1 / 26

Neural and Sensory

Neural and Sensory. Efferent innervation Neuromuscular junction a -, g -motorneurons Afferent innervation Muscle spindle Golgi tendon organ. Overview. Motor Unit Motorneuron + many muscle fibers Cholinergic synapse Spindle Enapsulated , specialized muscle-like cells

yanka
Download Presentation

Neural and Sensory

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Neural and Sensory • Efferent innervation • Neuromuscular junction • a-, g-motorneurons • Afferent innervation • Muscle spindle • Golgi tendon organ

  2. Overview • Motor Unit • Motorneuron + many muscle fibers • Cholinergic synapse • Spindle • Enapsulated, specialized muscle-like cells • Combined length-velocity proprioception • Tendon organ • Nerve endings woven through collagen • Active tension mechanorecption

  3. Dorsal/posterior Ventral/anterior MN density Efferent Innervation • a-motorneuron • 100 um cell body/soma • Ventral horn of spinal cord • Columnar organization by muscle • 8-18 um diameter axon • 60-120 m/s conduction velocity • Terminal branches within target muscle • Dendritic tree • 10,000+ inputs per MN • Excitatory glutamic synapses • Inhibitory glycinergic/GABAergic synapses Cervical Arm/hand Thoracic Lumbar Sacral Leg/foot

  4. Neuromuscular junction • Motor endings • Synaptic vessicles • Mitochondria • Synaptic cleft • Primary • Secondary invaginations • Muscle • Post-synaptic density • Mitochondria deHarven & Coers, 1959

  5. By SEM Sohn & al., 1999

  6. Synaptic vessicle anchoring • SV anchored by “pegs and ladders” Harlow & al., 2000

  7. Synaptic structure • Complementary • Presynaptic active zone • Postsynaptic density/receptor • ECM coordination • NerveagrinMuSK • MuscleLam 421/521VGCC • Electrical coordination • Nerve: ubiquitinylation preserves synaptotagmin • Muscle: depolarization degrades AChR

  8. Presynaptic side • Docking site • SNAP-25 • Syntaxin (T-SNARE) • Synaptic vesicle • Synaptobrevin (V-SNARE) • Synaptotagmin • Docking trimer: t/v-SNARE+SNAP • Calcium sensitivity: synaptotagmin

  9. Presynaptic active zone De Wit & al., 2009

  10. Presynaptic active zone Garner 2002

  11. Postsynaptic side • Post-synaptic density • MuSK/LRP4 receptor • Rapsyn/Dok-7 adapter • Src kinase • Acetylcholine receptor • Junctional folds • Sodium channels • Acetylcholinesterase

  12. Post-synaptic density Shi & al., 2012

  13. Afferent innervation • Afferent • Sensory • Dorsal root ganglion • Synapses in SC • Spindle • Muscle-likecells • Mechanosensitivenerve ending

  14. Muscle Spindle • Capsule • Polar regions • g-motorneurons • Striated contractile proteins • Equatorial region • Primary afferent (Ia) • Secondary afferent (II) • Non-contractile • Nuclear bag & chain Barker, 1948

  15. Spindle afferents Barker, 1948

  16. Spindle efferents • Dynamic bag/bag1 • Usually only influences the primary ending • Increases velocity gain • Static bag/bag2 • Offset both primary & secondary • Reduces length sensitivity of primary • Chain • Take up slack • Increase length sensitivity of secondary

  17. Spindle Mechanics • Equatorial stretch induces depolarization • Windings amplify length change • Stretch imposed from outside • Stretch imposed by contraction of poles • Accommodation • Viscoelastic creep/relaxation • Primary fast: velocity • Secondary slow: length

  18. Stretch response Primary ending Secondary ending Muscle length Afferent firing rate Houk & al, 1981

  19. Ian Boyd video clip

  20. Stretch Reflex • Ia afferent“homonymous” motorneuron • Servo-like length control • Tendon tap • Vibration illusions • IaIa interneuron • Inhibit antagonist(s) • Mechanical equivalence • Myotatic unit • IIdorsal horn interneurons • Distributed, slower excitation

  21. Golgi tendon organ • Free nerve endings embedded in capsule at muscle-tendon interface • Group Ib Nitatori, 1988

  22. Goldfinger & Fukami 1982

  23. GTO response • MTJ tension depolarizes afferent Muscle length GTO discharge rate Muscle force Crago & al., 1982

  24. GTO Reflex • IbIb interneuron • Delayed homonymous inhibition • Distributed excitation/inhibition • “Interaction” torques • Locomotor pattern integration • Polysynaptic pathways are subject to extra modulation

  25. Summary • a-motorneuron efferent forms coordinated NMJ • Presynaptic active zone for ACh release • Postsynaptic densities for ACh transduction • Monosynaptic stretch reflex • Combined length and velocity signal • Intrafusal fiber mechanics mimic extrafusal fibers • Polysynaptic GTO reflex • Force feedback • Distributed

More Related