Program: Bachelor of Physiotherapy (BPT)
course name: Human Physiology II
course code: BPTC202
Module 2 : Ascending tracts and Posterior Column
Sourav Mitra
Assist. Prof., Department of allied health sciences
O B JE C TIVES
1.
Tracts of spinal cord & brain stem
2.
Posterior column
3.
Origin
4.
Distribution
5.
Course
6.
Crossing
7.
Termination
8.
Applied
S p in a l Cord
Dorsal
Horns
Dorsal
Lateral
Ventral
Ventral
S pinal c ord
● Dorsal
horn - sensory input
● Lateral horn - autonomic N. S .
● Ventral horn - motor output
Ascending Pathways
● Three-neuron
pathways:
Primary sensory neurons:
From external receptors
Travel through dorsal roots of spinal cord
Secondary neurons:
brainstem
Make up tracts in spinal cord and
Tertiary neurons:
From thalamus to primary sensory cortex
Travel through internal capsule
Ascending Pathways
● For
conscious perception:
Spinothalamic system
Medial Lemniscal system
● For
unconscious perception:
S p inocerebellar
Spino-olivary
Spinotectal
Spinoreticular
Medial Lemniscus S y s tem
● Also
called posterior column system.
● Carries sensations for two-point
sensation (fine touch), pressure, and
vibration.
Medial Lemniscus S y s tem
● Primary
fibers ascend entire length of
spinal cord and synapse with
secondary neurons in medulla:
Fasciculus gracilis
Fasciculus cuneatus
Medial Lemniscus
● Red:
● Gracilis
● Blue
● cuneatus
Medial Lemniscus S y s tem
● Fibers
of fasciculus gracilis synapse in
nucleus gracilis:
Convey sensations from below midthoracic
level.
● Fibers
of fasciculus cuneatus synapse
in nucleus cuneatus:
Convey sensations from above midthoracic
level.
Also conveys proprioceptive sensation from
arms to cerebellum.
Medial Lemniscus S y s tem
● Secondary
fibers decussate.
● Secondary fibers ascend to synapse in
VPL of thalamus.
● Tertiary fibers ascend through
internal capsule to primary sensory
cortex.
Medial Lemniscus
Medial Lemniscus
Somatosensory Pathways
Crossover at spinal cord
Pain and Temperature
Tickle and Itch
Poorly localised touch
Crossover in medulla
Discriminative touch
Shape, size texture, weight
Vibration
Proprioception
Criteria for a sensory
pathway
● All
sensation has to
pass through
thalamus
● 3 Order Neuronal
pathwayis essential
● Body represented in
the contralateral
cerebral hemisphere
PO STERI O R C O LUMN
Spino
thalamic
(lateral &
anterior)
Description of a tract
❖Synonyms
❖Origin
❖Distribution
❖Course
❖Crossing
❖Termination
❖Function
❖Applied
Ascending Spinal Tracts
●
●
Convey sensory
information from
cutaneous
receptors,
proprioceptors and
visceral receptors to
cerebral cortex.
Sensory fiber tract
decussation may
occur in medulla or
spinal cord.
Ascending tracts
● Major
1) posterior
column
2) Anterolateral
system(spinoth
alamic)
3) Spino
cerebellar tract
Functions of posterior column
Sensations carried by Dorsal
columns:
Light touch (tactile sensation,
2. Tactile discrimination
3. Tactile localization)
4. Conscious proprioception –
5. Joint position and movement.
6. Vibration sensation
7. Stereognosis.
8.Pressure sensation with fine
gradations.
Somatosensory Cortex
Area on somatosensory cortex related to degree of innervation
c. Dorsal Column
Pathway
.The
axons from
these first-order
neurons pass
upward in the
fasciculus gracilis
or fasciculus
cuneatus.
c. Dorsal Column Pathway
The axons from the secondorder neurons (nucleus
gracilis or nucleus cuneatus)
cross to the opposite side of
the medulla and ascend to the
thalamus through the medial
lemniscus of the medulla,
pons, and midbrain.
Ascending Pathways
Figure 13.33a
Tracts of the Spinal Cord
Figure 13.32
The Spinal Cord
Dorsal
3 GROUP OF
CELLS IN THE
POSTERIOR
HORN
1. Substantia
gelatinosa of
rolando(sgr)
Ventral
2. Chief sensory
nucleus
3. Clarke’s
Posterior Column
Pinothalamic Pathways
Somatosensory cortex of Postcentral Gyrus
● Relative
sizes of
cortical areas
● proportional
to number
of sensory receptors
● proportional to the
sensitivity of each part
of the body
● Can
be modified with
learning
● learn
to read Braille &
will have larger area
representing fingertips
Sensory Homunculi
Sensory Homunculi
Somatic Sensory Pathways
● First-order
neuron conduct impulses to
brainstem or spinal cord
● either spinal or cranial nerves
● Second-order neurons conducts impulses from
spinal cord or brainstem to thalamus-- cross
over to opposite side before reaching thalamus
● Third-order neuron conducts impulses from
thalamus to primary somatosensory cortex
(postcentral gyrus of parietal lobe)
Posterior Column
Posterior Column
•
•
•
•
Proprioception, vibration,
discriminative touch, weight
discrimination &
stereognosis
Signals travel up spinal cord in
posterior column
Fibers cross-over in medulla to
become the medial lemniscus
pathway ending in thalamus
Thalamic fibers reach cortex
Two-Point Touch
discrimination
●
Minimum distance at which 2
points of touch can be
perceived as separate.
●
●
Measures of distance between
receptive fields.
Indication of tactile acuity.
●
If distance between 2 points is less
than minimum distance, only 1
point will be felt.
Receptive Fields
Receptive fields in
the thalamus have
centre-surround
organization.
Cortical receptive
fields (left) are
smaller in the fingers
and larger on the
hand and forearm.
STEREOGNOSIS
Thank
you.