator muscles
Pupillary light reflex
Light in either retina sends a signal via CN II to pretectal nuclei in midbrain that activates bilateral Edinger-Westphal nuclei; pupils contract bilaterally (consensual reflex).
Result: illumination of 1 eye results in bilateral pupillary constriction.
Marcus Gunn pupil (afferent pupillary defect)—due to optic nerve damage or severe retinal injury.
-bilateral pupillary constriction when light is shone in affected eye relative to unaffected eye.
Tested with the “swinging flashlight test.”
CN III
CN III has both motor (central) and parasympathetic (peripheral) components.
Motor output to ocular muscles—affected primarily by vascular disease (e.g., diabetes: glucose–>sorbitol) due to decr diffusion of oxygen and nutrients to the interior fibers from compromised vasculature that resides on outside of nerve. Signs: ptosis, “down and out” gaze.
Parasympathetic output—fibers on the periphery are 1st affected by compression (e.g., posterior communicating artery aneurysm, uncal herniation). Signs: diminished or absent pupillary light reflex, “blown pupil” often with “down-and-out” gaze.
Retinal detachment
Separation of neurosensory layer of retina (photoreceptor layer with rods and cones) from outermost pigmented epithelium (normally shields excess light, supports retina)–> degeneration of photoreceptors–>vision loss.
May be 2° to retinal breaks, diabetic traction, inflammatory effusions.
Breaks more common in patients with high myopia and are often preceded by posterior vitreous detachment (flashes and floaters) and eventual monocular loss of vision like a “curtain drawn down.”
Surgical emergency.
Age-related macular degeneration
Degeneration of macula (central area of retina). Causes distortion (metamorphopsia) and eventual loss of central vision (scotomas).
-Dry (nonexudative, > 80%)—deposition of yellowish extracellular material in and beneath Bruch membrane and retinal pigment epithelium (“drusen”) A with gradual decr in vision.
Prevent progression with multivitamin and antioxidant supplements.
-Wet (exudative, 10–15%)—rapid loss of vision due to bleeding 2° to choroidal neovascularization. Treat with anti-vascular endothelial growth factor injections (anti-VEGF) or
laser.
Visual field defects
Meyer loop—inferior retina; loops around inferior horn of lateral ventricle.
Dorsal optic radiation—superior retina; takes shortest path via internal capsule.
- Right anoxia (optic nerve lesion)
- Bitemporal hemianopia (pituitary lesion, chiasm)
- Left homonymous hemianopia (optic tract lesion)
- Left upper quadratic anopia (right temporal lesion, MCA)
- Left lower quadratic anopia (right parietal lesion, MCA)
- Left hemianopia with macular sparing (PCA infarct), macula
- -> bilateral projection to occiput
- Central scotoma (macular degeneration)
Note: When an image hits 1° visual cortex, it is upside
down and left-right reversed.
Internuclear ophthalmoplegia (INO)
Medial longitudinal fasciculus (MLF): pair of tracts that allows for crosstalk between CN VI and CN III nuclei. Coordinates both eyes to move in same horizontal direction. Highly myelinated (must communicate quickly so eyes move at same time). Lesions seen in patients with demyelination (e.g., multiple sclerosis).
Lesion in MLF = INO: lack of communication such that when CN VI nucleus activates ipsilateral lateral rectus, contralateral CN III nucleus does not stimulate medial rectus to fire. Abducting eye gets nystagmus (CN VI overfires to stimulate CN III). Convergence normal.
MLF in MS. When looking left, the left nucleus of CN VI
fires, which contracts the left lateral rectus and stimulates the contralateral (right) nucleus of CN III via the right MLF to contract the right medial rectus.
Directional term (e.g., right INO, left INO) refers to which eye is paralyzed.
