Flotte’s Outline of

Neuroscience

Edward R. Flotte, 2008

 

 

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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. (“13th 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) >