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