MESENCEPHALON Flashcards
________ is a mixture of gray and white matter dorsal to the central gray matter.
TECTUM
________ refer to the basal portion of the mesencephalon, which includes the cerebral peduncle and substantia nigra.
BASIS PEDUNCULI
________ level is characterized in histologic sections by the decussation of the superior cerebellar peduncle and by the fourth nerve (trochlear) nucleus. T
INFERIOR COLLICULI
__________ is characterized by the red nucleus, the third nerve (oculomotor) nucleus, and the posterior commissure.
SUPERIOR COLLICULUS
Afferent connections of the tectum
Lateral lemniscus. Contralateral inferior colliculus. Ipsilateral medial geniculate body Cerebral cortex Cerebellar cortex via the anterior medullary velum.
Efferent Connections of the tectum
Medial geniculate body via the brachium of the inferior colliculus
Contralateral inferior colliculus.
Superior colliculus.
Nucleus of the lateral lemniscus and other relay nuclei of the auditory system for feedback.
Cerebellum
Fibers in the medial lemniscus are somatotopically organized, with ______ fibers being most medial and ____l fibers most lateral.
cervical, sacral
The __________ is composed of the ventral secondary trigeminal tracts and travels close to the medial lemniscus on its way to the thalamus.
trigeminal lemniscus
_________ conveys fibers from the basal ganglia and midbrain to the inferior olive and occupies a dorsal position in the tegmentum, ventrolateral to the medial longitudinal fasciculu
CTT
fibers thru mesencephalon
Brachium conjunctivum (superior cerebellar peduncle) ML TL ST LL MLF RS CTT
It contains unipolar neurons with axons (the mesencephalic root of the trigeminal nerve) which convey proprioceptive impulses from the muscles of mastication and the periodontal membranes.
mesencephalic n.
reasons why trochlear nucleus is unique
It is the only cranial nerve that crosses before emerging from the brain stem, and it is the only cranial nerve that emerges on the dorsal aspect of the brain stem.
Actions of the SO
primary of intorsion, secondary of depression, and tertiary of abduction
. Neurons of the__________ are affected in patients with progressive supranuclear palsy,
pedunculopontine nucleus
__________serotonergic fibers to the substantia nigra, neostriatum (caudate and putamen), and neocortex.
Nucleus Supratrochlearis (Dorsal Raphe Nucleus)
The medially located corticopontine fibers constitute the _____ projection; the laterally located fibers constitute the ____projections
frontopontine
parieto-occipito-temporo-pontine
The SN is composed of two zones: a dorsal zona compacta containing ___pigment and a ventral zona reticulata containing ____ compounds
melanin, iron
Nonpigmented neurons contain:
GABA, Ach
Afferent connections to the striatum
Neostriatum: GABA Cerebral cortex GP: GABA STN: Glutamine Tegmentonigral Tracts serotonin and cholecystokinin,
Efferent connections to the striatum
Nigrostriate: from the pars compacta project to the neostriatum
Nigrocortical Tract: medial zona compacta and the adjacent ventral tegmental area, course through the medial forebrain bundle, and terminate in the limbic cortex
Nigropallidal Tract
Nigrorubral Tract
Nigrosubthalamic Tract
Nigrothalamic Tract
Nigrotegmental Tract and Nigrocollicular Tract
Nigroamygdaloid Tract
two other cell groups in the mesencephalic tegmentum are dopaminergic
ventral tegmental area of Tsai
retrorubral cell group
hyperactivity in the _______ subdivision is believed to play a role in the symptomatology of psychotic disorders, whereas a reduction in function may contribute to the cognitive abnormalities found in patients with Parkinson’s disease.
mesoallorcortical pathway
decrease in dopamine in this system may explain cognitive impairments in patients with Parkinson’s disease. A decrease in dopamine in the visual cortex has been implicated in photosensitive epilepsy
mesoneocortical system
types of response mode have been demonstrated in mesencephalic dopamine neurons: (1) a ____ response to reward and reward-predicting stimuli that have to be processed by the subject with high priority and (2) _____ mode response involved in maintaining states of behavioral alertness
phasic, tonic
The ________is a laminated mass of gray matter that plays a role in visual reflexes and control of eye movement.
superior colliculus
Afferent of SC
cortex: Fibers originating from the frontal lobe are concerned with conjugate eye movements and reach the superior colliculus by a transtegmental route.
retina: bilateral, with a preponderance of contralateral input.
Spinal cord: conveys pain sensation.
inferior colliculus: turns the neck and eyes toward the source of a sound.
Efferent tracts
Tectospinal tract: They are concerned with reflex neck movement in response to visual stimuli.
Tectopontocerebellar tract
Tectoreticular tract
Tectothalamic tract
This area is an important station in the reflex pathway for the pupillary light reflex and vertical gaze.
pre-tectal area
Parinaud’s components
vertical gaze palsies,
pupillary abnormalities (anisocoria, light-near dissociation),
conversion retraction nystagmus, lid retraction (Collier’s sign),
inappropriate conversion (pseudoabducens palsy),
impaired convergence,
skewed eye deviation in the neutral position,
papilledema, and
lid flutter.
Components of the red nucleus
It is composed of a rostral, phylogenetically recent small cell part (parvicellular) and a caudal, phylogenetically older large cell part (magnicellular).
Fiber system traversing red nucleus
(1) the superior cerebellar peduncle (brachium conjunctivum), (2) the oculomotor nerve (cranial nerve III) rootlets, and (3) the habenulointerpeduncular tract
Interruption of the ______system results in a volitional type of tremor that is manifested when the extremity is in motion (e.g., attempting to reach for an object).
cerebello-rubral
The triangular area bounded by the red nucleus, the inferior olive (in the medulla oblongata), and the dentate nucleus of the cerebellum is known as ___________
Mollaret’s triangle
Corticorubral fibers arise mainly from the motor and premotor cortices and project mainly to the _______ red nucleus.
ipsi
Efferent connections of RN
Rubrospinal: the rubro-spinal tract facilitates flexor motor neurons and inhibits extensor motor neurons.
rubrocerebellar: collaterals from the rubrospinal tract.
Rubroreticular fibers: offshoots from the rubrospinal tract
rubro-olivary tract
Oculomotor nucleus receives from
mesen
pons, medulla
cerebellum
Origin of Mesencephalic projections to the oculomotor nucleus
Cajal’s interstitial nucleus, the rostral interstitial nucleus of the medial longitudinal fasciculus (RiMLF), and the pretectal olivary nucleus: PLR
paralysis of upward gaze.
Cajal’s interstitial nucleus (CONTRA)
paralysis of downard gaze
the rostral interstitial nucleus of the medial longitudinal fasciculus (RiMLF_(IPSI)
Pontine and medullary projections to the oculomotor nucleus arise from:
the vestibular nuclei, the nucleus prepositus, and the abducens nucleus.
_______ to the somatic motor cell column arise from the contralateral dentate nucleus and are concerned with the regulation of eye movements
Cerebello-oculomotor fibers
functions of the PAG
vocalization, control of reproductive behavior, modulation of medullary respiratory centers, aggressive behavior, and vertical gaze, UB fillings, penile erection (hypothalamus, rostral medulla)
Afferent pathway of PLR
optic nerve —– optic tract ——- pretectal area—- posterior commissure —–Edinger-Westphal nuclei in the oculomotor complex.
Efferent pathway of PLR
EWN—-cilliary ganglion—–short ciliary nerves—–sphincter pupillae and ciliaris muscles.
A consensual light reflex is possible because of the projection ________ to both oculomotor nuclei.
pretecta;
Marcus Gunn phenomenon
paradoxical dilatation of both pupils that occurs when light is shone in the symptomatic eye (optic nerve lesion)
Pathway for MGP
The oculomotor nucleus senses the less intense light and shuts off the parasympathetic response, resulting in paradoxical pupillary dilatation
Adie’s pupil,
is characterized by a widely dilated pupil and a sluggish, prolonged pupillary contraction in reaction to light. When it is constricted, the pupil takes a long time to dilate. T
Pathology of Adies
pathology in the ciliary ganglion within the orbit.from redirection of regenerating parasympathetic fibers.
Innervation of the ciliary ganglion
Normally, 90 percent of parasympathetic nerves in the ciliary ganglion innervate the ciliary body and the remaining 10 percent innervate the iris sphincter.
accommodation-convergence reflex involves the following processes:
- assumption of a convex shape by the lens is secondary to contraction of the ciliary muscle,
- Contraction of both medial recti muscles for convergence brings the eyes into alignment.
- Pupillary constriction occurs as an aid in regulating the depth of focus for sharper images.
nucleus has been assumed to play a role in convergence
Perlia’s
Pathway of the accommodation-convergence
that afferent impulses from the retina reach the occipital cortex
and that the efferent pathway from the occipital cortex reaches the oculomotor complex after synapsing in the pretectal nucleus and/or superior colliculus
Important for vertical gaze
- Motor neurons in the oculomotor (cranial nerve III) and trochlear (cranial nerve IV) nuclei that supply ocular muscles
- RiMLF. This nucleus constitutes the neural substrate for vertical eye movements
- Interstitial nucleus of Cajal (INC)
- Post com
- Nucleus of Post com
- MLF
Lesions of the RIMLF
Bilateral: Vertical gaze paralysis
Unilatera;: down gaze paralysis
explanation for Lesions of the RIMLF
bilateral projections of the nucleus to elevator motor neurons and ipsilateral projections to the depressor motor neurons.
neural integrator for vertical gaze
INC
Because of the projections of the INC to ocular motor neurons (cranial nerves III and IV) and to the opposite INC via the posterior commissure, the result of the INC lesion is
bilateral lesion.
Commands for saccadic eye movements from which cerebral cortex part
The frontal eye field (area 8 in the frontal lobe), the angular gyrus (area 39), and the adjacent area 19 of the parieto-occipital cortices project to the superior colliculus.
the superior colliculus in turn projects to the brain stem pulse generators in the pons and midbrain.
two pathways concerned with saccadic movements
anterior pathway from the frontal eye fields directly and indirectly (via the superior colliculus) to the brain stem centers for saccadic movements (PPRF for horizontal saccades and the mesencephalic RiMLF for vertical saccades)
a posterior pathway from the parieto-occipital cortex to the superior colliculus and then to the brain stem centers for saccadic movements
The anterior pathway generates ____ saccades; the posterior pathway generates _____ saccades.
intentional,reflexive
Specific lesions in the_________ that are associated with smooth pursuit deficits in humans correspond to Brodmann areas 19, 37, and 39.
Lesions in the _____also have been associated with deficits in smooth pursuit.
temporo-occipito-parietal cortex,
FEF
Blood supply of the MB
- inferior colliculus (lower midbrain),
- lateral region of the midbrain
- which includes the trochlear nucleus, the cerebral peduncle, and the medial part of the medial lemniscus
- medial zone of the superior colliculus, which includes the third cranial nerve nuclear complex,
- tectum (dorsal zone)
- rest of MB
- upper midbrain (the pretectal level)
- paramedian
- SCA
- inconstant
- tip of basilar artery
- SCA
- posterior cerebral artery
- paramedian branches of the basilar art
