On the basis of the location of the tentorium(the double layer of inner dura mater locatedbetween the cerebellum and cerebral hemispheres)the brain is separated into supratentorial andinfratentorial divisions.Thus, the diencephalon is supratentorial in location,whereas the brainstem is infratentorial.
Neurons • Most neurons consist of a cell body and extensions called dendrites and axons. • Cell Body contains the nucleus • Dendrites carry impulses towards cell body • Axons carry impulses away from the cell body
All nerves within the PNS contain a thin membrane called the neurilemma• Neurilemma promotes the regeneration of damaged axons• Grey Matter – Nerves in the brain and spinal cord (CNS)that lack myelin and neurilemma• White matter – Nerves in the brain and spinal cord (CNS) that contain myelin and neurilemma
• Neuron• The basic conducting element in the nervous system is the nerve cell, or neuronGanglia. Sensory ganglia are found outside the central nervous system• Nuclei. Throughout the brain and spinal cord there are groupings of neurons• with a common functions; these are the nuclei.• Lamina. In the cerebral cortex, cerebellar cortex, and superior colliculus, the• gray matter is on the surface and organized anatomically into horizontal columns• and physiologically into vertical columns permitting a nearly infinite number of• interconnections.
Ganglia• Groups of neuron cell bodies that lie within the PNS• Not included with nerves since nerves only contain axons and dendrites
11.5: Brain• Functions of the brain: • Major parts of the brain: • Interprets sensations • Cerebrum • Determines perception • Frontal lobes • Stores memory • Parietal lobes • Reasoning • Occipital lobes • Makes decisions • Temporal lobes • Coordinates muscular movements • Insula • Regulates visceral activities • Diencephalon • Determines personality • Cerebellum • Brainstem • Midbrain • Pons • Medulla oblongata 17
CEREBRUMThe highest of human functions involve theintricate circuitry of the cerebral cortex, whichhas crucial roles in language, conceptualthinking, creativity, planning, and the ways inwhich we give form and substance to ourthoughts.
CEREBRUMThe hemispheres aremarked on the surface,by slitlike incisures calledsulciThe term fissure issometimes used todesignate a particularlydeep and constant sulcus.The raised ridge betweentwo sulci is a gyrus.
Cerebrum specialization• Regions specialized for different functions• Lobes frontal parietal – frontal • speech, control of emotions – temporal • smell, hearing – occipital • vision – parietal • speech, taste reading occipital temporal 2003-2004
The hemispheres areseparated from one anotherin the midline by thelongitudinal fissure (Fig.1.4).Each hemisphere isconventionally divided intosix lobes:frontal, parietal, occipital, temporal, central (insula), andlimbic (Figs. 1.3 and 1.7).
• The lobes are delineated from each• other by several major sulci
The lateral sulcus is a deep furrow that extendsposteriorly from the basal surface of the brainalong the lateral surface of the hemisphere, toterminate usually as an upward curve within theinferior part of the parietal lobe (Figs. 1.2 and1.3). The central sulcus of Rolando extendsobliquely from the region of the lateral sulcusacross the dorsolateral cerebral surface and, fora short distance, onto the medial surface (Figs.1.2 to 1.7).The cingulate sulcus is a curved clefton the medial surface extending parallel to thecurvature of the corpus callosum.The parietooccipitalsulcus is a deep cleft on the medialsurface located between the central sulcus andthe occipital pole (Fig. 1.7).
The boundaries of the lobes on the lateral cerebral surface are as follows: (1) Thefrontal lobe is located anterior to the central sulcus and above the lateral sulcus;(2) the occipital lobe is posterior to an imaginary line parallel to the parietooccipitalsulcus, which is on the medial surface;(3) the parietal lobe is located posterior to the central sulcus, anterior to the imaginaryparietooccipital line, and above the lateral sulcus and a projection toward the occipitalpole before it takes an upward curve;(4) the temporal lobe is located below the lateral sulcus and anterior to the imaginaryparietooccipital line; and(5) the central lobe is located at the bottom (medial surface) of the lateral sulcus ofSylvius, which is actually a deep fossa (depression). It can be seen only when thetemporal and frontal lobes are reflected away fromthe lateral sulcus.
The boundaries of the lobes on the medial cerebral surface (Fig. 1.7) are asfollows:(1) The frontal lobe is located rostral to a line formed by the central sulcus;(2) the parietal lobe is between the central sulcus and the parietooccipital sulcus;(3) the temporal lobe is located lateral to the parahippocampal gyrus;(4) the occipital lobe is posterior to the parietooccipital sulcus;and(5) the limbic lobe is a synthetic one formed by parts of thefrontal, parietal, and temporal lobes. It is located central to the curved line formed by the cingulate sulcus and thecollateral sulcus (the latter is located lateral to the parahippocampal gyrus).
The cell bodies of the pyramidalneurons and stellate (granule)neurons are present in laminae IIthrough VI.
In general, the main inputlayers of the cortex arelaminae I through IV. Themain output is fromlaminae V and VI.
Primary Motor Cortex• The neocortex has been parceled in several• ways; the most commonly used scheme is that• of Brodmann• The primary motor cortex is located in area• 4 of the precentral gyrus
Gray Matter vs. White Matter• Gray Matter – Absence of myelin in masses of neurons accounts for the gray matter of the brain – Cerebral Cortex• White Matter - Myelinated neurons gives neurons a white appearance – inner layer of cerebrum
Premotor Cortex and Supplementary Motor Area• The premotor cortex consists of areas 6 and• 8.• The supplementary motor area is in area 6 on the medial aspect of the frontal lobe.
• The primary somatic sensory (somatosensory)• cortex (SI) includes the postcentral gyrus• and its medial extension in the paracentral• gyrus (areas 3, 1, and 2 of the parietal lobe
• The cortical map of areas 3, 1, and 2 (postcentral• gyrus) comprises detailed somatotopically• organized modality-specific columns that• represent various submodalities.
• The secondary somatic sensory area (SII) is• located on the superior bank of the lateral fissure• below the primary motor and sensory areas.• SII is topographically organized with• respect to such general sensory modalities as• touch, position sense, pressure, and pain.
• Areas 5, 7,• and 40 of the parietal lobe comprise the• somatosensory association cortex.
• Taste is represented in area 43• Visual Cortex• The primary visual cortex (area 17),• The extrastriate association cortex includes• visual area II (area 18), visual area III (area 19),• angular gyrus (area 39), and inferotemporal• cortex (areas 20 and 21)• Through corticotectal fibers, the so-called• occipital eye field of areas 18 and 19 mediate• slow pursuit and vergence eye movements
• Auditory Cortex• The primary auditory cortex (area 41) is• located in the temporal lobe in the transverse• gyri of Heschl on the floor of the lateral fissure• Auditory area II (area 42) has a higher threshold• to sound intensity than the primary cortex• There are at least five auditory cortical areas in• the temporal lobe, including area 22 of the• superior temporal gyrus. Patients with lesions• of area 22 on the dominant side have profound• difficulty in the interpretation of sounds;
• (1) the visual cortex (areas 17, 18, and 19)• to (2) the angular gyrus (area 39) to (3) Wernicke’s area (area 22) via (4) the arcuate fasciculus to• (5) Broca’s speech areas 43 and 44, and, finally, (6) to the motor area 4, where the descending• motor pathways involved with vocalization originate
Basal Ganglia• The term basal ganglia refers to several• subcortical nuclei together with a nucleus of• the diencephalon and a couple in the midbrain• These are• the caudate nucleus, lenticular nucleus, subthalamic• nucleus, and substantia nigra.• The caudate nucleus and• the lenticular nucleus are collectively called• the corpus striatum; they are the deep nuclei of• the cerebral hemispheres. The lenticular nucleus• is subdivided into the putamen and globus• pallidus (pallidum, paleostriatum). The putamen• and the caudate nucleus are called the• striatum (neostriatum). The subthalamic nucleus• is located within the ventral thalamus (Chap.• 23). The substantia nigra is a nucleus located• within the midbrain
• The basal ganglia are nuclear complexes in• the cerebrum and midbrain that play a critical• role in the integration of motor activity
Hippocampus • Involved in the processing and storage of memories.
Amygdala• Involved in how we process memory.• More involved in volatile emotions like The emotion of anger has not changed much anger. throughout evolution.
• A whitish structure is seen in the depths of the fissure• — the corpus callosum• The corpus callosum is the largest of the commissural• bundles, as well as the latest in evolution.
• The temporal lobe extends medially toward the midbrain• and ends in a blunt knob of tissue known as the• uncus.
General Organization of the Basal Ganglia• On the basis of their neural connections, the• nuclei of the basal ganglia are organized as• input nuclei, intrinsic nuclei, and output nuclei• (see Table 24.2). The input nuclei receive• afferent information from outside the basal• ganglia and project their output to the intrinsic• nuclei. The intrinsic nuclei interact and have• connections with both other input nuclei and• output nuclei. After neural processing within• the basal ganglia, the output nuclei send• inhibitory signals to nuclei outside the basal• ganglia.
Diencephalon• The diencephalon, located in the ventromedial• portion of the cerebrum, is continuous caudally• with the midbrain• It consists of• four subdivisions: epithalamus, thalamus (dorsal• thalamus), hypothalamus, and ventral thalamus• (subthalamus).
• The epithalamus, choroid plexus of the third ventricle (Fig. 1.5), and the• pineal body (Fig. 1.8) form the upper margin• (roof) of the diencephalon. Ventral to the thalamus• is the hypothalamus, which includes the• mamillary bodies, and the hypophysis (pituitary• gland) (Figs. 1.5 and 1.9). The ventral• thalamus is located lateral to the hypothalamus.
• The thalamus is located between the third• ventricle medially and the posterior limb of the• internal capsule laterally• The thalamus• consists of several groups of nuclei.
• The hypothalamus is strategically located• between the cerebrum and the brainstem
Diencephalon• Thalamus • Gateway for sensory impulses heading to cerebral cortex • Receives all sensory impulses (except smell) • Channels impulses to appropriate part of cerebral cortex for interpretation• Hypothalamus • Maintains homeostasis by regulating visceral activities • Links nervous and endocrine systems (hence some say the neuroendocrine system 78
Internal Capsule• The internal capsule is a massive bundle of• nerve fibers, which contains almost all of the• fibers projecting from the subcortical nuclei to• the cerebral cortex and from the cerebral cortex• to subcortical structures in the cerebrum, brainstem,• and spinal cord (Fig. 13.4). It is divided• into an anterior limb, genu, and posterior limb
• The anterior (caudatolenticular)• limb is located between the caudate nucleus• and the lenticular nucleus. The genu (knee) is• located between the anterior and posterior• limbs. The posterior (thalamolenticular) limb• is located between the thalamus and lenticularnucleus. The retrolenticular (postlenticular)• part of the posterior limb is located lateral to• the thalamus and posterior to the lenticular• nucleus and the sublenticular part is ventral to• the lenticular nucleus.
RETICULAR FORMATION• The RF extends throughout the length of the• brainstem tegmentum.
Diencephalon The Limbic System• Consists of: • Functions: • Portions of frontal lobe • Controls emotions • Portions of temporal lobe • Produces feelings • Hypothalamus • Interprets sensory impulses • Thalamus • Basal nuclei • Other deep nuclei 85
LIMBIC SYSTEM• Anatomically, the limbic system comprises• a complex network of cortical areas and subcortical• structures interconnected by bidirectional• pathways. One component of the limbic• system, the hippocampus is important in mechanisms• of memory.
Brainstem: Medulla, Pons, and Midbrain• The brain stem is located in the posterior cranial fossa and consists of medulla,• pons, and midbrain.
Functions of the brainstem• serves as a conduit for the ascending tracts and descending tracts• control of respiration and cardiovascular systems• contains the important nuclei of cranial nerves III through XII.
• • The midbrain region (mesencephalon) has two• large “pillars” anteriorly called the cerebral• peduncles, which consist of millions of axons• descending from the cerebral cortex to various• levels of the brainstem and spinal cord.• •
• The three subdivisions of the midbrain are also clearly seen in• these figures. Above the level of the cerebral aqueduct lies the tectum and• between the aqueduct and the basis pedunculi is the grey matter of the• tegmentum separated from basis pedunculi by the deeply pigmented• lamina of the substantia nigra.
• The pons portion is distinguished by its bulge• anteriorly, the pons proper, an area that is composed• of nuclei (the pontine nuclei) that connect• to the cerebellum.• Vth, VIth and VIIth cranial nerves.
• • The medulla has two distinct elevations on• either side of the midline, known as the pyramids;• the direct voluntary motor pathway from• the cortex to the spinal cord, the cortico-spinal tract, is located within the pyramid. Behind• each is a prominent bulge, called the olive, the• inferior olivary nucleus, which connects with• the cerebellum.x• the rootlets of cranial nerves IX, X and XI
GROSS ANATOMY OF CEREBELLUMLocation: The term cerebellum is from “latin meaning” the little brain.It is a part of the hindbrain situated in the posterior cranial fossa. It is also present behind the pons and medulla ablongata,seperated from two structures by the cavity of fourth ventricle. It is covered by tentorium cerebelli and is connected to brain stem by three cerebellar peduncles. In adults the weight ratio between cerebellum and cerebrum is 1:10,Infants 1:20
Anatomy of cerebellum......contd.Consists of two laterally, large Horizontal fissure Hemispherehemisphere which are united by midlinevermis.Cerebellar surface is divided bynumerous curve transverse fissures giving Superior surfaceit a laminated appearanceOne conspicious fissure “horizontalfissure”extends around dorsolateral Vermisborder of each hemisphere from middlecerebellar peduncle tovallecula,seperating superior and inferiorsurface
External surface of cerebellum Primary fissureThe deepest fissure in the vermis is primaryfissure, which curves ventrolaterally in thesuperior surface of the cerebellum to meethorizontal fissure.Primary fissure divides the cerebellum intoanterior and posterior lobe. Anterior lobe Primary fissure Posterior lobe
Arbor vitae cerebelli Arbor vitae•In latin “ tree of life” it is the white matter of the white matter of cerebellum.•It is so called because of the tree like appearance.•It brings sensory and motorsensation to and from cerebellum. Fourth ventricle
The cerebellum is connected to Brain stem by three peduncles Superior cerebellar peduncle Midbrain Middle cerebellar peduncle PonsInferior cerebellar peduncle Medulla ablongata
LOBES OF CEREBELLUM Inferior surface Anterior lobeDivisions of lobes Anatomical Posterior lobe Flocculonodular lobe Anterior lobe Flocculonodular lobe Posterior lobe Superior surface Anterior lobe Posterior lobe
Division of lobes…..contd.Functional(Evolutionary) Paleocerebellum Neocerebellum Archicerebellum
Archi-cerebellumposterior lobe(Vestibular part)•It is formed of the flocculo-nodular lobe + associatedfastigial nuclei, lying on inf.Surface in front of postero-lateralfissure.•Embryologically, it is the oldestpart of cerebellum.•It receives afferent Fibres. Fromvestibular apparatus of internal earVia vestibulo-cerebellar tracts.•It is concerned with equlibrium Neocerebellum Archicerebellum Paleocerebellum
Archicerebellum …….contd.It has connections with vestibular &reticular nuclei of brain stem throughthe inferior cerebellar peduncle.Afferent vestibular Fibres. Pass fromvestibular nuclei in pons & medulla tothe cortex of ipsilateral flocculo-nodularlobe.Efferent cortical (purkinje cell) Fibres.Project to fastigial nucleus, whichprojects to vestibular nuclei & reticularformation.It affects the L.M.system bilaterally viadescending vestibulo-spinal & reticulo-spinal tracts.
Paleo-cerebellum(spinal part) :•it is formed of midlinevermis + surroundingparavermis + globose &emboliform nuclei.•It receives afferent proprio-ceptive impulses from Ms.&tendons Via spino-cerebellartracts (dorsal & ventral)mainly.•it sends efferents to rednucleus of midbrain.•it is concerned with muscle Paleocerebellumtone
It is concerned with muscle tone& posture.. Afferents spinal Fibres consist ofdorsal & ventral spino-cerebellartract from muscle, joint &cutaneous receptors to enter thecortex of ipsilateral vermis & paravermis Via inferior & superiorcerebellar peduncles .Efferents cortical fibres pass toglobose & emboliform nuclei, thenVia sup. C. peduncle to contra-lateral red nucleus of midbrain togive rise descending rubro-spinaltract.
Neo-cerebellum(cerebral part)•It is the remaining largest partof cerebellum.•It includes the most 2-cerebellarhemispheres + dendate nuclei.•It receives afferent impulsesfrom the cerebral cortex+ponsVia cerebro-ponto- cerebellarpathway.•it sends efferents to Ventrolateral nucleus of thalamus.•it controls voluntary movements Neocerebellum(muscle coordination).
It is concerned with muscularcoordination.It receives afferents from cerebralcortex involved in planning ofmovement- to pontine nuclei ,cross toopposite side Via middle Cerebellarpeduncle to end in lateral parts ofcerebellum (cerebro-ponto-cerebellartract).Neo-cerebellar efferents project todendate nucleus,which in turn projectsto contra-lateral red nucleus & ventrallateral nucleus of thalamus ,then tomotor cortex of frontal lobe, giving risedescending cortico-spinal & cortico-bulbar pathways.Efferents of dentate nucleus form amajor part of superior C. peduncle.
Other types of Divisions Afferent regions — Spinocerebellum — Pontocerebellum Efferent regions — Vestibulocerebellum — Lateral Hemisphere
Summary of classification ArchicerebellumClassification by phylogeneticOntogenic development Nodulus Archicerebellum Archicerebellum flocculus Paleocerebllum Neocerebellum PalaeocerebellumClassification by Afferent Connection Neocerebellum Vestibulocerebellum Spinocerebellum Pontocerebellum SpinocerebellumClassification by Efferent Connection Vermis Pontocerebellum Paravermal Region Cerebellar Hemisphere Vestibulocerebellum
Subdivision of lobesSubdivision of Flocculonodular lobe Vermis Hemisphere Nodulus Flocculus Nodulus Flocculus Subdivision of Anterior lobe Lingula Central lobue Vermis Hemisphere Ala of central lobule Lingula Central lobule Ala of the central l lobule
Superior surface Ant lobe Post lobe Inferior surface Post lobeAnt lobe
Structure Cerbellum consists of outer layer of grey matter known as cortex and inner layer of white matter known as medulla. The medullary core is composed of incoming and outgoing fibres projecting to and from the cerebellar cortex. Medullary core also contain the nucleuses of the cerebellum which are four in number.
Climbing fibres- from inferior olivary complex- direct action on individual Purkinje cell- powerful , sharply localised- Basket cells, stellate cells, Golgi cells actas inhibitory interneurons. Mossy fibres -from spinal cord / brain stem centres -indirect action on Purkinje cells via granule cells -diffuse ( thousands of Punkinje cells may be excited )
White matter of the cerebellum Consists of three types of nerve fibres in the white matterA. Axons of purkinje cells The only axons to leave cerebellar cortex to end in deep cerebellar nuclei specially dendate nucleus.B. Mossy fibres They end in the granular layer.C. Climbing fibres They end in the molecular layer
White matter of cerebellumThe internal circuity of cerebellum Donot leave the cerebellum,interconnect different regions of cerebellum. Some connect the same side. Some connect the two cerebellar hemisphereThe cerebellar efferent via middle cerebellar peduncle(MCP) and inferior cerebellar peduncle (ICP)The cerebellar afferent via superior cerebellar peduncle(SCP) and from fastigial from inferior cerebellar peduncle(ICP)
Intrinsic pathwayAfferent pathways to cerebellarcortex excite Purkinje cells.Basket, stellate and Golgi cellsregulate Purkinje cell activityEfferent pathways from thecerebellar cortex originate fromPurkinje cells -
Afferent pathway origin Destination viaCorticopontocerebellar Frontal,parietal, Pontine nuclei & temporal, mossy fibres to occipital cerebellar cortexCerebroolivocerebellar INF olivary N & climb fibres to cerebellar cortexCerebroreticulocerebellar Sensorimotor Reticular formation areasAnt spinocerebellar Muscle Mossy fibres to spindles,tendons, cerebellar cortexPost spinocerebellar jointsCuneocerebellarVestibular nerve Utricle, Mossy fibres to saccule,semicircu cortex of FN node lar canalsothers Red nuc, tectum cerebellar cortex
Cerebellar EFFERENT pathways• Axons of Purkinje cells synapse with the cerebellar nuclei.• Axons of the neurones form theefferent pathwaysConnect with • Red nucleus • Thalamus • Vestibular nuclei • Reticular formation
Functions of cerebellum Maintenance of Equilibrium - balance, posture, eye movement Coordination of half-automatic movement of walking and posture maintenace - posture, gait Adjustment of Muscle Tone Motor Leaning – Motor Skills Cognitive Function
Syndromes Ataxia: incoordination of movement - decomposition of movement - dysmetria, past-pointing - dysdiadochokinesia - rebound phenomenon of Holmes - gait ataxia, truncal ataxia, titubation Intention Tremor Hypotonia, Nystagmus Archicerebellar Lesion: medulloblastoma Paleocerebellar Lesion: gait disturbance Neocerebellar Lesion: hypotonia, ataxia, tremor
Cerebellar AtaxiaAtaxic gait and position: Left cerebellar tumora. Sways to the right in standing positionb. Steady on the right legc. Unsteady on the left legd. ataxic gait
Cerebellar MedulloblastomaCerebellar tumors on vermis - Truncal Ataxia - Frequent FallingThe child in this picture: - would not try to stand unsupported - would not let go of the bed rail if she was stood on the floor.
Cerebellar lesionsAre usually vascular, may be traumatic or tumour.Manifestations of unilateral cerebellar lesions :1-ipsilateral incoordination of (U.L) arm = intention tremors : it is aterminal tremors at the end of movement as in touching nose or button theshirt.2-Or ipsilateral cerebellar ataxia affects (L.L.) leg, causing wide-basedunsteady gait.Manifestations of bilateral cerebellar lesions (caused by alcoholicintoxication, hypothyrodism, cerebellar degeneration & multiplesclerosis) 1-dysarthria : slowness & slurring of speech.2-Incoordination of both arms.= intention tremors.3-Cerebellar ataxia : intermittent jerky movements or staggering ,wide-based, unsteady gait4-Nystagmus : is a very common feature of multiple sclerosis. It is due toimpairment coordination of eye movements /so, incoordination of eyemovements occurs and eyes exhibit a to-and-fro motion.Combination of nystagmus+ dysarthria + intension tremors constitutesCharcot’triad, which is highly diagnostic of the disease.