Incorrect operation knee reflex indicates serious disturbances in the functioning of the body. To diagnose a disease on early stages you should know what your reaction to a hammer blow under your knee indicates. Let's look at this in the article.
The reception of information from the outside and its transmission throughout the body: through the muscles, organs, spinal cord and brain is ensured by the stable functioning of the nerves. The brain has a standard scheme for transmitting impulses along the path. In cases where an immediate reaction is required, the reflex passes through. This reaction occurs, for example, if you step on a needle, then the leg suddenly withdraws. If the reflex went through the brain, there would definitely be a delay in the process, which can be dangerous for the life of the body.
The human knee-jerk reflex and its meaning. The arc of the knee reflex
So, a reflex is an instant response to an external stimulus; it is coordinated by the nervous system. And its path is called a reflex arc.The irritation signal is transmitted via afferent nerves to efferent centers in the spinal cord. It is then transmitted to the muscles, which contract. Lack of reflexes is a symptom of muscle disease, nervous system, brain, special emotional state. Vital body processes also operate reflexively, such as the production of saliva when food is consumed.
How to trigger the knee reflex?
The occurrence of the knee reflex is due to the fact that when a medical hammer hits the quadriceps tendon, it contracts. This contraction causes the leg to straighten. The blow must be applied exactly under the kneecap, because the tendon of the quadriceps extensor muscle is fixed at the beginning tibia. It is not necessary to hit with force, the main thing is that the muscles are as relaxed as possible.
You can cross one leg over the other, then when the patellar reflex occurs, it will jerk upward.
What if you need other methods?
If traditional way doesn’t work, there are several other techniques for demonstrating the knee-jerk reflex:
- The person should be seated on a chair with their toes touching the floor and their legs bent at an angle slightly greater than 90 degrees. The blow must be applied from top to bottom over the retracted patella. As a result, the patella rises;
- the knee of the required leg must be placed on top of the second knee;
- you can use a high seat so that your legs hang in a relaxed state;
- There is also a method when the patient is lowered onto his back with his knees stacked one on top of the other.
There are times when the patient is physically unable to sufficiently relax the limb being examined. Then specialists use methods of disinhibition of the knee reflex, for example, the techniques of Jendrassik and Shvetsov. The patient should also breathe deeply or solve simple mathematical problems out loud.
What do disturbances in the knee reflex indicate?
Muscles contract in a similar way on the upper pair of limbs and elsewhere in the body. But the significance of the knee reflex is that its violation is considered important symptom abnormalities in the functioning of the brain and spinal cord. The arc of the knee reflex is constant. Only in rare options healthy man may not have a knee reflex, but most likely childhood disease damaged his work. In the presence of diseases, it may be absent or, on the contrary, excessively intensified. This is explained by the fact that the center of the knee reflex is located in lumbar region spinal cord, or rather in the II-IV segment. For some diseases there are specific deviations in the manifestation of the knee reflex. For example, cerebral lesions cause a pendulum-shaped knee reflex. An enhanced reflex may indicate a form of neurosis. On the contrary, a reduced form of the reflex is a sign of infection or intoxication of the body. Complete absence knee reflex indicates significant damage to the nervous system. Also, the reflex may disappear in epileptics after a seizure, after using a tourniquet, during deep anesthesia or after heavy muscle strain. Only a specialist can make an accurate diagnosis.
What is a reflex arc?
The knee reflex occurs due to its reflex arc. Just as there is significant disruption to the overall functioning of a machine due to the presence of a damaged part, the human body is similarly unable to function when something is not working correctly.
A reflex arc is the path of a signal from the receptor that receives it to the organ that responds to it. It is also called the neural arch. This name is explained by the fact that the knee reflex occurs due to impulses in the nerves that travel a certain path. The reflex arc consists of chains of neurons that are formed from intercalary, receptor and effector neurons. They themselves and their processes create a path for the transmission of irritation.
What are the types of reflex arcs?
The peripheral nervous system has two types of reflex arcs:
- those that supply internal organs with signals;
- those related to skeletal muscles.
How does the knee jerk reflex arc work?
The arc of the knee reflex involves three sections of the back, from the second to the fourth. In this case, the fourth department is the most important in the process.
The reflex arc of the knee reflex has five components:
- Receptors. They receive the stimulus signal and become excited in response. These are the ends of axons or bodies located in epithelial cells. Receptors are found everywhere in human body, in organs, in the skin, the sense organs consist of them;
- sensitive, afferent or centripetal. It transmits the signal to the center. Neuronal bodies are located outside the central nervous system, namely near the brain and in the nerve ganglia near the spinal cord.
- The nerve center is the place where the signal is transmitted from afferent neurons to efferent ones. The centers of efferent neurons are located in the spinal cord.
- The nerve fiber is motor, centrifugal or efferent. As the name suggests, excitation along it goes from the central nervous system to a specific organ. The efferent fiber is an axon (or a long process) of a centrifugal neuron.
- Effector. An organ that responds to stimulation of a specific receptor. This is a muscle that contracts after processing a signal from the center, the gland, which exudes juice due to nervous excitement, and other.
How does the impulse move during the knee reflex?
To study the knee reflex in detail, its stages should be studied. The knee-jerk reaction proceeds as follows:
- hitting the tendon under the knee with a hammer causes this tendon to stretch, therefore, a receptor potential arises in the corresponding receptors;
- An action potential arises in the neuronal long process. It is chemically transmitted in the spinal cord;
- the axon of the efferent neuron serves as a signal path to the gastrocnemius muscle;
- due to muscle contraction, the leg twitches.
Now you know how the reflex works and for what purposes it is diagnosed.
Will the knee reflex and skin sensitivity be preserved if a person has a disruption in the conduction of excitation from the spinal cord to the brain?
& Work with computer
Refer to the disk. Study the lesson material and complete the assigned tasks.
http://www.medicinform.net /human/anatomy/anatomy1_ 1.htm
The spinal cord is a long cylindrical cord located in the spinal canal. Roots extend from the spinal cord
31 pairs spinal nerves. The spinal cord contains the centers of some simple reflexes. It performs reflex and conductive functions. The spinal cord will work
is under the control of the brain.
STRUCTURE AND FUNCTIONS OF THE BRAIN
Man has long sought to penetrate the mystery of the brain, to understand its role and significance in human life. Already in ancient times, the “father of medicine” Hippocrates connected consciousness and brain, but many hundreds more have passed
years before scientists began to unravel its mysteries.
Human brain- This is a complex organ capable of perceiving and processing a huge amount of information. Let's get acquainted with its structure and basic functions tions.
Brain It is located in the cranial cavity and has a complex shape. Brain weight in an adult
ka ranges from 1100 to 2000 g; averaging 1300-
Convolutions of the cerebral cortex
1400 g. This is only about 2% of body weight, but the cells that make up the brain consume up to 25% of the energy produced in the body!
Typically, the brain mass of women is slightly smaller than that of men; this difference is due to the different mass of the male and female body.
| / Furrow |
The human brain, like all vertebrates, consists of the brainstem, cerebellum and cerebral hemispheres.
Trunk includes several departments, they differ from each other in structure and functions. These are the medulla oblongata, pons, midbrain and diencephalon.
Medulla is a continuation of the spinal cord, so their structure has a lot in common. Only gray matter medulla oblongata located in separate clusters - nuclei. The functions are also similar: reflex and conductive. Many reflex processes are carried out through the nuclei of the medulla oblongata, for example, coughing, sneezing, lachrymation.
In the central part of the medulla oblongata begins reticular formation of the brainstem- an accumulation of a huge number of seemingly chaotically located neurons. Neurons of the reticular formation have connections with structures forebrain By sending impulses to the overlying sections, these neurons maintain the forebrain in a wakeful state. Damage to the reticular formation of the medulla oblongata leads to drowsiness, loss of consciousness, lethargic sleep, and memory loss.
leniya, etc. Here are also located nerve centers, responsible for the acts of swallowing and the functioning of the digestive glands. The medulla oblongata also contains vital centers involved in the regulation of respiration, the activity of the heart and blood vessels. Damage to these centers leads to human death.
Bridge- this is the place where the nerve fibers are located, along which nerve impulses go up to the cerebral cortex or back, down to the spinal cord, to the cerebellum, to the medulla oblongata. There are also centers associated with facial expressions and chewing functions.
midbrain, like the medulla oblongata, it is part of the brain stem. On its surface, facing the cerebellum, there are four small tubercles - quadrigeminal. Upper tuberosities Quadrigholmia - centers for primary processing of visual information, their neurons react to objects moving quickly in the field of view. The main functions of the neurons of the superior colliculus are controlling the direction of gaze and bringing the visual system into a state of heightened alertness under strong visual stimuli. Lower tuberosities The quadrigeminal region is the center for the primary processing of auditory stimuli. The neurons of these centers respond to strong sharp sounds, leading auditory system in a state of high readiness. If something flashes in a person’s field of vision or some noise is heard next to him, then the person involuntarily shudders and his muscles tense, and this happens even before he understands what is happening. If it turns out that something falls on a person, then his motor systems are already ready to flee or defend.
In the midbrain there are the most important clusters of neurons that perform motor functions - the red nucleus and
Black substance. Neurons of the red nucleus, together with neurons of the cerebellum, are involved in maintaining muscle tone and coordination of body posture. Neurons of the substantia nigra secrete the most important regulatory substance - dopamine. Dopamine is necessary for a person to make fast and precise movements, walk, and run. In addition, when there is a lack of dopamine, people experience negative emotions, their mood worsens, and they become depressed.
Cerebellum located on the back side of the brain stem: behind the medulla oblongata and middle sections. The weight of the cerebellum of an adult is 150 g. The structure of the cerebellum is similar to the structure of the entire brain. That's why its name translates as "little brain." The cerebellum is connected to the midbrain by three pairs of peduncles. It consists of a worm (the stem, the most ancient part) and hemispheres, divided by grooves into shares. The lobes, in turn, are divided into small grooves convolutions. The superficial layer of the hemisphere is gray matter, the so-called cerebellar cortex. The brain receives information from everyone propulsion systems: from the cerebral hemispheres, from the midsection and spinal cord.
The main functions of the cerebellum: regulation of body posture and maintenance muscle tone; coordination of slow voluntary movements; ensuring the accuracy of fast voluntary movements. The ancient stem part of the cerebellum is responsible for balance and coordination of movements of the trunk muscles, and its hemispheres are responsible for fast, precise movements. When the cerebellar vermis is destroyed, a person cannot walk or stand, his sense of balance is impaired.
news. With lesions of the cerebellar hemispheres, a decrease in muscle tone is observed, severe trembling limbs, impaired accuracy and speed of voluntary movements, rapid fatigue. In addition, oral and written speech is disrupted.
Diencephalon consists of the thalamus and hypothalamus (subcutaneous region). Down from the hypothalamus, on a thin stalk, there is an internal secretion gland - the pituitary gland.
Cerebellum slice
Thalamus is the center of ana-
| brain (slice) |
| ;;;::--.r--- SPINAL CORD (section) |
lysis of all types of sensations, except olfactory. The thalamus contains more than 40 pairs of nuclei (clusters of neurons) with various functions. In some nuclei, the analysis of visual, auditory and other information continues. Other nuclei are involved in the coordination of the brain's motor systems. The third group of nuclei compares and summarizes information received from various senses, creating a holistic image of the world around us.
Lower part of the diencephalon - hypothalamus- also performs essential functions, being the highest center of vegetative regulation. The anterior nuclei of the hypothalamus are the center of a pair of sympathetic influences, the posterior nuclei are the center of sympathetic influences. The hypothalamus also contains hunger and thirst centers, irritation of the neurons of which leads to uncontrollable absorption of food or drinking water.
Thus, we can say that the hypothalamus is necessary to regulate the work of all internal organs. Lesions of the hypothalamus are accompanied by severe disorders: a decrease or increase in pressure, a decrease or increase in heart rate, difficulty breathing, disturbances in intestinal motility, thermoregulation disorders, changes in blood composition, etc.
In the thickness of the white matter of the cerebral hemispheres there is a complex of subcortical brain nuclei, called limbic system. The limbic system contains the main centers responsible for emotional condition man of the century. Here are the centers of fear, rage, and pleasure. These centers provide an emotional assessment of the situation, assessment possible consequences this situation and the choice of one of the optimal forms of behavior. As a result the right choice In order to behave, the organism must come into line with its needs, for example, to avoid danger or provide itself with food, etc.
The nuclei of the thalamus are the highest center of pain sensitivity; it is here that painful sensation. When a person, for example, pinches a finger and feels pain in it, then in fact the pain arose in the representation of the finger in the nuclei of the thalamus, i.e., where the signals from the pain receptors of the pinched finger came. These nuclei may be associated with the so-called phantom pain, when pain is felt, for example, in a limb that has been amputated for a long time. Pain in this case is a consequence of pathological excitation of those neurons of the ventral nuclei that were once associated with a long-absent limb. In patients with destroyed ventral nuclei, the sense of time is often impaired. Apparently, these nuclei contain neurons that play the role of<< внут ренних часов,>our body.
If you want to find out if everything is okay with your cerebellum, then stand with your legs together, stretch your arms forward and close your eyes. A person with a damaged cerebellar trunk cannot stand in this position; he will begin to sway or even fall. Then try touching the tip of your nose at a fast pace index fingers then left, then right hand alternately. If you get where you want, then the hemispheres of your cerebellum are functioning normally.
With serious lesions of the cerebellum, both animals and humans move with great difficulty, raising their paws or legs high, stumbling, and swaying. They cannot estimate the distance to any object and get tired very quickly.
TEST YOUR KNOWLEDGE
1. Where is the brain located?
2. What parts does the brain consist of?
3. What parts make up the brain stem?
4. What are the similarities and differences in the functions of the brain stem and spinal cord?
5. What are the functions of the medulla oblongata?
6. How does the cerebellum work?
7. What functions does the cerebellum perform?
8. What are the functions of a bridge?
9. Name the functions of the midbrain.
1O. What functions do the pons and diencephalon perform?
Complete task No. 56 on p. 38 ( Workbook). Complete task No. 57 on p. 38 (Workbook). Choose the correct answer. Test 2 on p. 24, option 2 (Tes-
CENTRAL NERVOUS SYSTEM
TASK No. 1
A man with an injury was taken to the neurological department of the hospital.
spine. The doctor determined that his knee, Achilles and
plantar reflexes.
Question No. 1 Which parts of the spinal cord were injured?
Response standard
Knee reflex - L – III, Achilles – S-I, plantar – L-III – S-I.
Question No. 2 Remembering the classification of reflexes, answer: which ones, from different points of view,
are the reflexes listed above.
Response standard
Knee, Achilles – monosynaptic, somatic, tendon;
plantar – polysynaptic, somatic, cutaneous.
Question #3 Will pain sensitivity in the lower extremities persist after such
Response standard
It won't be saved.
Question #4 Will the ability for voluntary movements of the lower extremities be preserved?
after such an injury?
Response standard It won't be saved.
Question #5 What is the clinical significance of determining these reflexes?
Response standard
Determination of the functional integrity of the spinal cord.
TASK No. 2
Checking the patient's knee reflex revealed weak tension in the femoral
muscles. Repeated research using the distraction technique
examined (coupling-uncoupling of fingers) revealed not only
tension of the femoral muscle, but also extension of the lower leg.
Question No. 1 Specify the reason for the weak expression of the reflex during the first examination.
Response standard
Increased activity of additional inhibitory inputs.
Question No. 2.What is the reason for using the finger clutch-release technique?
of the person being examined when testing the knee reflex?
Response standard
Assessment of the nature and quality of descending influences in the central nervous system.
Question #3 Describe the correct position of the patient when examining the knee reflex.
Response standard
Sitting on a chair, crossing your legs.
Question #4 What is the physiological significance of tendon reflexes?
Response standard
They are one of the mechanisms for regulating and maintaining muscle tone.
Question No. 5. Where is the sensory neuron of the reflex arc of this reflex located?
Response standard
In the spinal ganglion.
TASK No. 3
The dog had electrodes implanted in the area of the reticular formation (a collection of polymorphic neurons along the brain stem)
Question No. 1 What happens if the electrodes irritate a sleeping dog?
Response standard
Awakening.
Question No. 2 From what brain structures can activating influences still come?
Response standard
Cerebral cortex, nonspecific nuclei of the thalamus.
Question #3 What happens when the reticular formation is destroyed?
Response standard
The animal will fall asleep.
Question #4 What happens if you cut the brain between the anterior and posterior
quadrigeminal tubercles?
Response standard
The animal will stop responding to all types of signals. Transection of the brain stem in an animal (for example, a cat) between the anterior and posterior colliculi (the operation of cutting the brain stem is called decerebration) causes a special condition of skeletal muscles, which is called decerebrate rigidity orcontractile tone. This condition is characterized by a sharp increase in the tone of the extensor muscles. The limbs of such an animal are strongly elongated, the head is thrown back, and the back is arched. This condition is called opisthotonos.
Question #5 What is the specific and nonspecific influence of the reticular formation?
Response standard
Specific - selective activating or inhibitory influence on different forms of behavior; nonspecific – regulation of the level of activity of the cortex
cerebrum, cerebellum, thalamus, spinal cord.
TASK No. 4
When an emergency situation arises in the fleet, the command “whistle” sounds.
everyone up!”, which requires combat readiness.
Question No. 1 When which part of the autonomic nervous system is excited does this occur?
a state similar to what this command requires?
Response standard
Sympathetic.
Question No. 2 What is the state of “combat readiness” during excitement?
sympathetic division of the autonomic nervous system?
Response standard
In the general mobilization of the body's resources.
Question #3 Where are the centers of the sympathetic nervous system located?
Response standard
In the spinal cord.
Question #4 What other departments, besides the sympathetic, are distinguished in the autonomic nervous?
Response standard
Parasympathetic, metasympathetic.
Question #5 Is there a connection between the autonomic and somatic nervous systems?
Response standard
Yes, they function in a friendly manner.
TASK No. 5
In one of D. London's stories, the hero decides to poison his friend
strychnine. As a result, both die after the occurrence of generalized
seizures Strychnine is known to block inhibitory synapses in the central nervous system.
Question No. 1 What type of central inhibition is turned off by the action of strychnine?
Response standard
Lateral. Strychnine blocks inhibitory synapses in the central nervous system (mainly glycinergic) and thereby eliminates the basis for the formation of the inhibition process. Under these conditions, irritation of the animal causes an uncoordinated reaction, which is based on diffuse (generalized) irradiation of excitation. In this case, adaptive activity becomes impossible.
Question No. 2 What underlies an uncoordinated reaction to stimulation during action?
strychnine?
Response standard
Diffuse irradiation of excitation when lateral inhibition is turned off.
Question No. 3. What other types of central inhibition based on neuronal
organizations other than the lateral one, do you know?
Response standard
Progressive inhibition is caused by the inclusion of inhibitory neurons along the path of excitation (Fig. 15).
Rice. 15. Scheme of progressive braking. T - inhibitory neuron
Returnable inhibition is carried out by intercalary inhibitory neurons (Renshaw cells). Impulses from motor neurons through outgoing from its axon collaterals activate the Renshaw cell, which in turn causes inhibition of the discharges of this motor neuron.
Rice. 16. Reverse braking circuit. The collaterals of the axon of the motor neuron (1) contact the body of the Renshaw cell (2), the short axon of which, branching, forms inhibitory synapses on motor neurons 1 and 3.
Lateral(lateral) braking. Intercalary cells form inhibitory synapses on neighboring neurons, blocking the lateral pathways of excitation propagation (Fig. 17). In such cases, excitation is directed only along a strictly defined path.
Rice. 17. Scheme of lateral (side) inhibition. T - inhibitory neuron.
It is lateral inhibition that mainly provides systemic (directed) irradiation of excitation to the central nervous system.
Reciprocal braking. An example of reciprocal inhibition is inhibition of antagonist muscle centers. The essence of this type of inhibition is that excitation of the proprioceptors of the flexor muscles simultaneously activates the motor neurons of these muscles and intercalary inhibitory neurons (Fig. 18). Excitation of interneurons leads to postsynaptic inhibition of motor neurons of extensor muscles.
Inhibition in the central nervous system can be classified according to various criteria:
According to the electrical state of the membrane - depolarizing and hyperpolarizing;
In relation to the synapse - presynaptic and postsynaptic;
According to neuronal organization - translational, lateral (lateral), recurrent, reciprocal.
Postsynaptic inhibition develops under conditions when the transmitter released by the nerve ending changes the properties of the postsynaptic membrane in such a way that the ability of the nerve cell to generate excitation processes is suppressed. Postsynaptic inhibition can be depolarizing if it is based on a process of long-term depolarization, and hyperpolarizing if it is based on hyperpolarization.
Presynaptic inhibition is due to the presence of intercalary inhibitory neurons that form axo-axonal synapses on afferent terminals that are presynaptic in relation to, for example, a motor neuron. In any case of activation of the inhibitory interneuron, it causes depolarization of the membrane of the afferent terminals, worsening the conditions for the conduction of AP through them, which thus reduces the amount of transmitter released by them, and, consequently, the efficiency of synaptic transmission of excitation to the motor neuron, which reduces its activity (Fig. 14) . The mediator in such axo-axonal synapses is apparently GABA, which causes an increase in the permeability of the membrane to chlorine ions, which exit the terminal and partially but lastingly depolarize it.
Question #4 What is braking?
Response standard
Active biological process aimed at weakening, stopping or
preventing the occurrence of the excitation process.
Question #5 What are the functions of braking?
Response standard
Coordinating and protective. Firstly, it coordinates functions, that is, it directs excitation along certain paths to certain nerve centers, while turning off those paths and neurons whose activity is in this moment is not needed to obtain a specific adaptive result. The importance of this function of the inhibition process for the functioning of the body can be observed in an experiment with the administration of strychnine to an animal. Secondly, braking performs protective or protective function, protecting nerve cells from overexcitation and exhaustion under the influence of extremely strong and prolonged stimuli.
Problem No. 7
During the first grade lesson, new material was taught in a playful way. All children were included in the game and took an active part in it. When there was noise in the corridor, none of the children reacted.
Question No. 1. What principle of coordination activity of the central nervous system does this situation reflect? This situation reflects the principle of coordination activity of the central nervous system, discovered by A.A. Ukhtomsky and called the principle of dominance.
Question No. 2. What is characteristic of the activity of the central nervous system according to this principle? Dominant is called general principle activity of the nervous system, which manifests itself in the form of a system of reflexes that dominates for a certain time, implemented by dominant centers that subjugate or suppress the activity of other nerve centers and reflexes.
Question No. 3. What properties does a dominant focus have? The dominant focus of excitation is characterized by the following properties:
Increased excitability;
Persistence of excitation (inertia), because it is difficult to suppress with other excitation;
The ability to summarize subdominant excitations;
The ability to inhibit subdominant foci of excitation in functionally different nerve centers.
Question No. 4. What is the physiological meaning of this principle? The principle of dominance allows you to concentrate attention and build behavior to achieve a specific intended goal. Question No. 5. What other principles of coordination activity of the central nervous system do you know?
1. Principle spatial relief. It manifests itself in the fact that the total response of the body under the simultaneous action of two relatively weak stimuli will be greater than the sum of the responses obtained during their separate action.
2. Principle occlusion. This principle is the opposite of spatial facilitation and is that the two afferent inputs jointly excite a smaller group of motoneurons compared to the effects of activating them separately.
3. Principle feedback. The processes of self-regulation in the body are similar to technical ones, which involve automatic regulation of the process using feedback. The presence of feedback allows us to correlate the severity of changes in system parameters with its operation as a whole. The connection between the output of a system and its input with a positive gain is called positive feedback, and with a negative coefficient - negative feedback.
4. Principle reciprocity(combination, conjugation, mutual exclusion). It reflects the nature of the relationship between the centers responsible for the implementation of opposite functions (inhalation and exhalation, flexion and extension of the limb, etc.).
5. Principle common final path. Effector neurons of the central nervous system (primarily motor neurons of the spinal cord), being the final ones in a chain consisting of afferent, intermediate and effector neurons, can be involved in the implementation of various reactions of the body by excitations coming to them from a large number of afferent and intermediate neurons, for which they are the final pathway (path from the central nervous system to the effector).
Task No. 8. When a certain part of the medulla oblongata is destroyed in an animal, death occurs from respiratory arrest. When certain structures of the midbrain and pons are destroyed, changes in respiratory movements are observed.
Question No. 1. What term combines these structures? These structures are united by the term “nerve center”.
Question No. 2. Define the nerve center.. A nerve center is a functionally connected set of neurons located in one or more structures of the central nervous system and providing regulation of certain functions of the body.
Question No. 3. What is a nerve center in the broad and narrow sense of the word? In a narrow sense
Question No. 4. What is the neural basis of the nerve center? The neurons of the nerve center, due to structural and functional connections (branching of processes and the establishment of synapses between different cells), are combined into nerve networks. The connections between nerve cells are genetically determined. There are 3 main types of neural networks: hierarchical, local, divergent with one input.
Question #5. List the properties of nerve centers. Nerve centers have the following properties:
1. Spatial and temporal summation.
2. Central delay.
3. Post-tetanic enhancement.
4. Aftereffect and prolongation.
5. Transformation of rhythm.
6. Background activity.
7. Tone of nerve centers.
8. Plasticity of nerve centers.
9. Reliability of nerve centers.
10. Fatigue of nerve centers.
Problem No. 9 . An athlete runs a marathon.
Question No. 1. What type of central inhibition allows for cyclic muscle work that underlies the activity of the skeletal muscles of his limbs? The cyclic work of muscles during running allows for reciprocal (conjugate) inhibition.
Question No. 2. What is the mechanism of this type of braking? .
Question No. 2. Reciprocal inhibition is based on the fact that signals along the same afferent pathways provide excitation of one group of neurons, and through intercalary inhibitory cells cause inhibition of another group of neurons, for example, at the level of motor neurons of the spinal cord innervating antagonist muscles (flexors-extensors) of the limbs .
Question No. 3. What is the biological significance of this type of inhibition? The existence of reciprocal inhibition excludes the possibility of simultaneous excitation of antagonist muscle centers on the same side and provides rhythmic reflexes.
Question No. 4. What is central inhibition? Inhibition is an active physiological process in the nervous system, caused by excitation and manifested in the weakening or suppression of other excitation. Question No. 5. Who discovered central inhibition? Central inhibition was discovered by I.M. Sechenov. Task No. 10. Question No. 1. The frog sits with its body curved towards the distant part of the cerebellum, because The muscle tone on the side with the preserved half of the cerebellum is greater. Question No. 2. When the hind limb of the frog is irritated, it makes a circular (manege) movement in the direction of damage: the frog with the right half of the cerebellum removed moves clockwise, and with the left half removed, counterclockwise. When jumping, the frog turns its body in the air. When a frog swims, manege movements are observed, as well as rotation of the body around the longitudinal axis. Task No. 11. In an experiment, half of the frog's cerebellum was destroyed and released into a basin of water. Question No. 1. How will the muscle tone of the frog's limbs change after surgery? Question No. 2. What movements will the frog make? . Question No. 3. Explain the reason for the change in muscle tone of the cerebellar frog. Question No. 4. What brain structures have an effect? similar to action cerebellum, on Deiters' nuclei? Question No. 5.What is the role of Deiters nuclei in the regulation of muscle tone?Problem No. 12 The animal underwent a transection between the medulla oblongata and midbrain. Question No. 1.What will happen to the animal's tone? Transection between the medulla oblongata and midbrain damages the rubrospinal tract, which in experimental animals is accompanied by a persistent increase in the tone of the extensor muscles of the trunk and limbs. Question No. 2. What is this type of tone called? This change in tone is called decerebrate rigidity. Question No. 3. Explain the reason for its occurrence. Decerebrate rigidity occurs when the red nuclei lose their connection with the reticular formation of the medulla oblongata. The main cause of decerebrate rigidity is the pronounced activating influence of the lateral vestibular nucleus on extensor motor neurons. This influence is maximum in the absence of inhibitory influences of the red nucleus and overlying structures, as well as the cerebellum. Question #4.What is the role of the red nuclei in the regulation of muscle tone? The red nuclei receive information from the motor zone of the cerebral cortex, subcortical nuclei and cerebellum about the impending movement and the state of the musculoskeletal system and send corrective impulses to the motor neurons of the spinal cord along the rubrospinal tract, regulating muscle tone and preparing its level for the upcoming voluntary movement. corrective impulses to the motor neurons of the spinal cord along the rubrospinal tract, regulating muscle tone and preparing its level for the upcoming voluntary movement. Question No. 5. What other types of tone do you know? Problem No. 13 . A section of frog intestine placed in a Petri dish with Ringer's solution continues to contract. Question No. 1. What explains this functional automation? This functional automation is explained by the presence of the metasympathetic division of the autonomic nervous system, in particular in the intestines, which provides motor functions to the intestines even after it is removed from the body. Question No. 2. What does the concept of metasympathetic nervous system include? The metasympathetic nervous system contains autonomic ganglia located in the walls of the internal organs (intramural). The ganglia of the metasympathetic nervous system are similar in their structural organization to the central nervous system; they contain most of the central nervous system mediators; these ganglia contain the entire set of structures that characterize the integrative function of the nervous system: sensory elements, interneurons, motor neurons and their own neurogenic pacemakers. Metasympathetic ganglia function as lower centers for the integration of visceral functions. Question No. 3. What is the morphological basis of the processes realized with the help of the metasympathetic nervous system? . Neurons of the metasympathetic ganglia have synaptic contacts with fibers of the sympathetic and parasympathetic divisions of the autonomic nervous system; these fibers modulate activity gastrointestinal tract. Question No. 4. What is the role of extraorgan influences (sympathetic and parasympathetic) on the metasympathetic nervous system. Question No. 5. List the features of the metasympathetic division that distinguish it from other divisions of the autonomic nervous system. ? The metasympathetic nervous system has the following signs: 1) Innervates only internal organs endowed with a motor rhythm (smooth muscles, absorptive and secreting epithelium, local blood flow, local endocrine and immune elements). 2) Receives external synaptic inputs from the sympathetic and parasympathetic parts of the autonomic nervous system and does not have direct synaptic contacts with the efferent part of the somatic reflex arcs. 3) Has its own sensory link. 4) has greater independence from the central nervous system than the sympathetic and parasympathetic parts.
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The structure and significance of the nervous system
You already know that the existence of an organism in a complex, constantly changing world is impossible without the regulation and coordination of its activities. The leading role in this process belongs to the nervous system. In addition, in humans, the nervous system forms the material basis of his mental activity(thinking, speech, complex forms of social behavior).
The basis of the nervous system is made up of nerve cells - neurons. They perform the functions of perception, processing, transmission and storage of information. Nerve cells consist of a body, processes and nerve endings. Cell bodies can be different in shape, and processes can be of different lengths: short ones are called dendrites, long – axons. Clusters of neuron cell bodies in the brain and spinal cord form Gray matter. The processes of neurons (nerve fibers) make up white matter brain and spinal cord, and also form part of the nerves. Depending on the functions performed, they are distinguished sensitive, insertable And motor neurons.
Nervous system
Long shoots nerve cells(axons) penetrate the body and provide communication between the brain and spinal cord and any part of the body. The branches of the neuron processes have nerve endings. The endings of the dendrites of sensory neurons convert perceived stimuli from external and internal environment into nerve impulses. Nerve impulses spread along nerve fibers at a speed of 0.5 to 120 m/s.
Diagram of the structure of the autonomic nervous system
Nerve cells form special contacts at the points of connection with each other - synapses. Neurons, in contact with each other, form chains. Nerve impulses travel along such chains of neurons.
The nervous system is divided into central and peripheral based on its location in the body. TO central nervous system include the spinal cord and brain peripheral- nerves, ganglia and nerve endings. Nerves are called bundles of long processes of nerve cells that extend beyond the brain and spinal cord. The bundles are covered with connective tissue that forms the nerve sheaths. Nerve nodes are clusters of neuron cell bodies outside the central nervous system.
According to another classification, the nervous system is conventionally divided into somatic and autonomic (autonomic). Somatic nervous system manages the work skeletal muscles. Thanks to it, the body maintains contact with the external environment through the senses. All human movements are performed by contracting skeletal muscles. The functions of the somatic nervous system are controlled by our consciousness. The highest center of the somatic nervous system is the cerebral cortex.
Autonomic (autonomic) nervous system controls the functioning of internal organs, providing them with best job upon changes external environment or a change in the type of activity of the body. This system is not usually controlled by our consciousness, unlike the somatic nervous system. The highest center of autonomic regulation is the hypothalamus - Bottom part diencephalon.
The autonomic nervous system is divided into two sections: sympathetic And parasympathetic.
Most organs of the human body are controlled by both the sympathetic and parasympathetic divisions of the autonomic nervous system. Sympathetic regulation often prevails in cases where a person is in an active state, performing some difficult physical or mental work. Sympathetic influences improve blood supply to muscles and enhance heart function. Parasympathetic nervous influences on organs increase in cases when a person is at rest: the heart’s work slows down, blood pressure increases arterial vessels decreases, but the work of the gastrointestinal tract increases. This is understandable: when should we digest food if not during rest, in a calm state.
The activity of the nervous system has reached great perfection and complexity. It is based on reflexes(from the Latin “reflexus” - reflection) - the body’s response to environmental influences or changes in it internal state performed with the participation of the nervous system.
Many of our actions occur automatically. For example, when the light is too bright, we close our eyes, turn our heads at a sharp sound, pull our hand away from a hot object - this without conditioned reflexes. They were developed in the process of evolution, as a result of adaptation to certain, relatively constant environmental conditions. Unconditioned reflexes are inherited, which is why they are also called innate. A conditioned reflexes- These are reflexes acquired as a result of life experience. For example, if you have been getting up at the same hour with an alarm clock for a long time, then after a while you will wake up at the right moment without a ringing.
Reflex arc of the flexion reflex
Sciatic nerve section
The path along which a nerve impulse passes from the place of its origin to the working organ is called reflex arc. The reflex arc can be simple or complex. It usually includes sensory neurons with their sensitive endings - receptors, interneurons And executive (effector) neurons (motor or secretory). The shortest reflex arc can consist of two neurons: sensitive and executive. Complex arcs consist of many neurons.
All our actions occur with the participation and control of the central nervous system - the brain and spinal cord. For example, a child, seeing a familiar toy, reaches out to it: a command came from the brain along the executive nerve pathways - what to do. These are direct connections. When the child grabbed the toy, signals about the results of the activity immediately went through the sensitive neurons. This feedbacks. Thanks to them, the brain can control the accuracy of command execution and make the necessary adjustments to the work of the executive organs.
The nervous and humoral ways of regulating the functions of our body are closely interconnected: the nervous system controls the work of the endocrine glands, and they, in turn, use hormones to influence the nerve centers. Thus, the system of endocrine glands, together with the nervous system, carries out neurohumoral regulation of organ activity.
Brain function requires a lot of energy. The main source of energy for the brain is glucose, which people absorb from food. But glucose still needs to be transported through the bloodstream from the gastrointestinal tract to the brain. This is why so much blood flows through the vessels of the brain: 1.0–1.3 liters per minute.
Brain neurons are very sensitive to interruption of oxygen and glucose supply. If you deprive the brain of blood flow, and therefore the delivery of substances to it, for just 1 minute, then loss of consciousness occurs. But with training you can achieve a lot. For example, girls involved in synchronized swimming can remain underwater for several minutes.
Test your knowledge
1. What function does the nervous system perform in the body? What other organ system performs a similar function?
2. Compare the speed of the nerve impulse with the speed of blood flow in the aorta (0.5 m/s). Draw a conclusion about the difference between nervous and humoral regulation.
3. How does the nervous system work? What is white matter, gray matter?
4. What is a synapse?
5. Using a drawing, tell about the structure of the human nervous system, indicating its central and peripheral parts.
6. Remember what type the human nervous system is. What other types of nervous system do you know? In what animals are they found? Arrange them in order of difficulty.
7. Give definitions of the concepts “receptor”, “nerves”, “nerve nodes”.
8. What does the somatic nervous system innervate? How does the function of the autonomic nervous system differ from the function of the somatic nervous system?
9. Compare the action of the sympathetic and parasympathetic nervous systems.
10. What is a reflex? What types of reflexes do you know? Draw a general diagram of a reflex arc, indicating its required parts.
Work with computer
1. http://www.medicinform.net/human/anatomy/anatomy1.htm
2. http://school-collection.edu.ru/catalog (Human Anatomy and Physiology / Nervous System)
The nervous system consists of central and peripheral parts. The central nervous system is formed by the brain and spinal cord, the peripheral - by nerves, ganglia and nerve endings. The structure of the nervous system is based on a nerve cell (neuron), and its activity is based on a reflex. The path along which excitation passes from the point of origin of the nerve impulse to the working organ is called a reflex arc.
Structure and functions of the spinal cord
Spinal cord By appearance It is a long, almost cylindrical cord up to 45 cm long and weighing 34–38 g. The spinal cord is located in the spinal canal and is covered by membranes. The spinal cord begins at the level of the foramen magnum of the skull and ends at the level of the second lumbar vertebra. Below are the spinal cord membranes that surround the roots of the lower spinal nerves.
If you look at a cross section of the spinal cord, you can see that its central part is occupied by a butterfly-shaped gray matter consisting of nerve cells. In the center of the gray matter there is a narrow central channel, filled cerebrospinal fluid. Outside the gray matter is the white matter. It contains nerve fibers that connect spinal cord neurons to each other and to neurons in the brain.
They arise from the spinal cord in symmetrical pairs spinal nerves, there are 31 pairs of them. Each nerve begins from the spinal cord in the form of two cords, or roots, which, when connected, form a nerve. Spinal nerves and their branches travel to muscles, bones, joints, skin and internal organs.
The spinal cord performs two functions in our body: reflex And conductive.
The spinal cord contains the centers of many unconditioned reflexes, for example, reflexes that provide movement of the diaphragm, respiratory muscles. The spinal cord (under the control of the brain) regulates the functioning of internal organs: heart, kidneys, digestive organs. The spinal cord closes reflex arcs that regulate the functions of the flexor and extensor skeletal muscles of the trunk and limbs.
Diagram showing the relationship between the spinal cord and brain
Cross section of the spinal cord
The spinal cord transmits nerve impulses from organs to the brain and from it to the organs. All centripetal nerve fibers of the spinal nerves, carrying nerve impulses from organs and tissues, approach the spinal cord. Centrifugal fibers emerge from the spinal cord, along which impulses travel to organs and tissues. Damage to the spinal cord disrupts its functions: areas of the body located below the site of injury lose sensitivity and the ability to move voluntarily.
The brain has a great influence on the activity of the spinal cord. All complex movements are under the control of the brain: walking, running, work.
Test your knowledge
1. Where in the human body is the spinal cord located and what is its structure?
2. How many spinal nerves arise from the spinal cord?
3. Match the diagram of the structure of the spinal cord (on a cross section) and the diagram of the reflex arc. What are the nerve ganglia on the dorsal roots of the spinal cord formed by? the dorsal roots themselves; anterior roots; the spinal nerves themselves?
4. Give examples of reflexes that occur through the spinal cord without the participation of the brain. Is the spinal cord involved in reflexes controlled by the brain? How?
5. Why is spinal cord injury so dangerous?
6. Will the knee reflex and skin sensitivity be preserved if a person has a disruption in the conduction of excitation from the spinal cord to the brain?
Execute laboratory work“Structure of the spinal cord” on p. 36 (Workbook).
Work with computer
Refer to the electronic application. Study the lesson material and complete the assigned tasks.
1. http://www.medicinform.net/human/anatomy/anatomy1_1.htm
The spinal cord is a long cylindrical cord located in the spinal canal. The roots of 31 pairs of spinal nerves depart from the spinal cord. The spinal cord contains the centers of some simple reflexes. It performs reflex and conductive functions. The work of the spinal cord is carried out under the control of the brain.
Structure and functions of the brain
Man has long sought to penetrate the mystery of the brain, to understand its role and significance in human life. Already in ancient times, the “father of medicine” Hippocrates connected consciousness and the brain, but many hundreds of years passed before scientists began to unravel its mysteries.
The human brain is a complex organ capable of perceiving and processing a huge amount of information. Let's get acquainted with its structure and main functions.
Convolutions of the cerebral cortex
Brain is located in the cranial cavity and has a complex shape. The weight of the brain in an adult varies from 1100 to 2000 g, averaging 1300–1400 g. This is only about 2% of body weight, but brain cells consume up to 25% of the energy produced in the body! Typically, the brain mass of women is slightly smaller than that of men; this difference is due to the different mass of the male and female body.
The human brain, like all vertebrates, consists of a brainstem, cerebellum and forebrain, including the diencephalon and telencephalon.
Brain
In the central part of the medulla oblongata, the reticular formation of the brain stem begins - an accumulation of a huge number of seemingly chaotically located neurons. Neurons of the reticular formation have connections with the structures of the forebrain, sending impulses to the overlying sections; these neurons maintain the forebrain in a wakeful state. Damage to the reticular formation of the medulla oblongata leads to drowsiness, loss of consciousness, lethargic sleep, memory loss.
Trunk includes several departments, they differ from each other in structure and functions. These are the medulla oblongata, pons and midbrain 1
To date, there is no consensus among scientists on the definition of the brain stem. Sometimes the diencephalon is also included.
Medulla is a continuation of the spinal cord, so their structure has a lot in common. Only the gray matter of the medulla oblongata is located in separate clusters - nuclei. The functions are also similar - reflex and conductive. Through the nuclei of the medulla oblongata, many reflex processes are carried out, for example, coughing, sneezing, lacrimation, etc. The nerve centers responsible for the acts of swallowing and the functioning of the digestive glands are also located here. The medulla oblongata also contains vital centers involved in the regulation of respiration, the activity of the heart and blood vessels. Damage to these centers leads to human death.
Bridge- this is the place where nerve fibers are located, along which nerve impulses go up to the cerebral cortex or back, down to the spinal cord, to the cerebellum, to the medulla oblongata. There are also centers associated with facial expressions and chewing functions.
midbrain, like the medulla oblongata, it is part of the brain stem. On its surface facing the cerebellum there are four small tubercles - quadrigeminal. Upper tuberosities quadrigeminals – primary processing centers visual information, their neurons respond to objects moving quickly in the field of view. The main functions of the superior colliculus neurons are to control the direction of gaze and to bring the visual system into a state of increased alertness to strong visual stimuli. Lower tuberosities The quadrigeminal region is the primary processing center for auditory stimuli. Neurons in these centers respond to strong, sharp sounds, putting the auditory system on high alert. If something flashes in a person’s field of vision or some noise is heard next to him, then the person involuntarily shudders and his muscles tense, and this happens even before he understands what is happening. If it turns out that something falls on a person, then his motor systems are already ready to flee or defend.
The midbrain contains the most important clusters of neurons that perform motor functions - the red nucleus and the substantia nigra. Neurons of the red nucleus, together with neurons of the cerebellum, are involved in maintaining muscle tone and coordinating body posture. Neurons of the substantia nigra secrete the most important regulatory substance - dopamine. Dopamine is necessary so that a person can make fast and precise movements, walk, and run. In addition, when there is a lack of dopamine, people experience negative emotions, their mood worsens, and they become depressed.
Diencephalon- This is part of the forebrain. It consists of the thalamus and hypothalamus (subthalamic region). Down from the hypothalamus, on a thin stalk, there is an endocrine gland - the pituitary gland. Thalamus is the center for the analysis of all types of sensations, except olfactory. The thalamus has more than 40 pairs of nuclei (clusters of neurons) with diverse functions.
In some nuclei, the analysis of visual, auditory and other information continues. Other nuclei are involved in the coordination of the brain's motor systems. The first assessment of the significance of information occurs in the thalamus. As a result, new and important signals, as well as information related to current activity, arrive from the thalamus to the corresponding areas of the cerebral cortex.
Lower part of the diencephalon - hypothalamus– also performs the most important functions, being the highest center of autonomic regulation. The anterior nuclei of the hypothalamus are the center of parasympathetic influences, the posterior nuclei are the center of sympathetic influences. The hypothalamus also contains centers of hunger and thirst, the irritation of which leads to uncontrollable absorption of food or drinking water.
Thus, we can say that the hypothalamus is necessary for regulating the functioning of all internal organs. Lesions of the hypothalamus are accompanied by severe disorders: a decrease or increase in pressure, a decrease or increase in heart rate, breathing difficulties, intestinal motility disorders, thermoregulation disorders, changes in blood composition, etc.
In the thickness of the white matter of the cerebral hemispheres there is a complex of subcortical nuclei, called limbic system. The limbic system contains the main centers responsible for a person’s emotional state: centers of fear, rage, and pleasure. These centers provide an emotional assessment of the situation, an assessment of the possible consequences of this situation and the choice of one of the optimal forms of behavior. As a result of the correct choice of behavior, the body must come into accordance with its needs, for example, to avoid danger or provide itself with food, etc.
Cerebellum located on the back side of the brain stem: behind the medulla oblongata and middle sections. The weight of the cerebellum of an adult is 150 g. The structure of the cerebellum is similar to the structure of the entire brain. That's why its name translates as "little brain." The cerebellum is connected to the midbrain by three pairs of peduncles. It consists of a worm (the stem, the most ancient part) and hemispheres divided by grooves into shares. The lobes, in turn, are divided into small grooves convolutions. The superficial layer of the hemispheres is gray matter, the so-called cerebellar cortex. The cerebellum receives information from all motor systems: from the cerebral hemispheres, from the midsection and spinal cord.
Cerebellum slice
The main functions of the cerebellum: regulation of body posture and maintenance of muscle tone; coordination of slow voluntary movements; ensuring the accuracy of fast voluntary movements. The ancient stem part of the cerebellum is responsible for balance and coordination of movements of the trunk muscles, and its hemispheres are responsible for fast, precise movements. When the cerebellar vermis is destroyed, a person cannot walk or stand, and his sense of balance is impaired. With lesions of the cerebellar hemispheres, a decrease in muscle tone, severe trembling of the limbs, impaired accuracy and speed of voluntary movements are observed, fast fatiguability. In addition, oral and written speech is disrupted.
The central canal of the spinal cord continues into the brain, forming four ventricles, the IV ventricle is located between the medulla oblongata and the cerebellum, the III - between the symmetrical halves of the diencephalon, I and II (lateral) - in the hemispheres of the telencephalon.
The nuclei of the thalamus are the highest center of pain sensitivity; it is here that the pain sensation is formed. When a person, for example, pinches a finger and feels pain in it, then in fact the pain arose in the representation of the finger in the nuclei of the thalamus, i.e., where the signals from the pain receptors of the pinched finger came. These nuclei may be associated with the so-called Phantom pain when pain is felt, for example, in a limb that has been amputated for a long time. Pain in this case is a consequence of pathological excitation of those neurons that were once associated with a long-absent limb.
If you want to know if everything is okay with your cerebellum, stand with your legs together, stretch your arms forward and close your eyes. A person with a damaged cerebellum cannot stand in this position; he will begin to sway or even fall. Then try quickly touching the tip of your nose with the index fingers of your left and right hands alternately. If you hit it correctly, then the hemispheres of your cerebellum function normally.
With serious lesions of the cerebellum, both animals and humans move with great difficulty, raising their paws or legs high, stumbling, and swaying. They cannot estimate the distance to any object and get tired very quickly.
Test your knowledge
1. Where is the brain located? How is he protected?
2. What parts does the human brain consist of? What parts make up the brain stem? Reflect this in the form of a general diagram.
3. What are the similarities and differences in the functions of the medulla oblongata and the spinal cord?
4. Explain why injuries at the junction of the skull and the spine often lead to death. In what situations can this happen?
5. Damage to which part of the brain is associated with impaired facial expression in humans?
6. How does the cerebellum work? What can damage it lead to?
7. Which part of the brain is responsible for responding to visual and auditory stimuli?
8. In what part of the human brain is the sensation of pain formed?
9. Where is it located? supreme center autonomic nervous system?
10. Which parts of the brain are more developed in humans compared to other vertebrates?
11. Make a summary table “Functions of parts of the brain.”
Laboratory and practical work
Complete work No. 2 “Study of the structure of the human brain (using dummies)” on p. 17 (Notebook for laboratory and practical work).
Work with computer
Refer to the electronic application. Study the lesson material and complete the assigned tasks.
1. http://www.medicinform.net/human/anatomy/anatomy1_2.htm (Brain)
2. http://school-collection.edu.ru/catalog (Anatomical and physiological atlas of man / Divisions of the nervous system)
The brain consists of the brainstem, cerebellum and cerebral hemispheres. The trunk consists of the medulla oblongata, pons, midbrain and diencephalon. The brain stem contains the centers of unconditioned reflexes; its main functions are the regulation of unconditioned reflex activity and the connection of the body with the cerebral cortex.
1. Where in the human body is the spinal cord located and what is its structure?
The human spinal cord is located in the spinal canal from the foramen magnum to the 2nd lumbar vertebra. It is covered with three membranes: it directly covers the spinal cord and fuses with its soft surface, or choroid, then in the form of a thin network is located arachnoid, hard shell comprises connective tissue and lines the spinal canal. The spaces between the membranes are filled with cerebrospinal fluid (CSF), which cushions the brain. The spinal cord consists of 31 segments, the structure of each of them is approximately the same. In the center there is a narrow central channel through which cerebrospinal fluid circulates. Gray matter lies around it in the form of a butterfly, formed by bodies nerve cells. The gray matter contains anterior, posterior and intercalary horns. Outside the gray matter lies white matter containing long processes of neurons, they connect the different levels of the spinal cord to each other, the spinal cord and the brain, they form 6 columns. Spinal nerves extend symmetrically from each segment on both sides in the form of two cords (roots). The anterior root is efferent (motor), the posterior root is afferent (sensitive), together they are connected in the intervertebral foramina.
2. How many spinal nerves arise from the spinal cord?
31 pairs of spinal nerves arise from the spinal cord.
3. Match the diagram of the structure of the spinal cord (on a cross section) and the diagram of the reflex arc. What are the nerve ganglia on the dorsal roots of the spinal cord formed by? the dorsal roots themselves; anterior roots; the spinal nerves themselves?
Based on this scheme, the nerve ganglia on the dorsal roots of the spinal cord are formed by the nuclei of sensory neurons that carry information from the receptor to rear horns the spinal cord, where there is a switch either to motor neurons directly or through interneurons, or to the ascending pathways of the spinal cord, which transmit information to the brain. The dorsal roots are formed by the axons of sensory nerves. The anterior roots consist of the axons of motor neurons. Spinal nerves are formed after the fusion of the anterior and posterior roots beyond the spinal ganglia after the roots emerge from the foramina between the vertebrae of the spinal column.
4. Give examples of reflexes that occur through the spinal cord without the participation of the brain. Is the spinal cord involved in reflexes controlled by the brain? How?
Basically, tendon reflexes close without the participation of the brain, such as the Achilles tendon reflex, the knee reflex, the flexion and extension elbow reflex, the cremasteric reflex (lifting the testicle when passed along the inner surface of the thigh) and others. The human spinal cord controls only the simplest motor acts; complex movements (walking, writing, speaking, labor) are carried out only with the participation of the brain. All centripetal nerve fibers of the spinal nerves approach the spinal cord, carrying nerve impulses from organs and tissues, which then upward paths go to the brain where they are processed. From the brain, information goes to the spinal cord, where along descending fibers it reaches the segments innervating the working organs or tissues, and switches to the motor nuclei of neurons. Centrifugal fibers emerge from the spinal cord, along which impulses travel to organs and tissues.
5. Why is spinal cord injury so dangerous?
In case of spinal cord injuries, depending on the level and degree (for example: complete separation of the spinal cord, damage to half, a separate column) of damage, the function of the damaged section and the corresponding sections below the site of injury is lost. That is, areas below the sites of innervation of the damaged sections lose sensitivity, motor activity… The higher the site of injury, the more function may be lost. Spinal cord injuries are most common reason disability of young people.
6. Will the knee reflex and skin sensitivity be preserved if a person has a disruption in the conduction of excitation from the spinal cord to the brain?
The knee reflex will remain, since it closes only at the level of the spinal cord, the sensitivity of the skin will disappear, since the processing of information from the skin occurs in the brain, where the information passes through the spinal cord pathways.
