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