Anatomy of the Limbic System and Thalamus Prof. Mujahid Khan اسم ورقم المقرر – Course Name and No. 6/15/2019

Objectives of the lecture: At the end of the lecture, the students should be able to: Describe the important relations of the thalamus. Describe the subdivisions of the thalamus. List the function and important connections of each of the thalamic nuclei. Describe briefly the main effects in case of lesion of thalamus. List the main nuclei and tracts of limbic system. List the important connections between parts of limbic system اسم ورقم المقرر – Course Name and No. 6/15/2019

The Limbic System Limbic means border, so it’s a group of structures lie in the border zone between cerebral cortex and hypothalamus The limbic system is believed to have a special role in emotion and behaviour: feeling, feeding, fighting, fleeing and mating It is concerned with memory and with visceral and motor responses involved in defense and reproduction

The Limbic System The major component and connection: 1- Cingulate gyrus 2- Parahippocampal gyrus 3- Mammillary bodies 4- Anterior thalamic nucleus 5- Hippocampal formation 6- Amygdaloid body (nucleus) 7-Hypothalamus 8- Alveus, fimbria, fornix 9- Mammillothalamic tract

LIMBIC LOBE The ring of grey matter on the medial aspect of each cerebral hemisphere, surrounding the corpus callosum It includes: The cingulate gyrus & the parahippocampal gyrus

The Hippocampal Formation Ant Location of Hippocampi (red) Hippocampus Dentate Gyrus Parts of the Parahippocampal Gyrus Subiculum Post Inferior view of ‘clear’ brain Hippocampus Parahippocampal gyrus Subiculum Parahippocampal gyrus

Hippocampus Formed by a curved elevation of gray mater of the inferomedial part of the temporal lobe into the inferior horn of the lateral ventricle Contains a layer of large, pyramidal shaped neurons (gray in illustration to the right), called the pyramidal cell layer. There are three regions of these cells: CA1, 2 and 3. The pyramidal cells in CA1 are exceptionally sensitive to hypoxia and begin to die after only a few minutes. Pathologists term this region ‘Sommer’s sector’

Hippocampus: Afferents and Efferents The hippocampus receives input from: Adjacent inferior temporal cortex Contralateral hippocampus (via the fornix) The hippocampus sends fibres to: Mammillary body of the hypothalamus (via the fornix) The Mammillary body in turn projects to the anterior thalamus Mamillary body

Memory Learning an association between two stimuli (e.g. face and name) requires an intact hippocampus The hippocampus is also required for recalling the memory for a time after it is acquired

Hippocampus from unaffected individual Hippocampus from patient with isolated bilateral hippocampal lesions Note damage to CA1 region (between arrowheads). This patient exhibited both anterograde amnesia (inability to form new memories), and retrograde amnesia (inability to recall memories acquired before the onset of amnesia). As with most patients, the retrograde amnesia was temporally graded, that is the patient could recall remote events more easily than recent ones (often this extends to decades)

Hypothalamus Serves as the main integrator of the autonomic and endocrine systems Receives diverse inputs, including from: Hippocampus Visceral afferents Somatosensory afferents Input from the septal area (responsible for basic emotional drives) Olfactory system Hypothalamus

Hypothalamus Efferents of the hypothalamus reach: Largest efferent bundle goes to the anterior thalamus Vagal nuclei (parasympathetic) Interomediolateral cell column of the spinal cord (sympathetic) Sacral autonomic nucleus (parasympathetic) Hypothalamus is also believed to participate in memory acquisition, subjective experience of emotions and, via the autonomic nervous system, the visceral manifestations of emotions

Amygdaloid Nucleus It resembles an almond Partly anterior and partly superior to the tip of the inferior horn of lateral ventricle Fused with the tip of the tail of the caudate nucleus Unilateral or bilateral destruction of amygdaloid results in increased appetite and hypersexuality

Amygdala Found near the temporal pole, deep to parahippocampal gyrus Inputs: Temporal cortex, septum and olfactory tract, brain stem Outputs: Chiefly to the hypothalamus Role in evaluating the significance of environmental events, and the association of environment events

Lesions associated with limbic lobe disorders Temporal lobe epilepsy Alzheimer’s disease Schizophrenia

Thalamus Large egg shaped mass of gray matter Two thalami situated on each side of 3rd ventricle Thus form the lateral walls of the 3rd ventricle Separated from hypothalamus by hypothalamic sulcus May be connected to opposite thalamus by interthalamic adhesion (connection)

Thalamus Thalamus has a narrow anterior end called tubercle of thalamus The expanded posterior end, called pulvinar

Surfaces 4 Surfaces: Superior Inferior Medial Lateral S L M l

Relations Superior: lateral ventricle Anterior: interventricular foramen Lateral: Internal capsule Medial: 3rd ventricle Inferior: Subthalamus & Hypothalamus Caudal: midbrain

Functions of the thalamus Receives and analyses all the sensory information (except olfactory) from the body Having extensive connections with the basal ganglia and the motor cortices, it plays a pivot role in voluntary motor activity Connections with the limbic system makes it important in the control of mood, emotional and sexual behavior, and memory

Internal Organization Thalamus is composed of grey matter, divided by two vertical sheaths of white matter called medullary laminae. External medullary lamina: Located laterally, separates reticular nucleus from the rest of the thalamic mass Contains thalamocortical & corticothalamic fibers Internal medullary lamina Y- shaped band, divides thalamus into Anterior, Medial & Lateral nuclear groups Contains: Fibers connecting thalamic nuclei with one another اسم ورقم المقرر – Course Name and No. 6/15/2019

Nuclear Groups Anterior nuclear group Lateral nuclear group: Divided into: dorsal & ventral tiers Medial nuclear group Intralaminar nuclei Reticular nucleus Midline nuclei اسم ورقم المقرر – Course Name and No. 6/15/2019

Functional Organization The whole of the cerebral cortex receives input from the thalamus اسم ورقم المقرر – Course Name and No. 6/15/2019 2323

Based on their connection with the cerebral cortex, the thalamic nuclei are divided into: Specific nuclei Nonspecific nuclei Specific nuclei: Have well-defined sensory and motor functions Have highly organized point-to-point connection with sensory & motor regions of cerebral cortex Lie within the ventral group of the lateral nuclear group Non-specific Nuclei: Receive less functionally distinct afferent input Connect with wider area of cortex, including associative and limbic regions Include nuclei of the dorsal tier of lateral group, and whole of the anterior and medial group

Ventral anterior Ventral lateral Ventral posterior: Lateral geniculate Lateral Nuclear Group, Ventral Tier Ventral anterior Ventral lateral Ventral posterior: (VPL) (VPM) Lateral geniculate Medial geniculate اسم ورقم المقرر – Course Name and No. 6/15/2019

Ventral Anterior Nucleus Influences motor activity Ipsilateral globus pallidus & substantia nigra Motor cortex Premotor & supplementary motor cortex

Ventral Lateral Nucleus Influences motor activity Ipsilateral globus pallidus & substantia nigra Contralateral dentate nucleus Primary motor cortex Primary motor cortex اسم ورقم المقرر – Course Name and No. 6/15/2019

Ventral Posterior Nucleus Chief sensory relay station General sensory afferents from the contralateral half of the Head & Neck (VPM) and Body (VPL) Primary somatosensory cortex

Lateral Geniculate Body Part of the Visual Pathway Ipsilateral temporal hemiretina Contralateral nasal hemiretina Optic radiation to the primary visual cortex

Medial Geniculate Body Part of the Auditory Pathway Inferior colliculus Auditory radiation to the primary auditory cortex

Lateral Nuclear Group, Dorsal Tier Lateral Dorsal Lateral Posterior Pulvinar اسم ورقم المقرر – Course Name and No. 6/15/2019

Lateral dorsal nucleus Part of Limbic System Hippocamus Cingulate gyrus Lateral posterior nucleus sensory association cortex of parietal lobe Pulvinar: Sensory association cortices of parietal, temporal & occipital lobes

Integrates emotion, thought, and judgment Medial Nuclear Group Integrates emotion, thought, and judgment Mediodorsal nucleus & Nucleus reuniens Hypothalamus, amygdala, other thalamic nuclei, prefrontal cortex Prefrontal cortex & limbic structures

Anterior Nuclear Groups Functionally part of the limbic system. Involved in control of instinctive drives, emotional aspect of behavior and in memory 3 parts: Anteroventral Anteromedial Anterodorsal اسم ورقم المقرر – Course Name and No. 6/15/2019

Intralaminar Nuclei Located within the internal medullary lamina Function as activator of the cerebral cortex Lesions reduce the perception of pain and level of consciousness

Reticular formation, spinothalamic & trigeminothalamic systems Widespread regions of cerebral cortex, caudate & putamen of the basal ganglia

Reticular Nucleus Regulates the activity of thalamus Located between the external medullary lamina & the internal capsule Collaterals of both Thalamocortical & Corticothalamic fibers Other thalamic nuclei اسم ورقم المقرر – Course Name and No. 6/15/2019

Thalamic Lesions Cerebrovascular lesions or tumors of thalamus lead to: Loss of sensation in the contralateral side of face and body followed by distressing discomfort, & burning and diffuse pain in the anesthetic areas (thalamic pain) Thalamic syndrome: Abnormal voluntary movements (chorea or hemiballismus) with hemisensory disturbance

References Clinical Neuroanatomy for Medical Students, Richard S. Snell-6th Edition. Clinical Neuroanatomy and related neuroscience. M.J.T. FitzGerald, Jean Folan-Curran, Fourth Edition. Crossman, AR and Neary D, Neuroanatomy: An Illustrated Colour Text. Haines, DE, Neuroanatomy: An Atlas of Structures, Sections and Systems. Agur, A. M. R. and A. F. Dalley. 2009. Grant’s Atlas of Anatomy, 12th Edition. Lippincott, Williams & Wilkins, New York. Moore, K. L., A. F. Dalley and A. M. E. Agur. 2010. Clinically Oriented Anatomy, 6th Edition. Lippincott, Williams & Wilkins, New York. Sadler, T. W. 2004. Langman’s Medical Embryology, 9th Edition. Lippincott, Williams & Wilkins, New York.

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