Clinical Neuroanatomy -- Unit 4

what makes up the diencephalon?

the thalamus, hypothalamus, subthalamus, and epithalamus

what is the thalamus?

a large centrally located structure that looks like a central bilateral large ovoid gray mass

what is the role of the thalamus?

the sensory waystation in the brain

what does thalamic white matter consist of?

the thalamic radiations and medullary laminas

what are thalamic radiations?

white matter fibers (axons) from neurons in the thalamus that “radiate” outward to synapse with neurons in different regions of the cerebral cortex

where does the superior thalamic radiation project axons to?

motor/premotor and sensory cortices

where does the anterior thalamic radiation project axons to?

the prefrontal cortex

where does the posterior thalamic radiation project axons to?

the occipital, temporal, and parietal cortex

where does the inferior thalamic radiation project axons to?

the temporal/auditory cortex

what is the internal medullary lamina (intralaminar)?

white matter fiber tracts (axons) within the thalamus connecting neurons in different parts of the thalamus

what is the external medullary lamina?

lateral white matter fiber tracts (axons) between the thalamus and neurons in the reticular nucleus

what are the four major groups of thalamic nuclei?

anterior nucleus, midline/medial nuclei, lateral nuclei, posterior nuclei

what is the anterior nucleus?

a major group of thalamic nuclei that forms the anterior tubercle — connect to the prefrontal cortex, frontal cortex, limbic system, cingulate gyrus, and hypothalamus

what are midline and dorsal/ventral medial nuclei?

a major group of thalamic nuclei located under the third ventricle — connect ventrally to the hypothalamus and periaqueductal gray area and bulk of the medial parts of the frontal cortex

what are lateral dorsal/posterior nuclei?

a group of thalamic nuclei that connect to sensory association cortices — part of the lateral nuclei

what are ventral anterior/lateral nuclei?

a group of thalamic nuclei that receive input from the basal ganglia and cerebellum and send information to the motor cortices — part of the lateral nuclei

what are ventral posterior medial/lateral nuclei?

a group of thalamic nuclei that receive input from second-order somatosensory neurons in the medulla via the medial lemniscus and send it to the somatosensory cortex — part of the lateral nuclei

what is the medial geniculate nucleus?

a group of thalamic nuclei that receive input from the inferior colliculus and sends information to the temporal cortex — part of the posterior nuclei

what is the lateral geniculate nucleus?

a group of thalamic nuclei that receive input from the optic tract and sends information to the occipital cortex — part of the posterior nuclei

what is the pulvinar nucleus?

a group of thalamic nuclei that receive input from the superior colliculus and sends information to the parietal and temporal cortices — part of the posterior nuclei (largest posterior group)

what thalamic nuclei are of the sensory type?

lateral geniculate, medial geniculate, ventral posterolateral, ventral posteromedial

what thalamic nuclei are of the motor type?

ventral anterior, ventral lateral

what thalamic nuclei are of the limbic type?

anterior

what thalamic nuclei are multimodal?

pulvinar, lateral posterior, lateral dorsal

what is the hypothalamus?

a bilateral centrally located brain area beneath the thalamus

what is the hypothalamus involved in?

autonomic, appetitive, and regulatory functions

in relation to the thalamus, where is the hypothalamus located?

just below and rostral

what are the four divisions of the hypothalamus?

preoptic region, anterior hypothalamus (chiasmatic/supraoptic region), central hypothalamus (tuberal region), posterior hypothalamus (mammillary region)  

what is in the preoptic region of the hypothalamus?

medial and lateral preoptic nuclei

what is in the anterior (chiasmatic/supraoptic region) hypothalamus?

supraoptic nucleus, suprachiasmatic nucleus, anterior hypothalamic nucleus, paraventricular nucleus

what is in the central (tuberal region) hypothalamus?

ventral/dorsal medial hypothalamic nuclei, arcuate, medial eminence

what is in the posterior (mammillary region) hypothalamus?

posterior hypothalamic nucleus, mammillary body

the ventral noradrenergic bundle, dorsal noradrenergic bundle, serotonergic neurons, and adrenergic neuron afferent tracts in the hypothalamus come from what?

the reticular formation in the brainstem

what example does the hypothalamus to pituitary gland signaling represent?

a perfect example of the “brain/body” relationship

what is hypothalamus to pituitary gland signaling?

how the hypothalamus controls the release of chemical signals into the blood (communicates with the blood vessels surrounding the pituitary gland)

what are the two mechanisms for how the hypothalamus signals to the pituitary gland?

posterior pituitary signaling and anterior pituitary signaling

the paraventricular nucleus and supraoptic nucleus in the hypothalamus signals to what in the pituitary via nerve fibers?

the venous channel in the posterior pituitary gland

the median eminence nucleus in the hypothalamus signals to what in the pituitary via nerve fibers?

arteries connecting to the anterior pituitary gland

how does the hypothalamus to posterior pituitary signaling work?

the synthesis of peptide hormones (vasopressin and oxytocin) occurs in neurons located in the hypothalamus (paraventricular and supraoptic), and those neurons release their peptide hormones directly into the blood supply that surrounds the posterior pituitary

what is vasopressin involved in?

water retention

what is oxytocin involved in?

uterine contractions during labor and milk letdown from mammary glands

what type of structure is the posterior pituitary gland?

a neural structure — contains pre-synaptic terminals from cells in the hypothalamus

how does the hypothalamus to anterior pituitary signaling work?

the synthesis and release of peptide hormones (corticotrophs, gonadotrophs, growth hormone, thyroid stimulating hormone, prolactin producing cells) occur from cells located within the anterior pituitary gland (pituicytes), and that synthesis and release is controlled by neurons in the hypothalamus (medial eminence)

how is the corticotropin releasing hormone (CRH) and gonadatropin releasing hormone (GnRH) released?

from neurons in the hypothalamus into the blood supply feeding the anterior pituitary gland

what does CRH do?

stimulate corticotrophs in the anterior pituitary to synthesize and secrete adrenocorticotrophic hormone (ACTH) into the blood supply

what does GnRH do?

stimulate gonadotrophs in the anterior pituitary to synthesize and secrete follical stimulating hormone (FSH) and leutinizing hormone (LH) into the blood supply

what type of structure is the anterior pituitary gland?

a neuroendocrine structure — contains endocrine cells (anterior pituitary hormones) that regulate important body functions

what are the functions of the hypothalamus?

eating, body temperature, water balance, anterior pituitary function, circadian rhythm, emotion

how does the hypothalamus influence eating?

the lateral hypothalamus evokes eating (feeding center), while the ventromedial hypothalamus stops eating (satiety center)

how does the hypothalamus influence body temperature?

causes autonomic responses that cause body heat loss (vasodilation), conservation (vasoconstriction), and production (shivering)

how does the hypothalamus influence water balance?

osmoreceptors in the supraoptic region of the hypothalamus (thirst center) trigger the release of vasopressin from the posterior pituitary gland

how does the hypothalamus influence anterior pituitary function?

regulates secretions from endocrine glands controlling reproduction, sexual behavior, stress response, and growth

how does the hypothalamus influence circadian rhythm?

the suprachiasmatic nucleus acts as a body clock that keeps the brain on a day-night cycle

how does the hypothalamus influence emotion?

emotions like rage, fear, adversion, sexual behavior, and pleasure are all subject to limbic system input

what does the subthalamus project to, and what is it involved in?

projects to basal ganglia and the substantia nigra; involved in extrapyramidal motor function

what is the epithalamus?

composed of two parts — the habenular trigone and pineal body

what is the habenular trigone?

a small depressed triangular area part of the epithalamus situated above and in front of the superior colliculus that regulates dopamine and serotonin neural systems connecting the forebrain and midbrain

what is the pineal body?

a part of the epithalamus that lies between superior colliculi that secretes melatonin (for circadian rhythm), stress and sex hormone, and DMT

the cerebral cortex consists of how many hemispheres and lobes?

two hemispheres, six lobes

what are the six lobes in the cerebral cortex?

frontal, parietal, temporal, occipital, insular, limbic

what is the structure of the anatomy of the cerebral cortex?

the cerebral cortex has a convoluted anatomy — consists of cortical folds/crests (gyri) and deep valleys (sulci) that increase the surface area of the cortex (50% of the cortex is hidden within sulci and fissures!)

what cortical maps are seen on the cerebral cortex?

motor, somatosensory, visual

what is cerebral white matter?

underlying myelinated fiber tracts leading to and from the cerebral cortex

what is deep subcortical gray areas?

underlying clusters of brain nuclei (ex. basal ganglia)

what is the function of the frontal lobe?

the motor cortex — plays a role in ideation, cognition, and thoughts of motions

what is the function of the parietal lobe?

holds the somatosensory and associative cortex

what is the function of the occipital lobe?

mainly plays the role as the visual cortex

what is the function of the temporal lobe?

mainly plays a role as the auditory cortex

what is the function of the insular lobe?

a mixed function cortex — plays a role in sensory processing, motor control, risk assessment, decision-making, self-awareness, and emotion

what is the function of the limbic lobe?

plays a role in motivation, emotion, learning, and memory

where is the limbic lobe located?

on top of the corpus callosum

what are gyri?

cortical folds/crests

what are sulci?

grooves WITHIN a lobe that distinguish gyri from one another

what are fissures?

clefts/grooves that SEPARATE one lobe from another

what is the lateral cerebral fissure (sylvian fissure)?

a groove that separates the temporal lobe from the frontal and parietal lobes

what is the central sulcus (fissure of rolando)?

a groove that separates the frontal and parietal lobes (despite being called a sulcus, by definition, it is a fissure)

what is the longitudinal cerebral fissure?

a groove that separates cerebral hemispheres

what is the circuminsular fissure (circular sulcus)?

a groove that separates insula from frontal, parietal, and temporal lobes (by definition, a fissure)

what is the parieto-occipital fissure?

a groove located on the medial surface of the posterior cortex that separates the parietal and occipital lobes

what is the calcarine fissure?

a groove located on the medial surface of the occipital pole and faces towards the parieto-occipital fissure (despite being called a fissure, by definition, it is a sulcus)