Dorsal column pathway

1. Dorsal column pathwayDorsal column pathway
DR SYED TOUSIF AHMED

2. General Sensory Receptors
Sensory pathways
Spinocerebellar
Pathway
Posterior Column
Pathways
Anteriolatheral
Pathways
Posterior
Tract
Anterior
Tract
Fasciculus
Cuneatus
Fasciculus
Gracilis
Latheral
Tract
Anterior
Tract
Sensory PathwaysSensory Pathways

3. Cutaneous sensory receptors
Smooth skin
(glaborous)
Hairy skin
Subcutis
Dermis
Epidermis
Free
nerve
endings
Merkel disks
detect steady
pressure & are
slowly adapting
Free nerve endings
around hair root can
be either rapid or slowly
adapting - depends
on hair type
Meissner’s corpuscles
detect flutter & are
rapidly adapting
Pacinian corpuscles
detect vibration & are
very rapidly adapting
Ruffini corpuscles
detect steady
pressure at higher
threshold & are
slowly adapting
Free nerve endings in the skin
are modality specific and can
detect either pain or touch or
pressure or temperature
The receptor
location and
its associated
structure can
alter the
stimulus and
influence
the response

4. Tactile SensationsTactile Sensations
arise by activation encapsulated
mechanoreceptors
–touch
–pressure
–vibration
arise by activation of free nerve endings
–itch
–tickle

5. TouchTouch
Crude touch
–ability to perceive that something contacted skin
–exact location, shape, size, or texture cannot be
detected
Fine touch
–provides specific information about location, shape,
size, and texture of stimuli

6. Proprioreceptors
Intrinsic knowledge of limb position is known as
kinaesthesia.
Information is provided by sensory input from muscle
spindles (Ia & II) and Golgi tendon organs.
These are mechanoreceptors and provide the CNS
with information on muscle length, position and
tension.
Muscle spindle group Ia afferent fibres are rapidly
adapting (dynamic) and are sensitive to rapid changes
in muscle length.
Muscle spindle group II afferent fibres are slowly
adapting (static) and single the fixed length of the
muscle.

7. Joint Kinesthetic ReceptorsJoint Kinesthetic Receptors
located within and around articular capsules of synovial
joints
perception of body movements
several types
–free nerve endings and type II cutaneous
mechanoreceptors
in capsules of joint and respond to pressure
–small lamellated corpuscles
respond to acceleration and deceleration of joints
during movement
–articular ligaments contain receptors similar to
tendon organs
adjust the contraction of adjacent muscles when
excessive strain is placed on joint

8. Two-Point DiscriminationTwo-Point Discrimination

9. Processing at Receptor LevelProcessing at Receptor Level
Receptor must have specificity for stimulus
activity
Stimulus must be applied to receptive field
Transduction must occur
Generator potential in 1
st
order neuron must reach
threshold
How is information about stimulus encoded?
Tonic receptors (slow adapting)
Phasic receptors (fast adapting)
Adaptation

10. Rapidly adapting cutaneous mechanoreceptors signal
the onset and offset (phasic) of a stimulus and give
rise to sensations such as vibration, touch, and
movement
Slowly adapting mechanoreceptors continuously
signal (tonic) the intensity of the stimulus and give
rise to the sensation of pressure.
Cutaneous receptors with small receptive fields are
involved in fine spatial discrimination, whereas
receptors with larger receptive fields are less spatially
precise.
Overlap of receptive fields allows lateral inhibition to
occur in the ascending pathways and increase sensory
acuity.
Cutaneous mechanoreceptors

11. Somatosensory system receptor Somatosensory system receptor
classificationclassification

12. First-Order Neuron First-Order Neuron
Sensory neuron delivers information to CNS
Cell body is located in dorsal root ganglion
Synapses with interneurons in CNS

13. Second-Order NeuronSecond-Order Neuron
Usually interneurons receiving information
from first order neurons
Axons cross to opposite sides of body
–Decussation
May be located in the spinal cord or brain
stem

14. Third-Order NeuronThird-Order Neuron
Located in thalamus
Carries information to cerebrum
Synapses with neurons of the primary
sensory cortex

15. Ascending Pathways to BrainAscending Pathways to Brain
What type of information do the neurons carry?
3 chains of successive neurons to brain
–1
st
order neurons
Where is cell body?
Conduct impulses from cutaneous receptors and
proprioceptors
Synapse w/ 2
nd
order
–2
nd
order neurons
Cell bodies in dorsal horn or in medullary nuclei
Transmit impulses to thalamus or cerebellum; synapse
–3
rd
order neurons
In thalamus
Where do they conduct information to?
No 3
rd
order neurons in cerebellum

16. First order neurons
–Sensory neurons that deliver sensory information to the
CNS
Second order neurons
–First order neurons synapse on these in the brain or
spinal cord
Third order neurons
–Found in the thalamus
–Second order neurons synapse on these
Only 1% of incoming sensory impulses actually reach the
cerebrum.
First, second, and third order neurons
The Organization of Sensory
Pathways

17. Posterior Column PathwayPosterior Column Pathway
Carries sensations of highly
localized (fine) touch, pressure,
vibration, proprioception
Spinal Tracts Involved:
–Left/right fasciculus gracilis
–Left/right fasciculus cuneatus

18. Peripheral nerves systemPeripheral nerves system

19. Sensory Pathways and Sensory Pathways and
Ascending Tracts in the Spinal Ascending Tracts in the Spinal
CordCord

20. dorsal
cloumn
pathway

21. Dorsal column pathwayDorsal column pathway

22. Dorsal-column leminiscal pathway
Principally conveys tactile
discrimination, vibratory and
position senses (Ab,large fibres).
1st order sensory neurones run on
the same side & synapse with 2nd
order neurones in the dorsal column
nuclei .
2nd order neurones integrate the
input and their axons cross to the
opposite side. These ascend through
the medial leminiscus
Further integration in the thalamus
& 3rd order neurones project to the
cortex.

23. The area of sensory cortex devoted to a body region is relative to
the number of sensory receptors.
The Posterior Column Pathway The Posterior Column Pathway
and the Spinothalamic Tractsand the Spinothalamic Tracts

24. Dorsal column pathwayDorsal column pathway
Large sensory nerves:
Touch, vibration, two-point
discrimination,
proprioception
Primary somatosensory
cortex (S1) in parietal
lobe
Thalamus
Medulla
Medial
lemniscus
Spinal cord
Dorsal column
Dorsal column
nuclei

25. Dorsal Dorsal
column column
damagedamage
dorsal column
pathway
Left
spinal cord injury
Loss of sense of:
•touch
•proprioception
•vibration
in left leg

26. Dorsal column damageDorsal column damage
Sensory ataxia
Patient staggers; cannot
perceive position or
movement of legs
Visual clues help movement

27. Central
Pathways

28. 3.3 Spinocerebellar pathway3.3 Spinocerebellar pathway
Carries unconscious
proprioception signals
Receptors in muscles &
joints
1
st
neuron: enters spinal
cord through dorsal root
2
nd
neuron: ascends to
cerebellum
No 3
rd
neuron to cortex,
hence unconscious

29. Coding in the sensory system Coding in the sensory system
could theoretically follow:could theoretically follow:
•The labeled-line principle in which each receptor
responds to a limited range of stimuli and sends
a direct line to the brain.
2. Across-fiber pattern in which each receptor
responds to a wider range of stimuli and
contributes to the perception of each of them.

30. THANK YOUTHANK YOU