Neuro-01-Emrbyo_Physio_Anat Flashcards
Development of neural tube and neural crest
• Occurs from day 18 to day 21
- The Notochord induces the overlying ectoderm to differentiate into neuroectoderm and form the neural plate
- the neural plate folds inward and gives rise to the neural tube, and the cells from the fold will become the neural crest
- The Notochord weill become the nucleus pulposus of the intervertebral discs
Alar and Basal plate
- The intermediate zone of the early neural tube has an alar plate and basal plate
- Alar plate (dorsal): sensory
- Basal plate (ventral): motor
Vesicles of developping brain
- 3 vesicle stage:
- Prosencephalon (Forebrain)
- Mesencephalon (Midbrain)
- Rhombencephalon (hindbrain)
- 5 vesicle stage:
- Telencephalon -> cerebral hemispheres; lateral ventricles
- Diencephalon -> thalamus; third ventricle
- Mesencephalon -> midbrain; cerebral aqueduct
- Metencephalon -> pons, cerebellum; upper part of fourth ventricle
- Myelencephalon -> Medulla; lower part of fourth ventircle
Neural tube defects
- Due to a failure of fusion of the Neuropores (happens around the fourth week)
- This leads to a persistent connection between the amniotic cavity and the spinal canal
- They are associated with low folic acid intake before conception
- Findings:
- Elevated alpha-fetoprotein (AFP) in amniotic fluid and maternal serum
- Elevated acetylcholinesterase (AChE) in amniotic fluid is a helpful confirmatory test (it lesks out from the fetal CSF)
Spina bifida occulta
- Failure of bony spinal canal to close, but there is no structural herniation
- Usually seen at lower vertebral levels
- Dura is intact
- Associated with tuft of hair or skin dimple at level of bony defect
Meningocele
Meninges (but not the spinal cord) herniate through spinal canal defect
Meningomycele
Both the meninges and the psinal cord herniate through the spinal canal defect
Anencephaly
- Malformation of anterior neural tube resulting in no forebrain, open calvarium (“frog-like apperance”)
- Associated with maternal diabetes (type I)
- Maternal folate supplementation decreases risk
- Findings:
- Increased AFP
- Polyhydramnios, because there is no swallowing center in brin
Holoprosencephaly
- Failure of hemispheres to separate, usually during weeks 5-6
- Complex multifactorial etiology; may be related to mutations in sonic hedgehog sinaling pathway
- Moderate form has cleft lifp/palate
- Most severe form results in cyclopia
Chiari II (Arnold-Chiari) malformation
- Significant herniation of cerebellar tonsils and vermis through the foramen magnum
- Leads to aqueductal stenosis and hydrocephalus
- Often presents with thoraco-lumbar myelomeningocele and paralysis below the defect
Dandy-Walker malformation
- Agenesis of cerebellar vermis
- Cystic enlargement of 4th ventricle (fills the enlarged posterior fossa)
- Associated with hydrocephalus and spina bifida
Derivatives of Nueroectoderm
- CNS neurons
- Ependymal cells (line ventricles; make CSF)
- Oligodendroglia
- Astrocytes
Derivatives of Neural crest
- PNS neurons
* Schwann cells
Derivatives of Mesoderm
Microglia (e.g., Macrophages) {Microglia like Macrophages originate from Mesoderm}
Properties of Neurons
- Signal-ptransmitting cells of the nervous system
- Permanent cells–do not divide in adulthood; as a general rule, have no progenitor stem cell population
- Dendrites receive input, and axons send output
- Cell bodies and dendrites can be stained via Nissl substance (stains RER), since RER is not present in the axon
- Axon injury leads to Wallerian degeneration: degeneration distal to injury, and axonal retraction proximally; allows for potential regeneration of axon (if in PNS)
Properties of Astrocytes
- Physical support and repair in CNS
- K+ metabolism
- Removal of excess neurotransmitter
- Maintain the blood-brain barier
- Reactive gliosis in response to injury
- GFAP is marker for astrocytes
Properties o Microglia
- CNS phagocytes of mesodermal origin
- Not readily discernible in nNissl stains
- Hame small, irregular nuclei and relatively little cytoplasm
- Scavenger cells of the CNS
- Respond to tissue damage by differentiating into large phagocytic cells
- HIV -infected microglia fuse to form multinuclated giant cells in the CNS
Properties of Myelin
- Wrap and insulate axons, leading to increased space constant and increased conduction velocity
- Increase conduction velocity of signals transmitted down axons
- Lead to saltatory conduction of action potentials between nodes of ranvier (where there are high concentrations of Na+ channels)
- Oligodendrocytes (CNS) and Schwann cells (PNS) are the myellinating cells of nervous system
Properties of oligodendroglia
- Each oligodendrocyte myelinates multiple CNS axons (up to 50 each)
- In Nissl stain, they appear as small nuclei with dark chromatin and little cytoplasm
- Predominant type of glial cell in white matter
- Look like fried eggs on H&E stains
- Oligondendrocytes are destroyed in multiple sclerosis
Properties of Schwann cells
- Each Schwann cell myelinates only one PNS axon
- Also promote axonal regeneration
- Derived from neural crest
- Schwann cells are destroyed in Guillain-Barre syndrome
Acoustic neuroma
Type of schwannoma typically located in internal acoustic meatus (CN VIII)
Free nerve endings
- Can be C fibers (slow, unmyelinated)
- Or can be A-delta fibers (fast, myelinated)
- Located on all skin, epidermis, and some viscera
- Sense pain and temperature
Meissner’s corpuscles
- Large, myelinated fibers
- adapt quickly
- Located on glabrous (hairless) skin
- Sense dynamic, fine/light touch, position sense
Pacinian corpuscles
- Large, myelinated fibers
- Located in deep skin layers, ligaments, and joints
- Sense vibration, pressure
Merkel’s discs
- Large, myelinated fibers
- adapt slowly
- Located on hair follicles
- Sense pressure, deep sstatic touch (e.g., shapes, edges), position sense
Structure of peripheral nerves
- Endoneurium invests single nerve fiber layres
- There is inflammatory infiltrate in Guillain-Barre
- Perineurium (Permeability barrier) surrounds a fascicle of nerve fibers
- Must be rejoined in microsurgery for limb reattachment
- Epineurium is a dense connective tissue that sourrounds the entire nerve, including fasicles and blood vessels
Synthesis and change in disease of Norepinephrine (NE)
- Synthesized in Locus ceruleus (Pons)
- increased in anxiety
- Decreased in depression
Synthesis and change in disease of Dopamine
- Synthesized in ventral tegmentum and SNc (midbrain)
- Increased in schizophrenia
- Decreased in depression
- Decreased in Parkinson’s
Synthesis and change in disease of Serotonin (5-HT)
- Synthesized in Raphe nucleus (pons)
- Decreased in anxiety
- Decreased in depression
Synthesis and change in disease of Acetylcholine (ACh)
- Synthesized in Basal nucleus of Meynert
- Decreased in Alzheimer’s
- Decreased in Huntington’s
- Increased in REM sleep
Synthesis and change in disease of GABA
- Synthesized in Nucleus accumbens
- Decreased in anxiety
- Decreased in Huntington’s
Behavior associations of Locus ceruleus
Stress and panic
Behavior associations of Nucleus accumbens and spetal nucleus
Reward center, pleasure, addiction, fear
Blood-brain barrier (BBB)
- Prevents circulating blood substances or bacteria from reaching the CSF/CNS
- Restricts drug delivery to the brain
- Formed by 3 structures:
- Tight junctions between nonfenestrated capillary endothelial cells
- Basement membrane
- Astrocyte foot processes
- Glucose and amino acids cross slowly by carrier-mediated transport mechanism
- Nonpolar/lipid-soluble substances cross rapidly via diffusion
- Infarction and/or neoplasm destroys endothelial cell tight junctions, leading to vasogenic edema
Regions of brain with fenestrated capillaries and no BBB
- Allow molecules in the blood to affect brain function (e.g., area postrema - vomiting after chemo; OVLT - osmotic sensing)
- Allow neurosecretory products to enter circulation (e.g., Neurohypophysis - ADH release)
- Hypothalamic inputs and outputs permeate the BBB
Other notable blood barriers
- Blood-testis barrier
* Maternal-fetal blood barrier of placenta
Function of the Hypothalamus
- Inputs (these areas are not protected by the BBB):
- OVLT: sense change in osmolarity
- Area postrema: responds to emetics
- {TAN HATS}
- Thirst and water balance
- Adenohypophysis (anterior pituitary) control via hormones
- Neurohypophysis (posterior pituitary) releases hormones produced in the hypothalamus
- Hunger
- Autonomic regulation
- Temperature regulation
- Sexual urges
Lateral area of the hypothalamus
- Positively controls hunger {If you zap your lateral nucleus, you shring laterally}
- Inhibited by leptin
- Destruction leads to anorexia, failure to thrive
Ventromedial area
- Positively controls satiety {If you zap your ventromedial nucleus, you grow ventrally and medially}
- Stimulated by leptin
- Destruction (e.g., craniopharyngioma) leads to hyperphagia
Anterior hypothalamus
- Positively controls cooling {Anterior nucleus = Cooling, pArasympthatic; A/C}
- Parasympathetic control
Posterior hypothalamus
- Positively controls Heating {If you zap your Posterior hypothalamus, you become a poikilotherm (cold-blooded, like a snake)
- Sympathetic control
Suprachiasmatic nucleus
Controls circaidan rhythm {You need sleep to be charismatic (chiasmatic)}
Posterior pituitary (neurohypophysis)
- ADH and oxytocin are madeby the hypothalamus but are stored and released by the posterior pituitary
- Receives hypothalamic axonal projections from supraoptic (ADH) and paraventricular (oxytocin) nuclei
- Oxys = quick; tocos = birth
Function of the thalamus
- Major relay for all ascending sensory information (except olfaction)
- Nuclei:
- Ventral posterolateral (VPL) nucleus
- Ventral posteromedial (VPM) nucleus
- Lateral geniculate nucleus (LGN)
- Medial geniculate nucleus (MGN)
- Ventral lateral (VL) nucleus
Ventral posterolateral (VPL) nucleus of the thalamus
- Input: spinothalamic and dorsal column/medial lemniscus
- Information: Pain and temperature, pressure, touch, vibration, and proprioception
- Destination: Primary somatosensory cortex
Ventral posteromedial (VPM) nucleus of the thalamus
- Input: trigeminal and gustatory pathway
- Information: face sensation and taste
- Destination: primary somatosensory cortex
- {Makeup goes on the face (VPM)}
Lateral geniculate nucleus (LGN) of the thalamus
- Input: CN II
- Information: vision
- Destination: Calcarine sulcus
- {Lateral = Light}
Medial geniculate nucleus (MGN) of the thalamus
- Input: Superior olive and inferior colliculus of tectum
- Information: Hearing
- Destination: Auditory cortex of temporal lobe
- {Medial = Music}
Ventral lateral (VL) nucleus of the thalamus
- Input: Basal ganglia
- Information: Motor
- Destination: Motor cortex
Limbic system
- Collection of neural structures involved in emotion, long-term memory, olfaction, behavior modulation, and autonomic nervous system function
- Structures:
- Hippocampus
- Amygdala
- Fornix
- Mammillary bodies
- Cingulate gyrus
- {5 F’s: Feeding, Fleeing, Fighting, Feeling, Sex}
Cerebellum
- Modulates movement; aids in coordination and balance
- Input: {Ipsilateral to body, while brain is contralateral}
- Contralatera cortex via middle cerebellar peduncle
- Ipsilateral proprioceptive information via inferior cerebellar peduncle from the spinal cord
- Input nerves: climbing and mossy fibers
- Output:
- Sends information to contralateral cortex to modulate movement
- Output nerves: pirkinje fibers send information to depe nuclei of cerebellum, which in turn send information to the contralateral cortex via the superior cerebellar peduncle
- Deep nuclei (from lateral to medial): Dentate, Emboliform, Globose, Fastigial {Don’t Eat Greasy Foods}
- Lateral cerebellum: voluntary movement of extremities
- When injured, there is a propensity to fall toward ipsilateral side
- Medial cerebellum: Balance, truncal coordination
Function of Basal Ganglia
- Important in voluntary movements and maing postural adjustements
- Receives cortical input, provides negative feedback to cortex to modulate movement
Components of striatum
- Putamen (motor)
- Caudate (cognitive)
- Anatomically and functionally related
Components of lentiform
- Putamen
- Globus pallidus
- Neighboring nuclei with different functions
Components of substantia nigra
- Substantia nigra pars compacta (SN-C): nigrostriatal dopaminergic neurons
- Substantia nigra pars reticulata (SN-R) similar to globus pallidus interna
Basal ganglia direct (stimulatory) pathway
- The cortext stimulates the striatum via Glu
- The striatum inhibits the GPi/SN-R via GABA
- The GPi/SN-R usually inhibits the thalamus via GABA
- The Thalamus stimulates the Cortex via Glu
• End result: The thalamus is disinhibited, resulting in stimulation of movement
Basal ganglia indirect (inhibitory) pathway
- The cortext stimulates the striatum via Glu
- The striatum inhibits the GPe via GABA
- The GPe usually inhibits the STN via GABA
- The STN usually stimulates the GPi/SNR via Glu
- The GPi/SNR inhibits the thalamus via GABA
- The thalamus usually stimulates the cortex via Glu
• End result: the STN is disinhibited, which inhibits the thalamus, resulting in inhibition of movement
Modulation of direct and indirect pathways by the SNc via Dopamine
- Dopamine binds to D1 receptors in striatum, stimulating the direct pathway; this leads to stimulation of motion
- Dopamine binds to D2 receptors in striatum, inhibiting the indirect; this leads to stimulation of motion
Parkinson’s disease
- Degenerative disorder of CNS associated with Lewy body inclusions (composed of alpha-synuclein)
- Leads to loss of dopaminergic neurons (depigmentation) of substantia nigra pars compacta
- Findings: {your body becomes a TRAP}
- Tremor at rest (e.g., pill-rolling remor)
- cogwheel Rigidity
- Akinesia or bradykinesia
- Postural instability
Huntington’s disease
- Autosomal-dominant trinucleotide repeat (CAG); anticipation
- Caudate loses ACh and GABA
- Leads to loss of striatal projections to Gpe; this leads to disruption of indirect pathway, leading to incrased movement
- Neuronal death via NMDA-R binding and glutamate toxicity
- Atrophy of striatal nuclei can be seen on imaging
- Presentation:
- Chorea
- aggression
- depression
- dementia
- Can sometimes be mistaken for substance abuse
Hemiballismus
- Sudden, wild flailing of 1 arm and maybe the ipsilateral leg
- Characteristic Lesion: Contralateral subthalamic nucleus (e.g., lacunar stroke)
- {Half of body ballistic}
Chorea
- Sudden, jerky, purposeless movements
- Characteristic lesion: Basal ganglia (e.g., Huntington’s)
- (Chorea = dancing)
Athetosis
- Slow, writhing, snake-like movements; especially seen in fingers
- Characteristic lesion: Basal ganglia (e.g., Huntington’s)
Myoclonus
- Sudden, brief, uncontrolled muscle contraction (e.g., jerks, hiccups)
- Common in metabolic abnormalities such as renal and liver failure
Dystonia
- Sustained, involuntary muscle contractions (e.g., Writer’s cramp, blepharospasm)
- Sporadic torticollis (neck) is the most common type of dystonia
Essential tremor (postural tremor)
- Action tremor; exarcerbated by holding posture/limb position
- Genetic predisposition
- Patients often self-medicated with EtOH, which reduced tremor amplitude
- Treatment: beta-blocers, primidone
Resting tremor
- Unctonrolled movement of distal appendages (most noticeable in hands–“pill-rolling tremor”)
- Tremor alleviated by intentional movement
- Characteristic lesion: Parkinson’s disease
Intention tremor
- Slow, zigzag motion when pointing/extending toward a target
- Characteristic lesion: cerebellar dysfunction
Important areas in Frontal lobe
- Principal motor area
- Premotor area (part of extrapyramidal circuit)
- Frontal eye fields
- Motor speech (Broca’s area; dominant hemisphere)
- Frontal association areas
Important areas in Parietal lobe
- Principal sensory areas
* Arcuate fasciculus (damage leads to conduction aphasia)
Important areas of the occippital lobe
Principal visual cortex
Important parts of the Temporal lobe
- Primary auditory cortex
* Associate auditory cortex (Wernicke’s area; dominant hemisphere)
Homunculus
- Topographical representation of sensory and motor areas in the cerebral cortex
- Can be used to localize lesion leading to specific defects (e.g., lower extremity deficit may indicate involvement of the ACA)
- Arrangement:
- Lower extremities medially, upper extremities more laterally
- Face is more lateral than upper extremity, but forehead is more medial and lips are more lateral
Consequence of lesion of Amygdala (bilateral)
- Kluver-Bucy syndrome: hyperorality, hypersexuality, disinhibited behavior
- Associated with HSV-1
Consequence of lesion of Frontal lobe
- Disinhibition and deficits in concentration, orientation, and judgement
- May have reemergence of primitive reflexes
Consequence of lesion of right parietal lobe
- Spatial neglect syndrome: agnosia of the contralateral side of the world
- Normally, right hemisphere is directed to both sides, whicle the left hemisphere is mainly concerned with the right (contralateral) side
Consequence of lesion of Reticular activating system (midbrain)
Reduced levels of arousal and wakefulness (e.g., coma)
Consequence of lesion of Mammillary bodies (bilateral)
- Wernicke-Korsakoff syndrome: confusion, opthalmoplegia, ataxia, memory loss (anterograde and retrograde amnesia), confabulation, personality changes
- Associated with thiamine (B1) deficiency and excessive EtOH use
- Can be precipitated by giving glucose without B1 to a B1-deficient patient
Consequence of lesion of Basal ganglia
- May result in tremor at rest, chorea, or athetosis
* Associated with Parkinson’s disease
Consequence of lesion of Cerebellar hemisphere
- Intention tremor, limb ataxia, and loss of balance
- Damage to the cerebellum results in ipsilateral deficits (fall toward side of lesion)
- {Cerebellar hemispheres are laterally located - affect lateral limbs}
Consequence of lesion of Cerebellar vermis
- Truncal ataxia, dysarthria
* {Vermis is centrally located - affects central body}
Consequence of lesion of Subthalamic nucleus
Contralateral hemiballismus
Consequence of lesion of Hippocampus
Anterograde amnesia: inability to make new memories
Consequence of lesion of Paramedian pontine reticular formation (PRRF)
- Eyes look away from side of lesion
* Usually the PPRF “pulls” eyes to its side
Consequence of lesion of Frontal eye fields
- Eyes look toward lesion
* Usually the FEF “push” eyes away from its side
Central pontine myelinolysis
- Massive axonal demyelinatio in pontine white matter tracts
- Commonly caused by overly rapid correction of Na+ levels
- Leads to acute paralysis, dysarthria, diplopia, and loss of consciousness
- Can caouse locked-in syndrome
- T2-weighted MRI with FLAIR shows abnormal increased signal incentral pons
Location of Broca’s area
Inferior frontal gyrus of frontal lobe
Location of Wernicke’s area
Superior temporal gyrus of temporal lobe
Aphasia vs. dysarthria
- Aphasia: higher-order inability to speak (language deficit)
- Dysarthria: Motor inability to speak (movement deficit)
Broca’s aphasia
- Nonfluent aphasia with intact comprehension
* {Broca’s Broken Boca}
Wernicke’s aphasia
- Fluent aphasia with impaired comphrehension
* {Wernicke’s is wordy but makes no sense; Wernicke’s = what}
Global aphasia
- Nonfluent aphasia with impoaire dcomprehension
* Booth Broca’s and Wernicke’s areas affected
Conduction aphasia
- Poor repetition but fluent speech and intact comprehension
- Can’t repeat phrases such as “No ifs, ands, or buts”
- Can be caused by damage to arcuate fasciculus
Arteries supplying the cortex
- Anterior cerebral artery supplies anteromedial surface
- Middle cerebral artery supplies lateral surface
- Posterior cerebral artoery supplies posterior and inferior surfaces
Watershed zones
- Between anterior cerebral and middle cerebral, or between posterior cerebral and meiddle cerebral arteries
- Damaged in severe hypertesion
- Would lead to upper leg or upper arm wakness, defects in higher-order visual processing
Regulation of cerebral perfusion
- Brain perfusion relies on tight autoregulation that is mainly driven by PCO2 (PO2 also modulates perfusion in severe hypoxia)
- Therapeutic hyperventilation (decreases PCO2) helps decrease intracranial presure in cases of acute cerebral edema (stroke, trauma) via decreasing cerebral perfusion
Effect of stroke in MCA (middle cerebral artery)
- Motor cortex (upper limb and face): contralateral paralysis of upper limb and face
- Sensory cortex (upper limb and face): contralateral loss of sensation of upper limb and face
- Temporal (Wernicke’s area) or frontal (Broca’s area) lobe: Aphasia if in dominant hemisphere (usually left); hemineglect if lesion affects nondominant side (usually right)
Effect of stroke in ACA (anterior cerebral artery)
- Motor cortex (lower limb): Contralateral paralysys of lower limb
- Sensory cortex (lower limb): Contralateral loss of sensation of lower limb
Effect of stroke in Lateral striate artery (branch of MCA)
- Striatum, internal capsule: contralateral hemiparesis (weakness) or hemiplegia (paralysis)
- Common location of lacunar infarcts; secondary to unmanaged hypertension
Effect of stroke in ASA (anterior spinal artery)
- Lateral corticospinal tract: contralateral hemiparesis (lower limbs)
- Medial lemniscus: decreased contralateral proprioception
- Caudal medulla (hypoglossal nerve): Ipsilateral hypoglossal dysfunction (tongue deviates ipsilaterally)
- Stroke commonly bilateral
- Medial medullary syndrome: causd by infarct of paramedian branches of ASA and vertebral arteries: leads to the symptoms described above
Effect of stroke in PICA (Posterior inferior cerebellar artery)
- Lateral medulla (vestibular nuclei, lateral spinothalamic tract, spinal trigeminal nucleus, nucleus ambiguus, sympathetic fibers, inferior cerebellar peduncle): Vomiting, vertigo, nystagmus, decreased pain and temperature sensation to limbs and face, dysphagia, hoarseness, decreased gag reflex, ipsilateral horner’s syndrome, ataxia, dysmetria
- Nucleus ambiguus effects are specific to PICA lesions {Don’t pick a (PICA) horse (hoarseness) that can’t eat (dysphagia)}
- Lateral medullary (Wallenberg’s syndrome) leads to the symptoms described above
Effect of stroke in AICA (anterior inferior cerebellar artery)
- Lateral pons (cranial nerve nuclei, vestibular nuclei, facial nucleus, spinal trigeminal nucleus, cochlear nuclei, sympathetic fibers): Vomiting, vertigo, nystagmus, paralysis of face, decreased lacrimation, salivation, decreased taste from anterior 2/3 of tongue, decreased corneal reflex, decreased pain and temperature sensation on face, ipsilateral hearing loss, ipsilateral horner’s syndrome)
- Facial nucleus effects are specific to AICA lesions {Facial droop means AICA’s pooped}
- Lateral pontine syndrome leads to symptoms described above
- Middle and inferior cerebellar peduncles: Ataxia, dysmetria
Effect of stroke on PCA (posterior cerebral artery)
• Occipital cortex, visual cortex: contralateral hemianopia with macular sparing
Effect of lesion on Anterior communicating artery
- Common site of sacular (berry) anneurism, leading to impingement on cranial nerves: visual field defects
- Lesions are typically aneurysms, not strokes