Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Act of September 9, 1965, in its current version, and permission for use must always be obtained from Springer. The complex topography of the brainstem presents a challenge even to neurologists experienced in localizing brainstem lesions and diagnosing brainstem disorders. One of the most attractive features of this book is the vast experience of our authors, evidenced by the many important contributions they have made to understanding brain function in recent years.
Development
Floor: fibrous layer consisting of the cerebral peduncles, the base of the pons and the pyramids. Due to this, the brain stem acquires a segmented structure (rhombomere), which is reflected in the organization of the cranial nerves and their nuclei. Each rhombomere is characterized by a specific gene expression pattern of the control gene, as well as by morphogenetic molecular factors.
External Characteristics
On its dorsal surface the pons forms the floor of the fourth ventricle and the floor of the rhomboid fossa caudally. Two lateral incisions are seen in the fourth ventricle at the level of the caudal pons. The abducens nerve (N. VI) exits the brainstem at the upper border of the pyramid and the lower edge of the pons (Fig. 1.3).
Internal Architecture
The corticorubral tract descends in the ipsilateral internal capsule to the parvocellular part of the red nucleus. Their axons project, among other things, towards the motoneurons of the diaphragm (C3-C7) in the spinal cord. Motor neurons in the tongue (hypoglossal nucleus), floor of the mouth, pharynx and larynx (nucleus ambiguus), as well as in the face (facial nucleus) are involved in a number of reflexes, e.g.
Pathways in the Brainstem
The topographic organization of the dorsal column is preserved after crossing over in the dorsal column nuclei. Recent studies have shown that a further visceral pain pathway runs in the dorsal columns and follows lemnic pathways to the ventral posterolateral nucleus of the thalamus. VIII and traverse in the internal acoustic canal to the cochlear nerve before reaching the outer (thick axons) and inner (thin axons) hair cells of the cochlea.
Brain Stem Vascularization
Branches of the lateral vascular group may originate from the PICA or from the vertebral artery and enter the medulla oblongata lateral to the inferior olive. The branches of the dorsal vascular group arise at the level of the obex from the PICA and the ascending branch of the posterior spinal artery. Büttner-Ennever JA, Horn AKE (1996) Pathways from cell groups of the paramedian tracts to the floccular region.
Neuroradiology
Endovascular therapy for stenoses in the vessels responsible for blood supply to the brain was introduced in the 1980s. Conversion of the frequency shift (kHz) to velocity values is not allowed in the case of an unknown insonation angle. However, this constellation can also be observed in the presence of proximal lesions of the cochlear nerve.
Unilateral changes in suppression may indicate the presence of a brainstem lesion (Ongerboer de Visser and Cruccu 1993). For stimulation of the motor cortex, a circular coil (mean diameter: 90 mm) or a double coil (mean diameter of each coil half: 70 mm) is placed 2 cm lateral to the vertex. More distally in the course of the nerve, electrical stimulation can be applied to the mandibular angle (Redmond and Di Benedetto 1988).
TMS of the right motor cortex does not evoke a contralateral CMAP in the buccinator muscle. MRI: Demyelinating lesion in the region of the dorsolateral pons on the left, with peripheral facial paresis on the left. During movements in the direction of the electrode, a positive deflection is observed (the positive cornea is located closer to the electrode than the negative cornea); on movements away from the electrode a negative deflection is noted (the negative retina lies closer to the electrode than the positive cornea).
Because eye movements can be recorded from closed eyes, studies of the vestibular system, e.g. Goodwill CJ (1968) The normal jaw reflex: measurement of the action potential in the muscles of mastication.
Disorders of ocular motility
Horizontal saccades on the side of the lesion are overshooting (hypermetric) and those on the opposite side are hypometric (undershooting). Misalignment of the visual axes is typically absent in the primary position (= looking straight ahead), which already in the first description of this disorder was thought to indicate a central, supranuclear lesion (Jampel and Fells 1968).
General Architecture
Mesencephalon
Around the sixth week of embryonic development, eight transverse swellings, the rhombomeres (Fig. 1.2), become temporarily visible on the floor of the fourth ventricle. The resulting damage would not only have an effect on the structures of the respective brain segments, but also on the tissue developing from the neural crest cells and placodes of the affected rhombomere (e.g. sensory cranial nerves and parasympathetic main ganglia, as well as parts of the cranial skeleton) (Kiernan et al. 2002). Upon removal of the leptomeninx, the small arteries (interpeduncular perforating arteries) are sloughed off leaving small holes in the brain substance, causing this area to be described as the posterior perforated substance.
Pons
The cerebral crus with the adjacent tegmentum is also referred to as the cerebral peduncle. At the midline between the cerebral crura lies the interpeduncular fossa, from which the oculomotor nerves (N. III) emerge.
Medulla Oblongata
Retinal Inputs
Cranial Nerves
The pseudounipolar or bipolar nerve cell bodies of the sensory afferents are found outside the central nervous system within compact ganglia. The ganglia are components of the peripheral nervous system and form, in view of embryonic development, a derivative of the neural crest (as opposed to the central nervous system which is a neural tube derivative). Muscles of chewing, floor of the mouth, tensor tympani muscle, tensor veli palatini muscle via V3 Muscles of chewing (proprioceptive); facial skin, mucous membrane of the nasopharyngeal space, tongue, anterior 2/3s, - mechanoreception) Lateral rectus muscle Proprioception.
Cranial Nerve Nuclei of the Brainstem
- Oculomotor Nucleus
- Trochlear Nucleus
- Abducens Nucleus
- Trigeminal Nucleus
- The Facial Nucleus
- Vestibular Nuclei
- Cochlear Nuclei
- Nuclear Groups of the Vagal System
- Nuclear Groups of the Accessory Nerve
- Nucleus Hypoglossus
The cell bodies of the proprioceptive afferents of the masseter muscle lie in the mesencephalic trigeminal nucleus (dark grey). A detailed description of the reflex pathways in the medulla is found elsewhere in the literature (Blessing 2004). The neurons of origin of the N.XI cranial root are located in the nucleus ambiguus (Fig. 1.5).
Reticular Formation: A Coordination Center
The spinal portion is purely motor: the alpha and gamma motor neurons lie in the anterior horn of C2-C6 in the nucleus of the accessory nerve (Fig. 1.5). The spinal portion leaves the accessory nerve as the external ramus and passes at the level of the neck to the pharyngeal arch derivatives, the sternocleidomastoid muscle and the trapezius (upper part) muscle. Modern classifications of the cranial nerves have assigned the cranial root to the vagus nerve and not to the accessory nerve (Table 1.1).
Ascending Activating System: Attention, Wake–Sleep
From the nucleus raphe magnus, these fibers descend bilaterally in Lissauer's canal and end almost exclusively in the dorsal horn, mainly in the substantia gelatinosa (Rexed layer I). Conversely, descending fibers of the nucleus raphe pallidus end mainly in the ventral horn and thus have an important influence on the entire motor system. It is important that the control of the spinal cord by raphe nuclei or the locus caeruleus is not topographically organized and is therefore effective throughout the system.
Limbic Control
Using their transmitter serotonin, these diffusely distributed terminals cause inhibition of the enkephalinergic interneurons in the dorsal horn. They are therefore able to control the sensory input to the spinal cord and produce stimulus- or stress-induced analgesia (Holstege 1991). However, in a life-threatening situation, endorphin effects from the hypothalamus can inhibit the periaqueductal gray matter and thus gain supraspinal control over pain afferents.
Premotor Control of Eye Movements
- Saccades
- Vestibulo-ocular Reflex
- Optokinetic Reflex
- Smooth Pursuit Eye Movements
- Convergence
- Gaze Stabilization
Retinal signals are transmitted from the optic nucleus and accessory optic nuclei to the vestibular nuclei via several parallel routes and involving the prepositus nucleus. Primary afferents from the semicircular canals are relayed to excitatory (red) and inhibitory secondary neurons (black axons) in the vestibular nuclei; these in turn travel to the motor neurons of the respective eye muscles, which activate them (red, with red arrow) while inhibiting their antagonists (gray, dotted arrow). During excitation of the horizontal canal (a), in addition to the lateral rectus muscle (LR), internuclear neuron (INT) motoneurons are also activated in the abducens nucleus. VI), which then excite the neurons of the medial rectus muscle (MR) in the contralateral oculomotor nucleus (III).
Parasympathetic and Sympathetic Pathways
Shown are sections at the level of the mesencephalon (a), the pons (b, c) and the medulla oblongata (d, e). The most important efferent connections from the hypothalamus to the brainstem consist of the medial forebrain bundle (medial telencephalic fasciculus) and the mammillotegmental tract. Further parasympathetic preganglionic neurons are located in the lateral horns of the sacral area of the spinal cord (pelvic parasympathetic, S2, S3 and S4).
Nuclear Regions of the Mesencephalon
- Overview
- Pretectum
- Superior and Inferior Colliculi
- Red Nucleus
- Substantia Nigra
- Periaqueductal Gray
Pretectal olivary nucleus: this nucleus plays an important role in mediating the pupillary light reflex. Stimulation in the rostral area of foveal representation leads to fixation of the eyes (Fig. 1.11 and p. 18). The afferent axons of the inferior colliculus converge in the lateral zone and form the brachium of the inferior colliculus.
Nuclear Regions of the Pons
- Overview
- Pontine Nuclei
- Parabrachial Nuclei
- Pontine Micturition Center
Functionally, the substantia nigra forms an integral part of the basal ganglia, which plays a role in the modulation or generation of movement. The GABAergic cells in the pars reticulata form (via the superior colliculus) the second most important output of the basal ganglia. All types of Parkinson's disease, not just the classic form, are characterized by progressive death of dopaminergic cells in the pars compacta of the substantia nigra.
Nuclear Regions of the Medulla Oblongata
- Overview
- Inferior Olive
- Ventrolateral Cell Groups of the Medulla
- Area Postrema
The main afferents of the inferior olive emerge from the red nucleus, nucleus of Darkschewitsch, pretectum and superior colliculus. Neurons in the circumventricular organs are therefore able to access the circulating humoral mediators in blood (McKinley et al. 2004). Neurons in the area postrema are very small and difficult to distinguish under a microscope from astroglia.
Descending Pathways
Most of these connections are reciprocal; additional afferents in the area postrema originate from the hypothalamus. The middle cerebellar peduncle (brachium pontis) projects fibers only from the pons to the cerebellum. The inferior cerebellar peduncle (restiform body) contains vestibulocerebellar and spinocerebellar reciprocal fibers, in addition to fibers arising from the inferior olive.
Ascending Pathways
- Lemniscal Systems
- Spinothalamic Tract
- Spinocerebellar Tracts
- Auditory Pathway
Only the anterior spinocerebellar tract uses the superior cerebellar peduncle as an entry route to the cerebellum. These images show that crosstalk between cerebellar efferents to the cortex is indispensable; crossing for afferents to the cerebellum occurs in the pontine nuclei and passage for efferents from the cerebellum ascending to the thalamus (dentate nucleus) occurs in the massive crossing of the superior cerebellar peduncle (Figures 1.14b, 1.16f). ). The main projection from the superior olive extends from the lateral lemniscus to the inferior colliculus.
Mesencephalon
The massive trapezoidal body is just one of the commissural pathways that characterize the auditory system (Fig. 1.1b,e). The neuronal relay for directional hearing is mediated via the medial and lateral nuclei of the superior olivary nucleus. Three cross-sections are shown at the level of the mesencephalon (a), the pons (b) and the medulla (c); the arteries are shown on the right and their supply areas on the left.
Pons
The dorsal vascular area, the tectum or the superior colliculus, receives blood from the quadrigeminal artery (usually a branch of the P1 segment of the posterior cerebral artery) and - more caudally at the level of N.
Medulla Oblongata
