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SENSORY PATHWAYS
REVIEW
Dr. G.R. Leichnetz
Somatosensory Systems
Postcentral gyrus/
paracentral lobule
Somatosensory (GSA)
Pathways-
VPL
Medial
lemniscus
Spinothalamic
tracts
Primary
afferents
from the body:
Lateral spinothalamic tractpain & temperature
Anterior spinothalamic
tract- simple (crude) touch
Dorsal column/ medial
lemniscus- proprioception,
vibratory sense, fine touch
Ascend to terminate in the
VPL nucleus of the
thalamus, which then
projects to the postcentral
gyrus and paracentral
lobule (leg).
Tabes Dorsalis: Lesion of the Dorsal Columns) involving
the fasciculus gracilis and/or cuneatus
Loss of conscious proprioception, vibratory sense, fine touch,
stereognosis below the level of the lesion. Positive Romberg sign.
FG
Lumbar
spinal cord
FG FC
Cervical
spinal cord
Syringomyelia
Syringomyelia
Syrinx (cavitation) in
cervical and upper
thoracic spinal cord
involves fibers
crossing to join the
anterior
spinothalamic tract.
Results in a bilateral
segmental loss of pain
and temperature at
the level of the syrinx.
Lateral
spinothalamic
tract
LSTT is intact.
Only crossing
fibers at level of
syrinx are
affected. Thus
segmental loss
of pain & temp.
Syrinx
Syrinx (cavitation)
disrupts second-order
spinothalamic axons,
preventing them from
joining the LSTT
Brown-Sequard
Syndrome
(hemisection of the
spinal cord)
involving the dorsal
column (fasc.
gracilis & cuneatus)
and lateral
spinothalamic tract.
FG
CST
LSTT
FG= fasciculus gracilis
CST= corticospinal tract
LSTT= lateral
spinothalamic tract
Ipsilateral loss of
conscious
proprioception,
vibratory sense, and
contralateral loss of
pain and temp.
sensation below the
level of the lesion.
Brown-Sequard Syndrome
Dorsal columns: fasciculus
gracilis & cuneatus
(hemisection of the spinal cord)
Lateral
spinothalamic tract
LSTT
Ipsilateral loss
of conscious
proprioception,
vibratory sense
(FG), and
spastic paralysis
(CST)
Contralateral
loss of pain &
temperature
(LSTT)
FG
Somatosensory Pathways
from head are related to
the trigeminal nerve.
Postcentral gyrus,
Head area
VPM
Trigeminal
lemniscus
Ophthalmic
Trigeminal
ganglion
Spinal
nucleus of V
Maxillary
Mandibular
Spinal Tract & Nucleus of Vpain & temperature
Chief Sensory Nucleus of Vprimarily touch (tactile)
Mesencephalic Nucleus of Vproprioception from muscles
of mastication.
The spinal nucleus and chief
sensory nucleus of V project
thru contralateral (ventral)
trigeminothalamic tract
(trigeminal lemniscus) to
terminate in the VPM
nucleus of the thalamus,
which projects to the head
area of the postcentral gyrus.
Wallenberg’s (Lateral
Medullary) Syndrome
Loss of pain
& temp. in
ipsilateral
face
Ipsilateral loss of pain and
temperature in head (spinal
tract and nuc. of V) with
contralateral loss of pain and
temperature in the body
(lateral spinothalamic tract).
Loss of pain & temp.
in contralateral body
Occlusion of branches of Posterior
Inferior Cerebellar Artery (PICA)
to dorsolateral medulla
Spinocerebellars (ataxia)
Spinal tract & nucleus of V
(loss of pain & temp./ head)
Spinothalamic tracts (loss of pain
& temp/ body)
Anterior Lobe,
cerebellum
Unconscious Proprioception
Lower Limb- dorsal & ventral
spinocerebellar tracts
Upper limb- cuneocerebellar tract
Upper limb
Lower limb
Visual System
Visual Pathway
Retinal ganglion cells
project their axons thru
the optic nerve, chiasm
and tract to the lateral
geniculate nucleus.
Ipsilateral projections to
LGN layers 2,3,5;
contralateral to 1,4,6.
The LGN projects via
the optic radiations to
the cuneus and lingual
gyri (area 17, primary
visual cortex).
Pretectum
Visual Reflex
(pupillary reflex)
Pathway
Edinger- Westphal
nucleus (OMC)
Ciliary
ganglion
Sphincter
pupillae
muscle
Retinal ganglion cells
project to the
pretectum and
superior colliculus.
The pretectum
projects to the
Edinger-Westphal
nucleus, which sends
parasympathetic
pregang. fibers to
ciliary ganglion;
postgang.’s to ciliary
and sphincter
pupillae muscles..
Visual
Pathway
Lesions:
Optic Nerve
Optic
Chiasm
Optic Tract
Meyer’s
Loop
Cuneus
Gyrus
Lingual
Gyrus
Auditory System
Receptor hair
cells in the organ
of Corti are on
the peripheral
processes of
bipolar neurons
of the spiral
(cochlear)
ganglion.
The central
processes travel
with the auditory
division of C.N.
VIII to terminate
in the dorsal and
ventral cochlear
nuclei.
Auditory System
Primary
auditory
cortex
MGN
Inferior
colliculus
Lateral
lemniscus
Second-order projections
from the dorsal and
ventral cochlear nuclei
ascend crossed &
uncrossed in the lateral
lemniscus to the inferior
colliculus and medial
geniculate nucleus of the
thalamus (with potential
synapses in the superior
olive, nuclei of the
trapezoid body). The MGN
projects to the superior
transverse temporal gyri of
Heschl, areas 41, 42, the
primary auditory cortex.
Vestibular System
Vestibular
complex
Vestibular
ganglion
Primary
vestibular fibers
(from
semicircular
canals, saccule,
utricle) in
vestibular
division of C.N.
VIII terminate
in all
subdivisions of
the vestibular
complex.
To
extraocular
motor nuclei
Medial
longitudinal
fasciculus
(MLF)
Vestibular
complex
Second-order vestibular
fibers originating from
the vestibular complex
ascend in the medial
longitudinal fasciculus
(MLF) to terminate in the
extraocular motor nuclei
(III, IV, and VI).
The basis of the
vestibulo-ocular reflex
Lesions of the vestibular
division of VIII, vestibular
complex, or MLF result in
nystagmus.
Vestibulospinal Tracts
Medial vestibulospinals
(desc. MLF) only goes to
cervical spinal cord
(neck muscle motor neurons)
The basis of the
vestibulo-colic reflex.
Desc. MLF
to cervical
spinal cord
LVST to
entire spinal
cord
Lateral vestibulospinals
extend the entire length
of the spinal cord
(affect posture/
equilibrium)
Brainstem lesions involving vestibular structures
(eg. vestibular division of C.N. VIII, vestibular
complex, MLF, flocculonodular lobe of cerebellum)
typically produce:
nystagmus, rhythmic involuntary oscillation of the
eyes; the eyes move slowly in one direction, and then
jerk quickly back to the opposite side;
or vertigo (dizziness, sense of room spinning);
and difficulties with balance/equilibrium (postural
problems).
Located in the
pontocerebellar
angle, a vestibular
schwannoma can
compress the
vestibulocochlear
nerve (C.N. VIII)
with partial or
complete deafness,
tinnitis, vertigo,
nystagmus, or
facial nerve (C.N.
VII) w weakness in
ipsilateral face.
Olfactory System
Olfactory Pathway
(SVA):
First-order bipolar
neurons in the olfactory
mucosa have central
processes that synapse on
mitral cells in the
olfactory bulb.
Mitral cells send their
axons thru the olfactory
tract to terminate in the
primary olfactory cortex
of the rostral temporal
lobe (prepyriform &
entorhinal cortex, and
amygdala). Some
olfactory projections go
to the septum/basal
forebrain region.
Gustatory System (Taste)
Taste Pathway (SVA):
SVA
Petrosal
ganglion
(IX)
GVA
Facial N. (VII)- ant. 2/3
Glossopharyngeal N. (IX)post. 1/3
Vagus N. (X)- epiglottis
Cell bodies of taste
neurons are in geniculate
ganglion, and inf. ganglia
of IX and X.
Nodosal
ganglion
(X)
The rostral solitary
nucleus is SVA (taste);
caudal part is GVA
(visceral sensation)
The solitary nucleus
is the only visceral
afferent nucleus in
the brainstem)
Taste
area
VPM
Hypothalamus
SVA
Solitary
nucleus
Taste Pathway (SVA)
Solitary nucleus projects via
tract which runs adjacent to the
medial lemniscus to the VPM
nucleus of the thalamus; with
relay to the tongue region of the
opercular part of the
postcentral gyrus and insular
cortex (consciousness of taste).
Some ascending taste- related
projections from the solitary
nucleus terminate in the
hypothalamus (effect on
appetite).
General Visceral Sensory
(GVA) Pathways
GVA fibers carrying visceral
sensation (other than pain),
have their cell bodies in the
inferior ganglia of C.N. IX
and X (petrosal & nodosal)
and have their central
connections with solitary
tract and nucleus. Then the
solitary nucleus projects to
the hypothalamus and VPM.
VPM
Hypothalamus
Solitary
Nucleus
GVA visceral pain fibers
travel with sympathetics,
thru splanchnic nerves, thru
sympathetic chain, white
comm. rami, and dorsal root.
Their cell bodies are in
dorsal root ganglia. Central
processes of unipolar neurons
synapse in the dorsal horn of
the spinal cord.
Thoracic splanchnics
Visceral Pain (GVA)
DRG has GVA
cell bodies
Lateral
spinothalamic
tract
Splanchnic nerves carry
GVA fibers from gut
GVA chemo- and mechanoreceptors in the gut
Visceral pain fibers from
thoracic & abdominal
viscera travel in the
reverse direction thru
splanchnics
(sympathetics) to the
spinal cord. Their cell
bodies are in the dorsal
root ganglia. Their
central processes
synapse in the dorsal
horn.
While some visceral pain
will travel with the
lateral spinothalamic
tract
(neospinothalamic),
most follows a multisynaptic and slower
ascending pathway
through the brainstem
to the thalamus
(paleospinothalamic).
Most GVA fibers carrying
visceral sensation (other
than visceral pain) travel
with cranial nerves IX and
X.
GVA fibers from carotid
sinus (blood pressure) and
carotid body (blood gases),
have their cell bodies in the
inferior ganglion of C.N. IX
(petrosal).
GVA fibers from the gut
have their cell bodies in the
inferior ganglion of C.N. X
(nodosal).
Central connections with
solitary tract and nucleus.
General Visceral Sensation (GVA)
CN IX
Solitary
nucleus
Petrosal
ganglion
CN X
The solitary nucleus
is the only visceral
afferent nucleus in
the brainstem
(GVA, SVA).
Nodosal
ganglion
Carotid
sinus
Thoracic splanchnics
Visceral pain
Cranial Nerves
Ventral Aspect of the
Brain
All cranial nerves exit
from the ventral aspect
of the brain, except the
trochlear nerve.
Telencephalon- I
Diencephalon- II
From the brainstem:
Mesencephalon- III, IV
Metencephalon- V
Myelencephalon- VI, VII,
VIII, IX, X, XI, XII
Functional Components of Cranial Nerves
GSA= receptors in skin & muscle GVA= receptors in gut & large blood vessels
SSA= receptors of special senses SVA= receptors for taste & smell
GSE= to muscles derived from somites (eg. extraocular and tongue muscles)
SVE= to muscles derived from visceral arches (branchiomeric muscle)
GVE= to smooth (gut, glands) & cardiac muscle (autonomic)
I
II
III
IV
V
VI
VII
Olfactory- SVA (smell)
Optic- SSA (vision)
Oculomotor- GSE (extraocular), GVE (ciliary, sphincter pup.)
Trochlear- GSE (extraocular, sup. oblique)
Trigeminal- GSA (pain, temp., head) , SVE (masticatory)
Abducens- GSE (extraocular, lat. rectus)
Facial- SVA (taste, ant. 2/3), SVE (facial), GVE (submaxillary
& sublingual salivary glands)
VIII Vestibulocochlear- SSA (audition)
IX Glossopharyngeal- GVA (carotid sinus & body), SVA (taste,
post. 1/3), SVE (stylopharyngeus), GVE (parotid saliv.gland)
X Vagus- GVA (gut), SVA (taste, epiglottis),
GVE (parasymp. to gut); SVE (laryngeal muscles)
XI Spinal Accessory- GSE (sternocleidomastoid & trapezius)
XII Hypoglossal- GSE (tongue)