cerebrum and functional areas of brain -...
TRANSCRIPT
Cerebrum and Functional Areas
Amadi O. Ihunwo, PhD School of Anatomical Sciences
Lecture Outline
• Review sulci and gyri of cerebral hemisphere
• Functional Areas
• White matter of the cerebral hemisphere
Cerebral Hemispheres
• Largest part of the brain
• Greatest degree of development is in humans
• Consist of an outer cerebral cortex and an inner white matter
• Gyri & sulci maximise surface of cerebrum;
• 70% of cerebrum is hidden in sulci.
Superolateral surface of cerebrum
• Lateral sulcus (Sylvius):
• Central sulcus (Rolando): • Frontal lobe: 3 sulci: Precentral
sulcus, Superior & inferior frontal sulci
• 4 gyri: Precentral gyrus, Superior, middle & inferior gyri t
Parietal Lobe Sulcus: Postcentral & Intraparietal Gyri: Postcentral, superior parietal lobule, inferior parietal lobule with supramarginal & angular gyri
Temporal lobe Sulci: superior & inferior Gyri: superior, middle & inferior.
Medial Surface
• Corpus callosum: most conspicuous structure; white matter
• Cingulate sulcus
• intervenes between cingulate gyrus & extension of superior frontal gyrus.
• Paracentral lobule
• Middle frontal gyrus
• Precuneus, Cuneus & Lingual gyri
• Parieto-occipital sulcus
• Calcarine sulcus – Occipital lobe
Diagram of Lobes & sulci of the Cerebrum
Superolateral surface
Medial surface
Functional Localization in cerebral cortex
• Conscious awareness, thought, memory and intellect.
• Region to which all sensory modalities ascend and are consciously perceived and interpreted based on previous experience.
• Cerebral cortex is the highest level at which motor systems is represented. • Actions are conceived and
initiated.
Motor – Frontal Lobe
• Primary motor cortex • Precentral gyrus + wall of central sulcus.
Voluntary skilled movement
• Premotor (2nd motor) area • Anterior to precentral gyrus: for internal
urge to carry out a movement. Programmes skill motor activity
• Frontal eye field • Anterior to premotor area (MFG): controls
voluntary conjugate movement of eyes
• Prefrontal cortex • Remainder of frontal lobe: highest brain
functions – abstract thinking, decision making, anticipated effects of specific line of action taken, social behaviour
• Broca’s expressive speech (44,45) • Left inferior frontal gyrus (in Rt handed
individuals)
Sensory – Parietal lobe
• Primary somatosensory area Postcentral gyrus – area 3,1,2; Tactile
sense, tingling sensation, fine touch, position, movements of parts of the body; post-central gyrus – area 3,1,2
• 2nd somatosensory area Medial surface of postcentral gyrus; Less
discriminative sensation
• Somatosensory association area Superior parietal lobule; identification of
3-dimensional object held in the hand without looking, contralateral half of body
Inferior lobule; interface with visual and auditory areas
• Gustatory (Taste) Inferior end of postcentral gyrus
Vision – Occipital lobe
• Primary visual cortex (Area 17) • Calcarine sulcus on medial
surface of occipital lobe
• Receives optic radiations for vision.
• Association visual cortex (Areas 18 & 19) • Rest of occipital lobe
surrounding primary visual cortex.
• Interprets visual information (shape & accommodation reflex
Hearing – Temporal lobe
• Primary auditory cortex superior surface of superior
temporal gyrus (transverse temporal gyri or Heschl’s convolutions).
Receives input from medial geniculate body of thalamus.
Hearing: perception of sound
• Auditory association cortex (sensory) “Wernicke’s area” posterior to
primary auditory cortex Understanding spoken word and
reading
Temporal Lobe: Hippocampus & Limbic system
Hippocampus (Ammon’s horn )
• Most prominent curved elevation along floor of inferior horn of lateral ventricle
• 2 or 3 shallow grooves that give a paw-like appearance, the pes
hippocampi.
Dentate gyrus: crenated medial structure between hippocampus and parahippocampal gyrus
Function: Memory & Learning. Emotional aspects of behaviour
Linking function to dysfunction
White matter of cerebral hemisphere
• Myelinated axons connecting one part of brain with the other
• Categorized based on their course & connections
• Consist of 3 Types of fibres
• Association fibre (intrahemispheric)
• Commissural fibres (interhemispheric)
• Projection fibres 14
Association (Intrahemispheric) fibres
• Connect cortical areas of the same hemisphere with each other
• Divided into
• Short Association fibres (intralobar)
• Long Association fibres (Interlobar)
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Examples of Long Association fibres
• Cingulum (frontooccipital & frontotemporal)
• Superior longitudinal fasciculus (frontooccipital)
• Inferior longitudinal fasciculus (tempero-occipital)
• Uncinate fasciculus (frontal – anterior temporal)
• Arcuate fasciculus (frontal – occipito temporal)
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Commissural fibres
• Connects corresponding cortical regions of one cerebral hemisphere to the other. E.g. • Corpus callosum & anterior
commissure • Connections that link same or
similar areas on each side – homotopic connections
• Opposite; heterotopic for heterogeneous connections
• Function: interhemispheric communication 17
Corpus callosum & Anterior Commissure
• Corpus Callosum: main commissural fibre. Shaped like a fishing hook.
• Parts:
• Rostrum:
• Genu:
• Body:
• Splenium:
Anterior Commissure: A round bundle of fibres which connects basal parts of temporal lobe and olfactory region.
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Internal Capsule: Main Projection fibre
• Connects cerebral cortex with subcortical structures (thalamus, striatum, brainstem & spinal cord)
• Begins from cortex and converge to form corona radiata
• Cuts into corpus striatum dividing it almost completely into 2: Lentiform and caudate nuclei 19
Parts of the Internal capsule & Fibres contained
• Anterior limb
• Frontopontine & anterior thalamic radiations
• Genu
• Corticobulbar fibres & superior thalamic radiations
• Posterior limb
• Corticospinal tract, frontopontine fibres, corticorubral fibres & superior thalamic radiations 20
Note nuclei related to the Internal capsule
Fibres in Internal capsule…
• Retrolenticular form • parietopontine,
occipitopontine fibres, occipitotectal, optic radiation, posterior thalamic radiations
• Sublenticular part • temporopontine & some
parietopontine, auditory radiation
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Blood supply to internal capsule
• Anterior choroidal (ICA) • posterior limb &
retrolentiform
• Medial striate (anterior cerebral) • anterior limb
• Lateral striate (lenticulostriate) of middle cerebral) • anterior limb, genu & posterior
limb • Charcot’s artery: Commonly
involved in ischemic and haemorrhagic strokes
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Lesion of Internal capsule
• Usually all parts of the tracts are involved
• Complete contralateral hemiplegia with associated sensory loss
• May extend to involve visual and auditory radiation (how?)
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Questions
• Draw a well-labelled diagram of the superolateral surface of the cerebral hemisphere indicating the lobes, gyri and sulci.
• List the functions associated with each lobe (or a named lobe).
• Which cortical areas are involved in the limbic system
• List the types of fibres present in the cerebrum. Give an example of each fibre type
• Describe parts of the internal capsule