GENERALITIES OF THE ADULT BRAIN

Size: px

Start display at page:

Download "GENERALITIES OF THE ADULT BRAIN"

Horace Burns
6 years ago
Views:

1 GENERALITIES OF THE ADULT BRAIN Average weight = kg o 2-3% of body weight Total intracranial volume = 1,700 ml o Brain = 1,400 ml (80%) o Blood = 150 ml (10%) o CSF = 150 ml (10%) Number of neurons = 100 Billion o Neocortical neurons of a Female = 19.3 Billion o Neocortical neurons of a Male = 22.8 Billion Number of glial cells = times greater than the number of neurons Total number of synapses = Trillion Length of myelinated fibers = 150, ,000 km Total surface area = 2.5 ft 2 Note: The brain is supratentorial It is above the tentorium cerebelli a fold of dura that inserts on top of the cerebellum Note: Diencephalon + Telencephalon = Encephalon (the brain) EVOLUTION, EMBRYOLOGY, AND HISTOLOGY OF THE TRIUNE BRAIN The Triune Brain Theory is a model of the evolution of the vertebrate forebrain and behavior as proposed by Dr. Paul D. MacLean. The triune brain consists of the following: Reptilian cortex (Lizard Brain/Dinosaur Brain) Instinctual Brain Paleomammalian cortex (The Limbic System) Emotional/Feeling Brain Neomammalian cortex (The neocortex, gyri) Rational/Thinking Brain Evolutionary explanation of the Triune Brain: The older inner tube containing the limbic lobe, amygdala, basal forebrain, olfactory structures, hypothalamus, and thalamic nuclei function mostly about Affection such as: o Internal regulation o Consciousness o Emotions o Motivation The newer outer tube containing the neocortex, basal ganglia, thalamic connections function in Cognition: o Higher cognition o Language o Motor programming o Sensory processing (visual, somatosensory, auditory) There are four processes that drive the maturation of the nervous system: DPMM (mnemonic: Di Pa Mature? Mag-isip!) DETERMINATION o Ectodermal involvement (neuron pre-cursor) Same ectodermal involvement to develop the skin o Neural induction by RAsturiano UST-FMS A-2019: #TheElusiveDoktora Page 1 of 13

2 PROLIFERATION o Driving force: Mitosis MIGRATION o After cell division, neurons migrate to their appropriate final destination and settle there The migration is regulated and directed by the radial glial cells MATURATION o Once neurons are settled, the neurons establish interconnections through dendritic/axonal connections o Myelination is the last step towards complete maturation Completed at 2 years old Note: The Cerebral Cortex is derived from the telencephalic vesicle The development is due to active migration of cells from the mantle layer (middle) o It outgrew the white matter, therefore, in the cortex: Outer gray Inner white The cortical mass adapts to limited cranium space o And the adaptation is exhibited by the convolutions as a result of the overexpansion of nervous tissue within the limited intracranial space Types of Cortices o Isocortex (Neocortex) Homogenetic cortex Has 6 cytoarchitectonic layers 1 1 st layer Molecular Layer a AKA Plexiform Layer b Few, small cells and numerous dendrites and axons; interwoven; parallel to surface c Cells here exhibit paucity due to the Horizontal Cells of Cajal which disappeared in the neonatal era 2 2 nd layer External Granular Layer 3 3 rd layer External Pyramidal Layer a Layers 2 and 3 contain small-medium pyramidal cells i Conical/Pear-shaped tips directed toward surface 4 4 th layer Internal Granular Layer (Stellate) a Well demarcated, small, compact, multipolar granule cells: chief receptive center for incoming impulses 5 5 th layer Internal Pyramidal Layer a Layer with the biggest cells in pre-central gyrus, chief discharge center for efferent impulses i Ex: Giant Pyramidal Cells of Betz 6 6 th layer Multiform layer (Fusiform) a Long axis perpendicular tosurface; contribute to efferents 7 Mnemonic: MoL-EG-EP-IG-IP-Mul Also has 6 myeloarchitectonic layers Deals with motor and sensory control by RAsturiano UST-FMS A-2019: #TheElusiveDoktora Page 2 of 13

3 More evolved The type of cortex seen in most mammalian brains o Allocortex Heterogenetic cortex Has 3 layers More primitive Can receive olfactory influences Seen in lower animals (rats) Two types of Allocortex: 1 Paleocortex a Has an entorhinal cortex b Has a primary olfactory cortex 2 Archicortex a Has a hippocampal formation seat of recent memory o Mesocortex Vary from 4-5 layers Cortical White Matter o It is a Homogenous mass o It below the cortex o It envelopes the: Corpus striatum Ventricular spaces o Function: Pathways for information TO and FROM the cortex o Types of Fibers: Association Fibers 1 Interconnection areas within the hemisphere 2 Types: a Short Association Fibers i Connect adjacent gyri b Long Association Fibers i Connect distant areas such as: Cingulum Uncinate Commissural Fibers 1 Interconnect corresponding structures between the 2 hemispheres a Corpus Callosum i Largest; superior to diencephalon ii Roofs the lateral ventricles iii Parts (rostrocaudal) Rostrum Genu rostrally interconnect frontal lobes via the minor forceps Body Splenium caudally interconnect occipital lobs via the major forceps by RAsturiano UST-FMS A-2019: #TheElusiveDoktora Page 3 of 13

4 b Anterior Commissure i Caudal to rostrum (frontal/temporal lobes) c Hippocampal Commissure i Inferior to Splenium (hippocampus) d Posterior Commissure i Connects caudal diencephalon ii Crosses base of the pineal gland posterior to the cerebral aqueduct e Habenular Commissure i Connects caudal diencephalon (habenular nuclei) Projection Fibers 1 Interconnects distal areas 2 Type of connection: a Corticopetal i From outside of brain to cerebral cortex b Corticofugal i From cerebral cortex to outside of brain 3 Contains the internal capsule a Large bundles! b Three parts: i Anterior Limb It is between caudate and lenticular nuclei Connection from thalamus to frontal lobe Contains the lentiform nucleus ii Posterior Limb Between dorsal thalamus and lenticular nuclei Anterior portion: Connects with corticospinal tract Posterior portion: connects with thalamus iii Genu Intersection; level of the interventricular foramen Connection with the corticobulbar tract The Corona Radiata o Radiating crown o Fibers (capsule) flare out, distal to Basal Ganglia o Converging corticofugal, diverging corticopetal Theory of Cerebral Dominance o Left Hemisphere dominant for comprehension and expression of language; arithmetic and analytical function o Right Hemisphere melodic function of speech; spatial perception by RAsturiano UST-FMS A-2019: #TheElusiveDoktora Page 4 of 13

IMPORTANT LANDMARKS OF THE CEREBRAL HEMISPHERES A. Lateral view of the brain B. Medial view (Midsagittal cut) of the brain Figure 1.

Legend: Yellow = Frontal Lobe, Green = Parietal Lobe, Blue = Occipital Lobe, and Red = Temporal Lobe Central Sulcus of Rolando o AKA Rolandic Sulcus

cm deep, but not deep enough to be called a fissure Lateral Fissure o AKA Sylvian Fissure o As the name implies, it is laterally located It is

lobe Corpus Callosum o Medially located o Connects the L and R cerebral cortices o Parts: Rostrum most anterior, most rostral part Genu Body

5 IMPORTANT LANDMARKS OF THE CEREBRAL HEMISPHERES A. Lateral view of the brain B. Medial view (Midsagittal cut) of the brain Figure 1. Views of the brain with their corresponding Brodmann Areas (the numbers). Legend: Yellow = Frontal Lobe, Green = Parietal Lobe, Blue = Occipital Lobe, and Red = Temporal Lobe Central Sulcus of Rolando o AKA Rolandic Sulcus o Vertically running with continuous gyri behind it and in front of it o Almost reaches the Lateral Fissure/Sylvian Fissure but it does not It is 2 cm deep, but not deep enough to be called a fissure Lateral Fissure o AKA Sylvian Fissure o As the name implies, it is laterally located It is horizontal and ascends o Separates the temporal lobe from the parietal lobe Parietooccipital Sulcus o Separates the Parietal lobe from the Occipital lobe Corpus Callosum o Medially located o Connects the L and R cerebral cortices o Parts: Rostrum most anterior, most rostral part Genu Body Splenium most posteror part, free-end LOBES OF THE CEREBRAL CORTEX A. Frontal Lobe anterior to the rolandic sulcus, above the sylvian fissure Pre-central gyrus o In front of the Rolandic sulcus by RAsturiano UST-FMS A-2019: #TheElusiveDoktora Page 5 of 13

6 o It is the primary motor area Functions for the initiate of highly skilled and fine movements 1 Lesion at this area results in apraxia difficulty to repeat a previously learned movement a Ex: Dressing up one s self o Classified as Brodmann s Area 4 (BA4) Anterior to BA4 is BA6 1 BA6 functions in voluntary motor function 2 Supplementary area for sequential performance of multiple movements Pre-central sulcus in front of the pre-central gyrus o Frontal lobe is divided by 2 sulci Superior Frontal sulcus Inferior Frontal sulcus o The 2 sulci divide the divide the frontal lobe into gyri Superior Frontal Gyrus Middle Frontal Gyrus Inferior Frontal Gyrus 1 The IFG is divided into 3 areas by the rami (branches) of the Sylvian Fissure: a Pars orbitalis b Pars triangularis c Pars opercularis d On the left side, the pars opercularis and pars triangularis are considered to be BA 44&45 (respectively) i They are important areas for motor aspect of speech ii Lesion at these areas brings about expressive aphasia AKA non-fluent aphasia/motor aphasia The inability/difficulty to speak Frontal Eyefield o Extends between BA 6&8 (at the depth of the pre-central sulcus) o For voluntary eye movement usually to catch motion in the visual field (visual pursuit) o Lesions: Irritative: Away from the lesion Destructive: Toward the lesion Pre-frontal cortex o BA 9, 10, 11 o Location is dorsolateral, orbitomedial o Function: For affective behavior, judgment, working memory, problem solving, basta it is the most thinking cortex/part of the brain by RAsturiano UST-FMS A-2019: #TheElusiveDoktora Page 6 of 13

7 Paracentral lobule o Located on the medial surface of the cerebral hemisphere o It is the continuation of the pre-central gyrus and post-central gyrus medially o Parts: Anterior Part 1 Extension of the pre-central gyrus medially 2 Motor in function a Controls urinary bladder sphincters Posterior Part 1 Extension of the post-central gyrus medially 2 Sensory in function B. PARIETAL LOBE posterior to the rolandic sulcus, above the sylvian fissure Post-central gyrus o Primary Sensory Area o Continuous with the posterior paracentral gyrus Post-central gyrus + Posterior paracentral gyrus = Primary Somatosensory Cortex 1 In the motor homunculus, the following are represented in the Primary Somatosensory Cortex: a Lateral 1/3 = face b Middle 1/3 = UE c Medial 1/3 = Hip, thigh, trunk d Paracentral lobule = Leg, foot, genitals 2 Function of the Primary Somatosensory Cortex: a Somesthetic i The appreciation and interpretation of sensation coming from the body o Borders: Rostrally: Imaginary line from rolandic sulcus to cingulate sulcus Caudally: Marginal sulcus o BA 3, 1, 2, (Bat hindi na lang BA 1,2,3? IDK. No one knows.) Area 1 rapidly adapting cutaneous receptors + proprioceptive impulses Area 2/Area 3A propioceptive impulses Area 3B slowly adapting cutaneous receptors o Lesion at the BA 3, 1, 2 results in: Loss of sensation of discriminative touch Loss of sensation of proprioception Loss of sensation of pain, temperature, and light touch Intraparietal sulcus o Divides parietal lobe into 2 lobules Superior Parietal Lobule (somesthetic association area) 1 AKA BA 5 and 7 2 Functions in the perception of shape, size, and texture identification of object by contact (stereognosis) by RAsturiano UST-FMS A-2019: #TheElusiveDoktora Page 7 of 13

8 a Ex: If you close your eyes and your friend puts a ball on your hands, you know that the object is a ball even without looking at it 3 Lesion at BA 5 and 7 will result in: a If lesion is at the left (dominant): Bilateral optical ataxia b If lesion is at the right (non-dominant): Contralateral hemineglect Inferior Parietal Lobule 1 Divided into 2 areas: a Supramarginal gyrus i Hugs the tip of the Sylvian Fissure b Angular gyrus i Hugs the tip of the Superior Temporal Sulcus ii At the left angular gyrus is where the Wernicke s Area (BA 39) is located Lesion at the Wernicke s Area makes the patient Alexic (Alexia) inability to read/cannot comprehend written word BA 39, together with BA 40, forms the Major Association Cortex (MAC) o Functions in higher order and complex multisensory perception Lesion at MAC will result in Agnosia inability to recognize/perceive sensory information despite intact sensory processing Note: Other Sensory Cortical Areas Primary gustatory cortex (BA 43) Parietal operculum Primary olfactory cortex pyriform cortex and periamygdaloid areas Secondary olfactory cortical area entorhinal cortex Primary vestibular cortex posterior insular cortex C. Temporal Lobe below the Sylvian Fissure, other functions of temporal lobe is associated with the limbic system and hippocampus Presence of 2 sulci o Superior Temporal Sulcus ends in angular gyrus o Middle Temporal Sulcus o The 2 sulci divide temporal lobe into 3 gyri Superior Temporal Gyrus 1 AKA BA 41 & 42 2 Functions as the primary auditory cortex 3 Within the lateral fissure area, the Temporal Gyrus of Heschl is seen 4 Lesion at STG produces impairment in sound localization in space and diminution of hearing bilaterally but more contralaterally by RAsturiano UST-FMS A-2019: #TheElusiveDoktora Page 8 of 13

9 a So, if the right STG is injured, hearing from both left and right ears will be impaired. However, the impairment is more marked in the contralateral side left ear Middle Temporal Gyrus Inferior Temporal Gyrus Wernicke s Area for Spoken Word o AKA BA 22 o Lesion at BA 22 results in Wernicke s aphasia or fluent aphasia or receptive aphasia The patient can hear verbalized words but cannot understand or make sense of the words o BA 22, together with BA 24 forms the Auditory Association Cortex AAC functions in the interpretation of spoken sound Medial view of the Temporal Lobe o Corpus Callosum connects left and right cerebral hemispheres. Parts of the CC are genu, body, and splenium: Genu sends information to the pre-frontal cortex Body sends information to the motor cortex Splenium sends information to the occipital lobe and parietal lobe Above the corpus callosum is the callosal sulcus 1 Above the callosal sulcus is the cingulate gyrus a Above the cingulate gyrus is the cingulate sulcus D. Occipital Lobe The important landmark that demarcates the end of the parietal lobe and the start of the occipital lobe is the parietooccipital sulcus o In the medial surface, parietooccipital sulcus separates cuneus (occipital) from the pre-cuneus (parietal) The occipital sulcus gives rise to: o Superior Occipital Gyrus o Inferior Occipital Gyrus The calcarine sulcus intersects the parietooccipital sulcus to divide the occipital lobe into to 2 areas: o Cuneus anterior/above to the calcarine fissure o Lingual Gyrus posterior/below to the calcarine fissure o The calcarine fissure Area that is directly bordering the lips of the calcarine fissure is the primary visual cortex (BA 17) 1 Located at the medial surface of the occipital lobe at each side of the calcarine fissure 2 Lesion at BA 17: a Homonymous hemianopia/hemianopsia i Both eye fields of both eyes have a blurred area. And the blurred area is at the same side of both eyes Ex: Close your left eye by RAsturiano UST-FMS A-2019: #TheElusiveDoktora Page 9 of 13

10 o The right ½ of the visual field is blurred in the right eye o Now, open left eye and close right eye The right ½ of the visual field is blurred in the left eye 3 There is a secondary visual cortex (BA 18&19) a Associated with form, color, and motion of objects E. Insular Lobe Oval cortex deep inside the lateral sylvian fissure and rolandic sulcus (insula) Has 2 kinds of gyri: o Gyri Longi (1 set) o Gyri Brevis (1 set) The insular lobe is continuous with the following lobes: o Frontal o Parietal o Temporal Function: o Receives nociceptive and visceromotor inputs F. Limbic Lobe Most medial of all the cerebral lobes; medial ring of cortex Parts: o Subcallosal gyrus o Cingulate gyrus o Isthmus o Parahippocampus o Uncus Function: o Memory o Learning o Behavior Final Notes: Summary of Clinical Disorders: AGNOSIAS o Inability to recognize perceived sensory information despite an intact sensory processing, clear mental state and naming ability o May involve any sensory modality (visual, auditory, tactile) In agnosia, the sensory processing is complete and intact. It is not injured. The sensory inputs from (example) skin reaches to the cortex. But since the somasthetic cortex is affected, you cannot make sense of the thing that touched your skin. You cannot recognize what touched your skin. ASTEREOGNOSIS by RAsturiano UST-FMS A-2019: #TheElusiveDoktora Page 10 of 13

11 o Intact touch, pain, position, and vibration sense but unable to tell object by touching Example: In the night when the lights are closed, you walk to the bathroom. The door is shut. You try to find the doorknob and when you finally find it, you know that it is the doorknob JUST BY touching it. Astereognosis takes away that ability. APRAXIA o Inability to perform learned complex acts in the absence of paralysis, sensory loss or disturbance of coordination Example: Dressing up 1 As you grow, you learn how to dress up 2 Dressing up is a complex motor skill because it requires sequential performance of movements 3 At age 20, you know how to dress up by yourself 4 But Dressing Apraxia makes it difficult for you to dress yourself APHASIA o A defect in the expression or comprehension of any form of language RECEPTIVE APHASIA OR WENICKE S APHASIA disorder in comprehending the symbols necessary for language communication; may involve written or spoken word 1 In simpler terms, difficulty/inability to comprehend what is being said to him or what the written text says EXPRESSIVE APHASIA OR BROCA S APHASIA disorder in programming the symbols for communication 1 In simpler terms, difficulty/inability to speak ALEXIA o Inability to comprehend written language In simpler terms, cannot verbalize written words/cannot read Table 1. Summary of the Functional Areas, their functions, their BA number, and their symptomatology once lesioned Functional designation Location BA # Lesions Somesthetic Parietal - postcentral gyrus Primary Sensory Postcentral gyrus, Cortex S1 post. Paracentral lobule Slowly adapting cutaneous receptors Proprioception 2, 3A Rapidly adapting 1 Secondary somesthetic 2 area Parietal - Inf. part of postcentral gyrus and sup bank and depth of lateral sylvian sulcus 3,1,2 Loss of discriminative touch and proprioception Crude awareness of pain, temp and light touch 3B by RAsturiano UST-FMS A-2019: #TheElusiveDoktora Page 11 of 13

12 Somesthetic association area (stereognosis) Perceive shape,size,texture, identiy by touch Primary visual cortex Secondary visual areas V2-V5 Form, color, motion Frontal eye field area Visual pursuit, conjugate gaze Primary auditory cortex Auditory association cortex Comprehension of spoken sound Wernike s area in dominat hemisphere Primary olfactory Secondary olfactory Entorhinal cortex Primary vestibular cortex Posterior insular cortex Superior parietal lobule Occipital - calcarine 17 fissure Occipital 18, 19 Frontal lobe 8 Temporal Heschl s gyrus Primary olfactory area, piriform cortex, periamygdaloid, prepiriform areas Postcentral gyrus, opposite auditory area in superior temporal gyrus 5,7 Bilateral optic ataxia Nondominant hemisphere produces contralateral neglect 41,42 Impairment in sound localization, more contralateral diminution 22,24 22 Primary gustatory Parietal operculum 43 cortex area Primary motor area Precentral gyrus 4 Skilled, fine movements Supplementary motor 6 area Sequential performance of multiple tasks Premotor area 6 by RAsturiano UST-FMS A-2019: #TheElusiveDoktora Page 12 of 13

13 Voluntary, input dependent Wernicke s area Spoken 22 Neologism, jargon, fluent, receptive/sensory aphasia Written word 39 Broca s speech area 44,45 Motor/expressive, telegraphic, nonfluent aphasia Prefrontal cortex Affective behavior and judgement Major Association Area High order, complex multisensory perception Limbic Emotion, memory Cingulate Parahippocampus Temporal Frontal 9,10,1 1 39, 40 23,34 38,26 References -end- 1. Transcription notes by RAsturiano (A-2019) from the lecturer 2. Cerebral Cortex Notes by Aimee Rose C. Tan Downloadable for free at: For any corrections you may find, content or otherwise, me at: ram.ustmedicine@gmail.com -THANKS- By RAsturiano #TheElusiveDoktora by RAsturiano UST-FMS A-2019: #TheElusiveDoktora Page 13 of 13

CEREBRUM Dr. Jamila Elmedany Dr. Essam Eldin Salama

CEREBRUM Dr. Jamila Elmedany Dr. Essam Eldin Salama Objectives At the end of the lecture, the student should be able to: List the parts of the cerebral hemisphere (cortex, medulla, basal nuclei, lateral