1. Somatosensory Pathways Lectures 11-13

2. Organization of the Course Spinal Cord Brainstem/ Cerebellum Sensory Pathways Cerebrum Motor Pathways Cranial Nerves Other Pieces of the puzzle Overview and Development

3. Last Friday Task due this Friday midnight (so I can grade them and provide feedback before exams!) Cerebellar histology – my office hours are this afternoon 2-3 and Wed. 2-3

4. Sensory Pathways Objectives Describe the structures, functions, locations, neurotransmitters, and decussation level for each sensory pathway ◦ DC/ML ◦ ALS  Spinothalamic  Spinotectal  Spinoreticular ◦ Trigeminal ◦ Solitary Analyze case studies using knowledge of the somatosensory pathways.

5. Overview of Sensory Pathways Dorsal Column / Medial Lemniscus ◦ Light touch, proprioception, vibration of body Anterolateral System ◦ Pain, temperature of body Trigeminal ◦ Light touch, proprioception, vibration of face ◦ Pain, temperature of face Solitary ◦ Visceral sensations of body and head

6. Dorsal Column / Medial Lemniscus Pathway Light touch, vibration, proprioception Conscious 3 neuron pathway Decussates in the lower medulla (arcuate fibers) AcH and Glutamate (excitatory)

8. DC/ML course ● 1st order - Cell body in DRG ○ Fasciculus Gracilis (FGr) (Posterior - Medial)-anything below T7 level and below ■ Light touch, vibration, position sense from ipsilateral leg and lower trunk ■ Periphery → FGr → Gracile Nucleus (NuGr) ○ Fasciculus Cuneatus (FCu) (Posterior - Lateral)- T6 Level and above ■ Same as above, but from ipsilateral arm and upper trunk ■ Periphery → FCu → Cuneate Nucleus (NuCu) ● 2nd order - Cell body in NuGr (LE); NuCu (UE) ○ Cross/decussate at Internal arcuate fibers (IAF) into ML ○ ML ends at Ventral posterolateral nucleus of thalamus nucleus (VPL) ● 3rd order - Cell body in VPL ○ VPL to Somatosensory cortex (Postcentral Gyrus; Brodmann 3,1,2)

10. Anterolateral System Spinothalamic Spinoreticular Spinotectal (aka Spinomesencephalic) Pain, temperature, pressure Conscious and subconscious 2-3 neuron pathway Decussates at level of Spinal Cord Glutamate, Substance P, enkephalin, cholecystokinin, serotonin (and others)

12. ALS course ● 1st order- Cell body in DRG ○ Periphery → DRG → Dorsal Horn (DH) ■ Synapses with 2nd order in DH ● 2nd order - Cell body in Dorsal Horn - Lamina 1&2 ○ Cross/decussate from DH through Anterior white commissure to Anterolateral system (ALS) ○ ALS = Primary route is Spinothalamic tract = conscious perception of pain ● Branch off → intralaminar nucleus (Thalamus) = alert/arousal ■ Main Branches: ● Reticular formation = Spinoreticular tract = wakefulness ● Midbrain = Spinotectal tract = Pain modulation ● Hypothalamus = Spinohypothalamic Tract = Emotional and autonomic responses to pain ● 3rd order - Cell Body in VPL ○ VPL to Somatosensory cortex (Postcentral Gyrus/ Posterior Paracentral Gyrus; Brodmann 3,1,2)

13. Post-synaptic Dorsal Column Pathway

14. Convergent, divergent, oscillating pathways/circuits Convergent pathways ◦ Many neurons synapse onto fewer neurons ◦ More typical within cerebral cortex Oscillating circuits ◦ Cerebellar cortex -> deep nuclei -> cerebellar cortex Divergent pathways ◦ One neuron synapses onto more neurons ◦ Transmits one signal to multiple places ◦ Post-synaptic dorsal column is an example ◦ Spinoreticular and spinotectal are examples

17. Analyzing Case Studies Your patient has damage to the Right dorsal column of the spinal cord from the T11-T12 vertebral disc. Which pathways are damaged? What functions are lost and where?

18. Brown-Sequard Syndrome Your patient has a hemisected spinal cord at SC level T8 (left side affected). What somatosensory pathways are damaged? What functions are lost and where? Hint: there might be a combination of segmental deficits and below the lesion deficits.

19. Research topics Small groups Take turns to discuss updates and thoughts about topics If you have a general plan for how to lay out your paper, explain it and get feedback GOAL: To work through thoughts, plans, organization by explaining it to another person. Producing communication (speaking, writing) often leads to more complete thoughts than just absorbing communication (listening, reading). Being able to articulate your thoughts now will lead to a better product in the end.

20. Sensation of face and viscera! Trigeminal Pathway ◦ Nuclei: ◦ Nerves: Solitary Pathway ◦ Nuclei: ◦ Nerves:

21. Trigeminal Nerve Opthalmic (V1) ◦ Sensation ◦ Sup. Orbital fissure Maxillary (V2) ◦ Sensation ◦ Rotundum Mandibular (V3) ◦ TM joint sensation ◦ TM joint musculature ◦ Ovale

22. Trigeminal Nuclei Chief Sensory Nucleus ◦ Fine + discriminative touch, vibration sense Mesencephalic Nucleus ◦ Proprioceptive input Trigeminal Motor Nucleus ◦ Motor to TMJ muscles Spinal Trigeminal Nucleus ◦ Pain + Temperature stimuli, Crude touch ◦ Spinal Trigeminal Tract ◦ From here, information travels to ___________

23. Motor Pathway (V) Proprioception from Mesencephalic N. Pain, temp, touch from Spinal N. Descending control from cerebral cortex (corticonuclear pathway, to be discussed) To Motor Nucleus Lower Motor Neurons through V3 (mandibular nerve) to muscles of mastication

25. Sensory of face Split into 3 parts: ◦ Proprioception  To Mesencephalic Nucleus  Decussates – contralateral ◦ Touch  To Sensory Nucleus  Bilateral ◦ Pain and temperature  To Spinal Nucleus  Decussates – contralateral All go to contralateral VPM (through trigeminal lemniscus) ◦ Touch also goes to ipsilateral VPM All also send info to: RF, Hypoglossal Nuc., Facial Nuc., V Motor Nuc. From VPM to sensory cortex (post-central gyrus)

27. Trigeminal Neurotransmitters Substance P (+) - pain CCK (+) Glutamate (+) Enkephalin (-) - pain

28. Solitary Pathway Sensory pathway for Cranial Nerves: ◦ VII Facial ◦ IX Glossopharyngeal ◦ X Vagus Solitary Nucleus ◦ Rostral part = taste ◦ Caudal part = throat, mouth sensation

29. Taste (Rostral part) Taste sensation from: ◦ ANT 2/3 of tongue  Facial Nerve (VII) ◦ POST 1/3 of tongue  Glossopharyngeal Nerve (IX) ◦ Taste buds at root of tongue, epiglottis  Vagus Nerve (X) Synapses in rostral part of solitary nucleus ◦ Ascends to ipsilateral VPM, synapses, continues to sensory cortex ◦ Sends info to hypoglossal nucleus ◦ Sends info to salivatory nucleus  (salivation reflex)

31. Visceral Sensations (Caudal part) IIV Facial Nerve  Glands (submandibular, sublingual, lacrimal) IX Glossopharyngeal Nerve  Parotid gland  Mucosa of pharynx  Tonsilar sinus  POST 1/3 of tongue  Carotid body X Vagus Nerve  Pharynx  Larynx  Aortic bodies  Thoracic & abdominal viscera  Ex. peristalsis

32. Visceral Sensations (Caudal part) Sensory information synapses in caudal solitary nucleus Information is relayed to: ◦ Ipsilateral Hypothalamus  (central regulatory center for autonomic functions) ◦ Ipsilateral Motor Nucleus of Vagus N.  (descending visceral motor control) ◦ Ipsilateral Nucleus Ambiguus  (gag reflex) ◦ Ipsilateral Amygdala  (fear center)

34. NICE TO KNOW Baroreflexes – Heart, vessels (ex. Carotid sinus) Chemoreflexes – Carotid & aortic bodies

35. Solitary Pathway Neurotransmitters GABA Substance P Enkephalins Somatostatin CCK

38. Review General Anatomy Development Support Systems Spinal Cord Brainstem Cerebellum & Pathways ◦ Spinocerebellar (4 parts), pontocerebellar, reticulocerebellar, ceruleocerebellar, raphecerebellar, hypothalamocerebellar, olivocerebellar ◦ Nucleocortical, corticonuclear, corticovestibular ◦ Efferent fibers Somatosensory Pathways ◦ DC/ML, ALS, postsynaptic ◦ Trigeminal ◦ Solitary