Complex (chain) brain stem reflexes

Structure

The brain stem is a collection of structures of the central nervous system with a length of 7 centimeters, located between the spinal cord and diencephalon. In the anatomical literature there are sometimes discrepancies : sometimes the diencephalon and cerebellum itself are included in the trunk. This set of sections contains the nuclei of the cranial nerves, which are responsible for maintaining life at the physiological level (respiratory processes, heartbeat centers, defecation and urination). The trunk is the most ancient formation in human evolution.

The sequence of locations of the brain stem sections is as follows (from top to bottom):

• Midbrain.
• Pons.
• Medulla.

Topographically, the brain stem begins from the slope of the base of the skull to the foramen magnum, located on the occipital bone. This formation is the largest information collector: the structures of the trunk regulate the flow of neural impulses between the telencephalon cortex and the formations of the spinal cord.

In addition to the large parts of the central nervous system, the brain stem also includes:

• red core;
• reticular formation;
• nervous structures of the tegmentum of the quadrigeminal;
• black substance.

Complex (chain) brain stem reflexes

Physiology of the brain. Brain stem.

The brain performs the highest regulation:

1) motor;

2) visceral;

3) endocrine functions;

4) Psychophysiological processes.

Divisions: telencephalon (cerebral cortex, white matter, basal ganglia), intermediate, middle, posterior (pons and cerebellum), medulla oblongata.

the brain stem (medulla oblongata, pons, midbrain) as a separate formation

Brain stem

The brain stem performs a number of functions:

Brainstem functions realized by cranial nerve nuclei

The brain stem contains the nuclei of the III - XII pairs of cranial nerves, through which sensitive (sensory), motor (somatic) and autonomic (parasympathetic) functions are carried out. In the medulla oblongata there are nuclei of 9-12 cranial nerves, in the pons - 5,6,7,8 (8 - on the border with the medulla oblongata), in the midbrain - 3,4.

(nucleus 1st pair: olfactory nerve

–
located in the olfactory bulb;
second pair: optic nerve -
has nuclei in the lateral geniculate bodies of the thalamus).
It should be noted that each nerve, as a rule, has several nuclei - sensory, motor, etc.

Cranial nerves, their functions and innervated organs

Complex (chain) brain stem reflexes

With the participation of the brain stem, complex somatic reflexes are carried out, each of which involves the nuclei of several cranial nerves:

A) oculomotor reflexes,

B) a reflex act of chewing (the center of chewing is located in the reticular formation of the medulla oblongata and the pons, causing rhythmic movements of the lower jaw. Voluntary (optional) chewing is possible due to signals from the masticatory area of ​​the frontal cortex to the chewing centers in the trunk),

B) reflex act of swallowing (the center of swallowing is in the medulla oblongata and the pons). Up to 20 nuclei in the trunk and upper segments of the spinal cord. The swallowing center is functionally connected with the breathing center, which stops during each swallowing act),

D) gag reflex (the vomiting center is located in the medulla oblongata). This is a protective reflex that occurs when receptors in the root of the tongue, stomach, and vestibular apparatus are irritated. It may also be excited due to a pathological process in the very center of vomiting, due to the influence of chemicals contained in the blood washing the center of vomiting.

D) cough reflex (the cough center is located in the medulla oblongata). The reflex occurs when receptors in the larynx, trachea, and bronchi are stimulated. The cough center triggers a hard-coded sequence of reactions in the spinal motor centers of the respiratory muscles: deep breath; contraction of the expiratory muscles and narrowing of the bronchi with a closed glottis; active exhalation against the backdrop of instant opening of the glottis and a powerful air flow through the mouth).

E) sneezing reflex (the sneezing center is located in the medulla oblongata). The exhalation is forced, as with a cough, but due to the lowering and relaxation of the soft palate, it is directed primarily through the nose.

Functions

The brain stem is responsible for the following simple and complex functions.

The simple include :

• Contraction of the oculomotor muscles and the muscle that lifts the upper eyelid.
• Change in pupil size (accommodation and constriction).
• Movement of the lower jaw, contraction of the masticatory muscles and tension of the eardrum.
• Receiving sensitive information from mucous membranes and skin. Data about temperature and pain in different parts of the body passes through the trunk.
• Contraction of facial muscles; contraction of the muscle located in the middle ear (regulation of sound flow).
• Regulation of the exocrine glands: sublingual, lacrimal, salivary.
• Control of body posture and balance.
• Innervation of the muscles of the pharynx and larynx - swallowing processes.

Complex include :

• A complete act of chewing, which includes regulation of the muscles of the tongue, jaw movement, salivation, and sensitivity of the oral mucosa.
• Reflex chain of the act of swallowing: root of the tongue – muscles of the soft palate – pharynx – esophagus.
• Vomiting reflex. It occurs when the mucous membrane of the tongue root, stomach, esophagus, and some parts of the intestinal tract are irritated.
• Cough reflexes. The mucous membrane of the larynx, trachea or bronchi perceives the stimulus and sends information about it to the brain stem. This, in turn, sends impulses to the respiratory center, which triggers a complex act of coughing with a strict sequence: deep inhalation - muscle contraction - narrowing of the bronchi (pressure in the lungs increases) - sharp and strong exhalation with instant opening of the glottis.
• Sneeze reflexes.
• Functions of the reticular formation. The reticular formation of the brain stem regulates the tone of some flexor and extensor muscles of the trunk. This structure is also responsible for both activation and inhibition of the cerebral cortex (wakefulness-sleep cycle). In addition, the Russian Federation takes part in the functions of breathing, changes in vascular tone, sneezing, swallowing and coughing.
• Antinociceptive function. Its essence lies in the fact that the structure of the brain stem produces neurohormones, the action of which is associated with the suppression of the feeling of pain. This function is activated in a number of cases when a person experiences severe pain: labor, fractures with dislocations, phantom pain.

MOTOR SYSTEMS OF THE BRAINSTEM

Physiologists include the medulla oblongata, pons, and midbrain in this part of the brain.

A. Nuclei of the brainstem. Here are the nuclei of the III-CP pairs of cranial nerves: the oculomotor nerve

(item osHotogons, III);
trochlear nerve
(n. xocyleanz, IV);
abducens
nerve

(item abaicens, VI), all of them control the movement of the eyes in different directions; trigeminal nerve

(n. grengerspis, V), innervating the masticatory muscles;
facial nerve
(n. [aaaPz, VII), the motor nucleus of which causes contraction of facial muscles;
vestibular-cochlear nerve
(n. vestilocochleash, VIII) - its vestibular nuclei receive impulses from vestibuloreceptors, participate in the regulation of body posture and balance, the cochlear nuclei innervate auditory receptors;
glossopharyngeal nerve
(item 1055orbaryngeu5, IX), containing motor, sensory and secretory parasympathetic fibers (stimulate the secretion of saliva from the parotid gland);
the vagus nerve
(n. vagus, X), which regulates the functions of internal organs (parasympathetic nerve);
the motor nucleus of the accessory nerve
(n. accessorogs, XI), causing contraction of the sternocleidomastoid and trapezius muscles;
the motor nucleus of the hypoglossal nerve
(n. Lyogis, XII) innervates the muscles of the tongue.
B. Motor systems of the medulla oblongata and pons. Of the listed nuclei, the medulla oblongata includes the nuclei of the 1X-CP pairs of cranial nerves, as well as the formation of the reticular formation.
The bridge is represented by the nuclei of the V-VIII pairs of cranial nerves and also the reticular formation. The brainstem contains ascending and descending nerve pathways. The vestibular nuclei play an important role in regulating the tone of the muscles of the trunk and limbs, the main of which is the Deiters nucleus.

1. Reflexes carried out by the medulla oblongata and the pons can be combined into three main groups:

1)
vital vegetative
(respiration, cardiovascular system, digestive system);
2) protective reflexes -
sneezing, coughing, blinking, tearing, gagging;
3) somatic reflexes
involved in the regulation of the tone and motor activity of the muscles of the trunk, limbs, neck, and face. Reflexes of any part of the central nervous system are studied after separation of the overlying parts of the brain. In a bulbar animal (the brain stem has been transected between the pons and the midbrain), all reflexes carried out by the spinal cord, as well as the indicated cranial nerves and their nuclei, are preserved. The Deiters nucleus plays a particularly important role in regulating the tone of the muscles of the trunk and limbs. With the help of this nucleus, in particular, the labyrinthine reflex of posture is carried out - an increase in the tone of the extensor muscles when the animal is positioned upside down. The reflex in natural conditions is aimed at maintaining the pose. It arises from the receptors of the vestibular apparatus (when it is destroyed, the reflex disappears). When studying this reflex, the proprioceptors of the neck muscles must be turned off, which is achieved by casting the neck (bending the neck and irritating the proprioceptors of the neck muscles are excluded).

B. The motor systems of the midbrain include the red nuclei, the anterior and posterior colliculi: the anterior primary visual centers along with the lateral geniculate bodies; posterior - primary auditory centers, together with the medial geniculate bodies, nuclei of the III and IV pairs of cranial nerves, substantia nigra, reticular formation, locus coeruleus. Reflexes carried out by the midbrain (mesencephalic animal) are more perfect, their range is much greater, muscle tone is close to normal, since the inhibitory effect of the red nucleus on the γ- and γ-motoneurons of the spinal cord is preserved, and slight muscle rigidity is observed (Fig. 5.9) . Somatic reflexes associated with changes in the position of the body (more precisely, the head) and its movement in space R. Magnus divided respectively into two groups - static and statokinetic.

Static reflexes

(redistribution of muscle tone when changing the position of the head), in turn, are divided into two groups:
postural reflexes (cervical and labyrinthine vestibular) and rectifying (straightening of the head and torso).
The head straightening reflex ( if, for example, the animal is lying on its side) arises from the receptors of the vestibular apparatus, skin and retina. At the same time, the proprioceptors of the neck muscles are excited and the body begins to straighten. When the skin or vestibular apparatus receptors are turned off, the rectifying reflexes are not impaired. When both of these reflexogenic zones are turned off, rectifying reflexes do not occur. To carry out righting reflexes, i.e. restoration of the disturbed posture, the mandatory participation of the red nuclei is necessary; their destruction in the experiment prevents the occurrence of righting reflexes. When the position of the head changes, reflexes of compensatory position of the eyes also arise, which ensure correct vision at various positions of the head relative to the body and in space. For example, if you turn your head to the right, the eyeball turns to the left, as if trying to maintain the original field of vision.

Statokinetic reflexes

occur during acceleration of linear and rotational movements of the body. Redistribution of tone is aimed at overcoming the accelerations acting on a person and maintaining a normal posture. For their implementation, the mandatory participation of midbrain structures is necessary.

An example of a straight-line acceleration reflex is the elevator reflex. At the beginning of a rapid ascent of an elevator (or the stop of a downward elevator), the tone of the extensor muscles in the lower extremities increases. At the beginning of the descent of the elevator (or the stop of the elevator moving upward), the tone of the flexors increases (there is another point of view about the reason for the flexion and extension of the limbs during the descent and ascent of the elevator). The reflex nature of the change in muscle tone of the limbs during the elevator reflex is evidenced by its absence in animals when the vestibular receptors are turned off by the destruction of the labyrinth.

In addition to regulating muscle tone, posture, and balance, brainstem structures are involved in the control of spinal automaticity of stepping and, therefore, in the control of locomotion (eg, walking). Voluntary locomotion is impossible without the participation of cortical neurons.

Functions of the locus coeruleus.

It has a modeling effect on the motor mechanisms of the spinal cord. Axons of noradrenergic neurons of the locus coeruleus go in the anterior and lateral funiculi to the a-motoneurons of the anterior horns of the spinal cord. It is believed that norepinephrine is an inhibitory transmitter for α-motoneurons.

Functions of the substantia nigra.

It is involved in the regulation of muscle tone, coordination of chewing and swallowing, small movements of the limbs (for example, typing, writing), and the expression of emotions. In case of damage to the substantia nigra, there is a lack of movement.

In all motor reactions and regulation of muscle tone, the reticular formation plays a very important role, the bulk of whose neurons are located in the brain stem.

Descending Paths

Descending projection pathways are a group of tracts that send neural information from the telencephalon cortex and subcortical formations to brainstem structures. These include:

• Pyramid path. This tract connects the motor gyrus with the motor nuclei of the brainstem. So, with the help of this path, a person manages to control the muscles of the neck, head, eyes, face and torso.
• Extrapyramidal pathway. Thanks to this tract, people maintain their balance in space.

Research methods

Diagnosis of the functional state and activity of the trunk is carried out using clinical and instrumental laboratory methods. The first includes:

• neurological study of the activity of cranial nerves;
• study of voluntary movements;
• diagnostics of coordination of limbs and body;
• sensitivity study;
• Laboratory methods include:
• spinal puncture and examination of cerebrospinal fluid;
• X-ray of the skull;
• ventriculography;
• pneumoencephalography;
• Dopplerography;
• electroencephalography;
• magnetic resonance imaging;
• computed tomography.