Neuroanatomy Flashcards
Thalamic blood supply
Primarily PCA + branches (some anterior supply laterally (anterior choroidal->LGN)
Paramedian
Tuberothalamic (PCOM branch)
Inferolateral
Posterior choroidal
Anterior thalamic syndrome
Perseverations, superimposition of unrelated information, apathy, amnesia, emotional facial paresis
Paramedian thalamic syndrome
Disinhibition, loss of self activation, and amnesia, vertical gaze paresis - thalamic dementia
Inferolateral thalamic syndrome
Ataxia, hypesthesia, executive dysfunction (pure sensory, sensiromotor, Dejerine-Roussy)
Posterior thalamic
Hypoesthesia, homonymous horizontal sectoranopsia, aphasia, neglect
Field cuts in LGN
Anterior choroidal
Lateral choroidal form posterior choroidal of posterior circulation
Anterior thalamic nuclei
Anterior, lateral dorsal
Medial thalamic nuclei
Medial dorsal
Lateral thalamic nuclei
VA, VL, VPM/VPL, LGN, MGN, pulvinar
Intralaminar thalamic nuclei
Midline thalamic nuclei - adjacent to third ventricle
Reticular
Thin layer surround thalamus
Thalamic relay nuclei: specific vs non-specific vs intralaminar vs reticular
Specific: unique functional and anatomic correlate to projection (e.g., retina,anterior visual pathway->LGN->occiptal cortex)
Non-specific: pulvinar receives input from multiple sensory modalities (SS, vision) and project to parietal, temporal and occipital association areas
Diffuse relay nuclei with other deep structures (BG, brainstem)
Reticular nucleus - inhibitory intrathalamic, reciprocal projections
What generates sleep spindles
Reticular nucleus
What special sense bypasses the thalamus?
Olfactory
Thalamic nuclei involved in sensory processing
Thalamic nuclei involved in motor control
Thalamic nuclei involved in oriented towards behaviorally relevant stimuli
Thalamic nuclei involved in emotional processing
Intralaminar nuclei
What causes thalamic dementia?
Infarct of paramedian artery or other lesion of DM nucleus
Bilateral thalamic infarcts from single occlusive event?
Artery of Percheron
Which thalamic nuclei does not project to the cortex?
Reticular nucleus - gates stimuli, generates sleep spindles
Which thalamic nuclei does not project to the cortex?
Reticular nucleus - gates stimuli, generates sleep spindles
STN
The only excitatory nuclei from the basal ganglia
Basal ganglia prefrontal circuit
Basal ganglia limbic circuits
BG hypodensities and calcifications are common in what condition?
MELAS
Where do you see bilateral putamen necrosis?
Methanol poisoning
Sxs from BG lesions 2/2 perinatal ischemia may be delayed for…?
7-14 years
BG are prominently affected in what condition?
Leigh’s syndrome
STN lesions result in…?
Contralateral ballismus
Spinal nerve
Formed by the junction of the anterior and posterior roots at the level of the neural foramen (which is just beyond the dorsal root ganglion).
– The anterior roots contain lower motor neuron axons from the anterior horn cells
– The posterior roots contain axons from the sensory cell bodies in the dorsal root ganglion
Spinal Root / Vertebrae Relationships above L1/L2
C1-C7 roots exit through the neural foramina above the corresponding vertebrae
– 1st cervical nerve exits the spinal canal between the Atlas and the occiput and does not project to the skin
The 8th cervical nerve exits the spinal canal between C7 and T1 vertebrae.
– There is no C8 vertebra
All other spinal nerves exit through the neural foramina beneath the vertebrae of their same number
– From T1-L1/2, directly off the spinal cord
– Below L1/2, from the cauda equina
Spinal nerve roots exiting below L1/L2
Below L1/2 in the cauda equina, the nerve roots are organized to exit the spinal canal.
– The nerve root exiting below its vertebrae is quite lateral.
– The nerve root that will be exiting below the next caudal vertebrae is central lateral
– The remaining nerve roots are cental.
Neural foraminal stenosis and disc herniation effects above L1/L2
Neural foraminal stenosis affects the nerve root exiting at that level.
Disc herniation above the conus medullaris affects the nerve root exiting at that level.
Above the C7 vertebrae, the inferior vertebrae for either neural foraminal stenosis or disc herniation correlates with the nerve root affected
- The C5 nerve root is impinged by C4/5 neural foraminal stenosis or disc herniation.
The C8 nerve root is impinged by C7/T1 neural foraminal stenosis or disc herniation.
From T1/2-L1/2, the superior vertebrae for either neural foraminal stenosis or disc herniation correlates with the nerve root affected
- The T5 nerve root is impinged by T5/6 neural foraminal stenosis or disc herniation.
Neural foraminal stenosis and disc herniation effects above L1/L2
Neural foraminal stenosis affects the nerve root exiting at that level.
Typical centro-lateral disc herniation at the level of the cauda equina affects the nerve root exiting 1 vertebral segment below that level.
Far lateral disc herniation at the level of the cauda equina affects the nerve root exiting at that level.
The L5 nerve root is impinged by an L4/5 centro-lateral disc herniation, L5/S1 far lateral disc herniation or L5/S1 neural foraminal stenosis
Radiculopathies
Classically present with neck or low back pain that radiates in the distribution of a nerve root
– Sensory symptoms are often vague because the dermatomes overlap. Focal severe sensory loss argues against a radiculopathy.
– Weakness of the muscles that receive innervation from that nerve root are usually mild to moderate in severity. Complete muscle paralysis is uncommon because the myotomes overlap.
Structural: Herniated discs, Spondylosis, or Mass lesions (metastases, abcess) - common in C5-C7, L5, S1
Infiltration: Carcinoma, Lymphoma, Sarcoid
Infection: Lyme, VZV, CMV, HSV
Infarction: Vasculitis, DM
Demyelination: Early GBS
Spinal nerve sympathetic component
The second order sympathetic neurons arise from the intermediolateral column from T1- L2.
Each spinal nerve from T1-L2 contains sympathetic axons that leave the spinal nerve in a white communicating ramus to enter the sympathetic chain.
– Sympathetic axons synapse at that level or ascend and descend in the sympathetic chain.
All spinal nerves receive third order sympathetic neurons from the sympatheic chain via a gray communicating ramus.
Spinal nerve sensory and motor
Each spinal nerve divides into a
Ventral primary ramus which innervates
-Plexus of a limb: anterior segment sensory receptors, limb / anterior trunk muscles
Dorsal primary ramus which innervates: posterior segment sensory receptors, paraspinal muscles (involvement of paraspinal muscles on EMG is specific but not sensitive for either a spinal nerve (radiculopathy) or anterior horn cell disease)
Conus vs cauda equina lesions
Spinal segments and nerves
There are 31 spinal segments and nerves
– 8 Cervical
– 12 Thoracic
– 5 Lumbar
– 5 Sacral
– 1 Coccygeal
Vertebral bodies
There are 33 vertebral bodies
– 7 Cervical
– 12 Thoracic
– 5 Lumbar
– 5 Sacral
– 4 Coccygeal
Spinal cord vs vertebral segments
Spinal Cord vs. Vertebral Body Levels
C1 cord at C1 Vertebral Body
C8 cord at C7 Vertebral Body
T1 cord at T1 Vertebral Body
T12 cord at T8 Vertebral Body
L1-L5 between T9 and T11 Vertebral Bodies
S1-S5 between T12 and L2 Vertebral Bodies
Spinal cord and vertebral column development
In the 1st Trimester, the spinal cord is the same length as the vertebral column
During fetal development and early childhood, the vertebral column grows while the spinal cord does not grow at same rate
– The spinal cord “migrates” upward
– In the Newborn, the spinal cord ends at L3 – In the Adult, the spinal cord end at L1/2.
Spinal cord tracts
Desending tracts
Appendicular Movement
Lateral Corticospinal tract
Rubrospinal tract
Lateral Vestibulospinal tract
Corticospinal tract decussation at the medulla
80-90% of axons cross in the medullary pyramids prior to forming the lateral corticospinal tract
– Axons to the upper extremity are more medial and anterior in the pyramid and cross rostral to the legs
– 2% of axons do not cross and enter the lateral corticospinal tract
8% of axons do not cross and enter the anterior corticospinal tract
Hemiplegia Cruciata
A lesion in the rostral medial medullary pyramid effecting the upper extremity axons after they have crossed and the lower extremity axons before they cross.
– This results in arm weakness ipsilateral to the lesion and contralateral leg weakness.
Lateral corticospinal cord in the spinal cord
Lateral Corticospinal tract
Descends posteriorly in the lateral compartment of the spinal cord.
– The arm fibers are medial and the leg fibers are lateral.
Synapses on the lower motor neurons in the anterior horn.
– Flexor muscles are medial in Rexed lamina IX and extensor muscles are lateral
Any lesion in the spinal cord, produces ipsilateral weakness.
Rubrospinal tract
Another appendicular movement tract
– Originates from the red nucleus in the midbrain.
– Decussates in the midbrain and descends just ventral to the lateral corticospinal tract in the lateral compartment
– Terminates in the cervical spinal cord
– Partially mediates upper limb flexion
Lateral Vestibulospinal tract
Another appendicular movement tract
– Originates from the lateral vestibular nucleus
– Descends ipsilaterally in the ventral compartment
– Synapses on interneurons that decussate at that level to innervate bilateral medial anterior horn cells that control balance and stimulates appendicular extension
– Partially mediates arm and leg extension
Ventral Corticospinal tract:
Descending axial tract
– Remains ipsilateral in the ventral compartment
– Stimulates axial movement
Tectospinal tract
Descending axial tract
– Originates from the deeper layers of the superior
colliclus.
– Decussate in the dorsal tegmentum and descend in the medial dorsal portion of the ventral compartment of the brainstem.
– Terminates in the cervical spine
– Mediates movement of the neck and upper trunk (probably in coordination with eye movements.
Medial Vestibulospinal tract
Descending axial tract
– Originates from the medial vestibular nucleus and descends bilaterally.
– Also mediates movement of the neck and upper trunk (probably in coordination with eye movements.
Pontine and Medullary Reticulospinal tracts
Descending axial tract
– Receives input from premotor cortex
– Originate in the pontine and medullary reticular formation, respectively
– Descends ipsilaterally in the vental compartment.
– Mediate automatic movement (e.g. maintain posture).
Anterolateral tracts - arms and legs
The lateral spinothalamic tract originates from sensory receptors for temperature and pain. Leg fibers are lateral and arm fibers are medial.
DCML - arms and legs
Arms lateral in cuneate fascilus and legs medial in cuneate gracilis
Spinocerebellar tracts - arms and legs
Dorsal spinocerebellar tract
– Large diameter axons from the legs and trunk synapse on Clarke’s nucleus (C8-L2) in the medial intermediate zone of the ventral horn.
– The axons from Clarke’s nucleus ascend ipsilaterally in the lateral column (lateral to the corticospinal tract).
Cuneospinocerebeller tract (The dorsal spinocerebellar tract for the arms) – Large diameter axons from the arms ascend to the medulla in the cuneatus fassicle of the dorsal columns but bypass the cuneatus nucleus to synapse on the accessory cuneate nucleus.
In the medulla, these axons enter the cerebellum via the inferior cerebellar peduncle.
Spinocerebellar tracts - spinal border cells
Ventral spinocerebellar tract
– Originates from spinal border cells in the thoracic and lumbar ventral horn
– These axons decussate in the ventral commisure and ascend the spinal cord in the lateral column (lateral to the ALS).
Rostral spinocerebellar tract (the Ventral spinocerebellar tract for the arms)
– Originates from spinal border cells in the cervical ventral horn. Also decussate in the ventral commisure to join the ventral spinocerebellar tract.
These axons enter the cerebellum via the bilateral superior cerebellar peduncles. Some fibers decussate again, while others do not.
Blood supply to spinal cord
The spinal cord is supplied by a single anterior spinal artery and a pair of posterior spinal arteries.
– These arteries arise from the vertebral arteries.
The anterior spinal artery supplies the anterior 2/3of the cord, which includes the anterior horn, ALS, and corticospinal tracts.
The posterior spinal arteries supply the dorsal columns.
The spinal arteries narrow in the thoracic cord (may even be noncontiguous).
As a result, the spinal arteries can be divided into 3 longitudinal segments based on their blood supply
– C1-T2: supplied by radicular arteries from the vertebral and ascending cervical arteries
– T3-T7: spinalarteriesfromT3-T7aresuppliedby radicular arteries from intercostal arteries
– T8-conus: suppliedby radicular arteries from the artery of Adamkiewicz
Blood flow to these segments is reconstituted by radiculomedullary arteries.
The radiculomedullary arteries originate from radicular arteries.
Radicular arteries
Radicular arteries originate from segmental arteries, which include the ascending cervical, intercostal, lumbar, and sacral arteries.
There are thirty-one pairs of radicular arteries, each passing through the neural foramina to supply each spinal nerve, the vertebral body and the dura via a small dural branch.
Only 6 to 10 radicular arteries have radiculomedullary branches
– Their exact number and anatomic location is quite variable.
Spinal AVMs
Oculosympathetics
Aniscoria
Physiologic (same in dark/light)
Small pupil (greater in dark) - Horner’s
Large pupil (greater in light) - CN III
None in PURE afferent disease! This has APD
Testing for Horner’s - confirming the dx
Topical cocaine is used to confirm the clinical diagnosis of ocular sympathetic denervation, or Horner Syndrome (HS). Cocaine blocks re-uptake of norepinephrine (NE) by sympathetic nerve terminals in the iris dilator muscle, transiently increasing its concentration in the synaptic junction. Norepinephrine activates alpha1 receptors in the iris dilator to cause pupil dilation. In HS, cocaine fails to dilate the affected pupil as much as the unaffected pupil, but its indirect action makes it a weak dilator, and the test can give equivocal results. Cocaine is also a controlled substance and therefore difficult to obtain. A practical and reliable alternative to cocaine is apraclonidine, an ocular hypotensive agent that has a weak direct action on alpha1 receptors and therefore minimal to no clinical effect on the pupils of normal eyes. Patients with HS have denervation supersensitivity of the alpha1 receptors in the iris stroma of the affected eye, making the pupil dilator responsive to apraclonidine. In patients with HS, reversal of anisocoria occurs after bilateral instillation of apraclonidine 1% or 0.5%.
Cocaine
Urine drug test for cocaine will be positive for a few days after testing (5)
Apraclonidine
Denervation must be present long enough for receptor upregulation to have occurred (14) Positive tests have been noted within hours of a carotid dissection but the onset of denervation sensitivity are variable (15) False negatives can occur in the setting of acute Horner syndrome or in long-standing cases if strict “reversal of anisocoria” criteria used (16, 17) Apraclonidine has limited use in pediatric Horner syndrome due to the risk of CNS and respiratory depression (18)
https://www.ophthalmologyreview.org/articles/horner-syndrome-pharmacologic-diagnosis
Horner’s localization
HYDROXYAMPHETAMINE
Hydroxyamphetamine remains a useful tool for localization of the lesion once a diagnosis of Horner syndrome has been confirmed (20). However, it is limited by accessibility and some considerations detailed below. Since it’s still tested (and important to understand from a mechanistic and historical perspective), you still need to know how it works and what it does.
Mechanism of action: increases the release of norepinephrine from the presynaptic neuron (21). In intact presynaptic (3rd order, postganglionic) neurons, this results in pupil dilation; if this neuron is not intact, the pupil does not dilate.
Note anisocoria (which pupil is small, which pupil is larger)
Instill 1 drop of hydroxyamphetamine (1%) in each eye
Wait 45-60 minutes
Re-evaluate anisocoria
Results:
In patients with normal pupils, there is a symmetric 2 mm dilation of each pupil (anisocoria remains) (22).
In patients with Horner syndrome, the reaction is based on whether or not there is an intact 3rd-order (postganglionic) neuron (23):
Both pupils dilate: intact 3rd-order neuron (localizes to 1st- or 2nd-order neuron)
Only non-Horner pupil dilates: not intact 3rd-order neuron (localizes to 3rd-order neuron)
https://www.ophthalmologyreview.org/articles/horner-syndrome-pharmacologic-diagnosis
Tonic pupil
Adie tonic’s pupil denotes a pupil with parasympathetic denervation that constricts poorly to light but reacts better to accommodation (near response)
Light-near dissociation causes
Pupils in coma
Metabolic - small, reactive
Midbrain - mid position, fixed
Pons - pinpoint
Third nerve (uncal) - dilated, fixed
Pupils in coma
Metabolic - small, reactive
Midbrain - mid position, fixed
Pons - pinpoint
Third nerve (uncal) - dilated, fixed
CN IV
Innervates superior oblique - acts to depress, best in ADduction
Inferior oblique
CN III
Action elevation, best in ADduction
Actions of extraocular muscles
Aberrant regeneration of the third nerve
Lid/gaze dyskinesis: retraction on downgaze, adduction
Pupil/gaze dyskinesis: constriction on downgaze, convergence/adduction
Indicates trauma, compressive etiology
Aberrant regeneration of the third nerve
Lid/gaze dyskinesis: retraction on downgaze, adduction
Pupil/gaze dyskinesis: constriction on downgaze, convergence/adduction
Indicates trauma, compressive etiology
Fourth nerve palsy signs
If nerve - ipsilateral eye, if nucleus/fascicle before decussation- contralateral eye
Bincoular, vertical/oblique diplopia, worse in contralateral and down gaze
Fourth nerve palsy often presents with a head tilt away from the affected eye.
With ipsilateral head tilt, the medial utricle is excited.
The medial utricle projects to the contralateral trochlear and oculomotor nucleus through the MLF.
With ipsilateral head tilt, the ipsilateral eye elevates (sup rectus) and intorts (sup rectus and sup oblique) while the contralateral eye depresses (inf rectus) and extorts (inf rectus and inf oblique)
The ocular counterrolling reflex (top) causes a compensatory cyclorotation of both eyes to maintain the subjective visual vertical. On left head tilt, the right eye infraducts and excyclotorts and the left eye supraducts and incyclotorts relative to the position of the head and true vertical. Head velocity signals are encoded by the semicircular canals. The eyes maintain this position tonically because of otolithic inputs from the utricle and saccule on the side of the lower ear. In a right superior oblique palsy (middle right), the right eye is extorted because of the lack of intorsion from the paretic superior oblique. Increased activity to the other intorter—the right superior rectus—causes a hypertropia that worsens when more intorsion is demanded by tilting the head to the right (middle left). A left ocular tilt reaction caused by abnormalities in the vertical vestibulo-ocular reflex projections from the left vestibular system causes a left hypotropia with bilateral torsion in the direction of head tilt (lower right). For each eye, the line through the cornea represents the torsional vertical axis.
Sixth neve palsy
Binocular, horizontal diplopia
Increased in ipsilateral gaze
Worse at distance
Skew deviation
Vertical misalignment
Hypertropia
Midbrain - ipsilateral
Medulla - contralateral
Skew deviation
Vertical misalignment
Hypertropia
Midbrain - ipsilateral
Medulla - contralateral
Downbeat, periodic alternating nystagmus
Localization: cervicomedullary junction,
Downbeat - Clonazepam, lioresal, gabapentin
Periodic alternative - lioresal, phenytoin
Upbeat
Localization: cerebellum, pontomesencephalic, pontomedullary
Convergence retraction
Localization: dorsal midbrain
Brun’s
Localization: cerebellopontine angle
Seesaw
Parasellar>>midbrain
Treatment: Lioresal, clonazepam
Oculopalatal myoclonus
Treatment: Valproic acid, gabapentin
Superior oblique myokymia
Treatment: Carbamazepine, gabapentin
Oculomasticatory myorhythmia
Treatment: CTX
Dx and tx of benign positional vertigo
https://geekymedics.com/dix-hallpike-and-epley-manoeuvres-osce-guide/
Ear down/torsional direction tells you which ear is affected
If upbeat - right PC, if downbeat right AC
Opsoclonus
Features and Causes of Opsoclonus
Dramatic involuntary conjugate multidirectional saccades (saccadomania)
Differs from flutter (no vertical component)
Causes:
- Paraneoplastic (neuroblastoma, anti-Ri, anti-Hu antibodies)
- Postinfectious, encephalitis
- May be benign in neonates
CRAO
Inherited retionpahties - leukodystrophies (Tay-Sachs, Niemann-Pick)
Cherry red spot
Inherited retionpahties - VHL
AD
Retinal angiomas, cerebellar hemangioblastoma
Inherited retionpahties - Kearns-Sayre syndrome
Mitochondrial disorder
Retinal degeneration, chronic progressive external ophthalmoplegia, cardiac conduction defects
Inherited retionpahties - Tuberous sclerosis
Autosomal dominant
Retinal hamartoma, epilepsy, adenoma sebaceum, renal angiomyolipoma, cardiac rhabdomyoma, ungual fibroma
Inherited retionpahties - SCA type 7
AD
Retinal degeneration and progressive ataxia
Acute papilledema
Chronic papilledema with hemorrhages resolved and “champagne cork gloss”
Pseudopapilledema
IIH
Foster Kennedy Syndrome
Optic nerve swelling and contralateral optic nerve pallor Intracranial mass (i.e., subfrontal meningioma) causing compressive optic neuropathy and papilledema
Optic neuritis
Nonarteric ischemic optic neuropathy
Nonarteric ischemic optic neuropathy
Ischemic optic neuropathy
Inflammatory optic neuropathy
Temporal arteritis
Compressive optic neuropathy
Optic neuropathy and neoplasms
Leber’s hereditary optic neuropathy
Mitochondrial, maternal inheritance (11778)
9:1 male predominance
Age 20-30
Painless sequential visual loss
Hyperemia, mild swelling, telangiectasias
Leber’s hereditary optic neuropathy
Mitochondrial, maternal inheritance (11778)
9:1 male predominance
Age 20-30
Painless sequential visual loss
Hyperemia, mild swelling, telangiectasias
Kjer’s dominant optic atrophy
Temporal excavation
Childhood presentation, insidious onset, then stable course
OPA gene mutation
Toxic/nutritional optic neuropathies
Painless, insidious, symmetric
Centrocecal scotoma
Causes: Tobacco-alcohol, B12, ethambutol, amiodarone
Optic nerve hypoplasia
Surrounding visible sclera
Evaluate for: Septo-optic dysplasia (DeMorsier’s syndrome)
– Absent septum pellucidum – Endocrine abnormalities – Cortical heterotopia
Superior disc hypoplasia associated with maternal diabetes
Chiasmal field deficits
Junctional scotoma
Inferior nasal fibers carries visual inferior from superior temporal visual field of contralateral optic nerve
Visual fields in LGN - anterior choroidal vs posterior choroidal
Optic radiations
Optic radiations
Occipital field defects
Macular sparing
The favored explanation for why the center visual field is preserved after large hemispheric lesions is that the macular regions of the cortex have a double vascular supply from the middle cerebral artery (MCA) and the posterior cerebral artery (PCA). If there is damage to one vascular pathway, like in the case of a MCA or PCA stroke, there is still another blood supply that the macular portions of the visual cortex can rely on. Vision in the center of the visual field is then preserved whereas vision in peripheral areas is lost due to the resulting infarct.
Cortical layers
I – molecular (aka tangential) layer. Abuts pia. Consists of horizontal cell axons and dendrites from pyramidal cells in other layers. NO CELL BODIES
II - external granular layer. Granule cell dendrites from molecular layer and axons to deeper layers.
III - external pyramidal (suprastriate) layer. 2 sublayers of pyramidal cells 1) superficial-medium cells (ipsilateral) 2) deeper-large cells (contralateral). dendrites reach to layer I, and axons to other cortical areas.
IV - internal granular layer (external band of Baillarger). stellate cells which mediate between inputs from other areas to pyramidal dendrites and axons, and from pyramidal dendrites and axons. Often divided into two sublayers IVa and IVb. External band of Baillarger is dense horizontal plexus of myelinated fibres in this layer.
V - internal pyramidal layer. pyramidal cells intermingled with granule and Martinotti cells. The dendrites of the large-sized pyramidal cells reach to layer I, the dendrites of the small-sized pyramidal cells reach only to layer IV, or stay within layer V.
VI – polymorphic layer (aka multiform or fusiform layer). Consists of spindle cells with axons perpendicular to the cortical surface. Larger ones send dendrites to layer I and smaller ones to layer IV.
White matter cortical connections
Projection fibers to and from the cortex - internal/external capsule
Commissural Fibers between hemispheres - anterior and posterior commissure and corpus callosum
Association Fibers between cortical areas within a hemisphere - arcuate fascilius, U fibers
Nucleus accumbens
Seen where the caudate and putamen are not divided by the anterior limb of the internal capsule
Septal nuclei and Nucleus Basalis of Meynert
Amygdala
Hippocampal formation
Papez circuit
Developmental of ventricle system
Ventricular System
Begins as a hole or space in the middle of the developing nervous system that runs from the most rostral end (lamina terminalis) down through the spinal cord
As the brain vesicles grow, the ventricular system grows and expands along with it.
BBB
Regulated interface between the peripheral circulation and the CNS
Components include endotheilial tight junctions, basal lamina, astrocyte processes
Tight junction is an intricate complex of transmembrane (junctional adhesion molecule-1, occludin, and claudins) and cytoplasmic (zonula occludens-1 and -2, cingulin) proteins linked to the actin cytoskeleton
A small number of regions in the brain (circumventricular organs, pineal gland) do not have a blood–brain barrier
Generally permeable to smaller, lipophillic molecules
Impermeable to most macromolecules, microorganisms
Specific activated transport for glucose and amino acids
Parasympathetic nervous system
Cell bodies located in the brain and sacral (S2-4) spinal cord
– Axons exit via cranial or sacral nerves and synapse with neurons located in a ganglion that is integrally associated with the target organ/viscera (Long pre-synaptic and short post-synaptic)
– Sacral paraspympathetic innervation includes bladder, ureter, kidneys, rectum, and colon beyond the left colonic flexure
Parasympathetic nervous system
Cell bodies located in the brain and sacral (S2-4) spinal cord
– Axons exit via cranial or sacral nerves and synapse with neurons located in a ganglion that is integrally associated with the target organ/viscera (Long pre-synaptic and short post-synaptic)
– Sacral paraspympathetic innervation includes bladder, ureter, kidneys, rectum, and colon beyond the left colonic flexure
Sympathetic nervous system
The second order sympathetic neurons arise from the intermediolateral column from T1-L2.
Each spinal nerve from T1-L2 contains sympathetic axons, which can either
– Leave the spinal nerve in a white communicating ramus to enter the sympathetic chain to either synapse at that level or ascend and descend in the sympathetic chain.
– Continue on to synapse in collateral ganglia (celiac, superior mesenteric, and inferior mesenteric ganglia) near their target.
All spinal nerves receive third order sympathetic neurons from the sympatheic chain via a gray communicating ramus.
CERVICAL spinal nerves do not have white rami, but they do have grey rami
Recall that there are eight cervical nerves -> eight sets of grey rami.
The cervical ganglia have undergone fusions
– superior cervical ganglion joins to C1-4
– middle cervical ganglion connects to C5 and C6
– inferior cervical ganglion connects to C7 and C8
Spinal nerves below L2 do not have white rami, but they do have grey rami
All presynaptic fibers for ganglia L3-5 and S1-4 enter the lateral chain via white rami of L1,L2.
Unlike with the cervical ganglia, there has been no fusion between any of the lumbosacral series
The coccygeal ganglia merge into a single midline ganglion.
Functional divisions of the cerebellum
Functional Divisions
Vestibulocerebellum: flocculus and nodulus
– Modulates gaze holding
Spinocerebellum (somatotopically organized): vermis and intermediate hemispheres
– The vermis modulates movement of the axial muscles. The dorsal vermis modulates saccadic accuracy
– The Intermediate hemispheres modulate limb movement.
Cerebrocerebellum: lateral hemispheres
– Plans movement and modulates fine movements.
Microanatomy of the cerebellum
The cerebellar circuit is a 3 or 4 neuron arc.
Mossy fibers enter the cerebellum to synapse and excite granular cell neurons, which excite Purkinje cell neurons, which inhibit deep cerebellar nuclei
Climbing fibers from the inferior olive enter the cerebellum to synapse directly and excite Purkinje cell neurons, which inhibit deep cerebellar nuclei
Cerebellar interneurons modulate this arc.
Modulating Interneurons of the Cerebellum
Stellate and Basket cells inhibit Purkinje cells – Basket cells have a stronger effect because they
synapse closer to the cell body.
Golgi cells inhibit granular cells
In total, all intrinsic cerebellar neurons are inhibitory except the granular cells!
Guillain-Mollaret Triangle
CL dentate
Aniscoria
Pathologic Anisocoria is always an Efferent Problem
Midbrain syndromes
CN III: nerve vs. nucleus
Ptosis and superior rectus are bilateral in lesions of the nucleus
CN VI: Lesion of peripheral nerve vs nucleus
Peripheral nerve - atrophy of ipsilateral LR, ipsilateral eye deviated medially, diplopia
Nucleus - inability to move moves both eyes past midline to look ipsilateral to the lesion, atrophy of ipsilateral LR, but not contralateral medical rectus
Horizontal eye movement dysfunction (VI)
Nuclear VI vs 1 and 1/2 syndrome
Nuclear VI affects both the ipsilateral lateral rectus muscle and the contralateral MLF
1 and ½ syndrome affects the ipsilateral abducens nucleus or PPRF (thereby affecting the ipsilateral later rectus and contralateral MLF) and the ipsilateral MLF
Pontine syndromes involving the 6th nerve
Cavernouos sinus
ICA
III, IV, VI
V1, V2
Cavernous sinus vs superior orbital fissure vs orbital apex
Lesions involving 3rd, 4th, 6th nerves and V1 (2)
Brachial plexus - what you need to know
Remember To Drink Cold Beer
Roots Trunks Divisions Cord Branches
MARMU
Musculocutanoeus Axillary Radial Median Ulnar
ULNAR nerves from the posterior cord
Upper subscapularis nerve Lower subscapularis nerve Nerve to lastissimus dorsi Axillary Radial
Good video https://www.youtube.com/watch?v=UlDFSlRBeCE&t=1089s
Radial nerve
Posterior interosseous nerve (superficial branch) - cutaneous innervation of lateral aspect of dorsal hand
Triceps - arm extension (at the axilla or more proximal only)
Brachioradialis - arm extension when half pronated
Extensor carpi radialis longus - wrist extension and medial deviation
Supinator - supination
Posterior interosseous nerve (deep branch) - wrist, finger, and thumb extension
Median nerve
Sensation over the radial aspect of palm of the hand and thumb and finger tips - distinction between via forearm vs via CT
Pronator teres - forearm pronation
Flexor carpi radialis - wrist flexion
Anterior interosseous muscles - inability to make OK sign (flexor digitorum profundus 2&3, flexor pollicis longus)
Via carpal tunnel - finger flexion, thumb abduction (abductor pollicis brevis)
Ulnar nerve
Sensation over medial aspect of hand - palmar +/- dorsal, depending on where the compression is
Flexor carpi ulnaris - wrist lateral flexion
First dorsal interosseus) - finger abduction/adduction
Flexor digitorum profundus 4&5 - 4th and 5th digit flexion
Lumbar plexus
L1-L4 (part with obturator)
I (twice) Got Lunch On Friday
Posterior - lateral femoral cutaneous and femoral, rest are anterior
Sacral plexus
L4 (part without obturator)-S4
Each branch will come from three nerve roots and if you put them in order the branches of the lumbrosacral plexus will start with one nerve root lower than the preceding branch
Obturator nerve
Sensation as below - small aspect of medial thigh
Adduction brevis, longus, magnus - thigh adduction
Femoral nerve
Sensation - medial aspect of thigh and lower leg
Hip flexion - femoral above the inguinal canal, not below; innervated by L1-L3 (psoas) and L2-L3 (illiaus) from branches off the femoral above the inguinal canal
Quadriceps vastus, rectus femoris - knee extension
Sciatic nerve
L4-S3 (L5-S2 tibial and common perineal (other sources say L4-S3))
Sensation to lateral lower leg - involving tibial and perineal territories
Semimembranosus, semitendinosus - hip extension
Tibial nerve
Part of the sciatic nerve nerve (L5-S2 (other sources say L4-S3 like sciatic))
Sensation to lateral aspect of the back of the lower leg and dorsum of the foot
Ankle and toe plantarflexion (calf): S1
Soleus
Gastrocnemius
Plantaris
Popliteus
Flexor digitorum longus
Flexor hallucis longus
Foot Inversion: Tibialis posterior L5
Peroneal
Common peroneal = fibular (L5-S2 (other sources say L4-S3 like sciatic) , predominantly L5)
Sensation to the lateral aspect of the front of the lower leg
Biceps femoris short head
Superficial peroneal
Peroneus longus and brevis - foot eversion
Deep peroneal
Extensor hallucis + digitorum longus - toe dorsiflexion
Tibialis anterior - ankle dorsiflexion
Upper arm weakness
Lower arm weakness
Hand weakness
Thigh weakness
Foot drop
Can’t stand on toes
Horner’s syndrome - sympathetic pathway
3 neuron pathway
1) 1st order: central - originate in the posterior hypothalamus and descend through brainstem to the first synapse located in the lower cervical and upper thoracic spinal cord (C8 to T2, aka clilospinal center of Budge)
2) Second order neurons exist spinal cord, travel near apex of lung, under subclavian artery, and ascend the neck and synapse in the superior cervical ganglion, near the bifurcation of the carotid artery at the level of the angle of the mandilbe
3) The third order neurons travel with the carotid artery - vasomotor and sweat fibers branch off at the superior cervical ganglion near the level of the carotid bifurcation and travel to the face with the ECA. The oclumosympathetic fibers continue with the ICA through the cavernous sinus to the orbit, where they travel with V1 division of the trigeminal nerve to their destinations.
Pathways that control horizontal eye movement
The PPRF is also known as the conjugate gaze center for horizontal eye movements.
The PPRF receives contralateral cortical input. Normally, on horizontal eye movement initiated by the contralateral premotor frontal cortex, the PPRF activates the ipsilateral abducens nerve nucleus and, thus, the ipsilateral lateral rectus muscle.
From the activated ipsilateral abducens nerve nucleus, fibers cross the midline, enter the contralateral MLF, and activate the contralateral medial rectus subnucleus of the oculomotor complex and, thus, the contralateral medial rectus muscle. The end result is a finely coordinated gaze deviation to one side, with abduction of one eye and adduction of the other.
Optic neuritis
Develops over hours to days and is associated with symptoms of reduced color perception (especially red → red desaturation), reduced visual acuity, visual loss, eye pain and photopsias.
⅓ patients have papilla’s with hyperemeia and swelling of the disc, blurring of disc margins, and distended veins. The rest of the cases have only retrobulbar involvement and therefore have a normal fundoscopic exam.
Treatment: IV Solumedrol followed by oral prednisone taper
Anterior ischemic optic neuropathy (vs PION)
AION is considered to be the most common optic nerve disorder in patients older than age 50. It can also affect the retrobulbar optic nerve in isolation, in which case it is termed posterior ischemic optic neuropathy (diagnosis of exclusion).
AION is a result of ischemic insult to the optic nerve head. Clinically, it presents with acute, unilateral, usually painless visual loss, although 10% of patients may have pain that can be confused with optic neuritis. Fundoscopic examination shows optic disc edema (unless retrobulbar), hyperemia with splinter hemorrhages, and crowded and cupless disc.
The painless vision loss is one key feature in differentiating AION from optic neuritis, which is often associated with painful eye movements.
Visual pathways
In contrast to giant cell arteritis (GCA), the optic disc edema in AION is more often hyperemic rather than pallid, as would be more common in GCA.
Optic atrophy, signs of chronic optic neuritis - persistent visual loss, color desaturation (especially red), and possibly a persistent relative afferent pupillary defect. In optic atrophy the disc appears shrunken and pale, especially in the temporal half, and this pallor extends beyond the margins of the disc.
Skull foramina and contents
Brachial plexus key points
The upper extremity receives innervation from the C5 to T1 nerve roots. In the intervertebral foramina, the motor and sensory roots join to form a spinal nerve, which then branches into ventral and dorsal rami before exiting the foramina. The ventral (anterior) rami of these nerve roots join to form a plexus of nerves known as the brachial plexus
The point where the C5 and C6 nerve roots meet is called Erb’s point.
The cords are named according to their relationship to the axillary artery.
As discussed and shown in Figure 9.5, both the dorsal scapular nerve and the long thoracic nerve arise directly from the ventral (anterior) rami of the nerve roots.
Median nerve
The median nerve is derived from the lateral and medial cords. The median nerve runs down the midline of the arm and crosses over the brachial artery to lie just medial to it as it passes under the bicipital aponeurosis in the antecubital fossa. In the forearm, the median nerve innervates pronator teres, flexor carpi radialis, and flexor digitorum superficialis. In the forearm, the median nerve gives off the anterior interosseous nerve that innervates flexor digitorum profundus to the second and third digits, flexor pollicis longus, and pronator quadratus.
Before entering the carpal tunnel, the median nerve gives off the palmar cutaneous sensory nerve, a pure sensory nerve. The median nerve then passes through the carpal tunnel (discussed in question 14) and gives off the thenar motor branch, which innervates abductor pollicis brevis and opponens pollicis. The median nerve also innervates the first and second lumbricals.
The lumbrical muscles of the hand flex the fingers at the metacarpophalangeal (MCP) joints, and extend them at the interphalangeal (IP) joints.
The median nerve provides sensory innervations to the lateral (radial) two-thirds of the palm and the distal dorsal aspect of the first to third digits and the distal lateral (radial) half of the fourth digit through the palmar cutaneous nerve and through digital branches.
The median nerve is prone to injury with supracondylar fractures. Median nerve palsy can also occur due to entrapment in ligaments or between muscles (
Sciatic nerve
The sciatic nerve originates from the L4, L5, S1, S2, and S3 roots. This nerve is the largest nerve in the body, and gives off two initial branches: the superior and inferior gluteal nerves. The superior gluteal nerve innervates the gluteus medius, minimus, and tensor fasciae latae. The inferior gluteal nerve innervates the gluteus maximus (Table 9.2).
The sciatic nerve is composed of two different nerves running together: the tibial nerve medially and the common peroneal nerve laterally. Both are in the same sheath, but remain separated throughout their course with no intercrossing fibers. The common peroneal nerve is more prone to injuries, because it is smaller, more lateral, and has less supportive tissue.
- In the thigh, the tibial division innervates the adductor magnus: adduction, semimembranosus+ semitendinosus: knee flexion, and long head of the biceps femoris: knee flexion. The short head of the biceps femoris: knee flexion is supplied by the common peroneal division. The tibial nerve then continues in the posterior aspect of the leg and gives innervation to the gastrocnemius, soleus, and tibialis posterior.
- The tibial nerve gives off the sural nerve that provides sensory innervation to the lateral aspect of the leg and foot.
- The peroneal nerve continues, and after the popliteal fossa, it passes behind the fibular head and divides into the superficial and deep peroneal nerves. The superficial peroneal nerve gives off branches to the peroneus longus and brevis, which permit foot eversion. The deep peroneal nerve supplies the tibialis anterior, extensor hallucis, extensor digitorum longus and brevis, and peroneus tertius.
- The superficial perineal nerve innervates the skin in the lower two-thirds of the lateral aspect of the leg and dorsum of the foot.
- _A lesion in the deep peroneal nerve produces foot drop with inability to dorsiflex the foot without impairing eversion of the foo_t. Preservation of foot inversion distinguishes peroneal neuropathy from L5 radiculopathy, in which the tibialis posterior muscle (innervated by the tibial nerve) is involved, impairing foot inversion.
- The sensory territory of the deep peroneal nerve is the web space between the first and second toes.
Femoral nerve
The femoral nerve is a large nerve that originates from the posterior divisions of L2, L3, and L4
- Travels through the psoas major muscle which it innervates, then through the iliacus muscle which it also innervates. After this course, the femoral nerve passes under the inguinal canal into the femoral triangle, located lateral to the femoral artery.
- It then divides into several terminal branches. There are three cutaneous branches: (1) the medial femoral cutaneous, (2) the intermediate femoral cutaneous, and (3) the saphenous nerve. These branches carry sensory information from the anteromedial thigh, medial leg, medial malleolus, and arch of the foot.
- The motor branches provide innervation to the quadriceps (rectus femoris, vastus lateralis, medialis, and intermedius), sartorius, and pectineus (Table 9.3).
- The patellar reflex is carried through the femoral nerve.
Femoral nerve injury will manifest as
- Weakness in hip flexion and knee extension, loss of the patellar reflex, and sensory findings in the anteromedial thigh and medial leg.
- The femoral nerve can be injured in the retroperitoneal or intrapelvic space, or at the inguinal ligament.
- Clinically, the distinction between injury at these sites can be made by detection of weakness on hip flexion, reflecting psoas compromise (before the inguinal canal), and electrophysiologically by the presence of fibrillations in the iliacus muscle. Both these muscles are innervated proximal to the inguinal ligament, and their compromise will suggest an intrapelvic injury rather than an inguinal injury.
- At the inguinal region, the femoral nerve can be damaged by inguinal masses or hematomas, during hip surgery or perineal surgeries, especially associated with prolonged lithotomy position, such as in this case.
It is important to distinguish femoral nerve injury from L2-L3-L4 radiculopathy and lumbar plexopathy. The presence of impairment of other nerves will suggest these possible diagnoses.
- For example, adductor weakness suggests involvement of the obturator nerve, which can occur in L2-L3-L4 radiculopathy or a lumbar plexopathy.
- Also, the presence of w_eakness in the distal lower extremity muscles will imply injury to other nerves, excluding a selective femoral nerve injury_.
- Abnormal SNAPs do not correlate with a radiculopathy from an intraspinal canal lesion, because SNAPs will be normal in these lesions
Reflexes
Tibial nerve - detailed
The tibial nerve is a division of the sciatic nerve, and at the level of the thigh, it provides innervation to the semimembranosus, semitendinosus, and long head of the biceps femoris (see Fig. 9.8) →knee flexion.
Proximal to the popliteal fossa, the tibial division of the sciatic nerve separates from the peroneal division and gives off the sural nerve, which provides sensory innervation to the lateral (posterior) aspect of the leg and foot. The tibial nerve then continues down the leg innervating the gastrocnemius + soleus: ankle plantar flexion, tibialis posterior →foot inversion, flexor digitorum longus, and flexor hallucis longus→toe plantar flexion
At the medial ankle, the tibial nerve passes under the flexor retinaculum through the tarsal tunnel and gives three terminal branches - calcaneal: pure sensory and innervates the heel, medial planter: innervates the abductor hallucis, flexor digitorum brevis, and flexor hallucis brevis, as well as the skin of the medial sole, and lateral plantar: innervates the abductor digiti quinti pedis, flexor digiti quinti pedis, adductor hallucis, and interossei, as well as the skin of the lateral sole.
An entrapment neuropathy of the tibial nerve at the level of the tarsal tunnel will not produce weakness on plantarflexion. This entrapment neuropathy may manifest with burning pain in the plantar region, worse with standing and walking, with sensory deficits in the sole and sometimes atrophy in this area. Sensation in the dorsum: top of the foot is normal, as well as the ankle reflex.
Ulnar nerve*
The ulnar nerve is a continuation of the medial cord. The medial cord gives a contribution to the median nerve and then gives off two branches: (1) the medial brachial cutaneous nerve and (2) medial antebrachial cutaneous nerve, which provide sensory innervation to the medial half of the arm and forearm, respectively. It then continues as the ulnar nerve. The ulnar nerve predominantly carries C8 and T1 fibers. If the upper extremity were to be divided into upper arm (above the elbow), forearm (elbow to wrist), and hand (below the wrist), the ulnar nerve does not innervate any muscles in the upper arm.
At the elbow, it emerges from the triceps and enters the postcondylar groove, a bony canal between the medial epicondyle and the olecranon of the ulna. This is where the ulnar nerve is most susceptible to injury (see questions 41 and 45). The ulnar nerve then travels down the forearm, where it gives branches to flexor carpi ulnaris and then flexor digitorum profundus to the fourth and fifth digits. It gives off two sensory branches: (1) the dorsal ulnar cutaneous nerve and (2) palmar ulnar cutaneous nerve. Proximal to the wrist it is joined by the ulnar artery.
The ulnar nerve then enters the hand via Guyon’s canal, which is bounded by the carpal bones dorsally and laterally, the transverse carpal ligament medially, and the palmar carpal ligament ventrally (the ulnar nerve does not pass through the carpal tunnel). The ulnar nerve then bifurcates into a deep motor branch and a superficial sensory branch distal to Guyon’s tunnel. The deep motor branch innervates hypothenar eminence muscles: abductor digiti minimi, flexor digiti minimi, and opponens digiti minimi. The ulnar nerve provides motor innervation to many of the intrinsic hand muscles, which are largely involved in fine finger movements: the fourth and fifth lumbricals, and the dorsal and palmar interossei. It also innervates two thenar muscles: (1) adductor pollicis and (2) flexor pollicis brevis.
The ulnar nerve provides sensory innervation to the hypothenar eminence, the palmar and dorsal medial portion of the hand, fifth digit, and half of the fourth digit.
Ulnar nerve sensation
With lesions at or distal to the wrist, sensation over the hypothenar eminence is spared because the palmar cutaneous branch arises proximal to Guyon’s canal.
Radial nerve*
The radial nerve is a continuation of the posterior cord. It carries C5, C6, C7, and C8 fibers (C5, C6: BR, C7, C8 Triceps for reflexes).
- The first branch of the radial nerve is the posterior cutaneous nerve to the arm.
- In the arm, the radial nerve gives branches to long, medial, and lateral heads of the triceps muscle (it is the sole innervation of the triceps) and then travels along the spiral groove (see Table 9.6 for root innervations and action of the muscles innervated by the radial nerve).
- It then gives off the posterior cutaneous nerve, which runs with the radial nerve in the spiral groove of the humerus.
- In the spiral groove, the radial nerve gives off the lateral cutaneous nerve to the arm.
- Distal to the spiral groove, it gives branches to the brachioradialis (a forearm flexor), and extensor carpi radialis longus and brevis.
Distal to the elbow, it bifurcates into the posterior interosseous and superficial sensory radial nerves. The posterior interosseous nerve innervates extensor carpi ulnaris, extensor digitorum communis, extensor digiti minimi, abductor pollicis longus, extensor pollicis longus and brevis, and extensor indices.
The radial nerve provides sensory innervation to the posterior arm through the posterior cutaneous nerve to the arm, to the lateral arm via the lateral cutaneous nerve to the arm, and to the posterior forearm through the posterior cutaneous nerve to the forearm. The superficial sensory radial nerve provides sensory innervation to the dorsolateral half of the hand, the proximal two- thirds of the thumb (including the lateral thumb, over the anatomic snuffbox), and the second and third digits (discussed in question 66). Remember that the distal dorsal aspects of the second and third digits are innervated by the median nerve.
Anterior interosseous nerve syndrome
The anterior interosseous nerve is a pure motor branch of the median nerve and innervates flexor digitorum profundus to the second and third digits, flexor pollicis longus, and pronator quadratus (Table 9.1). Weakness of these muscles, in the absence of sensory loss, suggests isolated involvement of the anterior interosseous nerve, as can occur with trauma, fracture, or in neuralgic amyotrophy (Parsonage–Turner syndrome; see question 52). Patients complain of weakness in grasping objects with their thumb and index finger, and on attempt to make an “okay sign,” the distal phalanges are unable to flex, and instead, the fingertip pulps touch.
Median nerve*
