Fifth tubercle of the quadrigemina. midbrain anatomy midbrain
It is important for each 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, after a course of school biology, remember the functions of the midbrain and purpose. There comes a need to understand complex medical terms already in adulthood, when a person begins to visit doctors or is going to enter a medical university himself.
If you want to know what the midbrain is and where it is located, you do not need to study complex medical encyclopedias and study at a medical school. Conscious 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 frightening 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 centers of the midbrain responsible for the assimilation of audio information and video information. This department is responsible for the coordination of movements. The third- cerebellum - connects the posterior and anterior sections. Fourth- middle - responsible for facial expressions, movements of the eyeballs, auditory pathways pass through it. That is what we will consider. Fifth- front - normalizes mental activity.
It is interesting. There is no relationship between brain size and intelligence in humans. Much more important is the number of neural connections.
Where is
The location corresponds to the name of the body. It is part of the stem. It is 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 took place in such a way that the anterior section became the most developed. And through the middle one began to pass conductive channels of signals to various departments.
How does the midbrain develop?
Children in their mother's womb have to go through many stages of development. During the embryonic stage, the midbrain grows out of a small vesicle and remains intact throughout life. Throughout development, new cells appear in this part, they compress the cerebral aqueduct. With violations 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. Each time a person remembers information, neural connections are formed. This means that the structures of various departments, including the midbrain, are constantly changing, it does not freeze in a certain state.
What role does
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 device
It is known that the human midbrain has different parts, each of which performs its own role. Four hills - the structure is a pair of hills. The upper ones are visual and the lower ones are auditory.
There is a black substance in the legs. Thanks to him, a person not only lies, but can make precise movements with his hands and eat. At some point, the middle section processes information about when to bring a spoon to your mouth, how to chew food, and what function will allow you to swallow it.
Good to know: Brain: functions, structure
The ocular motor nerve originates between the legs, from where it exits. 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 large hemispheres of the large brain, it is simple and has only two sections. The quadrigemina on the nearby two paired colliculi, which form upper wall. Remind by appearance plate. Legs - there are conducting channels going to the hemispheres of the anterior section and connecting it with the lower sections 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 with the help of grooves intersecting in pairs. The two upper hills are subcortical centers of vision regulation, and the remaining lower hills are auditory. Ventral - these are the so-called legs of the brain. The conducting channels to the anterior section are based here. The inner space of the brain has the form of a hollow channel.
Helpful information. If a person does not breathe oxygen for more than five minutes, the brain will be permanently damaged, leading to death.
Nuclei
Inside the tubercles of the quadrigemina, gray matter accumulates, the accumulations of which are called nuclei. The innervation of the eyes is called the main function of the nuclei. They are of the following types.
Reticular formation - takes part in the stabilization of the skeletal muscles. They activate the cells of the cerebral cortex of the head, and have an inhibitory effect on the spinal cord. The oculomotor nerve contains fibers that innervate the sphincter and eye muscles. Block nerve - supply nerves to the oblique muscle of the organ of vision. Black substance - the color is associated with the pigment melanin. The neurons of this substance themselves synthesize dopamine. Coordinate facial muscles, small movements. Red nuclei of the midbrain - activate the neurons of the flexor and extensor muscles
Prevention of pathologies
Brain without intellectual activity and physical activity cannot function correctly. Usually, malfunctions in 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, cease to maintain their health and lead a healthy lifestyle. However, there are also congenital pathologies in the midbrain, you can get sick at any age.
Good to know: Functions and structure of the brain bridge, its description
Regularly engage in sports to the extent of physical capabilities, walk in the fresh air, do gymnastics in the morning. Give up tobacco and alcohol. Switch to a healthy diet, eat as many fresh vegetables and fruits as possible. Do not eat foods with preservatives and emulsifiers. Train the mind - for this you can read books, solve crossword puzzles, play chess, gain new knowledge in a field of interest.
Get rid of beriberi - take vitamins and antioxidants. Since the brain is 60% fat, you can not refuse 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 blood pressure levels - hypertension can cause a stroke.
The midbrain is the smallest region of the brain. It is so modest, but very important - there are no unimportant sections in the brain. If you look at the size of the medulla oblongata and the pons, then each of them is about 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 hillocks that protrude from the surface of the midbrain. The upper pair of mounds (or anterior) and the lower pair (or posterior) are distinguished. In general, this is called the quadruple. The lower part of the midbrain is called the peduncles. Inside the legs, a tire, a base are isolated. The border between the quadrigemina and the legs of the brain is a narrow and thin canal that passes through the midbrain - it is called the cerebral aqueduct, or Sylvian aqueduct. 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 channel remains inside the tube. In the spinal cord, it gives rise to the spinal canal, and in the brain it expands in places, and the ventricular system arises. The fourth ventricle is located under the cerebellum, and its lower border is the upper side of the medulla oblongata and the bridge - 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 colliculus of the quadrigemina is the sensory centers of the midbrain. The anterior colliculus first appears in evolution, and these are the neurons that process visual signals. In fish, these are the most important visual centers, while in us they perform an auxiliary function, and in the anterior upper colliculus of the quadrigemina there are cells that respond to new visual signals. Four hills, strictly speaking, almost do not care what we see specifically, the main thing is that something has changed. Change is primarily the movement of objects in the field of view. Then neurons in the quadrigemina are triggered - novelty detectors, and a very characteristic reaction of turning the eyes towards the new signal is triggered. And if necessary, the head turns, and even the whole body. In fact, the work of the quadrigemnes is curiosity at its most ancient level, it is the desire of the brain to collect new information. Even Ivan Petrovich Pavlov called this reaction an orienting reflex. The orienting reflex is one of the most complex innate reflexes of our body, but it is just as innately set as the swallowing reflex or the reflex of pulling the hand away from the source of pain.
The lower colliculi of the quadrigemina appear in evolution much later, and they belong to the auditory centers. The processing of the auditory signal begins at the level of the medulla oblongata and the bridge, where the nuclei of the eighth nerve are located, and then the information is transmitted to the lower colliculi of the quadrigemina, and they perform approximately the same task as the superior colliculus - they respond to new auditory signals. If a new sound appears, or the sound source begins to shift, or the tonality changes, then an orienting reflex is also triggered, and we look at where something rustled, changed, because all this is colossally significant.
The oculomotor centers are very powerfully connected with the work of the quadrigemina. Inside the midbrain are motor neurons that just control eye movements. I must say that eye movements are the most subtle movements that our body performs. Of course, we know that our fingers move very subtly or the movements of the tongue and facial expressions are very subtle, but the most accurate movements, it turns out, are performed by our oculomotor muscles, which rotate the eye in the bone orbit and tune our vision to analyze one or another visual object.
As many as six oculomotor 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, and its nuclei are located at the top of the bridge with special projections called the facial hillocks. The fourth and third nerves are the nerves of the midbrain; the fourth nerve is called trochlear, and the third - oculomotor. The oculomotor nerve in this system is the most important, the largest, and four of the six oculomotor muscles are controlled by the third nerve. The trochlear nerve and the abducens share only one oculomotor muscle each. The oculomotor nerve fibers exit on the underside of the midbrain and travel to the eye. Inside the third nerve are not only motor axons, axons of motor neurons, but also autonomic axons, parasympathetic axons that control the diameter of the pupil and the shape of the lens.
The substantia nigra is perhaps the most famous structure of the midbrain. There are dopamine neurons here, which further direct their axons up to the cerebral hemispheres, and the level of our motor activity depends on the release of dopamine from these axons, 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 studied very actively, there is a search for medicines, there is a search for ways to stop and delay these neurodegenerations. But this is not the only function of the black substance. Dopamine neurons are located 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 mediator. These cells control eye movements and inhibit excessive oculomotor reactions, allowing us to control the work of the third, fourth and sixth oculomotor nerves.
Another structure that is associated with dopamine release and related to the midbrain is the ventral tegmental area. Its axons go to the cerebral cortex, to the nucleus accumbens of the transparent septum, 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.
The two upper mounds of the quadrigemina (tubercle, colliculus superior) are the subcortical centers of the visual analyzer
Neurons in the deep layers of the superior colliculus can trigger friendly eye movements (saccades) when it is necessary to track a new object or threatening visual, auditory, somatosensory stimuli. The superior colliculus sends impulses to the center of horizontal eye movement and to the center of vertical eye movement, providing friendly gaze movements.
The superior colliculus of the quadrigemina is a midbrain structure consisting of several cell layers (Fig. 35.24), in which the first three layers process exclusively visual information, while the subsequent ones receive multimodal inputs not only from the visual system, but also from the somatosensory system and the auditory system.
Retinal ganglion cells are projected to the neurons of the first three layers of the superior colliculus, whose axons go through the handle (brachium) of the superior colliculus. These ganglion cells belong to the W-cell and M-cell types and are located predominantly in the nasal half of the retina of the contralateral eye. The neurons of the surface layer also receive projections from the visual cortex, including the striate cortex. There are M-cell activated neurons in the cortical loop. In turn, the surface layer sends projections to several nuclei of the thalamus - the pillow (pulvinar), LKT, due to which it has indirect connections with vast areas of the visual cortex.
Thus, the superior colliculus is included in reflex reactions to the sudden appearance of new or threatening objects in the visual field. With the help of a similar mechanism, the corresponding eye and head, at an unexpected sound or touch, turn so that the source of the stimulus is visible. Descending paths provide interaction with
The midbrain is composed of the quadrigemina and the cerebral peduncles. The main formations are the red nucleus, which is located in the middle part of the cerebral stalk, the black nucleus and black substance, the nuclei of the 3rd and 4th nerves, the reticular formation surrounding the Sylvian aqueduct.
The nuclei of the quadrigemina, located on the spinal side of the midbrain, correspond to the posterior horns of the spinal cord, and the red nucleus, substantia nigra, and nuclei of the 3rd and 4th cranial nerves, located on the ventral side, correspond to the anterior horns of the spinal cord.
Participation of the midbrain in visual and auditory reflexes
In the anterior tubercles of the quadrigemina, part of the afferent nerve fibers ends, which are neurites of the second neurins of the visual pathway of the retina. These fibers of the optic nerve are in contact with the nuclei of the oculomotor nerves located in the anterior tubercles. The nuclei of the oculomotor nerves are reflexively excited simultaneously with the optic nerves, which causes the eye and pupillary constriction. Since the anterior tubercles are connected with the red nucleus and other nuclei, body movements also occur. The pupillary reflex also involves the gray matter located between the anterior tubercles of the quadrigemina and the thalamus.
The anterior tubercles are involved in the protective closure of the eyelids during a sudden flash, squinting and pulling back the head with a sudden approach of the object in question and turning the eyes and head in its direction. In the transmission of impulses from the retina to the cerebral cortex, causing visual sensations, the anterior colliculi do not participate. Therefore, their removal in higher animals and humans does not cause blindness.
In the posterior tubercles of the quadrigemina, the neurites of the second neurons of the auditory pathway terminate, which ensures the participation of the posterior tubercles and reflex contractions of the muscles of the middle ear, as well as in the reflex movements of the ear, head and body towards.
Consequently, the quadrigemina are not centers of vision and hearing, but when light and sound stimuli act on the eye and ear, they participate in complex coordinated reflex movements of turning the body, head, eyes and ears in the direction of the stimuli.
The role of the midbrain in the regulation of posture and movement
The red nucleus and the motor nuclei surrounding it are of the utmost importance for the implementation of all movements, since they reflexively regulate muscle tone. After separation of the midbrain from the medulla oblongata, the normal distribution of tone disappears in animals. The red core system is the main center involved in taking an active posture and allowing a number of complex motor acts to be performed. The red nucleus is associated with the cerebellum, thalamus, striatum and cerebral cortex.
It, in turn, sends impulses to the spinal cord along the rubrospinal path and to the inferior olive. If the integrity of these connections of the red nucleus with the medulla oblongata and spinal cord are violated, they sharply increase from proprioceptors and decerebrate rigidity develops. The onset of decerebrate rigidity in the forelimbs to a greater extent depends not on the receipt of afferent impulses from the receptors of the muscles of the forelimbs, but on their receipt from the cervical muscles and vestibular apparatus.
The substantia nigra is a nerve center that coordinates the act of eating (chewing, swallowing, etc.), as well as a center for the regulation of plastic muscle tone.
Since static and statokinetic reflexes are more pronounced after the removal of the cerebral hemispheres and diencephalon, this proves that the mesencephalon automatically regulates posture and movements due to the flow of impulses from the vestibular apparatus and proprioceptors.
The more highly developed an animal is, the more its coordinated movements are disturbed when parts of the nervous system located above the midbrain are removed. The more developed the animal organism, the more freely it takes postures, regardless of the adjusting reflexes.
1. What is the main function of the quadrigemina of the midbrain
A. Regulation of homeostasis of all autonomic functions
B. Implementation of orienting 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 trunk proprioceptors
D. Secondary analysis of information coming from visual and auditory receptors
E. All answers are wrong
3. What is the name of the type of muscle tone that occurs when the midbrain is cut below the level of the red nucleus?
A. Normal
B. Plastic
C. Weakened
D. Contractile
E. Lightweight
4. What 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 a 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 what brain structures can explain changes in muscle tone?
A. Substance nigra
V. Yader Gaull
C. Deiters kernel
D. Burdakh nuclei
E. Red nuclei
6. After a brain injury, the patient's fine movements of the fingers were disturbed, muscle rigidity and tremor developed. What is the reason for this phenomenon?
A. Cerebellar injury
B. Damage to the midbrain in the area of the red nuclei
C. Damage to the midbrain in the substantia nigra
D. Damage to Deiters nuclei
E. Brain stem injury
7. A patient with a disorder of cerebral blood flow has a disturbed act of swallowing, he may choke when taking liquid food. 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. Back group
D. Medial group
E. Front group
9. Which nuclei of the thalamus are involved in the formation of the phenomenon of "reflected pain"
A. Reticular
B. Associative
C. Intralaminar complex
D. Relay
E. Non-specific nuclei
10. The thalamus is...
A. Manifold afferent pathways, the highest center of pain sensitivity
B. Regulator of muscle tone
C. Regulator of all motor functions
D. Regulator of homeostasis
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.
TESTS FOR SELF-CONTROL according to the program "Krok-1":
1. In the experiment, one of the structures of the midbrain was destroyed in the dog, as a result, it lost the orienting reflex to sound signals. What structure was destroyed?
A. Vestibular nucleus of Deiters
B. Red core
C. superior tubercles
D. Inferior tubercles
E. Black substance
2. Animals with decerebrate rigidity are characterized by
A. Disappearance of rectifying reflections
B. Loss of the lift reflex
C. A sharp increase in the tone of the extensor muscles
D. All answers are correct
E. All answers are wrong
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 CNS are directly related to maintaining posture, chewing, swallowing food, secretion of digestive glands, respiration, heart activity, regulation of vascular tone?
A. Midbrain
B. Thalamus
C. hindbrain
D. spinal cord
E. Forebrain
5. Reflex reactions of which part of the CNS are directly related to the implementation of the "watchdog reflex"?
A. hindbrain
B. Thalamus
C. spinal cord
D. Cerebellum
E. Midbrain
6. How to experimentally prove that decerebrate rigidity is caused by a significant gamma-amplification of spinal myotatic reflexes?
A. Cut the posterior roots of the spinal cord
B. Cut the spinal cord
C. make a transection above the midbrain
D. make a transection below the midbrain
E. make a cut below the hindbrain
7. What is the name of a reflex reaction in a person with 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", lesion of the quadrigemina
C. reflex "what is it", lesion of the reticular formation
D. adaptive reaction, globus pallidus lesion
E. reflex "what is it", defeat of red nuclei
8. A person has hypokinesia and rest tremor. What part of the brain is affected?
A. pallidum and substantia nigra
B. 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, for the first time, all reflexes are closed, except ...
A. rectifier
B. statokinetic
S. pupillary
D. eye nystagmus
E. perspiration
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 for spinal reflexes, after transection of the spinal cord under the medulla oblongata? Breathing is supported artificially
2. The animal underwent two consecutive complete transections of the spinal cord under the oblongata at the level of C2 and C4 segments. Explain how the value of blood pressure will change after the first and second sections?
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 brainstem in order to obtain a change in muscle tone, schematically shown in the figure? What is the name of this phenomenon and what is its mechanism?
5. Explain what will happen to a cat that is in a state of decerebrate rigidity after cutting the brain stem below the red nucleus, if now the posterior roots of the spinal cord are also cut?
6. Explain how the tone of the muscles of the fore and hind limbs of a bulbar animal will change when its head is tilted forward? Draw a diagram of the position of the limbs and explain your answer?
7. From the skater when running at the turn of the track of the stadium, especially precise footwork is required. 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. Re-cutting will have no effect, since the connection has already been interrupted.
3. There are no vital centers in the cerebral cortex, but there are in the oblongata (respiratory, vasomotor, etc.). Therefore, a hemorrhage in the medulla oblongata is more life-threatening. It usually ends in death
4. The phenomenon of decerebrate rigidity (extensor hypertonicity) is obtained by transection of the brain stem between the middle and medulla oblongata, so that the red nucleus is higher than the place of transection.
5. Rigidity will disappear, as 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 forelimbs 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, he can lose balance and fall.
8. According to the nature of the reaction of pupils to light, anesthesiologists judge the depth of narcotic sleep. If the pupils stop responding to light, this means that 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 can turn off. The dose of the drug should be reduced.