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The Fore Brain

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The Fore Brain. Diencephalon. Diencephalon. This represents the central core of the forebrain and is surrounded by the cerebral hemispheres. It is made up of three major paired structures:  The thalamus The hypothalamus The epithalamus. Diencephalon. - PowerPoint PPT Presentation

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The Fore Brain

The Fore BrainDiencephalonDiencephalonThis represents the central core of the forebrain and is surrounded by the cerebral hemispheres. It is made up of three major paired structures:The thalamusThe hypothalamusThe epithalamusDiencephalonThalamus is a bilateral egg shaped nuclei that makes up 80% of the diencephalon. It is the relay station for information coming into the cerebral cortex. ThalamusThe thalamus is a collection of smaller nuclei, each having a functional specialty. All afferent impulses converge on to the thalamus and synapse with at least one of its nuclei. It serves as the gateway to the cerebral cortex.ThalamusAll the sensory fibers except olfaction go through one of the thalamic nuclei.For example the lateral geniculate nuclei receive input from the retina.The thalamus also plays an important role in sleep.

Dorsal nucleiMedialAnteriornucleargroupReticularnucleusVentralanteriorVentrallateralVentralpostero-lateralLateralgeniculatebodyMedialgeniculatebodyPulvinarLateraldorsalLateralposterior(a) The main thalamic nuclei. (The reticular nuclei that cap thethalamus laterally are depicted as curving translucent structures.) Ventral nucleiCopyright 2010 Pearson Education, Inc.6ThalamusDisorders of the Thalamus are usually due to stroke which can lead to the thalamic pain syndrome. HypothalamusHypothalamus lies just below the thalamus and forms the lower walls of the third ventricle. It is the major visceral control center of the body and is the major center for regulating the bodys homeostatic mechanisms. HypothalamusThese functions include:Autonomic control Emotional responseTemperature regulationFood intakeWater balanceSleep wake cyclesEndocrine function

Epithalamus forms the roof of the third ventricle. Its most visible landmark is the pineal gland which secretes melatonin and is involved in the sleep wake cycle.

Brains StemThe brain stem is made up of the midbrain, pons and medulla oblongata. The brain stem produces programmed automatic behaviors necessary for survival.It is similar in make up to the spinal cord and consists of projection fibers.PonsIt is noticeable as a bulge on the anterior surface of the brain stem.

It is made up of conduction tracts.

Dorsally it forms part of the forth ventricle.

Medulla OblongataIt is the most inferior part of the brain stem. As it passes through the foramen magnum, it becomes the spinal column.

Medulla OblongataThe medulla plays an important role in maintaining certain autonomic functions including:Heart rateRespirationSwallowing, sneezing & vomiting

HangingThe medulla oblongata is destroyed when a person is hung, leading to instant death.

Cerebellum

It consists of two hemispheres connected by the vermis. It is highly convoluted and has gyri known as folia.

The cerebellum controls body movements. It is also involved in recognizing the sequence of events so adjustments in limb action can be made. Disorders are described as an ataxia.Figure 12.17a Cerebellum.

(a)Medullaoblongata Flocculonodular lobeFourth ventriclePosteriorlobe Arbor vitaeCerebellarcortex Anterior lobeChoroid plexus PonsCopyright 2010 Pearson Education, Inc.19Functional Brain Systems

Functional brain systems are networks of neurons that incorporate various areas of the brain. Two major systems are the:Limbic systemReticular formationLimbic SystemLimbic System is a groups of structures located on the medial aspect of each cerebral hemisphere and the diencephalon. Its cerebral structures encircle the brain stem.Limbic SystemIt is a complex system with multiple functions. Included in it are the:Septal nucleiCingulate gyrusParahippocampal gyrusDentate gyrus HippocampusAmygdalaThese are all found in the cerebrumLimbic SystemIn the diencephalon:

HypothalamusThalamic nucleiLimbic SystemThe limbic system is our emotional brain.The Amygdala recognizes angry or fearful facial expressions and assesses danger.The cingulate gyrus plays a role in expressing our emotions through gestures and helping us to cope. The hippocampus is involved with long term memoryLimbic SystemThe limbic system is our emotional brain.Dentate gyrus is thought to regulate happiness Parahippocampal gyrus is thought to regulate spatial memory

Frontal eye fieldPrefrontalcortexProcesses emotionsrelated to personaland social interactions(b) Parasagittal view, right hemisphereOlfactory bulbOrbitofrontalcortexOlfactory tractFornixTemporal lobeCorpuscallosumPremotor cortexPrimarymotor cortexCingulategyrusCentral sulcusPrimary somatosensorycortexParietal lobeParieto-occipitalsulcusSomatosensoryassociation cortexOccipitallobeVisualassociationareaCalcarine sulcusParahippocampalgyrusUncusPrimaryolfactory cortexPrimaryvisual cortexPrimary motor cortexMotor association cortexPrimary sensory cortexSensory association cortexMultimodal association cortexCopyright 2010 Pearson Education, Inc.26

It looks like a sea horse?

Corpus callosumSeptum pellucidumOlfactory bulbDiencephalic structuresof the limbic systemAnterior thalamic nuclei (flanking 3rd ventricle)HypothalamusMammillary body Fiber tractsconnecting limbic system structuresFornixAnterior commissureCerebral struc-tures of the limbic systemCingulate gyrusSeptal nucleiAmygdalaHippocampusDentate gyrusParahippocampal gyrusCopyright 2010 Pearson Education, Inc.29Reticular Formation

This system extends from the medulla oblongata, pons and midbrain. The reticular formation is involved in actions such as awaking/sleeping cycle, and filtering incoming stimuli to discriminate irrelevant background stimuli.Reticular Formation

Lesions affecting the reticular formation cause severe alterations in level of consciousness and coma.Figure 12.19 The reticular formation.

VisualimpulsesReticular formationAscending generalsensory tracts(touch, pain, temperature)Descendingmotor projectionsto spinal cordAuditoryimpulsesRadiationsto cerebralcortexCopyright 2010 Pearson Education, Inc.32

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