Anatomy-discussion

							Board Review- CNS + Autonomic Anatomy

CSF Stuff
--Lateral ventricle  Foramen of Munro  Third Ventricle  aqueduct of Sylvius  Fourth Ventricle 
Foramen of Luschka or Magendie  cisterns  subarachnoid space arachnoid granulations -->
venous system

                                         --Cisterns: Perimesencephalic cisterns (interpeduncular,
                                         quadrigeminal, and ambient), prepontine, Cisterna Magna, and
                                         Lumbar.

                                         --Made in Choroid plexus of lateral (occipital and temporal [but
                                         not frontal!]), third, and fourth ventricles.

                                         --Total volume is ~150cc, made at ~20cc/hr



Bleeds
--subdural from bridging veins, Epidural from mid meningeal artery, SAH from aneurysms

Neurotransmitter Nuclei
--DA from substantia nigra pars compacta in ventral midbrain
--ACh from nucleus basalis of Meynert (affected in Alzheimers) in basal forebrain.
--NE from locus ceruleus (rostral pons)
--5HT from Raphe nucleus (in midbrain/pons/medulla)

Cranial Nerves
--Midbrain has nuclei of CN 3,4
Pons has nuclei of CN 5,6,7,8
Medulla has nuclei of CN 9,10,11,12.

CN2 – optic n to optic chiasm to optic tract (wraps around midbrain) synapses at LGN to optic radiations
(superior loop is parietal, inferior loop [Meyer’s] is temporal) synapses at visual cortex
CN3- nucleus in midbrain, pass through red nucleus, exits ventrally in interpeduncular fosssa, travels
between PCA and SCA and along the PComm, through cavernous sinus, exits through Sup. Orbital
Fissure and then divides into superior (innervates sup. rectus, levator palpebrae) and inferior divisions
(medial / inf. recti/ inf. oblique, and presynaptic parasympathetics to ciliary ganglia).
CN4- nucleus in midbrain. Decussates and exits dorsally at level of inf. colliculi, travels forward on the
under surface of the tentorium cerebelli, and enters cavernous sinus.
CN6- nucleus in pons. Exits at cerebellopontine angle, ascend upwards in subarachnoid space (longest
course) between pons and clivus and enters Dorello’s canal into cavernous sinus.
CN5- nucleus in pons. 2 roots: motor and sensory and 3 division (V1-3)
Motor: Pons  exits anteriorly  passes over Meckel’s cave  foramen ovale  joins with V3 to form
mandibular nerve to supply the muscles of mastication
Sensory: Main sensory ganglion = semilunar or gasserian ganglion, which is in Meckel’s cave, projects to
pons (spinal trigeminal tract), synapse in pons then project to VPM of thalamus
V1 travels through the cavernous sinus and exits through superior orbital fissure
V2 travels through the cavernous sinus and exits through foramen rotundum
V3 (see motor root above)
CN7- Starts in pons, fibers wrap around CN6 nucleus [facial colliculus] then exits ventrolaterally at CP
angle and enters internal auditory meatus. Important branches: branch to stapedius then chorda
tympani (taste) branches off right before CN7 exits the stylomastoid foramen. Posterior auricular
branches off right after the exit.

--Exits
CN1             cribiform plate (ethmoid bone)
CN2             optic canal
CN3,4,V1,6      superior orbital fissure
CNV2            foramen rotundum
CNV3            foramen ovale
CN7,8           internal auditory meatus, 7 continues on to exit through stylomastoid foramen
CN9, 10,11      jugular foramen
CN12            hypoglossal canal

                                                                  -- If lesion is after CN7 exits skull (red
                                                                  line), the pt will have only facial
                                                                  weakness. If lesion is between chorda
                                                                  tympani and br to stapedius (green
                                                                  line), then the pt will have facial
                                                                  weakness + loss of taste. If lesion is
                                                                  between br to stapedius and internal
                                                                  auditory meatus (purple line), then the
                                                                  patient will have facial weakness + loss
                                                                  of taste + hyperacusis.


                                                                  Source: http://www.medicallecturenotes.com/facial-
                                                                  nerve/




-- The CNs that innervate contralateral structures: CN4 and the superior rectus subnucleus of CN3
-- CNs with parasympathetics:
     CN3: Edinger Westphal nucleus  ciliary ganglion  papillary constrictor
     CN7: superior salivatory nucleus [2 branches]
         1.  greater petrosal nerve  pterygopalatine ganglion  lacrimal glands
         2. chorda tympani + lingual n submandibular ganglion  sublingual and submandibular
        glands
    CN9: inferior salivatory nucleus  tympanic nerve +lesser petrosal nerve  otic ganglion  parotid
               gland
    CN10: dorsal motor nucleus of CN10  ganglia near within or near organs (heart, gut, etc)
--The facial colliculus consists of CN6 nucleus + fibers from CN7 and is on the floor of fourth ventricle.
        Thalamus
                                                                 --Olfaction does not go through the thalamus
                                                                 -- Mammilothalamic tract/ fornix inputs to anterior
                                                                 nuclei of thalamus (from mammillary bodies).
                                                                 -- Ventral Lateral  motor
                                                                 Medial geniculate  hearing
                                                                 Lateral geniculate  vision
                                                                 Anterior  limbic system
                                                                 Ventral Posterolateral  somatosensory

                                                                 Others:
                                                                 Pulvinar  behavioral orientation to stimuli
                                                                 Medial dorsal  limbic pathways, relay to frontal
        From Blumenfeld                                          Intralaminar nuclei  consciousness/ alertness
                                                                Centromedian nuclei  motor relay to basal ganglia
                                                                Reticular nuclei  regulates other thalamic nuclei
        Hippocampus

                                                       --Septal nuclei receive input from fornix.
                                                       --Hippocampal formation receives input from the
     Septal nuclei                                     entorhinal cortex
                                                       --Fornix connects the hippocampus to the septal nuclei
                                                       (precommisural fornix) and mamillary bodies (post
                                                       commisural fornix)
                                                       --Perforant pathway connects the entorhinal cortex to the
                                                       hippocampus



Septal nuclei



        Adapted from www.wikipedia.com



        Basal Ganglia

        Striatum = Caudate + Putamen
        Lentiform nucleus = Putamen + Globus pallidus

        -- Major input to BG is from the cortex (to striatum)
        -- Major output from BG to the thalamus is Gpi
         (Ventral anterior nuc of thalamus specifically)
        -- STN is excitatory to Gpi
        -- Caudate is lateral to the lateral ventricles.


                                                                             Nature Reviews Neuroscience 7, 464-476 (June 2006)
Cerebellum
--Contains 3 layers: granule cell [innermost and most cell dense], Purkinje cell layer, and molecular layer
[outermost]. Granule cells receive the inputs. Purkinje cells are outputs. Molecular layer has granule
cells, Purkinje cell dendrites, and interneurons (basket and stellate cells).
--Input to cerebellum comes from climbing fibers or mossy fibers. Climbing fibers come only from
contralateral inferior olivary nucleus. The wrap around the cell body and dendrites of Purkinjes. Each
climbing fiber will supply ~10 Purkinje cells but each Purkinje cell has only 1 climbing fiber input.
Climbing fibers are excitatory on Purkinjes. Mossy fibers synapse onto granule cells which then
bifurcate into parallel fibers (run perpendicular the dendrites of Purkinje), which synapse onto the
dendrites of Purkinje cells. Purkinje cells are inhibitory on the deep cerebellar nuclei.
--Basket and stellate cells are in the molecular layer and receive excitatory input from parallel fibers and
cause inhibition of adjacent Purkinje cells. Golgi (in granule layer) cells also receive excitatory input
from parallel fibers and provide inhibition of granule cells. [see pages 660,661 in Blumenfeld]

-- Cerebellar cortex and peduncle lesions always produce ipsilateral findings because of “double
crossing.” First decussation is in superior cerebellar peduncle. The next decussation is in the
corticospinal tract. Superior cerebellar peduncle mainly carries output from the cerebellum, the middle
and inferior mainly carry inputs.
-- Purkinje cells carry the output of the cerebellum to the deep cerebellar nuclei (DEGF = dentate,
emboliform, globose, fastigial), primarily through the Superior Cerebellar Peduncle.
-- inferior olive supplies climbing fibers (only source of climbing fibers). The others enter cerebellum
through mossy fibers.
-- Stellate cells inhibit Purkinje cells.
-- Dentate nuclei send projections to VL nucleus of thalamus.
-- Climbing fibers originating in the left inferior olivary nucleus travel through the inferior cerebellar
peduncle to synapse with their cerebellar targets

Cortical Layers
-- Layer 4 is the primary input layer from the thalamus. Layer 5, 6 are primary output layers. 5 goes to
non cortical areas, 6 goes to the thalamus. 1 has dendrites, 2 and 3 have afferent and efferent
connections between other cortex.

Autonomic Stuff
Sympathetics arise cell bodies in intermediolateral cell columns of spinal cord from T1 to L3,
Parasympathetics from CN3,7,9,10 and S2-4. Both use nACh for preganglionic synapses. Sympathetics
use norepinephrine at end organs (except for mACh for sweat glands), parasympathetics use mACh.
-- Third order sympathetics (to the eye): neuron cell bodies are in superior cervical ganglion. First order
is from hypothalamospinal tract  intermediolateral cell column  super cervical ganglion 
cavernous sinus  Muller’s muscle + iris. Depending on lesion location, can get a partial Horner’s
because branches that innervate sweat glands come off more proximally.
                                                     Bowel / Bladder
                                                     Detrusor is innervated by parasympathetics. Bladder
                                                     dome and internal urethral sphincter are innervated
                                                     by sympathetics. External urethral sphincter is
                                                     striated muscle (voluntary). When bladder is full
                                                     (wall is stretched), afferents sends info up to cortex.
                                                     Frontal micturition inhibiting area / pontine
                                                     micturition centers activate the voiding reflex
                                                     (detrusor reflex). Sympathetics (T11-L1) are
                                                     inhibited and parasympathetics (S2-S4 Onuf’s
                                                     nucleus) are activated  causing the bladder wall to
                                                     contract and the sphincters to relax. Lesion to the
                                                     cortex cause incontinence. Lesions to the spinal cord
                                                     (above S2-4, acutely) cause an atonic bladder
                                                     (urinary retention, bladder distension, overflow
                                                     incontinence). Chronic spinal cord lesions cause a
                                                     hyperreflexic (spastic) bladder  urinary frequency
                                                     and urge incontinence due to detrusor sphincter
                                                     dyssynergia. Lesions to the peripheral nerves or S2-
                                                     S4 cause a flaccid areflexic bladder leading to
                                                     overflow incontinence.

                                                     --Detrusor wall muscle is innervated by
                                                     Parasympathetic S2-S4.

Other stuff
--epithalamus = posterior dorsal segment of the diencephalon. It includes the habenula + pineal gland.
The habenula projects to the interpeduncular nucleus in the midbrain. It connects the limbic system to
other parts of the brain.

--Area postrema, which is one of 8 circumventricular organs. Rest are: posterior pituitary, median
eminence, vascular organ of lamina terminalis, subfornical organ, pineal gland, subcommisural organ,
choroid plexus.

--Central Tegmental Tract. Palatal tremor is localized to Guillain - Mollaret’s Triangle, which consists of
dentate nucleus, contralateral red nucleus, and contralateral inferior olivary nucleus.
Sup Cerebellar Peduncle          Red Nucleus
                                       Central tegmental tract
Dentate Nucleus
   Inf Cerebellar Peduncle      Inf Olivary Nucleus


[All images from Blumenfeld, except for Papez circuit diagram, from wikipedia.com and BG circuits from
Nature Reviews Neuroscience 7, 464-476 (June 2006)]