1. Somatosensory Systems
Proprioception
Modalities
Touch (and Pressure), Vibration Sense, Proprioception, Kinesthesia, Stereognosis
Proprioception - sense of static and dynamic position of limbs and body
Kinesthesia - the ability to feel movements of the limbs and body
Stereognosis – ability to recognize objects based on touch alone
Today – Proprioception
Dorsal Column-Medial Lemniscus Pathway –Fine Touch from Body
Main Trigeminal Nucleus – Fine Touch from Head
Cerebellar Pathways – Non-Conscious Proprioception

2. The Basic Plan for Somatosensory Information to Consciousness
Quaternary (4 ) o 4
Adequate Stimulus – The stimulus modality to which a sense organ responds optimally.
Generator Potentials are depolarizations in receptors that are graded relative to the intensity and form of the stimulus. 3
Sensory responses involved in unconscious proprioception respond in similar ways at the receptor level – the receptors include muscle spindles and golgi-tendon organs, and some of this information is transmitted to the ipsilateral cerebellum, and these will be presented at the end of this lecture.
Action Potential
Initiation Site 2 1
Serial Path to consciousness involves 4 neurons and 3 synapses
Result of a lesion at each level
Outside the CNS!

3. Sensory information from the body to Consciousness: 2 Systems
Medial
Lemniscus
Spinal Lemniscus
Anterolateral Dorsal Column
pain & temp, fine touch discrimination gross touch
anterolateral dorsal
protopathic epicritic
primitive recent
Spinal Lemniscus Medial Lemniscus
An important anatomical difference is where they cross (spinal cord vs brainstem). 1
Dorsal / Posterior
At the level of the pons the ALS is ALSO called the spinal lemniscus
Lateral 1
Ventral / Anterior

4. Key Elements - Divisions
Dorsal Column – FAST and Discrete allowing fine discrimination. Modality is Fine Discrimination Touch (vibration, pressure, conscious proprioception)
Anterolateral System = Lateral and Anterior Spinothalamic Tracts – Slow and Crude. Modalities are Pain, Temperature and Course Touch.

5. Conduc-tion Speed (m/sec)
Afferent Fiber Types – vary in conduction speed and modality
Entire Peripheral Nerve
Group
Fiber Type
Fiber Diameter (mm)
Conduc-tion Speed (m/sec)
Receptor Type
Modality I
A alpha
80 – 120
Spindles & GTO
Conscious and NonconsciousProprioception II
A beta
5 - 12
35 – 75
Spindles & Cutaneous Mechanoreceptors
Touch, Pressure, and Vibration
A delta
1 - 5
5 – 30
Free Nerve Endings, noci-, thermo-, & other mechano-receptors
Fast Pain, Temp, Touch IV C
0.1 – 1.5
0.5 – 2.0
Slow Pain, Temp, Touch, itch
FAST
They will already have had much of this info from Rich’s lecture the day before!!
SLOW
Haines, p42.

6. Afferent Fiber Types – also vary in myelination and point of entry into the spinal cord
Haines, Fundamental Neuroanatomy, p254

7. Somatosensory Information from the Body to Consciousness

8. Dorsal Column – Medial Lemniscus Pathway
MIDLINE
Internal Arcuate Fibers =
Sensory Decussation:
Crosses the midline
QUATERNARY 4o 4
High degree of spatial and temporal resolution.
Modalities: tactile (2-point discrimination), vibration, pressure, position sense.
Primary Somatosensory Cortex
synapse
TERTIARY 3o
Thalamus - VPL
synapse 3
SECONDARY 2o
Medial Lemniscus
Medulla
synapse 2
Receptor skin/muscle/tendon
PRIMARY 1o
DRG
Spinal Cord
Dorsal Funiculus
Click for Slide Animation 1

9. Gracilius and Cuneatus: Lower body and Upper Body Aspects of the Dorsal Columns
Pons
sup
inf
Colliculi
Posterior Intermediate Sulcus
T6+
Cuneate
Gracile
Spinal Trigeminal Nucleus
Pyramidal
Tract
Sensory Decussation * *
Click for Slide Animation
Posterior funiculus is divided by a posterior intermediate sulcus into medial fasciculus gracilis and a lateral fasciculus cuneatus. Posterior intermediate septum divides these two – becomes discernable at T6. * *
Central processes of the primary afferent’s axon are located in the dorsal funiculus of the spinal cord.
Lower body is represented Medially = Gracilius
Upper body is represented laterally = Cuneatus

10. Key Questions for the Touch Pathway from the Body
The second order neuron crosses the midline.
Where does the crossing occur for the Dorsal Column-Medial Lemniscus System?
Second order neuron is located in the brainstem.
Therefore the CROSSING occurs in the brainstem
Medial Lemniscus – Cells of origin?
- Contralateral brainstem: Gracile Nucleus - Lower Body; Cuneate Nucleus – Upper Body)
Click for Slide Animation
Medial Lemniscus – projects to (terminates in):
- Ipsilateral VPL of thalamus

11. Dorsal Column System – Symptoms Associated with Lesions
What is the symptom associated with the lesion?

12. Lesions and Clinical Deficits - Syringomyelia
Gliosis and cavitation in midline of the spinal cord – CSF enters the cord. The larger the cavitation, the more tracts affected. One possible cause is a Chiari Malformation. Other causes include trauma, infection. (anything that compresses the CSF)
Symptoms:
Bilateral loss of pain and temperature at the level of the lesion (segments involved).
Area of lesion

13. Lesions and Clinical Deficits - Wallenberg’s
Lateral Medullary (Wallenberg’s) Syndrome – Symptoms include loss of pain and temperature on the ipsilateral head/face, contralateral loss of pain and temperature in the body, and ataxia.
ALS (lateral spinothalamic tract)
Trigeminal Nucleus
Spinal Trigeminal Tract
Dorsal
Spinocerebellar Tract
Ventral
Lateral Medullary (Wallenberg’s) Syndrome- lesion of the dorsolateral medulla (occlusion of posterior inferior cerebellar artery); produces ipsilateral loss of pain and temperature in the head/face (spinal tract & nucleus of V) and contralateral loss of pain and temperature in the body due to interruption of spinal lemniscus.
Now this commonly occurs with occlusion of the posterior inferior cerebellar artery, which as you can see here essentially wraps around the medulla.

14. Lesions and Clinical Deficits – Tabes Dorsalis
Degeneration of myelinated afferent fibers in the dorsal columns, (destroys large diameter axons), is a late stage of syphilis.
Symptoms:
Severe deficits in touch and position sense but often little loss of temperature perception and of nociception. Bilateral lesion = bilateral effects.
Area of Lesion

15. LESIONS and Clinical Deficits – Brown-Sequard Syndrome
Hemisection of the spinal cord, often in the cervical spinal cord – (it is rare for the entire hemisection to be affected, but this does occur, more often incomplete hemisection is found).
Symptoms:
a) Loss of fine discrimination touch, vibration, and position sense ipsilaterally for body regions from affected dermatome and down
b) Loss of pain and temperature contralaterally for body regions from affected dermatome and down (small region of bilateral loss of pain and temp at level of lesion and 2 segments below)
c) Motor Effects: – Ipsilateral Spasticity and Weakness
Click for Slide Animation DC
Arch Neurol (2001) 58: 1470.

16. Spinocerebellar Tracts
Conscious Somatosensation
Non-conscious
Proprioception
Spinocerebellar Tracts
(IPSILATERAL)
BODY
HEAD
Trigeminal
System
PAIN
& Temp
Fine
Touch
Pain
Touch
Lateral
Spino- Thalamic
Dorsal Column System
Spinal
Principal
(Main)

17. Trigeminal Nerve – Sensory Component – pain, temperature, touch, position sense
Ganglion
Opthalmic
Maxillary
Mandibular
Mesencephalic Nucleus (Proprioceptive)
Main Sensory Nucleus (fine touch, pressure)
Spinal Trigeminal Nucleus (pain, temp)
TRIGEMINAL NUCLEUS
Click for Slide Animation

18. Trigeminal System: Touch Component
Click for Slide Animation

19. Principal or Main Trigeminal Nucleus – Touch Sensation from the Face
SI Cortex
SI Cortex
Contralateral
VPM
VPM
synapse
synapse
Dorsal
Ventral
Trigemino-
Trigemino-
thalamic
thalamic
Tract
cross midline
Tract m
Principal Sensory i
Mid Pons
Nucleus d l i n
Second Order Neurons e

20. Similarities Between Body and Head Pathways
The trigeminal ganglion is functionally similar to what in the body representation pathway?
Both contain cell bodies of the ? order neurons of what morphological cell type?
The Mesencephalic Nucleus of V is a special case why?
Answer: Dorsal Root Ganglion
first
Answer: pseudounipolar neurons
Answer: It is the only place within the CENTRAL nervous system that contains primary afferent cell bodies.

21. Key Questions for the Ventral Trigeminal Thalamic Tract
What sensory modalities are associated with the Ventral Trigeminal Thalamic Tract at the level of the pons?
Touch (conscious proprioception), Pain & Temperature
Where are the cell bodies of origin of the Ventral Trigeminal Thalamic Tract?
Contralateral Trigeminal Nucleus (Spinal & Main Components)
Where does the VTT terminate?
Ipsilateral Ventral Posterior MEDIAL (VPM) Nucleus of the Thalamus

22. Trigeminal System – Symptoms Associated with Lesions
VPM
This is a diagram or cartoon of the brain stem, a little bit of the spinal cord down here and not shown are the thalamus and cortex, up here.

23. Spinocerebellar Tracts
Non-conscious
Proprioception
Conscious Somatosensation
Spinocerebellar Tracts
(IPSILATERAL)
BODY
HEAD
Trigeminal
System
PAIN
& Temp
Fine
Touch
Pain
Touch
Lateral
Spino- Thalamic
Dorsal Column System
Spinal
Principal
(Main)

24. Cerebellar Tracts: Non-Conscious Proprioception
Cerebellum – Master coordinator of movement, does not initiate.
Limb position, joint angles, muscle tension, muscle length.
Dorsal Spinocerebellar Tract - coordination of individual muscles of the lower trunk and lower extremity during postural adjustments and movements.
Ventral Spinocerebellar Tract - general coordination of muscles of the lower part of the body during movement (walking).
Cuneocerebellar Tract - coordination of individual muscles in the upper trunk and upper extremity. C2 – T4
Click for Slide Animation
The general rule is that the cerebellum receives information from the ipsilateral side of the body

25. Cerebellar Tracts: Non-Conscious Proprioception
Flocculonodular Lobe
Receptor
DRG
Spinal Cord:
Dorsal Nucleus of Clarke
Restiform Body s y n a p e
Primary 1 o
Secondary 2
Dorsal Spinocerebellar Tract
Anterior Lobe
Posterior Lobe
Paramedian Lobule
Cerebellar
Nuclei
Dorsal
Spino-
Cerebellar Tract
T1 to L2
Inferior Cerebellar Peduncle
Spinocerebellum
Click for Slide Animation
Cerebellar Nuclei: fastigial, globose, emboliform, dentate
For Dorsal Spinocerebellar, fibers entering dorsal roots below (caudal to) L2 ascend in dorsal funiculus to reach the nucleus.
Kandel and Schwartz 1985, p506.

26. Key Elements for Dorsal Spinocerebellar Tract
The dorsal spinocerebellar tract carries information from the lower part of the body and synapses within the cerebellum in such a way to maintain the somatotopic map of the body within the cerebellum.
Key Questions for the Dorsal Spinocerebellar Tract
Where are the Cells of Origin for the Dorsal Spinocerebellar Tract?
Ipsilateral Spinal Cord: Dorsal Nucleus of Clarke
Where does the tract terminate?
Ipsilateral Spinocerebellum

27. Cerebellar Tracts: Non-Conscious Proprioception
Flocculonodular Lobe
Receptor
DRG
Spinal Cord:
Dorsal Nucleus of Clarke
Restiform Body s y n a p e
Primary 1 o
Secondary 2
Dorsal Spinocerebellar Tract
Anterior Lobe
Posterior Lobe
Paramedian Lobule
Cerebellar
Nuclei
Dorsal
Spino-
Cerebellar Tract
T1 to L2
Inferior Cerebellar Peduncle
Cuneo-
Cerebellar Tract
Cuneocerebellar Tract
C2 to T4
Dorsal root fibers in spinal segments C2 to T4 carry muscle spindle and exteroceptive information in the ipsilateral cuneate fasciculus to the main cuneate nucleus
Medulla

28. Key Elements for the Cuneocerebellar Tract
The Cuneocerebellar tract originates in the brainstem and ascends ipsilaterally to the cerebellum, carrying information from the upper body (C2-T4).

29. Cerebellar Tracts: Non-Conscious Proprioception
Ventral Spinocerebellar Tract
Spinal border cells
Ventral Spinocerebellar Tract
Ventral
Spinocerebellar
Tract
Afferents TO the ventral spinocerebellar Tract are group I flexor reflex afferents and group II and III mechanoreceptors.
Ventral Spinocerebellar and Rostral Spinocerebellar – cutaneous tactile information from Meissner’s, Merkel’s and Pacinian mechanoreceptors, group II and III afferents to cerebellum L3 to S1

30. Lesions and Clinical Deficits - Wallenberg’s
Lateral Medullary (Wallenberg’s) Syndrome – Symptoms include loss of pain and temperature on the ipsilateral head/face, contralateral loss of pain and temperature in the body, and ataxia.
ALS (lateral spinothalamic tract)
Trigeminal Nucleus
Trigeminal Tract
Dorsal
Spinocerebellar Tract
Ventral

31. Lesions and Clinical Deficits – Tabes Dorsalis
Degeneration of myelinated afferent fibers in the dorsal columns, (destroys large diameter axons), is a late stage of syphilis.
Symptoms:
Severe deficits in touch and position sense but often little loss of temperature perception and of nociception. Bilateral lesion = bilateral effects.

32. LESIONS and Clinical Deficits – Brown-Sequard Syndrome
Hemisection of the spinal cord, often in the cervical spinal cord – (it is rare for the entire hemisection to be affected, but this does occur, more often incomplete hemisection is found).
Symptoms:
a) Loss of fine discrimination touch, vibration, and position sense ipsilaterally for body regions from affected dermatome and down
b) Loss of pain and temperature contralaterally for body regions from affected dermatome and down (small region of bilateral loss of pain and temp at level of lesion and 2 segments below)
c) Motor Effects: – Ipsilateral Spasticity and Weakness
Click for Slide Animation DC
Arch Neurol (2001) 58: 1470.