Neuroscience 1 - Trans 7 - Reticular Formation.pdf

1A NUEROANATOMY RETICULAR FORMATION AND LIMBIC SYSTEM DR. C. VIADO, M.D....

1A NUEROANATOMY RETICULAR FORMATION AND LIMBIC SYSTEM DR. C. VIADO, M.D.  INFERIORLY, reticular formation is continuous with the interneurons of the gray matter of the spinal cord Content Outline:  SUPERIORLY, impulse are relayed to the cerebral cortex. A. Reticular Formation  A substantial projection of fibers also leaves the reticular I. Overview formation to enter the cerebellum. II. General Arrangement III. Afferent Projections IIII. AFFERENT PROJECTIONS IV. Efferent Projections  From spinal cord: V. Function o Spinoreticular tracts B. Limbic System o Spinothalamic tracts I. Overview o Medial lemniscus II. Hippocampal formation  From the cranial nerve nuclei: III. Amygdaloid Nucleus o Vestibular pathway IV. Connecting Pathways o Visual pathway V. Structure of the hippocampus o Acoustic pathway VI. Afferent Connections  From Cerbellum VII. Efferent Connections o Cerebelloreticular pathway VIII. Functions  From subthalamic, hypothalamic, thalamic nuclei  From the corpus striatum and limbic system  Primary cortex of Frontal Lobe A. RETICULAR FORMATION  Somesthetic cortex of the parietal lobe I. OVERVIEW IV. EFFERENT PROJECTION  Nerve cells and nerve fibers that resembles a net  Extend down to the brainstem of spinal cord  Extends up through the axis of the CNS from the Spinal o Reticulobulbar tract Cord to the cerebellum o Reticulospinal tract  Sympathetic outflow and craniosacral parasympathetic outflow of the Autonomic Nervous System II. GENERAL ARRANGEMENT  Pathway extending to corpus striatum, the cerebellum, red  3 Longitudinal Columns: nucleus, substantia nigra, nuclei of the thalamus, 1. Median Column - Intermediate size neurons subthalamus and hypothalamus. 2. Medial Column – Large neuron 3. Lateral Column – Small neuron V. FUNCTIONS OF RF 1. Control of Skeletal Muscle – through the reticulospinal tract and reticulobulbar tracts, it influence the activity of the alpha and gamma motor neurons. o Modulate muscle tone and reflex activity  Polysympathetic pathways exists, both crossed and o Reciprocal inhibition: e.g. when the flexor muscles uncrossed ascending and descending pathways are contract, the antagonistic extensors relax present. Trans 7 | Brul, Andoy, Allida, Andam, 1 of 4  Neuroanatomy RETICULAR FORMATION AND LIMBIC SYSTEM o Assisted by the vestibular apparatus of the inner ear and o The convex ventricular surface is covered with ependyma, vestibular spinal tract, plays a role in maintaining the tone beneath which lies a thin layer of white matter called of the antigravity muscles when standing. alveus. o Respiratory centers of the brainstem, control of the o Fimbria – nerve fiber bundles consists of alveus originating respiratory muscle from the hippocampus. o Control of the muscles of facial expressions o Hippocampus terminates posteriorly beneath the splenium o The descending tracts are separate from the corticobulbar of the corpus callosum fibers, this means a stroke that involves corticobulbar fibers and exhibits facial paralysis on the lower part of the face is still able to smile symmetrically. ▪ Ascending pathways: sensory information by multi-neuron chains from body up to more rostral regions of CNS 2. Control of somatic and visceral sensation – influence all Dorsal column ascending pathway that pass to supraspinal levels, may be Spinothalamic tracts facilitative or inhibitory Spinocerebellar tracts o “gating mechanism” for the control of pain perception. ▪ Descending pathways: motor instructions from brain to more 3. Control of Autonomic Nervous System – Higher control of the caudal regions of the CNS ANS from the cerebral cortex, hypothalamus and other subcortical Pyramidal (corticospinal) most important to know nuclei, can be exerted by the reticulobulbar and reticulospinal tracts, All others (“extrapyramidal”) which descend to the sympathetic outflow and the parasympathetic craniosacral outflow. ▪ Most pathways cross (or decussate) at some point ( Take note where they decussate ) 4. Control of the endocrine nervous system – influence the ▪ Most synapse two or three times along the way, e.g. in brain synthesis of release or release-inhibiting factors thereby control the stem, thalamus or other activity of the hypophysis cerebri. 5. Influence on the biologic clocks Major fiber tracts in white matter of spinal cord ( Ascending and Descending Pathways ) 6. The reticular activating system – Arousal and the level of consciousness are controlled by RF. Dentate gyrus – is a narrow notched band of ray matter that lies o Causes a sleeping person to awaken between the fimbria of the hippocampus and parahippocampal o Different degree of wakefulness seem to depend on the gyrus. degree of activity of the RF. o Indusium griseum – a thin vestigial layer of gray matter o Incoming pain increase activity of RF that covers the superior surface of the corpus callosum. o Acethylcholine plays a key role as an excitatory o Medial and lateral longitudinal striae - two slender neurotransmitter in this process. bundles of white fibers on each side of the indusium griseum. B. LIMBIC SYSTEM I. OVERVIEW  Group of structures that lie in the border zone between the cerebral cortex and the hypothalamus.  Beyond the border zone in the control of emotion, behaviour and drive. II. HIPPOCAMPAL FORMATION  Hippocampal formation consists of the hippocampus, dentate gyrus and the parahippocampal gyrus. Hippocampus – curved elevation of gray matter that extends throughout the entire length of the floor of the inferior horn of the lateral ventricle. o It is named as such because it resembles a sea horse in coronal section. S1T7 2 of 4  Neuroanatomy RETICULAR FORMATION AND LIMBIC SYSTEM Parahippocampal gyrus - lies between the hippocampal fissure and the collateral sulcus and is continous with the hippocampus along V. STRUCTURE OF HIPPOCAMPUS AND DENTATE GYRUS the medial edge of the temporal lobe.  The cortical structure of parahippocampal gyrus is six layered, there is a gradual transition in the hippocampus from six to a three layered arrangement. III. AMYGDALOID NUCLEUS 1. Molecular layer – superficial, consist of nerve fibers and  Resembles an almond. scattered small neurons  Situated partly anterior and partly superior tot the tip of 2. Pyramidal layer – consist of many large pyramid shaped the inferior horn of the lateral ventricle neurons 3. Polymorphic layer  Consists of a complex of nuclei that can be grouped into a larger basolateral group and smaller corticomedial group  The dentate gyrus has three layers, but the pyramidal layer IV. CONNECTING PATHWAY OF THE LIMBIC SYSTEM is replaced by the granular layer.  Granular layer is composed of densely arranged rounded  The connecting pathway of the limbic system are the or oval neurons that give rise to axons that terminates alveus, the fimbria, the fornix, the mammilothalamic tract on the dendrites of the pyramidal cells to the and the stria terminalis hippocampus.  Alveus – is a thin layer of white matter on the superior or ventricular surface of the hippocampus VI. AFFERENT CONNECTION OF HIPPOCAMPUS  Afferent connections of the hippocampus may be divided  Fimbria – bundle formed at the medial border of the into six groups hippocampus 1) Fibers arising in the cingulate gyrus pass to the hippocampus.  Crus of the fornix – posterior end of the hippocampus. As 2) Fibers arising from the septal nuclei (nuclei lying within the the two crura converge now form the body of the fornix. midline close to the anterior commissure) pass posterior in the They are connected by transverse fibers called the fornix to the hippocampus. commissure of the fornix. This fibers decussate and join the hippocampi of the two sides. 3) Fibers arising from one hippocampus pass across the midline to the opposite hippocampus in the commissure of the fornix.  Mammilothalamic tract – provides connections between the mammilary body and the anterior nuclear group of the 4) Fibers from the indusium griseum pass posteriorly in the thalamus. longitudinal striae to the hippocampus. 5) Fibers from the entorhinal area or olfactory-associated cortex  Stria terminalis - emerges from the posterior aspect of the amygdaloid nucleus and runs as a bundle of nerve fibers pass to the hippocampus. posteriorly in the roof of the inferior horn of the lateral ventricle on the medial side of the tail of the caudate 6) Fibers arising from the dentate and parahippocampal gyri travel nucleus. to the hippocampus. IV. CONNECTING PATHWAY OF THE LIMBIC SYSTEM IV. CONNECTI VII. EFFERENT CONNECTIONS TO THE HIPPOCAMPUS 1. Fibers pass posterior to the anterior commissure to enter the mammillary body, where they end in the medial nucleus. 2. Fibers pass posterior to the anterior commissure to end in the anterior nuclei of the thalamus. 3. Fibers pass posterior to the anterior commissure to enter the tegmentum of the midbrain. 4. Fibers pass anterior to the anterior commissure to end in the septal nuclei, the lateral preoptic area, and the anterior part of the hypothalamus. 5. Fibers join the stria medullaris thalami to reach the habenular  Hypothalamus as being the major output pathway of the limbic system. S1T7 3 of 4 Neuroanatomy RETICULAR FORMATION AND LIMBIC SYSTEM VII. FUNCTION OF THE LIMBIC SYSTEM  Outflow of the autonomic nervous system and its control of the endocrine system  Emotional behaviour e.g. fear, anger and sexual behaviour  Converting short term memory to a long term memory REFERENCE  Clinical Neuroanatomy by Richard Snell S1T7 4 of 4