Located between the pons and the diencephalon. The midbrain is represented by the quadrigeminal and cerebral peduncles. A narrow canal passes through the midbrain - the cerebral aqueduct. The largest nuclei are the red nucleus, the substantia nigra, the nuclei of the cranial (III and IV) nerves, and the quadrigeminal. The reticular formation also passes through the midbrain.
The midbrain performs a somatic function due to the nuclei of the trochlear and oculomotor nerves, the red nucleus, and the substantia nigra.
The oculomotor nerve (III) is responsible for raising the upper eyelid, regulating the movements of the eye up, down, towards the nose, down towards the corner of the nose. Neurons of the accessory nucleus of the oculomotor nerve regulate the lumen of the pupil and the curvature of the lens, ensuring the process of accommodation. That. this nucleus is mixed - somato-vegetative
The trochlear nerve (IV) innervates the superior oblique muscle of the eye, ensures the rotation of the eye downward - outward, and is purely somatic.
Red kernels have descending motor connections with the cerebral cortex, basal ganglia, cerebellum, and spinal cord. They regulate the tone of skeletal muscles (somatic) - they increase the tone of the flexors and decrease the tone of the extensors.
Black matter located in the cerebral peduncles, it is involved in the regulation of the acts of chewing, swallowing and their sequence, as well as in the coordination of small and precise movements of the fingers, for example when writing, playing the violin, or playing the piano. In addition, the neurons of this nucleus synthesize dopamine, supplied by axonal transport to the basal ganglia of the brain (striatum). Dopamine plays an important role in the control of complex motor acts. Black matter has an inhibitory effect on thalamic neurons. The impulses further along the processes of the thalamic neurons reach the cortex. The development of Parkinson's disease is associated with impaired synthesis of dopamine in the substantia nigra.
The reticular formation of the midbrain is involved in the regulation of sleep and wakefulness.
The quadrigeminal region is divided into superior and inferior colliculi.
Upper tubercles of the quadrigeminal - This is the primary center of the visual analyzer, providing a visual orientation reflex - turning the head and eyes towards the light stimulus, fixing the gaze and tracking moving objects. The lower tuberosities of the quadrigeminal - This is the primary center of the auditory analyzer, participating in the indicative auditory reflex - turning the head towards the sound source.
In humans, the quadrigeminal reflex is a sentinel reflex that provides a start - a reaction to sudden sound and auditory stimuli. Activation of the midbrain occurs through the hypothalamus and therefore there is an increase in muscle tone, increased heart rate, and preparation for avoidance, a defensive reaction or attack. Let us note that, despite their names of the primary centers of the auditory and visual analyzers, the quadrigeminal region “does not see” and “does not hear.” It forms somatic reflexes, which are called indicative or sentinel reflexes (or start reflexes). I.P. Pavlov also called them “what is it” reflexes.
The midbrain is involved in the implementation static reactions at relative rest of the body, i.e. when standing, lying in various positions and statokinetic associated with changes in body position in space. Static reflexes are divided into tonic postural reflexes And rectifier. The midbrain is most characterized by righting or righting reflexes. Statokinetic reflexes manifest themselves during rotation and movement of the body in horizontal and vertical planes.
1.What is the main function of the midbrain quadrigeminal?
A. Regulation of homeostasis of all autonomic functions
B. Implementation of indicative reactions
C. Participation in memory mechanisms
D. Regulation of muscle tone
E. All answers are correct
2. The sensory function of the midbrain is manifested
A. Primary analysis of information coming from visual and auditory receptors
B. Primary central analysis of information coming from visual and secondary central analysis of information from auditory receptors
C. Primary analysis of information coming from the proprioceptors of the trunk
D. Secondary analysis of information coming from visual and auditory receptors
E. All answers are incorrect
3. What is the name of the type of muscle tone that occurs when the midbrain is transected below the level of the red nucleus?
A. Normal
B. Plastic
C. Weakened
D. Contractile
E. Lightweight
4. Which centers of the medulla oblongata are vital?
A. Respiratory, cardiovascular
B. Muscle tone; protective reflexes
C. Protective reflexes, food
D. Motor reflexes, food
E. Nutritional, muscle tone
5. The patient was diagnosed with hemorrhage in the brain stem. The examination revealed an increase in the tone of the flexor muscles against the background of a decrease in the tone of the extensor muscles. Irritation of which brain structures can explain changes in muscle tone?
A. Substantia nigra
V. Yader Goll
C. Deiters nuclei
D. Yader Burdakh
E. Red kernels
6. After a brain injury, a patient suffered from impaired fine movements of his fingers and developed muscle rigidity and tremor. What is the reason for this phenomenon?
A. Damage to the cerebellum
B. Damage to the midbrain in the area of the red nuclei
C. Damage to the midbrain in the substantia nigra area
D. Damage to Deiters nuclei
E. Brain stem damage
7. A patient with cerebral blood flow disorder has impaired swallowing and may choke when taking liquid food. Indicate which part of the brain is affected?
A. Cervical spinal cord
B. Thoracic spinal cord
C. Reticular formation
D. Medulla oblongata
E. Midbrain
8. The motor nuclei of the thalamus include
A. Ventral group
B. Lateral group
C. Posterior group
D. Medial group
E. Anterior group
9. Which nuclei of the thalamus are involved in the formation of the phenomenon of “referred pain”
A. Reticular
B. Associative
C. Intralaminar complex
D. Relay
E. Nonspecific nuclei
10. The thalamus is...
A. Collector of afferent pathways, the highest center of pain sensitivity
B. Regulator of muscle tone
C. Regulator of all motor functions
D. Homeostasis regulator
E. Body temperature regulator
Answers: 1.D, 2.B, 3.D, 4.A, 5.E, 6.C, 7.D, 8.A, 9.D, 10.A.
TEST TASKS FOR SELF-CONTROL according to the Krok-1 program:
1. In an experiment, one of the structures of the midbrain was destroyed in a dog, as a result of which it lost its orienting reflex to sound signals. What structure was destroyed?
A. Vestibular nucleus of Deiters
B. Red core
C. Superior colliculi
D. Inferior tuberosities
E. Substantia nigra
2. Animals with decerebrate rigidity are characterized by
A. Disappearance of righting reflexes
B. Disappearance of the elevator reflex
C. A sharp increase in the tone of the extensor muscles
D. All answers are correct
E. All answers are incorrect
3. The associative nuclei of the thalamus include...
A. Central and intralaminar
B. Ventrobasal complex
C. Anterior, medial and posterior groups
D. Nuclei of the medial and medial geniculate bodies
E. Ventral group
4. Reflex reactions of which part of the central nervous system are directly related to maintaining posture, chewing, swallowing food, secretion of digestive glands, breathing, cardiac activity, regulation of vascular tone?
A. Midbrain
B. Thalamus
C. Hindbrain
D. Spinal tissue
E. Forebrain
5. Reflex reactions of which part of the central nervous system are directly related to the implementation of the “guard reflex”?
A. Hindbrain
B. Thalamus
C. Spinal cord
D. Cerebellum
E. Midbrain
6. How can we experimentally prove that decerebrate rigidity is caused by a significant gamma enhancement of spinal myotatic reflexes?
A. Cut the dorsal roots of the spinal cord
B. Cut the spinal cord
C. make a cut above the midbrain
D. make a transection below the midbrain
E. make a transection below the hindbrain
7. What is the reflex reaction in a person called when there is a sudden action of a light or visual stimulus and what does its loss indicate?
A. Adaptive reaction, damage to the hypothalamus
B. “start reflex”, quadrigeminal lesion
C. “what is this” reflex, damage to the reticular formation
D. adaptive reaction, damage to the globus pallidus
E. “what is this” reflex, damage to the red nuclei
8. A person has hypokinesia and rest tremor. Which part of the brain is affected?
A. pallidum and substantia nigra
V. striatum, pallidum
C. substantia nigra, cerebellum
D. striatum, substantia nigra, cerebellum
E. pallidum and cerebellum
9. The hindbrain does not receive information from...
A. vestibuloreceptors
B. visual receptors
C. auditory receptors
D. proprioceptors
E. taste buds
10. At the level of the midbrain, all reflexes are closed for the first time, except...
A. rectifier
B. statokinetic
S. pupillary
D. eye nystagmus
E. sweating
Answers: 1.D, 2.D, 3.C, 4.C, 5.E, 6.A, 7.B, 8.A, 9.B, 10.E.
Situational tasks:
1. Explain whether the animal will retain any reflexes, except spinal ones, after transection of the spinal cord under the medulla oblongata? Breathing is supported artificially
2. In the animal, two complete transections of the spinal cord were made successively under the medulla oblongata at the level of the C 2 and C 4 segments. Explain how the blood pressure value will change after the first and second transections?
3. Two patients had a cerebral hemorrhage - in one of them in the cerebral cortex, in the other - in the medulla oblongata. Explain which patient has a more unfavorable prognosis?
4. At what level is it necessary to transect the brain stem in order to obtain a change in muscle tone, schematically depicted in the figure? Explain what this phenomenon is called and what is its mechanism?
5. Explain what will happen to a cat in a state of decerebrate rigidity after cutting the brain stem below the red nucleus, if the dorsal roots of the spinal cord are now cut?
6. Explain how the tone of the muscles of the front and hind limbs of a bulbar animal changes when its head is tilted forward? Draw a diagram of the position of the limbs and explain your answer?
7. When running on a turn in a stadium track, a skater is required to have particularly precise footwork. Explain whether in this situation it matters what position the athlete’s head is in?
8. It is known that during narcotic sleep during surgery, the anesthesiologist constantly monitors the reaction of the patient’s pupils to light. For what purpose does he do this and what could be the reason for the absence of this reaction?
answers to situational problems:
1. Those reflexes that are carried out through the nuclei of the cranial nerves will be preserved.
2. After the first transection, blood pressure will decrease, since the connection between the main vasomotor center in the medulla oblongata and local centers in the lateral horns of the spinal cord will be interrupted. Repeated cutting will not have any effect, since the connection has already been interrupted.
3. There are no vital centers in the cerebral cortex, but in the medulla oblongata there are (respiratory, vasomotor, etc.). Therefore, hemorrhage in the medulla oblongata is more life-threatening. As a rule, it ends in death
4. The phenomenon of decerebrate rigidity (extensor hypertonicity) occurs when the brainstem is transected between the midbrain and medulla oblongata, so that the red nucleus is above the transection site.
5. Rigidity will disappear, since the fibers of the gamma loop of the myotonic reflex are cut.
6. When the head is tilted forward, the tone of the flexors of the front and extensors of the hind limbs increases.
7. Impulses from the receptors of the neck muscles play an important role in the distribution of muscle tone in the limbs. Therefore, the athlete’s head must occupy a certain position when performing certain movements. So, if a skater turns his head in the direction opposite to the direction of the turn while turning, he may lose his balance and fall.
8. By the nature of the reaction of the pupils to light, anesthesiologists judge the depth of narcotic sleep. If the pupils stop responding to light, this means that the anesthesia has spread to those areas of the midbrain where the nuclei of the third pair of cranial nerves are located. This is a threatening sign for a person, as vital centers may turn off. The dose of the drug should be reduced.
Midbrain comprises:
Bugrov quadrigeminal,
red core,
substantia nigra,
Seam cores.
Red core– provides the tone of skeletal muscles, redistribution of tone when changing posture. Just stretching is a powerful activity of the brain and spinal cord, for which the red nucleus is responsible. The red core ensures the normal tone of our muscles. If the red nucleus is destroyed, decerebrate rigidity occurs, with a sharp increase in the tone of the flexors in some animals and the extensors in others. And with absolute destruction, both tones increase at once, and it all depends on which muscles are stronger.
Black substance– How is excitation from one neuron transmitted to another neuron? Excitation occurs - this is a bioelectric process. It reaches the end of the axon, where a chemical substance is released - a transmitter. Each cell has its own mediator. A transmitter is produced in the substantia nigra in nerve cells dopamine. When the substantia nigra is destroyed, Parkinson's disease occurs (the fingers and head constantly tremble, or there is stiffness as a result of a constant signal being sent to the muscles) because there is not enough dopamine in the brain. The substantia nigra provides subtle instrumental movements of the fingers and influences all motor functions. The substantia nigra exerts an inhibitory effect on the motor cortex through the stripolidal system. If it is disrupted, it is impossible to perform delicate operations and Parkinson's disease occurs (stiffness, tremors).
Above are the anterior tubercles of the quadrigeminal, and below are the posterior tubercles of the quadrigeminal. We look with our eyes, but we see with the occipital cortex of the cerebral hemispheres, where the visual field is located, where the image is formed. A nerve leaves the eye, passes through a number of subcortical formations, reaches the visual cortex, there is no visual cortex, and we will not see anything. Anterior tubercles of the quadrigeminal- This is the primary visual area. With their participation, an indicative reaction to a visual signal occurs. The indicative reaction is the “reaction what is it?” If the anterior tubercles of the quadrigeminal are destroyed, vision will be preserved, but there will be no quick reaction to the visual signal.
Posterior tubercles of the quadrigeminal This is the primary auditory zone. With its participation, an indicative reaction to the sound signal occurs. If the posterior tubercles of the quadrigeminal are destroyed, hearing will be preserved but there will be no indicative reaction.
Seam cores– this is the source of another mediator serotonin. This structure and this mediator takes part in the process of falling asleep. If the suture nuclei are destroyed, the animal is in a constant state of wakefulness and quickly dies. In addition, serotonin takes part in positive reinforcement learning (this is when a rat is given cheese). Serotonin provides character traits such as unforgivingness, goodwill; aggressive people have a lack of serotonin in the brain.
12) The thalamus is a collector of afferent impulses. Specific and nonspecific nuclei of the thalamus. The thalamus is the center of pain sensitivity.
Thalamus- visual thalamus. He was the first to discover his relationship to visual impulses. It is a collector of afferent impulses, those that come from receptors. The thalamus receives signals from all receptors except the olfactory ones. The thalamus receives information from the cortex, the cerebellum, and the basal ganglia. At the level of the thalamus, these signals are processed, only the most important information for a person at a given moment is selected, which then enters the cortex. The thalamus consists of several dozen nuclei. The nuclei of the thalamus are divided into two groups: specific and nonspecific. Through specific nuclei of the thalamus, signals arrive strictly to certain areas of the cortex, for example, visual to the occipital lobe, auditory to the temporal lobe. And through nonspecific nuclei, information diffuses to the entire cortex in order to increase its excitability in order to more clearly perceive specific information. They prepare the BP cortex for the perception of specific information. The highest center of pain sensitivity is the thalamus. The thalamus is the highest center of pain sensitivity. Pain is formed necessarily with the participation of the thalamus, and when some nuclei of the thalamus are destroyed, pain sensitivity is completely lost; when other nuclei are destroyed, barely bearable pain occurs (for example, phantom pain is formed - pain in a missing limb).
13) Hypothalamic-pituitary system. The hypothalamus is the center of regulation of the endocrine system and motivation.
The hypothalamus and pituitary gland form a single hypothalamic-pituitary system.
Hypothalamus. The pituitary stalk departs from the hypothalamus, on which it hangs pituitary- main endocrine gland. The pituitary gland regulates the functioning of other endocrine glands. The hypoplamus is connected to the pituitary gland by nerve pathways and blood vessels. The hypothalamus regulates the work of the pituitary gland, and through it the work of other endocrine glands. The pituitary gland is divided into adenohypophysis(glandular) and neurohypophysis. In the hypothalamus (this is not an endocrine gland, it is a part of the brain) there are neurosecretory cells in which hormones are secreted. This is a nerve cell; it can be excited, it can be inhibited, and at the same time hormones are secreted in it. An axon extends from it. And if these are hormones, they are released into the blood, and then go to the decision organs, i.e. to the organ whose work it regulates. Two hormones:
- vasopressin – promotes the conservation of water in the body, it affects the kidneys, and with its deficiency, dehydration occurs;
- oxytocin – produced here, but in other cells, ensures contraction of the uterus during childbirth.
Hormones are secreted in the hypothalamus and released by the pituitary gland. Thus, the hypothalamus is connected to the pituitary gland via nerve pathways. On the other hand: nothing is produced in the neurohypophysis; hormones come here, but the adenohypophysis has its own glandular cells, where a number of important hormones are produced:
- ganadotropic hormone – regulates the functioning of the sex glands;
- thyroid-stimulating hormone – regulates the functioning of the thyroid gland;
- adrenocorticotropic – regulates the functioning of the adrenal cortex;
- somatotropic hormone, or growth hormone, – ensures the growth of bone tissue and the development of muscle tissue;
- melanotropic hormone – is responsible for pigmentation in fish and amphibians, in humans it affects the retina.
All hormones are synthesized from a precursor called proopiomellanocortin. A large molecule is synthesized, which is broken down by enzymes, and other hormones, smaller in number of amino acids, are released from it. Neuroendocrinology.
The hypothalamus contains neurosecretory cells. They produce hormones:
1) ADH (antidiuretic hormone regulates the amount of urine excreted)
2) oxytocin (provides contraction of the uterus during childbirth).
3) statins
4) liberins
5) thyroid-stimulating hormone affects the production of thyroid hormones (thyroxine, triiodothyronine)
Thyroliberin -> thyroid-stimulating hormone -> thyroxine -> triiodothyronine.
The blood vessel enters the hypothalamus, where it branches into capillaries, then the capillaries gather and this vessel passes through the pituitary stalk, branches again in the glandular cells, leaves the pituitary gland and carries with it all these hormones, which each go with the blood to its own gland. Why is this “wonderful vascular network” needed? There are nerve cells in the hypothalamus that end on the blood vessels of this wonderful vascular network. These cells produce statins And liberins - This neurohormones. Statins inhibit the production of hormones in the pituitary gland, and liberins it is strengthened. If there is an excess of growth hormone, gigantism occurs, this can be stopped with the help of samatostatin. On the contrary: the dwarf is injected with samatoliberin. And apparently there are neurohormones for any hormone, but they are not yet discovered. For example, the thyroid gland produces thyroxine, and in order to regulate its production, the pituitary gland produces thyroid-stimulating hormone, but in order to control thyroid-stimulating hormone, thyreostatin has not been found, but thyroliberin is used perfectly. Although these are hormones, they are produced in nerve cells, so in addition to their endocrine effects, they have a wide range of extraendocrine functions. Thyroid hormone is called panactivin, because it improves mood, improves performance, normalizes blood pressure, and accelerates healing in case of spinal cord injuries; it is the only thing that cannot be used for disorders of the thyroid gland.
The functions associated with neurosecretory cells and cells that produce neurofebtides were previously discussed.
The hypothalamus produces statins and liberins, which are included in the body's stress response. If the body is affected by some harmful factor, then the body must somehow respond - this is the stress reaction of the body. It cannot occur without the participation of statins and liberins, which are produced in the hypothalamus. The hypothalamus necessarily takes part in the response to stress.
The following functions of the hypothalamus are:
It contains nerve cells that are sensitive to steroid hormones, i.e. sex hormones, both female and male sex hormones. This sensitivity ensures formation of a female or male type. The hypothalamus creates the conditions for motivating behavior according to the male or female type.
A very important function is thermoregulation; the hypothalamus contains cells that are sensitive to blood temperature. Body temperature can change depending on the environment. Blood flows through all structures of the brain, but thermoreceptive cells, which detect the slightest changes in temperature, are found only in the hypothalamus. The hypothalamus turns on and organizes two responses of the body: heat production or heat transfer.
Food motivation. Why does a person feel hungry?
The signaling system is the level of glucose in the blood, it should be constant ~120 milligrams% - s.
There is a mechanism of self-regulation: if our blood glucose level decreases, liver glycogen begins to break down. On the other hand, glycogen reserves are not enough. The hypothalamus contains glucoreceptive cells, i.e. cells that record the level of glucose in the blood. Glucoreceptive cells form hunger centers in the hypothalamus. When blood glucose levels drop, these blood glucose-sensing cells become excited and a feeling of hunger occurs. At the level of the hypothalamus, only food motivation arises - a feeling of hunger; to search for food, the cerebral cortex must be involved, with its participation a true food reaction arises.
The satiety center is also located in the hypothalamus, it inhibits the feeling of hunger, which protects us from overeating. When the saturation center is destroyed, overeating occurs and, as a result, bulimia.
The hypothalamus also contains the thirst center - osmoreceptive cells (osmatic pressure depends on the concentration of salts in the blood). Osmoreceptive cells record the level of salts in the blood. When salts in the blood increase, osmoreceptive cells are excited, and drinking motivation (reaction) occurs.
The hypothalamus is the highest control center of the autonomic nervous system.
The anterior sections of the hypothalamus mainly regulate the parasympathetic nervous system, the posterior sections mainly regulate the sympathetic nervous system.
The hypothalamus provides only motivation and goal-directed behavior to the cerebral cortex.
14) Neuron – structural features and functions. Differences between neurons and other cells. Glia, blood-brain barrier, cerebrospinal fluid.
I Firstly, as we have already noted, in their diversity. Any nerve cell consists of a body - soma and processes. Neurons are different:
1. by size (from 20 nm to 100 nm) and shape of the soma
2. by the number and degree of branching of short processes.
3. according to the structure, length and branching of axon endings (laterals)
4. by the number of spines
II Neurons also differ in functions:
A) perceivers information from the external environment,
b) transmitting information to the periphery,
V) processing and transmitting information within the central nervous system,
G) exciting,
d) brake.
III Differ in chemical composition: various proteins, lipids, enzymes are synthesized and, most importantly, - mediators .
WHY, WHAT FEATURES IS THIS ASSOCIATED WITH?
Such diversity is determined high activity of the genetic apparatus neurons. During neuronal induction, under the influence of neuronal growth factor, NEW GENES are turned on in the cells of the ectoderm of the embryo, which are characteristic only of neurons. These genes provide the following features of neurons ( the most important properties):
A) The ability to perceive, process, store and reproduce information
B) DEEP SPECIALIZATION:
0. Synthesis of specific RNA;
1. No reduplication DNA.
2. The proportion of genes capable of transcriptions, make up in neurons 18-20%, and in some cells – up to 40% (in other cells - 2-6%)
3. The ability to synthesize specific proteins (up to 100 in one cell)
4. Unique lipid composition
B) Privilege of nutrition => Dependence on level oxygen and glucose in blood.
Not a single tissue in the body is in such a dramatic dependence on the level of oxygen in the blood: 5-6 minutes of stopping breathing and the most important structures of the brain die, and first of all the cerebral cortex. A decrease in glucose levels below 0.11% or 80 mg% - hypoglycemia may occur and then coma.
On the other hand, the brain is fenced off from the blood flow by the BBB. It does not allow anything into the cells that could harm them. But, unfortunately, not all of them - many low-molecular toxic substances pass through the BBB. And pharmacologists always have a task: does this drug pass through the BBB? In some cases this is necessary, if we are talking about brain diseases, in others it is indifferent to the patient if the drug does not damage nerve cells, and in others it should be avoided. (NANOPARTICLES, ONCOLOGY).
The sympathetic nervous system is excited and stimulates the adrenal medulla - the production of adrenaline; in the pancreas - glucagon - breaks down glycogen in the kidneys to glucose; glucocarticoids produced in the adrenal cortex - provides gluconeogenesis - the formation of glucose from ...)
And yet, with all the diversity of neurons, they can be divided into three groups: afferent, efferent and intercalary (intermediate).
15) Afferent neurons, their functions and structure. Receptors: structure, functions, formation of an afferent volley.
It is important for every person to know how he works. And one of the most interesting organs to study is the brain, which has not yet been fully understood. Few people, after a school biology course, remember the functions of the midbrain and its purpose. The need to understand complex medical terms comes in adulthood, when a person begins to visit doctors or is about to enter a medical university.
If you want to know what the midbrain is and its location, you don't have to study complex medical encyclopedias or attend medical school. Conscientious patients, before going to a medical facility, want to learn more about the disease and what functions the diseased organ performs. Then hospital procedures will not seem so scary and incomprehensible.
Basic information
The central nervous system contains neurons with processes and glia. The brain has only five sections. First– oblong – continuation of the dorsal. It transmits information to and from other departments. Performs a regulatory function in relation to the coordination of movements. Second– bridge – here are the midbrain centers responsible for the assimilation of audio and video information. This department stands for coordination of movements. Third– cerebellum – connects the posterior and anterior sections. Fourth– middle – responsible for facial expressions, movements of the eyeballs, auditory pathways pass through it. This is exactly what we will consider. Fifth– anterior – normalizes mental activity.
This is interesting. There is no connection between brain size and mental abilities in humans. The number of nerve connections is much more important.
Where is
The location corresponds to the name of the organ. It is part of the stem part. Located under the intermediate and above the bridge. The formation of the human midbrain was influenced by the mechanism of perception of video information during the historical development of the organism. The process of evolution happened so that the anterior section became the most developed. And through the middle one, conducting signal channels began to pass to various departments.
How does the midbrain develop?
While in their mother's womb, children must go through many stages of development. During the embryonic stage, the midbrain grows from a small vesicle and remains intact throughout life. Throughout development, more and more new cells appear in this part, they compress the cerebral aqueduct. If there are disturbances at this stage, problems with the cerebral aqueduct may develop - partial or complete blockage. One of the most dangerous consequences is such a dangerous disease as hydrocephalus.
Helpful information. Every time a person remembers information, neural connections are formed. This means that the structures of various parts, including the midbrain, are constantly changing; it does not freeze in a certain state.
What role does it play?
It is the middle section that regulates muscle tone. His role corresponds to his intermediate position. Due to the fact that the midbrain has a special structure, its functions include the transmission of information. It has a lot of different purposes:
- sensory– to convey tactile sensations;
- motor– coordination depends on this part of the midbrain;
- reflex– for example, oculomotor, reaction to light and sound.
Due to the work of the middle section, a person can stand and walk. Without it, a person would not be able to fully move in space. Also, the work of the vestibular apparatus is controlled at the level of the midbrain.
Organ structure
It is known that the average human brain has different parts, each of which performs its own role. Quadrigeminal - the structure consists of paired hills. The upper ones are visual and the lower ones are auditory.
The legs contain a black substance. Thanks to it, a person not only lies, but can make precise movements with his hands and eat food. At a certain point, the middle region processes information about when to bring a spoon to the mouth, how to chew food, and what function will allow it to be swallowed.
Useful to know: Brain: functions, structure
The ocular motor nerve originates between the crura and exits from there. It is responsible for the constriction of the pupil and some motor functions of the eyeball. To understand the structure of the midbrain, you need to know where it is located. It is composed of the intermediate and cerebral hemispheres of the cerebrum, its structure is simple and has only two sections. Quadrigemole on nearby two paired colliculi, which form the upper wall. They resemble a plate in appearance. Legs - conductive channels are located there, going to the hemispheres of the anterior section and connecting it with the lower parts of the nervous system.
How many parts does the middle section have?
There are three parts in total. Dorsal - the roof of the middle section. It is divided into 4 mounds using grooves intersecting in pairs. The two upper hills are the subcortical centers for regulating vision, and the remaining lower ones are auditory. The ventral one is the so-called cerebral peduncle. The conductive channels to the anterior section are based here. The internal space of the brain looks like a hollow canal.
Helpful information. If a person does not breathe oxygen for more than five minutes, the brain will be permanently damaged, resulting in death.
Cores
Gray matter accumulates inside the quadrigeminal tubercles, clusters of which are called nuclei. The main function of the nuclei is called the innervation of the eyes. They come in the following types.
Reticular formation - takes part in stabilizing the work of skeletal muscles. They activate the cells of the cerebral cortex of the head, and have an inhibitory effect on the spinal cord. Oculomotor nerve - contains fibers that innervate the sphincter and eye muscles. Trochlear nerve - supplies nerves to the oblique muscle of the organ of vision. Substantia nigra - color associated with the pigment melanin. The neurons of this substance themselves synthesize dopamine. Coordinate facial muscles and small movements. Red nuclei of the midbrain - activate neurons of the flexor and extensor muscles
Prevention of pathologies
The brain cannot function correctly without intellectual activity and physical activity. Typically, disruptions in the functioning of the central nervous system are observed in people over 70 years of age. But diseases of this group are diagnosed in those who, after retirement, no longer maintain their health and lead a healthy lifestyle. However, there are also congenital pathologies in the midbrain; you can get sick at any age.
Useful to know: Functions and structure of the cerebral pons, its description
Exercise regularly to the best of your physical ability, walk in the fresh air, do gymnastics in the morning. Quit tobacco and alcoholic beverages. Switch to a healthy diet, eat as many fresh vegetables and fruits as possible. Do not eat products with preservatives and emulsifiers. Train your mind - for this you can read books, solve crosswords, play chess, gain new knowledge in an area of interest.
To get rid of vitamin deficiency - take vitamins and antioxidants. Since the brain is 60% fat, you cannot give up oil, but it must be natural. For example, olive oil is perfect. Avoid stressful situations. Do not engage in monotonous work too often, take breaks, switching to other activities. Monitor your blood pressure levels - hypertension can cause a stroke.
The midbrain is the smallest section of the brain. It is so modest, but very important - there are no unimportant parts of the brain. If you look at the size of the medulla oblongata and the pons, then each of them is approximately 3 centimeters, and the midbrain is only 2 centimeters. The midbrain is located between the pons and the diencephalon and belongs to the stem structures.
If we look at the macroanatomy of the midbrain, we see that its upper part, the roof, is four hills that protrude from the surface of the midbrain. The upper pair of hillocks (or anterior) and the lower pair (or posterior) are distinguished. In general, this is called the quadrigeminal. The lower part of the midbrain is called the cerebral peduncle. Inside the legs there is a tire and a base. The border between the quadrigeminal peduncle and the cerebral peduncles is a narrow and thin canal that passes through the midbrain - it is called the cerebral aqueduct, or the aqueduct of Sylvius. In the 17th century, when anatomists began to seriously understand the brain, this structure was described. The aqueduct of Sylvius connects two large cavities inside our brain - the third ventricle and the fourth ventricle.
When the neural tube forms in the embryo, a narrow canal remains inside the tube. In the spinal cord it gives rise to the spinal canal, and in the brain it expands in places, and a system of ventricles arises. The fourth ventricle is located under the cerebellum, and its lower border is the upper side of the medulla oblongata and the pons - the so-called rhomboid fossa. This fourth ventricle narrows and the canal dives into the midbrain and becomes the cerebral aqueduct. Already in the diencephalon, the cerebral aqueduct expands again and gives rise to a narrow, slit-like third ventricle.
The quadrigeminal colliculi are the sensory centers of the midbrain. The anterior pair of colliculi appears first in evolution, and these are the neurons that process visual signals. In fish these are the most important visual centers, but in us they perform an auxiliary function, and in the anterior superior colliculi of the quadrigeminal there are cells that respond to new visual signals. Four Hills, strictly speaking, almost doesn’t care what we specifically see, the main thing is that something has changed. Change is primarily the movement of objects in the field of view. Then, in the quadrigeminal region, neurons - novelty detectors - are triggered, and a very characteristic reaction of turning the eyes towards the new signal is triggered. And if necessary, the head and even the whole body turns. In fact, the work of the quadrigeminals is curiosity at its most ancient level, this is the desire of the brain to collect new information. Ivan Petrovich Pavlov called this reaction an indicative reflex. The orientation reflex is one of the most complex innate reflexes of our body, but it is just as innately given as the swallowing reflex or the reflex of withdrawing the hand from the source of pain.
The inferior colliculi of the quadrigeminal appear much later in evolution, and they belong to the auditory centers. Processing of the auditory signal begins at the level of the medulla oblongata and the pons, where the nuclei of the eighth nerve are located, and then the information is transmitted to the lower colliculi of the quadrigeminal, and they perform approximately the same task as the superior colliculi - they respond to new auditory signals. If a new sound appears, or the source of the sound begins to shift, or the tonality changes, then the orienting reflex is also triggered, and we look at where something rustled or changed, because all this is colossally significant.
The oculomotor centers are very powerfully connected with the work of the quadrigeminal region. Inside the midbrain are motor neurons that control eye movements. It must be said that eye movements are the most subtle movements that our body performs. We, of course, know that our fingers move very subtly or the movements of our tongue and facial expressions are very subtle, but the most precise movements, it turns out, are performed by our oculomotor muscles, which rotate the eye in the bony orbit and tune our vision to analyze this or that visual object.
As many as six extraocular muscles are associated with each eye, and they are controlled by three cranial nerves: the sixth, fourth and third. The sixth nerve is called the abducens nerve, and its nuclei are located in the upper part of the pons with special projections called the facial colliculi. The fourth and third nerves are the midbrain nerves; the fourth nerve is called the trochlear nerve, and the third is called the oculomotor nerve. The oculomotor nerve in this system is the most important, largest, and four of the six oculomotor muscles are controlled by the third nerve. The trochlear nerve and the abducens nerve account for only one extraocular muscle each. The fibers of the oculomotor nerve emerge from the underside of the midbrain and travel to the eye. Inside the third nerve there are not only motor axons, axons of motor neurons, but also autonomic axons, parasympathetic axons, which control the diameter of the pupil and the shape of the lens.
The substantia nigra is perhaps the most famous structure of the midbrain. Here there are dopamine neurons, which further send their axons upward, to the cerebral hemispheres, and the level of our motor activity depends on the release of dopamine from these axons, and the positive emotions that we experience during movements depend. If the substantia nigra is damaged, then a disease called “parkinsonism” occurs. Unfortunately, the substantia nigra is a delicate structure; parkinsonism is the second most common neurodegeneration after Alzheimer's disease. Therefore, Parkinson's disease is being very actively researched, the search for drugs is underway, and ways to stop and delay these neurodegenerations are being sought. But this is not the only function of the substantia nigra. Dopamine neurons are found only in the inner part of the substantia nigra; in the lateral or lateral part of the substantia nigra there are nerve cells that use gamma-aminobutyric acid (GABA) as a transmitter. These cells control eye movements and inhibit excessive oculomotor responses, allowing us to control the functioning of the third, fourth and sixth oculomotor nerves.
Another structure that is associated with the release of dopamine and belongs to the midbrain is the ventral tegmental area. Its axons are directed to the cerebral cortex, to the adjacent nucleus of the septum pellucidum, and this is a system for controlling the level of emotions, needs, a system associated with the speed of information processing in the cerebral cortex.
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