Neuroanatomy Flashcards
The nucleus incertus ?
This nucleus locates in the midline between the dorsal tegmental nucleus of both sides and display important projections to the hypothalamus, septum, amygdala and hippocampus and is able to modulate the hippocampal theta rhythm which is involved in learning and memory processes.
Dorsal tegmental, laterodorsal tegmental and pedunculopontine tegmental nuclei ?
These tegmental nuclei are located surrounding the MEDIAL LONGITUDINAL FASCICULE at the level between the PONS and the MEDULLA.
The laterodorsal and pedunculo-pontine tegmental nuclei are composed of CHOLINERGIC neurons involved in arousal and REM sleep.
The dorsal tegmental nucleus is a spheric –like nucleus which is involved in the configuration of spatial hippocampal maps, particularly in the generation of head orienting cells.
Substantia nigra and ventral tegmental area ?
These systems are :
- The main DOPAMINERGIC centers in the brain
- Located deep to the cerebral peduncles in the MIDBRAIN.
=> The substantia nigra
Is composed of two compartments : the part COMPACTA and the part RETICULATA.
-> The pars reticulata :
- Is located more ventrally betsween the bundles of descending cortical axons.
- Mainly composed of GABAergic neurons which project to the thalamus and superior colliculus.
- The pars reticulata deeper in respect to the former and is composed of dopaminergic neurons projecting to the striatum.
- Pathological degeneration of these neurons are the cause of Parkinson’s disease.
=> The ventral tegmental area :
- Is located in the midline between the substantia nigra of both sides.
- It is also composed of dopaminergic neurons projecting to both, the nucleus accumbens and the prefrontal cortex.
- Alterations in these projectos are on the bases of mental illnesses like addictions or schizophrenia.
Parabraquial nuclei ?
It is composed of two clearly defined regions :
- Medial and
- Lateral.
-> Medial region :
- Receives gustatory projections from the nucleus of the tractus solitaries.
Gustatory projections are sent to the ventral posteromedial thalamic nucleus.
-> Lateral region :
- Receive baroreceptor projections from the same nucleus.
Baroreceptor projections are mainly directed to the reticular formation mediating cardiovascular and respiratory reflexes.
Periaqueductal grey PAG ?
- It consist of a well differenciated cell group around the cerebral aqueduct at MIDBRAIN and PONTINE levels.
- PAG cells are arranged in longitudinal columns.
- The definitory element of the columns is the occurrence of NITRIC OXIDE SYNTHETASE (NOS) in the dorsolateral column which leaves a dorsolateral column medially and lateral and ventrolateral columns ventrally.
-> In total, the PAG is composed of :
- Dorsomedial,
- Dorsolateral,
- Lateral and
- Ventrolateral columns.
The PAG receives a strong projection from the prefrontal which deals with conflict situations like a predator atac, there is also an important amygdala projection which deals with fear responses, mainly freezing and hypothalamic projections which is responsible for metabolic adaptation in conflict situations.
In general, the PAG is mainly involved in two kinds of behavior i.e., afensive/defensive mechanisms and nociception.
The PAG organize cop mechanisms.
-> The anterior part of the dorsal column responds to conflict situation by facing the problem and confrontation.
-> The lateral column of the PAG is involved in a flying response to the danger.
Finally, the ventrolateral column is involved in fear responses which require quiescence and freezing.
On the other hand, PAG is involved in endogenous analgesia that is the reduction of nociceptive signal along its progress through the CNS by an inhibitory action starting in the PAG. This inhibitory action may start with opioid transmission in the PAG. Some opioid analgesics, like morphine, potentiate this mechanisms.
Locus coeruleus and adrenergic centers ?
- The locus coeruleus is a tiny structure located over the lateral border of the fourth ventricle at the pontine central grey.
- It is composed of noradrenergic neurons.
Other noradrenergic groups are dispersed in discrete groups of the reticular formation. These cellular groups provides a broad adrenergic projection throughout all the central nervous system. The main function of these projection is general arousal and control of REM sleep and cortical activation.
What is the graphe nuclei ?
It can be considered as the MIDLE RETICULAR FORMATION.
As a common feature for all these nuclei is the occurrence of SEROTONIN (5HT) as neurotransmitter.
From rostral to caudal it can be outline:
- At the midbrain, the dorsal and linear raphe nuclei
- At the pons, the median raphe (central superior) and the raphe pontis
- At the medulla, the raphe magnus, the raphe lucidus and the raphe obscurus
The raphe nuclei display widespread projections ascending and descending as well in such a way that may be considered as a general modulator of the neural function.
The projections from the MEDULLARY RAPHE nuclei are directed towards the SPINAL CORD and are directed to modulate the ascending NOCICEPTIVE information.
In contrast, MIDBRAIN and PONTINE RAPHE nuclei serotoninergic cells project to the TELENCEPHALON and modulates the general telencephalic function, thus mainly involved in AROUSAL.
What are the tegmental nuclei ?
Several of these nuclei can be considered at the same time as reticular or tegmental.
Although many discrete nuclei can be outline along the brainstem in the following description we are going to consider the following:
- The raphe nuclei,
- Locus coeruleus and adrenergic groups,
- Periaqueductal grey,
- Dorsal and ventral tegmental nuclei,
- Pedunculo-pontine tegmental nucleus,
- Laterodorsal tegmental nucleus,
- Midbrain cuneiform nucleus,
- Interpeduncular nucleus,
- Ventral tegmental area,
- Substantia nigra and
- Nucleus incertus.
Other structures next to the FR
Along the rostrocaudal axis a series of segments can be outline :
-> At the level of the MIDBRAIN :
- Most part is occupied by the RED NUCLEUS.
- This nucleus receives a strong projection from the CEREBELLUM and projects to the SPINAL CORD (the rubrospinal tract)
- Afferent fibers from the cerebellum cross the midline to get the red nucleus and in the same way efferents to the spinal cord also cross again to the contralateral side of the red nucleus.
- The red nucleus also receives an importan projection from the PREMOTOR CORTEX,
- In addition, the red nucleus also projects to the INFERIOR OLIVARY COMPLEX.
-> At the levels of the PONS :
- It ca be outline the RETICULARIS PONTIS ORALIS and RETICULARIS PONTIS CAUDALIS which are involved in arousal, including sleep regulation.
-> At the level of the MEDULA :
- The PARAMEDIAN FORMATION is involved in oculomotor modulation and coordination
- The RETICULARIS GIGANTOCELLULARIS is involved in motor coordination
- The RETICULARIS PARVOCELLULARIS in pain modulation.
Also in a diffuse way between the retiucular areas there are some centers involved in cardiorespiratory functions which regulate the rhythm of breathing and also the rhythm of cardiac beating and adjust them according to energy requirements.
Reticular formation
All along the brainstem, there are several groups of neurons dispersed among the ascending and descending pathways and surrounding the motor ans sensory nuclei. The group cells dispersed between bundles of ascending, descending and trasversal fiber in which limits and structural isolation is not aparents are refered as RETICULA FORMATION.
NB : Cells arranged in discrete groups that are easily defined are knons as tegmental nuclei.
The RF :
- The retiucular formation looks to be a continuum of neurons that runs from the SPINAL CORD -> THALAMUS.
- Typical reticular cell display star-like morphologies with dendritic extending at relatively long distances. Their axons also extend far away.
- Mainly composed of two longitudinal regions, i.e. MEDIAL and LATERAL
- In addition, the RAPHE NUCLEI occupy a MEDIAN column and a group of cells can also be defined between the raphe nuclei and the medial column and are defined as PARAMEDIAN column.
-> The MEDIAL region :
- Is composed of large neurons (magnocellular column)
- Extend their axions in rostrocaudal directions
- These neurons are involved in motor modulation and are the origin of the RETICULO-SPINAL PATHWAY.
-> The LATERAL :
- Or parvocellular column is mainly composed of small neurons
- Extending its axons in medial directions
- Involved in sensory modulation.
-> The PARAMEDIAN column :
- Is only present in caudal pons and rostral medulla.
- It is mainly involved in cerebellar functions and oculomotor systems
-> The MEDIAN column :
- Is composed of the RAPHE NUCLEI
- Mainly involved in arousal and as a main feature its cells produce and delivers serotonin.
Auditory sensitivity
The cochlear nuclei receive primary acoustic information from the SPIRAL GANGLION cells in the COCHLEA.
Cochlear nuclei locate in the jonction between the pons and the medulla.
Cochlear complex is composed of the :
- DORSAL cochlear nucleus
- VENTRAL SUP cochlear nucleus
- VENTRAL INF cochlear nucleus
Axon arising from the primal ganglion cells project to all of the three cohclear nuclei.
There is a TONOTOPICALLY arrangement of auditory in the three cochlear nuclei.
In the cochlea :
- HIGH frequencies stimulate preferentially the base of the cochlea
- LOWER frequencies are more affective in stimulating the apex
This organization is transferred to the cochlear nuclei in a similar way :
- HIGH : represented VENTRALLY
- LOWER : DORSALLY
This is the TONOTOPY.
Cochlear nuclei originates three bundles :
-> DORSAL
- Cross controlaterally through the floor of the fourth ventricule to form the LATERAL LEMNISCUS on the contralateral side
-> MIDDLE
- Projects to both, the ipsilateral ans controlatéral SUPERIOR OLIVARY COMPLEX
- A group of these fibers also run rostrally to join the lateral lemniscus
-> INFERIOR
- Also called TRAPEZOID DODY
- Also project to both the ipsilateral and controlateral SUPERIOR OLIVARY COMPLEX
The SUPERIOR OLIVARY COMPLEX :
- Is a group of nuclei : MEDIAL and LATERAL OLAVRY n. + PREOLIVARY n. + TRAPEZOID BODY n.
- Located ventrally between the pons and the medulla
- All components of this complex receive information from both acoustic organs
- The integrated information, the delay in arriving the signal from one ear or the other, and the differences in intensity between both ears are computer to locate the source the sound in the space.
The SUP OLIVARY COMPLEX + n. COCHLEAR = give rise to the LATERAL LEMNISCUS.
LEMNISCUS LATERAL :
- Is a bundle of fibers running through the label part of the brainstem
- This bundle arrive to the colliculus inferior
- Between the tract of the lateral lemniscus the are a groupe of cells which originates the nucleus of the lateral lemniscus (contribute to auditory processing)
INFERIOR COLLICULUS :
- Located in the caudal part of the midbrain
- Oval structure composed of a core (that is the central nucleus) and a shell, containing the dorsal and external nucleus
- The central nucleus receives direct ascending auditory projection which is tonotopically
The central nucleus of the INF COLLICULUS originates to pathway :
- One to the MEDIAL GENICULATE BODY witch will relay auditory information to the auditory cortex = LEMNISCAL PATHWAY
- One to the pericentral nuclei and from there to the deep layers of the superior colliculus subserving visual auditory reflex = EXTRALEMNISCAL PATHWAY
The acoustic tracts cross to the contralateral side in multiple places, but from the inf colliculus they do not cross anymore. These crossing alow to compare information from both ears at once and locates the source of the sound.
NB : In addiction to this ascending pathway to the thalamus and cortex, there e is a descending pathway that arise from the neocortex and targets the olivary complex.
Nucleus of the solitary tract ?
Baroreceptor and gustatory information is recovered by cranial nerves VII, IX and X.
Axons from these nerves meet together to form the solitary tract which runs dorsally along the caudal levels of the pons and rostral levels of the medulla. Surrounding this bundles différents groups of neurons receive its information and are collectively known as the nucleus of the solitary tract.
There is a topographic distribution of baroreceptive and gustatory information inside the nucleus of the solitary tract :
- Gustatory information is mainly represented in the rostral aspect of the nucleus
- Baroreceptor information is mainly managed in the caudal aspect of the nucleus.
In the same way :
- Fibers from the VII nerve : rostral level
- IX : intermediate level
- X : more caudally
What is the tectum ?
The tectum is composed of 4 tubercules = CORPORA CUADRIGEMINA + a transition between corpora quadrigemina and thalamus = PRETECTUM.
In turn, corpora quadrigemina is composed of :
-> SUPERIOR COLLICULI
- Devoted in vision
- Is a layered structure : composed of 3 k-layers of fibers : SUPERFICIAL GREY / INTERMEDIATE GREY / DEEP GREY, separated by corresponding layers of fibers : OPTIC layer, WHITE MIDDLE layer and DEEP WHITE layer
- OPTIC layer + WHITE superficial layer are involved in reception of projections from RETINA and relaying the to the pulvinar nucleus and pretectum
- The rest are mainly involved in OCULOMOTOR coordination and reflexes
-> INFERIOR COLLICULI
- Devoted to audition
- Composed of a CENTRAL nucleus and PERICENTRAL nucleus
The CENTRAL part belong to the direct auditory pathway :
-It receives projection from different components of the ascending auditory pathway which are organize tonotopically.
The PERICENTRAL nuclei : - Are the dorsal nucleus and the external nucleus
- Part of the indirect auditory pathway
- Participate to some aspect of audition
- Project to the deep layer of the colliculi responsible of auditory visuel reflex
PRETECTUM :
- Set of nuclei which receive direct information from the retina and from the superior layer of the colliculi superior
- In turn the pretectal nuclei projects to the accessory oculomotor nuclei = responsive of the coordination mainly referred to vertical gaze
Sensibility of the face ?
The sensibility of the face is collected by three nuclei :
- Mesencephalic trigeminal nucleus
- Principal trigeminal nucleus
- Spinal trigeminal nucleus
-> The mesencephalic trigeminal nucleus
- composed of a row of large cells located laterally in respect to the periacqueducal grey
- these neurons correspond to ganglion neurons as send one process directly to the receptor s in the roots of the teeth and another process to the motor trigeminal nucleus
- adjust the strength of the bite according to the pression of the teeth
-> The principal trigeminal nucleus
- received fibers from the triennal ganglion which carry out information from the three trigeminal branches
- located in the pons just at the level of the trigeminal fibers
-> The spinal trigeminal nucleus
- receive small diameter fibers conveying nociceptive information of high threshold and slow adaptation
located in a bundle lateral to the nucleus - there is a somatotopic representation in the spinal trigeminal nucleus (which is reversed to the way they are located in the face) :
- mandibular occupies rostral position
- maxillary nerve intermediate
- ophtalmic nerve is represented caudally
=> Axon from both principal and spinal trigeminal nuclei cross the midline and integrates in the medial aspects of the medial lemniscus, so that information regarding the face appears in continuity to that regarding the neck.
Efferents from the vestibular nuclei targets ?
Mainly :
- Cerebellum,
- Spinal cord,
- Oculomotor centers
- Thalamus
1) Cerebellum
- The pathway from the cerebellum arise from the medial ans inferior nuclei
- Targets the vestibulocerebellum as mossy fibers
2) Spinal cord
- The pathways to the spinal cord arises from the lateral and medial vestibular nuclei
- The lateral vestibulo-spinal tract (from the lateral nucleus) is a direct ipsilateral pathways which arrives to all levels in the spinal cord
- In contrast, the medial vestibular nucleus gives rise to bilateral fibres integrating the medial vestibulospinal tracts targets only the cervical ans upper thoracic levels of the spinal cord
3) Oculomotor centers
- Superior and rostral of the medial vestibular nuclei provides innervation to the oculomotor centers through the FLM
NB :
- The FLM regulating the gaze by meet in contact the oculomotor, the vestibular and the spinal nuclei, and also center integrating information regarding gaze coordination
- The mouvement of the head and eyes and neck are computed with the mouvement of the lymph in the semicircular ducts as being analyzed by the vestibular centers
4) Thalamus
- Part of the vestibular projections arrives to the thalamus where they are projected through a diffuse way over the ventral posterolateral nucleus.
