Hypothalamus Flashcards
Describe the function of the hypothalamus.
Drives initiate complex, coordinated sets of actions (in contrast with simple reflexes)
Homeostatic drives: maintain physiological homeostasis; e.g. feeding, thirst, salt, thermoregulation, sleep, sickness
Species survival drives: sexual behavior, parenting, social curiousity, aggression
Part of the “emotional brain” - highly connected with reward systems in the brain (limbic system)
HR/BP too
GVA stuff! visceral information coming from heart, kidney, GI, etc.
Describe the input/output to hypothalamus.
See diagram slide 3.
gets input from cerebellum, limbic structures, BG
sends output to limbic, pituitary gland (will have a hormonal response on smooth muscle, cardiac muscle, glands), reflexes, motor programs, autonomic motor neuron to autonomic ganglion
Describe the structure of the hypothalamus.
divided into clusters of cells (nuclei) but the nuclei are NOT morphologically distinct. Chemically and functionally, the nuclei may be heterogenous to various degrees. It is possible to only infer vague functional and anatomic boundaries for these hypothalamic nuclei
Where is the hypothalamus? Describe its boundaries.
(slide 4)
- The superior border is the hypothalamic sulcus directly beneath the thalamus.
- The inferior border is the tuber cinerum, which tapers to form the infundibulum or stalk of the pituitary gland.
- The rostral (anterior) border is limited by a vertical line through the anterior border of the anterior commissure and the optic chiasm.
- The caudal (posterior) border is limited by a vertical line through the posterior border of the mammillary body. The lateral borders are limited by the internal capsule.
Describe the following hypothalamic nuclei: arcuate nucleus suprachiasmatic nucleus paraventricular nucleus mammilary nucleus
arcuate nucleus- releasing hormones for ant. pituitary, affected by stress
suprachiasmatic- biological clocks - circadian and circannual
paraventricular- ant/pot pituitary hormones
mamillary- memory (from hippocampus via fornix) proj. to brainstem reticular formation and ant thalamic nuc.
MAIN point: no one nucleus in hypothalamus does only one thing -they do a lot of things
Each nuclei in the hypothalamus subserves a variety of functions, and most connections are bidirectional.
Many of the neurons specialized as neurosecretory - peptides - with long-lasting actions; results in the modification and modulation of many other control pathways & synapses.
Describe the hypothalamic inputs:
Fornix: The postcommissural fornix projects to the hypothalamus and anterior nucleus of the thalamus. This branch of the fornix arises from the subicular cortex of the hippocampal formation, and terminates largely in the medial hypothalamus and mammillary bodies.
Stria Terminalis: This important pathway arises from the medial amygdala, and the periamygdalar cortex projects to the bed nucleus of the stria terminalis and much of the rostro-caudal extent of the medial hypothalamus.
Medial forebrain Bundle: The medial forebrain bundle is the principal pathway that traverses the rostro-caudal extent of the lateral hypothalamus. Many of the fibers constitute hypothalamic efferent projections to the brainstem. Other fibers represent ascending monoaminergic projections from the brainstem that supply much of the forebrain, including the cerebral cortex. Still other fibers arise from the septal area and the diagonal band of Broca, and project directly to the lateral and medial hypothalamic regions including the mammillary bodies.
most fibers travel through medial forebrain bundle
What are three monoamine neurotransmitters of importance to hypothalamus?
dopamine, norpeinephrine, serotonin
2 dopaminergic systems in brain: nigrostriatal system in BG (substantia nigra compact)
and mesolimbic system (has cell bodies in ventral tegmentum that send projections to hypothalamus and other limbic areas
noradrenergic neurons of greatest importance to hypothalamus located in Locus ceruleus
serotonin found in dorsal and medial raphe nuclei. (this is the most widely distributed of the three - goes all throughout brain)
Describe the hypothalamic outputs.
Mamillary bodies
-function in “recollective memory”, spatial memory, integrating smells in our memories
Give rise to two groups of fiber projections:
ascending pathway is mammillothalamic tract - projects to anterior thalamic nucleus (a component of Papex circuit)
mammillotegmental tract- projects to midbrain tegmentum
other fibers forming a multisynaptic chain descend in the mammillary peduncle from the mammillary bodies to the reticular formation
Describe the connections between the hypothalamus and hippocampus, amygdala, thalamus, midbrain, cortex, spinal cord…
See diagram on slide 13.
Hypothalamus receives input from the amygdala via the Stria Terminalis and Diagnoal Band of Broca and Median Forebrain Bundle (also sends info to amygdala via the Median forebrain bundle… which is Olfactory Cx, preoptic area, septal area, accumbens NTS)
sends output to spinal cord (IML) via the hypothalamo-spinal tract
receives input from eye via retino-hypothalamus tract
Receives input from hippocampus via the fornix
Sends output and receives input from cortex via cortico-hypothalamic tract (cortex then sends info to hippocampus via parahippocampal Cx and Cingulate Cx)
Hippocampus sends ouput to thalamus via mammilo-thalamic tract (thalamus then sends ouput to cortex which talks to hippocampus)
Hypothalamus receives input from midbrain, sends info to midbrain via dorsal-longitudinal fasciculus of Schutz
Describe the Papez circuit - the limbic “system.”
originally described in CNS areas thought to be involved in emotion; expanded to include amygdala, hypothalamus, prefrontal and associational cortices.
See diagram slide 14.
cingulate gyrus sends info to hippocampus which sends info about emotional expression to mammillary body of hypothalamus via fornix (huge fiber bundle)
also sends info to amygdala which then sends info to hypothalamus
hypothalamus sends info to prefrontal cortex
mammillary body of hypothalamus sends info to anterior nucleus of the thalamus via mammillothalamic tract
ant. nucleus of thalamus talks to cingulate gyrus
emotional experiences are input to cingulate gyrus, and association cortex receives/sends into to and from cingulate gyrus
Describe the pituitary control.
Direct release of hormones is via posterior pituitary, or neurohypophysis.
Indirect control of hormones is via anterior pituitary, or adenohypophysis.
Describe biologic rhythms.
characterized by period (time to complete full cycle)
frequency (number of cycles per unit time)
phase (point of reference from a standard average value)
amplitude (magnitude of variation from the mean/average value)
most biologic rhythms are endogenous and self-sustaining.
hypothalamic circadian rhythms require a “clock” or timing device. This function is controlled primarily by the suprachiasmatic nucleus.
Describe the 4 categories of biological rhythms.
ultradian- much less than 24 hours (respiration, heart rate)
circadian- approx. 24 hours (corticosterone rhythm)
infradian- greater than 24 h but much less than 365 d (menstrual cycles)
circannual -seasonal approx 365 days (hibernation)
hypothalamic circadian rhythms require a “clock” or timing device. This function is controlled primarily by the suprachiasmatic nucleus.
What would damage to the suprachiasmatic nucleus result in?
When is the highest concentration of hormone output?
Describe a little bit more about annual/circannual rhythms.
Damage to the suprachiasmatic nucleus results in the inability to understand the light periodicity.
The secretion of many hormones is controlled by this rhythm, with the highest concentration of hormone output generally occurring during periods of sleep or quiet resting – usually during the night-time hours. These rhythms coincide with the deepest stages of sleep (stage four).
Annual or circannual rhythms are not linked exclusively to the hypothalamus. Environmental cues and the endogenous “biological clock” work together. Finally, certain rhythms require no environmental input, and can persist even with no specific cues.
