Topic 6.4 : Diencephalon & Cerebral Hemispheres

Most superior portion of the central nervous system

Brain (cerebrum)

Two major anatomical components forming the brain

Diencephalon and cerebral hemispheres

Embryonic vesicle giving rise to forebrain structures

Prosencephalon

Secondary brain vesicles derived from the embryonic prosencephalon

Telencephalon and diencephalon

Adult brain derivative of the embryonic telencephalon

Cerebral hemispheres

Secondary brain vesicles derived from the embryonic rhombencephalon

Metencephalon and myelencephalon

Ventricular cavity surrounded almost completely by diencephalic structures

Third ventricle

Four structural components forming the diencephalon

Epithalamus, thalamus, subthalamus, and hypothalamus

Two most functionally important diencephalic structures in humans

Thalamus and hypothalamus

Primary sensory relay function of the thalamus

Receives all sensory modalities except olfaction and relays them to cortex

Sole sensory modality that bypasses direct relay through the thalamus

Olfaction

Gray matter bridge connecting right and left thalami across third ventricle

Interthalamic adhesion (intermediate mass)

Thalamic anterior nuclei group functional connection

Limbic system (emotional control of memory and behavior)

Thalamic medial nuclei group functional connection

Mood and emotions

Thalamic intralaminar nuclei functional connection

Reticular formation (sleep-wake, pain, consciousness)

Thalamic lateral geniculate nucleus specific sensory role

Visual system relay

Thalamic medial geniculate nucleus specific sensory role

Auditory system relay

Large posterior thalamic nucleus affiliated with the limbic system

Pulvinar (dorsolateral nucleus)

Most ventral anatomical subdivision of the diencephalon

Hypothalamus

Two rounded lateral prominences on the posteroinferior hypothalamic surface

Mammillary bodies

Central hypothalamic region containing nuclei with neuroendocrine functions

Tuber cinereum

Structure connecting the hypothalamus to the pituitary gland

Pituitary stalk (infundibulum)

Bony cranial depression housing the hypophysis (pituitary gland)

Sella turcica of the sphenoid bone

Three anatomical components forming the epithalamus

Pineal gland (epiphysis), habenula, and medullary striae

Major endocrine hormone synthesized and secreted by the pineal gland

Melatonin

Primary physiological role of melatonin

Regulation of the sleep-wake cycle (circadian rhythm)

Functional system to which the epithalamus belongs

Limbic system (instinctive-affective control)

Deep groove separating the right and left cerebral hemispheres

Longitudinal (interhemispheric) fissure

Dural reflection situated vertically inside the longitudinal cerebral fissure

Falx cerebri

Sulcus separating the frontal lobe from the parietal lobe

Central sulcus (of Rolando)

Sulcus separating the parietal lobe from the occipital lobe

Parieto-occipital sulcus

Sulcus separating frontal and parietal lobes from the temporal lobe

Lateral sulcus (Sylvian fissure)

Cerebral lobe concealed deep within the lateral sulcus

Insular lobe (insula)

Medial sulcus separating the temporal and occipital lobes

Calcarine sulcus

Sulcus encircling the superior border of the corpus callosum

Callosomarginal (cingulate) sulcus

Cortical gyrus located between the corpus callosum and cingulate sulcus

Cingulate gyrus

Primary nuclear mass forming the basal nuclei internally

Corpus striatum

Two nuclear complexes composing the corpus striatum

Lentiform (lenticular) nucleus and caudate nucleus

Two anatomical subdivisions forming the lentiform nucleus

Globus pallidus and putamen

Medial lentiform division located closer to the thalamus

Globus pallidus

Lateral lentiform division located closer to the cerebral cortex

Putamen

C-shaped basal nucleus surrounding the thalamus

Caudate nucleus

Nuclear structure situated at the termination of the caudate nucleus tail

Amygdaloid nucleus (amygdala)

White matter tract separating the caudate nucleus from lentiform nucleus

Internal capsule

Thin gray matter sheet located lateral to lentiform nucleus deep to insula

Claustrum

Functional motor system containing the corpus striatum

Extrapyramidal motor system

Functional system containing the amygdaloid nucleus

Limbic system

Primary proposed functional role of the claustrum

Consciousness

Number of distinct histological layers forming the cerebral cortex mantle

Six layers

Approximate number of neurons in the human cerebral cortex

Approximately 10 billion neurons

Approximate number of synapses in the human cerebral cortex

Nearly 50 trillion synapses

Number of cytoarchitectonic cortical areas mapped by Korbinian Brodmann

52 Brodmann areas

Somatotopic cortical body representation map discovered by Penfield

Penfield homunculus

Cortical location of primary motor representation (motor homunculus)

Precentral gyrus of frontal lobe (anterior to central sulcus)

Cortical location of primary sensory representation (sensory homunculus)

Postcentral gyrus of parietal lobe (posterior to central sulcus)

White matter fibers connecting cortex with subcortical centers, stem, and cord

Projection fibers

White matter fibers connecting homologous areas across both hemispheres

Commissural fibers

White matter fibers connecting different cortical areas within same hemisphere

Association fibers

Major anatomical commissure formed by transverse interhemispheric fibers

Corpus callosum

Four anatomical parts of the corpus callosum from anterior to posterior

Rostrum, genu, body, and splenium

Most ventral recurved part of the corpus callosum

Rostrum

Anterior fiber radiation projecting from the genu of corpus callosum

Forceps minor

Largest central longitudinal portion of the corpus callosum

Body of corpus callosum

Most posterior expanded portion of the corpus callosum

Splenium

Posterior fiber radiation projecting from the splenium of corpus callosum

Forceps major

Cortical areas not interconnected across the corpus callosum

Poles of frontal/occipital lobes and basal temporal lobes

White matter projection fiber structures in the cerebral hemisphere

Corona radiata, internal/external/extreme capsules, and fornix

Major motor and sensory projection tracts passing through internal capsule

Corticobulbar, corticospinal, and corticothalamic tracts