The pathways are a collection of nerve endings and fibers that pass through certain areas of the brain and spinal cord. The pathways of the central nervous system provide a direct two-way connection between the brain and spinal cord. By studying them, you can understand how all the main organs of the body and the external environment are interconnected and how you can manage it all. At the same time, afferent, efferent and associative paths are distinguished.
Centripetal fibers
Afferent neural pathways are classified into unconscious and conscious sensory pathways. It is with the help of them that the connection between all the integration centers located in the brain is ensured. For example, they provide a direct link between the cerebellum and the cerebral cortex.
The main CNS afferent pathways of conscious general sensitivity are the fibers of pain, temperature and tactile sensitivity, as well as conscious proprioceptive. The main unconscious pathways of general sensitivity are the anterior and posterior spinal-cerebellar. To specialconductive include vestibular, auditory, gustatory, olfactory and visual.
Fibers of tactile, temperature and pain sensitivity
This path originates from receptors in the epithelium, the impulses from which enter the cells of the spinal ganglion, and then to the spinal cord, to the nuclei of the thalamus. Then to the cortex of the postcentral gyrus, in which their complete analysis takes place. Three tracts are involved in this pathway:
- Thalamo-cortical.
- Gangliospinal.
- The lateral spinothalamic tract, which runs in the lateral funiculus of the spinal cord and the tegmentum of the brainstem.
The trigeminal nerve is responsible for receiving tactile sensations in the front of the head and changes in body temperature. When it is damaged, a person begins severe pain in the face, which then disappear, then reappear. The trigeminal nerve passes through the cervical region, where the motor fibers of the corticospinal tract cross. Axons of sensory neurons of the trigeminal nerve pass through one of the parts of the medulla oblongata. Through these axons, the brain receives information about pain sensations in the oral cavity, teeth, as well as in the upper and lower jaws.
Fibers of conscious general sensitivity
This pathway carries all kinds of general sensitivity from head to neck. Receptors begin their journey in the muscles and skin, conduct impulses to sensitive ganglia and pass into the nucleitrigeminal nerve. Further, the path passes to the visual tubercles, and then extends to the cells of the postcentral gyrus. This turns on three main paths:
- thalamocortical;
- ganglionuclear;
- nucleo-thalamic.
Fibers of conscious proprioceptive sensitivity
This pathway originates from its receptors in tendons, periosteum, muscles and ligaments, as well as in joint capsules. At the same time, complete information is provided about vibrations, body position, degree of relaxation and muscle contraction, pressure and weight. The neurons of this pathway are located in the spinal nodes, the nuclei of the sphenoid and thin tubercles of the medulla oblongata, the visual tubercle of the diencephalon, in which the switching of impulses then begins. Information is analyzed and ends its journey in the central gyrus of the cerebral cortex. This path includes three paths:
- Thalamocortical, which ends in the projection center, that is, in the central gyrus of the brain.
- Thin and wedge-shaped bundles passing through the posterior funiculus of the spinal cord.
- The bulbar-thalamic tract, passing through the tegmentum of the brainstem.
Spinal fibers
Afferent pathways of the spinal cord are formed with the help of axons, or, as they are also called in another way, the endings of neurons. Axons are located only in the spinal cord and do not go beyond it, and also create a connection between all segments of the organ. Atomic structure of datafibers is that the length of the axons is quite large and connects to other nerve endings. Nerve signals are carried from the receptors to the central nervous system due to the afferent pathways of the spinal cord and brain. All nerve fibers located along the entire length of the spinal cord are involved in this process. The signal to the organs is carried from different parts of the central nervous system and between neurons. The unobstructed passage of a signal from the periphery to the central nervous system is achieved using the pathways of the spinal cord.
Posterior and anterior spinal tracts
The afferent pathways of the cerebellum are classified as unconscious and originate in the lateral funiculus of the spinal cord, and from there they carry information about the state of the organs of the musculoskeletal system. The anterior spinal tract enters the cerebellum through the superior peduncle, and therefore passes through the tegmentum of the medulla oblongata, midbrain, and pons. The posterior spinal tract passes through the medulla oblongata and enters through the inferior pedicle.
These two tracts transmit information to the cerebellum from ligaments, joint bags, muscle receptors, tendons, periosteum. They are responsible for maintaining balance and coordinating human movements, so their role in the body is very important.
Auditory fibers
This path carries information from the receptors of the organ of Corti, which is located in the inner ear. Nerve impulses enter the bridge, which contains the auditory nuclei along the fibers of the vestibulo-cochlear nerve. Through the auditory nuclei, information is transmitted to the nuclei of the trapezoid body. After that, the impulses arrive at the subcortical centers of hearing, which include the thalamus, lower colliculi and geniculate medial bodies.
Return reactions occur in the midbrain to these auditory stimuli, while the afferent auditory pathways switch to the nuclei of the thalamus, in which auditory stimuli are evaluated - they are responsible for movements that occur involuntarily: walking, running. Auditory radiance begins to emanate from the cranked bodies - this tract conducts impulses from the internal capsule to the projection center of hearing. It is only here that the evaluation of sounds begins to take place. In the back of the temporal gyrus, there is an associative auditory center. It is in it that all sounds begin to be perceived as words.
Taste analyzers
Impulses of the afferent pathway of taste analyzers develop from the receptors of the root of the tongue, which are part of the glossopharyngeal nerves and located on the tongue, which are part of the facial nerve. Impulses from them enter the medulla oblongata, and then to the nuclei of the facial and glossopharyngeal nerves. The smallest part of all the information received from these impulses is delivered to the cerebellum, thereby forming the nuclear-cerebellar pathway, and provides reflex regulation of the tone of the muscles of the tongue, head and pharynx. Most of the information enters the visual tubercles, after which the impulses reach the hook of the temporal lobe, where they are consciously analyzed.
Visualanalyzers
Afferent pathways of the CNS of the visual analyzer start from the cones and rods of the retina of the eyeball. Impulses enter the optic junction as part of the optic nerves, and then along the tract are sent to the subcortical centers of the brain, that is, to the visual tubercle, geniculate lateral bodies and superior hillocks located in the middle part of the brain.
In the midbrain, a response occurs to these stimuli, while the nuclei of the thalamus begin an unconscious evaluation of impulses that provide involuntary movements reproduced by a person. The main such unconscious movements are running and walking. In the projection center of vision or in the spur sulcus of the occipital lobe of the brain, impulses arrive by visual radiation from the geniculate bodies that are part of the internal capsule, after which a complete analysis of the incoming data begins. In the cortex, which is adjacent to the spur groove, the central part responsible for visual memory, which is also called the associative visual center, finds its location.
Olfactory analyzer
The afferent path of the olfactory analyzer originates from the receptors of the mucous membrane, localized in the upper part of the nasal passage. After that, the impulses are sent to the axons of the olfactory bulbs, and they flow along the fibers of the olfactory nerves. Then the impulses are sent to the projection center of smell,which is located in the region of the parahippocampal gyrus and hook. These impulses follow the path to the cortex of the temporal lobe of the brain. Most of the information received from the olfactory receptors is sent to the subcortical centers, which are located in the middle and intermediate parts of the brain. The subcortical centers of the brain in response to olfactory stimuli provide reflex regulation of muscle tone.
Based on this, it can be determined that the main feature of olfactory receptors is that nerve impulses initially enter the cortex of the cerebral hemispheres, and not in the subcortical centers of smell. In this regard, a person first feels the smell, then begins to evaluate it, and only after that the unconscious coloring of the stimulus is formed in the brain at the emotional level. The entire process takes only a fraction of a second.
Vestibular tract
The vestibular afferent pathway starts from the receptors of the semicircular canal of the inner ear, the uterus and the receptors that make up this organ. This tract in the central nervous system is responsible for coordinating movements and maintaining balance during physical and vestibular stress.
Afferent centripetal pathways and the peculiarity of their structure indicate that a person needs to make a lot of efforts to maintain the he alth and integrity of each organ individually and taken together. Each component of this path provides the body with all the necessary information, helps to immediately process it and carry out the implementation of allvital processes. This is important in the work of the whole organism as a whole and individual organs.
