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Lesson 11 Spinal cord physiology. Spinal cord role investigation in motor organism functions regulation

1.Topic studied actuality:

Spine represents main canal for afferent (cutaneous, temperature, proprioceptive and noceoceptive or pain) signalization from peripheral receptors to CNS highest parts. At afferent impulses conductance disorders through spine (at syphilitic spine injury i.e. tabes dorsalis) human being can not perform movements at closed eyes (ataxy). For example, mother can not take his baby on her arms. Spine is main canal of opposite afferentation about motor acts results. Also spine is a leading tract of excitement passage from CNS to motoneurons and associative neurons of lateral corns which form motor and vegetative reactions. One can tell that spine provides relatively primitive, simple, stereotypic activity. Spinal neurons excitability is low: exciting influence from brain is essential for their activity. Spine is responsible for most reflexes realization. Spinal reflexes are specifically changed or even disappeared at spine injury.

Spinal shock is observed after spine cutting. All spine functions disappear rapidly at this. Spinal reflector reactions are restored quickly in lower animals (in frogs – in 10-15 min), moreover, the lower alive organism is, the restoration time less is because they have developed subcortex comparatively to cortex. Cutted spine is practically not restored in human being. There are some theories of spinal shock. F.Goltz considered spinal shock as an irritation result. But Ch. Sherrington, G.Trendelenburgh also studied spinal shock at spine cooling blockade. Repeated cutting of spine lower than first cutting also does not cause spinal shock. All this indicates to the fact that spinal shock occurs due to spine separation from brain parts located above.

Microelectrode investigations demonstrated that motoneurons do not suffer at spinal shock. Associative neurons are injured due to which reactions to afferent stimuli are absent.

Paralyses belong to one of the most widely-spread motor disorders.

Main distinguishing features of central and peripheral paralyses are given in a table.

Paralysis type

Central or spastic

Peripheral, sluggish or atrophic

Injuries location

Cortex motor projectional area or pyramidal fascicles

Spine anterior corn, peripheral nerves anterior fascicles and anterior fibers

Paralysis distribution

More often diffused

More often limited

Muscles tone

Hypertony, spasticity

Hypotony, atrophy

Reflexes

Deep reflexes are increased, abdominal and plantar are decreased or lost

Deep and skin reflexes are decreased or lost

Pathological reflexes

Some of them are present

Absent

Conjugating movement

Present

Absent

Degeneration reaction

Absent

Present

Motor ways different floors injuries are accompanied by varies symptoms complexes:

1. Peripheral nerve injury causes peripheral paralysis in the area of muscles innervated by given nerve. Also sensitivity disorders are observed because biggest amount of nerves are mixed (with motor and sensor fibers).

2. Plexuses injuries lead to peripheral paralyses, pain and sensitivity disorders.

3. Spine anterior corns and anterior radixes (also cranial nerves motor nuclei) pathology causes only peripheral paralyses without pain and sensitivity disorders.

4. Spine lateral corn (with lateral cortico-spinal tract passing in it) injury causes diffused (central paralysis below from the injury locus); leg paralysis if thoracical part is injured; arm and leg central paralysis is observed if pyramidal fascicle is injured upper than cervical plexus. Also lateral corn injury is accompanied by noceoceptive and temperature sensitivity loosing on opposite side.

5. Spine transversal cutting gives lower extremities central paraplegia (pyramidal fascicles two-sided injury) – at location in thoracical part, or tetraplegia (all 4 extremities injury) – at upper (superior cervical injuries).

6. Brown-Sequard’ syndrome (spine half injury) – spastic paralysis and deep sensitivity disorders on the injury side and superficial sensitivity loosing on an opposite side.

7. Pyramidal fascicle injury in brain stem (pons cerebri, medulla oblongata, peduculi cerebri) gives central hemiplegia on opposite side because pyramidal ways are crossed below, on the boarder with spine. Usually cranial nerves are involved on the focus side. It creates the picture of so-called alternating (crossing) paralysis: cranial nerves injury on injury focus side, central hemiplegia – on opposite side.

8. Pyramidal fibers injury in internal capsule causes central hemiplegia (leg and arm on one side), facial musculature inferior part central paralysis on opposite side because cortico-nuclearis tract is also injured at the same time.

9. Motor projectional zone irritation causes epileptic fits (local or generalized).

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