Anatomy Cerebrospinal Fluid

Ascending tracts of the spine

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Ascending tracts of the spine

  • Posterior columns

    • Carry light touch/vibtation sensation

    • Ascend in fasciculus gracilis (lower body) and fasciculus cuneatus (upper body)

    • Synapse on secondary nuclei in the medulla

    • Fibers decussate as the internal arcuate fibers, become medial lemniscus

    • Medial lemniscus projects to VPL of the thalamus

  • Anterior spinothalamic tract

    • Carry pain and light touch sensation

    • Fibers from contralateral laminae I, IV, and V

    • Crosses anterior white commisure over several levels and ascends

    • Projects to VPL

  • Lateral spinothalamic tract

    • Carry pain and temperature sensation

    • Fibers may ascend or descend 1 level before entering spinal cord

    • Fibers cross in the anterior white commisure

    • Tract ventral to the dentate ligament

    • Projects to VPL

  • Spinotectal tract

    • Ascends with anterior spinothalamic tract

    • Terminated in deep contralateral superior colliculus

    • Conveys nociceptive impulses

  • Dorsal spinocerebellar tract

    • Uncrossed tract

    • Carries muscle spindle information from below T6

    • Synapses in the dorsal nucleus of Clark

    • Enters the cerebellum through the inferior cerebellar peduncle

  • Ventral spinocerebellar tract

    • Carries Golgi tendon organ information from below T6

    • Crosses twice

    • Enters the cerebellum through the superior cerebellar peduncle

  • Cuneocerebellar tract

    • Uncrossed tract

    • Carries muscle spindle information from above T6

    • Synapses in the accessory cuneate nucleus

    • Enters the cerebellum through the inferior cerebellar peduncle

  • Rostrocerebellar tract

    • Uncrossed tract

    • Carries Golgi tendon organ information above T6

    • Enters the cerebellum through the inferior cerebellar peduncle

Descending tracts of the spine

  • Corticospinal tracts

    • Arise from layer V of cortex

    • Largest fibers from giant pyramidal cells of Betz

    • 30% from premotor, 30% from motor, 30% from primary sensory cortex

    • 3 separate tracts

      • 90% crossed lateral corticospinal tract (dorsal to dentate ligament)

      • 8% uncrossed anterior corticospinal tract

      • 2% uncrossed lateral corticospinal tract

    • Terminate mostly in laminae VII

  • Tectospinal tract

    • From superior colliculus

    • Terminates in the upper cervical cord

    • Mediates reflexive movements in response to visual stimuli

  • Rubrospinal tract

    • From the magnocellular portion of the red nucleus

      • Receives information from contralateral cerebellum and ipsilateral motor cortex

    • Fibers cross in the ventral tegmental decussation

    • Flexor bias of the upper extremities – cortical lesion causes decorticate posturing

  • Interstitiospinal tract

  • Vestibulospinal tracts

    • Lateral vistibulospinal tract – from Deiter’s bucleus

      • Extensors to all extremities

      • Lesion above Deiter’s nucleus causes decerebrate posturing (no red nucleus flexor bias)

    • Medial vestibulospinal tract

      • Descends in the MLF

  • Reticulospinal tracts

    • Pontine reticulospinal tract

      • From the nuclei pontis caudalis and opalis

      • Descends in the medial portion of the anterior funiculus

      • Extensor bias, especially in response to pain

    • Medullary reticulospinal tract

      • From the nucleus reticularis gigantocellularis

      • Projects bilaterally

      • Flexor bias

    • Functions:

      • Facilitate/inhibit voluntary movement

      • Influence muscle tone

      • Affect phasic activities associated with respiration

      • Pressor/depressor effects on the circulatory system

      • Facilitate/inhibit central transmission of sensory impulses

Descending autonomic pathways

  • From hypothalamus to dorsal motor nucleus of X, intermediolateral cell column of thoracic and upper lumbar spine

  • Nucleus tractus solitarius to contralateral phrenic nerve nucleus (C3-5)

  • Locus coeruleus and group A5 cells (lateral to CN VII)

    • Major noradrenergic input to intermediolateral cell column


  • Nuclei cuneatus and gracils (medial)

  • Accessory cuneate nucleus

  • Spinal trigeminal nucleus

    • Runs along spinothalamic tract

    • Merges with substantia gelatinosa of the spinal cord (slow pain relays)

    • Pain and temperature sentation from the face

    • V3 dorsal, V1 ventral

    • Medial face represented anteriorly in the nucleus

    • Lateral face represented posteriorly in the nucleus

  • Inferior olivary complex

    • Output crosses median raphr, enters the inferior cerebellar peduncle

    • Climbing fibers to the Perkinje layer of the cerebellum

  • Raphe nuclei

    • Make seretonin (5-HT)

    • Involved in analgesia

    • Bilateral spinal projections in the dorsolateral funiculus terminate mostly in laminae I and II

  • CN XII – hypoglossal

    • Tongue deviates toward side of lesion

  • CN XI

    • Cranial portion – arises from caudal nucleus ambiguous

      • join CN X fibers to form inferior (recurrent) laryngeal nerve

    • Spinal portion – anterior horn from C1-C5 up to foramen magnum

      • project to the trapezius and sternocleidomastoid muscles

    • Lesions:

      • weakness turning head to the opposite side and downward and outward

      • rotation of the scapula

      • moderate sagging of the shoulder

  • CN X

    • Sensation

      • Superior ganglion – cutaneous back of ear and external auditory meatus

        • Projects to spinal trigeminal nucleus

      • Inferior (Nodose) ganglion – visceral and somatic sensation

        • Larynx, pharynx, trachea, epiglottis, thoracic and abdominal viscera

        • Projects to the nucleus tractus solitarius

        • Some fibers descend to the obex where the solitary nuclei of both sides merge to form the commissural nucleus of vagus

    • Fasciculus solitarius

      • Formed by visceral afferents from VII, IX, X

      • Taste information projected to VPM thalamus

    • Dorsal motor nucleus of X – afferents from hypothalamus

      • Parasympathetic preganglionics

      • “secretomotor” center and vasomotor center

    • Nucleus ambiguous

      • Projects to IX, X, and XI

      • Somatic motor efferents to muscles of the larynx and pharynx

  • CN IX

    • Sensation

      • Superior ganglion – cutaneous back of ear

        • Projects to trigeminal nucleus

      • Inferior ganglion – somatic and visceral sensation

        • Pharynx, posterior third of tongue, Eustachian tube, carotid sinus and body

      • Carotid sinus nerve – detects increases in BP (baroreceptor)

        • Projects to the nucleus tractus solitarius

        • Results in increased parasympathetic output

      • Carotid body receptor – detects changes in O2 tension (chemoreceptor)

    • Visceral efferent

      • Inferior salivatory nucleus projects through IX (becomes lesser petrosal nerve) to the otic ganglion

    • Somatic efferent

      • Nucleus ambiguus projects to the sytlopharyngeus muscle

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