The thalamus, also known as the dorsal thalamus, isDiencephalonThe largest oval gray matter nucleus in theThird ventricleOn both sides of the left and right thalamus by gray matter mass (calledIntermediate block）Connect.
The thalamus is the senior center of sensation and the most important relay station of sensory conduction.From all kinds of sensesConduction pathway(except for sense of smell), all were replaced in thalamusneuron, then project tocerebral cortex。In the thalamus, only the sense is roughlyanalysis and synthesis , thalamus andhypothalamus、StriatumThere are fibers connected with each other, and the three become many complexUnconditioned reflexThe subcortical center of the brain.[1]
The thalamus is covered by a Y-shaped white matter plate (called innerMedullary plate）They are divided into three major nuclear groups: anterior, medial and lateral.Nuclei of thalamus and their fiber connections:
Medial thalamic nucleus: receiving fibers from other thalamic nuclei, sending fibers projecting tofrontal lobeAnterior cortex.
Lateral thalamic nucleus: it is divided into smaller dorsal part and larger ventral part.The dorsal part receives fibers from other thalamic nuclei and sends fibers toparietal lobecortex.Ventral part, spinal cord, brain stem andcerebellumIt has extensive connections.[2]
Supra thalamus: atThird ventricleAround the top.It includes left and right triangles, commissure and rearPineal gland。The medullary stria of the thalamus, which starts from the olfactory center, ends in the trigonal gray matter, and sends fibers from the gray matter to the visceral motor nucleus of the brain stem.Therefore, the upper part of the thalamus is related to the olfactory visceral reflex.
lower part
Hypothalamus: It has two characteristics: one isnerve cellNot many, but the links are complex and extensive;Second, in addition to ordinary neurons, it also contains endocrine neurons, which have the characteristics of ordinary neurons andEndocrine cellsynthesishormoneFunction of.The volume of the hypothalamus is very small, but it controls many important functional activities of the body.asWater metabolism、Thermoregulation、Carbohydrate metabolism、Fat metabolism。
Nuclear cluster classification
According to the neural connections, the thalamic nuclei can be roughly divided into three categories[2]
Schematic diagram of main nuclei in the right thalamus
1. The first type (sensory replacement nucleus) is receptiveProjection fibre, and further projected toCerebral cortexThose cell groups in the sensory area, such as the lateral and medial parts of the posterior ventral nucleus (called the posterolateral ventral nucleus and the medial ventral nucleus, respectively)Medial geniculate body, lateral geniculate body, etc.The posterolateral ventral nucleus isSpinothalamic tractAndMedial lemniscusIt is related to the transmission of trunk and limb sensation;The posteromedial ventral nucleus isTrigeminal lemniscusIt is related to the transmission of head and face sensation.The fibers from the posterior ventral nucleusCerebral cortexSensory area projection, fibers from different parts have certain exchange in the posterior ventral nucleusspace distribution The sensation of lower limbs is at the outermost side of the posterior ventral nucleus, the sensation of head and face is at the medial side of the posterior ventral nucleus, and the sensation of upper limbs is at the middle part (Figure 10-22);This spatial distribution is related to theSpatial positioningCorrespondence.Medial geniculate bodyIt is the transformation station of auditory pathway, which sends out fibers to project to the auditory area of cerebral cortex.The lateral geniculate body isVisual conduction pathwayAnd send fibers to the cerebral cortexVisual areaproject.Therefore, the above cell group is the replacement site of all specific sensory impulses (except for smell) to the cerebral cortex, called the sensory replacement nucleus.
Figure 10-22 Projection of monkey's body surface to the left posterior ventral thalamic nucleus (posterolateral ventral nucleus and posteromedial ventral nucleus)
2. The second type (connecting nucleus) receives fibers from the first type of nucleus and other subcortical centers (but does not directly receive sensory projection fibers), and sends fibers to projectCerebral cortexA specific area of.For example, the anterior thalamic nucleus receiveshypothalamusThe papillary body originates from fibers and sends fibers to project to the cingulate cortex of the cerebral cortex to participate in the regulation of visceral activities;The lateral ventral nucleus of the thalamus mainly receives cerebellumGlobus pallidusAnd the posterior ventral nucleus, and send out fibers projecting to the cerebral cortexSports area, involved in cortical pairMuscle movementAdjustment of;The thalamus occipital receives fibers from the medial and lateral geniculate bodies and sends fibers to project to the cerebral cortexparietal lobe、Occipital lobeandTemporal lobeMiddle ofContact area, participate in the connection function of various senses.In addition, there are many cell groups in the thalamus, which send out fibers to the front of the hypothalamus and cerebral cortexfrontal lobeandOrbital regionOr the contact area of the headquarters behind the parietal lobe.These cell groups project toCerebral cortexThe connection area of the thalamus and cerebral cortex is functionally related to the connection and coordination of various senses at the level of the thalamus and cerebral cortex.
3. The third type (mainly the core group of the medullary plate) is the various structures within the so-called inner medullary plate near the midline, mainly the core group of the medullary plate, including the central middle nucleusParafascicular nucleus, central lateral nucleus, etc.It is generally believed that this type of cell group does not directly project fibers to the cerebral cortex, but some people think that some of its nuclei canMarginal leaf、Orbital gyrusproject.In fact, these cell populations can indirectlySynapseAfter replacement, it diffusely projects to the whole cerebral cortex, playing an important role in maintaining the excited state of the cerebral cortex.It is generally believed that these nuclei make diffuse projections to the cerebral cortex indirectly throughReticular nucleus of thalamusBut the specific projection path is not completely clear.Studies of the parafascicular nucleus indicate that it may be associated withsense of painofIrritatingThalamic tractThe paranuclear nucleus can aggravate the pain symptoms of patients, and the lesion of this area can alleviate the pain of patients;ParafascicularElectrophysiologyStudies have observed that there are indeed cells sensitive to nociceptive afferent impulses in the nucleus.
Projection system
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The thalamus is the replacement station of sensory conduction. Except for smell, various sensory conduction pathways replace neurons in the thalamus, and then project toCerebral cortex。In the thalamus, only rough analysis and synthesis of sensation are carried out, while in the cerebral cortex, fine analysis and synthesis of sensation are carried out.
According to the different projection characteristics of each part of the thalamus to the cerebral cortex, the thalamus can be divided into two major systems, one isSpecific projection systemThe other is nonspecificProjection system(also called diffuse projection system).
typicalSensory pathwayIt is generally completed by the replacement of tertiary neurons.The first level neurons are located inSpinal gangliaOr relatedCerebral nerveSensory ganglionInternal;The second level neurons are located in the dorsal horn of the spinal cord or the relevant nucleus of the brain stem;The third grade neurons are located in the ventroposterior lateral nucleus of the thalamus.butSpecial feeling(visual, auditory, olfactory)Conduction pathMore complex.Therefore, the thalamus is an important successor station of the specific conduction system. It gathers various afferent impulses (except for smell), makes preliminary analysis and synthesis, and produces rough feelings. However, the nature and intensity of the stimulus cannot be accurately analyzed.
Specific projection systemIt refers to the projection of the lateral nucleus, lateral geniculate body and medial geniculate body of the thalamus toCerebral cortexOffibreContact.The classic sensory pathway is through the thalamusSpecific projection systemIt then acts on the cerebral cortex.The specific area from the thalamus to the cerebral cortex is a point-to-point projection relationship, and each kind of sensory conduction has its own specific path.
first kindCell population, they castCerebral cortexThe specific area of the has a point-to-point projection relationship.
In structure, most of the second group of cells also have a specific projection relationship with the cerebral cortex, projecting to specific areas of the cortex, so they can also belong toSpecific projection system。
Nonspecific
Nonspecific projection system（unspecific projection system）。When sensory transmission is directed to the cerebral cortex projection, that is, when the fibers of the secondary neurons of the specific projection system pass through the brain stem, they send out collateral branches and brain stemReticular structureNeurogenesis ofSynapseConnect, and then pass the shortaxonIt is projected to a wide area of the cerebral cortex through multiple transformations.This projection system is a common way forward for different senses.Due to various feelings and impulsesReticular formation of brainstemAfter that, through the interaction of many intricate and interwoven neurons, the specificity of various feelings will be lost, and the projection to the cerebral cortex will no longer produce specific feelings.Therefore, this conduction system is called nonspecific projection system.One of the functions of this system is to stimulate the exciting activities of the cerebral cortex, so that the body canWaking stateTherefore, the nonspecific projection system is also called the ascending activating system of the brainstem reticular structure.When the afferent impulses of this system increase, the excitatory activity of the cortex increases, keeping the animals awake, and even causingExcited state；When the afferent impulse of this system decreases, the cortical excitatory activity weakens, making the animal in a relatively quiet state, and even the vast area of the cortex turns intoSuppression stateAnd cause sleep.The second is to regulate the sensory areas of cortexExcitability, which makes all kinds of special sensesSensitivityRaise or lower.If this system is damaged, the excitatory activity of the cortex will be weakened, and the animals will fall asleep.Because this system is a forward system with multi synaptic succession, it is vulnerable tonarcoticThe conduction barrier occurs due to the action of objects.SomeanaesthesiaMedicine such asHibernating spiritIt acts on the reticular structure of the brain stem, blocks this pathway, reduces the excitability of the cortex, and thus causes quiet and sleep.
Sensation in the cerebral cortex depends on the cooperation of specific and non-specific projection systems.Only through the impulse of the non-specific projection system can the sensory area of the cerebral cortex maintain a certain excitability.At the same time, only through the various sensory impulses of the specific projection system can specific feelings be generated in the cerebral cortex.
The second level of the above classical sensory conduction pathwayneuronOfaxon, when passing through the brain stem on the way to upload, send out lateral branches andReticular formation of brainstemNeurogenesis ofSynapseContact;Then, the neurons were repeatedly transformed in the reticular formation and ascended to reach the nucleus group in the medial part of the thalamus, and finally diffusely projected to the extensive area of the cerebral cortex.Experiments prove that stimulationmidbrainThe reticular structure can awaken the sleeping animals;When the reticular formation is cut off at the head end of the midbrain, the animals will be in a sleep like state.It has been observed clinically that patients with damage to the mesencephalic reticular structure also show lethargy.It can be seen that in the reticular formation of the brain stemCerebral cortexUplink wake-upFunctional systemIt is called the ascending activation system of brainstem reticular structure.The ascending excitatory system of brainstem reticular formation mainly works through the nonspecific projection system of thalamus.
Uplink reticular activation systemAnd thalamic nonSpecific projection systemFunctionally indivisible, forming a unified system, they are the common pathway of various sensory inputs, and their role is to maintain and improveCerebral cortexOfExcitatory state。Therefore, the nonspecific projection system of the ascending activation system thalamus of the brainstem reticular formation is sometimes called the nonspecific projection system of sensory afferent.
The nonspecific projection system of sensory afferent plays an important role in maintaining the arousal state of cerebral cortex.The more various afferent impulses, the more impulses entering the brainstem reticular structure through the collateral branches, thus the stronger the upward wake-up effect on the cerebral cortex, the better the excited state of the cortex, and the more perfect the sense of the specific projection system.Therefore, the specific projection system and the nonspecific projection system of sensory afferent are functionally interdependent and inseparable.
