Somatosensory Systems

1. Somatosensory Systems Kimberle M. Jacobs, PhD Sanger 11-046 827-2135 kmjacobs@vcu.edu

2. Somatosensory Systems Pain and Temperature LEARNING NEURONAL PATHWAYS REQUIRES REPETITION • Details of pathway: Where are cell bodies located, where is the synapse made, where do axons cross the midline, first structure, second structure, etc. • Location of nuclei and tracts within brain sections

3. Somatosensory Systems Somatosensory Systems – All senses other than Olfaction, Gustation, Audition, Vision, and Vestibular Sensation: Modalities Touch (and Pressure), Vibration Sense, Proprioception, Kinesthesia, Stereognosis, Pain & Temperature 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 • Pain and Temperature • Fine Discrimination Touch

4. Conscious Somatosensation Spinocerebellar Tracts (IPSILATERAL) BODY HEAD Trigeminal System PAIN & Temp Fine Touch Pain Touch Lateral Spino-Thalamic Dorsal Column System Spinal Principal (Main) Non-conscious Proprioception Information reaching consciousness goes to the Neocortex, Nonconscious Sensory Information goes to the Cerebellum

5. Somatosensory Information Travels from receptors in the Periphery (skin) to Consciousness in the Cortex The axons of the neurons carry action potentials that transmit the sensory signal. These pathways involve a serial chain. The first order neuron sends it’s axon to synapse with the second order neuron’s soma and dendrites. There are 4 neurons in the serial chain and 3 synapses.

6. o Quaternary (4 ) Action Potential Initiation Site The Basic Plan for Somatosensory Information to Consciousness 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 Crossing occurs either in spinal cord OR brainstem 2 1 2nd order neuron is located either in spinal cord OR brainstem Outside the CNS!

7. The basic plan for somatosensory information to consciousness involves 4 neurons and 3 synapses. • Cell bodies of the primary afferents are located outside of the central nervous system (in the dorsal root ganglion for body information and in the Trigeminal ganglion for head information). • Cell bodies of the second order neurons are located either in the spinal cord (anterolateral system) or in the brainstem (dorsal column system). • The axon of the second order neuron crosses the midline. • Cell bodies of the third order neurons are located in the thalamus (within VPL for body information and VPM for head information). • The fourth order neuron is located within the Primary Somatosensory cortex (Brodman’s areas 3, 1, 2). • If you lesion the pathway before it crosses you create IPSILATERAL deficits (loss of sensation on the same side of the body as the lesion). • If you lesion the pathway after it crosses you create CONTRALATERAL deficits (loss of sensation on the opposite side of the body as the lesion). • If you lesion the pathway AS it is crossing, you create BILATERAL deficits (both sides of the body affected). Key Elements of the Basic Plan: SS to Consciousness

8. IPSI IPSI IPSI This is the site of lost sensation after the lesion Lesion is ipsilateral to the receptor that begins coding the stimulus Before = IPSI, After = CONTRA PERCEPTION LEFT RIGHT Before Crossing After Crossing CONTRA STIMULUS

9. Conscious Somatosensation Spinocerebellar Tracts (IPSILATERAL) BODY HEAD Trigeminal System PAIN & Temp PAIN & Temp Fine Touch Pain Touch Lateral Spino-Thalamic Lateral Spino-Thalamic Dorsal Column System Spinal Principal (Main) Non-conscious Proprioception Information reaching consciousness goes to the Neocortex, Nonconscious Sensory Information goes to the Cerebellum

10. TERTIARY 3o synapse Thalamus VPL I II III IV Crosses the midline in the Ventral White Commissure Of the Spinal Cord V Spinal Cord: Lateral Funiculus VI SECONDARY 2o Spinal Cord: Dorsal Horn *ascend 2-3 spinal levels in Lissauer’s Tract (cap on dorsal horn) DRG Receptor (skin) Pain and Temperature Pathway: Anterior Lateral System 4 3 Lateral Spinothalamic Tract synapse 2 1 PRIMARY 1o MIDLINE

11. Dermatomes & Lissauer’s Tract Dermatome - the area of skin innervated by the sensory portion of a single cranial or spinal nerve. Primary afferents entering at T4 will synapse mainly in T2. Lesion at T2 in spinal cord: Area affected will include T4 since that is where the axons originally entered the spinal cord.

12. Key Elements - Lateral Spinothalamic Pathway • Transmits pain and temperature sensation from the body. • Located laterally in the spinal cord and remains relatively lateral through the brainstem and midbrain – (you will need to know the exact location – shown to you in video). • Crosses in the spinal cord. • Called the Lateral Spinothalamic Tract AFTER crossing in the spinal cord. • The tract travels from the spinal cord to the thalamus.

13. Thalamus Lateral Spinothalamic Tract Spinal Cord: Dorsal Horn Spinal Cord: Lateral Funiculus MIDLINE SECONDARY 2o Key Questions for the Lateral Spinothalamic Tract Where are the cell bodies of origin? Means where are the cell bodies connected to the axons that make up the tract – not where are the first order cell bodies. - Contralateral Dorsal Horn of the Spinal Cord Where does it project or terminate? Means where do those axons SYNAPSE? - Ipsilateral Ventral Posterior Lateral (VPL) of the Thalamus

14. Somatotopy is Maintained Throughout all CNS Levels S L T C

15. Lateral Spinothalamic Tract – Symptoms Associated with Lesions LEFT RIGHT

16. The Anterior Lateral System (ALS) The Lateral Spinothalamic Tract together with the Anterior Spinothalamic Tract is known as the ALS

17. CROSSES Anterior Spinothalamic Tract – Coarse or ‘light’ Touch Upper Medulla Lower Medulla Lateral Spinothalamic Tract Anterior Spinothalamic Tract Spinal cord

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

19. Opthalmic Maxillary Mandibular TRIGEMINAL NUCLEUS Mesencephalic Nucleus (Proprioceptive) Main Sensory Nucleus (fine touch, pressure) Spinal Trigeminal Nucleus (pain, temp) Trigeminal Nerve – Sensory Component – pain, temperature, touch, position sense Trigeminal Ganglion Human Brain Coloring Book, 6-11

20. Trigeminal NUCLEUS MIDBRAIN Opthalmic Maxillary Mandibular SPINAL CORD Human Brain Coloring Book, 6-12 TRIGEMINAL NUCLEUS Mesencephalic Nucleus (Proprioceptive) Main Sensory Nucleus (fine touch, pressure) Spinal Trigeminal Nucleus (pain, temp) Axons of Trigeminal Ganglion Cells Synapse in the Trigeminal NUCLEUS Trigeminal Ganglion

21. 1 1 1 2 2 2 Second Order Trigeminal System: All branches of the Trigeminal Nerve project to each of 3 components of the Trigeminal Nucleus

22. 1 2 First Order 1 2 2 1 2 2 2 Second Order Trigeminal System

23. 1 1 1 1 2 1 2 2 1 2 2 2 Second Order Trigeminal System First Order

24. 1 1 1 2 2 2 2 2 2 Trigeminal System 1 1 1 1

25. Similarities between Body and Face Pathways The trigeminal ganglion is functionally similar to the dorsal root ganglion. Both contain cell bodies of the PRIMARY AFFERENT pseudo-unipolar neurons. The Mesencephalic Nucleus of V is a special case because it is the only place within the CENTRAL nervous system that contains primary afferent cell bodies.

26. Trigeminal Nucleus: Spinal Component = Pain & Temp

27. Key Questions for the Tracts Spinal Trigeminal Tract Where are the cell bodies of origin? - Ipsilateral Cranial Nerve Ganglia of V, VII, IX, and X Where does it project or terminate? - Ipsilateral Spinal Trigeminal Nucleus Ventral Trigeminothalamic Tract Where are the cell bodies of origin? - Contralateral Trigeminal Nucleus Where does it project or terminate? - Ipsilateral VPM of the Thalamus

28. Left Right Left Right Spinal Trigeminal Pathways Ventral Trigemino- thalamic tract

29. 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 http://www.asap4sm.com/

30. Spinal Trigeminal Tract Trigeminal Nucleus Dorsal Spinocerebellar Tract Ventral Spinocerebellar Tract ALS (lateral spinothalamic tract) 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.

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