Flotte’s Outline of

Neuroscience

Edward R. Flotte, 2008

Home

NEUROANATOMY

Brainstem

Cranial nerves

· Cortical fibers synapse directly on V, VII, NucAmb, XII (NOT on III,IV,VI,DMNX)

· Corticobulbar fibers bilateral except to lower VII (contra) & XII.

I (Olfaction)

· SVA.

· 1° receptor cells (= bipolar cells) in mucosa, axons form olfactory nerve, through cribiform plate > 2°: mitral & tufted cells (= glomeruli) in bulb, (also has granule cells – no axons, inhibitory); > Olf. Tract >

1. Lateral olfactory stria: to anterior olfactory nuc. (aka olfactory tubercle, > medial forebrain bundle and stria medullaris), amygdala, and pyriform cortex (=primary, area 34, > entorhinal cortex (=secondary), DM thalamus, prefrontal cortex (conscious perception, input from pyriform and DM thalamus)), or

2. Medial olfactory stria > septal area, anterior commisure to contralateral areas

· Olfactory tubercle neurons project to directly, not to olfactory tract/bulb

· In mucosa: sustenacular cells support, basal cells are receptor precursors – olfactory neurons are only ones to continually regenerate.

· There are >2000 different receptor cells for odorants. Use G-proteins > cAMP or IP3. 2 specific glomeruli in bulb for each odorant.

· Accessory olfactory system: For detection of pheromones, rudimentary in humans. Vomeronasal organ > vomeronasal/ terminal n. (“13^th cranial nerve, CN0”) > accessory olfactory bulb > Vomeronasal nucleus in amygdala. Contain GnRH cells – related to GnRH cells in hypothalamus, mediates sexual dimorphism

· CN0 has Schwann cells > schwannoma

II Optic

· CNS tract – has oligodendroglial, not Schwann cells.

· SSA.

· (rods/cones) > bipolar cells (1°) > ganglion cells (2°) > 3° centers:

1. LGB > visual cortex (conscious vision) or

2. Pretectal/EW nuclei (pupillary reflex, see below) or

3. Superior colliculi (> tectopontine (> cerebellum) & tectospinal tracts; pursuit, head/neck mvmt) or

4. suprachiasmatic nucleus of hypothalamus (circadian rhythms)

Retina

· Part of CNS – has blood-retina barrier & Muller glia.

Receptor cells: rods/cones.

· Rhodopsin (rods) > transducin (G-protein) > PDE > cGMP to GMP > ¯ Na & Ca current (hyperpolarizing) > ¯ glutamate release to bipolar cells (> “on-center” cells stimulated, “off-center” cells inhibited, “on-center” bipolar cells stimulate its ganglion cells and inhibit ganglion cells from “off-center” bipolar cells also);

· Rods = B/W, dim light. Cone = color, daylight. Both Use glutamate.

· Conduct by electric conduction, not action potentials.

Ganglion cells

· Only cells in retina that can initiate action potential.

· Types:

o W = small, slow, tonic & phasic to SC & pretectum, dark;

o X (or P) = medium sized, tonic, to layers 3-6 LGB & pretectum, color; parvocellular stream;

o Y (or M) = rapid, phasic to layers 1&2 LGB & SC, B&W, magnocellular stream;

Horiztontal cells: Synapses from & to depolarize rods/cones for lateral inhibition

Amacrine cells: Bipolar > Amacrine > Ganglion cells

Fovea (center of macula) contains only cones. Rod goes to amacrine cell before ganglion cell.

Lateral Geniculate Body (LGB)

· Ipsilateral layers 2,3,5. Contralateral layers 1,4,6.

· Layers 1&2 magnocellular, 3-6 parvocellular,

· 3&4 off-center, 5&6 on-center (1&2 mixed).

· Ganglion cells and LGB cells have “on-center, off-surround” concentric fields.

Cortex

· Primary: Area 17

o Layer IVCa = magnocellular input, layers IVCb & IVA = parvocellular input,

o Layer IVB = cortical input, has stripe of Genarri

· Secondary: Areas 18 (±19) (no stripe of Gennari).

· No concentric fields, cells repond to lines, borders.

o Simple cells = position & orientation of line, rectangular fields.

o Complex cells = orientation, movement (not position in field).

o Hypercomplex cells = length, shapes.

· Ocular dominance columns in cortex alternate eye dominance, have orientation & location specificity.

o Together strips form ocular dominance bands.

o Absent in 2 areas of area 17: those representing blind spot of retina & monocular temporal crescent.

o Orientation columns also exist.

o Hypercolumn: 2 adjacent columns w/same field from each eye.

· Magnocellular stream: “where stream”.

o Y-cells > Layer 1/2 LGB > area 17 (layer IVCa) > parietal cortex.

o Spatial, movement, orientation (visual neglect, apraxia).

· Parvocellular stream: “what stream”

o X-cells > Layer 3-6 LGB > area 17 (layers IVCb & IVA) > inferior temporal.

o Color, shape (faces, etc. visual agnosias, achromotopsias)

· Critical period exists where inputs from both eyes need to form cortical connections. In amblyopia in kids patch dominant eye intermittently. NMDA receptors mediate connection forming.

Superior colliculi: lesion gives loss of pursuit (tracking) eye movement

Blindsight: nonconscious response to visual stiumli (ie threat) – from noncortical projections, superior colliculus

III Oculomotor

· GSE to extraocular mm: Superior rectus, inferior rectus, inferior oblique, medial rectus

· Levator palpebrae: Mullers muscle = sympathetic, less severe ptosis

· Parasymathetics (GVE): EW to short ciliary nn. (sympathetic = long & short) to iris (constriction) and ciliary mm. (accomodation).

· Accomodation: Ganglion cells(2°) to LGB to cortex to (directly and indirectly) EW & CN3 (motor) nuclei (not to pretectal nuclei) to Ciliary muscles (meridional and circular fibers)

o Causes eyeball to narrow, lens to relax and become more spherical for accommodation

· Pupillary light reflex: no LGB. (1°) bipolar cells in retina to (2°) ganglion cells to (3°) pretectal nuclei to (4°) EW nuclei (via posterior commisure) to (5°) ciliary ganglion to short ciliary nerves to iris

· Sympathetics to pupil: 1° hypothalamus > via hypothalamospinal tract > 2° C8-T3 lateral horn (Ciliospinal center of Budge) > 3° superior cervical gangion > around ICA > short & long ciliary n. > iris & Mullers muscle

· Runs between the PCA and SCA

IV Trochlear

· GSE

· Superior Oblique > eye down & In; only crossed n.;

· Lesion: worst = downgaze to opposite side.

· Bielschowskys sign: head tilted to opposite side; eye up & in. Difficulty walking down stairs.

V Trigeminal

· V1 = ophthalmic > SOF > nasociliary & lacrimal nn.

· V2 = maxillary > inferior orbital fissure or foramen rotundum.

· V3 = mandibular > foramen ovale.

· Motor (SVE): Motor nucleus of V (pons) > tensor palatini & tympani (hypoacusis), mastication (temporalis, masseter, pterygoids, anterior belly of digastric, mylohyoid). Weakness causes deviation of jaw away.

· Sensation (GSA):

o V1,2,3 > Trigeminal (aka Semilunar, Gasserian) ganglion (1°) > spinal tract of CNV > principal sensory nucleus (2°, touch, wide range of pressure, large receptive fields, in pons) and spinal nuclei of V (2°, pain/temp, in medulla down to C2).

§ Trigeminal Ganglion is in Meckle’s Cave

o Mesencephalic nucleus: proprioception, pressure. Contains 1° neurons (only nucleus in CNS w/1° sensory neurons, from neural crest, analogous to sensory ganglia).

· Tracts:

o Ventral trigeminothalamic = pain, crossed (from principal sensory & spinal).

o Dorsal = touch, uncrossed (principal sensory only).

o Both to VPM.

VI Abducent

· GSE.

· Lateral Rectus.

· Longest CN.

· Nerve lesion causes unilateral lateral gaze paralysis. Nuclear lesion causes deviation away bilaterally (i.e. of both eyes), gaze toward lesion is paralyzed (opposite of frontal eye fields) called “lateral gaze paralysis”

· PPRF – horizontal gaze center adjacent to CN6 nucleus.

o Inputs from cortex (FEFs), cerebellum, SC, & vestibular nuc.

o Output to cerebellum, vestibular nuc., pretectal region, IN of Cajal & Nuc. of Darkshevich to integrate horizontal & vertical eye movement

· Stimulation: rostral = vertical gaze; caudal = ipsilateral horizontal.

VII Facial

· Geniculate ganglion: sensory/ taste cell bodies only.

· Nervus intermedius carries sensory & parasympathetic fibers.

Parasympathetics (GVE): Input from hypothalamus & solitary nuc.

1. Superior salivatory nuc. (1°) > greater petrosal n. > pterygopalatine gang. (2°) > lacrimal gland

2. Superior salivatory nuc. (1°) >chorda tympani > submandibular gang. (2°) > submandibular, sublingual glands.

· Lesion distal to geniculate ganglion has no decreased lacrimation, greater petrosal n. already off

Motor (SVE): Facial nucleus > staepedius (hyperacusis), stylohyoid, posterior belly of digastric (anterior from CN5), facialmm. (part of motor nucleus supplying lower face receive crossed input only from cortex)

Taste (SVA): Anterior 2/3 tongue. Chorda tympani > geniculate ganglion (1°) > rostral nucleus solitarius (2°) > central tegmental tract > VPM thalamus (± parabrachial nuc. of pons) > insular cortex (perception) (parabrachial > amygdala/ hypothalamus for emotional response)

· Sweet (sucrose), bitter (alkaloids), & umami (glutamate) receptors are metabotropic, sour (H+) & salty (Na) are ionotropic. (Spicy-hot mediated by trigeminal nerve)

· Receptors may respond to multiple tastes, but usually 1 preferentially.

Sensation: ear (GSA), soft palate (GVA) > spinal nuc of V

Mobius syndrome: congenital absence of both facial nuclei (± abducens nucleus)

VIII Auditory

· SSA

· BAER: I° cochlear n. > II° cochlear nuc > (via trapezoid body) > III° Superior olive > IV° lateral lemniscus/ nucleus > V° Inf. Colliculus > VI° MGB > VII° Cortex

· Dorsal cochlear neurons bypass Sup olive & lateral lemniscus nuc, to Inf Coll (III°)

· Lesions above trapezoid body cause partial deafness (contra > ipsilateral)

· Commisure of Probst: in between lateral lemniscus nuclei. Also has Inferior Colliculi commissure.

Cochlea:

· Sound enters scala vestibuli, transmitted to scala media by Reissner’s membrane.

· Hair cells in scala media (organ of Corti) sit on basilar membrane, touch tectorial membrane; sit in endolymph (high K, low Na).

· Vibrations at apex have lower frequency.

· Scala vestibuli & tympani contain perilymph, communicates w/CSF.

· Cochlear nerve (bodies in spiral ganglion) synapse on hair cells.

Cochlear nuclei:

· Fibers group into 3 acoustic striae: ventral, dorsal (from respective nuclei) & intermediate (from both). Dorsal = high frequency, ventral = low. Ventral to superior olive, dorsal direct to inferior colliculus.

Superior olive:

· Attenuates loud sounds.

· Input is from contralateral cochlear n. via trapezoid body;

· Output is via olivocochlear bundle back to contralateral cochlea directly to hair cells to ¯ sensitvity to sounds and to tensor tympani (V3) and stapedius (7)

· Medial Sup. Olive = time differences

· Lateral Sup Olive = intensity difference

Trapezoid body is only commissure needed for sound localization

Cortex:

· AI = area 41, A2 = area 42.

· Area 22 = auditory association area.

· Wernickes = posterior area 22.

· Prosody = Right opercular (posterior temporal =- comprehension of prosody)

Vestibular system

· Utricle > superior vest ganglion > Lateral vestibuluar nucleus

· Saccule:

o Posterior part > inferior vest ganglion > inferior vestibular nucleus.

o Anterior part > Superior vestiblar ganglion > lateral vestibular nucleus.

· Detect linear movement: utricle in long axis of body, functions when upright; saccule in dorsoventral plane, fuctions when supine.

· When head is erect: utricle is horizontal, saccule vertical.

· Sensation occurs in macula – contain otoliths & hair cells.

Semicircular canals: Angular movement. Ampulla (dilation at 1 end) contains endolymph and crista ampullaris – sensory organ). Fluid remains still but hair cells move.

• Hair cells > Horizontal SC & anterior SC (aka superior) to superior ganglion, posterior SC to inferior ganglion (1°) > Vestibular nerve > medial & superior vestibular nuclei or floculonodular lobe directly (2°)

Vestibular nuclei:

· Lateral: (Dieter’s) from utricle ( & anterior saccule?) to lateral vestibulospinal tr. – extensor tone/posture; inhibited by anterior lobe of cerebellum; has no connections w/other nuclei;

· Inferior: from posterior saccule to cerebellum; integrates input from vestibular labyrinth & cerebellum;

· Medial: largest, crossed to all extraocular nuclei & cerebellum, medial vestibulospinal tract to neck mm.;

· Superior: uncrossed to CN3,4;

· Interstital: cells lie among fibers of vestibular root

MLF:

· Ascending: from medial & superior vestibular nuclei to CN 3,4,6 nuclei to control eye movement.

· Descending: medial vestibulospinal tract & medial reticulospinal tract to cervical cord motorneurons to influence head/trunk movements relating to eye & vestibular movement (from superior colliculus, PPRF, IN of Cajal, & medial vestibular nucleus).

Caloric nystagmus: COWS = fast phase, deviation is reverse

Postrotatory nystagmus: Slow phase in direction of rotation, fast phase opposite

IX Glossopharyngeal

Motor (SVE): Nuc. Ambiguus > stylopharyngeus

Parasympathetic (GVE): Inf salivatory nuc > tympanic n./plexus > lesser petrosal n. > otic gang. (2°) > parotid

Sensation (GSA): middle ear (tympanic n.), pharynx > Superior Gangion (1°) > Spinal Nuc of V

Carotid Sinus (GVA): Herrings n. > CN9 > Inferior Ganglion (1°) > nucleus solitarius (2°) > DMN of X ( BP decreases HR, TPR, force, BP, CO)

Carotid Bodies (SVA): Chemoreceptor (CO2) > Inf Ganglion > Reticular Formation > Reticulospinal fibers > inspiration.

Taste (SVA): nuc. Solitarius > VPM thalamus > postcentral gyrus

X Vagus

Motor (SVE): nuc. Ambiguus > pharyneal br. (all mm except stylopharyngeus (IX) and tensor veli palatini (V)) > sup. Laryngeal n. > internal (sensory) & external laryngeal (cricothyroid)

Recurrent laryngeal=(off ganglion)all laryngeal except cricothyroid

Taste (SVA): > solitary nuc.

Aortic sinus (GVA) Inf ganglion > solitary nuc.

Aortic Bodies (SVA): > Inf Ganglion > Reticular Formation

Parasympathetic (GVE): dorsal motor nuc.

Sensory (GSA): ear > spinal tract 5.

XI Accessory

· SVE.

· C1-6, to trapezius, SCM

XII Hypoglossal

· All tongue mm. except palatoglossus (X).

· Exits preolivary sulcus.

· GSE (not SVE – comes from somites not brachial arches).

· UMN crossed from contralateral cortex (UMN causes deviation away)

CN Nuclei

Nuc. Ambiguus: motor (9,10,11)

Solitary nuc.: rostral = taste (7,9,10), caudal = carotid sinus/body (9)

Superior salivatory: parasympathetic (7); Inferior salivatory: parasympathetics (9) (both in reticular formation)

Dorsal motor nuc. = parasymathetic (10)

Ganglia: Nodose = inferior vagal; Gasserian = CN5

Brainstem syndromes

Wallenbergs (lateral medullary): CN5 (ipsilateral facial analgesia), 8 (vertigo), 9, 10 (hoarse,etc), sympathetics (ipsilateral Horner’s), solitary nuc. (taste), cuneate/gracile nuc. (ipsilateral numbness), spinothalamic tract (contralateral pain/ temp loss – only 1 contralateral); no weakness

Webers: ventral midbrain; CN3 w/crossed hemiplegia

Claude: dorsal midbrain; CN3 w/ataxia

Benedikts: CN3 w/ ataxia and hemiplegia

Parinauds: upgaze palsy, loss of accomodation (fixed pupils) – only 1, large pupils w/ light/ near dissociation, convergence nystagmus, nystagmus retractorius, lid retraction

Millard-Gubler: base of pons, CN6 & 7 and contralateral hemiplegia

Medial medullary: contralat hemiparesis (not face), contralat numbness, ipsi CN12

Lateral pontine (SCA): ipsi ataxia, contralat pain/temp, deafness, N/V

Locked-in: Bilateral basilar pons

Pseudobulbar palsy: lesion of bilateral UMN corticobulbar tracts above brainstem (eg IC); unable to move eyes, mouth but can yawn & cry (reflexive). Brisk jaw-jerk/reflexes. Also frontal signs, emotional lability may occur due to adjacent frontal fiber damage.

Bulbar palsy: LMN CN palsy (usu IX-XII)

Top-of-the-Basilar: sudden onset AMS, EOM/ pupil/ visual (homonymous hemianopsia) abnormalities, usu. Embolic.

Brainstem Reflexes:

Pupil = 2 & 3.

Dolls = 3 & 8 (VestNuc > PPRF > CN3/6).

Jaw-jerk = 5 only.

Corneal = 5 & 7.

Pupillary = 2 & 3.

Gag = 9 & 10.

Cough = 10 only.

Oculocardiac: V1 to X.

Eye movement

Saccades = frontal eye fields (area 8) & parietal eye fields > contralateral PPRF (parietal synapse in Superior Colliculus 1^st > PPRF). Right PPRF = Right gaze.

Smooth Pursuit = eye > LGB > area 17 > temprorooccipital eye fields (>< FEFs) > dorsolateral pontine nucleus (DLPN) > vermis/flocculus > med vestibular nuc > NPH/CN nuclei;

Lateral Gaze: PPRF, CNVI nuclei (post limb IC);

Vertical Gaze: FEFs > ant limb IC > synapse in riMLF & interstitial nuc of Cajal 1^st > PPRF.

Lesion of one CN6 nuc. impairs both eyes from moving to that side

FEFs go to riMLF/PPRF, not to CN nuclei directly.

Stimulation: rostral PPRF = vertical; caudal PPRF = ipsilateral horizontal; Superior colliculus & FEFs = contralateral horizontal.

Lesion: cortex/ putamen = toward; thalamic = persistent down gaze; pons/ cerebellar = away, pontine = pinpoint; midbrain = towards

Pons/cerebellum (ie contralateral paramedian br. of basilar, contralateral SCA) eyes deviate away; FEFs (contralateral MCA) eyes devate towards

Opticokinetic reflex: keeps eyes straight when head is moving (eg. on a train). Direct opticokinetic path: Retina > nuc of optic tract & Nuc of accessory optic system > cerebellum/vestibular nuc. Indirect path: Same as pursuit path (temporalocciptal cortex); lesion gives defect with target moving towards same side

Nucleus prepositus hypoglossi: provides info to CN6 nucleus about current head/eye position.

Cerebral peduncle: lat>med: POTpontine > corticospinal/bulbar (UE>LE>CN) > frontopontine

Cerebellum

· Stimulation elicits nothing.

Lobes:

· Flocculonodular = vestibular (nystagmus, imbalance).

· Anterior = spinocerebellar, tone (sl. hyperreflexia).

· Posterior = pontine, coordination.

Zones:

· Vermis: truncal ataxia, scanning speech

· Intermediate: appendicular ataxia, hypotonia

· Lateral: tremor, decomposition, dyscoordination, delay of initiation. Note no hypertonia. Hypotonia from vermis or intermediate zones.

· Gait ataxia may be due to cerebellar or posterior column disease (Romberg only + in latter)

· Vermis & IZ have somatotopic organization, not lateral zone.

Layers:

· Molecular: basket, stellate cells.

· Purkinje: Purkinje cells

· Granular: granule, Golgi II cells.

Cells: Granule use glutamate, all others use GABA.

· Parallel fibers to Purkinje dendrites (spiny).

Climbing fibers: from inferior olive, crossed, to Purkinje dendrites (smooth)

Mossy fibers: all others. End in glomerulus (Both: glutamate)

Glomerulus: (granular layer) Mossy fibers & Golgi axons > Granule dendrites

Peduncles:

· Inferior:

o Restiform: All afferent.dorsal spinocerebellar, cuneocerebellar, olivocerebellar (contralateral, largest # of fibers).

o Juxtarestiform: Afferent: vestibulocerebellar (> flocculonodular lobe). Efferent: Cerebellovestibular.

· Middle: All afferent. Pontocerebellar (crossed)

· Superior: Afferent: ventral spinocerebellar, Efferent = Cerebellothalamic.

Cerebellothalamic tract:

· Dentate > decussates at inferior colliculus > contralateral VL (VA?/VPL) > motor cortex.

· VL: head medial, feet lateral, extremeties ventral, back dorsal.

· Only interposed synapse in caudal red nucleus.

· Some fibers descend to contralateral reticular nuclei and inferior olive then decussate back to ipsilateral cerebellar cortex.

Spinocerebellar tracts:

· Dorsal = LE, ICP, from dorsal nucleus of clarke (C8-L2);

· Ventral = LE, contralateral, SCP, L1-S2 cell bodies;

· Cuneocerebellar = UE, analogous to dorsal SCT. All go to anterior lobe.

· Note: propioception from LE in dorsal spinocerebellar, UE in posterior column

Ganglia: medial to lateral:

· Fastigial: to reticular formation & vestibular nuclei

· Interposed: (emboliform & globose) to red nucleus to thalamus to motor cortex

· Dentate: to VL (VA/VPL) thalamus to motor cortex

Inferior Olive: inputs from red nucleus, cortex, and spinal cord to contralateral ICP to cerebellum (ant & post lobes) via olivocerebellar tract

Red nucleus: inputs: 1) interposed nucleus of cerebellum to VL thalamus, 2) cortex. Output: rubrospinal tract, inferior olive (> contralateral cerebellum). Stimulation elicits contralateral flexion

Feedback circuits:

1. Frontal lobe > Pontine nuclei > Cerebellar cortex > Dentate nucleus > VL thalamus > Motor cortex (Area4)

2. Red nucleus > Inferior olive > Cerebellar cortex (ant & post) > Interposed nuclei > Red nucleus

3. Spinocerebellar tracts > Anterior lobe cerebellum > Fastigial Nucleus > Reticular formation/Vestibular Nuclei > Vestibulospinal & Reticulospinal tracts

Diencephalon

Diencephalon: thalamus, hypothalamus, subthalamus, epithalamus (pineal, habenulum, stria medullaris) (metathalamus = geniculate bodies)

Habenulum: Input/Output: septal area/ hypothalamus (via stria medullaris); fasiculus retroflexus (>< VTA >< raphe nuc)

Stria medullaris thalami: anterior thalamus, preoptic, septal areas to habenular nucleus

Pineal

· Composed of glia (5%) & pinealocytes.

· Secretes serotonin (>melatonin). Antigonadotropic.

· Overactivity delays puberty, hypofunction causes precocious puberty.

· Innervated by sympathetic n. – release NE to stimulate melatonin.

· Has corpa arenacea or brain sand (calcifications).

Hypothalamus

· Anterior/medial = parasympathetic; Posterior/lateral = sympathetic

· Ant/post = temperature, lat/med = feeding

· Nuclei:

Preoptic: GnRH (sexually dimorphic)

Suprachiasmatic: circadian rhythym

Supraoptic: ADH, uniform large cells (no distinct groups). Projects to pituitary only.

Paraventricular: oxytocin, distinct cell groups (magnocellular (oxytocin) & parvocellular). Projects to brain stem/spinal cord. Also TRH, CRH.

Arcuate: GHRH, dopamine.

Anterior: parasympathetic, heat loss

Ventromedial: staiety center

Dorsal: stimulation > feeding, savage behavior

Lateral: feeding center

Posterior: sympathetic, heat conservation, wakefulness

Median eminence: where axons from arcuate etc. release releasing hormones into venous plexus

· Pituitary axis:

o Supraoptic & paraventricular nuclei contain magnocelluar neurons > synapse directly on posterior lobe of pitutary. (Both have input from subfornicial organ)

o Arcuate etc. contain parvocellular neurons, synapse on venous plexus in median eminence > anterior pituitary.

· Feeding: Neuropeptide Y feeding thru paraventricular nucleus. Neuropeptide Y containing neurons in the arcutae nuc. Inhibited by leptin from fat cells. VMH & LH centers oversimplified.

· Input: MFB, fornix (hippocampus), stria terminalis (amygdala), DLF (midbrain central grey), retinohypothalamic, nucleus solitarius. Generally from limbic system/ amygdala/ hippocampus – not neoortex.

· Output: MFB, stria terminalis, Dorsal Longitudinal Fasiculus (parallels MFB thru medial hypothalamus), mamillothalamic, mammillotegmental, hypophyseal, descending autonomic

Tuberoinfundibular tract: hormones from arcuate nucleus (tuberal region) released in capillary plexus in median eminence to portal veins to capillaries in anterior pituitary

Supraopticohypophyseal tract: Magnocellular neurons from supraoptic & paraventricular nuclei (histologically identical, both nuclei in supraoptic region) to posterior pituitary

Pituitary

· Anterior lobe from ectoderm (Rathkes pouch), Posterior from neurectoderm (diencephalon)

· Vascular supply: Superior hypophyseal a. to infundibulum, median eminence, pars tuberalis. Inferior hypophyseal a. to pars nervosa. Anterior lobe has no direct supply.

Anterior:

· Pars distalis: hormone secretion. Basophils, acidophils, chormophobes.

· Pars intermedia: basophils, chromophobes, & colloid cysts (remnants of Rathke’s pouch). Produces MSH (melanotropin), stimulates melanocytes to produce melanin

· Pars tuberalis: around stalk. Squamous cells, follicles of suboidal cells, hypophyseal plexus veins

Posterior:

· Pars nervosa & infundibulum.

· Has pituicytes (resemble astrocytes). Has Herrings bodies (storage of ADH & oxytocin) & glomeruli

Thalamus

Sensory:

· VPL (body), VPM (face)(both to 3/2/1), VPI (vestibular), LGB (to 17), MGB (from inf coll. To 41/42, tonotopic)

Non-specific: to parietotemporal association areas:

· Pulvinar: Auditory/vision relay. Projects to sensory association corticies: occipital (18/19), parietal, & temporal (not frontal).

· LP: Output to 5/7 (SIII)

Motor:

· VL (VLo: from GP to area 6/8, VLc from cerebellar/red nuclei to area4);

· VA (from GP, to area6 & nonspecifically to cortex (esp prefrontal) for recruiting),

· Centromedian: (from GP/area4, to putamen. Stimulation at 6-12 Hz produces activity (recruiting) of large areas of cortex)

· All 3 receive input from GP via thalamic fasiculus.

Limbic/Behavioral:

· Anterior /LD: from MB (mammillo-thalamic tract) and hippocampus (fornix), to cingulate.

· DM: to/from prefrontal lobe (also input from limbic structures), affected in Korsakoffs, controls affective behavior/memory, smell (from olfactory areas)

Intralaminar:

· CM: To putamen (see above).

· Parafasicular nuc.: To caudate. Both receive ARAS/spinothalamic input & have diffuse cortical projections for arousal.

· Rostral intralaminar nuclei: thalamic pacemaker.

· Thalamic reticular nucleus: thin sheet on lateral wall. No cortical projections, projects to other thalamic nuclei & reticular formation. Receives all affarents & efferents w/ collaterals. Mostly GABAeric?

· Extremities ventral, back dorsal; head medial, caudal lateral

Basal Ganglia

· Caudate

· Putamen

· Globus Pallidus interna (GPi) and externa (GPe)

· Striatum: Caudate and Putamen

· GP = diencephalon, Put/Caud (& GPe?)= telencephalon.

· Subthalamic Nucleus (STN)

· Substantia Nigra

· Damage: GP = athetosis, STN = hemiballismus, Striatum = chorea, SN = rigidity, tremor

Control intensity & timing of movement

1. Direct Loop: thalamocortical excitation. Cortex (glu) > Striatum (GABA) > GPi (GABA) > VA/VL/CM (glu) > cortex (VL>motor, VA>premotor)

2. Indirect Loop: ¯ thalamocortical excitation: : Cortex (glu) > Striatum (GABA) > GPe (GABA) > STN (glu) > GPi (GABA) > thalamus > cortex

3. Nigrostriatal loop: Facilitates direct loop by D1 receptors & inhibits indirect loop by D2 receptors. Cortex (glu) > Striatum (GABA) > SNpr > SNpc (dop) > Striatum > GP > Thalamus > Cortex.

· D1 receptors on striatonigral neurons, D2 receptors on striatopallidal neurons.

o Dopamine does not directly excite/inhibit striatal neurons, but changes K conduction to raise/lower RMP.

Output

Striatum:

1. to GP: GABA & to GPe = enkephalin (spiny type I), to GPi = substance P (spiny type II) (Aspiny neurons are intrinsic Putamen only)

2. to SNpr (GABA)

GPe: to STN

GPi:

1. Thalamus: Ansa lenticularis + Lenticular fasiculus (Forel’s field H2) > Thalamic Fasiculus (Forel’s field H1) > VA/VL/CM (Thalamic fasiculus also contains fibers from cerebellar dentate nucleus)

2. Pallidotegmental: to VTA

· Thalamostriate fibers: from CM/ parafasicular nuc. to striatum

Subthalamus: Subthalamic nuclei + Zona incerta (grey matter b/t thalamic & lenticular fasiculi). Use glutamate

Substantia Nigra: Neurons contain melanin granules. Fibers to putamen, caudate, sup colliculus, thalamus (not GP). Pars Reticulata: input. Pars compacta: output, dopamine (to spiny neurons in putamen).

Cerebrum

Hippocampus

· Function: integrating short-term memory, assigns salience to stimuli for emotion (modulates limbic system/ hypothalamus) & memory. No olfaction.

· = Subiculum, hippocampus, dentate gyrus All archicortex - 3 layers. (Parahippocampal gyrus has 5 layers).

· Hippocampus proper = Ammon’s horn (Ammon = egyptian god with rams’ head)

· C-shaped: Parahippocampal gyrus (outside) > Subiculum (transition) > hippocampus (CA1>2>3) > Dentate gyrus (hilus = CA4) (curves back over subiculum).

· CA1=parvocellular (vulnerable to anoxia. = Sommer’s sector). CA3=magnocellular

Alveus: white matter b/t hippocampus & temporal horn composed of efferent fibers; most medial portion is Fimbria (> fornix)

Cellular Layers of Hippocampus (in to out): Polymorphic layer (axons,output) > pyramidal cell layer(soma) > molecular layer (input, dendrites). Dentate gyrus: pyramidal cell layer replaced by granule cell layer.

Input:

1. Entorhinal cortex, Via

A. Perforant pathway >dentate (mossy fiber) >CA3 (Schaffer’s collaterals) > CA1 >subiculum) or

B. Alvear pathway (straight to hippocampus),

2. Fornix (septal nuclei, substantia innominata etc)

3. Cingulate cortex

Output:

Fornix: Subiculum / pyramidal cells of hippocampus > alveus > fimbria > fornix.

Subiculum > postcommisural (Main output, to MB, ant thalamus, hypothalamus).

Hippocampus > precomissural (septal area > lateral hypothalamus).

Also direct output to entorhinal cortex & amygdala (small).

Hippocampal commisure: between fornices

Schaffer’s collaterals: branches of pyramidal axons which synapse on other hippocampal cells (i.e. CA3 to CA1)

Dentate: efferent fibers only to hippocampus (mossy fibers).

Indusium griseum: remnants of hippocampus over corpus callosum.

Fornix

· Main efferent from hippocampus.

· Body (rostral to thalamus) > Columns (posterior to anterior commissure).

· Forniceal commissure: aka psalterium. Is rostral to anterior commissure.

Papez circuit

· Probably serves short-term memory (MB, Ant. Thalamus) more than emotion.

· Bidirectional: Subiculum > fornix > MB > MT tract > Ant. Thalamus > Cingulum > entorhinal cortex > subiculum

Amygdala

Function: Interface between cortex and hypothalamus/brain stem for emotional response & emotional memory.

Stimulation: Fear & Rage

Corticomedial group: olfaction, > hypothalamus/pituitary (high concentration of enkephalins, somatostatin, and dopamine)

Central nucleus: input/output to hypothalamus & autonomic brainstem

Basolateral group = cortical, sensory input (temporal), uses glutamate

Input: Olfactory (lateral olfactory stria), taste (Nucleus solitarius), and auditory (temporal cortex). Sensory, prefrontal & cingulate cortex.

Output:

1. Stria terminalis (CM > hypothalamus, septal area),

2. Ventral amygdalofugal tract (BL > hypothalamus, PAG)

3. Diagonal Band of Broca (septal area)

4. Direct: Cortical/ hippocampus/ DM thalamus/ striatum/ brainstem.

Only meager projections back from hippocampus, thalamus & hypothalamus.

Kluver-Bucy: Bilateral damage. Docility, Hyperorality, hypersexulaity, visual agnosia (psychic blindness), hyperphagia, exploring

Limbic system

Amygdala, septal area, hypothalamus, anterior thalamus, anterior cingulate & orbitofrontal cortex, ± hippocampus.

Controls emotion (self & species preservation, learning, emotional processing/ social behavior).

Output of limbic system to brainstem: DLF (hypothalamus), fasiculus retroflexus (habenulum), Mamillotegmental fasiculus, MFB (amygdala/ septal area/ hypothalamus).

General path: hypothalamus (endocrine) > Midbrain PAG > Autonomic & Motor CN nuclei

All tracts are bidirectional.

Limbic system has analogous loops to basal ganglia:

1. Direct path: Limbic/Prefrontal cortex & intralaminar nuclei > NAcc (ventral striatum) > ventral pallidum > DM/Ant thalamus > cortex. responsiveness (memory/ emotion /learning) to stimuli.

2. Indirect Path: same as above but VP > STN > VP. Inhibitory

3. Mesolimbic: Nacc > VTA > Nacc. Excitatory. Analogous to SNpc. (both use dopamine).

LAMP = membrane glycoprotein marker for limbic system neurons

Septal area:

Subcallosal and paraterminal gyrus & septal nuclei (NucAcc, Meynert). Relay for hippocampal afferents to hypothalamus.

Input from fornix (hippocampus), brainstem, hypothalamus (MFB), anygdala (diagonal band of Broca), medial olfactory stria.

Output: MFB to hypothalamus, stria medullaris to habenulum, diagonal band of Broca to amygdala, also hippocampus (fornix), cortex, thalamus, MB. (not basal ganglia)

Medial Forebrain Bundle: septal area to hypothalamus to brainstem (reticular formation & autonomic areas). Bidirectional.

Sunstantia innominata = Nucleus basalis of Meynert.

Ach. Functions in sleep/wake, memory, emotion.

Input: amygdala, olfactory cortex. Output: diffuse cortex (activating). ¯ in Alzheimers.

Mesocorticolimbic system

Midbrain Ventral Tegmental Area (VTA, aka interpeduncular nucleus) to limbic system (NAcc, amygdala, hypothalamus, cortex);

Uses Dopamine; Acts similar to SN in BG system.

excitation of Nacc to stimulation of DM thalamus & limbic cortex to responsiveness to stimuli. Role in positive reinforcement/Addiction

Nucleus accumbens: where putamen & caudate meet anteriorly; functions w/septal nuclei. Recives VTA input. Role in addiction/ gratification.

Reticular system

Functions in pain, autonomic control, posture, eye movements, arousal, sleep/wake.

ARAS: ascending reticular activating system.

Pons & midbrain: locus ceruleus (NE), pedunculopontine nucleus (Ach), ventral tegmental area (Dop) and Raphe nuclei (serotonin) to

1. central tegmental tract to thalamus (intalaminar & reticular nuclei) and

2. medial forebrain bundle to septal nuclei/basal nucleus of Meynert

Raphe nucleus in low pons/medulla is inhibitory (serotonin)

Raphe nuclei & locus ceruleus also send descending fibers to spinal cord. To affect pain transmission (see analgesia)

Nucleus reticularis pontis oralis functions in wakefulness & REM sleep. Excited by hisaminergic neurons in posterior hypothalamus; inhibited by GABAergic neurons in anterior hypothalamus.

Parvocellular Area: BP manitenance, respiration?

Cortex

Neocortex

· 6 layers: Layers 2-3 corticocortical (2&3=association, 3=commisural), 4 = thalamocortical (input), 5=pyramidal (corticospinal), 6= corticothalamic (5&6=projection)

· Homotypic cortex: has typical layers (association areas). Idiotypic/ heterotypic cortex has altered layers (primary motor/sensory areas)

· Has columnar organiztion of 100-300 neurons w/same function.

· Parallel networks for language, attention, learning/memory, face/object recognition, & comportment.

· 2 heteromodal association areas: temporoparietal (sensory integration), and prefrontal (integrates motivation with stimuli – punishment/reward).

Allocortex

· 3 layers.

· Pyriform cortex (paleopallium, 3-5 layers), hippocampus and dentate gyrus (archipallium, 3 layers).

· Note entorhinal cortex = parahippocampus, pyriform cortex = uncus.

Mesocortex

· 3-6 layers.

· Paralimbic areas: cingulate/ subcallosal/ paraterminal gyri, parahippocampal gyrus, temporal pole, insula, & caudal orbitofrontal cortex.

Band of Baillerger: in layer 4b. In area 17 is Stripe of Gennari (not in 18/19 – extrastriate cortex).

Temporal lobe

Superior gyrus = language, middle & inferior = visual discrimination.

Vascular supply: Medial = PCA, superior/lateral = MCA.

Deficits: Bilat middle & inf = psychic blindness, Bilat heschls = deafness, unilat = slight contra loss; vestibular cortex (post to Heschl) = decreased OKN; time perception (either side); dom = auditory leaning, nondom = visual learning

Parietal lobe: Dominant = math/language, Nondominant = spatial perception;

Parietal lesions:

Dominant: Gerstmanns (finger agnosia, right-left confusion, acalculia, agraphia), also alexia, anomia, tactile agnosia, ideational & contsructional apraxia;

Non-Dominant: anosognosia (= neglect, denial of illness), dressing apraxia, topographic memory loss, constructional apraxia, asomatognosia (hemineglect)

Angular Gyrus: visual processing of words; damage causes alexia and agraphia - inability to read/ write with intact speech comprehension, Gerstmann’s

Occipital lobe:

Lesions:

Bilateral: cortical blindness; Anton’s syndrome (aka Anton-Babinski, denial of blindness);

Dominant: simultagnosia (identify parts of picture, not whole thing); prosoprognosia.

Right occiptotemporal: color agnosia, left = color anomia;

Balint syndrome: psychic gaze paralysis/peripheral inattention (bilateral posterior parietooccipital)

Primary motor (Area 4)

· Lesion = hypotonia, paresis (no fine movement); BG lesion = hypertonia.

· Neurons innervate synergistic sets of muscles (not individual mm.)

· Cortical columns represent movements, not individual muscles. Chiefly functions in distal mm.

· Hand area: middle bend of central sulcus

Premotor area (6)

· Planning/ timing.

· Lesion produces apraxia of complex, learned movements, unable to produced delayed response; has homonculus

SMA (medial area 6)

· LE anterior, face posterior.

· Functions in coordinating bilateral movements.

· Stimulation – gross bilateral movement w/urge to move (premotor – discreete movement, requires higher stim, no perception of urge to move).

· Movement on either side activates.

· Lesion –spasticity (vs area 4) and involuntary grasping, akinesia, poverty of speech (all resolve in 6 weeks). Unilateral lesions usually cause no permanent deficits.

· Both SMA & premotor send fibers directly to spinal cord, have homunculi, and higher threshold than MI.

Frontal Eye Fields (area 8)

· Area 8 > Superior colliculus, IN of Cajal, Darkschewitsch Nuc > PPRF > MLF > CN3,4,6 nuc.

· Fibers don’t go to CN nuclei directly.

· For voluntary saccades.

· Stimulation: bilateral deviation away

· Lesion: cant target objects on command (eyes tonically to same side).

Occipital Eye Fields

· aka posterior parietal, temporooccipital (widely dispersed).

· Subserve involuntary smooth pursuit.

· Stimulation: eye deviation away (like FEFs but higher threshold, longer latency).

· Lesion: eye deviation to same side (like FEFs) but can target w/ saccades and have problems following objects

Sensory Cortex

· 3a = muscle spindles, 3b = skin (slow & rapid), 1=rapidly adapt skin, 2 = pressure/joint. Input: 3b > 2 > 1.

· Damage causes topagnosia (decreased localization), astereognosis (no pain/temp loss).

· Each has separate homunculus.

· Vestibular & gustatory cortex lie in operculum.

SII:

· On superior bank of lateral sulcus. Homunculus is inverted.

· Stimulation elicits bilateral sensations.

· Role in identifying objects by touch & storing memories (old view – pain perception)

Somatosensory association (areas 5&7)

Agnosias

· Can’t identify objects.

· Visual = bilateral occipitotemporal (ex Prosoprognosia - faces).

· Tactile = area 40 (supramarginal).

· Auditory = area 22.

Apraxia

· Ideational = dominant parietal, failure to carry out sequences of acts, although can do parts. Have pt act as combing hair w/out comb.

· Ideomotor = Dominant Parietal (supramarginal gyrus/ arcuate fasiculus). Can perform acts spontaneously but not on command. Can conceive movement but not perform until cued; test by using utensils, dressing, etc.

· Note actions conceived in dominant parietal cortex, travels arcuate fasiculus to L frontal & corpus callosum to R frontal for performance.

Aphasia

· Wernicke’s: Receptive. Fluent but unable to comprehend. Paraphasias, “word salad”

· Broca’s: Expressive. Able to comprehend but non-fluent.

· Conduction: impaired repetition (like Wernickes (fluent paraphasic) but with retained comprehension & awareness of deficit),

· Transcortical motor/sensory: normal repetition, echolalia (sensory = temporoparietaloccipital jxn, motor = frontal lobe).

· Brocas & Wernickes both have impaired repetition.

· Pure word deafness (can still read, echolalia) = area 22, anterior (bilateral > left).

· Subcortical (Left BG) lesions may also cause aphasia.

· Exner’s area: superior to Brocas. Causes agraphia without aphasia.

Alexia without agraphia

· Left occipital lobe (geniculocalcarine tract and corpus callosum). Usually has hemianopsia & color anomia.

· With agraphia = left angular gyrus (Gerstmans).

· Without hemianopsia = rare, deep white matter, corpus callosum (not geniculocalcarine)

Color anomia: left mesial occipitotemporal lobe

Achromatopsia: right inferior occipitotemporal (color blindness)

Prefrontal cortex

· Orbitofrontal: social appropriateness (lesion – disinhibition), connects w/limbic system

· Dorsolateral: motivation (lesion – apathy), connects to motor areas.

Fasiculi

· Uncinate: antertior temporal to orbitofrontal

· Arcuate: Superior & Middle frontal gyri to temporal (Wernicke to Broca)

· Cingulate: medial frontal & parietal to parahippocampal.

Corpus callosum

· Does not have projections between areas 1,2,3 (S1),4 (M1), or 17 (V1).

· Section: splenium = unable to read left field; ant. 1/3 = nothing; all = left hand apraxia

· Tapetum: white matter lateral to temporal horn/ atrium (medial to optic radiations)

· Calcar avis: medial to temporal horn/ atrium

Gyri

· Precuneus: medal b/t paracentral lobule (S1) and cuneus (separated by parietooccipital sulcus);

· Lingual: posterior to parahippocampal gyrus (medial to collateral sulcus);

· Occipitotemporal: inferior, lateral to collateral sulcus.

· Inferior frontal: lateral: pars orbitalis > triangularis > opercularis. Medial: gyrus rectus > subcallosal area > paraterminal gyrus. (contiguous w/ cingulate)

· Supramarginal: end of Sylvian fissure.

· Angular: end of superior temoral fissure (more posterior)

o Both separated from superior parietal lobule by intraparietal sulcus.

· Cingulate: between cingulate sulcus (superior) & sulcus of corpus callosum

Corticobulbar fibers

· Project to sensory relay nuclei (gracilis, cuneatus, trigeminal, solitary nuclei), reticular formation, & motor CN nuclei.

· Fibers to gracilus & cuneatus nuclei leave pyramids & transverse reticular formation or medial lemniscus.

· Fibers to trigeminal & solitary nuclei are from frontoparietal cortex.

· Corticoreticular fibers from premotor, motor & sensory cortex to medulla (gigantocellular) & pons (oral pontine).

· Motor fibers from 1° motor area; bilateral except CN 7 (lower) & 12. (However lesion to fibers to 12 is asymptomatic or mild)

· Pseudobulbar palsy requires bilateral lesions.

Internal capsule

· Anterior limb: frontopontine, anterior thalamic radiations.

· Genu: corticobulbar, corticoreticular.

· Posterior limb: Corticospinal, Parieto-occipital-temporal-pontine, superior thalamic radiations, corticofugal fibers

· Sublenticular = auditory radiations, Retrolenticular = visual radiations.

Skull Base

Floor of 4^th ventricle

· Rostral to stria medullares: median eminence > facial colliculus > sulcus limitans.> inferior cerebellar peduncle.

· Caudal (Rhomboid fossa): hypoglossal trigone > vagal trigone. Area postrema most caudal.

· Below 4^th ventricle: dorsal median sulcus > gracile tuburcle > dorsal intermediate sulcus > tuberculum cinereum > dorsolateral sulcus.

· Ventral: pyramid > preolivary sulcus/ XII > olive > postolivary sulcus > IX, X, XI.

3^rd ventricle

· Infundibular recess: ventral to mamillary bodies.

· Floor of 3^rd ventricle: Ant to post: optic chiasm > infundibulum > tuber cinereum > MBs

Lateral ventricle:

· Medial to lateral: fornix/ septal v. > velum/ choroid > thalamus/thalamostriate/anterior caudate v

· Transvelum interpositum approach: between choroid & thalamus (lateral)

Circumventricular organs: pineal, subforniceal (at foramen of Monroe; detects serum osmolarity, controls ADH & oxytocin release, projects to supraoptic nucleus, angiotensin II receptors), subcommisural (below posterior commissure, has BBB), organum vasculosum of lamina terminalis (GnRH & somatostatin release), median eminence of hypothalamus (contains plexus for pituitary releasing hormones), neurohypophysis, area postrema (emesis, paired, sensitive to apomorphine & digitalis, consists of astroblasts & some neurons)

Nasal septum: ethmoid (superior) & vomer (inferior). Cartilage anterior

Orbit: maxilla (inferior), lacrimal (medial anterior), ethmoid (medial posterior), frontal (superior), sphenoid (posterior superior), palatine (posterior inferior), zygomatic (lateral)

Inferior orbital fissure: occ V2

Anterior clinoids: Optic canal & ICA medial, SOF lateral

ICA dural rings: Proximal = oculomotor membrane b/t ICA & CN3, roof of cavernous sinus. Distal = dura.

Lillequist’s membrane: Between CN3 medially, divides interpeduncular cistern from chiasmatic cistern. Seen b/t ICA & CN2.

Cavernous sinus: CN6 only one inside

Tendinous ring: CN2, 3, 6, nasocillary, & ophthalmic a. inside (Outside: frontal and lacrimal nn. off V1, CN4, ophthalmic v.)

Dura: innervation - supratentorial = V, infratentorial = X and C1-3 (no VII)

Falciform ligament: between anterior clinoids, over optic n.

Annulus of Zinn: In the superior orbital fissure. The CN 3,6 and nasocilliary nerve pass through it. Lacrimal, frontal, CN4, and ophthalmic vein travel lateral to it.

Pterion: frontal, greater wing of sphenoid, parietal, squamous temporal

Asterion, Bregma, opisthion

Houghtons lines

Petrous bone: Geniculate ganglion: posterolateral to ICA, posteromedial to formen spinosum, anterior to superior semicircular canal, medial to cochlea; lateral to middle ear cavity. GSPN: runs over & parallel to ICA. Dorello’s canal: contains CN6.

Petrous ICA: drill away Glasscocks triangle posteriormedial to foramen ovale (foramen spinosum to arcuate eminence to GSPN)

Cavum: septum pellucidum, vergae (posterior), velum interpositum (3^rd vent)

Cisterns: Ambient: SCA, CN4, basal v. Rosenthal. Interpeduncular: CN3, basilar a. Quadrigeminal: Vein of Galen. CPA: CN5,7,8, AICA. Prepontine: Basilar a. Lateral cerebellomedullary: PICA, choroid plexus of 4^th ventricle.

Internal Auditory Canal: Facial n.: anterior-superior; Cochlear n.: anterior-inferior; Superior vestibular n.: posterior-superior; Inferior vestibular n.: posterior-inferior

Transverse Crest: separates superior/inferior nerves. Bill’s Bar: separates facial n. from superior vestibular n.

Spinal Cord

Descending Tracts

Lateral motor system = corticospinal + rubrospinal

Medial motor system = vestibulospinal + reticulospinal

Corticospinal tract:

· Lateral: 90%. Cross at decussation.

· Anterior/Ventral: 10%, remain ipsilateral, then cross at level of termination in SC, posture control.

· All synapse on interneurons 1^st (2°) in ventral horn & use glutamate.

· When damaged rubrospinal takes over.

· Babinski from corticospinal (or cortical) damage.

· Note no direct connection to CN 3, 4, 6, DMN vagus.

· From: Betz cells 3%; Area 4 = 30%, area 6 = 30%; area 1,2,3 = 40%.

· 40% of fibers are poorly myelinated.

Rubrospinal tract: (Fibers from cortex 4/6 & cerebellum >) red nucleus > crosses in ventral tegmental decussation > cervical/thoracic cord. Flexor tone.

Vestibulospinal tracts

· Lateral: from lateral vestibular nuc, to all levels SC, extensor tone;

· Medial: from medial vestibular nuc., to cervical cord only, CNXI Nuc. (neck mm.), role in vestibular modulation of head position via neck, runs in MLF.

· Both remain ipsilateral.

Tectospinal: From superior colliculus, reflex movements for sight; cross at origin; to cervical levels only

Reticulospinal tracts

· Pontine reticular nuc > medial reticulospinal tr ipsilateral > extensors.

· Medullary reticular nuc > lateral reticulospinal tr bilateral > flexors & autonomic info.

Ascending Tracts

Lateral spinothalamic

· Pain & temperature

· Body in DRG (1°) > axons enter Lissauer’s tract > synapse in Lamina II on soma (2°) > cross @ level of entry in ventral white commissure > (most fibers to reticular formation = spinoreticular tract) > VPL/ VPI & intralaminar nuclei (3°) > sensory cortex. (some spinoreticular fibers remain ipsilateral)

· Paleospinothalamic tract: C fibers to layer 2 to reticular formation, intralaminar nuclei, PAG; burning pain.

· Neospinothalamic tract: Ad fibers to layer 1 to VPL, sharp pain

· Visceral pain: Ad & C fibers in sympathetic nerves > lamina 7 > spinothalamic tract (parasymathetics carry nonpainful sensation)

Anterior spinothalamic = light touch; cross @ level of entry. To VPL.

Nucleus dorsalis of Clarke: thoracic to C8, layer 7, proprioception, forms dorsal spinocerebellar tract

Dorsal spinocerebellar tract

· Muscle spindles & Golgi tendon organs of LE (1°) > synapse ND of Clarke (lamina 7, T1-L2) @ level of entry (2°) > DSCT > Inferior Cerebellar Peduncle > ipsilateral anterior lobe cerebellum.

· Uncrossed. Detects Individual muscles.

· At levels L3-S5 ascend in fasciculus gracilis to L1/2 then synapse in NDC (2°).

· Ventral: LE, synapses ventral horn (2°) > crosses @ level of entry > VSCT > crosses in pons to contralateral Superior cerebellar peduncle > ant lobe. L1-S2 cell bodies, Golgi tendons organs only, detects muscle groups (whole limb);

· Cuneocerebellar (& Rostral – cats only): UE, analogous to dorsal & ventral; enter @ C1-8 > ascend in fasiculus cuneatus > synapse in accessory cuneate nucleus in medulla (2°) > ant lobe cerebellum.

Dorsal Colums/Medial Lemniscus:

· Touch/Pressure.

· DRG (1°) > Gracilus (LE) / Cuneate (UE) Fasiculus > Gacilus/ Cuneate Nuc. (2°) > decussation > medial lemniscus > VPL thalamus (3°) > area 3/2/1 & SII ( > motor cortex for feedback)

· Note transmits proprioception only from UE, not LE.

· Lateral cervical system: (aka spinocervical thalamic tract). Light touch. Enter C8-L4 > synapse in lamina 4 > ascend in SCTT > synapse in lateral cervical nucleus (C1-4) > medial lemiscus > VPL > area 3/2/1

Rexed’s lamina

· Lamina I: fast pain.

· Lamina II: Substantiosa gelatinosa. Slow pain, ascend/descend several segments in Lissauer’s tract (outside lamina I).

o Both have substance P & glutamate receptors for 1° nociceptive afferents.

· Layer 3& 4: nucleus proprius (touch/pressure/proprioception);

· Layer 7: zona intermedia (dorsal nucleus of Clark);

· Layer 9: motor neurons.

Dorsal roots

· Ganglionic neurons use glutamate, substance P, somatostatin, CCK.

· Roots divide into medial (from encapsulated sensory organs, Golgi,muscle spindles, thick myelin) and lateral (from free nerve endings, thin myelin, pain/temp) bundles. In the spinal cord these divide into ascending & descending branches.

Ventral horn SC: flexors = dorsal, extensors = ventral (same as tracts); trunk = medial, hand = lateral

Somatotopic organization: Cortex, BG, Red nucleus, reticular formation, Vermis & intermediate zone of cerebellum

Anaglesia

PAG (midbrain) & PVG (hypothalamus) (both enkephalin) to nucleus raphe magnus in medulla (serotonin, NE) to dorsal horn of spinal cord (enkephalin) to inhibit nociceptive 1° sensory neuron axons and projection neurons’ dendrites. PAG stimulation elicits fear, diplopia, etc. PVG better tolerated.

Brainstem sections:

Medulla: Inferior Olive, accessory cuneate, dorsal nucleus X, nucleus ambiguus, solitary nucleus

Pons: Superior vestibular nucleus,

Peripheral Nerves

Brachial Plexus: Roots (C5-T1) > Trunks (Upper/ middle/ lower) > Divisions (ant/ Post) > Cords (Lateral/ Medial/ Posterior)

Arise from roots before plexus:

Dorsal scapular: C5. rhomboids, levator scapulae (stabilize scapula).

Long thoracic: C5,6,7. serratus anterior (abduct scapula > winged scapula, cut during axillary node dissection).

Arise from upper trunk:

Suprascapular: supra (abduction) & infraspinatus (ext rot)

Arise from cords:

Lateral & medial pectoral: pectoralis major; (lateral & medial cords)

Musculocutaneous: (lateral) brachialis, coracobrachialis, biceps (elbow flexion)

Median: (lateral & medial cords). Travels w/ brachial a. in arm. Goes thru 2 heads of pronator teres in forearm. Gives off anterior interosseous n. (FPL, index FDP, pronator quadratus). Palmar cutaneous branch: arises 5cm proximal to wrist. Recurrent motor br. To thenar muscles arises distal end carpal tunnel.

Muscles: Hand = LOAF: Lumbricals 1&2, opponens, APB, FPB (superficial); all other flexors/ pronators in forearm, palmaris longus.

Autonomous zone = tip of index finger.

Ulnar: (medial cord). Runs behind medial epicondyle, thru Guyons canal. Dorsal cutaneous branch (sensation to dorsum of digits 4 & 5) leaves in forearm.

Muscles: Adductor pollicis, FPB (deep), hand intrinsics; FCU, FDP3/4

Autonomous zone = tip of little finger

Subscapular: (posterior) teres major (adducts humerus), subscapularis (med rot humerus)

Thoracodoral: (posterior) lattisimus dorsi (adducts shoulder)

Radial: (posterior). Around spiral groove of humerus. Divides below elbow into posterior interosseous (thru arcade of Frohse, all muscles in forearm & hand) and superficial branch (sensory)

Muscles: triceps, brachioradialis (musculocutaneous = brachialis), extensors/ supinator, APL (injury from crutches). If cut in forearm no motor loss, only sensory.

Autonomous zone = 1^st web space dorsum

Axillary: (posterior) deltoid, teres minor (injured with anterior shoulder dislocation)

Thumb:

· Median = LOAF: FPL, Abductor pollicis brevis (perpendicular to palm), opponens,FPB (superfical)

· Ulnar = adductor policis, FPB (deep);

· Radial = abductor pollicis longus (parallel to palm).

· Ad/Abduction is perpendicular to palm, flex/extension is in plane of palm.

Interosseous muscles: palmar = adduct fingers; dorsal = abducts 1&4, flexes

Lumbricals: extends IP joints, flexes MCP joints

Carpal tunnel: contains FPL, FCR, Median N., FDS, FDP

Guyons canal: ulnar a. & n.

Lumbar plexus

Superior gluteal: gluteus medius, min. (thru greater sciatic foramen, above pyriformis m.; inf. Gluteal & sciatic below pyriformis)

Inferior gluteal: gluteus maximus

Femoral: iliopsoas, quads

Obturator: adductors, gracilis

Sciatic: hamstrings (biceps), part of adductor magnus, semitendinous, semimenbranous. To:

Tibial: gastroc, TP, FHL (all foot mm.)

Common peroneal: to

Superficial peronal: peroneus longus & brevis

Deep Peroneal: Tib ant, extensors

Biceps fermoris only has innervation from peroneal component of sciatic n. > differentiate sciatic from peroneal n. injuries

Ilioinguinal n.: at risk in appendectomies (McBurneys incision)

Ulnar n. vs C8 root injury: ulnar n. splits 4^th digit, C8 covers entire finger. C8: EMG ¯ ECU (radial), APB (median), paraspinous mm, NCV normal. Plexus (Lower trunk/ medial cord): normal paraspinal, abnormal sensory median antebrachial cutaneous n.

Radial n. vs C7 root: C7: FCR (median). Posterior cord: deltoid.

Peroneal n. vs L4/5: L4/5: loss of foot invertors

Femoral n. vs L3: L3: loss adductors/ quads

Spinal Anatomy

C1: has no dorsal ramus

Odontoid: 2 primary ossification centers at base, 1 secondary at apex.

Canal diameter: Cervical =18mm, stenosis = 12mm; Lumbar = 20-22mm, stenosis <15mm

Cervical ligaments: posterior longitudinal ligament becomes tectorial membrane

• C1/2: transverse & alar ligaments responsible for most stability

Facets: Cervical: inferior facet is medial. Thoracic: coronally oriented. Lumbar: superior facet is medial.

Neck:

· Recurrent laryngeal n.: left around aorta, right around subclavian a.; both off vagus, posterior to inferior thyroid a.

· Superior laryngeal n.: travels w/superior thyroid a. in 15%.

· Phrenic n.: anterior to anterior scalene, behind IJ.

· Subclavian a. & v. run between anterior & middle scalene.

· Stellate Ganglion: inferior cervical + upper thoracic ganglia

Bladder:

· Parasympathetics: pelvic n. (S2,3,4) to detrusor mm.

· Voluntary: Pudendal (S2,3,4) to external sphincter.

· Sympathetics: inferior splanchnic n. to inferior mesenteric ganglion to inferior hypogastric nn. to internal sphincter (a), & bladder wall relaxation by inhibiting parasympathetics in pelvic ganglion. (T10,11,12).

· UMN = spastic, propantheline or oxybutnin (Ditropan), imipramine (TCA, anticholinergic); LMN = atonic, bethanecol, methacholine.

Melanocytes located in cervicomedullary pia. Made by tyrosinase.

Spinal Vascular Anatomy

· PICA can arise from vertebral artery (VA) extradurally, can be injured during dissection of C1.

· VA is 3mm from lateral uncovertebral joint, may run through vertebral bodies.

· VA enters transverse foramen above C6 or at C7 in 13%.

· The left VA is dominant in 36% of patients, hypoplastic in 6%, and absent in 2%. The right is dominant in 23% of patients, hypoplastic in 9%, and absent in 3%. Equivalent right and left VA present in 40% of patients.

· 2% of VA do not enter BA or are otherwise anomalous at C1

· Artery of Adamkiewicz: Enters spinal canal at T9-12 on the left to supply T8 to conus.

Vascular

Vascular Supply

Internal capsule: Ant limb = Heubner; Genu = ICA perfs/ Heubner; Post limb = ant. choroidal; Ant & post = lenticulostriate a (from M1). No PCA

Striatum: Lenticulostriate a, Heubner, Ant choroidal

Thalamus: PCA: ant & post choroidals, thalamoperforators (basilar, PCOM, P1), thalamogeniculate (MCA doesn’t supply)

Substantia Nigra: PCA/Pcom

Cortex:

· ACA = hemiparesis (LE), mild sensory;

· Achor = hemiplegia, hemianesthesia, homonymous hemianopia.

· PCA = cortical blindness, Balints, prosopagnosia

Ventricles: lateral = anterior and lateral posterior choroidals, 3^rd = medial posterior

Superior Saggital Sinus drains to right transverse sinus

Aortic arch:

· R Innominate (> R CCA > R VA > R thyrocervical trunk > subclavian) > L CCA > L subclavian (> VA).

· L VA off aortic arch in 5%.

· Rarely can have nonbifurcating CCA w/ ECA branches.

Aberrant ICA: runs behind tympanum > pulsatile tinnitus. Do not biopsy.

Persistent stapedial a.: intratympanic, from petrous ICA to MMA

Intracranial ICA

Petrous: > vidian a. > caroticotympanic a > middle ear

Cavernous: meningohypophyseal a. C4/5 (tentorial of Bernasconi & Cassanari, inf. Hypophyseal, dorsal meningeal), inferolateral trunk C4, McConnel’s capsular.

Supraclinoid: Sup. Hypophyseal.

Intradural: ophthalmic > pcom > ant choroidal.

Hypophyseal a.: Inferior = post pituitary, superior = anterior pituitary

Ophthalmic a.: 0.5% arise from middle meningeal. May also arise from cavernous genu (C3)

Fetal P-comm: unilateral in 20%, bilateral in 8%

Anterior Choroidal

· Cisternal segment > Plexal point (enters choroidal fissure) > Plexal segment.

· Arises off of MCA or Pcom in 25% of patients

· Supplies: optic tract, post limb IC, BG, substantia nigra?, thalamus, amygdala, hippocampus (mostly from PCA), tail of caudate (not hypothalamus).

· Had been sacrificed as treatment for Parkinsons.

· Anterior temporal lobe masses displace it medially.

· Injury: Hemiplegia, hemihypesthesia, homonymous hemianopsia (cognition unimpaired)

ACA

· A1 to ACOM> A2 to pericallosal/ callosomarginal jxn> A3

· A1: medial lenticulostriate aa. (8-10 perfs to optic n, chiasm, hypothalamus, etc).

· ACOM: perfs to chiasm

· Heubner: (medial striate a.) arises from A2 (86%) > A1. Supplys anterior limb IC, BG. Damage causes hemiparesis (arm & face), aphasia (on left).

MCA

· M1 (to bifurcation)> M2 (insula, to circular sulcus of insula) > M3 (circular sulcus to edge of insula) > M4 (cortical, opercular)

· Sylvian point:most posterior branch of MCA leaving sylvian fissure

· (Lateral) Lenticulostriate a.: from M1. BG, IC.

· Anterior temporal a. from M1.

PCA

· P1 (to PCOM)> P2 (in ambient cistern) >P3 (in quadrigeminal cistern) > parietooccipital, calcarine

· Thalamoperforators: from basilar tip, pcom, P1

· Medial post choroidals: from P1; midbrain tectum, thalamus, 3^rd ventricle

· Lateral post choroidal: from P2; thalamus, lateral ventricle choroids

· Med & Lat thalamogeniculate a. : from P2, post thalamus, crus cerebri

· P3: Post temporal a. (anast. W/MCA); Internal occipital> Parietooccipital (to MCA), Calcarine (to ACA)

Vertebral a: Left dominant in 50%, right 25%, neither 25%. 40% one hypoplastic. 1-25% terminates in PICA. Both off subclavian a.

PICA: vermis, medial cerebellum. Loops around tonsils

AICA: anterolateral cerebellum.

Labyrinthine a.: off AICA in 85%, basilar in 15%.

SCA: supplies deep nuclei

Superior Sagittal Sinus: to Right transverse sinus (inferior SS to Left)

Trolard: to SSS. Labbe to transverse sinus

Deep veins: Anterior caudate + terminal vv. > Thalamostriate + septal (anterior) + epithalamic + atrial/ choroidal vv. > Internal cerebral v. (at venous angle) + Basal v Rosenthal > VOG.

Basal Vein of Rosenthal: ambient cistern

Thalamostriate v. : injury results insomnolence, hemiparesis, & mutism (not seizures).

Posterior fossa Vv.: Ant-Post: Precentral cerebellar v., Superior vermian v., (both to vein of Galen, both sacrificed in infratentorial supracerebellar approach) Inferior vermian (to straight sinus)

Adamkiewicz: Left T11 (T4-T8 most vulnerable to low flow)

Persistent fetal arteries: Persistent trigeminal: 0.1-0.5%, cavernous ICA to basilar, AVMs, aneurysms; Persistent hypoglossal: cervical ICA to basilar thru hypoglossal canal, basilar may be hypoplasic or absent below; Persistent otic: petrous ICA to basilar thru IAC; Proatlantal intersegmental: b/t arch C1 & occiput, ECA or ICA to vert.

Revised 6/1/09

Text Copyright 2009

Home

Please send comments and corrections to admin@flotte2.com

Disclaimer: This outline is complied, not original. Sources are being added retrospectively.

It is intended for personal educational use by students and residents. It is not intended to guide clinical decision making. Accuracy and timeliness cannot be guaranteed.