Neural Pathways



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Neural Pathways

Sensory Pathway

Function

Receptors (Peripheral)

1st Order Neuron

2nd Order Neuron

3rd Order Neuron

Synapses

Decussation

Lesions

Clinical Correlations

Medial Lemniscus

  1. Discrim. Touch

  2. Vibration

  3. Conscious Proprio

  1. Meissners, Merkels, Peritrichial

  2. Pacinian, Meissners

  3. Diffuse Nerve Endings

  • DRG to F. Gracilis and Cuneatus

  • Central process = medial root

  • Peripheral process = heavily myelinated

  • Nucleus Gracilis and Cuneatus

  • Form Internal Arcuate Fibers (course ventromedial)

  • Somatotopic Organization!

  • VPL (thalamus)

  • Via Internal Capsule to Area 3,1,2 (Somatosen. Cortex in postcentral gyrus)

  1. N. Gracilis and Cuneatus

  2. VPL

  • Caudal Medulla

  • Dorsal Column - ipsilateral loss of discrim, vibration, cons. proprio.

  • ML, VPL - contralateral loss

  • Romberg Sign -- test for cons. Proprio

  • Tabes Dorsalis (nerve degeneration)

  • Wide, staggering gait; foot slap

ALS

  1. Pain, Temp, Crude Touch

  1. Free Nerve Endings

  • DRG and ascend 1 level (posterolat. fasciculus)

  • Central process = lateral

  • Peripheral process = lightly myelinated

  • Superficial spinal cord lamina (I-IV)

  • VPL (thalamus)

  • Via internal capsule to area 3,1,2 (somatosen. cortex in postcentral gyrus)

  1. Superficical lamina (I-IV) of dorsal horn

  2. VPL

  • 1 level above in anterior white commissure

  • Lat. Funiculus - contralateral loss 1 level below lesion

  • Ant. White Commissure - bilateral 1+ dermatomes below

  • Syringomy. - cavitation of central canal, ant. white comm damage

  • Thalamic pain sydnrome (VPL damage)

  • Cordotomy to treat pain

Trigeminal - Spinal Nucleus

  1. Pain

  2. Temp

  3. Light Touch

  • Free Nerve Endings

  • Trigeminal Ganglion

  • To mid pons via Portio Major and descend to C2 level

  • Spinal Nucleus of V

  • VPM (thalamus)

  • Via POSTERIOR limb of IC to postcentral gyrus

  1. Spinal Nucleus of V

  2. VPM

  • C2 - medulla

  • Cross after leaving Spinal Nucleus of V to form VTTT

  • Ipsilateral loss of pain and temp to face




Trigeminal - Chief Nucleus

  1. Fine Touch

  2. Vibration

  1. Meissner’s, Merkel, Petrichial

  2. Pacinian

  • Trigeminal Ganglion

  • To mid pons via Portio Major

  • Chief Sensory Nucleus of V

  • VPM (thalamus)

  • Via POSTERIOR limb of IC to postcentral gyrus

  1. Chief Sensory Nucleus of V

  2. VPM

  • Uncrossed form DTTT, synapse in ipsilateral VPM

  • Pons to VTTT







Trigeminal -

Mesencephalic Nucleus

  1. Conscious Proprio

  1. Diffuse Endings in joint capsule

  • Mesencephal Nucleus of V IN CNS (rostral and mid pons!)

  • Mesencephal Nucleus of V IN CNS (rostral and mid pons!)

  • VPM

  • To 3,1,2 (ventral ½ of lateral surface)

  1. Mesenceh Nucleus of V

  2. VPM

  • Cross midpons to rostral midbrain

  • Form VTTT







  1. Uncons. Proprio

  1. Spindle and GTO

  • Cerebellum

  • Via ipsilateral cerebellar peduncle

  1. Mesenceph Nucleus of V

  2. Cerebellum

  • NONE







Auditory System

  1. Hearing (duh)

  1. Hair cells in organ of corti

  • Spiral Ganglion

  • Enter at cerebellar pontine angle

  • Dorsal cochlear nucleus - cross midline as DORSAL ACOUSTIC STRIA to join lateral lemniscus

  • Ventral cochlear nucleus - intermediate acoustic stria to lateral lemniscus -- ventral - some to superior olivary nucleus and trapezoid

  • Superior Olivary Nucleus -- cross midline to join LL

  • 3rd,4th order -- inferior colliculus receive from LL; send via brachium of inf. Coll. to MGN

  • MGN to Transverse Temporal Gyri of Heschl (primary - 41, associated - 42)

  1. a.Dorsal and ventral cochlear nuclei b.Superior olivary nucleus, trapezoid

  2. (Nucleus of LL to) Inf. Colliculus

  3. Medial Geniculate Nucleus

  • At level of cochlear and trapezoid nuclei (cerebellopon angle)

  • Commissure of inf. Coll.

  • Lateral Lemniscus - bilateral loss, worse in contralateral

  • Cochlea, CN VIII, Cochlear nuclei - ipsilateral

  • Conduction - impairment of soundwave passage

  • Perception - degeneration of hair cells, tumor, damage to nerve

  • Central - interference of pathway

Vestibular
(see pg 170-3 in BRS)

  1. Utricle/ Saccula - linear accel.

  2. Semicirc Canals - balance

  1. Macula

  2. Ampulla

  • Scarpa’s Ganglion

  • Hair cells in macula/ ampulla (deviation causes release of NTs onto Scarpa’s Ganglion

  • Vestibular nuclear complex - semi circ (superior and rostral medial), u/s (lateral); also an inferior




  • fastigial nucleus - ipsi, flocculonodular lobe (excitatory)

  • vestibulocerebellum -- ipsi input from flocculus, nodulus, post. Vermis (inhibitory)

  • Spinocerebell - ipsi input from ant. Vermis (inhibitory)

  • LVST - from lat nucleus to ipsi spinal cord alpha motorneurons (medial ventral horn - axial and proximal muscles)… oppose the force of gravity

  • MVST - through MLF, caudal ½ of vestibular complex (medial nucleus), reflex head and neck mvt

  • Eye Mvt - from rostral ½ bilaterally to abducens, trochlear, and oculomotor nuclei - horizontal rotation of head

  1. Vestibular Nuclear Complex/ Fastigial Nucleus

  2. LVST, MVST, Eye muscle nuclei (III, IV, VI)

  • Some fibers cross to contralateral motor nuclei (6… from there some cross back to ipsi lateral 3)



  • Nystagmus - slow phase is vestibular

  • Thermal Test - normal = nystagmus is CO, WS

Central Visual Pathway

  1. Vision

  1. Photoreceptors in retina

  • Ganglion cells (receives impulse from bipolar cells) - forms optic nerve

  • Nasal fibers cross in optic chiasma

  • Optic Tract - fibers from same visual fields

  • LGN - Optic radiations - to area 17; Cuneas (lower visual field, upper radiations); Lingula (upper visual field, lower radiations)

  • Suprachiasmatic - circadian rhythms

  • Pretectal - pupil diameter

  • Superior Collic - rapid eye mvt

  1. LGN

  2. Area 17

  • Optic Chiasma (rostral midbrain, caudal dienceph)

  • Optic Nerve - blindness in 1 eye

  • Optic Chiasma - bitemporal heteonymous hemianopsia

  • Optic Tract - contralateral homonymous hemianopsia

  • Meyer’s Loop - contralateral superior homonymous quadranopsia

  • Occlusion of post. Cerebral artery - macular sparing

  • Injury to back of head - macular blindness



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