Anatomy Cerebrospinal Fluid



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Tracts


  • Medial forebrain bundle

    • From: basal olfactory regions, septal nuclei, periamygdaloid region and subiculum (mainly formed by septal region fibers)

    • To: through hypothalamus to:

      • Ventral tegmentum to supercentral nucleus

      • Nuclei of diagonal band and medial septal nuclei to hippocampus via fornix

  • Amygdalo-Hypothalamic Fibers – Mostly via stria terminalis to:

    • Medial preoptic nuclei

    • Anterior hypothalamic nuclei

    • Ventromedial and arcuate nuclei

  • Brainstem afferents

    • Median raphe nuclei – serotonergic via MFB

    • Nucleus of the Solitary Tract – to medial (general visceral) and lateral (special visceral=taste) parabrachial nuclei

  • Retinohypothalamic fibers

    • From retina through chiasm to suprachiasmatic nuclei (circadian rhythms

  • Dorsal longitudinal fasciculus – Descending fibers

    • From: medial and periventricular hypothalamus

    • To: periaqueductal gray and tectum

  • Mammillary Efferents – from fasciculus mammilary princeps to:

    • Mamillary-tegmental tract – to midbrain

    • Mamillary-thalamic tract – to cingulate cortex, then to entorhinal cortex, then back to hippocampus

  • Tuberhypophyseal (tuberoinfundibular) tract

    • Formed by axons of cells of arcuate nucleus situated in uppermost part of infundibulum (median eminance)

    • End on sinusoids of hypophyseal portal system, carrying releasing hormones for anterior lobe of pituitary via hypophyseal portal vessels

    • Superior and inferior hypophyseal artery supply pituitary from internal carotid

    • Releasing hormones:

      • GHRF – growth hormone

      • CRF – ACTH (acts on adrenal cortex to make corticosteroids)

      • FRH, LRH – LSH, FSH

      • TRF – TSH (acts on thyroid gland to make thyroxine); also potentiates release of prolactin

      • PIF – inhibits dopamine secretion

      • Somatostatin RF – inhibits growth hormone

      • MSH – from intermediate lobes

  • Anterior Commissure – mainly connects middle temporal gyrus (some inferior temporal gyrus)

    • In front of fornix, behind septal nuclei

  • Corpus Callosum – gives rise to tapetum

Paleocortex, Archicortex, Limbic System


  • Olfaction – paleopallium

    • Rhinencephalon – olfactory bulb, tract, tubercle and striae, anterior olfactory nucleus, parts of amygdala, and parts of pyriform cortex

    • Olfactory nerve – first order neuron, bipolar with cell body in nasal mucosa

      • axon is unmyelinated, synapses with mitral cells and tufted cells in olfactory bulb (second order neurons, glu and asp) to form olfactory tract

    • Olfactory tract – to lateral olfactory striae to primary olfactory cortex

    • Primary olfactory cortex – pyriform cortex and periamygdaloid area; output to secondary olfactory cortex

    • Secondary olfactory cortex – entorhinal cortex (area 28); output via uncinate fasciculus to hippocampus, anterior insulae, and frontal cortex

    • Medial Forebrain Bundle – carries olfactory information to the hypothalamus and to habenula via stria medullaris; also via stria terminalis (from amygdala) to hypothalamus, finally to brainstem salivatory nucleus and dorsal nucleus of X (nausea, increased peristalsis, and gastric secretions)

  • Septal nuclei

    • Rostral to anterior commissure and preoptic area near base of septum pellucidum

      • From: hippocampus via fornix and MFB

      • To:

        • Stria medullaris to habenula

        • MFB to lateral hypothalamus and midbrain tegmentum

        • Fornix to hippocampus

    • Stria terminalis does not end in septal nuclei but in nuclei of stria terminalis lateral to fornix and dorsal to anterior commissure; some do end in anterior hypothalamic nucleus and medial preoptic nucleus

  • Hippocampus – archipallium – 3 layers (molecular, granule, polymorphic)

    • Dentate gyrus and Subiculum

    • Indusium griseum – end of hippocampus above corpus callosum; has white matter tracts within it – form medial and lateral longitudinal striae

    • Indirect olfactory afferents from entorhinal cortex (area 28)

    • Fornix – gives fibers to lateral septal nuclei (precommissural fibers) and anterior/lateral dorsal thalamic nuclei (postcommissural fibers)

    • Subiculum is major source of efferents in fornix and sole source of direct cortical projections

    • Korsakoff’s syndrome (amnestic confabulatory syndrome) – severe impairment of memory without clouding of consciousness, confusion and confabulation; lesion in mammillary bodies

    • Memory impairment with lesions of dorsomedial nucleus of thalamus and hippocampus, not with isolated lesions of amygdala or mamillary bodies

  • Amygdaloid complex

    • Afferents from olfactory fibers from lateral olfactory tract to corticomedial (NOT basolateral) group

    • Klüver-Bucy syndrome

      • Lesions in animals produce psychic blindness; compulsion to examine objects visually, tactually, and orally; and bizarre sexual behavior

  • Substantia innomonata = nucleus basalis – cholinergic to widespread cortex

  • Limbic system

    • Encompasses limbic lobe – subcallosal, cingulate, and parahippocampal gyrus (NOT amygdala)

    • Limbic system – limbic lobe + subcortical nuclei (amygdaloid, septal nuclei, hypothalamus, epithalamus, thalamus, and medial tegmentum of midbrain) – NOT fornix

    • Arrest reaction with stimulation – immediate cessation of other activities expression of surprise, movement of head/eyes to opposite side






Higher Cortical Function

  • anatomy of language

    • Wernicke’s (area 22) – posterior superior temporal in dominant side, behind primary auditory cortex, language comprehension area, important for higher intellectual function, stimulation elicits complex thought/memory/visual and auditory hallucinations

    • Angular gyrus (visual association area) – between Wernicke’s and occipital lobe – visual processing of words, damage leads to alexia

    • Auditory association area – damage produces word deafness

    • Lateral temporal-occipital junction – word naming

    • Broca’s (area 44, posterior inferior frontal gyrus) – word formation/execution, coordinates simulateous stimulation of respiratory/pharyngeal/laryngeal; straddles premotor and prefrontal

  • function of association cortex

    • parieto-occipital-temporal association cortex – integrates somatosensory, visual, auditory to determine spatial coordinates of body and surroundings

    • prefrontal association cortex – works with motor cortex to plan complex patterns/sequences; also involved with thought elaboration


Cerebellum

  • Archicerebellum

    • Oldest part – related to the vestibular system

    • Consists of the nodulus and the flocculus

    • Defined by the posteriolateral fissure

  • Paleocerebellum (anterior lobe)

    • Receives impulses from stretch receptors via spinocerebellar tracts

    • Helps regulate muscle tone

  • Neocerebellum

    • Coordinates somatic motor function

    • Inputs from contralateral cerebral cortex via pontine relays



  • Inferior cerebellar peduncle (restiform body)

  • Middle cerebellar peduncle (brachium pontis)

  • Superior cerebellar peduncle (brachium conjunctivum)

  • Midline lesions

    • Rostral – stance and gait affected

    • Caudal – Axial and tuncal posture and equilibrium

    • Lateral lesions – impair limb movement

  • Deep nuclei

    • Fastigial – axial muscles

      • Some fibers cross within the cerebellum

      • Crossed fibers exit as uncinate fasciculus (of Russel)

      • Uncrossed fibers project to brain stem via juxtarestiform body

      • Projects to bilateral VL, VPL

    • Globose/Emboliform – distal limb muscles

      • Project to caudal red nucleus

    • Dentate – aids in planning voluntary movements

  • Cell Types

    • Granule cells – excitatory cells in the granular layer

      • Input from mossy fibers (from spinocerebellar tracts and brain stem nuclei)

    • Basket cells – in the molecular layer

      • Inhibit Purkinje cell bodies and granule cell axons

  • Fiber Types

    • Parallel fibers – in the molecular layer (from granule cells)

      • Intersect dendrites of a row of Purkinje cells

      • Each Purkinje cells receives converging input from 200,000 parallel fibers

    • Climbing fibers – excitatory input from the inferior olivary nucleus

      • Each climbing fiber synapses on just one Perjunke cell body

  • Layers

    • Molecular layer – contains axons of granule cells (parallel fibers)

      • Contains basket and stellate cells

    • Purkinje cell layer – sole output of cerebellum (only myelinated axons in the cerebellum)

      • Inhibitory cells (use GABA)



  • Connections

    • Inferior Peduncle

      • Afferents

        • Dorsal spinocerebellar tract

        • Rostral spinocerebellar tract

        • Cuneospinocerebellar tract

        • Juxtarestiform body

          • Primary and secondary vestibulocerebellar fibers

        • Cerebellospinal tract

        • Olivocerebellar fibers (decussate)

        • Trigeminocerebellar fibers

      • Efferents

        • Cerebellovestibular nuclei (inhibitory fibers – lesion can unmask extensor tone)

    • Middle Peducnle

      • Afferents

        • Pontocerebellar fibers from motor and premotor cortex (decussate)

        • Fibers from pontine reticular formation

      • Efferents – none

    • Superior Peduncle

      • Afferents

        • Ventral spinocerebellar tract (via brachium conjunctivum)

        • Tectocerebellar fibers

        • Monoaminergic fibers

      • Efferents

        • Cerebellotegmental fibers

        • Dentatothalamic fibers

        • Dentatoruberal fibers

  • Function

    • Vestibulocerebellum (archicerebellum)

      • Connect with vestibular nuclei in the cerebellum

      • Helps to regulate body equilibrium and eye movements

      • Inhibits extensor posturing

    • Spinocerebellum – involved in movement feedback

      • Vermis (fastigial nucleus)

      • Intermediate zone (globose and emboliform nuclei)

        • Connects to red nucleus (magnocellular portion)

        • Regulates distal muscles

    • Cerebrocerebellum (dentate nucleus) – involved in movement planning

      • Connects to VPL of the thalamus

      • Output to motor and premotor cortex via the red nucleus (parvicellular portion)

  • Circuits

    • Vestibularcerebellar circuit

    • Spinocerebellar circuit

    • Cerebrocerebellar circuit

    • Olivocerebellar circuit

  • Lesions

    • Floculonodular lobe – ataxic gait, wide-based gait, nystagmus

    • Spinocerebellum – tremor, hypotonia (pendular reflexes, flaccid posture)

      • Vermis – disturbances in axial and truncal control

        • Titubation or tremor in trunk

        • Dysarthria, scanning speech

      • Interposed nuclei – limb ataxia, action tremor, hypotonia

    • Cerebrocerebellum

      • Delay in initiating and terminating movements

      • Terminal tremor at the end of a movement

      • Disorders in temporal coordination involving multiple joints

      • Disorders in spatial coordination

      • Terminal tremor


Basal Ganglia

  • Circuits

    • Striatum (caudate and putamen) receive input from motor, premotor, limbic, and association cortex

    • Dorsolateral striatum has input from sensorimotor system

    • Middle striatum has input from assiciation cortex

    • Ventromedial striatum has input from limbic system

    • Striatum and SN have reciprocal projections (DA from SN)

    • Striatum projects to GPe and GPi

    • GPe projects to STN which projects to GPi

    • GPi projects to VA and VL of the thalamus (thalamic fasciculus aka Fields of Forel) and the habenula

    • VA projects to frontal cortex (limbic system)

    • VL projects to premotor and motor cortex



  • Neurotransmitters

    • Cortex and thalamus use glutamate

    • BG circuitry uses GABA, an inhibitory neurotransmitter

    • DA from pars reticulata of the SN and the ventral tegmental area (limbic striatum)

    • Enkephalin from type II spiny neurons

    • Substance P from type I spiny neurons

    • Aspiny neurons – interneurons that modulate spiny neurons

      • Type I – GABA, neuropeptide Y, and somatostatin

      • Type II – giant cholinergic neurons



  • Diseases

    • Huntington’s disease

      • Type I spiny neurons affected first

    • Parkinson’s Disease

      • Depletion of DA-production cells of the SN

      • Increased STN activity (inhibits thalamic nuclei)

      • VL/VIN DBS for treatment of tremor

      • GPi or STN DBS for treatment of rigidity


Diencephalon




Nucleus

Category

Input

Output

Misc

Anterior (A)

Limbic

Hippocampus, mammillary bodies, Raphe nuclei, cholinergic nuclei

Cingulate gyrus

Part of Papez circuit, modulates alertness

DM

Association

Amygdala, basal forbrain, frontal, temporal and olfactory cortex, substantia nigra

Nuc basalis of Maynert, frontal cortex, frontal eye fields (portion that gets input from SN)

Lesions decrease emotional responsiveness, change reaction to pain




Nonspecific

Hypothalamus

Amygdala, striatum, cingulate gyrus

Involved with visceral activities

LD

Specific limbic

?

Cingulate gyrus




LP

Association

Sup. colliculus, pretectum, sup. and inf. parietal lobules

Reciprocal fibers to areas 5 and 7

Integrates information from visual cortex and secondary somatosensory cortex

Pulvinar

Association

Sup. colliculus, visual cortex (primary and secondary), inf. parietal lobule

Visual cortex (areas 17-19), areas 5 and 7

Receives some direct fibers from the retina

VA

Motor

GP and premotor cortex







VL

Motor

GP, deep cerebellar nuclei, motor cortex

Motor and premotor cortex

Lesions decrease tremors

VPL

Sensory

Medial lemniscus, spinothalamic tract, deep cerebellar nuclei (rostral portion)

Primary somatosensory cortex




VPM

Sensory

Trigeminothalamic tract, solitariothalamic tract

Lateral primary somatosensory cortex, parietal operculum




MGN

Sensory

Inferior colliculus, auditory cortex

Auditory cortex(transverse gyrus of Heschel, areas 41 and 42)




LGN

Sensory

Optic nerve

Primary visual cortex (area 17)




CM

Nonspecific

Reticular formation, frontal cortex, GP, CBL

Striatum, diffuse cortex

Thalamic pacemaker, involved in pain processing and sleep

  • Neurotransmitters

    • ACh from nucleus basalis of Maynert (substantia inominata)

    • GABA – most prominent neurotransmitter in the thalamus

    • Glutamate from cortex and cerebellum

Claustrum

  • Input from sensory connection, hypothalamus, CM thalamus, and locus coeruleus

  • Reciprocal fibers with layer VI of cortex

  • No subcortical efferents

Hypothalamus

  • Functional centers

    • Suprachiasmatic nucleus – biological rhythms

    • Ventromedial nucleus – satiety center

      • With lesion, can’t stop eating

    • Lateral nucleus – feeding center

      • With lesion, don’t eat

    • Anterior and medial regions – parasympathetic control

    • Posterior and lateral regions – sympathetic control

    • Anterior nucleus – dissipates heat

    • Posterior nucleus – retains heat

    • Sunstantia inominata – nucleus basalis of Maynert

  • Endocrine function

    • Supraoptic Nucleus – lateral to SCN

      • Magnocellular cells produce VP and OT

    • Paraventricular nucleus

      • Magnocellular cells produce VP and OT

      • Parvocellular cells make release factors (released into median eminence)

    • Arcuate nucleus – near entrance to infundibulum

      • Cells contain DA, ACTH, -endorphin, -LPH

      • Regulates anterior pituitary

      • Projects to brainstem, involved in cardiopulmonary function


Limbic System

  • Structures

  • Papez circrcut

    • Hippocampus to fornix to mammillary bodies to mammillothalamic tract to ant. thalamic nucleus to cingulated gryus to entorhinal cortex to hippocampus

  • Connections

    • Median Forbrain bundle

      • Arises from basal olfactory regions, septal nuclei, periamygdaloid region and subiculum

      • Projects to the hypothalamus

    • Diagonal band of Broca

      • From the hypothalamus to the hippocampus

    • Hypothalamus projects to ventral tegmentum

    • Stria terminalis – separates thalamus from the caudate

      • Connects the hippocampus and septal area

    • Stria medullaris – runs in the midline

      • Connects the septal nuclei, ant. thalamic nucleus, and lateral preoptic region to the habenular nuclei

    • Brainstem afferents

      • From median nuclei of Raphe – serotonin

      • From nucleus solitarius – visceral and taste sensation

    • Retrohypothalamic fibers from the retina to the suprachiasmatic nucleus

    • Dorsal longitudianal fasciculus

      • Descending fibers from medial and periventricular hypothalamus

      • Project to periaquaductal gray and tectum

    • Mammillothalamic and mammilotegmental tracts





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