9. Ascending sensory II Flashcards
Most neurons of the grey matter are classified as…
Multipolar neurons
What are the neuron types of the grey matter
- Primary sensory
- Motor (alpha, gamma, visceral)
- Interneurons
- Projection neurons
What is the role of projection neurons
Relay signals to distant CNS areas; form a tract as they ascend
What is the role of interneurons
Local circuit neurons; relay sensory info to motorneuron, other interneuron or projection neuron
Where is the cell body of alpha (extrafusal)/gamma (intrafusal) motorneurons vs visceral motorneurons
- Alpha/gamma: ventral horn of C6-T2 and L4-S3
- Visceral: intermediate substance of T1-L3 (intermediolateral nucleus) and S2-S3 (parasympathetic nucleus)
Organization of SC grey matter
What are the 3 ‘horns’/ zone of the SC grey matter
- DORSAL (sensory)
- INTERMEDIATE ZONE (autonomic) - contains a lateral horn, which is a bulge formed by lamina VI
- VENTRAL HORN (motor)
Organization of SC grey matter
What are the two schemes of oraganization of the spinal cord
- Nuclear - based on groups of cell bodies
- Laminar - 10 laminae of Rexed based on cell structure
Organization of SC grey matter
Describe the localization of each laminae
Slide 22
- Lamina I-VI: dorsal horn
- Lamina VII + X: intermediate zone
- Lamina VIII: ventral horn
- Lamine IX: embedded in intermediate zone + ventral horn
Organization of SC grey matter
Name the SC grey matter nuclei
Dorsal horn
* Marginal nucleus
* Substantia gelatinosa
* Nucleus proprius
* Nucleus thoracicus
* Lateral cervical nuclus
Lateral horn/intermediate zone
* Intermediolateral nucleus
* Sacral parasympathetic nucleus
Ventral horn
* Medial & medial motor nuclei
Organization of SC grey matter
Marginal nucleus
- Lamina I
- Pain, touch, temp (exteroceptive)
- Entire SC
Organization of SC grey matter
Substantia gelatinosa
- Lamina II
- Interneurons (pain, touch, temp)
- Entire SC
Organization of SC grey matter
Nucleus proprius
- Lamina III-IV
- Interneurons + projection neurons
- Entire SC
Organization of SC grey matter
Nucleus thoracicus
- Lamina VI
- Proprioceptive info from PLs
- Unonscious - dorsal/ventral (PL) spinocerebellar tracts
- Conscious - spinomedullary tract (PL)
- T1-L4
Organization of SC grey matter
Lateral cervical nucleus
- Dorsolateral edge of dorsal horn
- Projection neurons
- Part of spinocervicothoracic tract (touch > pain)
- C1-C2
Organization of SC grey matter
Intermediolateral nucleus
- Lamina VII (intermediate zone)
- Sympathetic preganglionic neurons
- T1-L3
Organization of SC grey matter
Sacral parasympathetic nucleus
- Lamina VII (intermediate zone)
- Parasympathetic preganglionic neurons (to pelvic viscera)
- S2-3
Organization of SC grey matter
Know table slide 32!
okay okay
Unconscious ascending afferents
2 ascending pathways that do NOT reach conscious perception
Do not reach cerebral cortex directly
- Spinocerebellar tracts (muscle proprioception)
- Ascending reticular formation (all other senses)
Name the 5 spinocerebellar tracts
Pelvic limbs:
* Dorsal spinocerebellar tract
* Ventral spinocerebellar tract
Thoracic limbs:
* Spinocuneocerebellar tract
* Cranial spinocerebellar tract
Neck: (De lahunta)
* Cervicospinocerebellar tract
Spinocerebellar tracts
DORSAL spinocerebellar tract
- Muscle spindle
- DRG
- Nucleus thoracicus
- Ipsi dorsal spinocerebellar tract
- Caudal c.p
Spinocerebellar tracts
VENTRAL spinocerebellar tract
- GTO
- Base of dorsal horn
- Immediately decussates
- Contra ventral spinocerebellar tract
- Rostral c.p.
- Decussates again in the cerebellum
Spinocerebellar tracts
SpinoCUNEOcerebellar tract
- Muscle spindle
- Ascends ipsi cuneate fascicle
- LATERAL CUNEATE NUCLEUS (medulla)
- Caudal c.p.
Spinocerebellar tracts
CRANIAL spinocerebellar tract
- GTO
- Base of dorsal hon
- ipsi cranial sinocerebellar tract
- Either rostral or caudal c.p.
Which spinocerebellar tract is called the DIRECT pathway and why?
DORSAL spinocerebellar tract.
* No decussation
* Remains close to dorsal horn
* closest (caudal) c.p.
Which spinocerebellar tract is the INDIRECT pathway and why?
VENTRAL spinocerebellar tract
* Decussates twice
* Remains far from dorsal horn
* Farthest (rostral) c.p.
How do spinocerebellar tract collaterals reach conscious perception (somatosensory cortex)?
- DORSAL spinocerebellar: reaches nucleus Z (medulla) -> medial lemniscus - > thalamus -> SI
- VENTRAL spinocerebellar: nuclear X -> ..
Ascending reticular formation
What are the components of the ascending reticular formation
- Spinal part, cranial part (medullary, pontine, midbrain, thalamic)
- Project to cortex via central group of thalamic nuclei
N.b. is a midline system
- Cell bodies lie in the grey matter surrounding the central canal
Axons have short collaterals projecting to both sides of the reticular formation
- Contains an ascending and descending system which are intimately interconnected via reticular neurons
Relays all sensory modailities from SC to cerebrum except proprioception
Name the 5 gate mechanisms of pain
Presynaptic inhibition
Enkephalinergic activation from superficial pain
Enkephalinergic activation through raphe spinal tract
Intense physical activity (endorphin release)
Hypnosis (unclear mechanism)
Gate mechanism of pain
PRESYNAPTIC INHIBITION from mechanoreceptors (rubbing)
- Inhibitory collaterals from gracile and cuneate fasciles carrying info from mechanoreceptors (e.g. rubbing) synapse on C-fiber terminals in the substantia gelatinosa
Gate mechanism of pain
Enkephalic activation from SUPERFICIAL PAIN (acupuncture)
Excitatory collaterals from superficial pain afferents synapse on inhibitory enkephalinegic interneurons in the substantia gelatinosa, which them synapse on neurons projecting to the spinoreticular tract
Gate mechanism of pain
Enkephalic activation from raphe spinal tract (2nd mechanism of acupuncture)
Excitatory serotoninergic collaterals from raphe spinal tract synapse on inhibitory enkephalinergic interneurons in the substantia gelatinosa
