Hypothalamus and Limbic System Flashcards
Hypothalamus input/ output
Hypothalamus receives input from cortical, limbic, and sensory sources, sends output in 3 types of motor control
All sorts of things regulated by hypothalamus:
Secretomotor (neuroendocrine hypothalamus)
Skeletomotor (GSE directly from HT)
Autonomics
At least 3 different types of outputs from the HT.
Traditionally, the hypothalamus has been associated with
Drive-related behaviors
Ingestive, reproductive, and defensive behaviors
or feeding, fighting, fleeing and mating
Brain’s center for homeostasis
My own opinion:
Hypothalamus = brain’s chief of staff
Coordinates all major input with the appropriate output to keep things running smoothly
(contrast this role with the thalamus as the brain’s gatekeeper)
4 longitudinal divisions of the hypothalamus contain nuclei with diverse functions
Preoptic
Anterior: Anterior, Paraventricular, supraoptic, and suprachiasmatic nucleus
Tuberal (infundibulum): Dorsal medial, ventral medial, arcuate
Posterior
PratP is rostral to caudal
There are 3 mediolateral divisions of the hypothalamus
Periventricular Few nuclei, mostly DLF fibers Medial Most hypothalamic nuclei Lateral Separated from medial by the fornix MFB Lateral Hypothalamic Area
The hypothalamus has a logical organization
Unlike the thalamus, hypothalamic nuclei follow patterns:
Neuroendocrine vs. endocrine output Anterior nuclei (parasympathetic) vs. posterior nuclei (sympathetic) Lateral nuclei = reticular formation/state control Bidirectional circuitry
The secretomotor (neuroendocrine) hypothalamus
Nuclei involved in release of hormones through the hypophysis
Neurohypophysis (posterior pituitary)
Direct release into
Adenohypophysis (anterior pituitary)
Release via a vascular link within the ant. pituitary
Supraoptic and Paraventricular nuclei Magnocellular subdivision Oxytocin Milk letdown reflex, uterine contractions ADH (vasopressin) Water reabsorption
Neural circuit of ADH release(aka preventing urination and inducing drinking behavior when dehydrated)
Circumventricular organs (no blood-brain barrier!)
6 in the brain, including OVLT (Organum vasculosum of lamina terminalis), neurohypophysis, median eminence (base of hypothalamus), pineal, SFO (subfornical organ), area postrema
Neuronal and glial structures that abut capillaries and aren’t protected by BBB
Monitoring osmololality
When low blood volume:
A) Kidney secretes renin, converted to angiotensin II, activates receptors in SFO
B) Osmoreceptors in OVLT activated
SFO and OVLT send axons to preoptic nucleus, these neurons send axons to paraventricular and supraoptic nuclei, stimulate ADH release
Adenohypophysis blood supply
Internal carotid artery branches into the superior hypophyseal artery that breaks up into a capillary bed in the median eminence
Blood recollects down pituitary stalk in hypophyseal portal vessels to carry releasing hormones and inhibiting hormones to endocrine cells in the anterior pituitary
Signaling molecules through adenohypophysis
Parvocellular neurons release the “releasing hormones” via the tuberoinfundibular tract
Hypothalamic nuclei involved are preoptic, supraoptic, paraventricular, ventromedial, and arcuate
Releasing hormones and their anterior lobe hormones(adenohypophysis)
CRH, --> ACTH TRH, --> Thyrotropin GHRH, --> Growth hormone GnRH, --> FSH/ LH Dopamine --> Prolactin
Preoptic Nucleus/Preoptic area
Parasympathetic centers Important for maintaining bp/heart rate Important for maintaining osmolality Important for induction of sleep Important for thermoregulation Important for GnRH neurons
Anterior region of the hypothalamus
Supraoptic nucleus
Regulates ingestive, reproductive behaviors
Vasopressin (ADH) and oxytocin
Paraventricular nucleus
Regulates ingestive, reproductive and stress behaviors
Vasopressin (ADH), oxytocin, CRH, TRH
Suprachiasmatic nucleus
Sits just on top of optic chiasm, contains body’s master circadian clock
Receives major direct sensory input from the retina
The retinohypothalamic tract (RHT) does what?
programs synchrony based on daily light cycles
Major nuclei along the medial axis: Tuberal region of the hypothalamus
Dorsomedial nuecleus
Regulates ingestive behaviors
Ventromedial nucleus
Regulates ingestive and reproductive behaviors
“satiety center”
Arcuate nucleus
Regulates ingestive behaviors
Parvocellular neurons to anterior pituitary (dopamine, GHRH)
Posterior region of the hypothalamus
Posterior nucleus
Sympathetic center
Mammillary bodies
Prominent posterior landmark
Afferents from hippocampus—damage here affects memory
Efferents to anterior nucleus of the thalamus
Damaged in Korsakoff’s syndrome
korsakoff’s syndrome
– alcoholism, some vitamin deficiency, memory loss. Suggests the mammillary bodies are related to memory in some way. Hippocampus to mammillary bodies.
Lateral hypothalamus and median forebrain bundle
Separated by the fornix
Consists of an ambiguous network—a continuation of the brainstem reticular formation
Contains massive fiber tract:
Median forebrain bundle
Connects brainstem tegmentum with basal forebrain
– Septal nuclei and Basal nucleus of Meynert
Major role in regulated behavioral state changes
Behavioral state control in the lateral hypothalamus (histamine and orexin)
Tuberomammillary nucleus
Major center of histamine-containing neurons
Project throughout the brain
Important for maintaining consciousness
Histamine neurons are inactive during sleep
Orexin+ neurons perifornical (around the fornix) in the lateral hypothalamus
Project to many targets
Active when emotionally aroused
Loss of orexin neurons is the cause of narcolepsy
3rd most common neurodegenerative disorder
Hypothalamic control of visceromotor circuits:
Paraventricular nucleus = “king” of the autonomic nervous system
Efferents to:
Reticular formation
Parasympathetic cranial nerve nuclei
Lateral horn of spinal cord
Hypothalamic inputs
Dorsal longitudnal fasciculus
Fibers from around the periaqueductal grey in the brainstem that fan out in the hypothalamic wall of the 3rd ventricle
Retina (only directly transduced sensory input)
Ascending reticular activating system
Catches a ride to the hypothalamus with the Median forebrain bundle
Cortex
Hippocampus and amygdala–LIMBIC
Rule of thumb for hypothalamic output:
If it sends something to the hypothalamus, it receives something from the hypothalamus
Exception with the retina as input
Neuroendocrine outputs
Hypothalamus is integrated into the center of the
limbic system
Amygdala is collection of nuclei. 2 pathways:
1 involves basolateral nucleus to central nucleus indirect
- This is slow response
- Fear association that isn’t immediate
1 involves visceral responses, direct
- This is a fast response
- Think “what happens when I see a snake”
Hippocampus has 4 major subregions
Dentate gyrus (DG) Hippocampus proper CA1-3 (Cornu ammonis) Subiculum Entorhinal cortex
Parahippocampal gyrus
is where diverse cortical info is brought into (and carried out) of hippocampus
Transitional zone from neocortex to paleocortex
Instead of 6 layers, 3 layers
Entorhinal cortex (“within the nose”)
Subiculum (“supporting”)
Pathway of information flow through parahippocampal gyrus:
How declarative memories are consolidated and retrieved
NEocortex –> parahippocampal region–> entorhinal cortex–> dentate gyrus–> CA 3–> CA1–> subiculum–> entorhinal cortex and back to parahippo and neocortex
Septohippocampal pathway and parahippocampal gyrus are
the outs and ins of the hippocampus
Septohippocampal pathway is bi-directional
Info leaves HC via fornix—”fimbria”
Fornix travels around to septal nuclei
Bifurcates on the way there, sends other arm to Mammillary bodies
Papez circuit:
A circuit to connect the hippocampus to the rest of the limbic lobe
Original circuit tied to emotion (1930’s)
Cingulate gyrus—Parahippocampal region—hippocampus—fornix—mammillary body—ant nuc. Thal.—cingulate gyrus
