The Human Brain: An Introduction to Its Functional Anatomy. By

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The Human Brain: An Introduction to Its Functional Anatomy. By John Nolt, 6th edition 4/9/2015 Cerebrum (大腦) = Diencephalon (間腦) + Telencephalon (終腦) = Central core + Cerebral hemispheres. Telencephalon= Basal ganglia + Cerebral cortex + White matter  Chapter 19 Basal Ganglia (基底神經核) Basal Ganglia: A Telencephalon, Subcortical structure: Gray matter near the base of each hemisphere. Associated with the lateral ventricle. Lesion in the area: causing movement disorders ‐‐ Parkinson, Huntington diseases… (A) The Basal Ganglia Include 5 Major Neuclei. Five major nuclei 1. Caudate nucleus (尾核) 2. Putamen (被殼) (+nucleus accumbens (伏核)) 3. Globus pallidus (abundant myelin, 蒼白球) 4. Subthalamic nucleus (底丘腦) (diencephalic) 5. Substantia nigra (黑質) (SN, both compact & reticular parts) (rostral midbrain) Striatum(紋狀體)=caudate + putamen + nucleus accumbens (most ventral) ‐‐ Putamen: approximately coextensive with insula (腦島). Putamen <‐‐ lateral medullary lamina —> globus pallidus ‐‐ Caudate: head, body, tail ‐‐ Head bulges into anterior horn of lateral ventricle. ‐‐ Tail borders on inferior horn of lateral ventricle. ‐‐ Head of caudate continues with anterior part of putamen via nucleus accumbens above orbital surface of frontal lobe. ‐‐ N. accumbens = ventral striatum Lentiform n.(豆狀核) = putamen + globus pallidus. Pallidum= Globus pallidus  External & internal segments‐‐‐ Separated by medial medullary lamina. (B) Basal Ganglia Circuitry Involves Multiple Parallel Loops That Modulate Cortical Output Principle circuit: Cerebral cortexStriatum and subthalamic nucleus Globus pallidus and SN Thalamus  Cerebral cortex. Interconnections of the Basal Ganglia Determine the Pattern of Their Outputs (a) The Cerebral Cortex, Substania Nigra, & Thalamus Project to the Striatum.  Motor & somatosensory cortex project to putamen. 1
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Association cortex areas project to caudate nucleus. ‐‐ Prefrontal cortex may project to head of caudate. Limbic cortex, hippocampus & amygdala project to ventral striatum. SNc projects to all areas of caudate nucleus and putamen. ‐‐ Destruction of this nigrostriatal pathway causes Parkinson’s disease. VTA projects to ventral striatum Intralaminar nuclei, centromedian and parafascicular nuclei, project to striatum. =thalamostriate pathway Different parts of the striatum are involved in movement, cognition and affect. Putamen: motor functions Caudate nucleus: cognitive functions Ventral striatum: drive‐related behavior (b) The Striatum Projects to Globus Pallidus (int. & ext. segments) & SN. ‐‐Striatum & subthalamic nucleus globus pallidus & SN. Subthalamic nucleus: a motor nucleus ‐‐interconnects with globus pallidus via subthalamic fasciculus. (c) The External Segment of the Globus Pallidus Distributes Inhibitory Signals within the Basal Ganglia ‐External segment of GP (GPe) projects to subthalamic nucleus (via subthalamic fasciculus) & int. seg of GP (GPi). (d) The Internal Segment of the Globus Pallidus and the Reticular Part of the Substantia Nigra Provide the Output from the Basal Ganglia ‐GPi projects to thalamus through 1. Lenticular fasciculus (LF)(豆狀束)‐‐> cut through internal capsule‐‐> between subthalamic nucleus and zona incerta ‐‐> *thalamic fasciculus‐‐>thalamus 2. Ansa lenticularis (豆狀環)‐‐> loops around medial edge of internal capsule  joins LF=thalamic fasciculus  thalamus *Thalamic fasciculus projects to VA, VL, DM, CM, PF nuclei of thalamus. VA/VL, DM project to frontal & other cortical areas. *Zona incerta (未定區): rostral continuation of midbrain reticular formation. ‐‐Between subthalamic nucleus and thalamus (e) The Subthalamic Nucleus Is Part of Additional Pathways Through Basal Ganglia. ‐‐ Subthalamic nucleus project excitatory fibers to GPi/SNr. GPe and motor cortex project to subthalamic nucleus. ‐‐ Direct pathway: cortexstriatumGpi/SNrthalamuscortex ‐‐ Indirect pathway: cortex striatum GPe subthalamic nucleus GPithalamuscortex. (f) Part of SN Modulates the Output of the Striatum ‐‐ SNc (dopamine neurons) projects to caudate and putamen. ‐‐ Modulate output from basal ganglia. ‐‐Defects result in movement disorders (putamen connections) and cognitive deficits (caudate connections). 2
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‐‐ VTA dopamine neurons project to ventral striatum. ‐‐ SNr projects to VA/VL, & DM of thalamus. SNr also projects to superior colliculus and reticular formation (C) Perforating Branches from the Circle of Willis Supply the Basal Ganglia ‐‐SN & subthalamic nucleus: by branches of posterior portions of the circle. ‐‐Penetrating branches of posterior cerebral & posterior communicating arteries. ‐‐ Striatum and globus pallidus: by anterior portions of the circle Striatum: Penetrating branches of middle cerebral artery (lateral striate or lenticulostriate arteries) Globus pallidus: anterior choroidal artery Nucleus accumbens/striatum: anterior cerebral artery. (D) Many Basal Ganglia disorders result in abnormalities of movement Huntington's disease, Hemiballismus, Parkinson's disease.  Chapter 22 Cerebral Cortex Topography (部位記載學) of the telencepalon (Chapter 3) Gyrus‐gyri(腦回), Sulcus‐Sulci(腦溝), Fissure(腦裂). Lateral sulcus, Central sulcus, Calcarine(禽距)sulcus, Parieto‐occipital sulcus. Lobes(葉): frontal (額), parietal (頂), temporal (顳), occipital (枕), insula (腦島).  Lateral surface ‐‐Frontal lobe: precentral sulcus, precentral gyrus. Superior & Inferior sulci‐> Sup., Mid, Inf. Frontal gyri. Inf. frontal gyrus‐> opercular (島蓋), triangular, orbital portions. ‐‐Parietal lobe: postcentral sulcus, postcentral gyrus. Intraparietal sulcus‐> sup. & inf. parietal lobules. Supramarginal gyrus, Angular gyrus. ‐‐Temporal lobe: Sup. & Inf. temporal sulci‐> sup., mid., inf. temporal gyri. Sup. temporal gyrus: transverse temporal gyri, planum temporale (顳平面). ‐‐Occipital lobe: calcarine sulcus. ‐‐Insular lobe: Covered by frontal, parietal, temporal opercula (島蓋); Outlined by a circular sulcus. Limen insulae (島閾). ※ Functions: Emotions, sensations. Receptors on skin and viscerathalamic nuclei: VM, VP, somatosensory cortex, amygdala cingulate cortex, prefrontal cortex, amygdala.  Medial Surfaces ‐‐Cingulate gyrus (扣帶回), cingulate sulcus; ‐‐Corpus callosum (胼胝體); Septum pellucidum (透明隔); ‐‐Indusium griseum (灰色被蓋): Very thin layer of gray matter, covers corpus callosum. ‐‐Paracentral sulcus‐> marginal, subparietal sulci; Paracentral lobule. 3
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‐‐Precuneus (楔前葉); Cuneus (楔狀葉). ‐‐Subcallosal gyrus; Septal area (中隔區). Inferior Surface ‐‐Lingual gyrus; Parahippocampal gyrus; Collateral sulcus. ‐‐Rhinal sulcus; Entorhinal area (內鼻區, olfactory, limbic); Uncus (鉤, olfactory). ‐‐Medial occipitotemporal gyrus; Occipitotemporal sulcus. Lateral occipitotemporal gyrus. ‐‐Orbitofrontal cortex: Olfactory bulb, olfactory tract. ‐‐Gyrus rectus (直回); Orbital gyri. ‐‐Hippocampal formation (海馬構造)= hippocampus + dentate gyrus + most parahippocampal gyrus. Limbic (邊緣) lobe= Cingulate gyrus + Isthmus (峽) (retrosplenial cortex) + Parahippocampal gyrus. Limbic system= limbic lobe+ hippocampus+ dentate gyrus + amygdaloid body (杏仁體)+ hypothalamus + septal area (中膈區)+ ant. nuclei of thalamus. ◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎ Cerebral Cortex: a sheet of neurons and their interconnections. ‐‐Area: 1800 cm2 (2.5 square feet), a few mm thick. ‐‐25 billions of neurons ‐‐100,000 km of axons ‐‐1014 synapses ‐‐ Language, abstract thinking, perception, movement, adaptive response to outside world. (A) Most Cerebral Cortex is Neocortex Neocortical area: uniform early development, 6‐layered structure. = Homogenetic cortex or Isocortex (等皮質部): 95% of total cortical area Neocortex: 6 layers: well developed‐‐ sensory & motor c. Heterogenetic cortex or Allocortex (異皮質): Never go through 6‐layered stage  Archicortex (原皮質): 3 layers, hippocampus.  Paleocortex (舊皮質): 3‐5 layers, olfactory cortex, some limbic areas. (a) Pyramidal Cells Are the Most Numerous Neocortical Neurons Cortical neurons: 100,000/mm2 75% of all cortical neurons are pyramidal cells. ‐‐Pyramidal cells (錐狀細胞): Conical cell body, apical dendrite, basal dendrites, dendritic spines 4
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10‐70m in diameter. Betz cell: 100 m, giant cells, in primary motor area of frontal lobe. Principle output neurons: long axons reach other cortical areas or various subcortical sites. ‐‐Nonpyramidal cells: Principle Interneurons: short axons remain within the cortex ‐‐Multipolar stellate (granule) cells (less than 10 m), Basket cells, Chandelier cell, Bipolar cells, & Double bouquet cells. (b) Neocortex Has 6 Layers ‐‐ (1) Molecular layer: dendrites, axons. ‐‐ (2) External granular layer: small pyramidal cells, interneurons. ‐‐ (3) External pyramidal layer: pyramidal cells. ‐‐ (4) Internal granular layer: pyramidal cells, stellate cells, interneurons. ‐‐ (5) Internal pyramidal layer: Larger pyramidal cells, giant pyramidal cells, interneurons. ‐‐ (6) Polymorphic (Multiform) layer: fusiform‐shaped modified pyramidal cells, interneurons. *(a) Outer band of Baillarger: in layer 4. Line of Gennari= outer line of Baillarger. (in visual cortex) *(b) Inner band of Baillarger: in layer 5. Variations in cytoarchitecture ‐‐Homotypical (同型): distinct 6 layers. ‐‐Heterotyical (異型): Granular: Primary sensory areas, ~1.5 mm thick Layer 2‐5 dominated by small cells (both pyramidal & nonpyramidal): 75% neurons are very small pyramidal cells. Agranular: Motor cortex, large pyramidal cells dominate 2‐5, ~4.5 mm Lack of stellate (granule) cells. (c) Different Neocortical Layers Have Distinctive Connections Afferent to cortex From other cortical areas or subcortical sites ‐‐Same hemisphere: association fibers ‐‐Contralateral hemispheres: commissural fibers Corticocortical fibers: excitatory (glutamate or aspartate). ‐‐Subcortical sites Thalamus: Excitatory. Claustrum Basal cholinergic forebrain nuclei of substantia innominata: Excitatory. Neurons in locus coeruleus: Noradrenergic axons, inhibitory. Rostral raphe (縫) nuclei: Serotonergic axons, inhibitory.  From ventral thalamic nuclei  end in middle layers.  From other thalamic nuclei ‐‐> other layers e.g. intralaminar nuclei ‐‐> layer 6  From other cortical areas layer 2, 3. 5
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Efferent from cortex: connect with other cortical areas or subcortical sites. Most efferents to subcortical sites descend through internal capsule  spinal cord  striatum  thalamus  superior colliculus, red nucleus, reticular formation, pontine nuclei, motor neurons of cranial & spinal nerves, sensory nuclei of brainstem & spinal cord. ‐‐Layer 3 ‐‐> corticocortical fibers ‐‐Layer 5 ‐‐> corticostriate fibers, corticobulbar, corticospinal fibers ‐‐Layer 6 ‐‐> corticothalamic fibers (1). The corpus callosum & anterior commissure interconnect the two cerebral hemispheres. Commissures (連合): connect 2 hemispheres. Corpus callosum: 300 million fibers. ‐‐ Rostrum—continuous with lamina terminalis (終板). ‐‐ Genu (膝)‐‐‐connects frontal lobes. ‐‐ Trunk‐‐‐radiation of corpus callosum. ‐‐ Splenium(壓部)‐‐‐connects occipital lobes. Anterior commissure: connects temporal lobes & anterior olfactory nucleus. (2). Association bundles interconnect areas within each cerebral hemisphere (1). Arcuate fibers: connect adjacent gyri. Short fibers. (2). Superior longitudinal fasciculus [arcuate fasciculus (弓狀神經束)] : connect parietal, temporal, occipital, and frontal lobes. Inferior longitudinal fasciculus: : lateral and ventral surfaces of the occipital and temporal lobes. (Geniculocalcarine tract: deep to ILF) (3). Superior occipitofrontal fasciculus (subcallosal bundle); Inferior occipitofrontal fasciculus & uncinate fasciculus: connects orbital cortex & ant. temporal cortex. (4). Cingulum (扣帶束): connects cingulate gyrus with parahippocampal gyrus & septal area below genu of corpus callosum. (d) Neocortex Also Has a Columnar Organization Horizontal lamination. Vertical slabs: stimulus orientation. Columnal functional unit: vertical (perpendicular to the surface) units. Each unit = 50‐500 m in diameter, height= thickness of cortex. e.g. Sensory areas, all neurons in one unit are activated by the same peripheral stimulus. = a piece of cortex supplied by a single axon from thalamus. (B) Neocortical Areas Are Specialized For Different Functions From clinicopathological studies and animal experiments: Consistent association of some deficits with certain areas of damage  functions are localized to specific cortical areas. 6
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(a). Different Neocortical Areas Have Subtly Different Structures Cytoarchitecture: based upon differences on the thickness of individual layers, neuronal morphology, details of nerve fiber lamination. Brodmann’s map (1909): 46 areas. (b). There are Sensory, Motor, Association, and Limbic Areas Primary areas occupy less cortical areas. Most human neocortex is association area. Association cortex is divided into two broad types: Unimodal association areas: Areas adjacent to a primary area: to elaborate primary area data. ‐‐ 18, 19: visual association area Superior parietal lobule: somatosensory Superior temporal gyrus: auditory Premotor cortex: motor Multimodal or heteromodal association areas Inferior parietal lobule & large portions of frontal and temporal lobes ‐‐ Neurons in these areas respond to multiple sensory modalities and may change their response properties under different circumstances. e.g. A neuron in inferior parietal lobule might respond to a visual stimulus but only if it was something interesting, such as a cue or a piece of food.  high level intellectual activities. (1). Primary somatosensory cortex is in the parietal lobe Primary sensory areas: destination of sensory pathways. General somatic sensation ‐‐Primary (1st) somatosensory cortex (S1): postcentral gyrus = area 3, 1 and 2. Input: from VPL & VPM of thalamus via posterior limb of internal capsule. ‐‐2nd somatosensory area (S2): dorsal wall of lateral sulcus and part of pariental operculum. Afferent: from S1 & VPL/VPM. (2). Primary visual cortex is in the occipital lobe ‐‐ Primary Visual area: surrounds the calcarine sulcus (禽距溝) on medial surface of occipital lobe (area 17)= striate area. Afferent: from lateral geniculate nucleus (外側膝狀核) ‐‐ Vision association areas: # 18, 19: Surround the primary visual area on the medial & lateral surfaces of hemisphere. Receive from area 17, & superior colliculus‐pulvinar pathway. # Temporal lobe areas. (3). Primary auditory cortex is in the temporal lobe 2 transverse temporal gyri on superior surface of temporal lobe (wall of lateral sulcus) = areas 41, 42 ‐‐ 41: Primary auditory area, A1 (granular cortex) ‐‐ 42: A2 7
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‐‐ Afferent: from medial geniculate nucleus (內側膝狀核) via sublenticular part of internal capsule. ‐‐ 22: auditory association cortex, flanks 42. (4). Primary vestibular gustatory and olfactory areas Vestibular Area ‐‐ Superior temporal gyrus, posterior insula (near auditory cortex), & parietal lobe adjacent to head in primary somatosensory cortex. ‐‐Vestibular nerve‐ ‐> VPm of thalamus‐> cortex. Taste ‐‐frontal operculum and part of anterior insula ‐‐Taste buds‐‐> solitary nucleus‐‐> VPm of thalamus‐‐> post. limbcortex. Olfaction ‐‐ Primary olfactory cortex: (no relay in thalamus) paleocortical cortex: Piriform cortex, periamygdaloid cortex, part of entorhinal cortex. ‐‐ Olfactory association cortex: on orbital surface of frontal lobe, receives direct projection from primary olfactory cortex or via dorsomedial nucleus. (5). Most motor areas are in the frontal lobe (1) Primary Motor areas: ‐‐ Low threshold electrical stimulation of the area‐> muscle contraction movement. ‐‐ Precentral gyrus + ant. part of paracentral lobule on med. surface of hemisphere=area 4: agranular: the thickest cortex. Efferent: pyramidal motor system: corticospinal and corticobulbar tracts. Betz cells (area 4) ‐> corticospinal fibers: Head: one third of the area 4. (2) Premotor area Area 6, no Betz cells. Agranular, ‐‐Efferent: pyramidal motor pathway, primary motor area ‐‐Function: To perform skilled motor activities, directs primary motor area. (3) Supplementary motor areas: ‐‐SMA: extension of area 6 in medial surface of hemisphere. ‐‐Efferent axons‐> corticospinal & corticobulbar tracts, motor regions of the reticular formation & primary motor area. Modulation sources: basal ganglia, cerebellum, some association cortex, portions of thalamus **Basal forebrain (loosely used term) Area at and near inferior surface of the telencephalon, between hypothalamus and orbital cortex. ‐‐ Inferior part: ant. perforated substance. ‐‐ Superior border: rostrum of corpus callosum. Substantia Innominata (無名質) ‐‐Area beneath anterior commissure. ‐‐Contains basal nucleus of Meynert: major collection of forebrain cholinergic neurons. ‐‐This nucleus & nearby nucleicholinergic projection ‐‐to all areas of cerebral cortex, hippocampus, amygdaloid body. 8
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Alzheimer’s disease: ‐‐ loss of acetylcholine ‐‐ loss of neurons in basal nucleus ‐‐ loss of cortical somatostatin‐containing neurons (c). Association Areas Mediate Higher Mental Functions PET: positron emission topography fMRI: functional magnetic resonance imaging ‐‐ Frontal lobe (prefrontal): judgment, foresight, emotion, memory. ‐‐ Limbic system: recent memory. ‐‐ Anterior temporal lobe: thought and memory. (1). The right & left cerebral hemispheres are specialized for different functions Hemisphere Dominance Left hemisphere: dominant hemisphere: Language. Planum temporale (顳平面) on superior temporal gyrus is larger in left than right. (2). Language Areas border on the lateral sulcus usually on the left. (a) Expressive (Motor) speech area (Broca’s area): The opercular & triangular parts of inferior frontal gyrus (areas 44 & 45). (b) Receptive (Sensory) language area: Posterior part of superior temporal gyrus (Auditory association cortex; Wernicke’s area) + Inferior parietal lobule. These areas are interconnected through the superior longitudinal (arcuate) fasciculus. Aphasia (失語症) Broca’s aphasia fluency ↓ repetition ↓ comprehension＋ Wernicke’s aphasia fluency＋ repetition ↓ comprehension ↓ (3). Parietal association cortex mediates spatial orientation Right hemisphere: ‐‐ 3‐dimensional or spatial perception. ‐‐ Singing and playing musical instruments, appreciation of music. Musical skills & comprehension lost following vascular occlusion in right hemisphere. (4). Prefrontal cortex mediates working memory and decision making The parts of frontal lobe anterior to area 4 & 6, do not cause movements when stimulated. Areas 9, 10, 11, 12: connect with parietal, temporal＆occipital lobes, amygdala, and DM thalamic nucleus. Phineas Gage’s brain: prefrontal cortex was destroyed. Changed personality Prefrontal lobotomy or leucotomy: 9
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for certain severe psychoses and other conditions : carefree & euphoric; lack of powers of concentration, attention span, initiative, spontaneity, and abstract reasoning. (a) Dorsal and lateral prefrontal: receive inputs from somatosensory, visual & auditory association areas. ‐‐for working memory= the ability to keep in mind recent events or the moment to moment results of mental processing. (b) Orbital and medial prefrontal cortex: receive more inputs from limbic structures, such as amygdala. Damage to this region: impulsive, difficult to suppress inappropriate responses and actions. Orbitofrontal dysfunction psychopathic conditions. (C). The Corpus Callosum Unites the Two Cerebral Hemispheres Nearly all cortical areas receive commissural fibers, with a few notable exceptions, such as the hand area of somatosensory and motor cortex, and almost all area 17. Sectioning corpus callosum has been used as a treatment of last resort for some human patients suffering from intractable epilepsy to prevent seizures from spreading from one hemisphere to the other. ‐‐ Left hemisphere: language, mathematical ability, ability to solve problems in a sequential, logical fashion. ‐‐ Right hemisphere: musical skills, recognition of faces, comprehension of spatial relationships. ‐‐ Commissurotomy (section of corpus callosum): For a right‐handed patient, his left hand can copy, draw, arrange blocks better than the right hand. (D) Consciousness and Sleep Consciousness: self‐awareness, access to memories, being able to manipulate abstract ideas & direct one’s attention. Arise from interactions among many neural structures. ARAS: ascending reticular activating system  Maintain normal cortical function. Cholinergic projection from RF Noradrenergic from LC Serotonergic from raphe *All these depolarize thalamic neurons cerebral cortex. *Bilateral destruction of ARAS causes coma. Sleep: a reversible state of unconsciousness There are two forms of sleep: non‐REM sleep and REM sleep Control circuits for REM sleep are located in the brainstem. ARAS Hypothalamus 10