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INTERNAL CAPSULE

INTERNAL CAPSULE. Reticular Formation. Objectives. 1.Describe the structure of the internal capsule 2.Identify different areas of the internal capsule 3.Describe the structure and distribution of reticular formation 4. List the afferent and efferent projections

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INTERNAL CAPSULE

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  1. INTERNAL CAPSULE Reticular Formation

  2. Objectives • 1.Describe the structure of the internal capsule • 2.Identify different areas of the internal capsule • 3.Describe the structure and distribution of reticular formation • 4. List the afferent and efferent projections • 5. List the functions of reticular formation

  3. INTERNAL CAPSULE • It is a V-shaped band of projection fibres • It is divided into: • Anterior limb • Genu • Posterior limb • Retrolenticularpart • Sublentiform

  4. INTERNAL CAPSULE Anterior limb: • Site:between head of caudate nucleus & lentiform nucleus • Contents: • Fibres from anterior nuclear group of thalamus to cingulate gyrus(Thalamocortical) • Fibres from medial nuclear group of thalamus to prefrontal cortex (Thalamocortical) • Frontopontinefibres

  5. INTERNAL CAPSULE Genu: • Site: between head of caudate nucleus & thalamus • Contents: • Part of superior thalamic radiation • Frontopontine • Corticonuclear

  6. INTERNAL CAPSULE Posterior limb: • Site: between thalamus & lentiform nucleus • Contents: • Corticospinalfibres (Ant. Two 3rds) • Fibers from ventral posterior nucleus of thalamus to postcentralgyrus(Thalamocortical) • Fibers from ventral anterior & ventral lateral nuclei of thalamus to motor regions of frontal lobes (Thalamocortical) • Temporopontine & parietopontinefibres

  7. INTERNAL CAPSULE Retrolenticular part: • Site: behind lentiform nucleus • Contents: • Fibers from medial geniculate body of thalamus to auditory cortex • Fibers from lateral geniculate body of thalamus to visual cortex • Parieto- temporo- & occipitopontinefibres

  8. D-Retrolenticular(RL) & Sublenticular (SL) partscontain optic radiations & auditory radiations respectively. A B A C D

  9. ANTERIOR LIMB • Anterior thalamic radiation • Frontopontine • GENU • Part of superior thalamic radiation • Frontopontine • Corticonuclear • RETROLENTIFORM • Post thalamic radiation - Optic radiation • Parieto-pontine • Temporo-pontine • SUBLENTIFORM • Inf thalamic radiation - Auditory radiation • POSTERIOR LIMB • Superior thalamic radiation • Frontopontine • Corticonuclear (corticobulbar) • Corticospinal • Extrapyrimidal Thalamocortical fibres Corticopontine fibres Corticonuclear & corticospinal fibres

  10. Brain Stem Reticular Formation • Reticular = “netlike” • Loosely defined nuclei and tracts • Extends through the central part of the medulla, pons, and midbrain • Intimately associated with • Ascending/descending pathways • Cranial nerves/nuclei • Input and output to virtually all parts of the CNS

  11. Reticular Formation RF is formed of 2 types of cells • 1- Sensory neurons : discharge impulses to motor neurons • 2- Motor neurons : receive impulses from sensory neurons. The axons of the motor neurons divide into: • a- descending branch : ventral and lateral reticulospinal tracts : spinal cord • b- ascending branch : reticular activating system (RAS) to cerebral cortex

  12. RETICULAR FORMATION RF receives impulses from: 1- All sensory pathways (general or special sensations) 2- Cerebral cortex 3- cerebellum 4- Basal ganglia 5- Vestibular nuclei 6- Red nuclei

  13. RETICULAR FORMATION The reticular nuclei are divided into two groups: 1- Pontine (excitatory) reticular system 2- Medullary (inhibitory) reticular system

  14. Reticular Formation • Connectivity is extremely complex • Many different types of neurons: • Innervate multiple levels of the spinal cord • Numerous ascending and descending collaterals • Some have bifurcating collaterals that do both • Many have large dendritic fields that traverse multiple levels of the brain stem

  15. Vestibulospinal and reticulospinal tracts descending in the spinal cord to excite (solid lines) or inhibit (dashed lines) the anterior motor neurons that control the body’s axial musculature

  16. Reticular Formation • Can be roughly divided into three longitudinal zones • Midline - Raphe Nuclei • Medial Zone - Long ascending and descending projections • Lateral Zone - Cranial nerve reflexes and visceral functions

  17. Reticular Formation Functions • I. Participates in control of movement through connections with both the spinal cord and cerebellum • Two reticulospinal tracts originate in the rostral pontine and medullary reticular formation • Major alternate route by which spinal neurons are controlled • Regulate sensitivity of spinal reflex arcs • Inhibition of flexor reflexes • Mediates some complex “behavioral” reflexes • Yawning • Stretching • Babies suckling • Some interconnectivity with cerebellar motor control circuitry

  18. Reticular Formation Functions • II. Modulates transmission of information in pain pathways • Spinomesencephalic fibers bring information about noxious stimuli to the periaqueductal grey • Periaqueductal grey also receives input from the hypothalamus and cortex about behavioral state • Efferentsfrom the periaqueductal grey project to one of the raphe nuclei and medullary reticular formation • These project to the spinal cord and can suppress transmission of pain information in the spinothalamic tract

  19. Reticular Formation Functions Cortex Thalamus Hypothal Spinothalamic Tract Periaqueductal Grey Raphe Spinal Cord Level

  20. Clinical Correlation • Pain Management • Periaqueductal grey has high concentration of opiate receptors • Natural pain modulation relies on endogenous opiates • Exogenous opiates are used for pain management

  21. Reticular Formation Functions • III. Autonomic reflex circuitry Reticular formation receives diverse input related to environmental changes Also receives input from hypothalamus related to autonomic regulation Output to : • cranial nerve nuclei • Intermediolateral cell column of the spinal cord Involved in: • Breathing • Heart rate • Blood pressure

  22. Reticular Formation Functions • IV. Involved in control of arousal and consciousness • Input from multiple modalities (including pain) • Ascending pathways from RF project to thalamus, cortex, and other structures. • Thalamus is important in maintaining arousal and “cortical tone” • This system is loosely defined, but referred to as the Ascending Reticular Activating System (ARAS) • ARAS is a functional system, not an anatomically distinct structure

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