Classification of Receptors Types of Receptors Types of skin receptors Special receptor organs of the skin Dermatomes Receptors in the deeper regions of the body Peripheral nerve, Nerve plexus and posterior root Classification of nerve fibers Ascending tracts Dorsal system – Medial lemniscus pathway Anterolateral system

1. Neuroanatomy of the pain
structures in the spinal cord
Tural Abdullayev

2. Receptors
• Exteroreceptors/Telereceptor
– Takes information about the changes in the external
environment
• Interoreceptors/Visceroceptors
– Sensory receptor that detects stimuli within the body
1. Osmoreceptors
2. Baroreceptors
3. Chemoreceptors
• Proprioceptors
– Information about:
1. Joint position
2. Tension in muscles and tendons
3. Movement or position of head etc.

3. Skin receptors
• Free nerve endings
1. Pain
2. Touch and light pressure
3. Temperature
• Encapsulated end organs
1. Vibration
2. Fine touch
3. Pressure
4. Discrimination

4. Skin receptor organs
• Mechanoceptors
1. Touch
2. Pressure
• Thermoreceptors
1. Cold
2. Warm
• Nociceptors
– Pain

5. Special receptor organs of the skin
1. Peritrichial nerve endings
– Around the hair follicles
– Activated by movement of hair
2. Tactile capsules of Meissner – touch and pressure
receptors
– Only on glabrous skin, on the lips, tip of the tongue and
genitals
3. Laminated Vater-Pacini capsules – pressure receptors
– In area between the cutis and subcutis
4. End bulbs of Krause – cold receptors
5. Corpuscles of Ruffini – warm receptors

6. Dermatomes

7. Receptors in the deeper regions of the
body
1. Muscle spindles
– Respond to stretching of muscle
– Contain intrafusal muscle fibers
– Afferent fiber in the middle of the muscle spindle
• Very thick myelin sheath (Ia)
2. Golgi tendon organs
– Thick myelin sheath
– Respond to muscle stretching but at higher treshold
3. Laminated Vater-Pacini corpuscles and Golgi
Mazzoni corpuscles
– Pressure and pain

8. Peripheral nerve
• Action potentials arising in a receptor organ of one of
the types described above are conducted centrally
along an afferent fiber, which is the peripheral process
of the first somatosensory neuron, whose cell body is
located in a dorsal root ganglion
• Circumscribed area of the body run together in a
peripheral nerve; such nerves contain not only fibers
for superficial and deep sensation (somatic afferent
fibers) but also efferent fibers to striated muscle
(somatic efferent fibers) and fibers innervating the
internal organs,

9. Nerve plexus and posterior root
• Once the peripheral nerve enters the spinal canal
through the intervertebral foramen, the afferent
and efferent fibers go their separate ways: the
peripheral nerve divides into its two “sources,”
the anterior and posterior spinal roots:
– Anterior root contains the efferent nerve fibers
exiting the spinal cord
– Posterior root contains the afferent fibers entering it.
• A direct transition from the peripheral nerve to
the spinal nerve roots is found, however, only in
the thoracic region

10. Sensory fibers of a sinle radicular
segment are grouped together once
again to supply a characteristic
region
Each muscle is suplied by a single
peripheral nerve, which contains
fibers from multiple nerve roots, so-
called Polyradicular/Plurisegmental
innervation

11. Classification of nerve fibers
• A fibers
1. 
• Somatic motor
• Proprioception
– Muscle spindle – Ia
– Golgi tendon organ – Ib
2. 
• Touch and pressure – II
3. 
• Motor to muscle spindles
4. 
• Fast pain
• Cold
• Touch
• B fibers
1. Preganglionic
2. Sympathetic
• C fibers – most numerous
1. Dorsal root
• Slow pain
• Hot
• Mechanic and others
• Receptors
2. Sympathetic
• postganglionic
III
Myelinated
Diameter
and velocity
decreases

12. Ascending tracts
1. Dorsal system – fast system
– Fine touch
– 2-point discrimination
– Proprioception
2. Anterolateral system – slow system
– Lateral tract / Lateral spinothalamic tract
– Anterior tract / Ventral spinothalamic tract
– Light touch, pain, pressure, tickle, and itch
sensations

13. Ascending tracts

14. Dorsal system – Medial lemniscus
pathway
Receptor
Dorsal root nuclei
Central process
Posterior part
Medial fiber
F.Gracilis
Connects with n. Gracilis
Lower medulla
F. Cuneatus
Connects with n.Cuneatus

15. Dorsal system – Medial lemniscus
pathway
1st order fibers terminates in n.Cuneatus and n. Gracilis and 2nd order fibers starts
Internal arcuate fibes
Medial lemniscus
VPL of thalamus ( 2ndorder fibers terminates here and 3rd order fibers starts)
Fibers pass through the posterior limb of internal capsule and move
upward
Corona radiata is formed
Post-sensory gyrus

16. Dorsal system – Medial lemniscus
pathway
• Sensation from the lower limbs is deposited
medially – Gracilis fibers
• Sensation from the upper limbs is deposited
medially – Cuneate fibers

17. Anterolateral system
Temperature and pain
Free nerve ending
A or C fiber pathway
Dorsal root ganglion
Fibers entering the spinal cord
Substantia gelatinosa
Fibers cross to contralateral white matter
Cruel/Weak touch
Free nerve ending
Dorsal root ganglion
Fibers entering the spinal cord
Substantia gelatinosa
Fibers are running to anterior part

18. Anterolateral system
Anterior and lateral tracts fuse in medulla
Travel towards the thalamus
VPL nucleus
Fibers pass through the posterior limb of internal capsule and move upward
Postcentral gyrus
Slow pain
Intralaminar nucleus of thalamus Reticular
formation

19. Anterolateral system
Postcentral gyrus
Fast pain fibers
Emotions
Singulate gyrus
Slow pain fibers
Nausea
Vomiting
Tachycaria etc.
Insular cortex