Analysis:
Brain stem: including medulla oblongata, pons and midbrain. Some people also include diencephalon.
The general structure of the brain stem is that there is a midbrain aqueduct in the center of the cross section on the dorsal side of the midbrain, with central gray matter around the aqueduct, a tetrad (coping) on the dorsal side and cerebral peduncle on the ventral side. The cerebral peduncle is divided into dorsal tegmentum and ventral floor by substantia nigra. The pons are divided into two parts: the basal part and the tegmental part. The basal part is located on the ventral side and contains a large number of transverse fibers. The tegmentum is a direct continuation of the medulla oblongata on the dorsal side. The medulla oblongata belongs to the tegmentum except the cone.
The internal structure of brain stem still retains the general structure of spinal cord in many aspects, such as gray matter and white matter, and many ascending and descending fibers pass through it. However, compared with the spinal cord, there are many characteristics in the brain stem: ① There are ⅲ ~ ⅹ ⅱ brain nuclei, both sensory and motor nuclei. ② There are many motor and sensory transmission nuclei. For example, the red nucleus receives fibers from the cerebral cortex and sends fibers to the spinal cord to control movement, which belongs to the motor transit nucleus. The fascicular nucleus and cuneiform nucleus receive afferent fibers from the dorsal cord of the spinal cord, and then send out fibers to project to the thalamus, belonging to sensory transmission nuclei. ③ Due to the continuous development of brain and cerebellum, the connection between them through brain stem is also developing, especially the basal part of pons, which is an important transit point of brain-pons-cerebellum pathway. ④ The appearance of reticular structure of brain stem.
The function of the brain stem is closely related to its position and its connection with various parts of the central nervous system. The brain stem is first of all a transit point for many ascending and descending nerve pathways, such as spinal cord to cerebellum, cerebellum to spinal cord, spinal cord to diencephalon, and brain to spinal cord. Secondly, the brain stem controls many sensory and motor functions of the head and face, which is related to the third cranial nerve it sends out. Thirdly, it is the location of many important functional centers, such as breathing, heartbeat, blood pressure maintenance, etc., which are controlled by the relevant centers of the brain stem. These parts used to be called the center of life.
The brain stem is also related to the maintenance of animal posture and righting reflex. Brainstem reticular structure also plays an important role in maintaining muscle tension and brain excitability.
The brain stem sends out the third to third cranial nerves, which are sensory, motor and mixed in nature. According to the structure of brain nerve distribution, the components of brain nerve fibers can be divided into the following seven categories (see Annex).
In these seven categories, the distribution of general visceral afferent and efferent, general somatic afferent and somatic efferent is basically similar to that of spinal nerves; The afferent fibers from the inner ear are called special somatic afferent fibers. The afferent fibers of taste buds in the mouth are called special visceral afferent fibers. Some muscles in the head and neck are derived from the mental arch in the embryonic period, so the efferent fibers that dominate these muscles are called special visceral efferent fibers.
Although the location of the nucleus from the third cranial nerve is different, it can be seen from careful observation that the nucleus of the cranial nerve is closer to the outside, which is due to the expansion of the fourth ventricle, which is equivalent to the lateral expansion of the wing plate of the neural tube. The motor brain nucleus is closer to the medial side.