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Multimedia support for lectures on “Fundamentals of Neurophysiology and GND” General physiology CNS and excitable tissues

Basic manifestations of vital activity Physiological rest Physiological activity Irritation Excitation Inhibition

Types of biological reactions Irritation is a change in structure or function under the influence of an external stimulus. Excitation is a change in the electrical state of the cell membrane, leading to a change in the function of a living cell.

Structure of biomembranes The membrane consists of a double layer of phospholipid molecules, covered on the inside with a layer of protein molecules, and on the outside with a layer of protein molecules and mucopolysaccharides. IN cell membrane There are very thin channels (pores) with a diameter of several angstroms. Through these channels, molecules of water and other substances, as well as ions with a diameter corresponding to the size of the pores, enter and leave the cell. Various charged groups are fixed on the structural elements of the membrane, which gives the channel walls a particular charge. The membrane is much less permeable to anions than to cations.

Resting potential Between outer surface a cell and its protoplasm at rest, there is a potential difference of the order of 60-90 mV. The surface of the cell is charged electropositively with respect to protoplasm. This potential difference is called the membrane potential, or resting potential. Its accurate measurement is possible only with the help of intracellular microelectrodes. According to the Hodgkin-Huxley membrane-ion theory, bioelectric potentials are caused by the unequal concentration of K+, Na+, Cl- ions inside and outside the cell, and the different permeability of the surface membrane to them.

Mechanism of MP formation At rest, the membrane of nerve fibers is approximately 25 times more permeable to K ions than to Na + ions, and when excited, sodium permeability is approximately 20 times higher than potassium. Great importance For the membrane potential to occur, there is a gradient of ion concentration on both sides of the membrane. It has been shown that the cytoplasm of nerve and muscle cells contains 30-59 times more K + ions, but 8-10 times less Na + ions and 50 times less Cl - ions than the extracellular fluid. The value of the resting potential of nerve cells is determined by the ratio of positively charged K + ions, diffusing per unit time from the cell outward along the concentration gradient, and positively charged Na + ions, diffusing along the concentration gradient in the opposite direction.

Distribution of ions on both sides of the cell membrane Na + K +A – Na +K + rest excitation

Na. Na ++ -K-K ++ - - membrane pump 2 Na +3K + ATP -ase

Action potential If a section of a nerve or muscle fiber is exposed to a sufficiently strong stimulus (for example, a push electric current), excitation occurs in this area, one of the most important manifestations of which is a rapid oscillation of the MP, called the action potential (AP)

Action potential In AP, it is customary to distinguish between its peak (the so-called spike) and trace potentials. The PD peak has an ascending and descending phase. Before the ascending phase, a more or less pronounced so-called local potential, or local response. Since the initial polarization of the membrane disappears during the ascending phase, it is called the depolarization phase; accordingly, the descending phase, during which membrane polarization returns to its original level, is called the repolarization phase. The duration of the AP peak in nerve and skeletal muscle fibers varies within 0.4-5.0 ms. In this case, the repolarization phase is always longer.

The main condition for the occurrence of AP and spreading excitation is that the membrane potential must become equal to or less than the critical level of depolarization (Eo<= Eк)

CONDITION OF SODIUM OUTPUT CHANNELS A L A D E P O L A R I S A T I O N S R E P O L A R I S A T I O N

Excitability parameters 1. Excitability threshold 2. Useful time 3. Critical slope 4. Lability

Threshold of stimulation The minimum value of stimulus strength (electric current) required to reduce the membrane charge from the resting level (Eo) to the critical level (Eo) is called the threshold stimulus. Threshold of irritation E p = Eo - Ek Subthreshold stimulus is less powerful than threshold Above-threshold stimulus is stronger than threshold

The threshold strength of any stimulus, within certain limits, is inversely related to its duration. The curve obtained in such experiments is called the “force-duration curve.” From this curve it follows that a current below a certain minimum value or voltage does not cause excitation, no matter how long it lasts. The minimum current strength that can cause excitation is called rheobase. The shortest time during which an irritating stimulus must act is called useful time. Increasing the current leads to a shortening of the minimum stimulation time, but not indefinitely. With very short stimuli, the force-time curve becomes parallel to the coordinate axis. This means that with such short-term irritations, excitation does not occur, no matter how great the strength of irritation.

LAW "STRENGTH IS DURATION"

Determining useful time is practically difficult, since the point of useful time is located on a section of the curve that turns into parallel. Therefore, it is proposed to use the useful time of two rheobases - chronaxy. Chronaximetry has become widespread both experimentally and clinically for diagnosing damage to motor nerve fibers.

LAW "STRENGTH IS DURATION"

The threshold value for irritation of a nerve or muscle depends not only on the duration of the stimulus, but also on the steepness of the increase in its strength. The irritation threshold has the smallest value for rectangular current impulses, characterized by the fastest possible increase in current. When the slope of the current increase decreases below a certain minimum value (the so-called critical slope), the PD does not occur at all, no matter to what final strength the current increases. The phenomenon of adaptation of excitable tissue to a slowly increasing stimulus is called accommodation.

The “all or nothing” law According to this law, under threshold stimuli they do not cause excitation (“nothing”), but with threshold stimuli, excitation immediately acquires a maximum value (“all”), and no longer increases with further intensification of the stimulus.

lability The maximum number of impulses that excitable tissue is capable of reproducing in accordance with the frequency of stimulation nerve - over 100 Hz muscle - about 50 Hz

Laws of excitation conduction Law of physiological continuity; Law of bilateral conduction; Law of isolated conduction.

The location where the axon originates from the nerve cell body (axon hillock) is of greatest importance in the excitation of the neuron. This is the trigger zone of the neuron; it is here that excitation occurs most easily. In this area for 50-100 microns. the axon does not have a myelin sheath, therefore the axon hillock and the initial segment of the axon have the lowest irritation threshold (dendrite - 100 mV, soma - 30 mV, axon hillock - 10 mV). Dendrites also play a role in the excitation of a neuron. They have 15 times more synapses than the soma, so PDs passing along the dendrites to the soma can easily depolarize the soma and cause a volley of impulses along the axon.

Features of neuronal metabolism High consumption of O 2. Complete hypoxia for 5-6 minutes leads to the death of cortical cells. Ability for alternative routes of exchange. The ability to create large reserves of substances. A nerve cell lives only with glia. Ability to regenerate processes (0.5-4 microns/day).

Classification of neurons Afferent, sensitive Associative, intercalary Efferent, effector, motor receptor muscle

Afferent stimulation is carried out along fibers that differ in the degree of myelination and, therefore, in the speed of impulse conduction. Type A fibers are well myelinated and conduct excitations at speeds of up to 130-150 m/s. They provide tactile, kinesthetic, as well as rapid pain sensations. Type B fibers have a thin myelin sheath and a smaller overall diameter, which also leads to a lower impulse conduction speed - 3-14 m/s. They are components of the autonomic nervous system and do not participate in the work of the skin-kinesthetic analyzer, but can conduct some of the temperature and secondary pain stimuli. Type C fibers - without a myelin sheath, impulse conduction speed up to 2-3 m/s. They provide slow pain, temperature and pressure sensations. Usually this is vaguely differentiated information about the properties of the stimulus.

Synapse(s) is a specialized zone of contact between neurons or neurons and other excitable cells, ensuring the transfer of excitation with the preservation, change or disappearance of its information value.

Excitatory synapse – a synapse that excites the postsynaptic membrane; an excitatory postsynaptic potential (EPSP) arises in it and the excitation spreads further. An inhibitory synapse is a synapse on the postsynaptic membrane of which an inhibitory postsynaptic potential (IPSP) arises, and the excitation that comes to the synapse does not spread further.

Classification of synapses Based on location, neuromuscular and neuroneuronal synapses are distinguished, the latter in turn divided into axo-somatic, axo-axonal, axo-dendritic, dendro-somatic. According to the nature of the effect on the perceptive structure, synapses can be excitatory or inhibitory. According to the method of signal transmission, synapses are divided into electrical, chemical, and mixed.

Reflex arc Any reaction of the body in response to irritation of receptors when the external or internal environment changes and carried out through the central nervous system is called a reflex. Thanks to reflex activity, the body is able to quickly respond to environmental changes and adapt to these changes. Each reflex is carried out thanks to the activity of certain structural formations of the NS. The set of formations involved in the implementation of each reflex is called a reflex arc.

Principles of classification of reflexes 1. By origin - unconditional and conditional. Unconditioned reflexes are inherited, they are enshrined in the genetic code, and conditioned reflexes are created in the process of individual life on the basis of unconditioned ones. 2. According to biological significance → nutritional, sexual, defensive, orientation, locomotor, etc. 3. According to the location of the receptors → interoceptive, exteroceptive and proprioceptive. 4. By type of receptors → visual, auditory, gustatory, olfactory, pain, tactile. 5. According to the location of the center → spinal, bulbar, mesencephalic, diencephalic, cortical. 6. According to the duration of the response → phasic and tonic. 7. By the nature of the response → motor, secretory, vasomotor. 8. By belonging to the organ system → respiratory, cardiac, digestive, etc. 9. By the nature of the external manifestation of the reaction → flexion, blinking, vomiting, sucking, etc.

TOPIC: CENTRAL NERVOUS SYSTEM (CNS) PLAN: 1. The role of the CNS in the integrative, adaptive activity of the body. 2. Neuron - as a structural and functional unit of the central nervous system. 3. Synapses, structure, functions. 4. Reflex principle of regulation of functions. 5. History of the development of reflex theory. 6.Methods for studying the central nervous system.

The central nervous system carries out: 1. Individual adaptation of the body to the external environment. 2. Integrative and coordinating functions. 3. Forms goal-oriented behavior. 4. Performs analysis and synthesis of received stimuli. 5. Forms a flow of efferent impulses. 6. Maintains the tone of body systems. The modern concept of the central nervous system is based on the neural theory.

The central nervous system is a collection of nerve cells or neurons. Neuron. Sizes from 3 to 130 microns. All neurons, regardless of size, consist of: 1. Body (soma). 2. Axon dendritic processes Structural and functional elements of the central nervous system. The cluster of neuron bodies makes up the gray matter of the central nervous system, and the cluster of processes makes up the white matter.

Each cell element performs a specific function: The neuron body contains various intracellular organelles and ensures the life of the cell. The body membrane is covered with synapses, therefore it perceives and integrates impulses coming from other neurons. Axon (long process) - conducts a nerve impulse from the body of a nerve cell and to the periphery or to other neurons. Dendrites (short, branching) - perceive irritations and communicate between nerve cells.

1. Depending on the number of processes, they are distinguished: - unipolar - one process (in the nuclei of the trigeminal nerve) - bipolar - one axon and one dendrite - multipolar - several dendrites and one axon 2. In functional terms: - afferent or receptor - (perceive signals from receptors and carried to the central nervous system) - intercalary - provide communication between afferent and efferent neurons. - efferent - conduct impulses from the central nervous system to the periphery. They are of 2 types: motor neurons and efferent neurons of the ANS - excitatory - inhibitory CLASSIFICATION OF NEURONS

The relationship between neurons is carried out through synapses. 1. Presynaptic membrane 2. Synaptic cleft 3. Postsynaptic membrane with receptors. Receptors: cholinergic receptors (M and N cholinergic receptors), adrenergic receptors - α and β Axonal hillock (axon extension)

CLASSIFICATION OF SYNAPSES: 1. By location: - axoaxonal - axodendritic - neuromuscular - dendrodendritic - axosomatic 2. By the nature of the action: excitatory and inhibitory. 3. By signal transmission method: - electrical - chemical - mixed

The transmission of excitation in chemical synapses occurs due to mediators, which are of 2 types - excitatory and inhibitory. Exciting agents - acetylcholine, adrenaline, serotonin, dopamine. Inhibitory – gamma-aminobutyric acid (GABA), glycine, histamine, β-alanine, etc. Mechanism of excitation transmission in chemical synapses

The mechanism of excitation transmission in the excitatory synapse (chemical synapse): impulse, nerve ending into synaptic plaques, depolarization of the presynaptic membrane (input of Ca++ and output of transmitters), neurotransmitters, synaptic cleft, postsynaptic membrane (interaction with receptors), generation of EPSP AP.

1. In chemical synapses, excitation is transmitted using mediators. 2. Chemical synapses have one-way conduction of excitation. 3.Fatigue (depletion of neurotransmitter reserves). 4.Low lability imp/sec. 5. Summation of excitation 6. Blazing a path 7. Synaptic delay (0.2-0.5 m/s). 8. Selective sensitivity to pharmacological and biological substances. 9.Chemical synapses are sensitive to temperature changes. 10. There is trace depolarization at chemical synapses. PHYSIOLOGICAL PROPERTIES OF CHEMICAL SYNAPSES

REFLECTOR PRINCIPLE OF REGULATION OF FUNCTION The activity of the body is a natural reflex reaction to a stimulus. In the development of reflex theory, the following periods are distinguished: 1. Descartes (16th century) 2. Sechenovsky 3. Pavlovsky 4. Modern, neurocybernetic.

METHODS OF RESEARCH OF THE CNS 1. Extirpation (removal: partial, complete) 2. Irritation (electrical, chemical) 3. Radioisotope 4. Modeling (physical, mathematical, conceptual) 5. EEG (registration of electrical potentials) 6. Stereotactic technique. 7. Development of conditioned reflexes 8. Computed tomography 9. Pathological method

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Physiology of the central nervous system. Lecture No. 8 Physiology of the Central Nervous System

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Central and peripheral nervous system 12 pairs of cranial nerves 31 pairs of spinal nerves Nerve plexus ganglia Brain and spinal cord

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Spinal cord Soft Arachnoid Dural Shell Spinal ganglion 31 segments: Cervical 8 Thoracic 12 Lumbar 5 Sacral 5 Coccygeal 1 Length 43 cm, weight 35 g 107 neurons Functions: Conductive Reflex (postural, scratching reflexes, etc.) Initial information processing Sympathetic ganglia

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Gray matter: Forms columns in volume Anterior horns - motor neuron bodies Posterior horns - intercalary neurons (axons to the anterior horns, opposite side, other segments) Lateral horns (gir, cingulum) - sympathetic preganglionics Sacral region - parasympathetic preganglionics Cervical and lumbosacral enlargements Central channel

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White matter Nerve fibers of the spinal cord spread in three directions: Ascending / to higher centers in the brain (sensory inputs) Descending / to the spinal cord from higher centers of the brain (motor output) Commissural - from one part of the spinal cord to another Ascending: Descending:

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White matter tracts 1. anterior cord: descending tracts: anterior pyramidal (from the cortex, voluntary movements) tegmental (indicative reaction, turning the head to a stimulus) vestibulospinal (balance) reticulospinal (involuntary movements, the oldest) 2: lateral cord : ascending pathways: posterior and anterior spinocerebellar tracts spinothalamic tract (pain, T) - descending pathways: red nuclear (complex motor programs), lateral pyramidal (from the cortex, voluntary movements) 3: posterior cord: ascending pathways: (from skin, muscles, ligaments, into the medulla oblongata) Thin - from the lower half of the body, Wedge-shaped - from the upper half of the body

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Embryogenesis 40 days 60 days 6 months Anlage from the ectoderm The neural tube is divided on the 30th day into 3 brain vesicles 60 days - into 5 brain vesicles From them 5 parts of the brain are formed: Medulla Oblongata Posterior Middle Intermediate Terminus Brain 1100-2000 g (average 1350)

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Brainstem The border of the medulla oblongata and the spinal cord passes through the intersection of the pyramids and at the site of exit of the roots of the first cervical segments of the spinal cord. Includes sections: Middle Posterior Medulla Oblongata Contains: Nuclei Pathways Reticular formation

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Medulla oblongata Rear view The border of the medulla oblongata and the pons passes along the medullary stripes at the bottom of the rhomboid fossa Contains: Axons (continuation of the spinal tracts) a) descending (anterior sections) b) ascending (posterior sections) 2. Nuclei: a) from 8 to 12 pairs cranially -cerebral nerves (vestibular-cochlear, glossopharyngeal, vagus, accessory, hypoglossal) b) olive (vestibular entrance to the cerebellum) c) reticular formation (8% of brain neurons): Switches of ascending and descending pathways activating system of the brain, movement, sleep cycle/ wakefulness, regulation of autonomic functions Functions: Conductive (white matter) Reflex (gray matter) 25 mm decussation of the pyramids of the Olive pyramid Superior cerebellar peduncles Front view

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Hindbrain The border of the medulla oblongata and the pons runs along the medullary striae (auditory tract) (striae medullares) The border of the pons and midbrain (cerebral peduncles) is determined by the exit site of the IV pair of nerves - the trochlear nerve Includes the Cerebellum, the Pons (Varoliev): Front view Middle peduncles cerebellum Posterior part - tegmentum: a) reticular formation b) nuclei of 5-7 nerves (trigeminal, abducens, facial) c) ascending pathways Anterior part - basis: a) descending pathways b) pontine nuclei On the posterior side - 4th ventricle Top - velum, bottom - rhomboid fossa, protruding nuclei of cranial nerves (sensory and motor) Functions: impulses from facial receptors, reflexes (coughing, swallowing, blinking, posture, etc.), breathing, pressure regulation, salivation.

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Cranial nerves (12 pcs.) Red - motor nuclei Blue - sensory nuclei Yellow - autonomic nuclei I Olfactory: Olfactory epithelium of the nose (olfaction) II Visual: Retina (vision) III Oculomotor: Proprioceptors of the muscles of the eyeball (muscular sense) Muscles that move the eye apple (together with IV and VI pairs); muscles that change the shape of the lens; muscles that constrict the pupil IV Trochlear: Same, Other muscles that move the eyeball V Trigeminal: Teeth and facial skin Some of the masticatory muscles VI Abductor: Proprioceptors of the muscles of the eyeball (muscle sense) Other muscles that move the eyeball VII Facial: Anterior taste buds parts of the tongue Facial muscles; submandibular and sublingual glands VIII Auditory: Cochlea (hearing) and semicircular canals (sense of balance, translation and rotation) IX Glossopharyngeal: Taste buds of the posterior third of the tongue; pharyngeal mucosa Parotid gland; muscles of the pharynx used in swallowing X Vagus: Nerve endings in many internal organs (lungs, stomach, aorta, larynx) Parasympathetic fibers going to the heart, stomach, small intestine, larynx, esophagus XI Accessory: Shoulder muscles (muscle sense) Shoulder muscles XII Sublingual: Muscles of the tongue (muscular feeling) Muscles of the tongue

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frontal section through the medulla oblongata and cerebellum Cerebellum (small brain) Functions: correlating motor commands with body position, memorizing motor programs Consists of: hemispheres of the vermis a) Cortex - forms grooves: ancient, old - tone, posture, new - motor skills three layers : -molecular, -ganglionic (Purkinje cell (gamma - exit), -granular b) White matter c) Nuclei (dentate, cork-shaped, spherical, tent) Three pairs of legs: - upper (to the midbrain) - middle (to the pons ) - lower (to the medulla oblongata)

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Midbrain Consists of: Roof tegmentum Cerebral peduncles Legs: conductive tracts nucleus of the oculomotor nerve (3) Roof (plate of the quadrigeminal): superior colliculi (visual), layered inferior colliculi (auditory), nuclei - handles of the colliculi to the geniculate bodies Functions: - motor reaction to light and sound, accommodation (quadrigeminal) - motor learning, control of limbs (red nucleus); pathology: extensor hypertonicity - positive reinforcement, initiation of complex motor acts (substantia nigra); pathology schizophrenia, parkinsonism. tegmentum - nuclei of the 3rd and 4th cranial nerves (oculomotor and trochlear) - red nucleus (beginning of the motor tract) - substantia nigra (melanin) (Dopamine) - reticular formation Sylvian aqueduct

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Diencephalon thalamus hypothalamus pineal gland geniculate bodies mammillary bodies pituitary gland optic tract (2nd part of the nerve) Thalamus (bottom of the third ventricle) - the end of the structures of the trunk, switching of all sensory pathways Hypothalamus - neuroendocrine organ (about 40 nuclei - ToS, exchange of v- c, vegetatives, emotions, nutritional, sexual, parental, etc., releasing factors) Pineal gland neuroendocrine organ (circadian rhythms, melatonin) Geniculate bodies continuation of the visual and auditory pathways Mastoid bodies - (part of the circle of Papez) Pituitary gland - higher endocrine gland a) neurohypophysis (hypothalamic axons) vasopressin, oxytocin b) adenohypophysis (glandular tissue) tropic hormones (6 pcs) c) intermediate lobe (melanocyte-stimulating hormone) up to 150 nuclei, the highest association center of reptiles

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The telencephalon consists of: basal nuclei of the cortex of the cerebral hemispheres commissures (connections between them) Input - from the motor zones of the cortex, output - into the thalamus, substantia nigra, etc. Basal nuclei: gray matter in the depths of each hemisphere, (under the lateral ventricles) Consists of : striatum (globus pallidus, putamen, caudate nucleus), septum (lateral to the globus pallidus), tonsils (deep in the temporal lobe) Function: organization of motor programs

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Cerebral cortex Layer I, molecular Layer II, outer granular Layer III, outer pyramidal Layer IY, inner granular Layer Y, inner pyramidal Layer YI, or multiform Modular principle of organization, for example, columns - in sensory areas, own blood supply. Different zones of the cortex have different development of layers: Sensory zones: Input - from the thalamus, Motor zones - layer V is developed, output - to motor neurons, trunk, basal ganglia. gray matter outside, 2-3 mm thick, ~ 14 billion neurons

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The cortex of the cerebral hemispheres forms protrusions - gyri, between them there are depressions - grooves, dividing the cortex into 5 lobes: Frontal - central sulcus - Parietal - lateral sulcus - Temporal - Occipital - Insular Inside the lobes, primary zones are distinguished (cortical representations of analyzers - analyzer maps). secondary (associated with primary zones), recognize associative images (at the boundaries of the parietal, temporal and occipital, in the frontal lobes). Analysis and synthesis. The zones are divided into 52 fields (Brodmann)

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Functions of the cortex 1. Movement: bodies (projections in the pre- and postcentral gyrus - Penfield’s man), writing, speech (Broca’s area) 2. perception (vision, hearing, smell, touch, taste), understanding speech, reading (Wernicke’s area) 3. emotions + memory (circle of Papez, limbic system): - declarative (hippocampus, mammillary bodies) - procedural (amygdala, cerebellum) Lateralization - separation of functions between the right and left hemispheres (writing and speech centers on the left in right-handed Europeans). Left hemisphere – emphasis on logic, words. Right hemisphere – on images, space, emotions.

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Circle of Papez (limbic system) Associative cortex - consciousness Cingulate gyrus - the highest center of emotions (input to the system) Hippocampus - “generator” of emotions (including input from Broca’s area) + long-term memory Mamillary bodies - memorization, assessment of the significance of emotions Thalamus – sensory input Hypothalamus – autonomic support of emotions Amygdala – weighing competing emotions (aggression/caution)

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White matter of the cerebral hemispheres (commissures and projection fibers) Projection fibers in the white matter of the cerebral hemispheres closer to the cortex form the corona radiata. The corpus callosum connects the hemispheres, the fornix connects the hippocampus with the hypothalamus and mammillary bodies

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Methods for measuring brain activity EEG NMR Removal of the slow component of the EMF of a brain region Emission of electromagnetic waves. radiation of hydrogen atoms (resonance) in a magnetic field Power spectrum Activation of zones during “parental behavior”

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Ventricles and membranes of the brain Lateral ventricles (right and left) each with three horns (anterior, posterior, lower) Third Fourth Meninges (connective tissue): Hard (2 layers: external adherent to the skull, internal forms folds) 2. Vascular / Arachnoid / (vessels feeding the brain pass through it) 3. Soft (thin membrane, repeats the pattern of grooves and convolutions, with cerebrospinal fluid above it)