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.

 

Diencephalon

It consists of:

· thalamus;

· hypothalamus;

· epithalamus.

Only thalamus deals with motor reactions. Other parts activity are linked with vegetative and behavioural reactions.

Thalamus – is a structure in which processing and integration of practically all signals coming into brain cortex are occurred. Such signals are originated from spine, midbrain, cerebellum, basal gangliums. There are more than 120 nuclei in it, forming complexes that are divided into: anterior, posterior, medial and lateral. Thalamus complicated structure, existance of interconnected specific, non-specific and associative nuclei allow to organize such motor acts as sucking, mastication, swallowing, loughing. Motor acts are integrated in thalamus with vegetative reflexes providing these movements.

 

Brain reticular formation

It is represented by neurons net with multiple connections practically with all brain parts. Its participation in movement: from it to spinal and cranio-cerebral nuclei motoneurons sygnals come which organize head, trunk status and pose. Reticular ways releasing spine motor systems activity are originated from all reticular formation parts. Ways coming from pons inhibit spine motoneurons activity (the latest innervate flexors and activate extensors motoneurons). Ways coming from medulla oblongata cause opposite effect. Reticular formation irritation leads to tremor, muscular hypertony or spinal reflexes inhibiting. It occurs when pose is necessary to be regulated and one movement must be changed by other one.

 

Cerebellum

Cerebellum sends efferent sygnals to spine and regulates muscular contractions force, permits durable tetanic muscular contraction, saving optimal muscular tone under rest and movement states, to measure arbitrary movements to perform fast transition from flexion to extension and on the contrary. It provides different muscles contractions synergy at complicated movements for example, in course of walking.

When cerebellum doesn’t regulate movements human being has different motor disorders.

· Astheny – muscular force contraction decreasing; fast muscles fatigue.

· Asthasy – loosing the ability to durable muscular contraction that makes standing, sitting difficult and even impossible.

· Athaxy – movements co-ordination disorders.

· Asynergy – co-operative movements disturbances (human being can’t sit from laying state without hands help).

· Dystony – muscular tone unarbitrary increasing or decreasing.

· Thremor – fingers, hand, head trembling under rest; this thremor is enforced during movement.

· Dysmetry – movements equality disorders expressed either in excessive or in insufficient movement.

· Dysarthry – speech disorder.

· Drunk walking – person is walking having arranged his leg widely, having shaked from one side to another.

· Adiadochokinesis – person can’t rotate fast his hands up and down.

· Writing disorders – megalography – very big letters.

At cerebellum injury medulla oblongata vestibular nuclei and reticular formation neurons are activated which stimulate spine motoneurons. Simultaneousely pyramidal neurons activity is decreased and thus their inhibitory influence to those spinal motoneurons is reduced. Finally, motoneurons cause muscular hypertonus having received stimulating sygnals from medulla oblongata while absence inhibitory sygnals from cortex.

 

Basal ganglions.

They include 3 pair structures:

1. Neostriatum:

· caudate nucleus;

· putamen (shell).

2. Paleostriatum:

· globus pallidus.

3. Claustrum.

Neostriatum – participates in musculature tone regulation. Injury symptoms - hyperkineses:

· unarbitrary mimic reactions;

· atethosis (worms-like fingers movements);

· thremor;

· torsion spasm;

· chorea (extremities and trunk trembling like at non-coordinated dance);

· motor hyperactivity as non-purposeful transfer from place to place.

Caudate nucleus injury symptoms:

· at two-sided injury – striving for unrestrained movement forward;

· at one-sided injury – rotatory (so-called manege) movements.

Paleostriatum (globus pallidus) triggers oriented reaction and extremities movement.

Symptoms of its destruction:

· hypodynamy;

· face as a mask;

· head and extremities thremor which is enforced under rest state and is disappeared at movements;

· myoklonuses (myoklony) – separate muscular groups or separate arms, back, face fast fascillations;

· movement beginning becomes difficult;

· additional and reactive movements disappearence at standing up;

· convergent arms movements injuries at walking.

Claustrum - is linked with cortex and the biggest amount of subcortical structures. Patients can’t talk at its injury. At its stimulation orienting reactions appear:

· head turn;

· masticatory movements;

· swallowing movements;

· sometimes – vomiting.