BrainstemThe brainstem is a smaller part of the brain located between the spinal cord and the mesencephalon, below the brain, and the medulla oblongata part of the brainstem is connected to the spinal cord. It is irregularly columnar in shape. The brainstem is composed of the medulla oblongata, pons, and midbrain from the bottom up.
The upper part is connected with the 3rd to 12th pairs of cerebral nerves. The white matter in the brainstem is composed of upward and downward conduction bundles, as well as nerve fibers emanating from various parts of the brainstem. It is an important pathway for the brain, cerebellum and spinal cord to communicate with each other. The gray matter in the brainstem is dispersed into gray matter blocks of different sizes called “nuclei”. The nuclei are involved in the reception of peripheral afferent and efferent impulses to innervate organs and in the conduction of upstream and downstream conduction bundles. In addition, there are reflex centers in the medulla oblongata and pons that regulate important physiological activities such as cardiovascular movement, respiration, swallowing, and vomiting. If these centers are damaged, it will cause serious impairment of heart beat and blood pressure, and even endanger life.
The medulla oblongata is caudally connected to the spinal cord at the foramen magnum, and the midbrain is cephalad to the mesencephalon. The medulla oblongata and the pons lie precisely on the slope of the skull base.
The function of the brainstem is mainly to maintain the life of an individual, including important physiological functions such as heartbeat, respiration, digestion, body temperature, and sleep, all of which are related to the function of the brainstem.
The nerve impulses transmitted from the spinal cord to the brain enter in a crossed manner: the impulses from the right side of the spinal cord are first transmitted to the left side of the brainstem and then to the brain; those from the left side of the spinal cord are first sent to the right side of the brainstem and then to the brain.
The shape of the brainstem
Ventral side of the brainstem (Figure)
At the median fissure of the medulla oblongata, there are crossed fibers from left to right, called conus interna, which is the division between the medulla oblongata and the spinal cord. The longitudinal bulges on both sides of the median fissure are the cones formed by the corticospinal tracts (or conus tractus). The lower end of the cerebral bridge is divided from the medulla oblongata by the pontine sulcus, and the upper end is connected to the cerebral peduncle of the midbrain.
1. The shape of the medulla oblongata: between the foramen magnum and the pontine sulcus of the medulla oblongata. There are conus, conus intersection, olive, hypoglossal nerve root, glossopharyngeal nerve, vagus nerve and paramedian nerve.
2, the shape of the cerebral bridge: there is the base of the cerebral bridge, the basal sulcus of the cerebral bridge, the pontine arm, the trigeminal nerve root, the spreading nerve, the facial nerve, the vestibulocochlear nerve, and the cerebral bridge cerebellar angle.
3. The shape of the midbrain: divided by the optic tract and the mesencephalon, there are cerebral peduncle, interpeduncular fossa, and motoneuron.
Dorsal side of the brainstem (Figure)
The medulla oblongata can be divided into two segments: upper and lower. The lower segment is called the closed section, and its ventricular cavity is a continuation of the central canal of the spinal cord. The median sulcus is flanked by the thin bundle nodes and the cuneate bundle nodes, in which the thin bundle nuclei and the cuneate nuclei are hidden respectively. The dorsal surface of the pons forms the upper part of the floor of the fourth ventricle. The base of the fourth ventricle has a transverse medullary stripe, which is the demarcation mark between the medulla oblongata and the cerebral bridge.
1.The medulla oblongata and the pons: there are the floor of the fourth ventricle, the rhombencephalic isthmus, the right and left superior cerebellar peduncles, the anterior and posterior medullary sails, and the pulvinar nerve
2.Rhombomere fossa: it is the base of the fourth ventricle. The inferior border of the rhombencephalic fossa: thin bundle, cuneiform bundle node, and inferior cerebellar peduncle. Upper border: superior cerebellar peduncle. Both lateral horns: the lateral saphenous fossa of the fourth ventricle. Medulla, boundary sulcus, medial bulge, facial mound, blue spot, lateral area, vestibular area, auditory node, subglottic nerve triangle, vagus nerve triangle.
3.The shape of the midbrain: parietal cap, superior and inferior colliculi, superior and inferior colliculi arms.
Brainstem structure
The brainstem includes the following four important structures.
The medulla oblongata resides in the lowermost part of the brain and is connected to the spinal cord; its main function is to control respiration, heartbeat, digestion, etc.
2, brain bridge (pons) brain bridge is located between the midbrain and the brain. The white matter nerve fibers of the pons, which pass to the cerebellar cortex, can transmit nerve impulses from one hemisphere of the cerebellum to the other hemisphere, so that it can play the function of coordinating muscle activities on both sides of the body.
3, the midbrain (midbrain) midbrain is located above the cerebral bridge, which happens to be the midpoint of the entire brain. The midbrain is the reflex center of vision and hearing, where the pupil, eye, muscle and other activities are controlled by the midbrain.
The reticular system resides in the center of the brainstem and is a reticular structure made up of many intricate neurons. The main function of the reticular system is to control different levels of consciousness such as wakefulness, attention and sleep.
The internal structure of the brainstem
The arrangement of neuronal nuclei in the brainstem is regular, from the boundary sulcus inwards to outwards.
General somatic motor nucleus, special visceral motor nucleus (migrating ventrally), general visceral motor nucleus, general visceral sensory nucleus, special visceral sensory nucleus, general somatosensory nucleus (migrating ventrally), special somatosensory nucleus.
1. General somatomotor nuclei.
Nucleus of the motoneuron: innervates the levator aponeurosis, superior rectus, internal rectus, inferior oblique, and inferior rectus muscles.
Nucleus pulposus: crossed out of the brain, innervates the superior oblique muscle.
Nucleus of the adductor nerve: external rectus muscle.
Nucleus of the hypoglossal nerve: internal and external tongue muscles.
2.Special visceral motor nuclei (migrating ventrally)
Trigeminal nerve motor nucleus: masticatory muscles, mandibular hyoid muscle, diastasis, anterior abdominal.
Facial nerve nucleus: innervates all expression muscles diastasis ventralis posterioris caudalis lingualis muscle stirrupus muscle. Dorsolateral nucleus: frontalis, orbicularis oculi.
Ventral nucleus: periorbital muscles.
Doubtful nucleus: fibers join the linguopharyngeal vagus parasympathetic nerve to innervate the pharyngeal muscles.
3.General visceral motor nucleus
Para-nucleus of the motoneuron: pupillary dilator ciliary muscle.
Superior salivary nucleus: fibers join the facial nerve to innervate the lacrimal gland sublingual gland submandibular gland and the glands of the oral nasal cavity.
Inferior salivary nucleus: fibers join the glossopharyngeal nerve via the auricular ganglion to innervate the secretion of the parotid gland.
Dorsal nucleus of the vagus nerve: fibers join the vagus nerve and exchange neurons within the organ and parasympathetic ganglia – postganglionic fibers manage the movement and secretion of smooth muscles, cardiac muscles and glands of the thoracic and abdominal viscera.
4.General visceral sensory nuclei
Solitary bundle nucleus: general visceral sensation in the mucosal vascular walls of visceral organs — linguopharyngeal vagal facial nerve — solitary bundle — solitary bundle nucleus — sends fibers to the superior to the mesencephalon, relaying to the higher centers.
Brainstem motor nuclei: involved in visceral reflexes, reticular formation, involved in respiratory circulation and vomiting reflexes.
5. Special visceral sensory nuclei
Small dorsal part of the solitary tract nucleus: receives gustatory fibers from facial nerve linguopharyngeal nerve afferents.
6.General somatosensory nuclei (migrating ventrally)
Trigeminal nucleus
Trigeminal spinal nucleus: pain-temperature-touch sensation of frontal nasal-oral mucosa.
Trigeminal sensory nucleus: tactile pressure sensation of the frontal nasal oral cavity.
Trigeminal midbrain nucleus: related to frontal-facial proprioception.
7. Special somatosensory nuclei
Snail nucleus: acoustic stimulation of the spiral apparatus around the synaptic ganglion central synaptic nerve anterior and posterior nucleus rhomboid (mostly crossed, partly uncrossed end up to the ipsilateral auditory center; some fibers of the snail nucleus stop midway in the superior olivary nucleus rhomboid nucleus lateral thalamic tract nucleus, involved in auditory reflexes) lateral thalamic tract medial geniculate body auditory radiation temporal lobe auditory center.
Vestibular nerve nucleus: part of the fibers of the vestibular nerve directly enter the cerebellum through the inferior peduncle of the cerebellum, and other fibers reach the vestibular nerve nucleus.
8.Other important nerve groups in the brainstem
Thin bundle nucleus and cuneate nucleus, cuneate parabrachial nucleus, superior collicular nucleus, inferior collicular nucleus, anterior parietal area, blue spot, nucleus cluster of reticular formation, red nucleus, substantia nigra, inferior olivary nucleus.
Horizontal section of brainstem
1, medulla oblongata: motor cross or conus cross plane, sensory cross or thalamus cross plane, middle olive plane.
2.Brain bridge: auditory nodal plane, facial nerve thalamus plane, trigeminal nerve root plane.
3, Midbrain: inferior collicular plane, superior collicular plane.
Functions of the brainstem
The function of brainstem is mainly to maintain individual life, including heartbeat, respiration, digestion, body temperature, sleep and other important physiological functions, all related to the function of brainstem.
Nerve impulses transmitted from the spinal cord to the brain enter in a crossed manner: impulses from the right side of the spinal cord are first transmitted to the left side of the brainstem and then to the brain; those from the left side of the spinal cord are first sent to the right side of the brainstem and then to the brain.