Download Sensory Pathways Review - Dr. Leichnetz

Review - Sensory Pathways
George R. Leichnetz, Ph.D.
See Summary Chart: Summary Chart of Origin, Course, and Termination of CNS, Sensory
Tracts
I.
SOMATOSENSORY PATHWAYS (GSA)
Body
Conscious - to thalamus/cortex; somatotopically-organized
First order neurons- cell bodies in dorsal root ganglia (DRG)
Lateral spinothalamic tract (pain/temp.) - from lam. I and V to contralateral VPL
Anterior spinothalamic tract (crude touch)
Dorsal column/medial lemniscus (conscious proprioception, vibratory, discriminative
(fine) touch, stereognosis)-from dorsal column nuclei to contralat. VPL
Unconscious - to cerebellum
Dorsal spinocerebellar tract (unconscious proprioception, lower limb) - from nuc.
dorsalis (Clarke) to anterior lobe cerebellar cortex (and post. lobe vermis)
Ventral spinocerebellar tract - from dorsal horn to anterior lobe, cerebellar cortex
Cuneocerebellar tract (unconscious proprioception, upper limb) - from lat. (acc.) cuneate
nuc. to ant. lobe, cerebellar cortex
Clinical Correlations: Tabes dorsalis, Syringomyelia, Wallenberg's syndrome, BrownSequard syndrome
Head
First order neurons in trigeminal ganglion (also geniculate(VII), and sup. ganglia of IX & X)
Trigeminal Lemniscus (ventral trigeminothalamic tract) - pain, temp., touch - from spinal &
chief sensory nuclei of V to VPM
Mesencephalic Tract (and nucleus) of V - proprioception from masticatory muscles; jaw jerk
reflex
II.
VISCERAL SENSORY (GVA general visceral sensation) (carotid sinus; carotid body)
First order neurons in inferior ganglia of IX & X (petrosal & nodosal ganglia)
(Caudal) Solitary Tract and Nucleus- ascending projections to VPM and hypothalamus
Visceral Pain- from thoracic and abdominal organs travel with sympathetics (splanchnics)
cell bodies in DRG; synapse in dorsal horn of spinal cord
III.
VISCERAL SENSORY (SVA taste, gustatory)
(Rostral) Solitary Tract and Nucleus (1st order neurons in geniculate gang. VII ant 2/3;
inferior ganglion of IX post 1/3; inferior ganglion of X epiglottal taste buds)
Ascending conn.'s through medial lemniscus to VPM and hypothalamus (appetite)
IV.
OLFACTION (SVA)
First order neurons (bipolar) in olfactory epithelium; C.N. I
Olfactory Bulb (mitral cells) via olfactory tract and lat. olfactory stria to primary olfactory
cortex (prepyriform cortex, entorhinal cortex, and amygdaloid complex)
V.
AUDITORY (SSA)
First order neurons (bipolar) in spiral ganglion; C.N. VIII vestibulocochlear nerve, auditory
division
Dorsal/Ventral Cochlear Nuclei- lateral lemniscus to inferior colliculus, and via brachium
of inf. colliculus. to medial geniculate nucleus (with possible intermediate synapses in sup.
olive and trapezoid body); MGN to superior transverse temporal gyri (primary auditory
cortex)
Clinical Correlations: tinnitus, loss of hearing
VI.
VESTIBULAR (SSA)
First order neurons (bipolar) in vestibular ganglion; C.N. VIII vestibulocochlear nerve,
vestibular division; synapse in vestibular complex and flocculonodular lobe, cerebellum
Vestibular Complex reciprocal conn.'s with flocculonodular lobe through the juxtarestiform
body
Ascending Conn.'s thru medial longitudinal fasciculus (MLF) to extraocular motor nuclei
(III, IV, and VI, vestibulo-ocular reflex)
Descending Conn.'s through descending MLF to cervical cord (vestibulocollic), and lateral
vestibulospinal tract (orig. from lat. vestibular nucleus to entire cord, excite extensors)
Clinical Correlations: VOR, nystagmus, vertigo, postural difficulties
VII.
VISUAL (SSA)
Rods and cones; bipolar neurons; ganglion cells
Visual Pathway: Retina via optic tract to lateral geniculate nucleus (LGN); optic radiations
to primary visual cortex (area 17; cuneus and lingual gyri)
Visual Reflex Pathway: Retina via brachium of sup. colliculus to pretectum and EdingerWestphal Nucleus to ciliary body (pupillary reflexes); to superior colliculus (proj.'s to
ret. form. and cervical cord for eye and head movements)
Clinical Correlations: homonymous hemianopsia, quadrantanopsia (Meyer’s loop),
anisocoria, mydriasis, Horner’s syndrome, Argyll-Robertson pupil, Marcus-Gunn
pupil (APD)
Advice for Studying for the Second Practical Exam
The second practical will consist entirely of questions on sensory systems and cranial nerves on
myelin-stained sections from the Haines’ Neuroanatomy Atlas. We have color images of the exact
sections in Haines to use for the PPT exam. On this second practical, the sections are in order from
spinal cord to thalamus. The questions will include:
Identify (very few of this type)
Where are the cell bodies of origin of this tract? This means where are the parent cells located of the
axons in the tract (not the origin of the entire sensory pathway). If the question says “be specific”
you must indicate whether the cell bodies of origin are ipsilateral (same side) or contralateral
(opposite side) to where the tract is. Example: Where are the cells of origin of this tract? (eg. medial
lemniscus) Be specific. Ans. Contralateral nucleus gracilis and cuneatus.
Where does this tract terminate? This means “where do these axons end?” Again, the question may
say “be specific” and you would have to indicate ipsilateral or contralateral. Example: Where does
this tract primarily terminate? (eg. optic tract) Be specific. Ans. Ipsilateral lateral geniculate
nucleus; or eg. medial lemniscus, Ans. Ipsilateral ventral posterior nucleus (VPL) of the thalamus.
Where does this nucleus project? This means “where do the neurons whose cell bodies are located
in this nucleus send their axons to terminate?” Again “be specific” would require ipsilateral or
contralateral. Example: Where does this nucleus project? Be specific. (eg. cuneate nucleus) Ans.
Contralateral ventral posterolateral (VPL) nucleus of the thalamus.
What sensory modality is associated with this structure? This means: pain & temperature, touch,
conscious proprioception, unconscious proprioception, vision, audition, vestibular sense, olfaction,
or taste. Do not confuse this with functional components.
What functional components are associated with this structure? This means general somatic afferent
(GSA), general visceral afferent (GVA, special somatic afferent (SSA), special visceral afferent
(SVA), general somatic efferent (GSE), special visceral efferent (SVE), or general visceral efferent
(GVE).
What is the result of a lesion of this tract? or nucleus? Be specific. Example: Lesion of medial
lemniscus. Ans. Contralateral loss of conscious proprioception in the body.