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Neuronal architecture of the spinal cord: prorioceptive and
nociceptive (withdrawal) reflex arcs
Viktória Vereczki M.D., PhD.Viktória Vereczki M.D., PhD.Department of Anatomy, Histology and Department of Anatomy, Histology and EmbryologyEmbryologySemmelweis UniversitySemmelweis University
Gross anatomy of spinal cord
•45 cm lon
from the atlas to L1-L2
•Maximal volumes:
Intumescentia cervicalis: 38mm
Intumescentia
lumbalis: 35 mm
Gross anatomy of spinal cord
Gross anatomy of spinal cord
Spinal ganglion
Pseudounipolar neurons in the spinal ganglion (HE)
Neuronal architecture of spinal cord
Cervical nerves 1-8
Thoracic nerves 1-12
Lumbar nerves 1-5
Sacral nerves 1-5
Coccygeal nerve 1
C3
C3
C6
C6
Th6
Th6
L3
L3
n. S2
S2
S2
n. L3
Neuronal architecture of spinal cord
White matter•Dorsal funiculus
•Ventral funiculus
•Lateral funiculus
•Anterior fissure
•Dorsal median sulcus
•Dorsal septum
•Sulcus dorsolateralis:Radices dorsales
•Sulcus ventrolateralis:radices ventrales
•Ventral white comissure
•Dorsolateral tract of Lissauer
cervical segment
thoracic segment
sacral segment
White matter:
Dorsolateral tract of Lissauer
Ascending pathways:
White matter:
Descending pathways:
White matter:
Fasciculus proprius: proriospinal fibers
•Posterior gray column dorsal horn( viscerosensory (enteroception) and somatic sensory neurons)
•Anterior gray column ventral horn(somatomotor neurons)
•Lateral gray column( only at thoracic segments) lateral horn (visceromotor neurons)
Neuronal architecture of spinal cord- gray matter
Neuron types: 1. radicular
2. funicular
3. internuncial
4. interneurons: f.i. Renshaw cells
Neuronal architecture of spinal cord- gray matter
Rexed laminae of spinal cord
( at the level of Th10)
1. Dorsal nucleus of Clarke-Stilling
2. Proper nucleus of dorsal comumn
3. Substantia gelatinosa (Rolandi)
4. Marginal zona
5.Intermediolateral cell column
6. Intermediomedial cell collumn
7. Motor neurons of ventral horn
Laminae of Rexed Afferent fibers, terminating here Efferent fibers , originating here
lamina I. –marginal zone Marginal neurons (Waldeyer-neurons): pain - and temperature sensory neurons, visceral afferents, from brain stem: monoaminoergic descending fibers
Tr. spinothalamicus
Dorsolateral tract of Lissauer
lamina II. -substantia gelatinosa (Rolandi)
From the skin nociceptive fibers: unmyelinated os myelinated, from brain stem: monoaminoergic descending fibers
The unmyelinated axons of substantia gelatinosa cels ascend or descend for up to four segments of the spinal cord; their branches synapse within the dorsal horn
lamina III-IV. nucleus proprius columnae dorsalis
Mechanoreceptors of skin Spinothalamic tract
lamina V-VI. Transmitting touch , pain and visceral signals
Spinothalamic tract
Fibers associating within the spinal cord
lamina VII. -nucleus dorsalis seu nucleus thoracicus (Clarke-Stilling nucleus)
Th1-L3:cornu laterale: • nucleus intermediolateralis• nucleus intermediomedialis
sacral part:
Proprioceptive and epicritic sensation of the skin of the lower part of the body
-internuntial neurons among the descending pathways and motoneurons, Renshaw cells
-tr.corticospinalis, tr. Reticulospinalis
Dorsal spinocerebellar tract (Flechsig)
-preganglionic sympathetic neurons
-preganglionaris parasympathicus neurons
lamina VIII. -comissural nucleus of Lenhossek
crossing fiber in the comisssura alba
lamina IX. –motor nuclei of ventral horn Aα-motoneurons
Aγ- motoneutons
lamina X.-substantia grisea centralis
Cervical segment: 1. Phrenic nucleus (C3-C5): Phrenic nerve
2. spinal accessory nucleus (C1-C5): spinal root of accessory nerveinnervating sternocleidomastoid adn trapezius muscle
S2 segment: 3. nucleus Onuf (motor nucleus of pudendal nerve: urinary and fecal continence,
innervating ischiocavernosus, bulbospongiosus muscles and pelvic floor
4. Lateral central nucleus
Bronislaw Onuf-Onufrowicz
(1863-1928)
Additional nuclei of lamina IX.:
Gray matter: 1.:
Cajal-Ag impregnation
II. lamina
Gray matter: 2.:
VII. lamina X. lamina
Schematic representation of motor neurons
1. Nucleus retrodorsolateralis: kis ujjizmok
2. Nucleus dorsolateralis: alkar és kéz izmai
3. Dorsalisan: hajlító izmok
4. N. ventromedialis et dorsomedialis:tarkó- és hátizmok, bordaközi és hasizmok
5. N. ventrolateralis: vállöv és felkar izmai
6. Ventralisan: feszítő izmok
1.2.
3.4.
5.6.
Ramus anterior
Plexuses
Ramus communicans albus
Ramus communicans griseus
Ramus posterior
Spinal nerve
Ramus meningeus
Typical arrangement of the spinal nerves
Reflexes of the spinal cord1. Proprioceptive, monosynaptic reflex
3.
1. Receptor :
Annulospiral endings of neuromuscular spindle
2. Afferent nerve: 1st neuron from spinal ganglion
Iα type sensory fibere its collaterals terminate on the same segment’s motoneuron, and more caudal segments’ inhibiting neurons
3. Central connections:
monosynaptic
4. Efferent nerve: 2nd neuron
Aα motoneuron innervating its own extrafusal fibers
5. Effector:
Its own muscle fiber
6. Additional connections:
a., reciprok inhibition
b., gamma-loop
1. Proprioceptive, monosynaptic reflexReflexes of the spinal cord
1.
2.
4.
5.
6. Additional connections : a., reciprok inhibition b., gamma-loop
1. Proprioceptive, monosynaptic reflex
specific inhibitory neuron
Antagonist muscle group is inhibited
6. Additional connections : a., reciprok inhibition
b., gamma-loop
gamma-loop
1.Descending axon
(pl. tr. reticulospinalis, tr. vestibulospinalis)
2. Aγ neuron (innervation intrafusal fibers)
3. Neuromuscular spindle: anulospiral receptor
4. Iα sensory neuron‘s fiber for the muscle spindle
5.Aα motoneuron (innervation of the extrafusal musclefiber)
1. Proprioceptive, monosynaptic reflex
1.
2.
3.
4.
5.
Function:Regulating muscle tone
Clinical importance of monosynaptic reflexes:Clinical tendon jerks
DIMINISHED
Lesion of „lower motoneurons”
(trauma, degeneration, demyelination disorder, infections, impairment of blood supply, tumors)
Flaccid paralysis of affected muscles: segmantal localization
Examples:patella-reflex L2-4, biceps-reflex C5-6, triceps-reflex C6-7, gastrocnemius-reflex S1-2
EXAGGERATED
Lesion of „upper motoneurons” -
lack of inhibitory pathways results in spastic palsy
Reflexes of the spinal cord
2. Polysynaptic, nociceptive (withdrawal) reflex arc
2. Polysynaptic, nociceptíve (withdrawal) reflex arc1. Receptor:
Nociceptors in skin , mucosa
2. Afferent nerve: 1st neuron from spinal ganglion
Aδ, C rostok (Lissauer –zone)
3. Central connections: 2nd or 3rd neuron:
Interneurons, funicular neurons: among many segments, Renshaw-inhibition
4. Efferent nerve : at least the 3rd neuron
Aα motoneuron
5.Effector:
Flexor muscles of the same side , and extensor muscles of the opposite side
Examples:
abdominal-reflex, cremasteric-reflex, cornea-reflex.
Reflexes of the spinal cord
3.
1.
2.
4.
5.
2. Polysynaptic, nociceptíve (withdrawal) reflex arc