14.4 The Forebrain

components of forebrain

diencephalon and telencephalon

diencephalon

encloses third ventricle, most rostral part of the brainstem

telencephalon

develops chiefly into the cerebrum

components of the diencephalon

thalamus, hypothalamus, and epithalamus

thalamus

ovoid mass on each side of the brain;perched at the superior end of brainstem beneath cerebral hemispheres; makes up 4/5 of diencephalon; composed of 23 nuclei in 5 groups

interthalamic adhesion

joins the right and left thalami medially

functions of thalamus

gateway to cerebral cortex, plays key role in motor control, memory and emotion

thalamus as a gateway

Nearly all input to cerebrum synapses in thalamic nuclei; Processes information on its way to cerebral cortex; Not all information passed along; thalamus screens out most of the information it receives

thalamus in motor control

Relays signals from cerebellum to cerebrum; Provides feedback loops between cerebral cortex and basal nuclei

hypothalamus

Forms part of walls and floor of third ventricle; Extends anteriorly to optic chiasm; Extends posteriorly to mammillary bodies; Attaches to the pituitary through infundibulum

hypothalamic nuclei role

hormone secretion, autonomic effects, thermoregulation, food/water intake, sleep and circadian rhythms, memory, emotional behavior/sexual response

hypothalamus hormone secretion

Controls anterior pituitary, thereby regulating growth, metabolism, reproduction, and stress responses; Produces posterior pituitary hormones for labor contractions, lactation, and water conservation

hypothalamus autonomic effects

Major integrating center for autonomic nervous system; Influences heart rate, blood pressure, gastrointestinal secretions, motility, etc.

hypothalamus thermoregulation

_________ thermostat monitors body temperature, activates mechanisms to adjust temperature if necessary

hypothalamus food/water intake

Regulates hunger and satiety; responds to hormones influencing hunger, energy expenditure, and long-term control of body mass; Osmoreceptors

osmoreceptors

monitor osmolarity of blood, can stimulate production of antidiuretic hormone to help conserve water

hypothalamus sleep/circadian rhythms

Suprachiasmatic nucleus controls 24-hour (circadium) rhythm

hypothalamus memory

Mammillary nuclei relay signals from hippocampus to thalamus

hypothalamus emotions

Anger, aggression, fear, pleasure, contentment, sexual drive

epithalamus

small mass composed of the pineal gland, Habenula, and a thin roof over the third ventricle

habenula

relay from the limbic system to the midbrain

cerebrum

develops from the telencephalon and is the largest, most conspicuous part of human brain; Seat of sensory perception, memory, thought, judgment, and voluntary motor actions

frontal lobe

Rostral to central sulcus; Voluntary motor functions, motivation, foresight, planning, memory, mood, emotion, social judgment, and aggression

parietal lobe

Between central sulcus and parieto-occipital sulcus; Integrates general senses, taste, and some visual information

occipital lobe

Caudal to parieto-occipital sulcus; Primary visual center of brain

temporal lobe

Lateral and horizontal; below lateral sulcus; Functions in hearing, smell, learning, memory, and some aspects of vision and emotion

insula

Deep to lateral sulcus; Helps in understanding spoken language, taste and integrating information from visceral receptors

cerebral white matter

Most of the volume of cerebrum; Glia and myelinated nerve fibers that transmit signals; Tracts

cerebral tracts

bundles of nerve fibers in the central nervous system; Three types of tracts: Projection tracts, Commissural tracts, Association tracts

projection tracts

Extend vertically between higher and lower brain and spinal cord centers

commissural tracts

Cross from one cerebral hemisphere to the other allowing communication between two sides of cerebrum; Most pass through corpus callosum; Others: anterior and posterior commissures

association tracts

Connect different regions within the same cerebral hemisphere; Long association fibers and short association fibers

short association fibers

connect gyri within a lobe

long association fibers

connect different lobes

cerebral cortex

Layer of gray matter (2-3 mm thick) covering surface of hemispheres; Constitutes about 40% of brain mass; Contains 14 to 16 billion neurons; satellite cells and pyramidal cells; 90% of human cerebral cortex is neocortex

neocortex

six-layered tissue that has relatively recent evolutionary origin

limbic center

Important center of emotion and learning; Cingulate gyrus, Hippocampus, Amygdala; Components are connected through a loop of fiber tracts allowing for somewhat circular patterns of feedback; Limbic system structures have centers for reward and aversion

basal nuclei

Masses of cerebral gray matter buried deep in the white matter, lateral to the thalamus; Involved in motor control

masses of basal nuclei

Caudate nucleus, Putamen, Globus pallidus; All three collectively called corpus striatum due to striped appearance; Putamen and globus pallidus together are called the lentiform nucleus (lens-shaped)