Lecture 4 Different cns levels role in motor acts regulation Spine role in motor acts regulation.

Spinal neurons functional classification:

• motoneurons (alpha- and gamma-);

• interneurons;

• parasympathetic system neurons;

• sympathetic system neurons.

Alpha-motoneurons have direct connections from afferent ways coming from extrafusal muscular fibres.

Gamma-motoneurons innervate intrafusal muscular fibers of muscular spindle.

Interneurons – intermediate neurons; they organize connections between spine structures in realizing the influence of ascendant and descendant ways on separate spine segments cells.

2 Spine functions:

• reflectory;

• conductive.

Reflectory spine function: spine performs regulation of many reflectory acts – clinically important among them are tendinous reflexes. These are multiple reflexes which are investigated by short doctor’s shock on tendon. It is essential in neurology because every reflex of this group has definite spinal closage level. These reflexes are the most expressed in extensors and flexors of upper and lower extremities (knee jerk reflex, Achilles’ tendon reflex et al.). For example, light shock on patella tendon causes femur muscles contraction and tibia extension. Reflectory arc of this reflex is following: quadriceps femori muscle tendineal receptors→spinal ganglion→posterior fasciculi→ posterior corns of the III-rd lumbal spinal segment→ motoneurons of anterior corns of the same segment→ quadriceps femori muscle extrafusal fibres.

Flexory reflexes – are directed into different injuring actions prevention. They occur at skin, muscles and visceral organs receptors irritation. Example: noceoceptors irritation (pinch, nipping)→flexors contraction→hand taking away. These reflexes provide protective function.

Rhythmical reflexes- walking, scratching (rhythmic contractions and relaxations, flexings and extensions).

Pose reflections - are large group of acts directed to definite pose support (standing, lying et al.).

Spinal shock - is a state observed in a case of spinal trauma and its complete intersection. Reason: stoppage of influencies coming from upper nervous system parts to spine. It is accompanied by deep body musculature paralysis. Such muscles are innervated by spine segments located below injury place, later they are partially restored. Arbitrary movements restoration depends on pyramid ways injury degree.

Stem role in motor functions regulation.

Brain stem includes following structures:

• medulla oblongata;

• Varoli pons;

• midbrain;

• dieencephalon;

• reticular formation.

Medulla oblongata is delt with realization of vegetative and somatic, gustatory, auditory and vestibular reflexes.

Distinguishing feature of medulla oblongata reflexes is their more duration comparatively to spinal reflexes; afteraction and intersegmentarity are more expressed in them. Medulla oblongata is necessary for pose supporting (of all motor acts). These reflexes are originated from vestibular apparatus receptors (cochlea vestibule and semicircular channels), then they are switched to superior vestibular nucleus and finally processed information is transmitted to medulla oblongata lateral and medial vestibular nuclei. Role of these nuclei is the following: to determine, what muscular systems, what spinal segments must participate in pose changing. That’s why the sygnal comes to corresponding spinal segments anterior corns (such segments innervate muscles) from medial and lateral nuclei through vestibulo-spinal tract.

One can tell about 2 groups of these pose reflexes:

• stathic – they provide equillibrium support and body status in space while standing, lying, sitting in different poses;

• statho-kinetic – they provide muscular tone redistribution for corresponding pose organization in course of movement, direct or rotatory (they are originated from semicircular channels receptors).

Varolii pons and midbrain. Cerebral pons – is one of brain stem structures which is tightly linked with midbrain. All ascendant and descendant ways connecting anterior brain (brain hemispheres) with cerebellum and other brain structures.

Midbrain is represented by corpora quadrigemina, nuclei - red, black substantia, of oculo-motor and trochanter nerve.

Red nucleus – regulates musculature tone, when sending corrigating impulses to spine motoneurons through rubro-spinal tract. At its function injury as well as its connection with midbrain one can see reaction described as decerebrative rigidity. It is characterized by extremities, neck and back extensors tension.

Black substantia – is located in cerebral peduncles. It regulates mastication, swallowing, provides exact movements co-ordination (at writing, playing musical instruments, performance surgical operations).

Oculo-motor and trochanter nerve nuclei – provide eyeball turning in all directions.

Corpora quadrigemina tubercles (coluses or bodies) – superior are primary subcortical visual; inferior – primary subcortical auditory centers. Main functions: reaction “becoming more alert” (“what’s this” according to I.P.Pavlov) on sudden unknown visual and auditory reactions.