The Human Brain lectures Brain structures parts functions
- 1. THE BRAIN Mr. Binu Babu Asst. Professor Mrs. Jincy Ealias Asst. Professor
- 2. • The brain is one of the most complex and magnificent organs in the human body. Brain gives us awareness of ourselves and our environment, processing a constant stream of sensory data. • It controls muscle movements, the secretions of glands, and even breathing and internal temperature.
- 4. The Brain: Embryonic development • Embryonic development of the human brain. – Formed by week 4, the neural tube quickly subdivides into the primary brain vesicles, which subsequently form the secondary brain vesicles by week 5. These five vesicles differentiate into the adult brain structures. The adult structures derived from the neural canal.
- 5. • The brain and spinal cord begin as an embryonic structure • called the neural tube. The neural tube forms, its anterior (rostral) end begins to expand and constrictions • appear that mark off the three primary brain vesicles – Prosencephalon or forebrain – Mesencephalon or midbrain – Rhombencephalon or hindbrain • The remaining caudal (“toward the tail”), or posterior, portion of the neural tube becomes the spinal cord.
- 7. Human Brain • The major components of the brain are – The cerebrum – The cerebellum – The brainstem
- 8. Cerebrum • The cerebrum is the largest and most developmentally advanced part of the human brain. It is responsible for several intellectual function, higher functions, including speech, higher emotion, integration of sensory stimuli of all types, initiation of the final common pathways for movement, and fine control of movement.
- 10. Cerebral hemispheres • The cerebrum is divided into a right and a left hemispheres. • The left hemisphere controls the majority of functions on the right side of the body, while the right hemisphere controls most of functions on the left side of the body • The crossing of nerve fibers takes place in injury the brain stem. Thus, to the left cerebral hemisphere produces sensory and motor deficits on the right side, and vice versa.
- 11. Lobes of the Cerebrum Fissures (deep grooves) divide the cerebrum into lobes Cerebrum is composed of pairs of Frontal lobe Parietal lobe Occipital lobe Temporal lobe
- 12. External features: Gyri – Elevated ridges “winding” around the brain. Sulci – Small grooves dividing the gyri – Central Sulcus – Divides the frontal lobe from the parietal lobe. – Lateral sulcus - outlines the flaplike temporal lobe and separates it from the parietal and frontal lobes. Fissures – Deep grooves, generally dividing large regions/lobes of the brain • Transverse Fissure – Separates the cerebrum from the cerebellum. • Longitudinal Fissure – Divides the two cerebral hemispheres • Sylvian/Lateral Fissure – Divides the temporal lobe from the frontal and parietal lobes
- 13. Gyrus
- 14. Sulcus
- 15. Surfaces
- 16. Boarders of cerebral hemispheres
- 17. Poles of Brain
- 18. Regions of cerebral hemisphere Cerebral hemisphere has three basic regions: 1. A superficial cerebral cortex of gray matter, which looks gray in fresh brain tissue 2. Internal white matter 3. Basal nuclei, islands of gray matter situated deep within the white matter
- 19. Grey matter • It is a major component of the central nervous consisting neuronal system of bodies, cell neuropil (dendrites and myelinat ed as well unmyelinated as axons) glial cells (astrocytes and oligodendrocytes) synapses and capillaries.
- 20. Grey matter in the spinal cord • Grey matter in the spinal cord is known as the grey column which travels down the spinal cord distributed in three grey columns that are presented in an "H" shape. • The forward-facing column is the anterior grey column • The rear-facing one is the posterior grey column • The interlinking one is the lateral grey column. • The grey matter on the left and right side is connected by the grey commissure. • The grey matter in the spinal cord consists of interneurons, as well as cell bodies.
- 21. Cerebral cortex • The cerebral cortex is the “executive suite” of the nervous system. • It enables us to be aware of ourselves and our sensations, to communicate, remember, understand and initiate voluntary movements. • The cerebral cortex is composed of gray matter: neuron cell bodies, dendrites, associated glia and blood vessels, but no fiber tracts. • It contains billions of neurons arranged in six layers. • 2–4 mm (about 1/8 inch) thick • It accounts for roughly 40% of total brain mass.
- 23. • Based on the differences in lamination the cerebral cortex can be classified into two parts – The large area of neocortex – The smaller area of allocortex
- 24. Neocortex • The neocortex (also known as the isocortex or neopallium) is the part of the mature cerebral cortex with six distinct layers.
- 27. Allocortex • The allocortex is the part of the cerebral cortex with less than six layers and has three regions, – The paleocortex with three cortical laminae – The archicortex which has four or five cortical laminae – The periallocortex – a transitional zone between the neocortex and the allocortex
- 28. White matter • The white matter is a network of fibers that enables regions of the brain to communicate with each other.
- 29. • White matter consists largely of myelinated fibers bundled into large tracts. These fibers and tracts are classified according to the direction in which they run as – Association Fibers – Projection Fibers – Commissural Fibers
- 31. • Association fibers: Connects different cortical areas of the same hemisphere to one another. – Eg:- superior longitudinal fasciculus • Projection fibers: Connects cerebral cortex to other parts of CNS like brain stem and spinal cord. – Eg: corona Radiata,internal capsule • Commissural fibers: Connects the corresponding parts of two hemispheres
- 32. White Matter of Cerebral hemisphere • Association tracts (fibers)- different regions in cerebral cortex. • Projection tracts (fibers)- cerebral cortex other masses of gray matter. • Commissures fibers - R L.
- 33. Internal capsule capsule is between the • Internal located lentiform laterally the thalamus caudate nucleus and and nucleus medially. • In a horizontal section of cerebral hemisphere, the internal capsule appears as a V-shaped bundle of fibers with the apex directed medially.
- 35. The internal capsule is divided into five parts. – Anterior limb: part of the internal capsule that lies between the anterior part of lentiform nucleus laterally and head of caudate nucleus medially. – Genu: It is the bend between the anterior and posterior limb of internal capsule. The concavity of the bend faces laterally. – Posterior limb: is that part of internal capsule which lies between the thalamus medially and the posterior part of lentiform nucleus laterally. – Retrolentiform part: is located posterior to the lentiform nucleus. – Sublentiform part: is located inferior to the lentiform nucleus.
- 37. Internal capsule contains both the motor fibers and sensory fibers Motor/Descending Fibers in Internal capsule • Corticopontine :originate from all the lobes of cerebrum and relay in ipsilateral pontine nuclei. • Pyramidal fibers: – Corticospinal: originate mainly in primary motor cortex and relay in contralateral anterior horn of spinal cord. – Corticonuclear: originate mainly in primary motor cortex and relay usually in contralateral (some bilateral) motor nuclei of cranial nerves. • Extrapyramidal fibersCoticorubral, corticostriate, corticonigral fibers etc.: these fibers originate in the motor and premotor areas of cerebral cortex relay in subcortical nuclei viz. red nucleus, corpus stiatum and substantia nigra respectively.
- 38. Internal Capsule - Sensory/Ascending Fibers • Thalmocortical and corticothalamic fibers: The thalamocortical fibers are the 3rd order neurons of ascending pathways. • The four thalamic radiation bands are: – Anterior thalamic radiation: Pass anteriorly to connect the anterior and dorsomedial nucleus of thalamus to the frontal lobe. – Superior thalamic radiation: Pass superiorly to connect the ventral tier of nucleus of thalamus to primary and premotor areas of frontal lobe and sensory areas of parietal lobe. – Posterior thalamic radiation (Optic radiation): pass posteriorly to connect the lateral geniculate body to the primary visual cortex. – Inferior thalamic radiation (Auditory radiation): pass inferiorly and laterally to connect the medial geniculate body to the primary auditory area.
- 40. Arrangement of Descending (Motor) and Ascending (Sensory) Fibers Anterior limb: Motor • Frontopontine fibers Sensory • Anterior thalamic radiation Genu Motor • Frontopontine fibers, • Corticonuclear • Corticospinal fibers for head and neck Sensory • Superior thalamic radiation Retorlentiform part Motor • Parietopontine • Occipitopontine fibers Sensory • Posterior thalamic ( Optic) radiation Sublentiform part Motor • Parietopontine • Occipitopontine fibers Sensory • Inferior thalamic ( Auditory) radiation
- 41. Basal Nuclei • Deep within the cerebral white matter is the third basic region of each hemisphere, a group of subcortical nuclei called the basal nuclei or basal ganglia. • Basal nuclei include the – Caudate nucleus – Putamen – Globus pallidus • The comma-shaped caudate nucleus arches superiorly over the diencephalon. Together with the putamen, it forms the striatum
- 43. • The putamen and globus pallidus together form a lens-shaped mass, sometimes called the lentiform nucleus. • The basal nuclei are functionally associated with the subthalamic nuclei of the diencephalon and the substantia nigra of the midbrain. • The basal nuclei receive input from the entire cerebral cortex, as well as from other subcortical nuclei
- 45. The substantia nigra • It is a brain structure located midbrain, in the and forms part of the basal ganglia. It is the largest nucleus in the midbrain. also plays • The substantia nigra an important role in reward and addiction.
- 46. Amygdaloid nucleus • A small oval structure in the temporal lobe of the brain that is closely connected to the hypothalamus, the hippocampus, and the cingulate gyrus. • The amygdaloid nucleus is part of the olfactory and limbic systems and plays a role in the sense of smell, motivation, and emotional behavior.
- 49. Ventricles • The ventricles are structures that produce cerebrospinal fluid, and transport it around the cranial cavity. They are lined by ependymal cells, which form a structure called the choroid plexus. It is within the choroid plexus that CSF is produced. • Embryologically, the ventricular system is derived from the lumen of the neural tube. • There are four ventricles; right and left lateral ventricles, third ventricle and fourth ventricle.
- 50. Lateral Ventricles • The left and right lateral ventricles are located within their respective hemispheres of the cerebrum. They have ‘horns’ which project into the frontal, occipital and temporal lobes. • The paired lateral ventricles, one deep within each cerebral hemisphere, are large C-shaped chambers that reflect the pattern of cerebral growth. • Anteriorly, the lateral ventricles lie close together, separated only by a thin median membrane called the septum pellucidum. • The volume of the lateral ventricles increases with age.
- 51. Third Ventricle • The lateral ventricles are connected to the third ventricle by the foramen of Monro. The third ventricle is situated in between the right and the left thalamus. The anterior surface of the ventricle contains two protrusions: – Supra-optic recess – located above the optic chiasm. – Infundibular recess – located above the optic stalk.
- 52. Fourth Ventricle • The fourth ventricle is the last in the system – it receives CSF from the third ventricle via the cerebral aqueduct. It lies within the brainstem, at the junction between the pons and medulla oblongata. From the 4th ventricle, the fluid drains into two places: – Central spinal canal – Baths the spinal cord – Subarachnoid cisterns – Baths the brain, between arachnoid mater and pia mater. Here the CSF is reabsorbed back into the circulation.
- 54. CORPUS CALLOSUM • It is the largest collection of commissural fibers of the cerebrum. • It located in the floor of the median longitudinal fissure and connects two cerebral hemisphere except lower and anterior part of the temporal lobe. • Corpus callosum closely related to lateral ventricle.
- 55. PARTS OF CORPUS CALLOSUM • 4 parts • Anterior end called genu • Central part is the Trunk • Posterior bulbous part called Splenium • Rostrum is the prologation from the upper part of the genu to the upper end of the lamina terminals
- 56. • Rostrum connects orbital surfaces of frontal lobe. • Forceps minor is made up of fibers of genu that connects the 2 frontal lobes. • Forceps major is made up of fibers of splenium that connects the 2 occipital lobes. • The tapetum formed by some fibers of the trunk and splenium of corpus callosum FIBERS OF CORPUS CALLOSUM FUNCTION OF CORPUS CALLOSUM COORDINATES THE ACTIVITIES OF THE TWO CEREBRAL HEMISPHERES
- 57. Diencephalon • The diencephalon consists largely of three paired structures:- the thalamus, hypothalamus, and epithalamus. • These gray matter areas collectively enclose the third ventricle
- 58. Thalamus • The thalamus consists of bilateral egg-shaped nuclei, which form the superolateral walls of the third ventricle. • The thalamus is the relay station for information coming into the cerebral cortex. • Large mass of grey matter, lies immediately lateral to third ventricle Two poles Anterior pole(or end) Lies behind the interventricular foramen Posterior pole(or end also called pulvinar lies just above and lateral to superior colliculus.
- 59. Two thalami on each side of slit like cavity of 3rd ventricle 3 cms length x 1.5 cms breadth Long axis 300 oblique to midline. Interthalamic adhesion
- 60. Superior surface Superior surface • The superior (dorsal) surface of the thalamus is covered by a thin layer of white matter, the stratum zonale • It extends laterally and forms the roof of the third ventricle • More laterally it forms part of the floor of the lateral ventricle. • Related laterally to caudate nucleus
- 61. Medial surface The medial surface • The medial surface of the thalamus is the superior (dorsal) part of the lateral wall of the third ventricle. • It is usually connected to the contralateral thalamus by an interthalamic adhesion behind the interventricular foramina. • The thalamus is continuous with the midbrain tegmentum, the subthalamus and the hypothalamus
- 62. Inferior surface of thalamus • Inferior surface of the tegmentum is related to hypothalamus anteriorly and to ventral thalamus posteriorly. • The ventral thalamus seperates the thalamus from tegmentum of midbrain.
- 64. Internal structure of the thalamus • Thalamus consists of mainly of grey matter • Superior surface is covered by a thin layer of white matter called stratum zonale • Lateral surface is covered by a similar layer called externalmedullary layer. • Internally, the thalamus is divided into anterior, medial and lateral nuclear groups by a vertical Y-shaped sheet of white matter, the internal medullary lamina • Nuclei of the anterior part. • Anterior nucleus. • Nuclei in the medial part • Largest nuclei among them medial dorsal nucleus.
- 65. Blood supply of thalamus • Perforating branches of the posterior cerebral artery • Posteromedial group (thalamo - perforating arteries) supply medial and anterior part. • Posterolateral group (thalamo-geniculate branches) supply • posterior and lateral part of thalamus. • Also recieves branches from posterior communicating anterior choroidal,posterior choroidal and middle cerebral artery.
- 66. Hypothalamus • Hypothalamus which lies below the thalamus. It the floor and lower parts of the lateral walls of the 3rd ventricle. • The hypothalamus caps the brain stem and forms the inferolateral walls of the third ventricle. • The hypothalamus extends from the optic chiasma (crossover point of the optic nerves) to the posterior margin of the mammillary bodies. • The mammillary bodies paired pea like nuclei that bulge anteriorly from the hypothalamus, are relay stations in the olfactory pathways.
- 67. • The hypothalamus is the main visceral control center of the body. • Small in size weighing only4gm, forms only 0.3 % of total brain mass. • Mainly acts through 3 systems. a. Autonomous nervous system b. Endocrine system c. The limbic system
- 68. Boundaries • Anteriory - lamina terminalis • Posteriorly -subthalamus • Inferiorly - structures in the floor of the 3rd ventricle.ie, tuber cinereum, infundibulam and mammillary bodies. • Superiorly – thalamus • Lateral boundary - internal capsule. • Medially - bounded by the cavity of 3rd ventricle.
- 69. Anteroposteriorly divided into • Preoptic region - area adjoining the lamina terminalis. • Supra optic region - above the optic chiasma • Tubreal region includes the tuber cinereum,infundibulam and area around it. • Mammillary region - includes the mammillary bodies and area around it.
- 70. Hypothalamic nuclei • Hypothalamus is made up of numerous small nuclear masses called hypothalamic nucleus. • They are divided into groups according to their regional distribution and they differ in their functions also.
- 71. The subthalamic nuclei • The subthalamic nuclei are small paired structures that are part of the functional basal ganglia. • They are located ventral to the thalamus, dorsal to the substantia nigra and medial to the internal capsule. • The subthalamic nucleus receives its main input from the lateral pallidum (external segment of the globus pallidus). Excitatory, glutamatergic inputs come from the cerebral cortex.
- 73. Region Nucleus Functions Preotic region Preoptic nucleus Contains the sexually dimorphic nucleus, which releases GnRH Supraoptic region Supra optic nucleus Vassopressin release Anterior nucleus Thermo regulation, sweating Paraventricular nucleus TRH, CRH Corticotropin & Oxytocin release Tuberal region Arcuate (infundibular nucleus) GHRH, feeding and Dopamine release Ventromedial nucleus Satiety centre Dorsomedial nucleus Controls BP, HR and GI stimulation
- 76. Autonomic control of body • Hypothalamus controls autonomic functions of body fibres including cardiac, through sympathetic as well as parasympathetic and respiratory activity, vasomotor tone of blood vessels ,digestive process .
- 77. Part of limbic system The limbic system is a complex set of structures that lies on both sides of the thalamus, just under the cerebrum. It includes the hypothalamus, the hippocampus, the amygdala, and several other nearby areas. It appears to be primarily responsible for our emotional life, and has imp. Role in formation of memories.
- 78. Regulation of sleep • Ventro lateral preoptic area
- 79. Regulation of Food & water intake • The extreme lateral part of the ventromedial nucleus of the hypothalamus is responsible for the control of food intake. Stimulation of this area causes increased food intake. Bilateral lesion of this area causes complete cessation of food intake. •
- 80. Temperature regulation • The cold and heat sensors located in the hypothalamus respond appropriately to maintain the body temperature at optimum level in diverse conditions. • The ant. Portion of hypothalamus prevents the rise in body temperature while, • Posterior portion promotes heat conservation and heat production.
- 81. Circadian rhythm • Hypothalamus regulates the cyclic activities of the body ,viz sleeping and waking cycle but itself affected by diurnal rhythm. • The circadian rhythm for many body functions is of about 24 hours.
- 82. Sexual dimorphism • Several hypothalamic nuclei are sexually dimorphic i.e. there are clear differences in both structure and function between males and females.
- 83. Other functions • EMOTIONAL EXPRESSION:_ Hypothalamus regulates the expression of emotions through its control over the ANS (laughting,crying,sweating,cryi ng etc.) • Fear processing:_The medial zone of hypothalamus is part of a circuitry that controls motivated behaviors, like defensive behaviors.
- 84. APPLIED ANATOMY • Lesions in the hypothalamus will cause one of the following syndromes; • Obesity • Diabetes insipidus • Sexual disturbance • Disturbance in sleep: somnolence,narcolepsy • Hyperglycemia and glycosuria • Diencepahlic autonomic epilepsy : characterized by flushing,sweating,salivation,lacrimation,tacycardia,r etardation of respiartory rate,unconsciousness etc.
- 85. Epithalamus • The most dorsal portion of the diencephalon • The epithalamus forms the roof of the third ventricle. Extending from its posterior border and visible externally is the pineal gland or body. • The pineal gland secretes the hormone melatonin and, along with hypothalamic nuclei, helps regulate the sleep-wake cycle. • The posterior commissure forms the caudal border of the epithalamus.
- 86. The brain stem • The brain stem regions are – Midbrain – Pons – Medulla oblongata
- 87. Midbrain • Connects the pons and cerebellum with the forebrain. • It is about 0.8 inch in length • The midbrain is traversed by a narrow channel called cerebral aqueduct filled with CSF.
- 90. Anterior Surface ⚫Anteriorly, it presents two large bundles of fibers, one on each side of the midline, called crus cerebri. ⚫The oculomotor nerve emerges from the medial aspect of the crus of the same side ⚫The crus cerebri bounds the interpeduncular fossa on either side.
- 91. Posterior Surface ⚫ Posteriorly, the midbrain presents four rounded swellings called colliculi- One Superior and inferior colliculi one on each side. ⚫ Each colliculus is laterally related to a ridge called brachium. ⚫ Superior and inferior brachium arises from respective colliculi ⚫ Superior brachium connects the superior colliculus to lateral geniculate body. ⚫ Inferior brachium connects the inferior colluculus to medial geniculate body ⚫ In the midline below the inferior colliculus, the trochlear nerve emerges which then winds round the side of the midbrain to reach its ventral aspect.
- 92. Lateral view
- 93. Structure of Midbrain • The midbrain comprises two lateral halves called the Cerebral peduncles; • The Cerebral peduncles are separated in to two parts by a pigmented band of gray matter called substantia nigra – Anterior part - crus cerebri – Posterior part - tegmentum The central narrow cavity is called the cerebral aqueduct or aqueduct of Sylvius, which connects the 3rd and 4th ventricles. ⚫The tectum is the part of the midbrain posterior to the cerebral aqueduct; it has four small surface swellings referred to previously; these are two superior and two inferior colliculi.
- 95. Blood Supply Artery – • posterior cerebral artery • superior cerebellar artery • basilar artery Veins – • Drained by basal or great cerebral veins
- 96. PONS • It is situated anteriorly to the cerebellum measuring about 1 inch in length. • Connects the medulla oblongata to the midbrain. • Its also connects two cerebellar hemispheres and its name comes from this bridge like appearance.
- 98. Anterior surface of Pons Pons has a convex anterior surface marked by transversely running fibers which laterally form a bundle called middle cerebellar peduncle. Main Features: • The trigeminal nerve emerges from the anterior surface at its junction with middle cerebellar peduncle. • Presents a basilar sulcus in the midline which lodges basilar artery • In the groove between Pons and the medulla oblongata, there emerge, from medial to lateral, abducent, facial and vestibulocochlear nerves.
- 100. Posterior Surface • Posterior surface contains median sulcus which is bounded by medial eminence on both sides. • Inferior end of medial eminence is slightly expanded to form facial colliculus, which is produced by facial nerve root. • The upper end of sulcus limitans presents a bluish-gray coloration called substantia ferruginosa.
- 101. • Respiratory nuclei: • Apneustic & pneumotaxic centers work with the medulla to maintain respiratory rhythm • Nuclei & tracts that process and relay info to/from the cerebellum • Ascending, descending, and transverse tracts that interconnect other portions of the CNS
- 102. Structure of Pons Posterior Part • Tegmentum Anterior part • Basis pontis traversed by running fibers of Trapezoid body.
- 103. Blood Supply
- 104. APPLIED ANATOMY • Unilateral lesions in the lower part of the pons results in paralysis of facial nerve in the same side and limbs in the opposite side.
- 105. Medulla Oblangata • The medulla oblongata (medulla) is one of the three regions that make up the brainstem. It is the most inferior of the three and is continuous above with the pons and below with the spinal cord. The medulla houses essential ascending and descending nerve tracts as well as brainstem nuclei
- 106. • Relays ascending sensory pathway impulses from skin and proprioceptors through nuclei cuneatus and gracilis – Contains visceral nuclei controlling heart rate, blood vessel diameter, respiratory rate, vomiting, coughing, etc. – Relays sensory information to the cerebellum through inferior olivary nuclei – Contains nuclei of cranial nerves VIII–XII – Contains projection fibers – Site of decussation of pyramids
- 108. Structures of the Medulla Oblongata • Flanking the midline on the medulla’s ventral aspect are two longitudinal ridges called pyramids, formed by the large pyramidal (corticospinal) tracts descending from the motor cortex most of these fibers cross over to the osite side before continuing into the spinal cord. • This crossover point is called the decussation of the pyramids
- 109. • The olives are oval swellings. These swellings are caused mainly by the wavy folds of gray matter of the underlying inferior olivary nuclei. These nuclei relay sensory information stretch in muscles on the and joints to degree of the cerebellum.
- 110. External Anatomy of the Medulla • The superior margin of the medulla is located at the junction between the medulla and pons • The inferior margin is marked by the origin of the first pair of cervical spinal nerves. This occurs just as the medulla exits the skull through the foramen magnum. • Length is about 3 cm, width is about 2 cm • Surfaces shows series of fissures – Anterior median fissure – Posterior median fissure
- 111. Anterior median fissure Pyramid Anterolateral fissure Olive
- 112. Anterior Surface • There are several structures visible on the anterior surface of the medulla – namely the three fissures/sulci, the pyramids, the olives, and five cranial nerves. – Anterior median fissure, which is continuous along the length of the spinal cord. Two sulci are visible – the ventrolateral sulcus and the posterolateral sulcus. – The pyramids are paired swellings found between the anterior median fissure and the ventrolateral sulcus. – The olives are another pair of swellings located laterally to the pyramids – between the ventrolateral and posterolateral sulci. • Arising from the junction between the pons and medulla is the abducens nerve (CN VI). Extending out of the ventrolateral sulcus is the hypoglossal nerve (CN XII). In the posteriolateral sulcus, three more cranial nerves join the medulla (CN IX, CN X, and CN XI).
- 114. Ventral surface of medulla oblongata contains Pyramid Olive • Pyramid • It is an elevation between anterior median and anterolateral sulcus • Formed due to decussation of corticospinal fibres. Olive • Oval swelling between anterolateral posterolateral sulcus,half an inch long • Produced by large mass of gray matter called inferior olivary nucleus
- 115. The posterior surface • The posterior surface has a midline structure – the posterior median sulcus – which is continuous below as the posterior median sulcus of the spinal cord. Above, the sulcus ends at the point in which the fourth ventricle develops. • As we move lateral from the midline, the fasciculus gracilis and fasciculus cuneatus are seen, separated by the posterior intermediate sulcus.
- 117. Internal Anatomy of the Medulla • The internal structures of the medulla must be viewed in cross section to understand the layout. Three levels of the medulla are typically discussed (inferior – superior): – Level of decussation of the pyramids – Level of decussation of the medial lemnisci – Level of the olives
- 118. • The medulla contains gray matter, while the outer portions consist of white matter. The posterior white matter contains the fasiculus gracilis and the more lateral fasiculus cuneatus. Corresponding portions of gray matter extend to these regions and are the nucleus gracilis and nucleus cuneatus associated with a tract called the medial lemniscus.
- 120. Functions of the Medulla Oblongata • The small size of the medulla belies its crucial role as an autonomic reflex center involved in maintaining body homeostasis. The medulla contains these important functional groups of visceral motor nuclei: Cardiovascular center. Adjusts the force and rate of heart contraction to meet the body’s needs, and the vasomotor center, which changes blood vessel diameter to regulate blood pressure. Respiratory centers. These generate the respiratory rhythm and control the rate and depth of breathing. Various other centers. Additional centers regulate such activities as vomiting, hiccuping, swallowing, coughing, and sneezing
- 121. The Limbic System • The limbic system is a group of structures located on the medial aspect of each cerebral hemisphere and diencephalon. • These functional system: – Includes cerebral and diencephalon structures (e.g., hypothalamus and anterior thalamic nuclei) – Mediates emotional response – Involved in memory processing
- 123. • The limbic system is our emotional, or affective (feelings), brain. • Amygdaloid body is critical for responding to perceived threats such as angry or fearful facial expressions with fear or aggression. • The cingulate gyrus plays a role in expressing our emotions through gestures and in resolving mental conflicts when we are frustrated. • Rhinencephalon helps the brain in responds to odors.
- 124. Reticular Formation • The reticular formation is a set of interconnected nuclei that are located throughout the brainstem. The reticular formation is not anatomically well defined because it includes neurons located in diverse parts of the brain. • A functional system: – Maintains cerebral cortical alertness (reticular activating system) – Filters out repetitive stimuli – Helps regulate skeletal and visceral muscle activity
- 125. Reticular Activating System • The neurons of the part of the reticular formation known as the reticular activating system (RAS). • Reticular activating system send a continuous stream of impulses to the cerebral cortex, keeping the cortex alert and conscious and enhancing its excitability. Impulses from all the great ascending sensory tracts synapse with RAS neurons, keeping them active and enhancing their arousing effect on the cerebrum.
- 126. • The reticular formation is divided into three columns: – Raphe nuclei (median), – Magnocellular red nucleus (medial zone), – Parvocellular reticular nucleus(lateral zone).
- 127. • The raphe nuclei is the place of synthesis of the neurotransmitter serotonin, which plays an important role in mood regulation. • The magnocellular red nucleus is involved in motor coordination. • The parvocellular nucleus regulates exhalation.
- 128. THANK YOU