4-13 Hypothalamus and Limbic System Flashcards
Behavior is expressed in what type of commands?
ALL behavior expressed in motor commands
Skeletomotor
Secretomotor
Visceromotor
In a general sense, what does the hypothalamus do?
Receives info:
basic sensory, cognitive, behavioral state, limbic
Integrates info
Sends output:
hormonal, adrenaline/cortisol release, ANS, muscle tension
What does the hypothalamus work on in order to do skeletomotor, visceromotor, and secretomotor outputs?
Skeletomotor - reflexes, motor programs, reticulospinal tracts
Secretomotor - hypothalamus, pituitary, adrenal axis (HPA axis)
Visceromotor - ANS ganglia
What types of behaviors has the hypothalamus been associated with?
Drive related: ingestive, defensive, reproductive
4 F’s
Works to maintain homeostasis
What are the longitudinal divisions of the hypothalamus?
Preoptic
Anterior
Tuberal/infundibulum
Posterior
What are the 3 mediolateral divisions of the hypothalamus?
Periventricular
Medial
Lateral
What is the makeup and innervation of the periventricular division of the hypothalamus?
Few nuclei
Mostly DLF fibers
DLF pathway is connection between PAG - periaqueductal gray - and hypothalamus
What does the DLF do?
DLF - communication between hypothalamus and PAG
PAG regulates many behaviors and staes
DLF does visceral and survival related behaviors between hypothalamus ad PAG
What does the medial division of the hypothalamus contain?
Most hypothalamic nuclei
What does the lateral division of the hypothalamus do? What does it contain?
Lateral is separated from the medial division by the fornix
Contains:
Medial Forebrain Bundle
Lateral Hypothalamic area
What do the following areas in the hypothalamus tend to do:
anterior nuclei
lateral nuclei
posterior nuclei
Anterior nuclei - parasympathetics
Lateral nuclei - reticular formation and state control
Posterior nuclei - sympathetic
What patterns of activity would you expect to see in the hypothalamus of someone who is asleep?
More activity anteriorly
Less activity posteriorly
What changes does Fatal Familial Insomnia cause in the hypothalamus? Sleeping sickness?
FFI: Lesions in anterior hypothalamus
- this portion has many parasympathetic nuclei
- Inability to sleep, always fatal
Sleeping sickness: lesions in the posterior hypothalamus
- poor ability to maintain wakefulness
What is another name for the secretomotor hypothalamus? What are the 2 parts of it?
Secretomotor = neuroendocrine hypothalamus
Neurohypophysis
Adenohypophysis
How does the neurohypophysis secrete hormones?
Secretes directly into posterior pituitary and capillary beds
How does the adenohypophysis secrete hormones?
Directly via a vascular link within anterior pituitary
How many nuclei does the neurohypophysis have? What do these nuclei have in common?
2: Supraoptic and paraventricular nuclei
Both have magnocellular and parvocellular neurons
What does the supraoptic nuclei make? What behaviors does it regulate?
Magnocellular neurons release ADH/arginine vasopressin
Regulates ingestive and reproductive behaviors
What does the paraventricular nuclei make? What behaviors does it regulate?
Oxytocin via magnocellular division
Also makes ADH, CRH and TRH
Regulates ingestive, reproductive and stress behaviors
- regulates HPA axis, very important in stress response
What does the basal forebrain (FB) do?
Sends AcH into cortex to increase wakefulness
Considered an extension of the reticular formation
What are the circumventricular organs in the brain?
OVLT - Organum vasculosum of Lamina Terminalis
Neurohypophysis
Median eminence - base of hypothalamus
Pineal gland
SFO - SubFornical Organ
Area Postrema
What is the purpose of circumventricular organs in the brain?
Monitor osmolality
What is the sequence of events that is kicked off by low blood volume/high osmolality leading to ADH release?
low blood volume/high serum osmolality
kidney secretes renin
renin converted to ANG II
ANG II activates receptors in SFO
Osmoreceptors in OVLT also activated
SFO and OVLT send axons to preoptic nucleus
Preoptic nucleus sends fibers to paraventricular and supraoptic nuclei
ADH release stimulated
What can happen to the pathway from SFO and OVLT to the paraventricular and supraoptic nuclei as we age?
Pathway can break down, leading to less release of vasopressin
Pathway can break down as a result of age, resulting in nocturnal polyuria - frequent nighttime urination
What makes up the capillary bed in the median eminence? Why is this important?
Internal carotid artery branches into superior hypophysial artery, breaks into a capillary bed in the median eminence
Releasing hormones are leaked into this capillary bed by parvocellular neurons. Releasing hormones are carried to anterior pituitary, and cause release of actual hormones.
How are releasing hormones carried from parvocellular neurons to the capillary beds?
Via tuberoinfundibular tract
What are the major nuclei along the medial axis of the hypothalamus?
Preoptic
Anterior
Tuberal
Posterior
What are the functions of the preoptic nucleus?
Parasympathetic centers
Maintains BP, heartrate, osmolality, induction of sleep, thermoregulation
Also has GnRH neurons
What happens when the temperature of the area in and around the preoptic nucleus drops?
Sleep is induced
Vasodilation is induced in the brain so that the temp rises
What is Kallmann’s syndrome?
Lack of GnRH neurons in the preoptic nucleus, no GnRH hormone to start puberty. Can be treated in males with exogenous testosterone, and person will develop normally.
What nuclei are in the anterior region of the hypothalamus?
Supraoptic nucleus
Paraventricular nucleus
Suprachiasmatic nucleus
What does the suprachiasmatic nucleus do?
Runs the body’s master circadian clock
Sits right on top of optic chiasm, receives input from retina directly
How does the retina send info to the SCN?
Via the retinohypothalamic tract (RHT).
Helps program synchrony based on daily light schedules
What major nuclei are in the tuberal region of the hypothalamus?
Dorsomedial nucleus
Ventromedial nucleus
Arcuate nucleus
What is the function of the dorsomedial nucleus?
Regulates ingestive behaviors
What is the function of the ventromedial nucleus? What does it release?
Regulates ingestive and reproductive behaviors
Satiety center - releases ghrelin, neuropeptide Y
Lesion here will make you overeat compulsively
What is the function of the arcuate nucleus?
Regulates ingestive behaviors
- contains neurogenic neurons - can generate new neurons
- inability to generate new neurons here leads to obesity, ceases satiety
Parvocellular neurons to anterior pituitary
- releases dopamine (inhibits PRL), GHRH
What nuclei do the posterior region of the hypothalamus have?
Posterior nucleus - sympathetic center
Mammillary bodies
What is the function of the mammillary bodies?
Prominent posterior landmark
No relation to sympathetics
Receives afferents from hippocampus - helps with memory and learning
Efferents to anterior nucleus of the thalamus
Contains tuberomammillary nucleus
What is the function of the tuberomammillary nucleus?
Secretes histamine
promotes consciousness, wakefulness
Projects throughout the brain
These neurons are inactive during sleep
What is Korsakoff’s syndrome?
Lesion of mammillary bodies due to thymine deficiency secondary to EtOH overconsumption
Difficulty in forming new memories, creating working memoreis
What is the median forebrain bundle and where does it go?
Runs through fornix
Connects brainstem tegmentum with basal forebrain
(specifically septal nuclei and Basal nucleus of Meynert)
Has a major role in regulated behavioral state changes - helps release AcH to cortex to promote wakefulness
What is the lateral zone in the lateral hypothalamus?
Poorly defined, mostly an extension of the reticular formation, helps promote wakefulness
Where do orexin containing neurons exist? When are they active?
Exist in the perifornical area in hte lateral hypothalamus
Tend to be active when you are emotionally aroused
What causes narcolepsy?
Loss of orexin neurons
3rd most common neurodegenerative disorder
Sleep happens when you are active
What does orexin do?
Orexin is a neuropeptide that has feeding, reward, and staying awake capabilities
What is cataplexy? What causes it, and how does it differ from narcolepsy?
Cataplexy is loss of muscle tone and subsequent collapse from a potent emotional stimulus - frightened, laughing, surprised
People will collapse but will still be conscious
Caused by complete loss of orexin neurons, frequently co-morbid with narcolepsy
narcolepsy = disordered sleep, cataplexy = transient paralysis
- locus coeruleus ends up being inhibited, inhibition of reticulospinal pathways happens, motor pathways freeze
What entities, together, regulate wakefulness?
Asecending Reticular Activating System
Medial Forebrain Bundle
Basal Forebrain
What is the king of the ANS?
Paraventricular nucleus
What does the PVN send efferents to?
Reticular formation
Parasympathetic CN nuclei
Lateral horn of spinal cord
The stress response in the brain is bidirectionally mediated. Explain.
HPA (hypophysis - pituitary - adrenal) axis
CNS innervation causing release of CRH, which works on adrenal medulla to cause global release of NE and epinephrine
Direction innervation to sympathetic chain, and subsequent innervation of adrenal medulla
What are the inputs to the PAG to regulate behavior?
Limbic cortex
Amygdala
Hypothalamus
Spinal Cord
Regulates defensive reactions, vocalizations, mating behavior
What are the 5 inputs to the hypothalamus?
Dorsal longitudinal fasciculus
Retina
Ascending Reticular activating system
Cortex
Hippocampus and Amygdala - limbic lobe
What is the path of the DLF?
Fibers from around PAG will fan out to hypothalamic wall of 3rd ventricle
What paths does the amygdala take into the hypothalamus?
Stria Terminalis - c-shaped pathway, goes many places
Amygdalofugol pathway, faster
What is the rule of thumb for hypothalamic outputs?
If it receives something from the hypothalamus, it also sends something to the hypothalamus.
What are the physical parts of the limbic system related to the hippocampus? Amygdala?
Hippocampus:
posterior cingulate gyrus
parahippocampal gyrus
Amygdala:
anterior cingulate gyrus
uncus
subcortical areas
The amygdala evolved with the BG. Why?
BG - helps with smooth, repetitive motions, like running
Amygdala - processes fear and emotions. Amygdala speeds up decision making process significantly by adding emotional inputs.
If you need to run away from a hungry bear/Dr. Buck/neuro course, you rely on both these systems.
The amygdala has 2 important pathways. What are they?
Basolateral Nuclei Group - BNG
multimodal association cortex - assigns value judgement to scary/stressful stimuli
-slow, fear response that isn’t immediate
Projects to central nucleus, indirect
Central Nucleus of Amygdala - CNA
- fast, learned fear response, direct response
(What happens when someone sees a snake, spider, etc.)
What are the afferent pathways to the amygdala?
thalamus
hypothalamus
OFC
olfactory tract
Association cortices
What are the 4 major subregions of the hippocampus?
Dentate gyrus
Hippocampus proper (CA 1-3)
Subiculum
Entorhinal cortex
What is the path of the parahippocampal gyrus?
Diverse cortical info is brought in and out of hippocampus
Neocortex –> parahippocampal region –> Entorhinal cortex –> dentate gyrus –> CA 1-3 –> subiculum –> fimbrae or back out the way it came
What is the septohippocampal pathway out of the hippocampus?
Info leaves hippocampus via fornix fimbria
Fornix travels around to septal nuclei
Bifurcates on the way there, sends other arm to mammillary bodies
What is the papez circuit?
Circuit to connect hippocampus to rest of the limbic lobe.
Cingulate gyrus –> parahippocampal region –> hippocampus –>fornix –> mammillary bodies –> anterior nucleus of the thalamus –> cingulate gyrus
What is Kluver-Bucy syndrome? What does it tell us about goal driven behavior?
Loss of limbic lobes, resulting in fearlessness, placidity, hypersexuality, curiousity
Drives are still intact, but ability to satisfy the drives isn’t
Also, poor ability to learn and learn from mistakes.
Emotional component essential to learning, learning from mistakes, and satisfying wants.
